WO2002067293A2

WO2002067293A2 - Microelectromechanical systems (mems) device including an analog or a digital

Info

Publication number: WO2002067293A2
Application number: PCT/US2002/004824
Authority: WO
Inventors: Jeffrey R. Annis; Ernst H. Dummermuth; Richard D. Harris; Patrick C. Herbert; Michael J. Knieser; Robert J. Kretschmann; Henric Larsson; Winfred L. Morris; Jun J. Yao
Original assignee: Rockwell Automation Technologies, Inc.
Priority date: 2001-02-20
Filing date: 2002-02-20
Publication date: 2002-08-29
Also published as: WO2002067293A9; EP1386347A4; AU2002255563A1; EP1386347A2; JP2005503267A; JP4464607B2; WO2002067293A3

Abstract

The microelectromechanical system (MEMS) analog isolator (10) or digital isolator (210) may be created in which an actuator (12, 212) such as an electrostatic motor (66, 68) drives a beam (20, 220) against an opposing force set or predefined force set, for example, by another electrostatic motor. Motion of the beam may be sensed by a sensor (18, 218) also attached to the beam. The beam itself is electrically isolated between the locations of the actuator and the sensor. The structure may be incorporated into integrated circuits to provide on-chip isolation. In a MEMS device, a specific beam (312) is supported by transverse arms (314, 316, 318) which have flexible terminations resulting in either the selective biasing to the beam or mechanical advantage in the sensing of beam structure. Additionally, a MEMS device may be created to have reduced noise sensitivity.

Description

MICROELECTROMECHANICAL SYSTEM (MEMS) DEVICE

CROSS-REFERENCE TO RELATED APPLICATIONS

I.

[0001] This application is a continuation in part of U.S. Patent applications Serial No. 09/406,364 filed September 28, 1999; Serial No. 09/406,654 filed September 27, 1999, Serial No. 09/400,125 filed September 21, 1999, and Serial Number 09/406,509 filed September 28, 1999.

FIELD OF THE INVENTION

[0002] I. The present invention relates to electrical isolators and in particular to a microelectromechanical system (MEMS) device providing electrical isolation in the transmission of analog electrical signals.

[0003] II. The present invention further relates to a MEMS device providing electrical isolation in the transmission of digital signals.

[0004] III. The present invention further relates to MEMS devices employing beams supported for movement on flexible transverse arms.

[0005] IN. The present invention further relates to a MEMS device providing electrical isolation in the transmission of electrical signals while limiting motion-induced noise.

BACKGROUND OF THE INVENTION

I.

[0006] Electrical isolators are used to provide electrical isolation between circuit elements for the purposes of voltage level shifting, electrical noise reduction, and high voltage and current protection.

[0007] Circuit elements may be considered electrically isolated if there is no path in which a direct current (DC) can flow between them. Isolation of this kind can be obtained by capacitive or inductive coupling. In capacitive coupling, an electrical input signal is applied to one plate of a capacitor to transmit an electrostatic signal across an insulating dielectric to a second plate at which an output signal is developed. In inductive [0008] coupling, an electrical input signal is applied to a first coil to transmit an electromagnetic field across an insulating gap to a second coil, which generates the isolated output signal. Both such isolators essentially block steady state or DC electrical signals.

[0009] Such isolators, although simple, block the communication of signals that have significant low frequency components. Further, these isolators can introduce significant frequency dependent attenuation and phase distortion in the transmitted signal. These features make such isolators unsuitable for many types of signals including many types of high-speed digital communications.

[0010] In addition, it is sometimes desirable to provide high voltage (> 2 kV) isolation between two different portions of a system, while maintaining a communication path between these two portions. This is often true in industrial control applications where it is desirable to isolate the sensor/actuator portions from the control portions of the overall system. It is also applicable to medical instrumentation systems, where it is desirable to isolate the patient from the voltages and currents within the instrumentation. [0011] The isolation of digital signals is frequently provided by optical isolators. In an optical isolator, an input signal drives a light source, typically a light emitting diode (LED) positioned to transmit its light to a photodiode or phototransistor through an . insulating but transparent separator. Such a system will readily transmit a binary signal of arbitrary frequency without the distortion and attenuation introduced by capacitors and inductors. The optical isolator further provides an inherent signal limiting in the output through saturation of the light receiver, and signal thresholding in the input, by virtue of the intrinsic LED forward bias voltage.

[0012] Nevertheless, optical isolators have some disadvantages. They require a relatively expensive gallium arsenide (GaAs) substrate that is incompatible with other types of integrated circuitry and thus optical isolators often require separate packaging and assembly from the circuits they are protecting. The characteristics of the LED and photodetector can be difficult to control during fabrication, increasing the costs if unit-to- unit variation cannot be tolerated. The power requirements of the LED may require signal conditioning of the input signal before an optical isolator can be used, imposing yet an additional cost. While the forward bias voltage of the LED provides an inherent noise thresholding, the threshold generally cannot be adjusted but is fixed by chemical properties of the LED materials. Accordingly, if different thresholds are required, additional signal conditioning may be needed. Finally, the LED is a diode and thus limits the input signal to a single polarity unless multiple LEDs are used. [0013] It is common to process analog electrical signals using digital circuitry such as microprocessors. In such situations, the analog signal may be periodically sampled and the samples converted into digital words input by an analog to digital converter (A D) to and processed by the digital circuitry. Conversely, digital words produced by the digital circuitry may be converted into an analog signal through the use of a digital-to-analog converter (D/A) to provide a series of analog electrical values that may be filtered into a continuous analog signal. Isolation of such signals at the interface to the digital circuitry is often desired and may be performed by placing an optical isolator in series with the electrical signal representing each bit of the relevant digital word after the A/D converter and before the D/A converter. Particularly in the area of industrial controls where many isolated analog signals must be processed and output, a large number of optical isolators are required rendering the isolation very costly or impractical.

II.

[0014] Electrical isolators are used to provide electrical isolation between circuit elements for the purposes of voltage level shifting, electrical noise reduction, and high voltage and current protection.

[0015] Circuit elements may be considered electrically isolated if there is no path in which a direct current (DC) can flow between them. Isolation of this kind can be obtained by capacitive or inductive coupling. In capacitive coupling, an electrical input signal is applied to one plate of a capacitor to transmit an electrostatic signal across an insulating dielectric to a second plate at which an output signal is developed. In inductive coupling, an electrical input signal is applied to a first coil to transmit an electromagnetic field across an insulating gap to a second coil which generates the isolated output signal. Both such isolators essentially block steady state or DC electrical signals. [0016] Such isolators, although simple, block the communication of signals that have significant low frequency components. Further, these isolators can introduce significant frequency dependent attenuation and phase distortion in the transmitted signal. These features make such isolators unsuitable for many types of signals including many types of high-speed digital communications. [0017] In addition, it is sometimes desirable to provide high voltage (> 2 kV) isolation between two different portions of a system, while maintaining a communication path between these two portions. This is often true in industrial control applications where it is desirable to isolate the sensor/actuator portions from the control portions of the overall system. It is also applicable to medical instrumentation systems, where it is desirable to isolate the patient from the voltages and currents within the instrumentation. [0018] The isolation of digital signals is frequently provided by optical isolators. In an optical isolator, an input signal drives a light source, typically a light emitting diode (LED) positioned to transmit its light to a photodiode or phototransistor through an insulating but transparent separator. Such a system will readily transmit a binary signal of arbitrary frequency without the distortion and attenuation introduced by capacitors and inductors. The optical isolator further provides an inherent signal limiting in the output through saturation of the light receiver, and signal thresholding in the input, by virtue of the intrinsic LED forward bias voltage.

[0019] Nevertheless, optical isolators have some disadvantages. They require a relatively expensive gallium arsenide (GaAs) substrate that is incompatible with other types of integrated circuitry and thus optical isolators often require separate packaging and assembly from the circuits they are protecting. The characteristics of the LED and photodetector can be difficult to control during fabrication, increasing the costs if unit-to- unit variation cannot be tolerated. The power requirements of the LED may require signal conditioning of the input signal before an optical isolator can be used, imposing yet an additional cost. While the forward bias voltage of the LED provides an inherent noise thresholding, the threshold generally cannot be adjusted but is fixed by chemical properties of the LED materials. Accordingly, if different thresholds are required, additional signal conditioning may be needed.

[0020] Particularly in the area of industrial controls where many isolated control points are required, the use of optical isolators may be very costly or impractical.

III.

[0021] MEMS devices are extremely small machines fabricated using integrated circuit techniques or the like. The small size of MEMS devices allows the production of high speed, low power and high reliability mechanisms. The fabrication techniques hold the promise of low cost mass production. [0022] The parent applications to this present application describe a MEMS electrical isolator in which a beam is supported for longitudinal movement on a set of axially flexible arms, the latter of which are tied to a substrate. Motion of the beam caused by a MEMS actuator at one end of the beam, transmits a signal to a sensor positioned at the other end of the beam and separated from the actuator by an insulating segment. [0023] The structure of a beam supported by transverse flexible elements provides an extremely simple and robust MEMS device. Nevertheless, the precision required for certain applications, particularly those related to sensors, may be difficult to achieve using mass-production integrated circuit processes.

IV.

[0024] Electrical isolators are used to provide electrical isolation between circuit elements for the purposes of voltage level shifting, electrical noise reduction, and high voltage and current protection.

[0025] Circuit elements may be considered electrically isolated if there is no path in which a direct current (DC) can flow between them. Isolation of this kind can be obtained by capacitive or inductive coupling. In capacitive coupling, an electrical input signal is applied to one plate of a capacitor to transmit an electrostatic signal across an insulating dielectric to a second plate at which an output signal is developed. In inductive coupling, an electrical input signal is applied to a first coil to transmit an electromagnetic field across an insulating gap to a second coil, which generates the isolated output signal.

Both such isolators essentially block steady state or DC electrical signals.

[0026] Such isolators, although simple, block the communication of signals that have significant low frequency components. Further, these isolators can introduce significant frequency dependent attenuation and phase distortion in the transmitted signal. These features make such isolators unsuitable for many types of signals including many types of high-speed digital communications.

[0027] In addition, it is sometimes desirable to provide high voltage (> 2 kV) isolation between two different portions of a system, while maintaining a communication path between these two portions. This is often true in industrial control applications where it is desirable to isolate the sensor/actuator portions from the control portions of the overall system. It is also applicable to medical instrumentation systems, where it is desirable to isolate the patient from the voltages and currents within the instrumentation. [0028] The isolation of digital signals is frequently provided by optical isolators. In an optical isolator, an input signal drives a light source, typically a light emitting diode (LED) positioned to transmit its light to a photodiode or phototransistor through an insulating but transparent separator. Such a system will readily transmit a binary signal of arbitrary frequency without the distortion and attenuation introduced by capacitors and inductors. The optical isolator further provides an inherent signal limiting in the output through saturation of the light receiver, and signal thresholding in the input, by virtue of the intrinsic LED forward bias voltage.

[0029] Nevertheless, optical isolators have some disadvantages. They require a relatively expensive gallium arsenide (GaAs) substrate that is incompatible with other types of integrated circuitry and thus optical isolators often require separate packaging and assembly from the circuits they are protecting. The characteristics of the LED and photodetector can be difficult to control during fabrication, increasing the costs if unit-to- unit variation cannot be tolerated. The power requirements of the LED may require signal conditioning of the input signal before an optical isolator can be used, imposing yet an additional cost. While the forward bias voltage of the LED provides an inherent noise thresholding, the threshold generally cannot be adjusted but is fixed by chemical properties of the LED materials. Accordingly, if different thresholds are required, additional signal conditioning may be needed. Finally, the LED is a diode and thus limits the input signal to a single polarity unless multiple LEDs are used. [0030] It is common to process analog electrical signals using digital circuitry such as microprocessors. In such situations, the analog signal may be periodically sampled and the samples converted into digital words input by an analog-to-digital converter (A/D) to and processed by the digital circuitry. Conversely, digital words produced by the digital circuitry may be converted into an analog signal through the use of a digital-to-analog converter (D/A) to provide a series of analog electrical values that may be filtered into a continuous analog signal. Isolation of such signals at the interface to the digital circuitry is often desired and may be performed by placing an optical isolator in series with the electrical signal representing each bit of the relevant digital word after the A/D converter and before the D/A converter. Particularly in the area of industrial controls where many isolated analog signals must be processed and output, a large number of optical isolators are required rendering the isolation very costly or impractical. BRIEF SUMMARY OF THE INVENTION

[0031] I. The present invention provides a mechanical isolator manufactured using

MEMS techniques and suitable for transmitting analog signals without prior conversion to digital signals. A special fabrication process forms a microscopic beam whose ends are insulated from each other. One end of the beam is connected to a microscopic actuator, which receives an analog input signal to move the beam in proportion to a generated actuator force. The other isolated end of the beam is attached to a sensor detecting movement of the beam to provide a corresponding analog value. The small scale of the total device provides inexpensive, fast and reliable response. [0032] Specifically, the present invention provides a microelectromechanical system (MEMS) analog isolator having a substrate and an element supported from the substrate for continuous movement between a first and second position with respect to the substrate, where at least a portion of the element between a first and second location on the element is an electrical insulator to electrically isolate the first and second locations from each other. An actuator attached to the first portion of the element receives an input electrical signal and exerts a force dependent on the input electrical signal urging the element toward the second position. A control device attached to the element to exert a force dependent on the displacement of the element toward the first position and a sensor assembly communicating with the second portion of the element provide an analog output electrical signal dependent on movement of the element between the first position and the second position.

[0033] It is one object of the invention to produce a simple mechanical isolation system using MEMS techniques suitable for direct isolation of an analog signal overcoming the need for many optical isolators and further avoiding many of the disadvantages of current optical isolators in costs, interdevice consistency, and incompatibility with other integrated circuit components. In addition, the present invention requires no preconditioning of the input signal. The input voltage, current, or mechanical displacement can be applied directly to the device with no pre-processing. [0034] The control element may be a spring or its equivalent and the sensor assembly may include a sensor providing the analog output electrical signal based on the amount of movement of the element. [0035] Thus another object of the invention is to provide the possibility of a simple open- loop analog isolator where the analog signal is transmitted over an insulated beam by motion of the beam.

[0036] Alternatively, the control element may be a second actuator attached to the element to receive a feedback electrical signal and exert a force dependent on the feedback electrical signal urging the element toward the first position. In this case, the sensor assembly may include a sensor indicating a location of the element with respect to a null position and an error detector receiving the output electrical signal to generate the feedback electrical signal so as to tend to restore the element to the null position. The output electrical signal is derived from the feedback signal.

[0037] Another object of the invention is thus to permit a more complex analog isolator using feedback techniques where the analog signal is transmitted as forces permitting minimal movement of the beam thus avoiding mechanical non-linearities. [0038] The control element may further include a third actuator attached to the element to receive a second feedback signal and exert a force dependent on the second feedback electrical signal urging the element toward the second position.

[0039] It is thus a further object of the invention to permit a feedback control of the beam allowing feedback signals that may exert either a force urging the element toward the first position or a force urging the element toward the second position. [0040] The above described error detector may produce a binary electrical feedback signal indicating a position of the beam with respect to the null location between the first and second positions and further including a pulse width demodulator circuit evaluating the duty cycle of the feedback signal to produce the output electrical signal. [0041] It is thus another object of the invention to provide a simple method of extracting a multi-bit digital signal from the isolator of the present invention. The duty cycle demodulator may be a simple counting circuit.

[0042] The actuator may be an electrostatic motor or a Lorenz-force motor or a piezoelectric motor or a thermal-expansion motor or a mechanical-displacement motor. [0043] It is therefore another object of the invention to provide an isolator that may receive a variety of different electrical signals that may not be compatible with an optical isolator LED, for example, those having a voltage of less than 0.7 volts. [0044] Similarly, the control element may be an electrostatic motor, a Lorenz-force motor, a piezoelectric motor, a thermal-expansion motor, a mechanical-displacement motor, or a mechanical spring. [0045] Thus the invention may provide both for an extremely simple control element that requires no electrical connection (e.g. a mechanical spring) or an adjustable control element that allows the null point of the beam to be freely adjusted.

[0046] The sensor may be a capacitive sensor or a piezoelectric sensor or a photoelectric sensor or a resistive sensor or an optical switching sensor.

[0047] It is therefore another object of the invention to provide flexible variety of sensing techniques suitable for different purposes.

[0048] In one embodiment of the invention, the element may be a beam attached to the substrate for sliding motion between the first and second positions. The beam may be supported by flexing transverse aπn pairs attached at longitudinally opposed ends of the beam to extend outward therefrom.

[0049] Thus it is another object of the invention to provide a simple mechanism that may be implemented on a microscopic scale using MEMS technologies for supporting the element for motion.

[0050] The flexing transverse arms may include a cantilevered first portion having first ends attached to the beam and second ends attached to an elbow portion removed from the beam and a cantilevered second portion substantially parallel to the first portion and having a first end attached to the substrate proximate to the beam and a second end attached to the elbow portion. Further the beam and the transverse arms may be symmetric across a longitudinal beam access.

