JP2003284182A - Ultrasonic wave sensor element, ultrasonic wave array sensor system, and adjustment method of resonance frequency therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic wave array sensor system for recognizing an object including position measurement of the object to be measured. <P>SOLUTION: The ultrasonic wave sensor element 20 comprises a piezoelectric sensor that is formed by using two electrodes 16, 18 to have a PZT ceramic thin film layer 17 being a ferroelectric substance inbetween and has a prescribed resonance frequency to sense an ultrasonic wave, and is characterized in that the resonance frequency of the ultrasonic wave sensor element 20 is changed by applying a prescribed bias voltage between the two electrode 16 and 18 during the measurement of the ultrasonic wave sensor element 20. Further, in an ultrasonic wave array sensor system 30 comprising parallel connections of a plurality of the ultrasonic wave sensor elements 20, a prescribed bias voltage is applied between the two electrodes 15 and 18 of each ultrasonic wave sensor element 20 respectively so as to change the resonance frequencies of the ultrasonic wave sensor elements 20 so that they are substantially coincident with each other during the measurement of a plurality of the ultrasonic wave sensor elements 20. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic sensor element composed of a piezoelectric sensor, an ultrasonic array sensor device composed of a plurality of ultrasonic sensor elements, and a method of adjusting their resonance frequencies.

[0002]

2. Description of the Related Art Heretofore, for example, an ultrasonic array sensor device has a plurality of ultrasonic sensor elements, which are piezoelectric sensors having a predetermined resonance frequency and capable of detecting ultrasonic waves, arranged in a predetermined two-dimensional shape. It has been practically used to obtain a measurement image of a three-dimensional shape by object recognition by electronic scanning using
In the ultrasonic array sensor device, by processing the output signal from each ultrasonic sensor element, it is possible to electrically scan the measurement direction while the sensor element itself is fixed. Here, in particular, a compact ultrasonic array sensor device is conventionally called a "resonant ultrasonic microarray sensor device", but when it is considered to be mounted on a small device using this, mechanical scanning in this device is performed. It is essential to lose parts.

Next, the object recognition by electronic scanning performed using this ultrasonic array sensor device will be described below. FIGS. 3 to 5 show the concept of received wave scanning by delay addition in ultrasonic measurement, and FIG. 3 is a schematic diagram showing an object position measuring method using ultrasonic waves in the related art. 4 is a block diagram showing a circuit unit of an object position measuring device using the object position measuring method of FIG.
FIG. 5 is a waveform diagram showing signal waveforms at various parts in the circuit part of the object position measuring device of FIG.

As shown in FIG. 3, the ultrasonic sensor element 20
The ultrasonic sensor element 20 emits ultrasonic waves from the ultrasonic sound source 40 installed on the side of the object, and the ultrasonic waves reflected by the objects 51 and 52 to be returned are received by the ultrasonic sensor element 20 to include the azimuth angle of the object to be measured. Recognize position. At this time, from the propagation time of the ultrasonic wave in each incident direction to each ultrasonic sensor element 20 (the time from the transmission from the ultrasonic sound source 20 to the return to each ultrasonic sensor element 20), the measured object in each direction The distribution of the distance d of 51 and 52 (distance in the depth direction) is measured.

Here, ultrasonic waves are simultaneously incident on each of the ultrasonic sensor elements 20 from all directions, and it is necessary to extract and process a signal in a specific direction from the ultrasonic waves.
FIG. 4 shows an outline of the processing for extracting this specific direction component, and FIG. 5 shows an example of a concrete waveform. The first incident wave in FIG. 4 reaches the ultrasonic array sensor device 30 at a _first angle θ ₁ with respect to the surface 30sa parallel to the incident surface 30s of the ultrasonic array sensor device 30. Therefore, the output signal from each ultrasonic sensor element 20 has a signal waveform having a time delay for each ultrasonic sensor element 20, as shown in FIG. This is set to the first delay pattern corresponding to the first angle θ ₁ , and the variable delay units 31-1 to 31-3 are set.
By passing 1-5, the phase of the incident wave I can be aligned as shown by the waveform of the first delayed signal.
Here, in FIG. 5, each of the variable delay units 31-1 to 31-3
The horizontal lengths of 1-5 correspond to the lengths of the set delay times, respectively. In the first delay pattern, the variable delay unit 31-5 compares the delay time with that of the variable delay unit 31-1. Is set to be long. Further, by adding these signals by the adder 32, as shown in the waveform of the first post-addition signal, only the signal waveform of the first incident wave is made much larger than the other signal waveforms. It is possible to take out by in-phase synthesis (by multiplying the number of elements).

