WO2000032094A1

WO2000032094A1 - Miniature spherical semiconductor transducer

Info

Publication number: WO2000032094A1
Application number: PCT/US1999/028091
Authority: WO
Inventors: Akira Ishikawa; Nabuo Takeda; Suzanne I. Ahn; Samuel S. Ahn; Steven R. Hays; F. Andrew Gaffney
Original assignee: Ball Semiconductor, Inc.
Priority date: 1998-11-25
Filing date: 1999-11-24
Publication date: 2000-06-08
Also published as: AU2032300A

Abstract

A semiconductor ball (10) comprises on a spherical substrate, one or more transducers/actuators (12) for sensing/stimulating body medium. The sensor/actuator (12) interfaces to processing circuitry (14) for communicating thereto. A power regulator (16) provides a relatively constant DC voltage to all onboard circuits, the power coupled from an external source via a coil (18) having coil ends (18a) and (18b). The processing circuitry (14) provides an output to a transmitter (20) that radiates a radio frequency signal to an external monitoring station (120).

Description

MINIATURE SPHERICAL SEMICONDUCTOR TRANSDUCER

TECHNICAL FIELD OF THE INVENTION

This invention is related to transducers, and more particularly to miniature semiconductor transducers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. 119(e) from U.S. Provisional

Patent Application Serial No. 60/110,103 filed on November 25, 1998, having the same title as this application.

This application is related to co-pending U.S. Patent Application Serial No. 09/323,585 (Atty. Dkt. No. BASI-24,635) entitled "IMPLANTABLE EPICARDIAL ELECTRODE," filed on June 2, 1999; U.S. Provisional Patent Application Serial No. 60/137,071 (Atty. Dkt. No. BASI-24,658) entitled "GLUCOSE SENSOR," filed on June 2, 1999; U.S. Patent Application Serial No. (Atty Dkt. No. BASI-24,784) entitled "SPHERICALLY- SHAPED BIOMEDICAL IC," filed of even date herewith; and U.S. Patent Application Serial No. (Atty Dkt. No. BASI-24,787) entitled "INTERNAL THERMOMETER," filed of even date herewith. BACKGROUND OF THE INVENTION

Semiconductor transducers are being made ever smaller as improvements in miniaturization techniques are made. Such miniature sensors and actuators, which are sometimes referred to as MEMS, an acronym for micro-electromechanical systems, are often fabricated using specially adapted semiconductor fabrication processes, including advanced complementary metal-oxide semiconductor (CMOS) technologies.

Presently, conventional semiconductor process technologies are characterized by fabrication of flat circular wafers. Each wafer typically has multiple identical chips or dies that are separated at the end of the wafer fabrication process. Each chip is then encapsulated in a plastic or ceramic housing that hermetically seals the chip therein and provides leads for external connections to the chip. Such chips have integrated circuitry that is embodied in stacked layers of conductors, insulators and semiconductor materials, all of which is formed in a thin, surface portion of the chip lying atop a square or rectangular substrate.

The present invention exploits a technological innovation in semiconductor processing in which very small, spherical-shaped, or ovoid- or ellipsoidal-shaped substrates are used to fabricate integrated circuits. A description of this innovative processing technology is provided in co-pending, commonly-assigned U.S. Patent Application Serial No. 08/858,004, filed May 16, 1997, entitled "Spherical Shaped Semiconductor Integrated Circuit," which is hereby incorporated by reference. The diameter of such semiconductor "balls" can be made very small, facilitating miniaturization of many integrated circuits and enabling novel circuit functions for specialized electronic applications. Described herein are applications of the spherical semiconductor process technology to the miniaturization of various transducers.

SUMMARY OF THE INVENTION

The invention disclosed and claimed herein is a semiconductor device comprising a substantially spherical semiconductor substrate. The substrate has disposed thereon a transducer which is in a position to interact with a medium. Integrated circuitry is formed on the substrate and is operatively interconnected to the transducer, such that the transducer converts energy from one form to another in communicating information between said medium and said integrated circuitry.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying Drawings in which:

FIGURE 1 illustrates a schematic side view of a spherical-shaped semiconductor device incorporating a transducer in accordance with a disclosed embodiment;

FIGURE 2 illustrates an enlarged cross section of a portion of the device of FIGURE 1 showing an example of a transducer structure in accordance with a disclosed embodiment; FIGURE 3 illustrates a plan view of the transducer of FIGURE 2; FIGURE 4 is an implementation of a transducer circuit in accordance with a disclosed embodiment;

FIGURE 5 illustrates a block diagram of a transducer communication system in accordance with a disclosed embodiment;

FIGURE 6 illustrates a graphical illustration of a data transmission technique that may be used with a disclosed embodiment;

FIGURE 7 illustrates a block diagram of a ball with an integral transducer in combination with an RF communication system in accordance with a disclosed embodiment;

FIGURE 8 illustrates a schematic diagram of an alternative embodiment of a transducer ball and antenna/coil arrangement; FIGURE 9 illustrates a schematic diagram of another embodiment of a transducer ball with three overlapping antenna/coil members;

FIGURE 10 illustrates a schematic block diagram of the monitor and the remote system for the powering/detection operation illustrated in FIGURE 7;

FIGURES 11 A-l IC illustrate alternate embodiments for the transmit/receive operation; FIGURE 12, illustrates a side view of an alternative embodiment utilizing additional circuitry or structure attached to the ball sensor for providing a local power source;

FIGURE 13, there is illustrated a schematic block diagram of the ball sensor using a battery as the local power supply system;

FIGURE 14, illustrates a cross-sectional diagram of the surface of the ball sensor illustrating the conductive strips forming the inductive element; FIGURE 15, illustrates a perspective view of a ball sensor, wherein the inductive element is illustrated as being strips of conductive material wrapped around the exterior of the ball sensor;

FIGURE 16 illustrates a cross-sectional view of an output pad, in an alternative embodiment where an actuator is employed;

FIGURE 17 illustrates a schematic block diagram of the actuator circuit and the remote system for the powering/detection operation; and

FIGURE 18 illustrates a schematic block diagram of the actuator circuit with the use of a battery.

