JP2006332991A - Controller and control method for resonance frequency of piezoelectric resonance type sensor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a controller etc., for the resonance frequency of a piezoelectric resonance type sensor element whose manufacturing processes are simple and manufacturing cost can be reduced. <P>SOLUTION: An ultrasonic sensor element 20 as the piezoelectric resonance type sensor element is composed of a piezoelectric resonance type sensor element which is constituted by sandwiching a PZT ceramics thin film layer 17 as a ferroelectric substance between two electrodes 16 and 18 and has a specific resonance frequency to detect an ultrasonic wave, and a specific DC bias voltage is applied between the two electrodes 16 and 18 from a variable DC voltage source 30 during measuring operation of the ultrasonic sensor element 20 to vary the resonance frequency of the ultrasonic sensor element 20. The current of the output signal from the ultrasonic sensor element 20 is amplified by a current amplifying amplifier 31 and output as a detection signal, a frequency counter 32 measures the frequency of the detection signal, and a comparator 33 compares a signal indicating the measured frequency with a DC voltage corresponding to a desired resonance frequency to control the DC bias voltage of the variable DC voltage source 30 so that they substantially match each other. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control device and a control method for controlling a resonance frequency of a piezoelectric resonance sensor element, for example, an ultrasonic sensor element, a sound wave sensor element, or a vibration sensor element.

  Conventionally, for example, using an ultrasonic array sensor device in which a plurality of ultrasonic sensor elements each having a predetermined resonance frequency and capable of detecting ultrasonic waves are juxtaposed in a predetermined two-dimensional shape. Although it is practical to obtain a three-dimensional measurement image by object recognition by electronic scanning, in the ultrasonic array sensor device, the sensor element itself is fixed by processing the output signal from each ultrasonic sensor element. It is possible to electrically scan the measurement direction as it is.

  For example, Patent Document 1 discloses an ultrasonic sensor element for performing object recognition including position measurement of an object to be measured. In the ultrasonic sensor element, two PZT ceramic thin film layers that are ferroelectrics are provided. It consists of a piezoelectric sensor that is sandwiched between two electrodes and detects ultrasonic waves with a predetermined resonance frequency, and applies a predetermined bias voltage between the two electrodes during the measurement operation of the ultrasonic sensor element. Thus, the resonance frequency of the ultrasonic sensor element is changed. Further, in the ultrasonic array sensor device in which a plurality of ultrasonic sensor elements are juxtaposed, a predetermined bias voltage is applied between the two electrodes of each ultrasonic sensor element during the measurement operation of the plurality of ultrasonic sensor elements. Thus, the resonance frequency of each ultrasonic sensor element is changed so as to substantially coincide with each other.

JP2003-281182A.

  Ultrasonic sensors that can be angle-scanned by phased array, abnormal sound / vibration detection sensors, etc. need to have the resonance frequency precisely matched to the desired value. Therefore, it is necessary to adjust the resonance frequency by adjusting trimming after the device is manufactured, which causes a problem that the manufacturing process becomes complicated and the manufacturing cost increases.

  An object of the present invention is to provide a control device and a control method for a resonance frequency of a piezoelectric resonance type sensor element, which solves the above-described problems, has a simpler manufacturing process than the conventional example, and can reduce the manufacturing cost. It is in.

The control device for the resonance frequency of the piezoelectric resonance sensor element according to the first invention comprises a ferroelectric substance sandwiched between two electrodes, detects a vibration wave having a predetermined resonance frequency, and detects the result. In the control device for controlling the resonance frequency of the piezoelectric resonance sensor element that outputs the output signal of
A variable DC voltage source for applying a predetermined DC bias voltage to the output signal;
A current amplifying means for amplifying the current of the output signal and outputting the current amplified signal as a detection signal;
Frequency measuring means for measuring the frequency of the detection signal and outputting a signal indicating the measured frequency;
Input means for inputting a desired resonance frequency;
The input resonance frequency is compared with the measured frequency, and the variable DC voltage source is set so that the input resonance frequency and the measured frequency substantially coincide with each other based on the comparison result. And a control means for controlling the direct current bias voltage.