[0051] Thus it is another object of the invention to provide a microscopic structure that is resistant to thermal expansion due to processing temperatures or to changes in the operating temperature. The symmetry ensures that the beam remains centered with thermal expansion while the doubling back of the flexible transverse arms provides for a degree of stress relief.

[0052] The flexing transverse arms may attach to the substrate through a spring section allowing angulations of the ends of the transverse arms with respect to the substrate.

[0053] It is thus another object of the invention to allow an effective pivoting of the flexible transverse arms so as to decrease the stiffness of the beam structure.

[0054] One embodiment of the invention may include a magnetic field, which may be produced by a magnet, crossing the beam and at least one flexing transverse arm may be conductive to an electrical signal and exert a force dependent on the electrical signal urging the beam toward a position. [0055] It is thus another object of the invention to provide that the same structure used to support the beam may provide for its actuation or control.

[0056] The beam may include transverse extending primary capacitor plates attached to the beam and extending out from the beam proximate to secondary capacitor plates. The effective area of the primary capacitor plates may be equal across the longitudinal axis of the beam and the capacitor plates may be attached to the beam between attachment points of at least two of the flexing transverse aπn pairs. In one embodiment, the capacitors may include interdigitated fingers. Parallel plate capacitors will also work (although they have less linearity).

[0057] Another object of the invention is to provide a method for the integration of an electrostatic motor to the isolator in a way that balanced and well-supported forces may be obtained.

[0058] The primary capacitor plates may be positioned with respect to the secondary capacitor plates so as to draw the primary capacitor plates toward the secondary capacitor plates on one side of the beam while to separate the primary capacitor plates from the secondary capacitor plates on the other side of the beam. Conversely, the capacitor plates may be positioned so that all draw together with a given motion.

[0059] Thus it is another object of the invention to allow the capacitor plates to be used as a sensor in which a comparison of capacitance values reveals a position of the beam or as an electrostatic motor.

[0060] The beam may include a first and second micro -machined layer, the first of which is insulating to provide the portion of the electrical insulator in a region where the second layer is removed.

[0061] Thus it is another object of the invention to provide a simple method for forming insulating and conductive elements required by the present invention.

[0062] The electrical insulator of the beam may be between the actuator and the control element or between the control element and the sensor or both.

[0063] It is further an object of the invention to provide that the controlling circuit may be placed on either side of the isolation or to provide redundant isolation for greater total isolation.

[0064] The analog isolator may include a second sensor at a first portion of the element to provide a second output electrical signal indicating movement of the element to the second position, the output second electrical signal being electrically isolated from the first output electrical signal. [0065] Thus it is another object of the invention to provide for an isolator that produces a signal indicating movement of the beam and thus operation of the isolator from the isolated side.

[0066] The isolator may further include a second actuator as a second portion of the element to receive a second input signal and exert a force dependent on the second input electrical signal urging the element toward the second position.

[0067] Thus it is another object of the invention to provide for a bi-directional electrical isolator suitable for use in multi-level control loops or for the purpose of resetting a scaling factor.

[0068] The present invention provides a mechanical isolator manufactured using MEMS techniques and suitable for transmitting digital signals. A special fabrication process forms a microscopic beam whose ends are insulated from each other. One end of the beam is connected to a microscopic actuator which receives an input signal to move the beam against a biasing force provided by a biased device. The other isolated end of the beam is attached to a sensor detecting movement of the beam only when the actuator force exceeds the countervailing force of the biased device. The small scale of the total device provides inexpensive, fast and reliable response.

[0069] Specifically, the present invention provides a micro electromechanical system digital isolator having a substrate and an element supported by the substrate for movement between the first and second position with respect to the substrate. At least a portion of the element between a first and second location on the element is an electrical insulator to electrically isolate the first and second locations from each other. An actuator is attached to the first portion of the element to receive an input electrical signal and exert a force dependent on the input electrical signal urging the element toward the second position. A bias structure is attached to the element to exert a predetermined opposite force on the element urging the element toward the first position. Finally, a sensor is attached to the second portion of the element to provide an output electrical signal indicating movement of the element between the first position and the second position whereby an input signal above a predetermined magnitude overcomes the opposite force to cause the element to move rapidly from the first to the second position to produce the output electrical signal electrically isolated from the input electrical signal. [0070] It is one object of the invention to produce a simple mechanical isolation system using MEMS techniques suitable for a wide variety of binary signals and yet which overcomes many of the disadvantages of current optical isolators in costs, interdevice consistency, and incompatibility with other integrated circuit components. In addition, the present invention requires no preconditioning of the input signal. The voltage or current is applied directly to the device with no pre-processing.

[0071] The actuator may be an electrostatic motor or a Lorenz force motor or a piezoelectric motor or thermal-expansion motor or a mechanical displacement motor.

[0072] It is therefore another object of the invention to provide an isolator that may receive a variety of different electrical signals that may not be compatible with an optical isolator LED, for example, those having a voltage of less than 0.7 volts.

[0073] Similarly, the bias structure may be an electrostatic motor, a Lorenz force motor, a piezoelectric motor, a thermal-expansion motor, a mechanical displacement motor, or a mechanical spring.

[0074] Thus the invention may provide both for an extremely simple force biasing that requires no electrical comiection (e.g. a mechanical spring) or an adjustable bias structure that allow the threshold of activation of the device to be freely tailored to different circumstances. In this way, unlike with optical isolators, an input threshold voltage may be tailored to the particular application.

[0075] The sensor may be a capacitive sensor or a piezoelectric sensor or a photoelectric sensor or a resistive sensor or an optical switching sensor.

[0076] It is therefore another object of the invention to provide flexible variety of sensing techniques suitable for different purposes.

[0077] The travel of the element may be limited by stops to between the first and second position.

[0078] In this way, the invention may provide signal limiting comparable to that provided by an optical isolator for signals beyond the threshold needed to trigger the device.

[0079] hi one embodiment of the invention, the element may be a beam attached to the substrate for sliding motion between the first and second positions. The beam may be supported by flexing transverse arm pairs attached at longitudinally opposed ends of the beam to extend outward therefrom.

[0080] Thus it is another object of the invention to provide a simple mechanism that may be implemented on a microscopic scale using MEMS technologies for supporting an element for motion. [0081] The flexing transverse amis may include a cantilevered first portion having first ends attached to the beam and second ends attached to an elbow portion removed from the beam and a cantilevered second portion substantially parallel to the first portion and having a first end attached to the substrate proximate to the beam and a second end attached to the elbow portion. Further the beam and the transverse arms may be symmetric across a longitudinal beam access.

[0082] Thus it is another object of the invention to provide a microscopic structure that is resistant to thermal expansion due to processing temperatures or changes in the operating temperature. The symmetry ensures that the beam remains centered with thermal expansion while the doubling back of the flexible transverse aπns provides for a degree of cancellation of thermal expansion of these aπns.

[0083] The flexing transverse arms may attach to the substrate through a spring section allowing angulation of the ends of the transverse arms with respect to the substrate.

[0084] It is thus another object of the invention to allow an effective pivoting of the flexible transverse arms so as to decrease the stiffness of the beam structure.

[0085] One embodiment of the invention may include a magnetic field, which may be produced by a magnet, crossing the beam and at least one flexing transverse arm may be conductive to an electrical signal and exert a force dependent on the electrical signal urging the beam toward a position.

[0086] It is thus another object of the invention to provide that the same structure used to support the beam may provide for its actuation or bias.

[0087] The beam may include transverse extending primary capacitor plates attached to the beam and extending out from the beam proximate to secondary capacitor plates. The effective area of the primary capacitor plates may be equal across the longitudinal axis of the beam and the capacitor plates may be attached to the beam between attachment points of at least two of the flexing transverse arm pairs. In one embodiment, the capacitors may include interdigitated fingers. Parallel plate capacitors will also work (although they have less linearity).

[0088] Another object of the invention is to provide a method for the integration of an electrostatic motor to the isolator in a way that balanced and well-supported forces may be obtained.

[0089] The primary capacitor plates may be positioned with respect to the secondary capacitor plates so as to draw the primary capacitor plates toward the secondary capacitor plates on one side of the beam while to separate the primary capacitor plates from the secondary capacitor plates on the other side of the beam. Conversely, the capacitor plates may be positioned so that all draw together with a given motion.

[0090] Thus it is another object of the invention to allow the capacitor plates to be used as a sensor in which a comparison of capacitance values reveals a position of the beam or as an electrostatic motor.

[0091] The beam may include a first and second micro-machined layer, the first of which is insulating to provide the portion of the electrical insulator in a region where the second layer is removed.

[0092] Thus it is another object of the invention to provide a simple method for foπning insulating and conductive elements required by the present invention.

[0093] The electrical insulator of the beam may be between the actuator and the bias structure or between the bias structure and the sensor or both.

[0094] It is a further object of the invention to provide that the biasing circuit may be placed on either side of the isolation or to provide redundant isolation for greater total isolation.

[0095] The digital isolator may include a second sensor at a first portion of the element to provide a second output electrical signal indicating movement of the element to the second position, the output electrical signal being electrically isolated from the output electrical signal.

[0096] Thus it is another object of the invention to provide for an isolator that produces a signal indicating movement of the beam and thus operation of the isolator from the isolated side.

[0097] The isolator may further include a second actuator as a second portion of the element to receive a second input signal and exert a force dependent on the second input electrical signal urging the element toward the second position.

[0098] Thus it is another object of the invention to provide for a bi-directional electrical isolator suitable for use with bi-directional data lines.

πi.

[0099] The present inventors have recognized that the complex multicomponent integrated circuit materials from which MEMS devices are constructed, have widely varying coefficients of expansion which may create distortions and stress in the MEMS beam structure (particularly in the flexible anns supporting the beam) as the MEMS device cools from high processing temperatures, or when the MEMS devices is used at different operating temperatures, or when the MEMS device is subject to local self-heating from the conduction of current. These distortions and stresses limit the beam structure's application to certain precision applications.

[00100] Accordingly, the present invention provides several techniques to compensate for such dimensional distortions and stress in beam-type MEMS devices, allowing mass-production of increasingly precise and accurate mechanisms. The present invention further provides methods of controlling the typical distortions in the flexible aims to provide increased functionality in beam-type MEMS devices.

[00101] In this regard, the invention provides improved methods of attaching the flexible arms that support the beam to the substrate. These attachment methods are augmented by enforcement of conditions of symmetry on the beam and its structure.

Control of bowing of the transverse anns, discovered by the inventors in connection with their study of temperature induced distortions of the MEMS stracture, is used to add bias or bi-stability or mechanical amplification to the MEMS device.

[00102] Specifically then, the present invention provides a MEMS system having a beam supported on flexible transverse arms to move longitudinally along a substrate wherein ends of the transverse arms removed from the beam are connected to the substrate by elements allowing transverse movement of the ends of the arms. This transverse movement may be provided, for example, by a flexible longitudinally extending wrist.

[00103] It is one object of the invention, therefore, to provide an attachment system for the transverse arms that accommodates transverse dimensional changes in the arms caused by temperature changes and which, if uncon-ected, can cause buckling of the aπns, stress stiffening of the aims, or offset of the beam from its null position.

[00104] The wrist elements may attach to the transverse arms via arcuate sections.

[00105] Thus, it is another object of the invention to eliminate points of concentrated stress at the arm ends.

[00106] The wrist elements may include serpentine sections, and/or the serpentine sections may be placed at the ends of the transverse arms where they are attached to the wrist elements.

[00107] Thus, it is another object of the invention to provide an attachment mechanism for the transverse aπns that is both transversely and rotationally unrestrained so as to mimic a "free beam" whose ends are unrestrained. Transverse arms that approximate a free beam provides a less stiff bending force with movement of the supported beam and avoid stress stiffening such as may change the dynamic characteristics of the MEMS device.

[00108] The beam may be supported at longitudinally opposed ends by pairs of transverse aπns extending from either side of the beam and the wrist elements for the transverse aπns may either all extend toward the center of the beam or all extend away from the center of the beam.

[00109] Thus, it is another object of the invention to balance any forces on the beam caused by a slight bowing of the transverse aims such as may be incurred by an expansion of those aπns or other distortions by encouraging countervailing bowing. It is a further object of the invention to compensate for any Lorentz forces that may occur on the wrists when current is passed through the transverse aπns. By facing the wrists in the same direction, a transverse balancing of Lorentz forces from the wrists is obtained.

[00110] The beam may be supported at its center by a pair of transverse arms extending from the beam on opposite sides of the beam and the wrist elements for the center transverse ann may extend in opposite longitudinal directions.

[00111] Thus it is another object of the invention to promote an S-shape bending for a transverse aπn centered on the beam such as prevents any longitudinal biasing of the beam as would occur with an uninflected bowing. Such a central beam may have no current flowing through it to eliminate any issues with Lorentz forces.

[00112] The beam may be designed to stabilize at a dimension that places the respective pairs of transverse aπns on either end of the beam in equal and opposite flexure: either bowing in or bowing out.

[00113] Thus, it is another object of the invention to balance any of the forces that may be placed on the beam by distortions in the lengths of the flexible aπns.

[00114] The transverse arms may also be made of equal length. The points of attachment of the transverse arms to other than at ends of the beam may be centered between the points of attachment of the transverse arms at the end of the beam. The actuator and biasing structures for the beam may be placed at the end of the beam.

[00115] Thus, it is another object of the invention to enforce a longitudinal and transverse symmetry on the MEMS device so that other effects of dimensional distortion in the transverse arms and beam are balanced out.

[00116] In one embodiment, the beam may be supported on at least one pair of flexible transverse arms, which are bowed to present a force that increasingly resists longitudinal motion of the beam in a first direction up to a snap point after which the force abruptly decreases. The force may change direction after the snap point or keep the same direction.

[00117] Thus, it is another object of the invention to provide a bistable or monostable mode of operation of the beam device.

[00118] After the snap point, the bow may increasingly resist longitudinal motion of the beam in a second direction opposite the first direction up to a second snap point at which the force abruptly decreases. The second snap point may be different from the first snap point.

[00119] Thus, it is another object of the invention to provide for a hysteresis actuation of the beam using mechanical elements.

[00120] In a different embodiment, the beam may be supported by at least one flexible transverse arm, which is angled to also extend longitudinally. A sensor detecting transverse motion may receive the first transverse ami at an end removed from the beam.

[00121] Thus, it is another object of the invention to provide for a mechanical amplification of either the force or motion of the beam as transmitted to the sensor structure.

IV.

[00122] The present invention provides a mechanical isolator manufactured using MEMS techniques and suitable for transmitting analog or digital signals. The isolator uses a specially fabricated microscopic beam supported on a substrate and whose ends are insulated from each other. One end of the beam is com ected to a microscopic actuator, which receives a user input signal to move the beam based on that signal. The other end of the beam is attached to a sensor detecting movement of the beam to provide a corresponding value.

[00123] Acceleration of the substrate, which might move the beam in the absence of a user signal, is compensated for by fabricating a second identical beam that measures inertial force and removes it from the signal. This technique can be used generally not just with isolators but also with any MEMS device in which forces or movement caused by acceleration of the substrate must be canceled. In addition, this approach also applies to other common mode noise sources other than acceleration or inertia; such as: temperature, pressure, etc.

[00124] Specifically then, the present invention provides a microelectromechanical system (MEMS) with reduced inertial sensitivity. The invention includes a substrate and a first element supported from the substrate for movement relative to the substrate with respect to an axis. A first actuator is attached to the first element to exert a force thereupon dependent upon a parameter to be measured and urging the element toward a second position. The device also includes a second element supported from the substrate also for movement with respect to the axis. A sensor assembly communicates with the first and second elements to detect movement of the first and second elements and to provide an output subtracting their movements so as to be less sensitive to substrate acceleration or other common mode noise.

[00125] Thus it is one object of the invention to provide a MEMS sensor with reduced sensitivity to acceleration interfering with measurement of the desired parameter.

The small size of the MEMS device allows two matched elements to be fabricated in close proximity to each other so as to be identical and to experience the same inertial forces so that one may provide an inertial reference signal that can be used to cancel the inertial contribution to the parameter measurement.

[00126] The second element may not have an input signal applied or an actuator or functioning actuator so as to detect only inertial forces or it may include a functional actuator which exerts a force upon the second element dependent upon the parameter to be measured but urging the second element in the opposite direction as the first element.

[00127] Thus it is another object of the invention to pennit a simple cancellation, which reduces inertial noise, or a more sophisticated cancellation that reduces inertial noise while also boosting the desired signal.

[00128] The parameter may be an electrical signal and the second and first actuators may receive the input electrical signal related to the parameter and exert a force dependent on the input electrical signal. In this case, the device may include an inverting circuit receiving the parameter electrical signal and producing an inverted electrical signal for the second actuator.

[00129] Thus it is another object of the invention to pennit the inertial noise cancellation with identical MEMS structures simply by inverting an electrical signal to one MEMS structure so that it operates in the opposite direction.

[00130] The MEMS device may include a second actuator attached to the second element but not communicating with the parameter to be measured and thus not exerting a force thereupon dependent upon the parameter to be measured.