DETAILED DESCRIPTION OF THE INVENTION

The spherical geometry of the semiconductor ball devices disclosed herein offers a number of advantages compared to conventional semiconductor devices having a planar or two- dimensional geometry. By way of illustration, a few of these advantages include the following: a spherical device has a smooth, rounded shape which is easily implanted or injected into a biological medium and which passes easily through a biological medium if necessary in a particular application. Further, the large surface area of a spherical device relative to its overall dimensions provides for the maximum of surface area devoted to functional regions in contact with the biological medium such as transducers and other circuitry. Further, the spherical device permits disposition of transducers aligned on all three geometric axes for maximum transducer function on a single device.

Referring to FIGURE 1 , one example of a layout of a spherical-shaped semiconductor device or ball is illustrated and designated generally by reference numeral 10. The ball 10 includes a transducer 12 fabricated on a surface portion that can be exposed to a medium to be sensed. The transducer 12 is coupled to integrated circuitry including signal processing circuitry

14, which in this example includes an analog-to-digital (A/D) converter. The transducer 12, signal processor 14 and other integrated circuitry on the ball 10 are powered by a power regulator 16, which provides a relatively constant DC voltage of about 3.0 volts to the circuits on the ball 10. A disclosed power source for the ball 10 is a coil 18, coupled to a power regulator 16, that is energized by a separate nearby source (not shown) that generates a varying magnetic field.

Alternatively, the ball 10 can be powered by a miniature battery connected to the ball 10 (which is discussed in greater detail hereinbelow), as well as to clusters of similar balls with different functions, such as memory. The miniature battery can also be in the shape of a ball (battery ball) to accommodate a common connection scheme between adjacent balls. Preferably, battery balls can be fashioned as electrical double-layer condensers from such materials as manganese dioxide, lithium or lithium ion, samarium-cobalt, carbon, etc. Since such a battery ball is a greater capacity energy source than an RF energy receiving coil, longer communication distances can be achieved by this means.

The coil 18 is represented by coil ends 18a and 18b that are connected by subsurface conductors (not shown) to the other circuit elements on the ball 10. It will be appreciated that the coil 18 may have many more windings than the three windings actually shown. The signal processor 14 provides an output to a transmitter 20 that preferably radiates a radio-frequency (RF) signal to a receiver (not shown) at another location. Both the magnetic field generator and receiver can be included in a computer-controlled apparatus or CPU station within proximity of the ball 10, at least, but not limited to periods when its operation is required.

Referring to FIGURE 2, a transducer 12' is shown in schematic cross section and represents one of many different possible implementations of the transducer 12 of FIGURE 1. The transducer 12' is formed over a semiconductor substrate 22, which is preferably doped with P-type impurities and serves as the electrical ground for the circuits on the ball 10. A dielectric layer 24 lies on the outer surface of the substrate 22 and overlies a cavity 26 cut down into the substrate 22. Lying on the dielectric layer 24 and juxtaposed with the cavity 26, is an electrode 28. Extending along a surface portion of the substrate 22 and beneath the cavity 26 is a first N-type region 30, which may be formed by selectively introducing a dopant such as phosphorus by a conventional technique such as ion implementation. The region 30 has a portion 30a to the left of the cavity 26 and a portion 30b underneath the cavity 26. A second N-type region 32 is provided at a surface portion of the substrate 22 as shown to the right of the cavity 26. An extension 34 of the electrode 28 makes contact to region 32 through an opening in the dielectric layer 24.

Referring now to FIGURE 3, there is illustrated a possible layout for the electrode 28 and cavity 26 therebelow. The extension 34 is shown extending out to a contact point 36 where contact to the N-type region 32 is made through the dielectric layer 24, as depicted in FIGURE 2. It will be appreciated that the structure of the transducer 12' of FIGURES 2 and 3 forms a variable capacitor with the electrode 28 serving as one capacitor plate, and the portion 30b of N-type region 30 beneath the cavity 26 serving as the other capacitor plate. The N-type regions 30 and 32 extend to points of interconnection (not shown) with other circuitry, as will be described below with reference to FIGURE 4. The variable capacitor is responsive to changes in pressure applied to the electrode 28. The top surface of electrode 28 is exposed to a medium, such as a fluid, gel, elastic or viscoelastic material, that exerts a variable pressure on the electrode 28. The force of this pressure is applied by the electrode 28 to the underlying portion of the dielectric layer 24, designated 24a in FIGURE 2, which serves as a diaphragm. The dielectric diaphragm

24a is sufficiently flexible to respond to the force of the pressure variations, such as atmospheric pressure, by moving down slightly into the cavity 26 with increasing pressure and back up to the position shown at a base-line pressure. It will be appreciated that the capacitance of the capacitor defined by the plates 28 and 30b will thus vary as a function of the pressure variations seen by the transducer 12'. The extension 34 is sufficiently thin and narrow that it will flex as the dielectric diaphragm 24a flexes up and down.

For the transducer application of FIGURES 2 and 3, the ball 10 of FIGURE 1 is preferably about one millimeter in diameter. For other applications, it may be possible to make the diameter much smaller, limited only by the process technology and other practical considerations.

Techniques for producing a diaphragm above a cavity that can be used to implement the structure generally shown in FIGURE 2 in a more specific structure, are known in the art, such as are disclosed in U.S. Patent No. 4,665,610, entitled "Method of Making a Semiconductor Transducer Having Multiple Level Diaphragm Structure," issued May 19, 1987, and which is hereby incorporated by reference. It will be appreciated that other implementations of a pressure transducer that are known in the art can be employed as alternatives to the transducer 12' of

FIGURE 2.

Referring now to FIGURE 4, there are illustrated other circuit elements of the transducer 12'. The variable capacitor C has its upper plate 28 connected to an oscillator circuit 40, and has its lower plate 30b connected to the substrate 22, which is indicated by the ground potential symbol. A resistor 42, designated by the letter R, is connected in parallel with the capacitor C.

The oscillator circuit 40 provides an output 44 that oscillates at a frequency that is a function of the product of the values of R and C. This phenomenon and specific circuitry for implementing an oscillator such as oscillator 40 are well known. Accordingly, it will be appreciated that the oscillator output 44 will oscillate at a frequency that is proportional to the capacitance of capacitor C, which varies with the sensed pressure variations as described above.

Referring now to FIGURE 5, there is illustrated a generalized circuit for communicating the output of a transducer 12, such as the specific transducer 12', to a nearby CPU station 46 by RF transmission. The transducer 12 has its output connected to signal processor 14, which in this case is an A/D converter. The A/D converter 14 can have its output amplified, as needed, by a first amplifier 48a, and then input to RF transmitter 20. A second amplifier 48b amplifies the output of the RF transmitter 20 and energizes an antenna 50. The CPU station 46 includes an antenna 52 that receives the RF signal radiated by the antenna 50.

