WO2006126401A1

WO2006126401A1 - Oscillation controller for piezoelectric resonant sensor element

Info

Publication number: WO2006126401A1
Application number: PCT/JP2006/309494
Authority: WO
Inventors: Kaoru Yamashita; Masanori Okuyama
Original assignee: Osaka University
Priority date: 2005-05-25
Filing date: 2006-05-11
Publication date: 2006-11-30

Abstract

A piezoelectric resonant ultrasonic sensor element (20) is provided with an oscillation controlling outer electrode (19) formed in the vicinity of the periphery of an inner electrode (18) in addition to two inner electrode (18) and common electrode (16) pairs. (A pair is formed by the outer electrode (19) and the common electrode (16).) A detection signal detected by the pair of electrodes (16, 18) and outputted through a terminal (T1) is amplified by a variable gain amplifier (31) by a prescribed gain controlled and set by a gain controller (30), and a reverse phase oscillation control signal is applied to the oscillation controlling outer electrode (19) through a terminal (T2), and oscillation of the detection signal, which is obtained when an ultrasonic wave, i.e. an oscillation wave, is detected, is controlled to be attenuated.

Description

Specification

Vibration control device for piezoelectric resonance sensor element

Technical field

The present invention relates to a vibration control device and a vibration control method for a piezoelectric resonance sensor element such as an ultrasonic sensor element, a sound wave sensor element, or a vibration sensor element.

Background art

[0002] Recently, three-dimensional imaging (imaging) technology using ultrasonic waves has attracted much attention from the viewpoint of applications such as vehicle control, distance measurement, and assistance for the disabled. In particular, the piezoelectric resonance type ultrasonic sensor element on the silicon diaphragm has an advantage that the manufacturing process is simple and the integration into the semiconductor device is easy (for example, see Non-Patent Document 1).

[0003] The present inventors have invented a highly sensitive piezoelectric ultrasonic microsensor element using a piezoelectric PZT ceramic thin film on a silicon diaphragm (for example, see Non-Patent Document 2). . In early sensor manufacturing processes, the polarization change at the center always had the opposite direction to that of the periphery on the vibrating diaphragm, so the top electrode was only formed at the center of the diaphragm (e.g., (See Non-Patent Documents 3 and 4.) ₀

[0004] The above-described conventional piezoelectric resonance type ultrasonic sensor element has a problem that its sensitivity is relatively low and the output voltage is easily affected by external noise. In order to solve the above-mentioned problems, the present inventors have increased the sensitivity compared to the prior art and are less susceptible to external noise! (For example, refer to Patent Document 1.) o The piezoelectric resonance type ultrasonic sensor element according to the conventional example is characterized in that it is configured as follows. In a piezoelectric ultrasonic sensor element comprising a ferroelectric substance sandwiched between at least a pair of electrodes and having a predetermined resonance frequency and detecting an ultrasonic wave, it is provided on one side of the ferroelectric substance. The common electrode provided, the inner electrode provided on the other side of the ferroelectric and substantially at the center of the ferroelectric, and the other side of the ferroelectric provided outside the inner electrode. And an outer electrode. Here, output between the inner electrode and outer electrode when detecting ultrasound Detect voltage. Further, when detecting ultrasonic waves, the outer electrode is provided at a position where the sign of the output voltage at the inner electrode relative to the common electrode and the sign of the output voltage at the outer electrode relative to the common electrode are different from each other.

[0005] Patent Document 1: Japanese Patent Laid-Open No. 2005-039720.

Non-Patent Literature 1: T. Faoula et al., Analytical and unite element modeling of resonant s ilicon microsensors ", Sensors and Materials, Vol. 9, No. 8, pp. 501-519, 1997.

Patent Document 2: K. Yamashita et al., "Arrayed ultrasonic microsensors with high direc tivity for in-air use using PZT thin film on silicon diaphragms, Sensors and Actuator s A, Vol.97-98., Pp.302- 307 , 2002.

Non-Patent Document 3: K. Yamashita et al., "Ultrasonic Array Sensor Using Piezoelectric Film on Silicon Diaphragm and Its Resonant-Frequency Tuning, Transducer '03, Vol.1, No.5, pp.939—942, 2003.

Patent Document 4: J. T. Bernstein et al., “Micromachined High Frequency Ferroelectric Sonar Transducers, IEEE Transactions on Ultrasonic Ferroelectric Frequency Count, Vol.44, pp.960—969, 1996.

Disclosure of the invention

Problems to be solved by the invention

[0006] When the vibration type sensor element is used for an ultrasonic sensor element or the like, the resonance characteristic becomes a problem. The higher the mechanical quality factor (Q value) of resonance, the larger the output can be obtained with less input energy, and the higher the relative sensitivity can be configured, but when performing distance measurement with an ultrasonic sensor element, etc. If the Q value is high, the damping of the vibration is slow and a long tail is drawn, resulting in a decrease in distance resolution. In the conventional example, the Q value was lowered to obtain the required distance resolution, and the element device was configured with low sensitivity and low sensitivity.

An object of the present invention is to provide a vibration control device and a vibration control method for a piezoelectric resonance sensor element that can solve the above problems and can effectively attenuate vibration without lowering the Q value. It is in.

Means for solving the problem

[0008] A vibration control device for a piezoelectric resonance sensor element according to a first aspect of the present invention includes at least one piezoelectric body. In a vibration control device for a piezoelectric resonance type sensor element that is sandwiched between a pair of electrodes, detects a vibration wave with a predetermined resonance frequency, and outputs a detection signal.

The piezoelectric resonance sensor element is separate from the pair of electrodes that output the detection signal.

, Further comprising a vibration control electrode formed in the vicinity of the electrode,

Amplifying means for amplifying the detection signal with a predetermined gain and applying a vibration control signal having a reverse phase to the vibration control electrode so as to attenuate the vibration of the detection signal when a vibration wave is detected. It is provided with.

[0009] The vibration control device for the piezoelectric resonance type sensor element further includes control means for setting a gain of the amplification means. The pair of electrodes are preferably formed at the center of the piezoelectric body and have a circular shape, a substantially circular shape, a substantially elliptical shape, or a substantially square shape.