[00131] Thus it is another object of the invention to provide for virtually identical

MEMS structures, including actuators, so as to be equally sensitive to inertial noise. [00132] The foregoing objects and advantages may not apply to all embodiments of the inventions and are not intended to define the scope of the invention for which purpose claims are provided. In the following description, reference is made to the accompanying drawings, which form a part hereof, and in which there is shown by way of illustration, a preferred embodiment of the invention. Such embodiment also does not define the scope of the invention and reference must be made therefore to the claims for this purpose.

BRIEF DESCRIPTION OF THE DRAWINGS

I.

[00133] Fig. 1 is a simplified block diagram of the present analog isolator showing its elements of an actuator, a control element and a sensor communicating along a single mechanical element that may move to transmit data between the actuator and sensor and showing insulating portions of the moving element;

[00134] Fig. 2 is a top plan view of one embodiment of the isolator of Fig. 1 using three electrostatic motors and a capacitive sensor showing support of a moving beam connecting these components by means of flexible transverse arms and showing implementation of the insulating sections of the beam;

[00135] Fig. 3 is a simplified perspective view of an insulating section of the beam of Fig. 2 showing the use of laminated conductive and nonconductive layers and the removal of the conductive layer to create the insulating section;

[00136] Fig. 4 is a fragmentary view of one transverse ann of Fig. 2 showing an optional doubling back of the ann at an elbow so as to provide stress relief;

[00137] Figs. 5a and 5b are fragmentary detailed views of the elbow of Fig. 4 showing the incorporation of a spring allowing angulation of the portion of the transverse ann attached to the beam for improved force characteristics;

[00138] Fig. 6 is a view of one pair of transverse arms of Fig. 2 showing electrical separation of the arms of the pair to allow a current to be imposed on the arm to create a

Lorenz-force motor such as may be substituted for the electrostatic motors of Fig. 2;

[00139] Fig. 7 is a figure similar to that of Fig. 1 showing the addition of a second sensor and second actuator on opposite ends of the beam to allow for a bi-directional isolator or with the additional sensor alone, a high reliability isolator; and [00140] Fig. 8 is a detailed view of the sensor of Fig. 1 and its associated processing electronics for extracting a digital word from the isolator of the present invention.

II.

[00141] Fig. 9 is a simplified block diagram of the present digital isolator showing its elements of an actuator, a bias structure and a sensor communicating along a single mechanical element that may move to transmit data between the actuator and sensor and showing insulating portions of the moving element;

[00142] Fig. 10 is a top plan view of one embodiment of the isolator of Fig. 9 using two counterpoised electrostatic motors and a capacitive sensor showing support of a moving beam connecting these components by means of flexible transverse arms and showing implementation of the insulating sections of the beam;

[00143] Fig. 11 is a simplified perspective view of an insulating section of the beam of Fig. 10 showing the use of laminated conductive and nonconductive layers and the removal of the conductive layer to create the insulating section;

[00144] Fig. 12 is a fragmentary view of one transverse arm of Fig. 10 showing a doubling back of the arm at an elbow so as to reduce the effects of expansion caused by thermal changes;

[00145] Figs. 13a and 13b are fragmentary detailed views of the elbow of Fig. 12 showing the incorporation of a spring allowing angulation of the portion of the transverse ann attached to the beam for improved force characteristics;

[00146] Fig. 14 is a view of one pair of transverse arms of Fig. 10 showing electrical separation of the aims of the pair to allow a current to be imposed on the arm to create a Lorenz force motor such as may be substituted for the electrostatic motors of Fig.

10;

[00147] Fig. 15 is a figure similar to that of Fig. 9 showing the addition of a second sensor and second actuator on opposite ends of the beam to allow for a bi-directional isolator or with the additional sensor alone, a high reliability isolator.

III.

[00148] Fig. 16 is a simplified block diagram of a beam-type MEMS device of the present invention in which the beam is supported on three sets of transversely extending arms; [00149] Fig. 17 is a detailed, top plan view of the beam-type device of Fig. 16 for use as an electrical isolator, the device using three electrostatic motors and a capacitive sensor attached to the beam and having wrist elements attaching the transverse arms to the substrate;

[00150] Fig. 18 is a schematic diagram of a simplified wrist element of Fig. 17 such as provide transverse movement of the ends of the transverse arms and balanced

Lorentz forces;

[00151] Fig. 19 is a perspective fragmentary view of a wrist element of Fig. 18 showing an arcuate transition to reduce stress concentration;

[00152] Fig. 20 is a figure similar to that of Fig. 18 showing an exaggeration . expansion of the outer transverse arms that cause an inward bowing of the outer arms such as produces countervailing forces and an S bowing of the center transverse arms that produces a torsion but no net longitudinal force;

[00153] Fig. 21 is a fragmentary view similar to that of Fig. 19 showing the addition of an expansion outrigger to the wrists counteracting expansion induced stress in the transverse arms;

[00154] Figs.22 and 23 show the addition of serpentine portions to the wrists and ends of the transverse aπns such as provide both additional transverse compliance and rotational freedom simulating a free beam structure;

[00155] Fig. 24 is a diagram similar to Fig. 16 showing major axes of symmetry, which are preserved in the invention to counteract additional forces;

[00156] Fig. 25 is a figure similar to that of Fig. 18 showing an exploitation of expansion induced bowing to create a bistable biasing on the beam;

[00157] Fig. 26 is a plot of force versus longitudinal displacement of the beam showing the snap action created by buckling of the bowed transverse aπn of Fig. 25;

[00158] Fig. 27 is a figure similar to that of Fig. 25 showing a fabricated stress-free bowing of a pair of transverse aπns to provide a monostable biasing of the beam;

[00159] Fig. 28 is a plot similar to that of Fig. 26 showing the monostable biasing provided by the bowing of the transverse ann of Fig. 27;

[00160] Fig. 29 is a figure similar to that of Fig. 27 showing attachment of the bowed transverse arm to movable position sensors, the arm such as may provide a mechanical leverage increasing sensitivity of the sensors to longitudinal movement of the beam; and [00161] Fig. 30 is a geometric diagram showing the mechanical amplification provided by the bowed beam of Fig. 29 reduced to a trigonometric approximation.

IV.

[00162] Fig. 31 is a simplified block diagram of the present analog isolator showing its elements of an actuator, a control stracture and a sensor coimnunicatiiig along a single mechanical element that may move to transmit data between the actuator and sensor and showing insulating portions of the moving element; [00163] Fig. 32 is a top plan view of one embodiment of the isolator of Fig. 31 using three electrostatic motors and a capacitive sensor showing support of a moving beam connecting these components by means of flexible transverse anns and showing implementation of the insulating sections of the beam;

[00164] Fig. 33 is a simplified perspective view of an insulating section of the beam of Fig. 32 showing the use of laminated conductive and nonconductive layers and the removal of the conductive layer to create the insulating section; [00165] Fig. 34 is a fragmentary view of one transverse ann of Fig. 32 showing a doubling back of the arm at an elbow so as to provide stress relief; [00166] Figs. 35a and 35b are fragmentary detailed views of the elbow of Fig. 34 showing the incorporation of a spring allowing angulation of the portion of the transverse arm attached to the beam for improved force characteristics; [00167] Fig. 36 is a view of one pair of transverse arms of Fig. 32 showing electrical separation of the anns of the pair to allow a cuπent to be imposed on the arm to create a Lorenz-force motor such as may be substituted for the electrostatic motors of Fig. 32;

[00168] Fig. 37 is a figure similar to that of Fig. 31 showing the addition of a second sensor and second actuator on opposite ends of the beam to allow for a bidirectional isolator or with the additional sensor alone, a high reliability isolator; [00169] Fig. 38 is a detailed view of the sensor of Fig. 31 and its associated processing electronics for extracting a digital word from the isolator of the present invention;

[00170] Fig. 39 is a figure similar to that of Fig. 31 showing the use of two MEMS devices for the purpose of canceling out the effects of acceleration of the substrate on measurements of the mechanical elements by subtraction of the signals from two parallel elements; [00171] Fig, 40 is a figure similar to that of Fig. 39 showing an alternative embodiment where the two MEMS mechanical elements are driven by mutually inverted electrical signals in opposite directions so that the subtraction doubles the measured signal as well as reducing inertial noise;

[00172] Fig. 41 is a figure similar to that of Fig. 39 wherein the ultimate subtraction of the signals from the two MEMS devices is accomplished with reduced electrical circuitry; and

[00173] Fig.42 is a figure similar to that of Fig. 40 wherein the ultimate subtraction of the signals from the two MEMS devices is accomplished with reduced electrical circuitry.

DETAILED DESCRIPTION OF THE INVENTION

I. FIRST EMBODIMENT

[00174] Referring now to Fig. 1, a MEMS analog isolator 10 per the present invention includes an actuator 12, control.element 14, and a sensor 18 mechanically interconnected by a movable beam 20.

[00175] The actuator 12 includes terminals 22a and 22b and 22c+22d through which an analog electrical input signal 21 may be received and converted into a mechanical force tending to move the beam 20 in an actuation direction 24 indicated by an arcow. In the microscopic scale of the MEMS analog isolator 10, the actuator may be a piezoelectric actuator, a thermal-expansion motor, a mechanical-displacement motor, an electrostatic motor, or a Lorenz-force motor generally known in the art, the latter two to be described in more detail below. For a Lorenz-force motor or thermal-expansion motor, the analog electrical input signal 21 will be a current, for the piezoelectric or electrostatic motor, the input electrical signal will be a voltage. [00176] The actuator 12 communicates with a first end of the beam 20. An opposite end of the beam 20 is received by the sensor 18 which detects movement of the beam 20 and through its terminals 26a and 26b and 26c+26d produces an electrical signal that may be measured directly or further processed by processing electronics 28 to produce the output signal 30 indicating movement of the beam 20. The sensor 18 may be a piezoelectric-type sensor, a photoelectric sensor, a resistive sensor, an optical switching sensor, or a capacitive sensor according to techniques known in the art of MEMS design. In the preferred embodiment, the sensor 18 uses counterpoised movable plate capacitors as will be described in more detail below.

[00177] Attached to the beam 20 between the actuator 12 and the sensor 18 is the control element 14 which provides both a force on the beam 20 opposite the actuation direction 24 and tending to resist the operation of the actuator 12 or with the actuation direction 24 augmenting the operation of the actuator 12, as indicated by double headed arrows 35.

[00178] Absent an analog electrical input signal 21, the control element 14 may hold the beam 20 in a position toward the sensor 18. Ideally, the control element 14 provides a force that increases with motion of the beam 20 in the actuation direction 24. In this way, a simple relationship between actuation force and movement of the beam 20 is generated (e.g., with a simple spring-type system). The MEMS analog isolator 10 provides extremely low friction and inertia so this movement or force is consistent and rapid. Alternatively, the control element 14 may provide a rapidly increasing force (in a feedback system) arresting the movement of the beam 20 for any actuation force. Here the magnitude of the arresting force provides the output signal. [00179] As described, the force provided by the control element 14 may be adjustable by varying a current or voltage to the stracture and used in a feedback mode to essentially eliminate all but a small movement of the beam 20. Some movement of the beam 20 is necessary for the sensor 18 to provide the necessary countervailing feedback, but the movement may be reduced to an extent that non-linearities in the actuators and mechanical elements of the MEMS analog isolator 10, that might occur with more pronounced movement, are eliminated. Specifically, in this mode, the movement of the beam 20 is detected by processing electronics 28 to produce a position signal. The position signal is compared against a reference signal 29 to produce an enor signal 31 which is directed to the control element to produce a restoring force returning the beam 20 to the null point. The comiection between the eιτor signal to the control element 14 may be direct or may be further modified by a feedback network 33 providing compensation for the system according to well-known feedback teclmiques. The feedback network 33 may steer voltage to either tenninals 38c and 38d with a return at terminal 50 for actuation toward the sensor 18 or to tenninals 38a and 38b with a return at terminal 50 for actuation toward the actuator 12 reflecting the fact that the electrostatic motors provide only a single direction of force. [00180] The beam 20 includes conductive portions 32a and 32b, located at the actuator 12 and sensor 18, respectively, and such as may form part of the actuator 12 or sensor 18. Insulating portions 34a and 34b separate conductive portions 32a and 32b from a centeπnost conductive portion 32c that may be part of the control element 14; the insulating portions 34a and 34b thus defining three regions of isolation 36a-c. The first region 36a includes the actuator 12 and conductive portion 32a, the second region 36b includes the center conductive portion 32c and the control element 14, and the third region 36c includes the conductive portion 32b and sensor 18. [00181] The insulated beam 20 provides a mechanism by which the analog electrical input signal 21 acting through the actuator 12 may produce a corresponding output signal 30 at the sensor 18 electrically isolated from the analog electrical input signal 21. The control element 14 may be electrically isolated from either the input signal and/or the output signal 30.

[00182] The control element 14 is preferably a Lorenz-force motor or an electrostatic motor of a type that will be described below. For the former of these two control elements, terminals 38a and 38b and return 50 are provided to provide a bidirectional current dictating the countervailing force provided by the control element 14. The direction of the cunent dictates the direction of the force. For the latter electrostatic stracture, terminals 38a, 38b, 38c, and 38d are provided. Voltage is applied either to teπninal pair 38a and 38b (with reference to return 50) or to teπninal pair 38c and 38d (with respect to return 50) to determine the direction of the force. [00183] Referring now to Fig. 2, the beam 20 may extend above a substrate 42 along a longitudinal axis 40 passing along a midline between transversely opposed pylons 44 attached to a substrate 42. The pylons form the terminals 22a and 22b, 38a-38d, 26a, and 26b described above. Ideally, the substrate 42 is an insulating substrate and thus pylons 44 are all mutually isolated and particular conductive layers are placed or wire bonding used to make the necessary connections.

[00184] The beam 20 is supported away from the substrate 42 and held for movement along the longitudinal axis 40 by means of flexing arm pairs 46 extending transversely on opposite sides of both ends of the beam 20 and its middle. The flexing aims 46 extend away from the beam 20 to elbows 48 transversely removed from the beam 20 on each side of the beam 20. The elbows 48 in turn connect to expansion compensators 50, which return to be attached to the substrate 42 at a point near the beam 20. As mentioned above, these expansion compensators are not absolutely required. They serve as stress relief if that is needed. The flexing transverse arms 46 are generally parallel to the expansion compensators 50 to which they are connected. The flexing transverse aπns 46, elbows 48 and expansion compensators are conductive to provide electrical connections between the conductive portions 32a, 32b, and 32c and stationary electrical terminals (not shown).

[00185] Refenϊng now to Fig. 4, the length L_\ of each expansion compensator 50 between its point of attachment 52 to the substrate 42 and its connection to a coπ-esponding flexing transverse aim 46 at elbow 48 and the length L₂ of the flexing transverse ann 46 defined as the distance between its comiection to beam 20 and the elbow 48 are set to be nearly equal so that expansion caused by thermal effects in the flexing transverse arm 46 is nearly or completely canceled by expansion in the expansion compensator 50. In this way, little tension or compression develops in the flexing transverse arm 46. Both the flexing transverse arm 46 and the expansion compensator 50 in this embodiment are fabricated of the same material, however it will be understood that different materials may also be used and lengths _\ and L₂ adjusted to reflect the differences in thermal expansion coefficients. Note that a doubling back of the arm is not required. A straight comiection will also work. The doubling back of the arm is a stress- relieving feature. Stress in the beam will affect the spring constant. Depending on the spring constant desired, and other geometric and process (e.g. substrate choice) considerations, stress relief may or may not be needed or desirable. [00186] Refeπing to Fig. 5a, the elbow 48 may include a serpentine portion 54 extending longitudinally from the expansion compensator 50 to its flexing transverse ann 46. As shown in Fig. 5b, the serpentine portion 54 allow angulation α between the flexing transverse ann 46 and expansion compensator 50 such as provides essentially a radius adjusting pivot, both decreasing the force exerted by the flexing transverse arm pairs 46 on the beam 20 with movement of the beam 20 and decreasing the stiffness of the structure.

[00187] Refeπing again to Figs. 2 and 3, in between the flexing transverse arm pairs 46 the beam 20 expands to create T-bars 56 flanking insulating portion 34a and 34b. Insulating material 58 attached to these T-bars 56 create the insulating portions 34. Generally the beam 20 may be fabricated using well-known MEMS processing techniques to produce a structure suspended above the substrate 42 and composed of a laminated upper conductive layer 60 (for example polycrystalline silicon or crystalline silicon optionally with an upper aluminum layer) and a lower insulating layer 62 such as silicon dioxide or silicon nitride. The insulating portions 34 may be obtained simply by etching away the upper layer in the region 34a or 34b according to techniques well known in the art using selective etching techniques. An improved method of fabricating these structures is described in US patent 6,159,385 issued 12/12/2000 hereby incorporated by reference. The edges and comers of the T-bars 56 may be rounded to increase the breakdown voltage between them.