Referring now to FIGURE 6, there is illustrated one implementation of the RF transmitter 20 where its output signal has a series of pulses, each pulse being at one of two different RF frequencies. Pulses representing binary "ones" are transmitted at a relatively high frequency, and pulses representing binary "zeros" are transmitted at a relatively low frequency. A start signal is used to begin each data transmission by the transmitter 20 and synchronize reception by the CPU station 46. For example, the start signal can be a start byte of eight "ones" in a row. The A/D converter 14 can be programmed so that it never outputs a data string containing eight "ones" in a row. Thus, the CPU station 46 can receive the start byte and following data string, and then extract the binary data from the data string. It will be appreciated that other known data transmission techniques can be used in implementing the present invention. A lookup table stored in a memory (not shown) in the CPU station 46 can be used to interpret the binary data as values corresponding to the condition of the medium sensed by the transducer 12.

Now referring to FIGURE 7, there is illustrated an alternative system for communicating with a transducer ball 110 (similar to transducer ball 10) with more complex integrated circuitry. The ball 110 includes circuitry for receiving power by magnetic coupling and transmitting data by radio-frequency transmission to a remote receiver in a monitoring station. The basic circuit functions performed by a semiconductor ball are illustrated and designated generally by reference numeral 110, which communicates with a monitoring station designated generally by reference numeral 120.

The ball 110 includes an antenna/coil 111, which serves the dual purpose of receiving power from the station 120 and transmitting data on an RF carrier signal to the station 120. The power may be received by the antenna/coil 111 by direct magnetic coupling if the station 120 is sufficiently close to the ball 110. Alternatively, an electromagnetic wave can be used to transmit power from the station 120 to the ball 110, whereby the magnetic field component of the electromagnetic wave induces a current in the coil, in accordance with known techniques. The power signal received by the antenna/coil 111 is rectified and smoothed by an RF rectifier smoother circuit 112. The output of the circuit 112 is connected to a DC power storage device 113, such as a capacitor. Such capacitor might also be of assistance in performing the waveform smoothing function. A voltage regulator 114 is used to make the DC voltage stable regardless of the distance between the station 120 and the ball 110. For example, a Zener diode or other suitable clamping circuit can perform this function. The resulting DC voltage is supplied to all circuits of the ball 110.

The ball 110 includes at least one transducer 115, which may be a sensor or an actuator. It will be appreciated that more than one sensor or actuator can be constructed on the ball, with communication and control via multiplexing circuitry. In the case of a sensor, a condition or parameter of the environment in which the ball is located is sensed. For example, pressure can be sensed through a change in capacitance or resistance. Such semiconductor pressure transducers are known in the art and can be adapted to fabrication on a spherical semiconductor substrate. A variable-resistance strain gauge is disclosed in commonly-assigned U.S. Provisional Patent Application Ser. No. 60/110,106, and entitled "Intraluminal Monitoring System," which is hereby incorporated by reference. In the case of multiple sensors on a single ball, more than one condition or parameter of the environment of the ball is sensed. For example, temperature, as well as pressure sensing can be accomplished by suitable means on a single ball. In the case of an actuator, a stimulus is applied to the tissue or medium in which it comes in contact. A separate actuator signal may need to be transmitted to the ball 110, in addition to the power signal for powering the ball 110. The actuator signal then directs a control logic circuit 116 to control the actuator to perform the desired function.

A converter 115', which may be an A/D converter, is used to convert the condition sensed by the transducer 115 to a signal that can be transmitted out to the station 120. The converter 115' can be part of the transducer 115, such as a variable capacitor for generating a signal depending upon the variations in capacitance. The control logic 116, which can be part of an onboard processor that controls not only the converter 115', but also other circuitry on the ball

110, is provided in accordance with known techniques. An RF oscillator 117 generates a radio- frequency carrier signal at a predetermined frequency in the RF band. An RF modulator 118 modulates the output of the converter 115' onto the carrier frequency signal. The resulting modulated signal is amplified by RF amplifier 119, and then transmitted to the outside through the antenna coil 111. The monitoring station 120 includes an antenna/coil 121 that serves the dual purpose of generating the electromagnetic wave for transmitting power to the ball 110, and receiving the RF data signal transmitted by the ball 110. It is preferred that the frequency of the electromagnetic wave that is output by the antenna/coil 121 is different from the carrier frequency generated by the RF oscillator 117. An RF amplifier 122 is used to couple the electromagnetic wave for power transmission to the antenna/coil 121. The frequency of the electromagnetic wave that is output by the station 120 is determined by an RF oscillator 123. The data signal received by the antenna/coil 121 is detected by an RF detector 124 and then amplified by an RF amplifier 125. Preferably, the signal from the RF amplifier 125 is converted by a converter 126 to a digital signal, which in turn is input to control logic 127. The control logic 127 may be a special- purpose CPU an interface to a general-purpose CPU or computer. The control logic 127 extracts the data from the signal received by the station 120 from the ball 110 and displays that information on a suitable display 128, such as a CRT screen. The technique for transmitting data from the ball 110 to the station 120 using the carrier frequency generated by the RF oscillator 117, can be in any form, using any suitable protocol. The modulation can be AM, FM, PM or any other suitable modulation technique.

Although a single ball can include the foregoing functions, more complex monitoring functions with multiple transducers can be implemented using multiple ball systems attached to catheters, needles and other insertable devices. These systems can be affixed to body surfaces, or can be attached to catheters, needles, and other insertable devices. In the case of insertable devices, these systems can be arranged so as to remain fixed at a specified site, to can be permitted to be transported through body conduits by various means, including convection, peristalsis, diffusion, etc.