[0010] The vibration control device for a piezoelectric resonance sensor element according to the second invention comprises a piezoelectric body sandwiched between at least one pair of electrodes, and detects and detects a vibration wave having a predetermined resonance frequency. In a vibration control device for a piezoelectric resonance sensor element that outputs a signal,

In response to the detection signal, the rising force of the detection signal is delayed by a predetermined time, and then a predetermined vibration control signal is applied to the vibration control electrode to detect the detection signal when the vibration wave is detected. It is characterized by comprising control means for controlling the vibration to be damped.

[0011] In the vibration control device of the piezoelectric resonance type sensor element, the control means is configured such that when the level of the detection signal exceeds a predetermined threshold, the vibration wave has a substantially half-cycle number. A predetermined vibration control pulse signal is applied to the vibration control electrode after being delayed by a period. The pair of electrodes are preferably formed at the center of the piezoelectric body and have a circular shape, a substantially circular shape, a substantially elliptical shape, or a substantially square shape.

[0012] A vibration control method for a piezoelectric resonance type sensor element according to a third aspect of the present invention includes a piezoelectric body sandwiched between at least a pair of electrodes, and detects and detects a vibration wave having a predetermined resonance frequency. In the vibration control method of the piezoelectric resonance type sensor element that outputs a signal! The piezoelectric resonance sensor element is separate from the pair of electrodes that output the detection signal.

A step of amplifying the detection signal with a predetermined gain and applying a vibration control signal having a reverse phase to the vibration control electrode, so as to attenuate the vibration of the detection signal when a vibration wave is detected; It is characterized by including.

[0013] The vibration control method for the piezoelectric resonance sensor element further includes a step of setting the gain. The pair of electrodes are preferably formed at the center of the piezoelectric body and have a circular shape, a substantially circular shape, a substantially elliptical shape, or a substantially square shape.

[0014] A vibration control method for a piezoelectric resonance sensor element according to a fourth aspect of the present invention includes a piezoelectric body sandwiched between at least a pair of electrodes, and detects and detects a vibration wave having a predetermined resonance frequency. In the vibration control method of the piezoelectric resonance type sensor element that outputs a signal!

The piezoelectric resonant sensor element further includes a vibration control electrode formed in the vicinity of the electrode, in addition to the pair of electrodes that output the detection signal.

In response to the detection signal, the rising force of the detection signal is delayed by a predetermined time, and then a predetermined vibration control signal is applied to the vibration control electrode to detect the detection signal when the vibration wave is detected. It includes a control step for controlling the vibration to be damped.

[0015] In the vibration control method of the piezoelectric resonance type sensor element, the control step includes substantially a half cycle or a few cycles of the vibration wave when the level of the detection signal exceeds a predetermined threshold value. After the delay, a predetermined vibration control pulse signal is applied to the vibration control electrode. The pair of electrodes are preferably formed at the center of the piezoelectric body and have a circular shape, a substantially circular shape, a substantially elliptical shape, or a substantially square shape. The invention's effect

Therefore, according to the vibration control device and the vibration control method of the piezoelectric resonance sensor element according to the first and third inventions, the detection signal is amplified with a predetermined gain, and the vibration control signal having the reverse phase is obtained. By applying to the vibration control electrode, the vibration of the detection signal when the vibration wave is detected is controlled to be attenuated. It can be carried out. Therefore, the piezoelectric resonance sensor element can be configured as a device having high sensitivity and good vibration damping characteristics. In the prior art, sensitivity has been sacrificed with priority given to distance resolution in ultrasonic distance measurement, but the present invention achieves both high sensitivity and high distance resolution. In addition, in a phased array that performs angle measurement using a phase difference using a plurality of piezoelectric resonance sensor elements, the resonance frequency is required to be exactly the same for a sensor that vibrates for a long time. Limiting the resonance frequency in a short time with the use of a, reduces the restriction on the resonance frequency, simplifies the manufacturing process, eliminates the need for frequency adjustment after trimming, reduces the product defect rate, etc. Can be lowered.

[0017] Further, according to the vibration control device and the vibration control method of the piezoelectric resonance type sensor element according to the second and fourth inventions, in response to the detection signal, a predetermined time from the rising edge of the detection signal. After a certain delay, a predetermined vibration control signal is applied to the vibration control electrode to control the vibration of the detection signal when a vibration wave is detected. Attenuation can be performed effectively. Therefore, the piezoelectric resonant sensor element can be configured as a device with high sensitivity and vibration damping characteristics. In the conventional technology, sensitivity has been sacrificed with priority on distance resolution in ultrasonic distance measurement. However, high sensitivity and high distance resolution are compatible with the present invention. In addition, for a phased array that performs angle measurement using a phase difference using a plurality of piezoelectric resonance type sensor elements, a sensor that continuously vibrates for a long time requires that the resonance frequency be exactly the same. However, by suppressing vibrations in a short time using the present invention, the restriction on the resonance frequency is relaxed, and as a result of simplification of the manufacturing process, trimming after manufacturing `` no need for frequency adjustment, reduction in product defect rate, etc. The manufacturing cost can be reduced.

Brief Description of Drawings

FIG. 1 is a block diagram showing a configuration of a vibration control device of a piezoelectric resonance type ultrasonic sensor element 20 according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a vibration control device of a piezoelectric resonance type ultrasonic sensor element 20 according to a second embodiment of the present invention.

3 is a longitudinal sectional view showing the structure of the piezoelectric resonance type ultrasonic sensor element 20 of FIGS. 1 and 2. FIG. 4] A plan view showing the structure of the piezoelectric resonance type ultrasonic sensor element 20 of FIGS. 1 and 2. FIG. [5] In the piezoelectric resonance type ultrasonic sensor element 20 shown in FIGS. 1 and 2, the signal waveform (a) of the input ultrasonic signal when vibration control is not performed, the amount of diaphragm sag (b), and the sensor output signal ( FIG.