Similarly for the second incident wave, the second
By using the second delay pattern corresponding to the angle θ ₂ of, the second incident wave alone can be enlarged and in-phase combined and extracted as shown in the waveform of the second post-addition signal. As described above, the variable delay units 31-1 to 31 on the receiving side
By changing the variable delay pattern of -5 and performing delay addition, it is possible to scan in the angular direction without a mechanically movable part.

Next, object recognition using the pseudo array will be described below. Using the ultrasonic sensor element 20 manufactured as described above, whether or not electronic scanning by delay addition is possible in principle was verified using a pseudo array. Here, the “pseudo array” does not actually form an array using a plurality of ultrasonic sensor elements arranged on a semiconductor chip, but uses only a single ultrasonic sensor element 20 and its position. The ultrasonic wave is transmitted and received while changing the, and electronic scanning is performed based on the received waveform obtained thereby. By using the pseudo array, the principle of electronic scanning itself by delay addition is not affected by variations in characteristics (sensitivity, resonance frequency, and attenuation rate) between the ultrasonic sensor elements 20 in the ultrasonic array sensor device 30. Can be verified. In this case, in reality, the reception waveforms of all the ultrasonic sensor elements 20 can be obtained by transmitting and receiving the ultrasonic waves once, but in the case of the pseudo array, the waveforms obtained by transmitting and receiving the ultrasonic waves multiple times are used. The variation of the ultrasonic waveform itself during each transmission / reception becomes a problem.
When the ultrasonic oscillation waveform was actually measured, there was no significant change in the waveform itself between each oscillation, and the intensity of the ultrasonic wave for each oscillation itself was calibrated using a standard microphone to obtain the actual array sensor. I confirmed that it can be emulated sufficiently.

The arrangement of the array used for the pseudo array this time is shown in FIG. 6 (a). 600 μm for the ultrasonic sensor element 20
The angle and the resonance frequency were 100 kHz, and the element spacing was also d _i = 1.7 mm. The calculated values of the directional characteristics in this case are shown in FIG. Half-width is about 28 °, so 3
It has a directional characteristic that can separate an object separated by about 0 ° or more.

FIG. 7 shows a schematic view of the arrangement of the object to be measured and the ultrasonic sensor element 20 used for the measurement. Measured object 51,
As 52, a cylindrical metal rod was used. When measuring
The ultrasonic sensor element 20 is fixed to the automatic stage, the oscillation signal of the pulse ultrasonic wave and the reception signal are repeatedly captured by the control of the computer 60, and the stage is moved repeatedly, and calculation is performed using all the finally obtained signal waveforms. We tried the object recognition including the position measurement of the object by delay addition.

FIG. 8 shows the waveforms of the reception signals actually output from the ultrasonic sensor elements 20-1 to 20-4.
A combination of the reflected signal waveforms from the two measured stages 51 and 52 is output from each ultrasonic sensor element 20, but due to the difference in the positional relationship with the measured objects 51 and 52, 2
The two ultrasonic waves interfere with each other, and it is possible to obtain output signals that are greatly different for each ultrasonic sensor element 20. FIG. 9 shows waveforms obtained by loading the signal waveforms of FIG. 8 into the computer 60 and performing delay addition by calculation. In the calculation, the azimuth angle θ is delayed and added every 2 degrees, but FIG. 9 shows a typical output signal waveform for the azimuth angle θ. The output signal waveform alone suggests that the measured objects 51 and 52 exist at different distances on the front left side and the right side.

In order to actually reconstruct the arrangement of the objects, it is judged for each predetermined azimuth angle θ whether or not the measured objects 51 and 52 exist, and if so, at what distance. go. As shown in FIG. 10, the maximum amplitude of the reflected wave and the delay time (the time from the transmission of the ultrasonic sound source 40 to the reception of each ultrasonic sensor element 20) are used as the criterion. The maximum amplitude of the reflected wave gives the certainty that the object exists, and the delay time t gives the distance d to the object. The calculation of this distance d can be executed using the following equation.

[0012]

## EQU1 ## h = c × t / 2

[Expression 2] c = 331 + 0.6 × Tr

Here, c is the velocity of ultrasonic waves and Tr is the temperature.