  In the resonance frequency control device for the piezoelectric resonance type sensor element, the frequency measuring means, the control means, and the current amplifying means are configured by an FPGA (Field Programmable Gate Array), an A / D converter, and a D / A converter. It is characterized by that.

According to a second aspect of the present invention, there is provided a method for controlling a resonance frequency of a piezoelectric resonance type sensor element comprising a ferroelectric substance sandwiched between two electrodes, detecting a vibration wave having a predetermined resonance frequency, and detecting results. In the control method for controlling the resonance frequency of the piezoelectric resonance sensor element that outputs the output signal of
Applying a predetermined DC bias voltage to the output signal;
Amplifying the current of the output signal and outputting the current amplified signal as a detection signal;
Measuring the frequency of the detection signal, and outputting a signal indicating the measured frequency;
Inputting a desired resonance frequency;
The input resonance frequency is compared with the measured frequency, and the variable DC voltage source is set so that the input resonance frequency and the measured frequency substantially coincide with each other based on the comparison result. And controlling the direct current bias voltage.

  Therefore, according to the control device and the control method of the resonance frequency of the piezoelectric resonance type sensor element according to the present invention, the resonance frequency can be dynamically controlled after the element device is completed. No accuracy is required, and a trimming process after completion is not necessary. As a result, the device manufacturing process is simplified, the defective product rate is reduced, and the total cost can be greatly reduced. In addition, since the resonance frequency can be dynamically controlled even during use of the apparatus, it is possible to automatically correct a frequency shift due to a change with time, thereby reducing maintenance labor and running costs. Furthermore, even a single element device can be sequentially changed to a frequency other than the specific frequency of the initial value according to the usage situation, so that the same element device can continue to be used even if there is a change in measurement specifications. .

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In addition, in each following embodiment, the same code | symbol is attached | subjected about the same component.

First embodiment.
FIG. 1 is a block diagram showing a configuration of a resonance frequency control device for an ultrasonic sensor element 20 according to a first embodiment of the present invention, and FIG. 3 shows a first embodiment and a second embodiment to be described later. It is a longitudinal cross-sectional view which shows the structure of the ultrasonic sensor element 20 used by FIG.

  As shown in FIG. 3, the ultrasonic sensor element 20, which is a piezoelectric resonance sensor element according to the present embodiment, is formed by sandwiching a PZT ceramic thin film layer 17 that is a ferroelectric material between two electrodes 16 and 18. 1 is constituted by a piezoelectric resonance type sensor element having a predetermined resonance frequency and detecting an ultrasonic wave. During the measurement operation of the ultrasonic sensor element 20, the variable DC voltage source shown in FIG. The resonance frequency of the ultrasonic sensor element 20 is changed by applying a predetermined DC bias voltage from 30. In the ultrasonic sensor element 20, as shown in FIG. 1, the current of the output signal from the ultrasonic sensor element 20 is amplified by a current amplification amplifier 31, and the signal after current amplification is output as a detection signal. 32 measures the frequency of the detection signal, compares the signal indicating the measured frequency with a DC voltage corresponding to a set desired resonance frequency from the variable DC voltage source 34 by means of a comparator 33, and calculates the desired resonance. The DC bias voltage of the variable DC voltage source 30 is controlled so that the frequency and the measured frequency substantially coincide with each other.

  First, the structure and manufacturing method of the ultrasonic sensor element 20 used in this embodiment will be described below. As the thin plate structure of the sound sensing part of the ultrasonic sensor element 20, a diaphragm (four sides fixed), a bridge (two sides fixed) or a cantilever (one side fixed) is generally used. As is well known, these thin plate structures have the same relationship between the resonance frequencies fd, fb, and fc of the square plate as long as the materials and dimensions are the same. In this specification, the number number of the black brackets in which the mathematical formula is imaged and the formula number of the square brackets in which the mathematical formula is input are used in combination. The formula number is assigned to the last part of the formula using the format of “formula (1)” as the formula number.