[00188] Each of the upper conductive layer 60 and lower insulating layer 62 are perforated by vertically extending channels 64 such as assists in conducting etchant beneath the layers 60 and 62 to remove a sacrificial layer that noπnally attaches layers 60 and 62 to the substrate 42 below according to techniques well known in the art. [00189] Referring now to Fig. 2 again, portion 32a of the beam 20, such as provides a portion of the actuator 12 may have transversely outwardly extending, moving capacitor plates 66 overlapping with coπesponding transversely inwardly extending stationary capacitor plates 68 attached to the pylons 44 representing tenninals 22a and 22b. Each of the moving capacitor plates 66 and their coπesponding stationary capacitor plates 68 may have mutually engaging fingers (as opposed to being simple parallel plate capacitors) so as to provide for a more uniform electrostatic force over a greater range of longitudinal travel of the beam 20. The thus fomied electrostatic motor operates using the attraction between the capacitor plates 66 and 68 with the tenninals 22b and 22a connected to a more positive voltage than that of beam 20 (connected to terminals 22c+22d), to urge the beam 20 in the actuation direction 24. For this reason, stationary capacitor plates 68 are after the moving capacitor plates 66 on both sides of the beam 20 as one travels along the actuation direction. Capacitor plates 66 and 68 are cantilevered over the substrate 42 by the same under etching used to free the beam 20 from the substrate 42.

[00190] The pylons 44 flanking portion 32c of the beam such as form pads 38a-38d likewise include moving and stationary capacitor plates 66 and 68 in two distinct pairs. As noted, this section provides the control element 14 and as such, two electrostatic motors; one (using terminals 38c and 38d) created to produce a force in the opposite direction of actuator 12 with the moving capacitor plates 66 following the stationary capacitor plates 68 as one moves in the actuation direction 24 and the other (using tenninals 38a and 38b) created to produce a force in the same direction to the actuator 12 with the moving capacitor plates 66 preceding the stationary capacitor plates 68 as one moves in the actuation direction 24. These two actuators are used in combination to give the best possible control of the closed loop system.

[00191] Referring still to Fig. 2, portion 32b of the beam also supports moving capacitor plates 66 and stationary capacitor plates 68. However in this case, the capacitor plates do not serve the purpose of making an electrostatic motor but instead serve as a sensing means in which variation in the capacitance between the moving capacitor plates 66 and stationary capacitor plates 68 serves to indicate the position of the beam 20. In this regard, the order of the stationary and moving capacitor plates 66 and 68 is reversed on opposite sides of the beam 20. Thus, the moving capacitor plates 66 precede the stationary capacitor plates 68 on a first side of the beam (the upper side as depicted in Fig. 2) as one moves in the actuation direction 24 (as measured between terminal 26a and terminals 26c+26d) whereas the reverse order occurs on the lower side of the beam 20 (as measured between tenninal 26b and tenninals 26c+26d). Accordingly as the beam 20 moves in the actuation direction 24, the capacitance fonned by the upper moving capacitor plates 66 and stationary capacitor plates 68 increases while the capacitance formed by the lower plates decreases. The point where the value of the upper capacitance crosses the value of the lower capacitance precisely defines a null point and is preferably set midway in the travel of the beam 20.

[00192] Techniques for comparing capacitance well known in the art may be used to evaluate the position of the beam 20. One circuit for providing extremely accurate measurements of these capacitances is described in co-pending application Serial No. 09/677,037 filed September 29, 2000, hereby incorporated by reference. [00193] Generally, the operating stracture of the MEMS analog isolator 10 is constracted to be symmetric about an axis through the middle of the beam 20 along the longitudinal axis 40 such as to better compensate the thermal expansions. In addition, the operating area of the plates of the capacitors, plates 66 and 68 on both sides of the beam 20 for the actuator 12 and the control element 14, are made equal so as to be balanced. For similar reasons, the capacitors of the electrostatic motors and the control element 14 are placed between flexing transverse am pairs 46 so as to better control slight amounts of torsion caused by uneven forces between the capacitor plates 66 and 68. [00194] Referring now to Fig. 6, it will be understood that one or both of the electrostatic motors forming the actuator 12 and the control element 14 described above, may be replaced with Lorenz-force motors 75 in which forces are generated not by electrostatic attraction between capacitor plates but by the interaction of a current with a magnetic field. In the Lorenz-force motor 75, a magnetic field (e.g. with a permanent magnet, not shown) may be generated adjacent to the MEMS analog isolator 10 to produce a substrate-noπnal magnetic flux 70. The expansion compensators 50 supporting the flexing transverse aim 46 on opposite sides of the beam 20 are electrically isolated from each other so that a voltage may be developed across expansion compensators 50 to cause a current 72 to flow through the flexing transverse ann 46. This cuπent flow in the magnetic field generated by the magnet will produce a longitudinal force on the beam 20 that may act in lieu of the electrostatic motors. The amount of deflection is generally determined by the flux density of the magnetic field 70, the amount of current and the flexibility of the flexing transverse arm pairs 46 in accordance with the right hand rule. [00195] The Lorenz-force motors 75 are two quadrant, meaning they will accept currents in either direction to produce a force with or opposed to the actuation direction 24. Hence with Lorenz-force motors 75 (or the bi-directional electrostatic motor of the control element 14 described above), the MEMS analog isolator 10 may operate with two polarities unlike an optical isolator.

[00196] Referring now to Fig. 7, the actuator 12 positioned on beam portion 32a, may be teamed with a second sensor 74 for sensing motion of the beam 20 and that sensor 74 may be used to provide isolated feedback to a device producing the analog electrical input signal 21 as to motion of the beam 20 such as may be used to ensure greater reliability in the transmission of signals.

[00197] Alternatively or in addition, the sensor 18 may be teamed with an actuator

76 having the same orientation of actuator 12 but positioned in isolation portion 32b. When actuator 76 is teamed with sensor 74, they together provide a bi-directional analog isolator in which isolated signals may be sent from either end of the beam 20 to the other end. It will be understood that another variation of this embodiment may eliminate the control element and instead the actuators 76 and 12 may be used during transmission by the other actuator as the control element. Such a device may be useful in some multi-loop analog system or for scaling adjustment.

[00198] It will be understood with greater circuit complexity that certain of the elements of the actuator 12, control element 14 and sensor 18 may be combined into individual structures and hence, these terms should be considered to cover the functional equivalents of the functions of actuator control element 14 and sensor 18 whether or not they are realized as individual structures or not. Further the relative location of the control element 14, the actuator 12 and the sensor 18 may be swapped and still provide isolated signal transmission.

[00199] Referring now to Fig. 8, a digital word output 100 can be obtained from the sensor 18 by making use of an eiτor signal 31 resulting directly from a comparison of the capacitors of the sensor 18 by capacitive comparison circuit 102 of a type well lαiown in the art. One such circuit for providing extremely accurate measurements of these capacitances in described in co-pending application Serial No. 09/677,037 filed September 29, 2000, hereby incorporated by reference. As so configured, the error signal 31 (when connected to the control element 14) will tend to restore the beam 20 to a null position dependent on the location where the values of the capacitors of the sensor 18 change their relationship of which is greater than the other. The output of the capacitive comparison circuit 102 will generally be a duty cycle modulated square wave 104 produced as the beam 20 wanders back and forth across the null point under the influences of the actuation force and the restoring force. The beam 20 provides an inertial averaging of the error signal 31 so that its average force is proportional to the actuation force. Counter 106 measures the percentage of time that the eπor signal 31 is in the high state. In one embodiment, the output of the capacitive comparison circuit 102 may be logically ANDed with a high rate clock signal to cause the counter 106 to count up during the time the eπor signal 31 is high and not otherwise. The counter may be reset periodically by a second time interval signal 110. The value on the counter 106 just prior to the resetting will be proportional to the duty cycle of the eπor signal 31 and therefore to the actuation signal. The frequency of the clock signal 108 and the period of the time interval signal 110 may be selected according to the desired resolution in the digital word output 100 according to methods well lαiown in the art.

[00200] Referring again to Fig. 2, MEMS fabrication allows that a portion of the substrate 42 may also include integrated circuits 73 having a number of solid-state devices such as may implement, for example, the capacitor sense circuitry described above. A number of the MEMS analog isolators 10 may be placed on a single integrated circuit with appropriate interconnects made for providing them with the currents required. Generally, using the MEMS analog isolator 10 of the present invention, a single integrated circuit of arbitrary complexity, such as an industrial controller, may include isolators on the same substrate 42 manufactured conciurently with each other. These MEMS analog isolators 10 may provide for either inputs to the remaining integrated circuitry in the fonn of a digital word or, through the use of an on-board digital to analog converter, isolated analog outputs from the integrated circuit 73.

II. SECOND EMBODIMENT

[00201] Refeπing now to Fig. 9, a MEMS digital isolator 210 per the present invention includes an actuator 212, bias stracture 214, and a sensor 218 mechanically interconnected by a movable beam 220.

[00202] The actuator 212 includes terminals 222a and 222b and 222c+222d through which an electrical input signal 221 may be received and converted into a mechanical force tending to move the beam 220 in an actuation direction 224 indicated by an arrow. In the microscopic scale of the MEMS digital isolator 210, the actuator 212 may be a piezoelectric actuator, a thennal-expansion motor, a mechanical-displacement motor, an electrostatic motor or a Lorenz force motor generally lαiown in the art, the latter two to be described in more detail below. For a Lorenz force motor or thermal- expansion motor, the electrical input signal 221 will be a cuπent, for the piezoelectric or electrostatic motor, the input electrical signal will be a voltage. [00203] The actuator 212 communicates with a first end of the beam 220. An opposite end of the beam 220 is received by the sensor 218 which detects movement of the beam 20 and, through its tenninals 226a, 226b and 226c+226d, produces an electrical signal that may be measured directly or further processed by processing electronics 228 to produce the output signal 230 indicating movement of the beam 220. The sensor 218 may be a piezoelectric-type sensor, a photoelectric sensor, a resistive sensor, an optical switching sensor, or a capacitive sensor according to techniques lαiown in the art of MEMS design. In the prefeπed embodiment, the sensor 218 uses counterpoised movable plate capacitors as will be described in more detail below.

[00204] Attached to the beam 220 between the actuator 212 and the sensor 218 is the bias stracture 214 which provides a force on the beam 220 opposite the actuation direction 224 as indicated by arrows 235 and tending to resist the operation of the actuator 212.

[00205] Absent an electrical input signal 221, the bias stracture 214 holds the beam in a position toward the sensor 218. Ideally, the bias stracture 214 provides a force that is fixed or that decreases slightly with motion of the beam 220 in the actuation direction 224. In this way, a precisely defined threshold is created for the actuation force. Electrical input signal 221 inducing a force on the beam slightly below the force produced by the bias structure 214 will cause no motion of the beam 220. In one embodiment, electrical input signal 221 inducing a force even slightly above that produced by the bias stracture 214 will cause a rapid and complete movement of the beam 220 to its further extent in the actuation direction 224. Alternative embodiments may provide for linear or non-linear behavior including but not limited to hysteresis in the movement of the beam 220 using mechanical or electrical teclmiques. In this way, a binary signal imposed on the electrical input signal 221 is unambiguously converted into movement of the beam 220 to one extreme in the actuation direction 224 or the other. The MEMS digital isolator 210 provides extremely low friction and inertia so this movement is both extremely well defined and rapid.

[00206] As will be described, the force provided by the bias stracture 214 may be adjustable by varying a current or voltage to the stracture. In the case where the force on the bias stracture 214 is adjustable, it is desirably set so that the bias force is the midpoint between defined high and low values of the force produced by the electrical input signal 221. If the structures used to implement the actuator 212 and bias stracture 214 are essentially the same and the input and bias are current, the current applied to the bias stracture may be approximately set to equal half the desired range of the input current electrical input signal 221. If the structures used to implement the actuator 212 and bias stracture 214 are essentially the same and the input and bias are voltage, the voltage applied to the bias stracture may be approximately set so that its square is equal to the midpoint of the squares of the high and low values of the desired range of the input voltage electrical input signal 221. Note, generally, the electrostatic force is proportional to V². Thus, for example, if : V(low) = 0, V(high) = 10, the squares are 0 and 100, so V(bias) should be the square root of 50 = 7.1 , if the actuator 212 and the bias structure 214 are constructed the same.

[00207] The invention also will work with a less than ideal bias stracture 214 such as a regular spring where a constant force opposite the actuation direction 224 is not realized but where the force provided by the bias stracture 214 increases slightly with movement of the beam 220 in the actuation direction.

[00208] In yet an alternative embodiment, the biasing force could be provided by a prestressing of flexing aπn pairs 246 to operate like an over-center spring whose force of resistance drops off sharply with motion against that force (like a child's clicker). The flexing aπn pair 246, thus configured, could add latching to the stracture. The bias structure 214 now could be used to reset the latching. Building the flexing arm pairs 246 in a curve could thus add bias without the need for the bias capacitive motor.

[00209] Alternatively, a "snap action" could be obtained by using non-symmetrical bias capacitor fingers 266 and 268 or parallel plates. As mentioned above, parallel plates have a square-law force/displacement characteristic. The same effect can be obtained with the capacitor fingers by graduating the longitudinal length of the fingers as one moves transversely.

[00210] The beam 220 includes conductive portions 232a and 232b located at the actuator 212 and sensor 218, respectively, and such as may fonn part of the actuator 212 or sensor 218. Insulating portions 234a and 234b separate conductive portions 232a and

232b from a centeimost conductive portion 232c that may be part of the bias structure

214; the insulating portions 234a and 234b thus defining three regions of isolation 236a-c.

The first region 236a includes the actuator 212 and conductive portion 232a, the second region 236b includes the center conductive section 232c and the bias structure 214, and the third region 236c includes the conductive section 232b and sensor 218.

[00211] The insulated beam 220 provides a mechanism by which the electrical input signal 221 acting through the actuator 212 may produce a corresponding output signal 230 from the sensor 218 electrically isolated from the electrical input signal 221.

The bias stracture 214 may be electrically isolated from either the input signal and/or the output signal 230.

[00212] The bias stracture 214 is preferably an electrostatic motor or a Lorenz force motor of a type that will be described below. For these latter two electronic bias structures, terminals 238a+238b and 238c+238d are provided to provide a voltage or current dictating the countervailing force provided by the bias stracture 214. Thus the precise threshold at which the digital isolator changes state from unactuated to actuated may be tailored for the particular circumstance, an option not available in optical isolators.

[00213] Refeπing now to Fig. 10, the beam 220 may extend above a substrate 242 along a longitudinal axis 240 passing along a midline between transversely opposed pylons 244 attached to a substrate 242. The pylons fonn the terminals 222a, 222b, 222c,

222d, 226a, 226b, 226c, 226d, 238a, 238b, 238c and 238d described above.

[00214] Ideally, the substrate 242 is an insulating substrate and thus pylons 244 are all mutually isolated and particular conductive layers are placed to make the necessary connections. [00215] The beam 220 is supported away from the substrate 242 and held for movement along the longitudinal axis 240 by means of flexing aπn pairs 246 extending transversely on opposite sides of both ends of the beam 220 and its middle. The flexing aims 246 extend away from the beam 220 to elbows 248 transversely removed from the beam 220 on each side of the beam 220. The elbows 248 in turn connect to expansion compensators 250 which return to be attached to the substrate 242 at a point near the beam 220. These expansion compensators 250 are not absolutely required. They serve as stress relief if that is needed. The flexing transverse aims 246 are generally parallel to the expansion compensators 250 to which they are connected. The flexing transverse arms 246, elbows 248 and expansion compensators are conductive to provide electrical connections between the conductive portions 232a, 232b, and 232c and stationary electrical terminals (not shown).

[00216] Referring momentarily to Fig. 12, stops 261 may be added between the flexing transverse ann 246 and the expansion compensators 250 or other stationary stracture so as to prevent overtravel of the beam 220 effectively limiting or clamping the output of the digital isolator in a manner analogous to that provided by other isolation techniques.

[00217] Referring now to Fig. 12, the length Li of each expansion compensator

250 between its point of attachment 252 to the substrate 242 and its connection to a corresponding flexing transverse arm 246 at elbow 248 and the length L of the flexing transverse aim 246 defined as the distance between its comiection to beam 220 and the elbow 248 are set to be nearly equal so that expansion caused by thermal effects in the flexing transverse ann 246 is nearly or completely canceled by expansion in the expansion compensator 250. hi this way, little tension or compression develops in the flexing transverse arm 246. Both the flexing transverse arm 246 and the expansion compensator 250 in this embodiment are fabricated of the same material, however it will be understood that different materials may also be used and lengths Li and L₂ may be adjusted to reflect the differences in thennal expansion coefficients. [00218] Referring to Fig. 13a, the elbow 248 may include a serpentine portion 254 extending longitudinally from the expansion compensator 250 to its flexing transverse arm 246. As shown in Fig. 13b, the serpentine portion 254 allows angulation α between the flexing transverse ann 246 and expansion compensator 250 such as provides essentially a radius adjusting pivot, both decreasing the force exerted by the flexing transverse ann pairs 246 on the beam 220 with movement of the beam 220 and decreasing the stiffness of the structure.