6) In the piezoelectric resonance type ultrasonic sensor element 20 of FIGS. 1 and 2, the signal waveform (a) of the input ultrasonic signal when the vibration control is performed by the vibration control device of FIG. 1 and the amount of sag of the diaphragm ( It is a signal waveform diagram which shows b) and a sensor output signal (c).

圆 7] In the piezoelectric resonance type ultrasonic sensor element 20 of FIGS. 1 and 2, the signal waveform (a) of the input ultrasonic signal when the vibration control is performed by the vibration control device of FIG. 2 and the amount of sag of the diaphragm ( It is a signal waveform diagram which shows b) and a sensor output signal (c).

8] A diagram for explaining the optimal arrangement of the electrodes of the piezoelectric resonance type ultrasonic sensor element 20 according to the present embodiment, which is a three-dimensional diagram showing the vibration amplitude and in-plane strain distribution of the diaphragm.

FIG. 9 is a diagram showing a scale that is the degree of in-plane distortion at the gray scale used in the graphs showing the distribution of in-plane distortion in FIGS. 8 and 10 to 14.

FIG. 10 is a plan view for explaining the arrangement of detection electrodes and vibration control electrodes in the piezoelectric resonance type ultrasonic sensor element 20 according to the present embodiment.

FIG. 11 is a plan view showing the shape of a substantially circular detection electrode showing the optimum arrangement and in-plane strain distribution when the parasitic capacitance is relatively small in FIG.

[12] FIG. 12 is a plan view showing the shape of a circular detection electrode showing an appropriate arrangement according to the optimum arrangement and an in-plane strain distribution when the parasitic capacitance is relatively small in FIG.

FIG. 13 is a plan view showing the shape of a substantially rectangular detection electrode showing the optimum arrangement and in-plane strain distribution when the parasitic capacitance is relatively large in FIG.

[14] FIG. 14 is a plan view showing the shape of a substantially rectangular detection electrode showing an appropriate arrangement according to the optimum arrangement and an in-plane strain distribution in FIG. 10 when the parasitic capacitance is relatively large.

FIG. 15 is a diagram for explaining the difference between the piezoelectric resonance type ultrasonic sensor element 20 according to the present embodiment and the piezoelectric resonance type ultrasonic sensor element disclosed in Patent Document 1; 3 is a schematic plan view of a resonant ultrasonic sensor element 20. FIG.

FIG. 16 is a longitudinal sectional view taken along line AA ′ of FIG.

FIG. 17 is a diagram for explaining the difference between the piezoelectric resonance type ultrasonic sensor element 20 according to the present embodiment and the piezoelectric resonance type ultrasonic sensor element disclosed in Patent Document 1; 6 is a schematic plan view of a modification of the ultrasonic sensor element 20 of a type. FIG.

FIG. 18 is a longitudinal sectional view taken along line BB in FIG.

Explanation of symbols

lO -... Semiconductor wafer chip,

l l-semiconductor substrate,

12, 13, 15 ... Insulating film layer,

14 · Semiconductor active layer,

16 ··· Common electrode,

16a, 16b ... counter electrode,

17 ••• PZT ceramic thin film layer,

18 ··· Inner electrode,

19 "" outer electrode,

21, 22, 25, 25a, 25b ... connecting conductor,

30 ... gain controller,

31 · Variable gain amplifier,

35 · "Comparator,

36 ... variable DC voltage source,

40 · “one-shot oscillator,

41 ··· Delay circuit,

42 ... Variable DC voltage source,

43 · “Switch,

T1, Tla, T2, T2a, T3, Ti ... terminals.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments according to the present invention will be described with reference to the drawings. Each of the following In the embodiment, the same constituent elements are denoted by the same reference numerals.

[0021] First Embodiment.

FIG. 1 is a block diagram showing the configuration of the vibration control device of the piezoelectric resonant ultrasonic sensor element 20 according to the first embodiment of the present invention, and FIG. 3 shows the piezoelectric resonant ultrasonic wave of FIGS. FIG. 4 is a longitudinal sectional view showing the structure of the sensor element 20, and FIG. 4 is a plan view showing the structure of the piezoelectric resonance type ultrasonic sensor element 20 shown in FIGS.

[0022] In the piezoelectric resonance ultrasonic sensor element 20 according to the first embodiment, apart from the two pairs of inner electrode 18 and common electrode 16 that output detection signals from the ultrasonic sensor element 20, the inner The vibration control outer electrode 19 (here, one pair of the outer electrode 19 and the common electrode 16 on the ground side) formed near the periphery of the electrode 8 is further provided and detected by the pair of electrodes 16 and 18. The detection signal output via the terminal T1 is amplified by the variable gain amplifier 31 with a predetermined gain that is controlled and set by the gain controller 30, and the vibration control signal of the reverse phase is amplified via the terminal T2. Then, by applying to the vibration control outer electrode 19, control is performed so as to attenuate the vibration of the detection signal when the ultrasonic wave as the vibration wave is detected.

As shown in FIG. 2, the piezoelectric resonant ultrasonic sensor element 20 according to this embodiment includes a PZT ceramic thin film layer 17 that is a ferroelectric, a pair of inner electrodes 18 and a common electrode 16, 1 It is sandwiched between a pair of outer electrodes 19 and a common electrode 16, and is composed of a piezoelectric resonance type sensor element that has a predetermined resonance frequency and detects ultrasonic waves. In addition, as shown in FIG. 4, a rectangular inner electrode 18 having a length L is formed at a substantially central portion of the upper surface of the PZ T ceramic thin film layer 17.

a

An outer electrode 19 having a width L and having a substantially rectangular shape as a whole is formed on the outer periphery so as to be spaced apart from the inner electrode 18 and surround the inner electrode 18. Inner electrode 18 is

b

The connection electrode 21 is connected to the terminal T1, and the outer electrode 19 is connected to the terminal T2 via the connection conductor 22.