Referring now to FIGURE 8, there is illustrated an alternative embodiment of a transducer ball, and designated generally by reference numeral 210. The ball 210 may have similar circuitry including a transducer 215 (similar to transducer 115). An antenna coil 211 is shown with several windings, although it will be understood that many more windings can be provided. The windings of the antenna/coil 211 encircle the ball 210 over regions that include circuit elements therebelow. Specifically, the antenna coil 211 overlies an RF rectifier-smoother 212 and an RF amplifier 219, which are similar to the circuit elements 112 and 119 described above with reference to FIGURE 7. The antenna coil 211 includes connections, as indicated by the dots, to both of these circuit elements 212 and 219. In the manufacturing process, the antenna/coil 211 can be deposited by conventional aluminum deposition adapted to the spherical shape of the semiconductor ball 210. The deposition can occur following other circuit formation steps at levels below, or on the surface of the ball 210. Except for the connection points indicated by the dots, the antenna/coil 211 is insulated from the underlying circuitry. Also, as an option, a ferromagnetic material can be deposited as a thin film beneath the antenna/coil 211, and insulated therefrom, and from the underlying circuit elements.

Referring now to FIGURE 9, there is illustrated a further embodiment with a multiple- coil arrangement, and designated generally by reference numeral 310. The ball 310 can have circuitry formed on its surface similar to the circuit elements described above with reference to the ball 110 of FIGURE 7. In addition, the ball 310 is shown having three coil elements designated 31 la, 31 lb, and 311c. It will be appreciated that in view of the different orientations of the separate coil elements, at least one of them will be favorably oriented in the magnetic field that is generated by the monitoring station, such as described above with reference to the monitoring station 120 of FIGURE 7. Therefore, a ball with windings constructed as shown in

FIGURE 9, can receive energy from the monitoring station without regard to its orientation relative thereto. It will also be appreciated that the separate coils 311a, 311b and 311c can be connected in series to provide a single power source for the ball 310.

The disclosed architecture has application to any of various transducers that can be fabricated using semiconductor processes. The transducer may be a sensor that senses a condition of a medium, as with the pressure transducer described above, or the transducer may be an actuator that energizes a medium in response to on-board electrical signals. For example, a strain gauge or piezoresistive element can be used for sensing pressure, particular implementations of which are described in U.S. Patent Nos. 4,050,313 and 4,618,844, entitled "Semiconductor Pressure Transducer," issued October 21, 1986, which is hereby incorporated by reference. Numerous examples of photodiodes for sensing light and light emitting diodes (LEDs) for transmitting light are known in the semiconductor arts. Ionic sensors such as pH sensors are known in the art, an example being disclosed in U.S. Patent No. 5,814,280. Other possibilities include acoustic sensors (miniature microphones) and acoustic actuators (miniature loudspeakers). Also, the cavity described in relation to FIGURE 2, or multiple cavities of similar design, can be filled with gel or other medium, containing drug, chemotherapy agent, to other deliverable therapeutic agent for controlled release into the body. Release can be effected by suitable energization of the cantilever 34. Also, accelerometers can be fabricated using semiconductor processing techniques as disclosed in U.S. Patent No. 5,656,512. The patents referred to above are hereby incorporated by reference.

Referring now to FIGURE 10, there is illustrated a schematic block diagram of the monitor and the remote system for the powering/detection operation illustrated in FIGURE 7. A ball sensor 110 (similar to ball sensor 24 described hereinabove), is operable to provide the transducer 115 for interfacing with the desired quantitative condition. The illustrated embodiment of FIGURE 10 is that associated with a "passive" system, which term refers to a system having no battery associated therewith. In order to operate the system, there is provided an inductive coupling element 1004 in the form of an inductor, which is operable to pick up an alternating wave or impulse via inductive coupling, and extract the energy therein for storage in the inductive element 1004. This will create a voltage across the inductive element 1004 between a node 1006 and a node 1008. A diode 1010 is connected between the node 1008 and the node 1012, with the anode of diode 1010 connected to node 1008 and the cathode of diode 1010 connected to a node 1012. Typically, the diode 1010 will be fabricated as a Schottky diode, but can be a simple PN semiconductor diode. For the purposes of this embodiment, the PN diode will be described, although it should be understood that a Schottky diode could easily be fabricated to replace this diode. The reason for utilizing a Schottky diode is that the Schottky diode has a lower voltage drop in the forward conducting direction.

The diode 1010 is operable to rectify the voltage across the inductive element 1004 onto the node 1012, which has a capacitor 1014 disposed between node 1012 and node 1006. Node 1012 is also connected through a diode 1016 having the anode thereof connected to node 1012 and the cathode thereof connected to a node 1018 to charge up a capacitor 1020 disposed between node 1018 and 1006. The capacitor 1020 is the power supply capacitor for providing power to the ball sensor 110. The capacitor 1014, as will be described hereinbelow, is operable to be discharged during operation of the system and, therefore, a separate capacitor, the capacitor 1020, is required for storing power to power the system of the ball sensor 110.

There is also provided a switching transistor 1031 which has one side of the gate/source path thereof connected to a node 1028, which is the output of the transducer 115 and the other side thereof connected to a node 1032. The gate of transistor 1031 is connected to the output of the switch control 1030. Node 1032 is connected to the input of a buffer 1034 to generate an analog signal output thereof which is then converted with an analog-to-digital converter 1036 to a digital value for input to a CPU 1038. The CPU 1038 is operable to receive and process this digital input voltage. A clock circuit 1040 provides timing to the system. A memory 1039 is provided in communication with the CPU 1038 to allow the CPU 1038 to store data therein for later transmittal back to the remote location or for even storing received instructions. This memory 1039 can be volatile or it can be non- volatile, such as a ROM. For the volatile configuration, of course, this will lose all information when the power is removed. The CPU 1038 is operable to provide control signals to the switch control 1030 for turning on the transistor

1031 at the appropriate time. In addition to the transistor 1031 being toggled to read the transducer 115, transistor 1031 could be a pass-through circuit such that the CPU 1038 can continually monitor the voltage at the output of the transducer 115. System power to all power- consuming elements of the ball sensor 110 is provided at the SYSTEM PWR output node.

In order to communicate with the CPU 1038 for transferring data thereto and for allowing the CPU 1038 to transfer data therefrom, a receive/transmit circuit 1042 is provided for interfacing to node 1012 through a resistive element 1044. This allows RF energy to be transmitted to node 1012. It is important to note that the semiconductor junction across diode 1010 is a capacitive junction. Therefore, this will allow coupling from node 1012 to node 1008. Although not illustrated, this could actually be a tuned circuit, by selecting the value of the capacitance inherent in the design of the diode 1010. In any event, this allows an RF connection to be provided across diode 1010 while allowing sufficient energy to be input across conductive element 1004 to provide a voltage thereacross for rectification by the diode 1010 and capacitor 1014. Typically, the frequency of this connection will be in the MHz range, depending upon the design. However, many designs could be utilized. Some of these are illustrated in Beigel, U.S.