[Equation 1]
fd: fb: fc = 35.99: 22.37: 3.494 (1)

  For the same shape, the resonance frequency decreases in inverse proportion to the square of the length of one side. Therefore, if the resonance frequency is the same, the ultrasonic sensor element 20 having a smaller bridge than the diaphragm and the cantilever than the bridge can be manufactured, and the ultrasonic sensor element 20 is formed in a limited chip area. An ultrasonic array sensor device can be configured.

However,
(1) These thin plate structures are formed by bulk micromachining using anisotropic etching of silicon.
(2) As the piezoelectric layer, a PZT ceramic thin film by a sol-gel film forming method having good piezoelectricity is effective.
In order to deal with the problem of array sensors (especially synthetic aperture type) that the function of the whole chip is lost when there is a defective part in the part of the array and (3) part of the array, it is anisotropic. The process of forming a piezoelectric layer by a sol-gel film forming method as a post process on a diaphragm that has been subjected to reactive etching is considered to have the highest production yield. Therefore, in the process according to the present embodiment, the ultrasonic sensor element 20 is manufactured based on this policy.

  FIG. 3 is a cross-sectional view showing the structure of the ultrasonic sensor element 20 according to this embodiment. The resonance frequency fr [Hz] of a square diaphragm having a side length a [m] can be obtained by the following equation.

  Here, each variable is as shown in the following table.

[Table 1]
Each variable that determines the resonance frequency of the diaphragm ―――――――――――――――――――――――――――――――――――
Variable Unit Meaning ――――――――――――――――――――――――――――――――――――
α Coefficient by vibration mode. In the lowest order of the square plate, α ≒ 35.99.
ν Poisson's ratio of the entire diaphragm (here 0.3).
t [m] The total thickness of the diaphragm.
t _i [m] Film thickness of the i-th layer.
ρ [kg / m ³ ] Volume mass density of the entire diaphragm.
ρ _i [kg / m ³ ] Density of the material of the i-th layer.
E _i [Pa] Young's modulus of the material of the i-th layer.
h _i [m] Height of the i-th layer.
K [Nm] Bending rigidity of the diaphragm.
―――――――――――――――――――――――――――――――――――

  When the length of one side of the diaphragm is 0.5 mm or 0.6 mm, the resonance frequency fr of the structure shown in FIG. 2 is calculated from the above equation (2), and the following equation is obtained.

[Equation 2]
When fr = 147 [kHz] and a = 0.5 [mm] (3)
[Equation 3]
When fr = 102 [kHz] and a = 0.6 [mm] (4)

  Since these values are all material constants in bulk, there is a possibility of deviation from this value in a piezoelectric resonance type sensor element composed of an actually manufactured thin film. The size of the array is actually limited by the chip size determined for each specific application. Here, the TO-79 type metal package is used as a reference size as a chip size that can be comprehensively applied to the application according to the present embodiment. For example, by arranging an array using a plurality of ultrasonic sensor elements 20, an array of, for example, a total of 37 ultrasonic sensor elements can be constructed at the maximum triple ring plus center. With such a configuration, even if the characteristics of each element vary, by selecting a group of elements with relatively uniform characteristics, a linear array or a small-scale ring array is configured to evaluate the characteristics. You can also.

  Next, a manufacturing process of the ultrasonic sensor element 20 will be described below. As described above, the thin plate structure is a diaphragm structure, and the 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 or the like is formed by spin coating (gel film) and crystallized by heat treatment. . 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 forming method is shown in the following table.

[Table 2]
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 Pb _1.15 Zr _0.52 Ti _0.48 O _3.15 as 15% wt
―――――――――――――――――――――――――――――――――――

(A) A semiconductor chip wafer 10 having a commercially available SOI (Silicon On Insulator) structure is used as a starting substrate. Here, the semiconductor chip wafer 10 has an insulating film layer 13 made of SiO ₂ having a thickness of 0.1 μm on an Si semiconductor substrate 10 having an insulating film layer 11 made of SiO ₂ having a thickness of 0.4 μm on the back surface. A Si semiconductor active layer 14 having a thickness of 2.2 μm is formed via One 4-inch substrate is diced into two. Four chips are arranged per wafer.