FIG. 11 shows a plot of the maximum amplitude and the delay time of FIG. 10 for each predetermined azimuth angle θ. The condition for determining the existence of an object here is that a certain threshold value is set for the maximum amplitude, and the object exists at the point of the maximum value in the area exceeding the threshold value. From this, it can be seen that an object exists in two azimuth directions (azimuth θ = ± 12 degrees). The distances d to the object in those directions are 39.8 cm and 38 cm, respectively. FIG. 12 shows polar coordinates of the azimuth θ and the distance d. This shows that the object arrangement in the experimental system has been reconstructed.

Strictly speaking, the method of setting the threshold value with respect to the maximum amplitude in recognizing an object including the measurement of the position of the object involves arbitrariness. In actual object recognition for a specific object to be measured in a specific application, it is needless to say that it is necessary to perform preliminary measurement for various arrangements in advance and obtain an appropriate threshold value. However, as a target verification experiment of object recognition, it is important to be able to determine a certain threshold value in FIG.

[0016]

Further, the recognition of a plurality of objects by electronic scanning using the ultrasonic array sensor device 30 which is a linear array will be described below. From the above-described verification experiment using the pseudo array, it was found that object recognition can be performed in principle using a plurality of ultrasonic sensor elements 20. In the following, object recognition is attempted using the ultrasonic array sensor device 30 provided on the actual semiconductor chip.

The ultrasonic array sensor device 30 to be used has a plurality of ultrasonic sensor elements 20 in the same manner as that used above.
Are arranged in an array shape, and each ultrasonic sensor element 20 has a 600 μm square, a resonance frequency of 100 kHz,
The element spacing d _i = 1.7 mm, and the arrangement of the ultrasonic sensor elements 20 is the same as in FIG. 6A. The arrangement of the ultrasonic array sensor device 30, the ultrasonic sound source 40, and the measured objects 51 and 52 is also the same as in FIG. 7, but since the actual array is used this time, the ultrasonic sensor element 20 must be moved. Instead, the output signal from each ultrasonic sensor element 20 obtained by transmitting and receiving the ultrasonic signal of one pulse was taken into the computer 60, and delay addition was performed by calculation.

The waveform of the output signal from each ultrasonic sensor element 20 is shown in FIG. Similar to FIG. 8 described above, the reflected wave signals from the two measured objects 51 and 52 can be clearly seen.
FIG. 14 shows a signal waveform after delay-adding these. Unlike the case of the pseudo array, amplitude peaks at each azimuth angle θ appear intricately, and it does not appear that an object exists at a specific position. Similarly to FIG. 8, when the maximum amplitude and the delay time are actually plotted for each azimuth angle from FIG. 14, FIG.
It becomes 5. There is no clear peak of maximum amplitude and no specific threshold can be determined. Therefore,
It is impossible to reconstruct the object arrangement from FIG.

As described above, in the ultrasonic array sensor device 30 of the prior art, the measured objects 51, 52 are
There is a problem that it is not possible to perform object recognition including position measurement.

The object of the present invention is to solve the above problems, and in the ultrasonic array sensor device 30, the object 5 to be measured is
An object of the present invention is to provide means such as an apparatus and method capable of performing object recognition including 1,52 position measurement.

[0021]

According to a first aspect of the present invention, there is provided a method of adjusting a resonance frequency of an ultrasonic sensor element, wherein a ferroelectric material is sandwiched between two electrodes and has a predetermined resonance frequency. A method for adjusting a resonance frequency of an ultrasonic sensor element, which comprises a piezoelectric sensor for detecting ultrasonic waves by applying a predetermined bias voltage between the two electrodes during operation of the ultrasonic sensor element. The method is characterized by including the step of changing the resonance frequency of the ultrasonic sensor element.

In the method of adjusting the resonance frequency of the ultrasonic array sensor device according to the second invention of the present application, the ferroelectric substance is sandwiched between two electrodes, and the ultrasonic wave is detected with a predetermined resonance frequency. A method for adjusting an ultrasonic array sensor device in which a plurality of ultrasonic sensor elements each of which is a piezoelectric sensor are arranged side by side, wherein each of the ultrasonic sensor elements is in operation during operation of the plurality of ultrasonic sensor elements. And applying a predetermined bias voltage between the two electrodes to change the resonance frequencies of the ultrasonic sensor elements so as to substantially match each other.