Patent No. 4,333,072, entitled "Identification Device," issued June 1, 1982, and Mogi et al., U.S. Patent No. 3,944,982, entitled "Remote Control System For Electric Apparatus," issued March 16, 1976, which are incorporated herein by reference. With these types of systems, power can continually be provided to the node 1012 and subsequently to capacitor 1020 to allow power to be constantly applied to the ball sensor 110. The remote system 120, which is disposed outside of the body and proximate to the ball sensor 110, includes an inductive element 1050 which is operable to be disposed in an area proximate to the skin, yet exterior to the body, in the proximity of the ball sensor 110. The inductive element 1050 is driven by a driving circuit 1052 which provides a differential output that is driven by an oscillator 1054. This will be at a predetermined frequency and power level necessary to couple energy from inductive element 1050 to inductive element 1004. Since this is an external system, the power of the oscillator can be set to a level to account for any losses through the body tissues. To allow information to be transmitted, a modulation circuit 1056 is provided which is modulated by a transmitter signal in a block 1058 that allows information to be modulated onto the oscillator signal of the oscillator 1054, which oscillator signal is essentially a

"carrier" signal. However, it should be understood that the information that is transmitted to the ball sensor 110 could merely be date information, whereas the CPU 1038 could operate independent of any transmitted information to provide the correct timing for the output pulses and the correct waveshape therefor.

Alternatively, entire control of the system could be provided by the transmit signal 1058 and the information carried thereon, since power must be delivered to the illustrated embodiment due to the lack of any independent power in the ball sensor 110. Note also that the distance of the remote system 120 to the ball sensor 110 may need to be varied such that the power signal coupled to the sensor 110 is of sufficient energy to receive an RF signal back from the sensor 110. The strength of the signals exchanged between the sensor 110 and the remote system 120 varies according to the number of tissues and body parts between the sensor 110 and the remote system 120. For example, where a sensor 110 is introduced in a vein close to the surface of the skin, the signal strength is less likely to be affected since the remote system 120 can be placed very closely to the sensor 110. On the other hand, where the sensor 110 is introduced into an artery near the heart, the signal strength of the remote system 120 may need to be increased to power the monitor 110 having the on-board sensor 110. Alternatively, where the power output of the remote system 120 is limited, the remote system 120 may need be inserted into the body to come into closer proximity of the monitor system 110.

When the information is received from the ball sensor 110, it is superimposed upon the oscillator signal driving the inductive element 1050. This is extracted therefrom via a detector

1060 which has the output thereof input to a first low pass filter 1062, and then to a second low pass filter 1064. The output of low pass filters 1062 and 1064 are compared using a comparator 1066 to provide the data. The filter 1062 provides an average voltage output, whereas the filter 1064 provides the actual digital voltage output. The output of the comparator 1066 is then input to a CPU 1070 which also is powered by the oscillator 1054 to process the data received therefrom. This can then be input to a display 1072.

Referring now to FIGURES 11 A-l IC, there are illustrated alternate embodiments for the transmit/receive operation. In FIGURE 11 A, there is provided an oscillator 1100 which drives an external inductive element 1102. Typically, there is some type of load 1104 disposed across the inductive element 1102. This is the primary power that is provided to the system. A separate inductive element 1106 is provided on the ball sensor 110, for being inductively coupled to the inductive element 1102. Thereafter, a voltage is generated across the inductive element 1106, the inductive element 1106 being connected between nodes 1108 and 1110. A diode 1112 is connected between node 1108 and a power node 1114, and a power supply capacitor 1116 is disposed across node 1114 and a node 1110. This allows the voltage on node 1108 to be rectified with diode 1112.

In the alternative embodiment of FIGURE 1 IB, the receive operation utilizes a separate inductive element or antenna 1124 in the ball sensor 110, which is operable to be connected between nodes 1109 and 1111. Node 1109 is capacitively coupled to a transmit node 1130 with a capacitor 1132, the capacitor 1132 being a coupling capacitor. A transmitter 1134 is provided for transmitting received data from a line 1136 to the node 1130, which is then coupled to the node

1109 to impress the RF signal across the inductive element 1124.

A corresponding inductive element 1140 is disposed on the external remote controller of remote location 120, which inductive element 1140 is operable to be disposed proximate to the inductive element 1124, but external to the human body. The inductive element 1140 is basically a "pick-up" element which is operable to receive information and function as an antenna, and provide the received signal to a receiver 1142. The structure of FIGURE 1 IB is a separate structure, such that node 1109 is isolated from node 1108, the power receiving node. However, it should be understood that any harmonics of the oscillator 1100 would, of course, leak over into the inductive element 1106. This can be tuned out with the use of some type of tuning element 1144 on the ball sensor 110 disposed across inductive element 1124, and also a tuning element 1146 disposed across the inductive element 1140, i.e., the antenna.

Referring now to FIGURE 1 IC, there is illustrated a simplified schematic diagram of the receive portion. The ball sensor 110 has associated therewith a separate receive antenna or inductive element 1150 disposed between node 1113 and a node 1152. Node 1152 is capacitively coupled to a receive node 1154 with a coupling capacitor 1156. A receiver 1158 is provided for receiving the information transmitted thereto and providing on the output thereof data on a data line 1160. The receiver 1158 is operable to receive the RF signal, demodulate the data therefrom, and provide digital data on the output 1460. External to the human body and the ball sensor 110 is a transmitter 1162 which is operable to impress a signal across an external inductive element 1164. The inductive element 1164 basically provides the RF energy and is essentially tuned with a tuning element 1166. A corresponding tuning element 1168 is provided on the ball sensor 110 and disposed across inductive element 1150, the inductive element 1150 acting as an antenna, as well as the inductive element 1164.

Note that in circumstances where the signals of the ball sensor 110 cannot be adequately received therefrom and/or power coupled thereto, the external location circuitry 120 may need to be inserted into the body proximate to the ball sensor 110 in order to couple the transmit/receive signals and power. Furthermore, where more than one sensor ball 110 is used, communication of power and data signals between the various ball sensors 110 may need to employ distinct time periods (i.e., time multiplexing) when communication occurs using a single common frequency, or discrimination circuits may need to be used where communication occurs simultaneously with the plurality of implanted ball sensors 110 having different oscillator frequencies.