Here, the inner electrode 18 and the outer electrode 19 are, for example, the sign of the output voltage at the inner electrode 18 with respect to the common electrode 16 and the output at the outer electrode 19 with respect to the common electrode 16 when ultrasonic waves are detected. The outer electrode 19 is formed at a position where the signs of the voltages are the same (in this case, the vibration control signal is set in phase with the detection signal in such a case that the positions may be different from each other). . More preferably, when the ultrasonic wave is detected, the common electrode 16 The output voltage at the inner electrode 18 with respect to the first electrode has a first sign (for example, plus) and its absolute value is substantially the maximum, and the output voltage at the outer electrode 19 with respect to the common electrode 16 is different from the first sign. The outer electrode 19 is formed at a position where the absolute value of the sign (eg, minus) is substantially the maximum value. Details of these codes and the design method of the formation position of the outer electrode 19 are disclosed in Patent Document 1.

[0025] First, the structure and manufacturing method of the ultrasonic sensor element 20 used in the present embodiment will be described below. As the thin plate structure of the sound sensing part of the ultrasonic sensor element 20, a force that is commonly used is a diaphragm (four sides fixed), a bridge (two sides fixed) or a cantilever (one side fixed). In this embodiment, a square diaphragm is used. Use 100. In addition, a sol-gel film forming method by spin coating is used as the piezoelectric layer. This sol-gel film-forming method is a film-forming process in which a precursor solution obtained by adjusting the viscosity of a composite metal alkoxide solution by hydrolysis, polycondensation, etc. is formed by spin coating (gel film) and crystallized by heat treatment. It is. The piezoelectric layer is formed after the anisotropic etching is completed. The composition of the PZT sol-gel precursor solution used in the sol-gel film formation method is shown below.

[0026] [Table 1]

Composition of PZT sol-gel precursor solution Solvent 2-methoxyethanol

Pb component Lead acetate trihydrate

Zr component Zr normal butoxide

Ti component Ti isopropoxide

PZT composition Pb: Zr: Ti = 115: 52: 48

Concentration 15% wt as Pb Zr Ti O

(A) A semiconductor wafer chip having a commercially available SOI (Silicon On Insulator) structure as a starting substrate 10 (active layer 2 m, oxide layer 1 μm) is used. One 4-inch substrate is diced into two. Four chips are arranged per wafer.

(B) Both surfaces of the wafer are thermally oxidized for insulation between the mask for anisotropic etching and the common electrode 16 as the lower electrode. At the furnace temperature of 1,140 ° C, first 5.0 L of O

Dry acid for 5 minutes with 2 Z only, then O (5.0 liters)

2 Z min) + H (4.5 liters

18 at 2 Z min)

Wet oxidation for 0 minutes. The oxide insulation layer 17 has a thickness of about 1 μm and is anisotropically etched with EPW (Ethylenediamine Pyrocatechol Water) and TMAH (Tetramethy lammonium Hydroxide). Thick enough to withstand.

[C] (c) BHF (Buffered Hydro-Fluoric acid; buffered hydrofluoric acid (weakly acidic liquid), that is, hydrofluoric acid and ammonium fluoride. Etched with a mixed solution, mainly used to etch silicon oxide.

[0030] (d) The silicon of the support layer is anisotropically etched by EPW. Etching is performed for about 5 to 6 hours while maintaining the temperature at about 115 ° C., and the thickness of the support layer is set to 50 to 100 / ζ πι. This thickness is sufficient to withstand ultrasonic cleaning in the subsequent step (g).

(E) PtZTi is deposited as a common electrode 16 as a lower electrode by an RF sputtering apparatus. In an Ar gas flow rate of 44 sccm and lPa atmosphere, first, Ti is sputtered at 500 W for 1 minute, and then Pt is sputtered at 200 W for 10 minutes to obtain film thicknesses of 0.02 m and 0.2 m, respectively. Although it cannot be heated at the time of film formation because it is patterned by lift-off using a photoresist, when the produced film is evaluated by an XRD (X-Ray Diflfractometer), Pt (111) single orientation Thus, it was confirmed that a sufficiently high-quality thin film was formed as the common electrode 16 of the PZT ceramic thin film. The lift-off pattern is patterned using a double-sided mask aligner so that the electrode pattern exactly overlaps the diaphragm shape formed by the etching hole on the back.

[0032] (f) PZT ceramic thin film layer 17 is formed as a piezoelectric layer by a sol-gel film forming method. After forming the piezoelectric layer, PZT is used as the contact hole for the lower electrode. HF: HNO: H 0 = 1: 1

3 2

: Etching in 1). When it takes to etch 1 μm thick PZT ceramics The interval is 10 to 30 seconds, and the amount of side etching at this time is 5 to 10 μm.

(G) Pt is formed as an upper electrode and an inner electrode 18 and an outer electrode 19 by an RF sputtering apparatus and is patterned by lift-off. The film forming conditions are the same as in step (e), and the film thickness is 0.2 μm.

[0034] (h) A square diaphragm structure is formed by anisotropic etching. Although the etching rate varies slightly, the etching almost stops at the I layer of the SOI structure, so the square diaphragm structure was completed by performing etching in accordance with the etch hole with the slowest etching rate. In addition, it is confirmed that the PZT ceramic thin film layer 17 obtained by the sol-gel film forming method has almost no deterioration in electrical characteristics when boiling in EPW for about 90 minutes, so there is no need to protect the surface during etching. ,.

[0035] (i) The I layer of the SOI structure is indispensable as the above-mentioned anisotropic etching stop layer, but the final structure may cause internal stress, so it is removed after the anisotropic etching is completed. There is a need. Since it is a normal thermal oxide film, it is removed by etching with BHF. After the sensor is manufactured by the above process, the wafer is diced to separate the chip, fixed to the socket, and each electrode is bonded to complete the sensor chip.

[0036] After the ultrasonic sensor element 20 is manufactured by the above process, the wafer 10 is diced, the chip is separated, fixed to the socket, and connected to the connection conductors 31 and 32 connected to the electrodes 18 and 19, respectively. Connect each lead wire to the terminals Tl and T2 (see Fig. 1 and Fig. 4) after bonding each lead wire by bonding, and complete the sensor chip by bonding.