In the method of adjusting the resonance frequency of the ultrasonic sensor element according to the third aspect of the present invention, the ferroelectric substance is sandwiched between two electrodes, and the ultrasonic wave is detected with a predetermined resonance frequency. A method of adjusting the resonance frequency of an ultrasonic sensor element comprising a piezoelectric sensor, wherein a predetermined voltage is applied between the two electrodes for a predetermined time before the operation of the ultrasonic sensor element. The method is characterized by including a step of changing the resonance frequency of the ultrasonic sensor element by applying an electric field and polling the ultrasonic sensor element.

In the method of adjusting the resonance frequency of the ultrasonic array sensor device according to the fourth aspect of the present invention, the ferroelectric substance is sandwiched between two electrodes, and the ultrasonic wave is detected with a predetermined resonance frequency. A method for adjusting an ultrasonic array sensor device in which a plurality of ultrasonic sensor elements, each of which is a piezoelectric sensor, are arranged side by side, and before the operation of the plurality of ultrasonic sensor elements, for a predetermined time, A predetermined electric field is applied between the two electrodes of each ultrasonic sensor element to apply a predetermined electric field, and the plurality of ultrasonic sensor elements are polled so that the ultrasonic sensor elements The method is characterized by including changing the resonance frequencies so as to substantially match each other.

The ultrasonic sensor element according to the fifth invention of the present application uses the method for adjusting the resonant frequency of the ultrasonic sensor element according to the first invention so that the resonant frequency of the ultrasonic sensor element becomes a predetermined resonant frequency. The feature is that it is set.

An ultrasonic array sensor device according to a sixth aspect of the present invention uses the method for adjusting the resonant frequency of the ultrasonic array sensor device according to the second aspect to determine the resonant frequencies of a plurality of ultrasonic sensor elements. Is set to the same resonance frequency of.

The ultrasonic sensor element according to the seventh invention of the present application sets the resonant frequency of the ultrasonic sensor element to a predetermined resonant frequency by using the method for adjusting the resonant frequency of the ultrasonic sensor element according to the third invention. The feature is that it is set.

The ultrasonic array sensor device according to the eighth invention of the present application uses the method for adjusting the resonant frequency of the ultrasonic array sensor device according to the fourth invention to determine the resonant frequencies of a plurality of ultrasonic sensor elements. Is set to the same resonance frequency of.

[0029]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

In the embodiment according to the present invention, in the ultrasonic array sensor device 30, the objects to be measured 51, 5 are measured.
Means such as apparatus and methods capable of performing object recognition including two position measurements are provided. FIG. 1 is a sectional view showing a structure of an ultrasonic sensor element 20 according to an embodiment of the present invention, and FIG. 2 is an array arrangement using a plurality of ultrasonic sensor elements 20 shown in FIG. It is a top view which shows the ultrasonic array sensor apparatus 30 which shows the element arrangement at this time.

Ultrasonic sensor element 20 according to the present embodiment
As shown in FIG. 1, a PZT ceramic thin film layer 17 which is a ferroelectric substance is sandwiched between two electrodes 16 and 18, and is composed of a piezoelectric sensor which has a predetermined resonance frequency and detects ultrasonic waves. The resonance frequency of the ultrasonic sensor element 20 is changed by applying a predetermined bias voltage between the two electrodes 16 and 18 during the measurement operation of the ultrasonic sensor element 20. Also, FIG.
As shown in FIG. 3, in the ultrasonic array sensor device 30 in which a plurality of ultrasonic sensor elements 20 are juxtaposed, between the two electrodes 16 of each ultrasonic sensor element 20 during the measurement operation of the plurality of ultrasonic sensor elements 20. , 18 are applied with predetermined bias voltages, respectively, so that the resonance frequencies of the ultrasonic sensor elements 20 are changed so as to substantially match each other.

Further, before the measurement operation of the ultrasonic sensor element 20, a predetermined electric field is applied by applying a predetermined voltage between the two electrodes 16 and 18 for a predetermined time of, for example, 1 second to 1 hour. Then, the resonance frequency of the ultrasonic sensor element 20 is changed by polling the ultrasonic sensor element 20. Further, in the ultrasonic array sensor device 30, before the measurement operation of the plurality of ultrasonic sensor elements 20, for a predetermined time, for example, 1 second to 1 hour, between the two electrodes 16, 18 of each ultrasonic sensor element 20. A predetermined electric field is applied to each of the plurality of ultrasonic sensor elements 20 to poll the plurality of ultrasonic sensor elements 20 so that the resonance frequencies of the ultrasonic sensor elements 20 substantially match each other. Change to.