(B) Both sides of the semiconductor chip wafer 10 are thermally oxidized for masking during anisotropic etching and for insulation between the lower electrode layers 16. At a furnace temperature of 1,000 ° C., O ₂ was first dry oxidized at 5.0 liters / minute for 5 minutes, then O ₂ (5.0 liters / minute) + H ₂ (4.5 liters / minute). Oxidize for 90 minutes. The insulating film layer 17 has a thickness of 0.38 to 0.44 μm and is a mixture of EPW (Ethylenediamine Pyrocatechol Water; ethylenediamine (strongly alkaline liquid), pyrocatechol (particulate alcohol), and water. This is an etching solution used for anisotropic etching.) Thick enough to withstand anisotropic etching.

(C) Pt / Ti is formed as the lower electrode layer 16 by an RF sputtering apparatus. In an atmosphere of Ar gas flow rate of 44 sccm and 1 Pa, 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 μm and 0.2 μm, 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 X-ray diffractometer (hereinafter referred to as XRD (X-Ray Diffractometer)), PZT ceramics with a single Pt (111) orientation It has been confirmed that a sufficiently high quality thin film is formed as the lower electrode layer 16 of the thin film layer 17.

(D) The insulating film layer 11 on the back surface is made of BHF (Buffered Hydro-Fluoric acid), that is, a mixed solution of hydrofluoric acid and ammonium fluoride as a window for anisotropic etching. Used for etching silicon oxide).). At this time, pattern matching is performed by a double-sided mask aligner so that the pattern of the window on the back surface accurately overlaps the electrode pattern of the lower electrode 16 of the sensor diaphragm on the front surface.

(E) A diaphragm structure is formed by anisotropic etching. Etch is used as an etchant, and etching is performed at 114 ° C. for 8 to 10 hours. Although the etching rate varies slightly in each etching hole in the semiconductor chip wafer 10, the etching is almost stopped in the insulating film layer 13 which is the I layer of the SOI structure, so that the etching is performed according to the etching hole having the slowest etching rate. By doing so, the diaphragm structure was completed.

(F) The insulating film layer 13, which is the I layer of the SOI structure, is indispensable as a stop layer for the above-mentioned anisotropic etching. However, since the final structure may cause internal stress, Need to be removed. Since it is a normal thermal oxide film, it is removed by etching with BHF.

(G) A PZT ceramic thin film layer 17 is formed as a piezoelectric layer by a sol-gel film forming method. After forming the piezoelectric layer, the PZT ceramic is etched with hydrofluoric acid (HF: HNO ₃ : H ₂ O = 1: 1: 1) as a contact hole of the lower electrode. The time required for etching the PZT ceramic thin film layer 17 having a thickness of 1 μm is 10 to 30 seconds, and the amount of side etching at this time is 5 to 10 μm.

(H) A photoresist layer is formed and patterned as an insulating film layer 25 for short circuit protection of the PZT ceramic thin film layer 17 and area control of the upper electrode layer 18. In order to increase the resistance of the photoresist to organic solvents, the temperature is gradually raised from 120 ° C. to 200 ° C. in a post bake and cured. As a result, the resist hardly dissolves in acetone.

(I) Pt is formed as the upper electrode layer 18 by an RF sputtering apparatus. The film forming conditions are the same as in step (c) and the film thickness is 0.2 μm. The upper electrode layer 18 of the ultrasonic sensor element 20 is not required to be patterned because the electrode shape is formed by the photoresist layer in the step (h). In addition, since the high-temperature baking in the step (h) causes a sufficiently gentle taper at the step portion of the resist, the upper electrode layer 18 is not disconnected. A heat-resistant Kapton tape is used for masking the contact hole of the lower electrode layer 16.