[0037] In the vibration control device for the piezoelectric resonant ultrasonic sensor element 20 according to the first embodiment, the detection electrode 18 is provided at the center of the diaphragm, and mechanical vibration is detected using the piezoelectric effect. However, in this embodiment, the vibration control electrode 19 is also provided in the vicinity of the periphery of the detection electrode 18. This is used to suppress the persistence of vibration associated with resonance. That is, as shown in FIG. 1, the sensor output signal from the detection electrode 18 is amplified by the variable gain amplifier 31, and an anti-phase vibration control signal (feedback signal) is generated and applied to the vibration control electrode 19. In this way, vibration is canceled out by the inverse piezoelectric effect. The vibration control signal is also output as a detection signal to an external circuit via the terminal T11. As a result, the diaphragm itself does not vibrate. The force applied to the moving body can be extracted as the magnitude of the vibration control signal. As a result, the vibrating body vibrates slightly with the vibration suppressed, and then is forcibly suppressed by the inverse piezoelectric effect.

[0038] FIG. 5 shows the signal waveform (a) of the input ultrasonic signal when the vibration control device of FIG. 1 does not perform vibration control in the piezoelectric resonant ultrasonic sensor element 20 of FIG. It is a signal waveform diagram which shows (b) and a sensor output signal (c). FIG. 6 shows the signal waveform (a) of the input ultrasonic signal when the vibration is controlled by the vibration control device of FIG. 1 in the piezoelectric resonance type ultrasonic sensor element 20 of FIG. 1 and FIG. FIG. 6 is a signal waveform diagram showing a sampling amount (b) and a sensor output signal (c). As is clear from the comparison between FIG. 5 and FIG. 6, by generating a vibration control signal having an antiphase and applying the vibration control signal to the vibration control electrode 19, the vibration is canceled by the reverse piezoelectric effect. The force applied to the vibrating body that does not vibrate can be extracted as the magnitude of the vibration control signal. This allows the vibrating body to vibrate slightly by virtue of the inverse piezoelectric effect after being vibrated slightly. Is done.

Therefore, in the present embodiment, the piezoelectric resonance ultrasonic sensor element 20 can rapidly attenuate a sustained vibration while maintaining a high Q value, and has a high sensitivity and a high level. It is possible to achieve both distance resolution. For this purpose, the vibration control system is configured with a very simple structure by utilizing the fact that a piezoelectric body can be used as both a sensor (conversion of mechanical quantity → electrical quantity) and a drive source (conversion of electrical quantity → mechanical quantity). can do.

[0040] As described above, according to the present embodiment, it is possible to effectively attenuate vibration without lowering the Q value. Therefore, the piezoelectric resonant sensor element can be configured as a device with high sensitivity and good vibration damping characteristics. In the prior art, sensitivity has been sacrificed in order to prioritize the distance resolution in ultrasonic distance measurement, but this embodiment achieves both high sensitivity and high distance resolution. In addition, in a phased array that performs angle measurement using a phase difference using a plurality of piezoelectric resonance sensor elements, the resonance frequency is required to be exactly the same for a sensor that vibrates for a long time. By restricting vibration in a short time using the embodiment, the restriction on the resonance frequency is relaxed, and manufacturing is simplified as a result of simplification of the manufacturing process, trimming after manufacturing 'no need for frequency adjustment, lower product defect rate, etc. Cost can be reduced. [0041] As a specific example of this embodiment, it can be used in an ultrasonic distance measurement system including angle scanning, proximity alarms in robot control, security systems, etc., obstacle detection to three-dimensional measurement, three-dimensional shape measurement, surroundings It can also be used for space recognition.

[0042] Second embodiment.

FIG. 2 is a block diagram showing the configuration of the vibration control device of the piezoelectric resonance type ultrasonic sensor element 20 according to the second embodiment of the present invention. The vibration control device of the piezoelectric resonance type ultrasonic sensor element 20 according to the second embodiment is a one-shot instead of the gain controller 30 and the variable gain amplifier 31 compared to the vibration control device of FIG. It is characterized by comprising an oscillator 40, a comparator 35, and a variable DC voltage source 36. Hereinafter, differences from the first embodiment will be described in detail.

In FIG. 2, a predetermined DC voltage that is detected and detected by the variable DC voltage source 36 is applied to the inverting input terminal of the comparator 35. A detection signal from the electrode 18 of the ultrasonic sensor element 20 is input to the non-inverting input terminal of the comparator 35 via the terminal T1. The comparator 35 compares the input detection signal with the above threshold value, and when the level of the detection signal is equal to or greater than the threshold value S, that is, when the detection signal is greater than the predetermined threshold value. At this time, a pulse signal having a predetermined time width is generated and input to the control terminal of the switch 43 via the delay circuit 41. Here, the delay time td (see FIG. 7) of the delay circuit 41 is, for example, a half cycle to several cycles (preferably a half cycle (in the case of FIG. 7) of an ultrasonic wave that is a vibration wave to be detected. It may be 3 cycles.). When a pulse signal is input to the control terminal of switch 43, switch 43 is turned on, and the vibration control pulse signal having a predetermined DC voltage from the variable DC voltage source 42 is output as a sensor output signal via the terminal T11. And applied to the vibration control external electrode 19 via the terminal T2. Thereby, the vibration is canceled by the inverse piezoelectric effect. The vibration control signal is also output as a detection signal to the external circuit via terminal T11. As a result, the force applied to the vibrating body that the diaphragm itself does not vibrate can be extracted as the magnitude of the vibration control signal. As a result, the vibration body is vigorously suppressed by the inverse piezoelectric effect after greatly vibrating for half a cycle.