Referring now to FIGURE 12, there is illustrated a side view of an alternative embodiment utilizing additional circuitry or structure attached to the ball sensor 110 for providing a local power source. As described hereinabove, the ball sensor 110 requires a power- generating structure for storing a power supply voltage such that diodes must be provided for receiving and rectifying a large amount of power and charging up a power supply capacitor. Alternatively, the ball sensor could be configured to interface to an attached power supply system 1200 comprising either a battery or a capacitor. The local power supply system 1200 is illustrated as disposed on a circuit board 1203 defined by supporting structures 1202 and 1204. The circuit board 1203 contains electronics for interfacing the local power supply system 1200 to the ball sensor 110.

Referring now to FIGURE 13, there is illustrated a schematic block diagram of the ball sensor 110 using a battery as the local power supply system 1200. A battery 1301 is provided as a source of self-contained power and is connected across a capacitor 1300 to providing smoothing of any power output to the system power-consuming elements of the ball sensor 110. Power for all on-board components is obtained from the SYSTEM POWER output by providing sufficient charge to the capacitor 1300. The capacitor 1300 could be formed on the surface of the ball sensor 110 or it could actually be part of the battery structure 1301. Additionally, the capacitance 1300 could actually be the capacitance of the battery 1301. Additional structure could be provided for powering the CPU 1338 and the other circuitry on the ball sensor 110 from the battery 1301. As such, there would only be required a smaller inductive element 1302 and a capacitor 1304 to allow the receive/transmit block 1042 to receive/transmit information from and to the remote exterior station 120. The switch control 1030 controls the gate of the switching transistor 1031 to switch output of the transducer 115 through the switching transistor 1031 source/drain path to the CPU 1038.

Referring now to FIGURE 14, there is illustrated a cross-sectional diagram of the surface of the ball sensor 110 illustrating the conductive strips forming the inductive element 1004. The conductive strips, referred to by reference numeral 1410, are spaced above the surface of the integrated circuit of the ball sensor 110 by a predetermined distance, and separated therefrom by a layer of silicon dioxide. A passivation layer 1411 is then disposed over the upper surface of the conductive strips 1410. The conductive strips 1410 can be fabricated from polycrystalline silicon but, it would be preferable to form them from the upper metal layer to result in a higher conductivity strip. This will allow the strips 1410 to be narrower and separated from each other by a larger distance. This separation would reduce the amount of capacitance therebetween.

One end of the strip 1410 is connected to a diode structure 1413. The diode structure 1413 is formed of an N-well implant region 1414 into which a P-well implant region 1416 is disposed, and an N-well implant region 1414 disposed within the P-well implant region 1416. This forms a PN diode where one end of the conductive strips 1410, a conductive connection 1420, is connected to the P-well 1416 implant region, and a conductive layer 1422 is connected at one end to the N-well implant region 1414. This conductive layer or strip 1422 extends outward to other circuitry on the integrated circuit and can actually form the capacitor. Since it needs to go to a capacitor directly, a lower plate 1424 formed of a layer of polycrystalline silicon or metal in a double-metal process, could be provided separated therefrom by a layer of oxide.

Referring now to FIGURE 15, there is illustrated a perspective view of a ball sensor 110, wherein the inductive element 1004 (inductive element 1302 being similar thereto) is illustrated as being strips of conductive material wrapped around the exterior of the ball sensor 110. The inductive element 1004 is formed of a conductive strip wrapped many times around the ball sensor 110. The length of inductive element 1004 depends upon the receive characteristics that are required. As described hereinabove with reference to FIGURES 11 A-l IC, there could be multiple conductive strips, each associated with a receive function, a transmit function, or a power function, or they could all share one single conductive element or strip. On one end of the ball sensor 110 there is provided a transducer interface 1500 of the transducer 115 having, optionally, one or more interface balls 1502 (or partial balls, called nodules) associated therewith extending from the transducer interface surface to provide enhanced engagement of the measuring surface or physical entity. The interface balls 1502 can be made of non-reactive material, e.g., gold to prevent degradation while in the body. Note that in some applications, the interface nodules 1502 are not required for obtaining the desired quantitative data. On the other end of the ball sensor 110 are provided interconnect balls 1504 (or nodules) for interconnecting to one or more other spherical balls which may provide similar functions such as monitoring of quantitative data, or unique functions such as supplying only power or data buffering and storage.

Referring now to FIGURE 16, there is illustrated a cross-sectional view of an output pad, in an alternative embodiment where an actuator is employed. In general, an output pad 1600 (similar to output pad 1700) is required to provide a conductive interface between the transistor 1728 and, for example, the myocardium muscle. This therefore requires some type of metallic interface that is non-reactive. Such an interface would require a metal such as gold, platinum and the like. In the disclosed embodiment, gold would be provided.

After the formation of the upper metal layer via a deposition technique with metal such as aluminum or copper, a passivation layer of oxide 1602 is disposed over the substrate to basically prevent oxidation of the metal layers and protect the semiconductor circuits in general. The contact layer 1614 extends beyond the active region 1612 to an output pad region 1604 and is separated from the active region 1612 by a layer of field oxide 1608 or some type of isolation oxide. There may be some type of channel stop implant disposed below the field oxide layer 1608. The contact 1614 extends from the source/drain implant 1616 to the region 1604. This contact 1614 is required to be fairly conductive. Typically, polycrystalline silicon is not of sufficient conductivity to meet this requirement. Therefore, some type of polysilicide process will be required, wherein the upper surface is converted to some type of suicide such as titanium disilicide to lower the surface resistivity thereof. Alternatively, a metal layer could be provided which is connected to the contact region 1614.

Once the contact 1614 is formed and the passivation layer 1602 is disposed over the entire structure, vias 1606 are formed therein. These vias are then filled with metallic plugs 1608 by forming a layer of metal over the substrate and then etching the substrate to remove the undesired portions. The metal plugs 1608 may be formed of metal such as aluminum or gold. If they were formed of gold, this would allow for soldering if they were to be used as contacts. However, in this context, these plugs 1608 are utilized for conductivity purposes. Therefore, an aluminum plug would be sufficient if it were covered with a thin layer of gold to render the aluminum non- reactive and prevent oxidation thereof. Alternatively, in the disclosed embodiment, the plug may, of course, be gold. However, it should be understood that any type of non-reactive metal could be utilized as long as the surface thereof is sufficiently non-reactive, and the conductance of the plug is sufficiently high to result in a low resistance path between the exterior of the spherical IC and a capacitive plate (not shown). The reason for this is that the stored charge must be discharged into a resistance as low as 500 Ohms and any significant resistance disposed between the upper plate of the capacitor and the exterior must be minimized.