[00219] Referring again to Figs. 10 and 11, in between the flexing transverse arm pairs 246, the beam 220 expands to create T-bars 256 flanking insulating portions 234a and 234b. Insulating material 258 attached to these T-bars 256 create the insulating portions 234. Generally the beam 220 may be fabricated using well-known integrated circuit processing techniques to produce a structure suspended above the substrate 242 and composed of a laminated upper conductive layer 260 (for example, polysilicon or crystalline silicon optionally with an upper aluminum layer) and a lower insulating layer 262 such as silicon dioxide or silicon nitride. The insulating portions 234 may be obtained simply by etching away the upper layer in the region 234a or 234b according to techniques well-known in the art using selective etching techniques. An improved method of fabricating these structures is described in co-pending application Method for Sensing Current, Serial No. 09/406,364 filed September 28, 1999 and hereby incorporated by reference.

[00220] Each of the upper conductive layers 260 and lower insulating layers 262 are perforated by vertically extending channels 264 such as assists in conducting etchant beneath the layers 260 and 262 to remove a sacrificial layer that nonnally attaches layers 260 and 262 to the substrate 242 below according to techniques well known in the art. [00221] Referring now to Fig. 10 again, section 232a of the beam 220 such as provides a portion of the actuator 212, may have transversely outwardly extending, moving capacitor plates 266 overlapping with corresponding transversely inwardly extending stationary capacitor plates 268 attached to the pylons 244 representing terminals 222a, 222b, 222c and 222d. Each of the moving capacitor plates 266 and their corresponding stationary capacitor plates 268 may have mutually engaging fingers so as to provide for a more uniform electrostatic force over a greater range of longitudinal travel of the beam 220. The capacitor plates could also be simple parallel plate arms, which would have less linearity than the mutually engaging fingers. The thus formed electrostatic motor operates using the attraction between the capacitor plates 266 and 268 with the tenninals 222a+222b and 222c+222d connected to a more positive voltage than that of beam 220 to urge the beam 220 in the actuation direction 224. For this reason, stationary capacitor plates 268 are after the moving capacitor plates 266 on both sides of the beam 220 as one travels along the actuation direction. Capacitor plates 266 and 268 are cantilevered over the substrate 242 by the same under etching used to free the beam 220 from the substrate 242.

[00222] The pylons 244 flanking section 232c of the beam such as fonn pads 238a,

238b, 238c and 238d likewise include moving and stationary capacitor plates 266 and 268. As noted, this section provides the bias stracture 214 and as such, the electrostatic motor created operates in the opposite direction to the actuator 212 with the moving capacitor plates 266 following the stationary capacitor plates 268 as one moves in the actuation direction 224.

[00223] The mutual area of the capacitor plates 266 and 268 and their separation for an unactuated position of the beam 220, for the actuator 212 and bias structure 214, may be substantially equal so that the voltage on the bias stracture pads 238a+238b and 238c+238d approximately define the threshold over which the input voltage on terminals 222a+222b and 222c+222d must pass in order to actuate the MEMS digital isolator 210. [00224] Referring still to Fig. 10, section 232b of the beam also supports moving capacitor plates 266 and stationary capacitor plates 268. However in this case, the capacitor plates do not serve the purpose of making an electrostatic motor but instead serve as a sensing means in which variation in the capacitance between the moving capacitor plates 266 and stationary capacitor plates 268 serves to indicate the position of the beam 220. In this regard, the order of the stationary and moving capacitor plates 266 and 268 is reversed on opposite sides of the beam 220. Thus, the moving capacitor plates 266 are right of the stationary capacitor plates 268 on a first side of the beam (the upper side as depicted in Fig. 10) "downstream" with respect to the actuation direction 224 whereas the reverse order occurs on the lower side of the beam 220 with the moving capacitor plates 266 are left of the stationary capacitor plates 268. Accordingly as the beam 220 moves in the actuation direction 224, the capacitance formed by the upper moving capacitor plates 266 and stationary capacitor plates 268 increases while the capacitance formed by the lower plates decreases. The point where the value of the upper capacitance crosses the value of the lower capacitance precisely defines a null point and is preferably set midway in the travel of the beam 220.

[00225] As mentioned above, it is not absolutely necessary that both capacitors are variable. Using a variable capacitor plus a fixed capacitor would provide an alternative embodiment where the same qualitative affect on the voltage at the center tap is realized. Having both capacitors move in the same direction does not work for the three terminal stracture shown in Fig. 10. An alternative method of measuring the capacitances and a different tenninal structure, as will be recognized by one of ordinary skill in the art, must be adopted.

[00226] Techniques for comparing capacitance well lαiown in the art may be used to evaluate the position of the beam 220. One circuit for providing extremely accurate measurements of these capacitances is described in co-pending application Serial No. 09/677,037 filed September 29, 2000 and hereby incorporated by reference. [00227] Generally, the operating structure of the MEMS digital isolator 210 is constructed to be generally symmetric about an axis through the middle of the beam 220 along the longitudinal axis 240 such as to better compensate the thermal expansions. In addition, the operating area of the plates of the capacitors plates 266 and 268 on both sides of the beam 220 for the actuator 212 and the bias stracture 214 are made equal so as to be balanced. For similar reasons, the capacitors of the electrostatic motors and the bias structure 214 are placed between flexing transverse arm pairs 246 so as to better control slight amounts of torsion caused by uneven forces between the capacitor plates 266 and 268.

[00228] Refeπing now to Fig. 14, it will be understood that one or both of the electrostatic motors foπning the actuator 212 and the bias structure 214, described above, may be replaced with Lorenz-force motors 275 in which forces are generated not by electrostatic attraction between capacitor plates but by the interaction of a current with a magnetic field. In the Lorenz force motor 275, a magnetic field (e.g., using a permanent magnet not shown) may be generated adjacent to the MEMS digital isolator 210 to produce a substrate-normal magnetic flux 270. The expansion compensators 250 supporting the flexing transverse arm 246 on opposite sides of the beam 220 are electrically isolated from each other so that a voltage may be developed across expansion compensators 250 to cause a cun-ent 272 to flow through the flexing transverse arm 246. This cunent flow in the magnetic field generated by the magnet will produce a longitudinal force on the beam 220 that may act in lieu of the electrostatic motors. The amount of deflection is generally determined by the flux density of the magnetic field 270, the amount of current and the flexibility of the flexing transverse aπn pairs 246 in accordance with the right hand rale.

[00229] Referring now to Fig. 15, the actuator 212 positioned on beam section

232a, may be teamed with a second sensor 274 for sensing motion of the beam 220 and that sensor 274 may be used to provide isolated feedback to a device producing the electrical input signal 221 as to motion of the beam 220 such as may be used to ensure greater reliability in the transmission of signals.

[00230] Alternatively or in addition, the sensor 218 may be teamed with an actuator 276 having the same orientation of actuator 212 but positioned in isolation section 232b. When actuator 276 is teamed with sensor 274, they together provide a bidirectional digital isolator in which isolated signals may be sent from either end of the beam 232 to the other end. It will be understood that another variation of this embodiment may eliminate the bias stracture 214 and instead the actuators 276 and 212 may be used during transmission by the other actuator as the bias structure. Such a device might be useful for so-called tri-state or bi-directional input lines. [00231] It will be understood with greater circuit complexity that certain of the elements of the actuator 212, bias structure 214 and sensor 218 may be combined into individual stractures and hence, these terms should be considered to cover the functional equivalents of the functions of actuator bias stracture 214 and sensor 218 whether or not they are realized as individual structures or not. Further the relative location of the bias stracture 214, the actuator 212 and the sensor 218 may be swapped and still provide isolated signal transmission.

[00232] Referring again to Fig. 10, MEMS fabrication allows that a portion of the substrate 242 may also include integrated circuits 273 having a number of solid-state devices such as may implement, for example, the capacitor sense circuitry described above. A number of the MEMS digital isolators 210 may be placed on a single integrated circuit with appropriate interconnects made for providing them with the currents required. Generally, using the MEMS digital isolator 210 of the present invention, a single integrated circuit of arbitrary complexity, such as an industrial controller, may include isolators on the same substrate 242 manufactured concurrently with each other. These MEMS digital isolators 210 may provide for either inputs or outputs to the remaining integrated circuitry.

[00233] It should be noted that the sensor 218, actuator 212 and bias stracture 214 may be located at any relative position on the beam 220 as determined by the demands of the particular application. As an example the input signal could be received by an actuator 212 located in the middle of the beam 220. Generally, symmetry is not necessary.

III. THIRD EMBODIMENT [00234] Referring now to Fig. 16, a MEMS device 310 of the present invention may include a longitudinal beam 312 supported on tliree pairs of transverse aπns 314, 316 and 318, where transverse arms 314 extend from opposite sides of the leftmost longitudinal end of the beam 312, transverse arms 316 extend from opposite sides of the longitudinal center of beam 312, and transverse arms 318 extend from opposite sides of the rightmost longitudinal end of the beam 312. As supported by flexing of the transverse aπns 314, 316 and 318, the beam 312 is free to move along a longitudinal axis 320. [00235] This beam structure can provide a number of useful MEMS by employing a combination of an actuator 322, sensor 324 and biasing means 326 distributed along the beam 312 and possibly separated by insulating sections 328 and 330. Generally, the actuator 322 and biasing means 326 may be any of a Lorentz force motor, an electrostatic motor, a piezoelectric motor, a thermal-expansion motor, and a mechanical-displacement motor, and the sensor 324 may be any of a capacitive sensor, a piezoelectric sensor, a photoelectric sensor, a resistive sensor, an optical switching sensor, or inductive sensor. [00236] Referring now to Fig. 17, a MEMS device 310 for use as an electrical isolator and constructed according to the beam structure of Fig. 16, provides a beam 312 divided into conductive beam portions 312a, 312b and 312c separated by insulating sections 328 and 330. The actuator 322 may be a Lorentz force actuator conducting a current along the transverse arm 314 in the presence of a magnetic field 332 to produce a force along longitudinal axis 320. Cunent may be provided to the transverse arm 314 through terminals 334.

[00237] A sensor 324 may be provided by capacitor banks 335 having interdigitated capacitor plates 336a and 336b, where the spacing of plates 336a increases with rightward longitudinal movement of the beam 312 and the spacing of plates 336b decreases with rightward movement. A comparison of the capacitances of plates 336a and 336b accessible through tenninals 338a, 338b and 338c provides a position measurement of the beam 312 with a null position ideally being where the capacitances of plates 336a and 336b are equal. Precise location of the beam 312 both in a longitudinal and transverse manner is desired for proper operation of the capacitor plates 336a and 336b.

[00238] Finally, a biasing means 326 is provided by a Lorentz force motor formed by current passing through transverse arm 318 introduced by means of terminals 340 in magnetic field 332. [00239] The stracture of the MEMS device 310 generally includes as many as three layers including, for example, a metal layer, a silicon layer and an oxide layer. The stracture of the beam 312 and transverse arms 314, 316, and 318, shown in Fig. 17 may include all tliree layers which are cut away from a substrate 342 to be free therefrom, with the ends of the transverse anns 314, 316, and 318 distal to the beam 312, connected to the substrate 342 only at the terminals 334, 338 and 340. The insulating sections 328 and 330 may be produced by removing an upper layer of metal and silicon 344 leaving only a bridge of oxide, or by other similar methods.

[00240] In operation, a cunent passing through transverse ann 314 creates an actuation force via its interaction with the magnetic field 332 causing movement of the beam 312 against a biasing force created by current passing through transverse arm 318. The net effect is sensed by capacitor banks 336a and 336b. In this way, an analog or digital isolator may be produced or a sensitive magnetic field measuring or current measuring device as well as many other devices.

[00241 ] Referring now to Fig. 18, each of the transverse arms 314, 316 and 318 may be connected through longitudinal wrist elements 346 to stationary pylons 348 being attached to the substrate 342. The longitudinal wrist elements 346 allow some transverse movement of the distal ends of the transverse anns 314, 316 and 318 in the event of dimensional variations or expansion caused by electrical conduction. [00242] Refeπing to Fig. 20, this transverse compliance provided by the wrists 346 reduces the bowing or distortion of the transverse anns 314, 316 and 318 (exaggerated in Fig. 20) and prevents stress stiffening of the transverse arms 314, 316 and 318 such as would change the resonate frequency (or spring constant) of the beam 312 or the forces necessary to actuate the beam 312.

[00243] In order to neutralize the effects of the Lorentz forces on the wrists 346, the wrists 346 of cunent conducting transverse arms 314 and 318 are both directed in the same direction for transverse arm pairs 314 and 318. Further, the wrists 346 of transverse anns 314 and 318 may be directed in opposite directions either both facing outward or both facing inward so as to direct any bowing in the transverse arms 314 and 318 in opposite directions so as to cancel the resulting force on the beam 312. Judicious selection of the expansion characteristics of the beam 312 may promote an inward or outward bowing so as to ensure this balanced opposite bowing force. [00244] In contrast, the wrists 346 of the conductive transverse aπns 316 extending from the center of the beam 312 face in opposite longitudinal directions. This creates a more complex S shape bowing shown in Fig. 20 with relative lengthening of the transverse ann 316 which provides a slight torsion but no net longitudinal force to the beam 312. In this way, the null position of the beam (for example, as dictated by a midrange separation of the capacitor plates of the sensor) is preserved despite dimensional distortions caused by uneven contraction or expansion rates of the various components of the MEMS device 310.

[00245] Referring now to Fig. 19, the wrists 346 may be attached to any of the transverse arms 314, 316 or 318 by means of a smoothly curving arcuate section 352 such as eliminates points of concentrated stress.

[00246] The above-described wrist elements 346 may accommodate dimensional changes caused by the manufacturing process or by local self-heating caused by currents used in the Lorentz actuators and biasing means. Variation in these dimensions caused by different ambient operating conditions may be reduced by the use of outriggers 354 of Fig. 21 (one pair associated with each of transverse arms 314, 316 and 318) attached to pylons 348 adjacent to the beam 312 and extending transversely outward by nearly the full length of the transverse arms 314, 316 and 318. The transverse arms 314, 316 and 318 may be attached by the laterally extending wrists 346 to the outboard ends of the outriggers 354 which are ideally constructed of the same materials as the wrists 346 and transverse arms 314, 316 and 318 to provide for compensating expansion. It will be understood that by using the outriggers 354, expansion of the material of the transverse aπns 314, 316 and 318 such as would cause a slackening of transverse arms 314, 316 and 318 is compensated for by nearly equal expansion of outriggers 354, and vice versa. [00247] Referring now to Fig. 21, the outriggers 354 are attached only at pylons

348 leaving the remainder of the wrists 346 and the transverse anns 314, 316 and 318 free above but lying in the plane of substrate 342.

[00248] Referring to Fig. 22, the wrists 346 may be modified to provide for a serpentine portion 351 providing both the transverse freedom shown by arrow 356 and increased rotational freedom shown by arrow 358 such as simulates a "free beam" configuration for transverse arms 314, 316 and 318 providing a less stiff and more uniform characteristic to their flexure.

[00249] Referring to Fig. 23, it will be seen that the serpentine portion 351 may be extended to the distal ends of the transverse anns 314, 316 and 318 to provide further flexure and further may be placed on the distal ends of the transverse arms 314, 316 and 318, in lieu of their placement on the wrists 346 (not shown). The serpentine portions 351 may be crenellated as shown or may be a smoother curve to eliminate stress concentrations.

[00250] Refeπing again to Fig. 17, the wrists 346, in an alternative embodiment particularly suited for transverse arm 316 may provide for two opposed wrist portions 346a and 346b extending in opposite longitudinal directions from the distal end of the transverse ann 316 to a T-configuration such as also may provide a neutral compensation for expansion of transverse arm 316 without the need for the S shaped bowing. [00251] Refeπing now to Fig. 24, improved immunity to dimensional changes occurring during the fabrication process may be obtained by providing for strict symmetry of the MEMS device 310 along a longitudinal axis 320 passing through the beam 312 along its midpoint and a transverse axis 362 cutting the beam 312 transversely into two equal segments with respect to transverse arms 314 and 318. This provides equal length of the transverse aπns 314, 316 and 318 causing forces induced by these arms in contraction or expansion to be roughly equal preserving the midline alignment of the beam 312 along longitudinal axis 320, whereas positioning transverse arm 316 midway between transverse anns 314 and 318 provide that the null point measured at the midpoint of the beam 312 remain roughly at the same location with respect to the substrate despite length differences in the beam 312 itself such as may draw the transverse arms 314 and 318 into a bow or expand them outward.

[00252] For similar reasons the actuator 322 and biasing means 326 may be placed symmetrically on opposite sides of the beam 312 and the sensor 324 sensing the null point as close as possible to the center of the beam 312 as detennined by the connections of the beam 312 to the transverse arms 314 and 318.