FIG. 7 shows the vibration control of FIG. 1 in the piezoelectric resonance type ultrasonic sensor element 20 of FIG. 1 and FIG. FIG. 5 is a signal waveform diagram showing a signal waveform (a) of an input ultrasonic signal, vibration amount (b) of a diaphragm, and sensor output signal (c) when vibration control is performed by the apparatus. As can be seen from the comparative force in FIGS. 5 and 7, the vibration control pulse signal is generated and applied to the vibration control electrode 19, thereby canceling the vibration by the reverse piezoelectric effect, and the diaphragm itself. The force applied to the vibrating body that vibrates can be extracted as the magnitude of the vibration control signal, and this causes the vibrating body to vibrate largely by half a cycle and then forcibly suppress the vibration by the inverse piezoelectric effect. The

[0045] The vibration control device according to the second embodiment configured as described above has the same functions and effects as those of the first embodiment.

[0046] Explanation of optimal arrangement of electrodes.

Hereinafter, the optimum shape of the electrodes of the piezoelectric resonance type ultrasonic sensor element 20 according to the present embodiment and the arrangement method thereof will be described with reference to FIGS.

FIG. 8 is a diagram for explaining the optimal arrangement of the electrodes of the piezoelectric resonant ultrasonic sensor element 20 according to the present embodiment, and is a three-dimensional graph showing the vibration amplitude and in-plane strain distribution of the diaphragm. FIG. 9 is a diagram showing a scale which is the degree of in-plane distortion in the gray scale used in the graphs showing the distribution of in-plane distortion in FIGS. 8 and 10 to 14. In Fig. 8, the diagonal left direction is the X direction position, the diagonal right direction is the Y direction position, and the height direction indicates the vibration amplitude. Here, the in-plane distortion is shown using the scale in FIG. FIG. 10 is a plan view for explaining the arrangement of the detection electrodes and the vibration control electrodes in the piezoelectric resonant ultrasonic sensor element 20 according to the present embodiment. Furthermore, FIG. 11 is a plan view showing the shape of a substantially circular detection electrode showing the optimal arrangement and in-plane strain distribution when the parasitic capacitance is relatively small in FIG. 10, and FIG. 12 is a comparison of the parasitic capacitance in FIG. FIG. 6 is a plan view showing the shape of a circular detection electrode showing an appropriate arrangement according to the optimum arrangement and an in-plane strain distribution when the size is small. 13 is a plan view showing the shape of a substantially rectangular detection electrode close to an ellipse indicating the optimal arrangement and in-plane strain distribution when the parasitic capacitance is relatively large in FIG. 10, and FIG. 14 is a parasitic capacitance in FIG. FIG. 6 is a plan view showing a shape of a substantially rectangular detection electrode showing an appropriate arrangement according to the optimum arrangement and an in-plane strain distribution when the is relatively large.

FIG. 8 shows the vibration amplitude and in-plane strain distribution of the vibrating diaphragm. In-plane distortion Are different signs at the center and the periphery of the diaphragm. Since the piezoelectrically generated polarization is proportional to the in-plane strain, it is preferable to install the sensor electrode (detection electrode) so as to correspond to the polarization distribution (strain distribution) and to design the highest output voltage. The output voltage V is

Since the amount of electric charge generated piezoelectrically is divided by the capacitance, ideally, it is desirable to install an electrode with a zero area at the point where the polarization is the largest. However, since the actual sensor has a parasitic capacitance Cp, it requires a certain amount of electrode area. Here, the output voltage V is expressed by the following equation.

[0049] [Equation 1] l APdA

v =

C + C _p

[0050] where

[Equation 2]

Λ

C = s- d

It is.

[0051] The parasitic capacitance Cp is a constant.

[0052] where Δ Ρ is piezoelectrically generated polarization, A is the area of the detection electrode, C is the capacitance of the capacitor by the detection electrode, ε is the dielectric constant of the piezoelectric body, d is the thickness of the piezoelectric body. The parasitic capacitance Cp does not depend on the area of the detection electrode.

As can be seen from the above equation, the area A of the detection electrode needs to be increased as the parasitic capacitance Cp increases. The vibration control electrode needs to have as large an area as possible because it is necessary to efficiently suppress vibration by the inverse piezoelectric effect. Therefore, it is necessary to install it outside the detection electrode whose area and shape are determined by the parasitic capacitance Cp, etc., in a region extending over the entire remaining part of the diaphragm, for example, as shown in FIG.

Next, FIGS. 11 to 14 show examples of actual electrode arrangement. Here, the force shows only the shape of the inner detection electrode. In the actual structure, as shown in Fig. 10, it is necessary to install the vibration control electrode outside the detection electrode. Figure 11 shows an example where the parasitic capacitance Cp is small. The electrodes are placed in a region concentrated near the comparative center. Its shape is the distribution of strain (polarization) It becomes a substantially circular shape that is a shape close to a circle matched to the shape. Fig. 12 shows an example in which geometrical perfect circle electrodes are installed in the same area as a similar shape. Fig. 13 shows an example where the parasitic capacitance Cp is larger, and it has a square shape (approximately rectangular or approximately elliptical shape close to an ellipse) with rounded corners and sides along the strain (polarization) distribution. Fig. 14 shows an example in which square (round or square) electrodes with rounded corners are installed.

[0055] As described above, the electrode 18 and the electrodes 16, 16a opposed to the electrode 18 are preferably formed at the center of the piezoelectric PZT ceramic thin film layer 17, and are circular, substantially circular, or substantially elliptical. It has a shape or a substantially square shape.

[0056] Differences between this embodiment and Patent Document 1!

Further, differences between the piezoelectric resonance type ultrasonic sensor element 20 according to the present embodiment and the piezoelectric resonance type ultrasonic sensor element disclosed in Patent Document 1 will be described below with reference to FIGS. 15 to 18. .