First, the structure and manufacturing method of the ultrasonic sensor element 20 in the ultrasonic array sensor device 30 used in this embodiment will be described below. As the thin plate structure of the sound sensing portion of the ultrasonic sensor element 20, a diaphragm (fixed on four sides), a bridge (fixed on two sides) or a cantilever (fixed on one side) is generally used. As is well known, these thin plate structures have the same resonance frequency fd, f in a square plate if the materials and dimensions are the same.
b and fc have the following relationship.

[0034]

Fd: fb: fc = 35.99: 22.37:
3.494

For the same shape, the resonance frequency decreases in inverse proportion to the square of the length of one side. Therefore, if the resonance frequencies are the same, the ultrasonic sensor element 2 having a smaller size in the bridge than in the diaphragm and in the cantilever than in the bridge
Therefore, the ultrasonic array sensor device 30 including a large number of ultrasonic sensor elements 20 can be configured in a limited chip area.

However, (1) these thin plate structures are formed by bulk micromachining utilizing 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 the array sensor (particularly the synthetic aperture type) that (3) the function of the entire chip is lost if there is a defective portion in a part of the array, It is considered that the production yield is highest in the process of forming the piezoelectric layer by the sol-gel film forming method as a post process on the diaphragm that has completed the property etching. Therefore, in the process according to the present embodiment, the ultrasonic sensor element 20 is
It was decided to produce.

FIG. 1 is a 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 calculated by the following equation.

[0038]

[Equation 4]

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

[0040]

[Table 1] Variables that determine the resonance frequency of the diaphragm ―――――――――――――――――――――――――――――――――――― Variable Unit Meaning ――――――――――――――――――――――――――――――――――― α Coefficient by vibration mode. At the lowest order of square plate, α ≈ 35.99. ν Poisson's ratio of the whole diaphragm (here, 0.3). t [m] Total diaphragm thickness. t _i [m] 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.

[0042]

[Equation 5] When fr = 147 [kHz] and a = 0.5 [mm]

[Equation 6] When fr = 102 [kHz] and a = 0.6 [mm]

Since all of these values are material constants in bulk, there is a possibility that they will deviate from these values in a sensor formed of an actually manufactured thin film. The size of the array is actually limited by the chip size, which depends on the particular application. Here, a 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. In this package, the pins are arranged at 0.1-inch intervals, and the vertical and horizontal nines form a "B" shape, so the center of the pin is 0.8-inch square = 20.32mm square, and the mountable chip The size is about 19 mm. The size fits almost in a wristwatch. Considering these points, the ring array is arranged as shown in FIG. Two types of ultrasonic array sensor devices 30 having element sizes a = 0.5 mm and a = 0.6 mm were manufactured. Each element is
They are arranged at the vertices of the regular hexagon, the center, and the equal points of the sides, and the adjacent element intervals are b = 1.7 mm and b = 2.2 mm.
And Here, regarding the combination of the element size and the element spacing, a =
0.5 mm, b = 2.2 mm, and electronically scannable a = 0.6 mm, b = without influence of grating lobe
Two types of ultrasonic array sensor device 3 of 1.7 mm
It was set to 0.

The array arrangement shown in FIG. 2 makes it possible to construct an array of 37 ultrasonic sensor elements 20 in total at the center of the triple ring plus. With such a configuration, even if the characteristics of each element vary, a group of elements having relatively uniform characteristics is selected to configure a linear array or a small-scale ring array to perform characteristic evaluation. You can also

Next, the manufacturing process of the ultrasonic sensor element 20 will be described below. As described above, the thin plate structure is the 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
This is a film forming process in which a precursor solution in which a complex metal alkoxide solution has a viscosity adjusted by hydrolysis and polycondensation 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.