Referring now to FIGURE 17, there is illustrated a schematic block diagram of the actuator circuit and the remote system for the powering/detection operation. The actuator circuit

1713 is operable to provide two output interfaces, an output pad 1700 as an anode and an output pad 1702 as a cathode, for interfacing with the cardiac muscle tissue. The spacing between these two pads or contacts 1700 and 1702 is approximately 0.5 cm. The illustrated embodiment is that associated with a "passive" system, which term refers to the fact that there is no battery associated therewith. In order to operate the system, there is provided an inductive coupling element 1704 in the form of an inductor, which is operable to pick up an alternating wave or impulse via inductive coupling and extract the energy therein for storage in the inductive element 1704. This will create a voltage across the inductive element 1704 between a terminal 1706 and a terminal 1708. A diode 1710 is connected between the node 1708 and a node 1712, with the anode of diode 1710 connected to node 1708 and the cathode of diode 1710 connected to a node 1712. Typically, the diode 1710 will be fabricated as a Schottky diode, but can be a simple PN semiconductor diode. For the purposes of this embodiment, the PN diode will be described, although it should be understood that a Schottky diode could easily be fabricated to replace this diode. The reason for utilizing a Schottky diode is that the Schottky diode has a lower voltage drop in the forward conducting direction.

The diode 1710 is operable to rectify the voltage across the inductive element 1704 onto the node 1712, which has a capacitor 1714 disposed between node 1712 and node 1706. Node 1712 is also connected through a diode 1716 having the anode thereof connected to node 1712 and the cathode thereof connected to a node 1718 to charge up a capacitor 1720 disposed between node 1718 and 1706. The capacitor 1720 is the power supply capacitor for providing power to the actuator circuit 1713. The capacitor 1714, as will be described hereinbelow, is operable to be discharged during operation of the system and, therefore, a separate capacitor, the capacitor 1720, is required for storing power to power the system.

The node 1712 is connected to the anode of a diode 1722, the cathode thereof connected to a node 1724. A main capacitor 1726 has one side connected to node 1724 and the other side thereof connected to node 1706. The capacitor 1726, as will be described hereinbelow, is operable to provide the primary discharge energy to, for example, the myocardium or any other tissue to which a stimulus may be applied, via the output pad 1700, the anode of the actuator circuit 1713. This node 1724 is connected to one side of the gate/source path of a drive transistor 1728, the other side thereof connected to the output pad 1700. The gate of drive transistor 1728 is connected to the output of a switch control circuit 1730. Drive transistor 1728 is operable to be turned on for a short period of time to connect to the top plate of capacitor 1726 to the output pad 1700, and subsequently, to conduct cuπent to the desired tissue.

In addition to transmitting energy out on output pad 1700, there is also provided a sense transistor 1731 which has one side of the gate/source path thereof connected to the output pad 1700 and the other side thereof connected to a node 1732. The gate of sense transistor 1731 is connected to the output of the switch control 1730. Node 1732 is connected to the input of a buffer 1734 to generate an analog signal output thereof which is then converted with an analog- to-digital converter 1736 to a digital value for input to a CPU 1738. The CPU 1738 is operable to receive and process this digital input voltage. A clock circuit 1740 is provided for providing timing to the system. A memory 1739 is provided in communication with the CPU 1738 to allow the CPU 1738 to store data therein for later transmittal back to the remote location or for even storing received instructions. This memory 1739 can be volatile or it can be non-volatile, such as a ROM. For the volatile configuration, of course, this will lose all information when the power is removed.

The CPU 1738 is operable to provide control signals to the switch control 1730 for turning on the drive transistor 1728 or the sense transistor 1731 at the appropriate time. Typically, the drive transistor 1728 is controlled to turn on for a period of approximately 0.5 microseconds 60-80 times per minute. Once drive transistor 1728 is turned off, then sense transistor 1731 can be turned on. Alternatively, sense transistor 1731 could be a pass-through circuit such that the CPU 1738 can always monitor the voltage on the output pad 1700.

However, it is desirable with the sense transistor 1731 and the sensing operation to sense depolarization in the desired tissue after an output voltage has been provided thereto for a short duration of time.

In order to communicate with the CPU 1738 for transferring data thereto and for allowing the CPU 1738 to transfer data therefrom, a receive/transmit circuit 1742 is provided for interfacing to node 1712 to a resistive element 1744. This allows RF energy to be transmitted to node 1712. It is important to note that the semiconductor junction across diode 1710 is a capacitive junction. Therefore, this will allow coupling from node 1712 to node 1704. Although not illustrated, this could actually be a tuned circuit, by selecting the value of the capacitance inherent in the design of the diode 1710. In any event, this allows an RF connection to be provided across diode 1710 while allowing sufficient energy to be input across conductive element 1704 to provide a voltage thereacross for rectification by the diode 1710 and capacitor 1714. Typically, the operating frequency of this connection will be in the MHz range, depending upon the design of which a variety are possible. For example, some possible designs are illustrated in U.S. Patent No. 4,333,072 entitled "Identification Device," issued June 1, 1982, and

Mogi et al., U.S. Patent No. 3,944,982, entitled "Remote Control System For Electric Apparatus," issued March 16, 1976, both of which are incorporated herein by reference. With these types of systems, power can continually be provided to the node 1712 and subsequently to capacitors 1720 and 1726 to allow power to be constantly applied to the actuator circuit 1713. The diode 1722 may not be required in order to provide the sufficient charge to capacitor 1726, but some type of isolation is required between the capacitor 1726 and the capacitor 1720.

Voltage regulation may also be required in order to provide a shaped pulse on the output pad 1700. This could be provided by the switch control 1730.