  After the ultrasonic sensor element 20 is manufactured by the above process, the wafer 10 is diced, the chip is separated, fixed to the package, and the lead wires 21 and 22 are connected to the electrode layers 16 and 18 by bonding 19. The lead wires 21 and 22 are connected to the terminals T1 and T2 and bonded to complete the sensor chip.

  FIG. 4 is a graph showing the bias voltage dependence characteristics of the resonance frequency in the ultrasonic sensor element 20 of FIG. That is, FIG. 4 is a plot of the frequency of the resonance point of the ultrasonic sensor element 20, that is, the change in the resonance frequency against the DC bias voltage. As is apparent from FIG. 4, it can be seen that a hysteresis with two peaks is drawn. Therefore, the resonance frequency can be adjusted by changing the DC bias voltage applied to the ultrasonic sensor element 20. In other words, during the measurement operation of the ultrasonic sensor element 20, by applying a predetermined bias voltage between the two electrodes 16 and 18 without using a bias voltage that may damage the ferroelectric. The resonance frequency of the ultrasonic sensor element 20 can be changed.

  Further, the configuration of the resonance frequency control device of FIG. 1 will be described in detail below.

  In FIG. 1, the current of the output signal from both terminals T1 and T2 of the ultrasonic sensor element 20 is amplified by a current amplification amplifier 31 having a relatively small input impedance, and the signal after the current amplification is detected as a detection signal at a terminal T3. And output to the frequency counter 33. Next, the frequency counter 32 measures the frequency of the detection signal and outputs a signal indicating the measured frequency to the non-inverting input terminal of the comparator 33. On the other hand, a desired resonance frequency to be set is input by an operator to a frequency setting device 35 that is an input control device, and the frequency setting device 35 is variable so that a DC voltage corresponding to the input desired resonance frequency is output. The DC voltage source 34 is controlled. A DC voltage corresponding to a desired resonance frequency from the variable DC voltage source 34 is input to the inverting input terminal of the comparator 33. The comparator 33 compares the measured frequency with a DC voltage corresponding to the set desired resonance frequency from the variable DC voltage source 34, and the desired resonance frequency and the measured frequency substantially match. Thus, the DC bias voltage of the variable DC voltage source 30 is controlled.

  That is, the principle of the control device is as follows. When a bias voltage is applied to the ferroelectric, its polarization characteristics can be changed and the dielectric constant can be controlled. The piezoelectricity of the ferroelectric has a close relationship with the polarization characteristics, and the piezoelectricity can be similarly controlled by applying a bias voltage. In the piezoelectric vibrating body of the piezoelectric resonance sensor element, the effect equivalent to changing the elastic modulus equivalently through electrical / mechanical coupling can be obtained by changing the dielectric constant and the piezoelectric constant. The frequency can be changed. By extracting a sensor signal as a current output and feeding back a bias voltage applied to the sensor from the value of the frequency to an appropriate value, the resonance frequency can be controlled dynamically.

  As described above, according to the control device according to the present embodiment, the polarization state of the ferroelectric substance of the ultrasonic sensor element 20 is changed by applying a DC bias voltage from the variable DC voltage source 30 to the ultrasonic sensor element 20. By controlling, the resonance frequency of the ultrasonic sensor element 20 can be dynamically controlled. Since the resonance frequency can be measured from the sensor output signal waveform, the resonance frequency is controlled by applying a DC bias voltage for correcting a deviation from the desired resonance frequency to the ultrasonic sensor element 20. Here, since the sensor output signal is current-amplified by the current amplification amplifier 31, the output signal can be taken out without being affected by the bias voltage application.

  The following can be considered as specific examples of the present embodiment. In a phased array type ultrasonic sensor element in which matching of the resonance frequencies is strictly required, it is used to keep the resonance frequencies of all elements at the same constant value. In the abnormal sound / abnormal vibration detection sensor element, it is used to match the frequency of the specific sound / specific vibration to be detected, and the spectrum is analyzed with a single element by sequentially changing the detection frequency. In the vibration type acceleration sensor / gyro, the vibration frequency is controlled with high accuracy.