[0046]

[Table 2] Composition of PZT sol-gel precursor solution ―――――――――――――――――――――――――――――――――――― Solvent 2-methoxy Ethanol ―――――――――――――――――――――――――――――――――――― Pb component Lead acetate trihydrate Zr component Zr Normal butoxide Ti Ingredients Ti isopropoxide ―――――――――――――――――――――――――――――――――――― PZT composition Pb: Zr: Ti = 115: 52:48 Concentration Pb _1.15 Zr _0.52 Ti _0.48 O 15% as _3.15 % w t ――――――――――――――――――――――――――― ――――――――――

(A) A commercially available SOI (Sili
semiconductor chip wafer 1 having a con on insulator structure
0 is used. Here, the semiconductor chip wafer 10 has a thickness of 0.1 μm of SiO on the Si semiconductor substrate 10 having an insulating film layer 11 of SiO ₂ having a thickness of 0.4 μm on the back surface.
Si thickness 2.2μm through the insulating film layer 13 made at ₂
The semiconductor active layer 14 is formed. One 4-inch substrate is diced into two 2-inch octagons.
4 chips are arranged per 2 inch wafer.

(B) For mask during anisotropic etching and
Semiconductor chip wafer 1 for insulation between lower electrode layers 16
Both sides of 0 are thermally oxidized. At the furnace temperature of 1,000 ° C,
First O _TwoDry oxidation for 5 minutes with only 5.0 liters / minute
After doing O_Two(5.0 liters / minute) + H_Two(4.5 ri
Wet oxidize for 90 minutes at 90 minutes. Insulating film layer 17
Has a thickness of 0.38 to 0.44 μm, and EPW (Ethylene
diamine Pyrocatechol Water; ethylenediamine (strong
Lucarily liquid) and pyrocatechol (granular alco
Mixture of water) and water, anisotropic etching of silicon
It is an etching solution used for etching. ) Anisotropic etch
It is thick enough to withstand

(C) Pt / Ti is deposited as the lower electrode layer 16 by an RF sputtering device. Ar gas flow rate 44s
In an atmosphere of ccm and 1 Pa, first, Ti was changed to 5
Sputtering was performed at 00 W for 1 minute and then at 200 W for 10 minutes to obtain film thicknesses of 0.02 μm and 0.2 μm, respectively. The film cannot be heated during film formation because it is patterned by lift-off with a photoresist, but the formed film is processed by an X-ray diffractometer (hereinafter referred to as XRD).
When evaluated by (X-Ray Diffractometer), Pt (1
11) It has been confirmed that a sufficiently good quality thin film is formed as the lower electrode layer 16 of the PZT ceramics thin film layer 17 with a single orientation.

(D) As a window for anisotropic etching, the insulating film layer 11 on the back surface is covered with BHF (Buffered Hydro-Fluoric Acid).
d; Buffered hydrofluoric acid (weakly acidic liquid), that is, a mixed solution of hydrofluoric acid and ammonium fluoride, which is mainly used for etching silicon oxide. ) Etching solution. At this time, pattern matching is performed by a double-sided mask aligner so that the pattern of the window on the back surface exactly overlaps with 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. EPW is used as an etchant, and etching is performed at 114 ° C. for 8 to 10 hours. Although the etching rate slightly fluctuates in each etching hole in the semiconductor chip wafer 10, since the etching is almost stopped at the insulating film layer 13 which is the I layer of the SOI structure, the etching rate is adjusted to the etching hole having the slowest etching rate. By doing so, the diaphragm structure was completed.

(F) Insulating film layer 1 which is the I layer of the SOI structure
3 is indispensable as the above-mentioned anisotropic etching stop layer, but since it can cause internal stress in the final structure, it must be removed after the anisotropic etching is completed. 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 the sol-gel film forming method. After forming the piezoelectric layer, PZT ceramics was used as a contact hole for the lower electrode by using hydrofluoric nitric acid (HF: HNO ₃ : H ₂ O = 1: 1: 10).
Etching with 0). The time required to etch the PZT ceramic thin film layer 17 having a thickness of 1 μm is 1
0 to 30 seconds, the side etching amount at this time is 5 to 10
μm.

(H) A photoresist layer is formed and patterned as the insulating film layer 25 for short circuit protection of the PZT ceramics thin film layer 17 and area control of the upper electrode layer 18. To increase the resistance of photoresist to organic solvents,
The temperature is gradually raised from 120 ° C to 200 ° C by post-baking to cure. As a result, the resist becomes almost insoluble in acetone.

(I) Pt is deposited 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. As the upper electrode layer 18 of the ultrasonic sensor element 20, the electrode shape is formed by the photoresist layer in the step (h), so patterning is not particularly required. Further, since the high temperature baking in the step (h) causes a sufficiently gentle taper in the step portion of the resist, the upper electrode layer 18 is not broken. The lower electrode layer 1
Heat-resistant Kapton tape is used for masking the contact hole of No. 6.