[00253] Refeπing now to Figs. 25 and 26, the bowing of a beam 312, for example, of transverse arm 318 (or any of the transverse arms) may be exploited to provide a biasing force to the beam 312. Under this constraction, the actuator 322 would be positioned at one end of the beam 312 and the sensor 324 positioned at the other end of the beam 312. The bowing creates a snap action occurring as the beam 312 is moved from left to right. As a result of the bowing of the transverse ann 318, which in this example is to the right, the force 366 resisting the rightward longitudinal movement of the beam is positive (rightward) and increases up to a snap point 368 whereupon the bow of the transverse arm 318 buckles and reforms as a bow in the opposite direction shown by dotted line of transverse ann 318'. This in turn results in a reversal of the force 366 to negative (leftward) past snap point 368. [00254] Now motion of the beam 312 in the opposite direction from left to right causes the experience of an increasing negative force pushing the beam backward to the left up to a second snap point 370 whereupon the force reverts again to a positive direction and the beam moves fiilly to the right if unimpeded. The two snap points 368 and 370 provide a degree of hysteresis that may be desirable for certain applications and create in effect a bistable beam 312 as may be useful to provide a memory element. This mechanical memory element may be combined with other devices including accelerometers or isolators, or c urent or magnetic field sensors. [00255] Referring now to Figs. 27 and 28, the bowing created by the transverse arm 318 of Fig. 25 was induced by exploiting the differences in expansion coefficients of the various MEMS materials and thus puts transverse arm 318 in a stressed state. However, a bowing may also be created in a stress-free fransverse aim 318 by forming the transverse arm 318 into a bowed configuration during fabrication, for example, etching the transverse arm 318 in a bowed shape. In this case, the force 371 may be employed in a monotonically increasing region 372 providing a simple biasing force always in a positive direction or may be used outside of region 372 to a buckling point 374 after which the force 371 decreases returning only to an increasing mode after some additional distance is traversed, however, at no point becoming a negative force such as would create the bi-stability of the device of Fig. 25. In this way, a monostable device may be created.

[00256] Referring now to Fig. 29, an intentional bowing of transverse arm 316, for example, may provide for a mechanical lever communicating between the beam 312 and a position sensor 324' in this case formed of interleaving capacitor plates 375 and 376 with capacitor plate 375 being movable in the transverse direction and capacitor plates 376 being fixed. Capacitor plates 375 are attached to the distal end of transverse arm 316 removed from the beam 312 so as to be pushed outward by the transverse ann 316 with motion, in this case leftward, by the beam 312. This transverse motion is controlled by the slight longitudinal bending of the transverse arm 316 such as approximates a triangle 380 as shown in Fig. 30. Via the transverse aπn 316, small longitudinal motions Δx of the beam 312 being converted to the greater or lesser transverse motions Δy acting on capacitor plates 375. Depending on the particular angle of the transverse arm 316, the leverage may create additional motion or additional force. The decree of additional motion or mechanical advantage was determined by the amount of longitudinal extent of the transverse arm 316 according to well-understood trigonometric principals. [00257] In an alternative embodiment, the position sensors 324' may be operated as electrostatic motors to change the stress in the transverse aim 316 and therefore its frequency characteristics and those of the system, where tightening the transverse ann 316 would increase the natural resonant frequency of movement of the beam 312. In yet a further alternative embodiment, the motors could be used to adjust the bowing of the transverse arms 316 so as to move the beam 312 as a bias method or to control the amount of bias force on the beam 312.

IV. FOURTH EMBODIMENT

[00258] Referring now to Fig. 31 , a MEMS analog isolator 410 per the present invention includes an actuator 412, control element 414, and a sensor 418 mechanically interconnected by a movable beam 420.

[00259] The actuator 412 includes terminals 422a and 422b and 422c+422d through which an analog electrical input signal 421 may be received and converted into a mechanical force tending to move the beam 420 in an actuation direction 424 indicated by an ariOw. In the microscopic scale of the MEMS analog isolator 410, the actuator may be a piezoelectric actuator, a thennal-expansion motor, a mechanical-displacement motor, an electrostatic motor, or a Lorenz-force motor generally known in the art, the latter two to be described in more detail below. For a Lorenz-force motor or thennal-expansion motor, the analog electrical input signal 421 will be a current, for the piezoelectric or electrostatic motor, the input electrical signal will be a voltage. [00260] The actuator 412 communicates with a first end of the beam 420. An opposite end of the beam 420 is received by the sensor 418 which detects movement of the beam 420 and through its tenninals 426a and 426b and 426c+426d produces an electrical signal that may be measured directly or further processed by processing electronics 428 to produce the output signal 430 indicating movement of the beam 420. The sensor 418 may be a piezoelectric-type sensor, a photoelectric sensor, a resistive sensor, an optical switching sensor, or a capacitive sensor according to techniques lαiown in the art of MEMS design, hi the prefeπed embodiment, the sensor 418 uses counterpoised movable plate capacitors as will be described in more detail below. [00261] Attached to the beam 420 between the actuator 412 and the sensor 418 is the control element 414 which provides both a force on the beam 420 opposite the actuation direction 424 and tending to resist the operation of the actuator 412 or with the actuation direction 424 augmenting the operation of the actuator 412, as indicated by double headed arrows 435.

[00262] Absent an analog electrical input signal 421, the control element 414 may hold the beam 420 in a position toward the sensor 418. Ideally, the control element 414 provides a force that increases with motion of the beam 420 in the actuation direction 424. In this way, a simple relationship between actuation force and movement of the beam 420 is generated (e.g., with a simple spring-type system). The MEMS analog isolator 410 provides extremely low friction and inertia so this movement or force is consistent and rapid. Alternatively, the control element 414 may provide a rapidly increasing force (in a feedback system) an-esting the movement of the beam 420 for any actuation force. Here the magnitude of the aπesting force provides the output signal. [00263] As described, the force provided by the control element 414 may be adjustable by varying a current or voltage to the structure and used in a feedback mode to essentially eliminate all but a small movement of the beam 420. Some movement of the beam 420 is necessary for the sensor 418 to provide the necessary countervailing feedback, but the movement may be reduced to an extent that non-linearities in the actuators and mechanical elements of the MEMS analog isolator 410, that might occur with more pronounced movement, are eliminated. Specifically, in this mode, the movement of the beam 420 is detected by processing electronics 428 to produce a position signal. The position signal is compared against a reference signal 429 to produce an error signal 431 which is directed to the control element to produce a restoring force returning the beam 420 to the null point. The connection between the enor signal to the control element 414 may be direct or may be further modified by a feedback network 433 providing compensation for the system according to well-known feedback teclmiques. The feedback network 433 may steer voltage to either tenninals 438c and 438d with a return at teπninal 450 for actuation toward the sensor 418 or to terminals 438a and 438b with a return at teπninal 450 for actuation toward the actuator 412 reflecting the fact that the electrostatic motors provide only a single direction of force.

[00264] The beam 420 includes conductive portions 432a and 432b, located at the actuator 412 and sensor 418, respectively, and such as may form part of the actuator 412 or sensor 418. Insulating portions 434a and 434b separate conductive portions 432a and 432b from a centermost conductive portion 432c that may be part of the control element 414; the insulating portions 434a and 434b thus defining three regions of isolation 436a-c. The first region 436a includes the actuator 412 and conductive portion 432a, the second region 436b includes the center conductive portion 432c and the control element 414, and the third region 436c includes the conductive portion 432b and sensor 418. [00265] The insulated beam 420 provides a mechanism by which the analog electrical input signal 421 acting through the actuator 412 may produce a corresponding output signal 430 at the sensor 418 electrically isolated from the analog electrical input signal 421. The control element 414 may be electrically isolated from either the input signal and/or the output signal 430.

[00266] The control element 414 is preferably a Lorenz-force motor or an electrostatic motor of a type that will be described below. For the fonner of these two control elements, terminals 438a and 438b and return 450 are provided to provide a bidirectional current dictating the countervailing force provided by the control element 414. The direction of the current dictates the direction of the force. For the latter electrostatic stracture, tenninals 438a, 438b, 438c, and 438d are provided. Voltage is applied either to terminal pair 438a and 438b (with reference to return 450) or to terminal pair 438c and 438d (with respect to return 450) to deteπnine the direction of the force. [00267] Referring now to Fig. 32, the beam 420 may extend above a substrate 442 along a longitudinal axis 440 passing along a midline between transversely opposed pylons 444 attached to a substrate 442. The pylons form the tenninals 422a and 422b, 438a-438d, 426a, and 426b described above. Ideally, the substrate 442 is an insulating substrate and thus pylons 444 are all mutually isolated and particular conductive layers are placed or wire bonding used to make the necessary connections. [00268] The beam 420 is supported away from the substrate 442 and held for movement along the longitudinal axis 440 by means of flexing ann pairs 446 extending transversely on opposite sides of both ends of the beam 420 and its middle. The flexing arms 446 extend away from the beam 420 to elbows 448 transversely removed from the beam 420 on each side of the beam 420. The elbows 448 in turn connect to expansion compensators 450, which return to be attached to the substrate 442 at a point near the beam 420. As mentioned above, these expansion compensators are not absolutely required. They serve as stress relief if that is needed. The flexing transverse arms 446 are generally parallel to the expansion compensators 450 to which they are connected. The flexing transverse arms 446, elbows 448 and expansion compensators are conductive to provide electrical connections between the conductive portions 432a, 432b and 432c and stationary electrical tenninals (not shown). [00269] Refeπing now to Fig. 34, the length Li of each expansion compensator

450 between its point of attachment 452 to the substrate 442 and its connection to a corresponding flexing transverse arm 446 at elbow 448 and the length L of the flexing transverse aπn 446 defined as the distance between its connection to beam 420 and the elbow 448 are set to be nearly equal so that expansion caused by thennal effects in the flexing transverse ami 446 is nearly or completely canceled by expansion in the expansion compensator 450. In this way, little tension or compression develops in the flexing transverse arm 446. Both the flexing fransverse ann 446 and the expansion compensator 450 in this embodiment are fabricated of the same material, however it will be understood that different materials may also be used and lengths L] and L adjusted to reflect the differences in thennal expansion coefficients. Note that a doubling back of the ann is not required. A straight connection will also work. The doubling back of the arm is a stress-relieving feature. Stress in the beam will affect the spring constant. Depending on the spring constant desired, and other geometric and process (e.g. substrate choice) considerations, stress relief may or may not be needed or desirable. [00270] Referring to Fig. 35a, the elbow 448 may include a serpentine portion 454 extending longitudinally from the expansion compensator 450 to its flexing transverse arm 446. As shown in Fig. 35b, the serpentine portion 454 allow angulation α between the flexing transverse ann 446 and expansion compensator 450 such as provides essentially a radius adjusting pivot, both decreasing the force exerted by the flexing transverse arm pairs 446 on the beam 420 with movement of the beam 420 and decreasing the stiffness of the stracture.

[00271] Referring again to Figs. 32 and 33, in between the flexing transverse arm pairs 446 the beam 420 expands to create T-bars 456 flanking insulating portion 434a and 434b. Insulating material 458 attached to these T-bars 456 create the insulating portions 434. Generally the beam 420 may be fabricated using well-known MEMS processing techniques to produce a structure suspended above the substrate 442 and composed of a laminated upper conductive layer 460 (for example polycrystalline silicon or crystalline silicon optionally with an upper aluminum layer) and a lower insulating layer 462 such as silicon dioxide or silicon nitride. The insulating portions 434 may be obtained simply by etching away the upper layer in the region 434a or 434b according to teclmiques well lαiown in the art using selective etching teclmiques. An improved method of fabricating these structures is described in US patent 6,159,385 issued 12/12/2000 hereby incorporated by reference. The edges and corners of the T-bars 456 may be rounded to increase the breakdown voltage between them.

[00272] Each of the upper conductive layer 460 and lower insulating layer 462 are perforated by vertically extending channels 464 such as assists in conducting etchant beneath the layers 460 and 462 to remove a sacrificial layer that nonnally attaches layers 460 and 462 to the substrate 442 below according to teclmiques well known in the art. [00273] Refeπing now to Fig. 32 again, portion 432a of the beam 420, such as provides a portion of the actuator 412 may have transversely outwardly extending, moving capacitor plates 466 overlapping with corresponding transversely inwardly extending stationaiy capacitor plates 468 attached to the pylons 44 representing terminals 422a and 422b. Each of the moving capacitor plates 466 and their coιτesponding stationary capacitor plates 468 may have mutually engaging fingers (as opposed to being simple parallel plate capacitors) so as to provide for a more uniform electrostatic force over a greater range of longitudinal travel of the beam 420. The thus fonned electrostatic motor operates using the attraction between the capacitor plates 466 and 468 with the terminals 422b and 422a connected to a more positive voltage than that of beam 420 (connected to terminals 422c+422d), to urge the beam 420 in the actuation direction 424. For this reason, stationary capacitor plates 468 are after the moving capacitor plates 466 on both sides of the beam 420 as one travels along the actuation direction. Capacitor plates 466 and 468 are cantilevered over the substrate 442 by the same under etching used to free the beam 420 from the substrate 442.

[00274] The pylons 444 flanking portion 432c of the beam such as fonn pads 438a-

438d likewise include moving and stationary capacitor plates 466 and 468 in two distinct pairs. As noted, this section provides the control element 414 and as such, two electrostatic motors; one (using terminals 438c and 438d) created to produce a force in the opposite direction of actuator 412 with the moving capacitor plates 466 following the stationary capacitor plates 468 as one moves in the actuation direction 424 and the other (using tenninals 438a and 438b) created to produce a force in the same direction to the actuator 412 with the moving capacitor plates 466 preceding the stationary capacitor plates 468 as one moves in the actuation direction 424. These two actuators are used in combination to give the best possible control of the closed loop system. [00275] Refenϊng still to Fig. 32, portion 432b of the beam also supports moving capacitor plates 466 and stationary capacitor plates 468. However in this case, the capacitor plates do not serve the purpose of making an electrostatic motor but instead serve as a sensing means in which variation in the capacitance between the moving capacitor plates 466 and stationary capacitor plates 468 serves to indicate the position of the beam 420. In this regard, the order of the stationary and moving capacitor plates 466 and 468 is reversed on opposite sides of the beam 420. Thus, the moving capacitor plates 466 precede the stationary capacitor plates 468 on a first side of the beam (the upper side as depicted in Fig. 32) as one moves in the actuation direction 424 (as measured between tenninal 426a and terminals 426c+426d) whereas the reverse order occurs on the lower side of the beam 420 (as measured between terminal 426b and terminals 426c+426d). Accordingly as the beam 420 moves in the actuation direction 424, the capacitance formed by the upper moving capacitor plates 466 and stationary capacitor plates 468 increases while the capacitance formed by the lower plates decreases. The point where the value of the upper capacitance crosses the value of the lower capacitance precisely defines a null point and is preferably set midway in the travel of the beam 420. [00276] Techniques for comparing capacitance well known in the art may be used to evaluate the position of the beam 420. One circuit for providing extremely accurate measurements of these capacitances is described in co-pending application Serial No. 09/677,037 filed September 29, 2000 and hereby incorporated by reference. [00277] Generally, the operating stracture of the MEMS analog isolator 410 is constructed to be symmetric about an axis through the middle of the beam 420 along the longitudinal axis 440 such as to better compensate the thermal expansions. In addition, the operating area of the plates of the capacitors, plates 466 and 468 on both sides of the beam 420 for the actuator 412 and the control element 414, are made equal so as to be balanced. For similar reasons, the capacitors of the electrostatic motors and the control element 414 are placed between flexing transverse arm pairs 446 so as to better control slight amounts of torsion caused by uneven forces between the capacitor plates 466 and 468.

[00278] Referring now to Fig. 36, it will be understood that one or both of the electrostatic motors forming the actuator 412 and the control element 414 described above, may be replaced with Lorenz-force motors 475 in which forces are generated not by electrostatic attraction between capacitor plates but by the interaction of a current with a magnetic field. In the Lorenz-force motor 475, a magnetic field (e.g. with a permanent magnet, not shown) may be generated adjacent to the MEMS analog isolator 410 to produce a substrate-normal magnetic flux 470. The expansion compensators 450 supporting the flexing transverse ann 446 on opposite sides of the beam 420 are electrically isolated from each other so that a voltage may be developed across expansion compensators 450 to cause a current 472 to flow through the flexing transverse aπn 446. This current flow in the magnetic field generated by the magnet will produce a longitudinal force on the beam 420 that may act in lieu of the electrostatic motors. The amount of deflection is generally determined by the flux density of the magnetic field 470, the amount of current and the flexibility of the flexing transverse aπn pairs 446 in accordance with the right hand rule.

[00279] The Lorenz-force motors 475 are two quadrant, meaning they will accept currents in either direction to produce a force with or opposed to the actuation direction 424. Hence with Lorenz-force motors 475 (or the bi-directional electrostatic motor of the control element 414 described above), the MEMS analog isolator 410 may operate with two polarities unlike an optical isolator.

[00280] Referring now to Fig. 37, the actuator 412 positioned on beam portion

432a, may be teamed with a second sensor 474 for sensing motion of the beam 420 and that sensor 474 may be used to provide isolated feedback to a device producing the analog electrical input signal 421 as to motion of the beam 420 such as may be used to ensure greater reliability in the transmission of signals.