FIG. 15 illustrates a difference between the piezoelectric resonance type ultrasonic sensor element 20 according to the present embodiment and the piezoelectric resonance type ultrasonic sensor element disclosed in Patent Document 1 (hereinafter referred to as a comparative example). FIG. 16 is a schematic plan view of the piezoelectric resonant ultrasonic sensor element 20, and FIG. 16 is a longitudinal sectional view taken along the line AA ′ of FIG. FIG. 17 is a diagram for explaining the difference between the piezoelectric resonance type ultrasonic sensor element 20 according to the present embodiment and the piezoelectric resonance type ultrasonic sensor element disclosed in Patent Document 1. FIG. 18 is a schematic plan view of a modification of the piezoelectric resonance type ultrasonic sensor element 20, and FIG. 18 is a longitudinal sectional view taken along line BB ′ of FIG. In FIGS. 15 and 17, the electrodes 16, 16a, and 16b are shown as solid lines for the sake of simplification of the illustration of the forces that should be shown as dotted lines because of the V that is hidden and visible. Further, in FIGS. 16 and 18 which are schematic diagrams, the members 11 to 15 are not individually illustrated.

That is, FIG. 15 to FIG. 18 are schematic diagrams of the electrode structure of the sensor element, and the structure of the embodiment that the present inventor has prototyped is the structure of FIG. 15 to FIG. In order to explain this clearly, Figures 17 to 18 are easier to understand. The terminal T3 in FIGS. 15 and 16 corresponds to a short circuit between the terminal Tla and the terminal T2a in FIGS.

[0059] In Fig. 15 and Fig. 16 showing the sensor element according to the embodiment, the inner electrode 18 is connected. The conductor 21 is connected to the electrode Tl, and the outer electrode 19 is connected to the electrode T2 via the connecting conductor 22. The common electrode 16 facing the electrodes 18 and 19 is connected to the terminal T3 via the connection conductor 25. On the other hand, in FIG. 17 and FIG. 18 showing the sensor element according to the modified example, the common electrode 16 of the embodiment is divided into an electrode 16a facing the electrode 18 and an electrode 16b corresponding to the electrode 19. Here, the inner electrode 18 is connected to the electrode T1 via the connection conductor 21, and the outer electrode 19 is connected to the electrode T2 via the connection conductor 22. The counter electrode 16a facing the electrode 18 is connected to the terminal Tla via the connection conductor 25a, and the counter electrode 16b facing the electrode 19 is connected to the terminal T2a via the connection conductor 25b.

That is, FIG. 15 to FIG. 18 schematically show the electrode structure of the sensor diaphragm portion in the sensor element according to the embodiment and the comparative example. Hereinafter, the sensor element according to the embodiment will be referred to as a “vibration control type sensor element”, and the sensor element according to the comparative example will be referred to as a “polarization complementary sensor element” because of the difference in purpose.

In the polarization complementary sensor element according to the comparative example, the potential difference between the terminal T1 and the terminal T2 is detected as an output signal. Each electrode 18, 19 is used to detect the voltage generated by the piezoelectric effect. The electrode sizes La and Lb are determined so as to maximize the output voltage V in the following equation, taking into account the corresponding parasitic capacitances Cpa and Cpb.

[0062] [Equation 3]

Figure 15-16

-V _T2a ) Figure 17-18

[0063] where V is the detection voltage at terminal T1, V is the detection voltage at terminal T2, and V is

Tl T2 Tla This is the detection voltage at terminal Tla, and V is the detection voltage at terminal Tib. Figure 15 and Figure 16

Tib

The terminal T3 and the terminals Tla and Tib in Figs. 17 and 18 do not need to be pulled out of the diaphragm when the sensor element is actually used in the polarization complementary operation.

In contrast, in the vibration control type sensor element according to the present embodiment, a voltage generated by the piezoelectric effect is detected between the terminal T1 and the terminal Tla (in FIGS. 17 to 18). A vibration control voltage for control is applied between terminal T2 and terminal T2a (in the case of Fig. 17 to Fig. 18) and is used to control vibration by the inverse piezoelectric effect. Here, the terminal Tla and the terminal Tib are The same applies to the terminal T3 shown in FIGS. 15 and 16 by connecting these terminals Tla and Tib. The electrode size of the electrode 18 connected to the terminal T1 is maximized by setting the optimum size in consideration of the parasitic capacitance Cp based on the same principle as described in `` Dipolar complementary sensor element ''. . On the other hand, the shape of the electrode 19 connected to the terminal T2 maximizes the vibration control effect due to the inverse piezoelectric effect, so that the maximum area that can be taken on the diaphragm (that is, the remaining total area not occupied by the electrode 18) is reduced. It needs to be shaped.

[0065] Modification.

In the above embodiment, the force explaining the ultrasonic sensor element 20 as an example of the piezoelectric resonant sensor element. The present invention is not limited to this, and the acoustic sensor element, the mechanical vibration using the piezoelectric resonant sensor element. It may be a detection sensor element or the like.

In the above embodiment, the piezoelectric material used in the piezoelectric resonance type ultrasonic sensor element is, for example, a ferroelectric material that is the PZT ceramic thin film layer 17. However, the present invention is not limited to this, for example, ZnO And it is not a ferroelectric material such as A1N!

Industrial applicability

As described in detail above, according to the vibration control device and the vibration control method of the piezoelectric resonance type sensor element according to the first and third inventions, the detection signal is amplified by a predetermined gain to have a reverse phase. By applying the vibration control signal to the vibration control electrode, the vibration of the detection signal when the vibration wave is detected is controlled to be attenuated, effectively reducing the vibration attenuation without lowering the Q value. It can be carried out. Therefore, the piezoelectric resonance sensor element can be configured as a device with high sensitivity and good vibration damping characteristics. In the prior art, sensitivity has been sacrificed in order to prioritize distance resolution in ultrasonic distance measurement, but the present invention achieves both high sensitivity and high distance resolution. In addition, in a phased array that performs angle measurement using a phase difference using a plurality of piezoelectric resonance sensor elements, the resonance frequency is required to be exactly the same for a sensor that vibrates for a long time. Reducing the vibration frequency in a short time using the invention alleviates the restriction on the resonance frequency, simplifying the manufacturing process, trimming after manufacturing 'no need for frequency adjustment, lower product defect rate, etc. Can be lowered. In addition, according to the vibration control device and the vibration control method for the piezoelectric resonance sensor element according to the second and fourth inventions, in response to the detection signal, the detection signal is delayed for a predetermined time from the rising edge of the detection signal. After that, by applying a predetermined vibration control signal to the vibration control electrode, control is performed to attenuate the vibration of the detection signal when the vibration wave is detected, so it is effective to attenuate the vibration without lowering the Q value. Can be done automatically. Therefore, the piezoelectric resonant sensor element can be configured as a device with high sensitivity and vibration damping characteristics. In the conventional technology, sensitivity has been sacrificed with priority on distance resolution in ultrasonic distance measurement. However, high sensitivity and high distance resolution are compatible with the present invention. In addition, for a phased array that performs angle measurement using a phase difference using a plurality of piezoelectric resonance type sensor elements, a sensor that continuously vibrates for a long time requires that the resonance frequency be exactly the same. However, by suppressing vibrations in a short time using the present invention, the restriction on the resonance frequency is relaxed, and as a result of simplification of the manufacturing process, trimming after manufacturing `` no need for frequency adjustment, reduction in product defect rate, etc. The manufacturing cost can be reduced.