The remote system which is disposed external to the body and proximate to the actuator circuit 1713 includes an inductive element 1750 which is operable to be disposed in an area proximate to the skin exterior to the body in the proximity of the actuator circuit 1713. The inductive element 1750 is driven by a driving circuit 1752 which provides a differential output that is driven by an oscillator 1754. This will be at a predetermined frequency and power level necessary to couple energy from inductive element 1750 to inductive element 1704. Since this is an external system, the power of the oscillator can be set to a level to account for any losses through the body tissues. To allow information to be transmitted, a modulation circuit 1756 is provided which is modulated by a transmitter signal in a block 1758 that allows information to be modulated onto the oscillator signal 1754, which oscillator 1754 provides a "carrier" signal. However, it should be understood that the information that is transmitted to the actuator circuit 1713 could merely be date information whereas the CPU 1738 could operate independent of the information being transmitted to provide the correct timing and wave shape for the output pulses.

Alternatively, the entire control of the system may be provided by the transmit signal 1750 and the information carried thereon, because power must be delivered to the illustrated embodiment when there is a lack of an independent power source in the actuator circuit 1713.

The information received from the actuator circuit 1713 is modulated upon the oscillator signal driving the inductive element 1750. This information is extracted therefrom via a detector

1760 which has the output thereof input to a first low pass filter 1762 and then to a second low pass filter 1764. The output of low pass filters 1762 and 1764 are compared with a comparator 1766 to provide the data. The filter 1762 will provide an average voltage output, whereas the filter 1764 will provide the actual digital voltage output. The output of the comparator 1766 is then input to a CPU 1770 which also is powered by the oscillator 1754 to process the data received therefrom. This can be input to a display 1772. Referring now to FIGURE 18, there is illustrated a schematic block diagram of the actuator circuit 1713 with the use of a battery. A battery 1802 is provided which is connected to a capacitor 1800. The capacitor 1800 could be identical to the capacitor 1726 of FIGURE 17 in that it could be formed on the surface of the spherical IC 10, or it could actually be part of the structure 1200 shown in FIGURE 12. The battery 1802 is provided across the capacitor 1800 to provide sufficient charge therefor. Additionally, the capacitance 1800 could actually be the capacitance of the battery 1802. Additional structure could be provided for powering the CPU 1738 and the other circuitry on the chip from the battery 1802. As such, there would only be required a smaller inductive element 1804 and a capacitor 1806 to allow the receive/transmit block 1742 to receive/transmit information from and to the remote exterior station.

Turning now to another class of alternate embodiments, it can be appreciated that the spherical semiconductor ICs can be applied to the sensing of chemical parameters and variables within biological tissues. Included in this class of embodiments are the pH sensors, ionic activity or concentration sensors and sensors for all kinds of substances in the human body such as glucose, carbohydrates, proteins, sugars, enzymes, hemoglobin, lipids and phospholipids, neurotransmitters, cell integrins and other cell receptors. These are just some of the possible substances that may be monitored by the spherical semiconductor IC devices of the present disclosure described herein.

Although the preferred embodiment has been described in detail, it should be understood that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A semiconductor device, comprising: a substantially spherical semiconductor substrate; a transducer disposed on said substrate in a position to communicate with an adjacent medium; and integrated circuitry formed on said substrate and operatively interconnected with said transducer; whereby said transducer converts energy from one form to another in communicating information between said medium and said integrated circuitry.

2. The device of Claim 1, wherein said transducer is a sensor that senses a quantitative condition of said medium and converts said sensed quantitative condition to electrical energy.

3. The device of Claim 2, wherein said transducer senses a pressure level in said medium and converts said pressure level into a corresponding electrical signal.

4. The device of Claim 3, wherein said transducer includes a variable capacitor whose capacitance varies in response to changes in pressure in said medium.

5. The device of Claim 1, wherein said transducer is an actuator that converts electrical energy from said integrated circuitry to energy in a different form that is communicated to said medium.

6. The device of Claim 5, wherein said transducer is a light emitting diode.

7. The device of Claim 1, wherein said substrate has a diameter equal to approximately one millimeter.

8. The device of Claim 1, wherein said diameter of said substrate is less than one millimeter.

9. The device of Claim 1, further comprising means for energizing said integrated circuitry.

10. The device of Claim 9, wherein said energizing means comprises a coil in which a current is induced in response to a varying magnetic field directed at the device by an external source.

11. The device of Claim 1 , further comprising a transmitter for transmitting electromagnetic waves carrying information corresponding to a condition sensed by said transducer.

12. The device of Claim 11 , wherein said transmitter transmits digital data using first and second carrier waves of different frequencies, whereby a series of zero bits and one bits can be transmitted to a nearby receiving station.

13. The device of Claim 1, wherein said substrate further comprises an onboard energy source.

14. The device of Claim 13, wherein said onboard energy source is a capacitor.

15. A method of implementing a semiconductor device, comprising: providing a spherical semiconductor substrate; fabricating a transducer on the substrate in a position to communicate with an adjacent medium; and forming integrated circuitry on the substrate which is operatively interconnected with the transducer; whereby the transducer converts energy from one form to another in communicating information between the medium and the integrated circuitry.

16. The method of Claim 15, wherein the transducer is a sensor that senses a quantitative condition of the medium and converts the sensed condition to electrical energy.

17. The method of Claim 15, wherein the transducer senses a pressure level in the medium and converts the pressure level into a corresponding electrical signal.

18. The method of Claim 15, wherein the transducer includes a variable capacitor whose capacitance varies in response to changes in pressure in the medium.

19. The method of Claim 15, wherein the transducer is an actuator that converts electrical energy from the integrated circuitry to energy in a different form that is communicated to the medium.

20. The method of Claim 15, wherein the transducer is a light emitting diode.

21. The method of Claim 15, wherein the diameter of the substrate equal to about one millimeter.

22. The method of Claim 15, wherein the diameter of the substrate is less than one millimeter.

23. The method of Claim 15, further comprising means for energizing the integrated circuitry.

24. The method of Claim 23, wherein the energizing means comprises a coil in which a current is induced in response to a varying magnetic field directed at the device by an external source.

25. The method of Claim 15, further comprising a transmitter for transmitting electromagnetic waves carrying information corresponding to a condition sensed by the transducer.

26. The method of Claim 25, wherein the transmitter transmits digital data using first and second carrier waves of different frequencies, whereby a series of zero bits and one bits can be transmitted to a nearby receiving station.

27. The method of Claim 15, wherein the substrate further comprises an onboard energy source.

28. The method of Claim 27, wherein the onboard energy source is a capacitor.