[00281] Alternatively or in addition, the sensor 418 may be teamed with an actuator 476 having the same orientation of actuator 412 but positioned in isolation portion 432b. When actuator 476 is teamed with sensor 474, they together provide a bidirectional analog isolator in which isolated signals may be sent from either end of the beam 420 to the other end. It will be understood that another variation of this embodiment may eliminate the control element and instead the actuators 476 and 412 may be used during transmission by the other actuator as the control element. Such a device may be useful in some multi-loop analog system or for scaling adjustment. [00282] It will be understood with greater circuit complexity that certain of the elements of the actuator 412, control element 414 and sensor 418 may be combined into individual structures and hence, these terms should be considered to cover the functional equivalents of the functions of actuator control element 414 and sensor 418 whether or not they are realized as individual structures or not. Further the relative location of the control element 414, the actuator 412 and the sensor 418 may be swapped and still provide isolated signal transmission.

[00283] Referring now to Fig. 38, a digital word output 500 can be obtained from the sensor 418 by making use of an enor signal 431 resulting directly from a comparison of the capacitors of the sensor 418 by capacitive comparison circuit 502 of a type well known in the art. One such circuit for providing extremely accurate measurements of these capacitances in described in co-pending application Serial No. 09/677,037 described above. As so configured, the enor signal 431 (when connected to the control element 414) will tend to restore the beam 420 to a null position dependent on the location where the values of the capacitors of the sensor 418 change their relationship of which is greater than the other. The output of the capacitive comparison circuit 502 will generally be a duty cycle modulated square wave 504 produced as the beam 420 wanders back and forth across the null point under the influences of the actuation force and the restoring force. The beam 420 provides an inertial averaging of the eπor signal 431 so that its average force is proportional to the actuation force. Counter 506 measures the percentage of time that the error signal 431 is in the high state. In one embodiment, the output of the capacitive comparison circuit 502 may be logically ANDed with a high rate clock signal to cause the counter 506 to count up during the time the enor signal 431 is high and not otherwise. The counter may be reset periodically by a second time interval signal 510. The value on the counter 506 just prior to the resetting will be proportional to the duty cycle of the eπor signal 431 and therefore to the actuation signal. The frequency of the clock signal 508 and the period of the time interval signal 510 may be selected according to the desired resolution in the digital word output 500 according to methods well known in the art.

[00284] Referring again to Fig. 32, MEMS fabrication allows that a portion of the substrate 442 may also include integrated circuits 473 having a number of solid-state devices such as may implement, for example, the capacitor sense circuitry described above. A number of the MEMS analog isolators 410 may be placed on a single integrated circuit with appropriate interconnects made for providing them with the currents required. Generally, using the MEMS analog isolator 410 of the present invention, a single integrated circuit of arbitrary complexity, such as an industrial controller, may include isolators on the same substrate 442 manufactured concurrently with each other. These MEMS analog isolators 410 may provide for either inputs to the remaining integrated circuitry in the fonn of a digital word or, through the use of an on-board digital to analog converter, isolated analog outputs from the integrated circuit 473. [00285] Referring now to Fig. 39, the analog isolator 410 may be fabricated adjacent to a second analog isolator 410' constracted so that an axis 40' of the second analog isolator 410' is parallel to axis 440 of the analog isolator 410 and so that the devices are in physically close proximity. In this way, acceleration of the substrate indicated by arrow 520 along axis 440 and 440' will be essentially identical for both isolators 410 and 410' even in the presence of a rotational component removed from the axes 440 and 440'. Note that the direction of the inertial force need not be along the axis of the device. In an ideal device it is only the component of the force that is along the axis that contributes to a signal. In a non-ideal device non-axial forces can also cause motion that will be detected. But, ideal or not, as long as the two devices are identical and the system is linear, the effect of inertia is the same on both devices, and so it is possible to subtract out the effect.

[00286] The analog isolator 410' is fabricated so as to be nearly identical to the analog isolator 410 having an actuator 412', a control element 414', a sensor 418', and processing electronics 428' operating in the same maimer as described above with respect to analog isolator 410. The single exception to the otherwise identical constraction of the analog isolator 410' is that it receives no input signal 421. Thus movement of the beam 420' of analog isolator 410' will be caused solely by acceleration of the substrate 442. [00287] In operation, an input signal 421 representing a parameter to be measured, urges beam 420 toward a second position (e.g. the left-hand side of Fig. 39). Beam 420 will also be affected by any inertial force 520 on the substrate 442, for example, an acceleration of the substrate 442 to the left which will act to urge both beams 420 and 420' to the first position (e.g. to the right).

[00288] In the feedback configuration described above, in which the control elements act to hold the beams 420 and 420' at a null position, the output signal 430 of the analog isolator 410 will be approximately proportional to: p+m_/a [00289] where p is the force on the beam 420 exerted by the measured parameter, mj is the mass of the beam 420 and the elements it carries, and a is the acceleration of the substrate 442 (where a can be either positive or negative). The value of the spring constant is not an additive effect either here in closed loop or later in open loop discussion. It is a multiplicative effect that is part of the proportionality constant which relates force to displacement to electrical signal. As long as the spring constant is a constant, it is acceptable to work with a value that is proportional to the exact value, as the relative results will still be con-ect

[00290] In contrast, the output signal 430' of the analog isolator 410' will be approximately proportional to: [00291] where mj = m because of the identical construction of the analog isolators

410 and 410'.

[00292] Subtracting the output signal 430' from the output signal 430 thus provides a measure of p without the inertial noise ma. This subtraction can be accomplished by a conventional summing junction 522 realized by an operational amplifier circuit, digital summer, or the like.

[00293] As mentioned above, the analog isolator 410 may be realized without feedback, using the control stracture 414 simply to provide a spring. In this case, the output signal 430 of the analog isolator 410 will still be approximately proportional to:

[00294] If the displacement is large enough that the spring constant becomes non- constant (i.e. displacement is no longer a linear function of force) then the fundamental linearity of the system breaks down and the ability to cancel (subtract) the inertial force is compromised. It is an important advantage of the closed loop system that the displacements stay small and so do not violate this linearity requirement. For this reason, a system with a potentially non-linear spring function is better handled in closed loop than in open loop.

[00295] In this case, the output signal 430' of the analog isolator 410' will still be approximately proportional to:

[00296] Thus, subtracting the output signal 430' from the output signal 430 provides a measure of p without the inertial noise ma. Again, the subtraction can be accomplished by a conventional summing junction 522 realized by an operational amplifier circuit, digital summer, or the like.

[00297] Although there is no need for a functional actuator 412' for moving the beam 420' in analog isolator 410', at least those components of the actuator that are attached to the beam 420' may be included in the analog isolator 410' as to modify the mass and other physical characteristics of the beam 420', and its motion, so as to be as nearly identical to that of beam 420 as possible. Thus for example, the beam supporting the electrostatic actuators and the like may all be attached to beam 420 even though they are not connected to an input signal 421. Note that there are other concerns than just the mass that will essentially require that the entire actuator be present. For example, the small spaces between the interdigitated fingers provides damping to the motion and so the entire finger stracture must be present to duplicate the damping effects in the non- powered device. There may however, be some features that can be removed with no significant affect.

[00298] The signal 430' may be provided to other MEMS devices (not shown) sharing the subsfrate 442 so as to provide an inertial signal to the entire substrate that may be used to cancel out inertial noise from other isolators and other similar devices throughout the substrate.

[00299] Referring now to Fig. 40, an improved signal to noise ratio may be obtained by using a fully functional actuator 412' in analog isolator 410' connected to the input signal 421 through an inverter 526. The inverter, such as may be realized by an operational amplifier, effectively multiplies the signal 421 by negative one. [00300] In this case, for a system using feedback, the signal 430 will be approximately proportional to: p+m_/a and the signal 430' will be approximately proportional to:

-p+m_∑a. [00301] Subtraction of signal 430' from signal 430 yields 2p providing improved signal strength, and assuming the inertial noise is not completely cancelled, as will be the case, improved signal to noise ratio. Inspection of the above description with respect to the system not using force feedback reveals that a similar output 524 is obtained of 2p in that case.

[00302] Note that in this case, if a Lorenz force motor were being used as actuators

412 and 412', input signal 421 may be directed through actuator 412' in the opposite direction to actuator 412, so as to allow the input signal 421 to operate on the beam 420' in the opposite direction of the beam 420. Or when using an electrostatic actuator stracture for 412 and 412', they must be fabricated so as to act in the opposite directions to each other, with regard to the input signal 421.

[00303] In this case, the signal 430' is unique to the input signal 421 and is not shared among other MEMS devices.

[00304] Refeπing now to Fig. 41, the system of Fig. 39 is modified such that processing electronics 428 uses the signal 418' as the reference signal. As such, the signal from 418' replaces the signal 429, shown in Fig. 39. The two devices operate similarly to the way they operate in Fig. 39, with device 410 being sensitive to both the input electrical signal and the inertial signal, while device 410' is sensitive to only the inertial signal. However, in this implementation, the subtraction of the inertial signal from the input electrical signal takes place within the processing electronics 428 and the summer

522 is not needed. The error signal 431 is still only due to the value of the input electrical signal and so is applied only to control element 414.

[00305] Referring now to Fig. 42, the system of Fig. 41 is modified such that the input electrical signal to device 410 is inverted and applied to device 410'. The subtraction of the signal from device 410 and device 410' which takes place in processing electronics 428 now results in twice the input signal. As both devices see the input electrical signal, they must also both see the enor signal 431, although it must be inverted by 526' before being applied to control element 414'.

[00306] It will be recognized that this technique is not limited to the use in making analog isolators and may be used also for digital isolators in which the control elements

414 have a fixed bias or one that decreases slightly with movement of the beams 420 against the bias so as to provide a sharp threshold of movement of the beam 420 suitable for digital isolation.

[00307] Further, it will be understood that the parameter being measured need not be an electrical parameter but may be any physical parameter which may be converted to movements of a beam 420 on a microscopic level. Thus for example, the parameter may be pressure with the actuators 412 and 412' directly connected to a flexible diaphragm or the like. Further the beams 420 need not be set for linear motion but in fact may rotate about the axis 440 in which case, the first and second position would be counterclockwise or full clockwise rotation points, hi this case, the inertial noise would be that of rotational acceleration.

[00308] It will be understood that the above described techniques are applicable not just to reduce the effects of inertial noise but to reduce any common mode noise including those caused by thermal expansion, pressure, mechanical distortion of the substrate and the like.

[00309] It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but that modified fonns of those embodiments including portions of the embodiments and combinations of elements of different embodiments also be included as come within the scope of the following claims.

Claims

CLAIMS WE CLAIM:I.

1. A microelectromechanical system (MEMS) analog isolator, comprising: a substrate; an element supported from the substrate for movement between a first and second position with respect to the substrate, where at least a portion of the element between a first and second location on the element is an electrical insulator to electrically isolate the first and second locations from each other; an actuator attached to the first portion of the element to receive an input electrical signal and exert a force dependent on the input electrical signal urging the element toward the second position; a control element attached to the element to exert a force dependent on the displacement of the element toward one of the first position and the second position; and a sensor assembly communicating with the second portion of the element to provide an output electrical signal dependent on movement of the element between the first position and the second position.

2. The MEMS analog isolator of claim 1 wherein the control element is a spring and the sensor assembly includes a sensor providing the analog output electrical signal.

3. The MEMS analog isolator of claim 1 wherein the control element is a second actuator attached to the element to receive a feedback electrical signal and exert a force dependent on the feedback electrical signal urging the element toward the first position; and including wherein the sensor assembly including a sensor indicating a location of the element with respect to a null position and an error detector receiving the output electrical signal to generate the feedback electrical signal so as to tend to restore the element to the null position and wherein the output electrical signal is derived from the feedback signal.

4. The MEMS analog isolator of claim 1 wherein the control element further includes a third actuator attached to the element to receive a second feedback signal and exert a force dependent on the second feedback electrical signal urging the element toward the second position; whereby more complex feedback control of the element may be accomplished.

5. The MEMS analog isolator of claim 3 wherein the error detector produces a binary electrical feedback indicating a position of the beam with respect to a null location between the first and second positions and further including a pulse width demodulator circuit evaluating the duty cycle of the feedback signal to produce the output electrical signal.

6. The MEMS analog isolator of claim 1 wherein the actuator is selected from the group consisting of: an electrostatic motor, a Lorenz-force motor, a piezoelectric motor, a thennal-expansion motor, and a mechanical-displacement motor.

7. The MEMS analog isolator of claim 1 wherein the control element is selected from the group consisting of: an electrostatic motor, a Lorenz-force motor, a piezoelectric motor, a thennal-expansion motor, a mechanical-displacement motor, and a mechanical spring.

8. The MEMS analog isolator of claim 1 wherein the sensor is selected from the group consisting of a capacitive sensor, a piezoelectric sensor, a photoelectric sensor, a resistive sensor, or an optical switching sensor.

9. The MEMS analog isolator of claim 1 wherein the element is a beam attached to the substrate for sliding motion between the first and second positions.

10. The MEMS analog isolator of claim 8 wherein the beam moves with respect to the substrate along a longitudinal axis and including flexing transverse aim pairs attached at longitudinally opposed ends of the beam to extend outward therefrom to support the beam with respect to the substrate.

11. The MEMS analog isolator of claim 9 wherein the flexing transverse anns attached to the substrate at points proximate to the beam and where the flexing transverse anns include:

(i) cantilevered first portions having first ends attached to the beam and second ends attached to an elbow portion removed from the beam; and

(ii) cantilevered second portions substantially parallel to the first portions and having first ends attached to the substrate and second ends attached to the elbow portion; whereby expansion of the first portion is offset by substantially equal expansion of the second portion so that the amount of stress in the beam can be controlled.

12. The MEMS analog isolator of claim 9 wherein the flexing transverse anns attach to the substrate through a spring section allowing angulation of the end of the transverse arm with respect to the substrate.

13. The MEMS analog isolator of claim 9 wherein the beam and transverse anns are symmetric across a longitudinal axis.

14. The MEMS analog isolator of claim 9 including further a magnetic field crossing the beam and wherein at least one flexing transverse ann pair is conductive to receive an electrical signal and exert a force dependent on the electrical signal urging the beam toward position.

15. The MEMS analog isolator of claim 9 including transverse extending primary capacitor plates attached to the beam and extending outward from the beam proximate to secondary capacitor plates.

16. The MEMS analog isolator of claim 14 wherein an effective area of the primary capacitor plates is equal across the longitudinal axis of the beam.

17. The MEMS analog isolator of claim 14 wherein the capacitor plates attach to the beam between the attachment points of at least two of the flexing transverse aim pairs.

18. The MEMS analog isolator of claim 14 wherein the primary capacitor plates are positioned with respect to the secondary capacitor plates so as to draw the primary capacitor plates toward the secondary capacitor plates on one side of the beam while to separate the primary capacitor plates from the secondary capacitor plates on the other side of the beam with a given motion.

19. The MEMS analog isolator of claim 14 wherein the primary capacitor plates are positioned with respect to the secondary capacitor plates so as to draw the primary capacitor plates toward the secondary capacitor plates on both sides of the beam with a given motion.

20. The MEMS analog isolator of claim 1 wherein the beam includes first and second micro-machined layers, the first of which is insulating to provide the portion of electrical insulator in a region where the second layer is removed.

21. The MEMS analog isolator of claim 1 wherein the portion of electrical insulator of the beam is between the actuator and the controlling device.

22. The MEMS analog isolator of claim 1 wherein the portion of electrical insulator of the beam is between the controlling device and the sensor.

23. An isolated circuit module comprising: a substrate; a plurality of interconnected solid-state electronic devices fonned on the substrate into an integrated circuit having analog input and output points; a mechanical analog isolator also formed on the substrate and electrically attached to at least one of the integrated circuit input and output points, the mechanical analog isolator including: a substrate; an element supported from the substrate for movement between a first and second position with respect to the substrate, where at least a portion of the element between a first and second location on the element is an electrical insulator to electrically isolate the first and second locations from each other; an actuator attached to the first portion of the element to receive an input electrical signal and exert a force dependent on the input electrical signal urging the element toward the second position; a control element attached to the element to exert a force dependent on the displacement of the element toward the first position; a sensor assembly communicating with the second portion of the element to provide an output electrical signal dependent on movement of the element between the first positions.

24. The isolated circuit module of claim 23 wherein the actuator of the mechanical analog isolator is attached to at least one output point of the integrated circuit whereby the output electrical signal provides an isolated output for the at least one output point.

25. The isolated circuit module of claim 23 wherein the sensor of the mechanical analog isolator is attached to at least one input point of the integrated circuit whereby the output electrical signal provides an isolated input to at least one output point.

26. The MEMS analog isolator of claim 1 including further a second sensor at the first portion of the element to provide a second output electrical signal indicating movement of the element to the second position, the second output electrical signal being electrically isolated from the output electrical signal.

27. The MEMS analog isolator of claim 26 including further a second actuator at the second portion of the element to receive a second input electrical signal and exert a force dependent on the second input electrical signal urging the element toward the second position.