Claims

The scope of the claims

[1] In the vibration control device for a piezoelectric resonance type sensor element comprising a piezoelectric body sandwiched between at least one pair of electrodes, detecting a vibration wave having a predetermined resonance frequency, and outputting a detection signal. The resonant sensor element is separate from the pair of electrodes that output the detection signal.

Amplifying means for amplifying the detection signal with a predetermined gain and applying a vibration control signal having a reverse phase to the vibration control electrode so as to attenuate the vibration of the detection signal when a vibration wave is detected. A vibration control device for a piezoelectric resonance type sensor element, comprising:

2. The vibration control device for a piezoelectric resonance sensor element according to claim 1, further comprising control means for setting a gain of the amplification means.

[3] The piezoelectric resonance type according to [1], wherein the pair of electrodes is formed in a central portion of the piezoelectric body and has a circular shape, a substantially circular shape, a substantially elliptical shape, or a substantially square shape. Sensor element vibration control device.

4. The piezoelectric resonance type according to claim 2, wherein the pair of electrodes are formed in a central portion of the piezoelectric body and have a circular shape, a substantially circular shape, a substantially elliptical shape, or a substantially square shape. Sensor element vibration control device.

[5] In the vibration control device for a piezoelectric resonance type sensor element comprising a piezoelectric body sandwiched between at least one pair of electrodes, detecting a vibration wave having a predetermined resonance frequency, and outputting a detection signal. The resonant sensor element is separate from the pair of electrodes that output the detection signal.

In response to the detection signal, the rising force of the detection signal is delayed by a predetermined time, and then a predetermined vibration control signal is applied to the vibration control electrode to detect the detection signal when the vibration wave is detected. A vibration control device for a piezoelectric resonance type sensor element, comprising control means for controlling the vibration to be attenuated.

[6] When the level of the detection signal exceeds a predetermined threshold value, the control means delays the vibration wave by substantially a half cycle or several cycles, and then transmits the predetermined vibration control pulse signal 6. The piezoelectric resonance type sensor according to claim 5, wherein the piezoelectric resonance type sensor is applied to a vibration control electrode. A vibration control device for the element.

7. The piezoelectric resonance type according to claim 5, wherein the pair of electrodes are formed in a central portion of the piezoelectric body and have a circular shape, a substantially circular shape, a substantially elliptical shape, or a substantially square shape. Sensor element vibration control device.

8. The piezoelectric resonance type according to claim 6, wherein the pair of electrodes are formed in a central portion of the piezoelectric body and have a circular shape, a substantially circular shape, a substantially elliptical shape, or a substantially square shape. Sensor element vibration control device.

[9] In the vibration control method of a piezoelectric resonance type sensor element comprising a piezoelectric body sandwiched between at least one pair of electrodes, detecting a vibration wave having a predetermined resonance frequency, and outputting a detection signal. The resonant sensor element is separate from the pair of electrodes that output the detection signal.

A step of amplifying the detection signal with a predetermined gain and applying a vibration control signal having a reverse phase to the vibration control electrode, so as to attenuate the vibration of the detection signal when a vibration wave is detected; A vibration control method for a piezoelectric resonance type sensor element.

10. The vibration control method for a piezoelectric resonant sensor element according to claim 9, further comprising the step of setting the gain.

[11] The piezoelectric resonance type according to [9], wherein the pair of electrodes is formed in a central portion of the piezoelectric body and has a circular shape, a substantially circular shape, a substantially elliptical shape, or a substantially square shape. Sensor element vibration control method.

12. The piezoelectric resonance type according to claim 10, wherein the pair of electrodes are formed in a central portion of the piezoelectric body and have a circular shape, a substantially circular shape, a substantially elliptical shape, or a substantially square shape. Sensor element vibration control method.

[13] In the vibration control method of a piezoelectric resonance type sensor element comprising a piezoelectric body sandwiched between at least one pair of electrodes, detecting a vibration wave having a predetermined resonance frequency, and outputting a detection signal. The resonant sensor element is separate from the pair of electrodes that output the detection signal.

In response to the detection signal, the rising force of the detection signal is delayed by a predetermined time, and then a predetermined vibration control signal is applied to the vibration control electrode. A method for controlling vibration of a piezoelectric resonance sensor element, comprising: a control step of controlling so as to attenuate vibration of a detection signal when detecting the vibration.

[14] In the control step, when the level of the detection signal exceeds a predetermined threshold, the vibration signal is delayed by substantially a half cycle to several cycles, and then the predetermined vibration control pulse signal is transmitted. 14. The method for controlling vibration of a piezoelectric resonance type sensor element according to claim 13, wherein: is applied to the vibration control electrode.

15. The piezoelectric resonance type according to claim 13, wherein the pair of electrodes are formed in a central portion of the piezoelectric body and have a circular shape, a substantially circular shape, a substantially elliptical shape, or a substantially square shape. Sensor element vibration control method.

16. The piezoelectric resonance type according to claim 14, wherein the pair of electrodes are formed in a central portion of the piezoelectric body and have a circular shape, a substantially circular shape, a substantially elliptical shape, or a substantially square shape. Sensor element vibration control method.