  Therefore, according to the control device and the control method for the resonance frequency of the ultrasonic sensor element 20 according to the present embodiment, the resonance frequency can be dynamically controlled after the element device is completed. High accuracy is not required, and a process such as trimming after completion is not necessary. As a result, the device manufacturing process is simplified, the defective product rate is reduced, and the total cost can be greatly reduced. In addition, since the resonance frequency can be dynamically controlled even during use of the apparatus, it is possible to automatically correct a frequency shift due to a change with time, thereby reducing maintenance labor and running costs. Furthermore, even a single element device can be sequentially changed to a frequency other than the specific frequency of the initial value according to the usage situation, so that the same element device can continue to be used even if there is a change in measurement specifications. .

Second embodiment.
FIG. 2 is a block diagram showing the configuration of the resonance frequency control device of the ultrasonic sensor element 20 according to the second embodiment of the present invention. The resonance frequency control apparatus for the ultrasonic sensor element 20 according to the second embodiment uses the frequency counter 32, the comparator 33, the variable DC voltage source 34, and the variable DC voltage source 30 shown in FIG. It is characterized by comprising an FPGA (Field Programmable Gate Array) 40 with an input device 50, an A / D converter 36 and a D / A converter 37. Hereinafter, differences from the first embodiment will be described in detail.

  In FIG. 2, the detection signal from the current amplification amplifier 31 is A / D converted into a digital detection signal by the A / D converter 36 and then input to the FPGA 40 via the input / output interface 44. The FPGA 40 includes a CPU 41 of a controller that is a central processing unit, a RAM 42 that stores software programs and data executed in the FPGA 40 and operates as a working memory, an input interface 43 connected to the data input device 50, and an A / D An input / output interface 44 to which the converter 36 and the D / A converter 37 are connected is configured via a bus 45. Here, the software program stored in the FPGA 40 has at least the functions of the frequency counter 32, the comparator 33, and the variable DC voltage source 34. A desired resonance frequency to be set by the operator is input in advance using the data input device 50, and the data is input to the CPU 42 via the input interface 43 and further temporarily stored in the RAM 42. The CPU 41 measures the frequency of the detection signal input from the A / D converter 36 via the input / output interface 44, compares the measured frequency with a desired resonance frequency input in advance, and compares the desired frequency. A DC bias voltage is calculated so that the resonance frequency and the measured frequency substantially coincide with each other, and a digital voltage signal indicating the DC bias voltage is output to the D / A converter 37 via the input / output interface 44. The D / A converter 37 D / A converts the input digital voltage signal to an analog DC voltage, and then applies it to both terminals T 1 and T 2 of the ultrasonic sensor element 20.

  In the control device according to the second embodiment configured as described above, similarly to the control device according to the first embodiment, the resonance frequency of the ultrasonic sensor element 20 is dynamically set to a desired resonance frequency. That is, it has the same effect as the first embodiment.

Modified example.
In the above embodiment, the ultrasonic sensor element 20 is described as an example of the piezoelectric resonance sensor element. However, the present invention is not limited to this, and the acoustic sensor element and the machine using the piezoelectric resonance sensor element are not limited thereto. It may be a vibration detection sensor element or the like.

  In the above embodiments, PZT ceramics are used as the ferroelectric for the piezoelectric resonance sensor element. However, the present invention is not limited to this, and ceramics such as barium titanate or lead titanate, or polyfluoride are used. A polymer material such as vinylidene may be used.

  In the above embodiment, an electric field in the vertical direction (thickness direction) is applied to the ferroelectric using the piezoelectric resonance type sensor element made of the ferroelectric sandwiched between the two electrodes 16 and 18. However, the present invention is not limited to this. By applying a bias voltage or a polling voltage to two electrodes formed at a predetermined interval on the ferroelectric, the ferroelectric is applied to the ferroelectric. An electric field in the horizontal direction (parallel plate direction) may be applied.