II.

28. A microelectromechanical system (MEMS) digital isolator, comprising: a substrate; an element supported by the substrate for movement between a first and second position with respect to the substrate, where at least a portion of the element between a first and second location on the element is an electrical insulator to electrically isolate the first and second locations from each other; an actuator attached to the first portion of the element to receive an input electrical signal and exert a force dependent on the input electrical signal urging the element toward the second position; a bias structure attached to the element to exert a predetermined opposite force on the element urging the element toward the first position; and a sensor attached to the second portion of the element to provide an output electrical signal indicating movement of the element between the first position and the second position; whereby an input signal of above a predetem ined magnitude overcomes the opposite force to cause the element to move rapidly from the first to the second position to produce the output electrical signal electrically isolated from the input electrical signal.

29. The MEMS digital isolator of claim 28 wherein the actuator is selected from the group consisting of: an electrostatic motor, a Lorenz force motor, a piezoelectric motor, a thermal-expansion motor, and a mechanical-displacement motor.

30. The MEMS digital isolator of claim 28 wherein the bias stracture is selected from the group consisting of: an electrostatic motor, a Lorenz force motor, a thermal-expansion motor, a mechanical-displacement motor, and a mechanical spring.

31. The MEMS digital isolator of claim 28 wherein the sensor is selected from the group consisting of a capacitive sensor, a piezoelectric sensor, a photoelectric sensor, a resistive sensor, and an optical switching sensor.

32. The MEMS digital isolator of claim 28 wherein the element is a beam attached to the substrate for sliding motion between the first and second positions.

33. The MEMS digital isolator of claim 32 wherein the beam moves with respect to the substrate along a longitudinal axis and including flexing transverse ann pairs attached at longitudinally opposed ends of the beam to extend outward therefrom to support the beam with respect to the substrate.

34. The MEMS digital isolator of claim 33 wherein the flexing transverse arms attached to the substrate at points proximate to the beam and where the flexing transverse arms include:

(i) cantilevered first potions having first ends attached to the beam and second ends attached to an elbow portion removed from the beam; and

(ii) cantilevered second portions substantially parallel to the first portions and having first ends attached to the substrate and second ends attached to the elbow portion; whereby expansion of the first portion is offset by substantially equal expansion of the second portion to control the amount of stress in the beam.

35. The MEMS digital isolator of claim 33 wherein the flexing transverse arms attach to the substrate through a spring section allowing angulation of the end of the transverse aπn with respect to the substrate.

36. The MEMS digital isolator of claim 33 wherein the beam and transverse arms are symmetric across a longitudinal axis.

37. The MEMS digital isolator of claim 33 including further a magnetic field crossing the beam and wherein at least one flexing transverse arm pair is conductive to receive an electrical signal and exert a force dependent on the electrical signal urging the beam toward a position.

38. The MEMS digital isolator of claim 33 including transverse extending primary capacitor plates attached to the beam and extending outward from the beam proximate to secondary capacitor plates.

39. The MEMS digital isolator of claim 38 wherein an effective area of the primary capacitor plates is equal across the longitudinal axis of the beam.

40. The MEMS digital isolator of claim 38 wherein the capacitor plates attach to the beam between the attachment points of at least two of the flexing transverse arm pairs.

41. The MEMS digital isolator of claim 38 wherein the primary capacitor plates are positioned with respect to the secondary capacitor plates so as to draw the primary capacitor plates toward the secondary capacitor plates on one side of the beam while to separate the primary capacitor plates from the secondary capacitor plates on the other side of the beam with a given motion.

42. The MEMS digital isolator of claim 38 wherein the primary capacitor plates are positioned with respect to the secondary capacitor plates so as to draw the primary capacitor plates toward the secondary capacitor plates on both sides of the beam with a given motion.

43. The MEMS digital isolator of claim 38 wherein the beam includes a first and second micro-machined layer, the first of which is insulating to provide the portion of electrical insulator in a region where the second layer is removed.

44. The MEMS digital isolator of claim 28 wherein the portion of electrical insulator of the beam is between the actuator and the bias stracture.

45. The MEMS digital isolator of claim 28 wherein the portion of electrical insulator of the beam is between the bias stracture and the sensor.

46. An isolated circuit module comprising: a substrate; a plurality of interconnected solid state electronic devices fonned on the substrate into an integrated circuit having input and output points; a mechanical digital isolator also formed on the substrate and electrically attached to at least one of the integrated circuit input and output points, the mechanical digital isolator including:

(1) an element supported by the substrate for movement between a first and second position with respect to the substrate, where at least a portion of the element between a first and second location on the element is an electrical insulator to electrically isolate the first and second locations from each other;

(2) an actuator attached to the first portion of the element to receive an input electrical signal and exert a force dependent on the input electrical signal urging the element toward the second position; (3) a bias stracture attached to the element to exert a predetermined substantially fixed force on the element urging the element toward the first position; and (4) a sensor attached to the second portion of the element to provide an output electrical signal indicating movement of the element to the second position, the output electrical signal being electrically isolated from the input electrical signal; whereby an input signal of above a predeteimined magnitude overcomes the fixed force to cause the element to move rapidly from the first to the second position.

47. The isolated circuit module of claim 46 wherein the actuator of the mechanical digital isolator is attached to at least one output point of the integrated circuit.

48. The isolated circuit module of claim 46 wherein the sensor of the mechanical digital isolator is attached to at least one input point of the integrated circuit.

49. A method of providing electrical isolation of a digital signal to a circuit employing a MEMS digital isolator of a type having:

(i) a substrate; (ii) an element supported by the substrate for movement between a first and second position with respect to the substrate, where at least a portion of the element between a first and second location on the element is an electrical insulator to electrically isolate the first and second locations from each other; (iii) an actuator attached to the first portion of the element to receive an input electrical signal and exert a force dependent on the input electrical signal urging the element toward second position; (iv) a bias stracture attached to the element to exert a predetermined substantially fixed force on the element urging the element toward the first position; and (v) a sensor attached to the second portion of the element to provide an output electrical signal indicating movement of the element to the second position, the output electrical signal being electrically isolated from the input electrical signal, the method comprising the steps of: (1) identifying a logical threshold for an input signal beyond which a logical trae is indicated and beneath which a logical false is indicated;

(2) adjusting the bias stracture to exert a fixed force on the elements toward the first position sufficient so that the actuator cannot move the element toward the second position for input signals beneath the threshold; and (3) providing an output logical trae signal only with movement of the element to the second position.

50. The method of claim 49 wherein the biased device is an electrostatic motor and the force is adjusted by changing a voltage on the electrostatic motor.

51. The method of claim 49 wherein the threshold is a voltage level and wherein the actuator and bias stracture are matched electrostatic motors and wherein the voltage on the bias stracture is set to the threshold voltage level.

52. The method of claim 49 wherein the bias stracture is a Lorenz force motor and the force is adjusted by changing a cuirent through the Lorenz force motor .

53. The method of claim 51 wherein the threshold is a current level and wherein the actuator and bias stracture are matched Lorenz motors and wherein the voltage on the bias stracture is set to the threshold current level.

54. The MEMS digital isolator of claim 28 including further a second sensor at the first portion of the element to provide a second output electrical signal indicating movement of the element to the second position, the second output electrical signal being electrically isolated from the output electrical signal.

55. The MEMS digital isolator of claim 54 including further a second actuator at the second portion of the element to receive a second input electrical signal and exert a force dependent on the second input electrical signal urging the element toward the second position.

πi.

56. A microelectromechanical system (MEMS) comprising: a beam supported on flexible transverse anns to move longitudinally along a substrate, wherein ends of the aπns removed from the beam are comiected to the substrate by flexible elements allowing transverse movement of the ends of the arms.

57. A microelectromechanical system (MEMS) comprising: a beam supported on flexible transverse arms to move longitudinally along a substrate, wherein ends of the arms removed from the beam are connected to the substrate by flexible longitudinally extending wrist elements.

58. The microelectromechanical system of claim 57 wherein the wrist elements join to the arms via an arcuate section.

59. The microelectromechanical system of claim 57 wherein the wrist elements are serpentine.

60. The microelectromechanical system of claim 59 wherein the ends of the anns removed from the beam are serpentine.

61. The microelectromechanical system of claim 57 wherein the ends of the arms removed from the beam are serpentine.

62. The microelectromechanical system of claim 57 wherein the beam is supported at longitudinally opposed ends by respective pairs of transverse aπns extending from the beam on opposite sides of the beam and wherein the wrist elements for the transverse arms extend in a longitudinal direction toward the center of the beam.

63. The microelectromechanical system of claim 57 wherein the beam is supported at opposed ends by respective pairs of transverse anns extending from the beam on opposite sides of the beam and wherein the wrist elements for the transverse arms extend in a longitudinally direction away the center of the beam.

64. The microelectromechanical system of claim 57 wherein the transverse aπns and wrist elements are conductive.

65. The microelectromechanical system of claim 57 wherein including a magnetic field.

66. The microelectromechanical system of claim 57 wherein the beam is supported at its center by a pair of transverse anns extending from the beam on opposite sides of the beam and wherein the wrist elements for the transverse aπn extend in opposite longitudinal directions.

67. The microelectromechanical system of claim 57 wherein the beam is supported at longitudinally opposed ends and at an intermediate point by respective pairs of transverse anns extending from the beam on opposite sides of the beam and wherein the wrist elements for the transverse arms at the opposed ends of the beam extend in the same longitudinally direction and wherein the wrist element for the transverse arms at the intermediate point of the beam extend in opposite longitudinal directions.

68. The microelectromechanical system of claim 57 wherein the transverse anns are of equal length.

69. The miciOelectromechanical system of claim 57 wherein a point of attachment of the transverse arms at the inteπnediate point is centered between points of attachment of the transverse anns at the opposed ends of the beam.

70. The microelectromechanical system of claim 57 wherein a first opposing of the beam supports an actuator selected from the group consisting of a Lorentz force motor, an electrostatic motor, a piezoelectric motor, a thermal-expansion motor, and a mechanical-displacement motor.

71. The microelectromechanical system of claim 57 wherein the center arm supports a sensing device selected from the group consisting of: a capacitive sensor, a piezoelectric sensor, a photoelectric sensor, a resistive sensor, an optical switching sensor and an inductive sensor.

72. The microelectromechanical system of claim 57 wherein the ends of the transverse anns removed from the beam are connected to a free end of a fransverse expansion element attached to the substrate only at a point proximate to the beam.

73. The microelectromechanical system of claim 57 wherein the beam is supported at longitudinally opposite ends by respective pairs of transverse arms extending from the beam on opposite sides of the beam and wherein the beam is sized to place the respective pairs of transverse arms in equal and opposite flexure.

74. The microelectromechanical system of claim 57 at least one pair of flexible transverse arms extends in a bow to present force increasingly resisting longitudinal motion of the beam in a first direction up to a snap point after which the force abruptly decreases.

75. A microelectromechanical system (MEMS) comprising: a beam supported on flexible transverse arms to move longitudinally along a substrate, wherein ends of the arms removed from the beam are connected to a free end of a transverse expansion element attached to the substrate only at a point proximate to the beam.

76. A microelectromechanical system (MEMS) comprising: a beam supported on flexible transverse arms to move longitudinally along a substrate, wherein the beam is supported at longitudinally opposite ends by respective pairs of transverse arms extending from the beam on opposite sides of the beam and wherein the beam is sized to place the respective pairs of transverse arms in equal and opposite flexure.

77. The microelectromechanical system of claim 76 wherein the respective pairs of transverse anns are flexed concavely with respect to the center of the beam.

78. The microelectromechanical system of claim 76 wherein the respective pairs of transverse arms are flexed convexly with respect to the center of the beam.

79. The microelectromechanical system of claim 76 wherein the transverse aπns are of equal length.

80. The microelectromechanical system of claim 76 wherein a point of attachment of the transverse arms at the intermediate point is centered between points of attachment of the transverse arms at the opposed ends of the beam.

81. The microelectromechanical system of claim 76 wherein a first opposing of the beam supports an actuator selected from the group consisting of: a Lorentz force motor, an electrostatic motor, a piezoelectric motor, a thennal-expansion motor, and a mechanical-displacement motor.

82. The microelectromechanical system of claim 76 wherein the center arm supports a sensing device selected from the group consisting of: a capacitive sensor, a piezoelectric sensor, a photoelectric sensor, a resistive sensor, an optical switching sensor and an inductive sensor.

83. A microelectromechanical system (MEMS) comprising: a beam supported on at least one pair of flexible transverse arms to move longitudinally along a substrate extending in a bow to present force increasingly resisting longitudinal motion of the beam in a first direction up to a snap point after which the force abraptly decreases.

84. The miciOelectromechanical system of claim 83 wherein the force changes direction after the snap point.

85. The microelectromechanical system of claim 84 wherein after the snap point the bow increasingly resisting longitudinal motion of the beam in a second direction opposite the first direction up to a second snap point at which the force abruptly decreases.

86. The microelectromechanical system of claim 83 wherein the second snap point is different from the first snap point.

87. The microelectromechanical system of claim 83 wherein the force maintains the same direction after the snap point.

88. A microelectromechanical system (MEMS) comprising: a beam supported for longitudinal motion along a substrate on at least one pair of flexible transverse anns, a first of which is angled so as to also extend longitudinally; a sensor detecting transverse motion receiving the first transverse arm at an end removed from the beam; whereby longitudinal motion of the beam may be amplified for detection by the sensor.

89. The miciOelectromechanical system of claim 88 wherein the sensor is selected from the group consisting of: a capacitive sensor, an optical sensor, a resistive sensor, a piezoelectric sensor, and an inductive sensor.

IV.

90. A microelectromechanical system (MEMS) with reduced noise sensitivity, comprising: a substrate; a first element supported from the substrate for movement between first and second positions with respect to an axis relative to the substrate; a first actuator attached to the first element to exert a force thereupon dependent upon a parameter to be measured and urging the element toward the second position; a second element supported from the substrate for movement between the first and second positions with respect to the axis relative to the substrate, and a sensor assembly communicating with the first and second elements to detect movement of the first and second elements and to provide an output subtracting measurement of movement of the first and second elements so as to provide an output with reduced influence from common mode noise acting to move the first and second elements.

91. The MEMS device of claim 90 including further a second actuator attached to the second element but not communicating with the parameter to be measured to not exert a force thereupon dependant upon the parameter to be measured.

92. The MEMS device of claim 90 including further a second actuator attached to the second element to exert a force thereupon dependant upon the parameter to be measured and urging the element toward the first position.

93. The MEMS device of claim 90 wherein the parameter is an electrical signal and wherein the first and second actuators receive input electrical signals related to the parameter and exert a force dependant on the input electrical signal.

94. The MEMS device of claim 90 further including an input circuit receiving the input electrical signal and producing a first input electrical signal for the first actuator and a second input electrical signal for the second actuator wherein the first input electrical signal is inverted with respect to the second electrical signal.

95. The MEMS device of claim 90 wherein the second element is not connected to an actuator exerting a force thereupon dependant upon the parameter to be measured and wherein the sensor assembly subtracts the sensed position of the second element from the sensed position of the first element to provide the output.

96. The MEMS device of claim 90 wherein the sensor assembly subtracts the sensed position of the second element indicating the inverted parameter plus the effects of substrate acceleration from the sensed position of the first element indicating the noninverted parameter plus effects of substrate acceleration to provide the output.

97. The MEMS device of claim 90 wherein the first and second actuators are selected from the group consisting of: an electrostatic motor, a Lorenz force motor, a piezoelectric motor, a thennal-expansion motor, and a mechanical-displacement motor.

98. The MEMS device of claim 90 wherein the sensor assembly includes sensors to detect movement of the first and second elements selected from the group consisting of capacitive sensors, piezoelectric sensors, photoelectric sensors, resistive sensors, and optical switching sensors.

99. The MEMS device of claim 90 wherein the first and second elements are beams attached to the substrate for sliding motion along an axis parallel to an adjacent surface of substrate.

100. The MEMS device of claim 90 wherein the first and second actuators are connected in opposite directions to the first and second beams.

101. The MEMS device of claim 90 wherein the sensor assembly includes capacitors attached to the first and second beams so as to provide an opposite change in capacitance for corresponding capacitors of the first and second beams.

102. The MEMS device of claim 97 wherein the beams move with respect to the substrate along a longitudinal axis and including flexing transverse arm pairs attached at longitudinally opposed ends of the beam to extend outward therefrom to support the beam with respect to the substrate.

103. The MEMS device of claim 90 further including: a first control element attached to the first element to exert a force dependent on the displacement of the first element toward the first position; and a second control element attached to the second element to exert a force dependent on the displacement of the first element toward the first position.

104. The MEMS device of claim 90 further including: a first control element attached to the first element to exert a predeteimined substantially constant force on the first element toward the first position; and a second control element attached to the second element to exert a predetermined substantially constant force on the first element toward the first position.

105. The MEMS device of claim 90 wherein at least a portion of the first element between the first actuator and the sensor assembly is an electrical insulator to electrically isolate the first actuator from the sensor assembly.