  As described above in detail, according to the control device and the control method of the resonance frequency of the piezoelectric resonance type sensor element according to the present invention, the resonance frequency can be dynamically controlled after the element device is completed. Therefore, a very high accuracy is not required, and a process such as trimming after completion is not necessary. As a result, the device manufacturing process is simplified, the defective product rate is reduced, and the total cost can be greatly reduced. In addition, since the resonance frequency can be dynamically controlled even during use of the apparatus, it is possible to automatically correct a frequency shift due to a change with time, thereby reducing maintenance labor and running costs. Furthermore, even a single element device can be sequentially changed to a frequency other than the specific frequency of the initial value according to the usage situation, so that the same element device can continue to be used even if there is a change in measurement specifications. .

It is a block diagram which shows the structure of the control apparatus of the resonant frequency of the ultrasonic sensor element 20 which is 1st Embodiment based on this invention. It is a block diagram which shows the structure of the control apparatus of the resonant frequency of the ultrasonic sensor element 20 which is the 2nd Embodiment which concerns on this invention. It is a longitudinal cross-sectional view which shows the structure of the ultrasonic sensor element 20 used by 1st and 2nd embodiment. 4 is a graph showing a bias voltage dependence characteristic of a resonance frequency in the ultrasonic sensor element 20 of FIG. 3.

Explanation of symbols

10: Semiconductor chip wafer,
11 ... Semiconductor substrate,
12, 13, 15, 25 ... insulating layer,
14 ... Semiconductor active layer,
16, 18 ... electrode layer,
17 ... PZT ceramic thin film layer 19 ... bonding,
20 ... ultrasonic sensor element,
21, 22 ... Lead-out conductors,
30, 34 ... Variable DC voltage source,
31 ... Current amplification amplifier,
32 ... Frequency counter,
33 ... Comparator,
35 ... frequency setting device,
36 ... A / D converter,
37 ... D / A converter,
40 ... FPGA,
41 ... CPU,
42 ... RAM,
43 ... Input interface,
44 ... I / O interface,
45 ... Bus
50 ... Data input device,
T1, T2, T3 ... terminals.

Claims (3)

For controlling the resonance frequency of a piezoelectric resonance type sensor element that sandwiches a ferroelectric material between two electrodes, detects a vibration wave having a predetermined resonance frequency, and outputs an output signal as a detection result In the control device,
A variable DC voltage source for applying a predetermined DC bias voltage to the output signal;
A current amplifying means for amplifying the current of the output signal and outputting the current amplified signal as a detection signal;
Frequency measuring means for measuring the frequency of the detection signal and outputting a signal indicating the measured frequency;
Input means for inputting a desired resonance frequency;
The input resonance frequency is compared with the measured frequency, and the variable DC voltage source is set so that the input resonance frequency and the measured frequency substantially coincide with each other based on the comparison result. And a control means for controlling the direct current bias voltage of the piezoelectric resonance type sensor element.   2. The piezoelectric resonance according to claim 1, wherein said frequency measuring means, said control means and said current amplifying means are constituted by an FPGA (Field Programmable Gate Array), an A / D converter and a D / A converter. Control device for resonance frequency of the sensor element. For controlling the resonance frequency of a piezoelectric resonance type sensor element that sandwiches a ferroelectric material between two electrodes, detects a vibration wave having a predetermined resonance frequency, and outputs an output signal as a detection result In the control method,
Applying a predetermined DC bias voltage to the output signal;
Amplifying the current of the output signal and outputting the current amplified signal as a detection signal;
Measuring the frequency of the detection signal, and outputting a signal indicating the measured frequency;
Inputting a desired resonance frequency;
The input resonance frequency is compared with the measured frequency, and the variable DC voltage source is set so that the input resonance frequency and the measured frequency substantially coincide with each other based on the comparison result. And a method for controlling the resonance frequency of the piezoelectric resonance sensor element.

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