After the ultrasonic sensor element 20 is manufactured by the above process, the octagonal 2-inch equivalent wafer 10 is diced to separate 4 chips, which are fixed in a package and bonded 19 to each electrode layer 16 and 18. After connecting the lead wires 21 and 22 by, the lead wires 21 and 22 are connected to the terminals T1 and T2 and bonded to complete the sensor chip.

Next, the ultrasonic array sensor device 3 in which the ultrasonic sensor elements 20 manufactured as described above are juxtaposed.
The "cause that object recognition is impossible" described in the section of the prior art in an object position measuring device by electronic scanning equipped with 0 will be considered.

In FIG. 13, there are large reflected waves near 3.4 ms and 4 ms, and it can be estimated that a reflecting object exists at a location corresponding to these delay times. It seems that many reflection waveforms are appearing. However, looking at this in detail, it can be seen that the sharp rising due to the reflection by the object is only around 3.4 ms and 4 ms, and the other peak waveforms have a dull rising shape. Suggests that the "beat phenomenon" is occurring. Actually, the signal waveform of FIG. 13 was Fourier-transformed to obtain the resonance frequency of each element, and the values were as shown in the following table.
It was found that there was a difference of 2.1 kHz. This is
It is in good agreement with the "beat" period of about 0.083 milliseconds shown in Fig. 4.

[0059]

[Table 3] Obtained from the received waveform in FIG. Resonant frequency of each ultrasonic sensor element 20 of the linear array ――――――――――――――――――――― Ultrasonic sensor element 20 resonance frequency ――――――――――――――――――――― 20-1 95.4 kHz 20-2 107.5 kHz 20-3 97.7 kHz 20-4 100.1 kHz ――――――――――――――――――――― (Note) Frequency resolution: 61Hz

In electronic scanning by delay addition, an incident wave from a specific direction causes a phase shift due to a difference in arrival time for each ultrasonic sensor element 20 due to the angle formed by the wavefront and the array surface 30s. It is possible to extract the specific direction component by electronically correcting the direction opposite to the deviation. However, when the frequencies of the signals output from the ultrasonic sensor elements 20 are not uniform, even if the ultrasonic sensor elements 20 have a correct phase relationship near the rising edge of the reflected wave, the signals are not completely attenuated by the time they are completely attenuated. A phase shift occurs due to the frequency difference between the ultrasonic sensor elements 20, and waves that should originally cancel each other remain or disappear, or waves that should strengthen each other in the same phase disappear. When the frequency difference between the ultrasonic sensor elements 20 is remarkable, it is considered that this phenomenon caused a “beat” and a signal waveform as shown in FIG. 14 was generated.

There are two possible methods for avoiding this "beat" phenomenon. One is to make the attenuation extremely steep so that the phase is completely attenuated before a large phase shift occurs, and the other is to make the resonance frequencies of the ultrasonic sensor elements 20 coincide with each other. The former means to make the mechanical Q value of the ultrasonic sensor element 20 extremely small,
In other words, the resonance is not used. However, since the current ultrasonic sensor element 20 obtains a large output by using resonance to obtain a large amplitude, lowering the Q value means lowering the sensitivity. At present, since the output signal from the ultrasonic sensor element 20 is on the order of 100 μV, if the sensitivity is lowered, it becomes difficult to detect the signal-to-noise power ratio (S / N). Therefore, here, the latter method of matching the resonance frequencies will be examined.

It is known that in a structure in which a ferroelectric film is formed on a diaphragm, its vibration frequency can be changed by applying a bias voltage (for example, in prior art document 1 “P. Muralt et al. , "Piezoelectric act
uation of PZT thin-film diaphragms at static and r
esonant conditions ", Sensors and Actuators, Elsevi
er Science SA, A53, pp.398-404, 1996 ”. ). This prior art document 1 discloses that the vibration frequency is changed by applying a bias voltage to the piezoelectric sensor.

Ultrasonic sensor element 2 manufactured as described above
16 to 19 show changes in the frequency characteristics of the capacitance with respect to 0 for the bias voltage. In this measurement, the frequency characteristic of the capacitance was measured using a signal in which the bias voltage shown below was superimposed on the AC signal of 50 mV. Here, the bias voltage was measured for these characteristics in the following cases. Further, the measured capacitance (electrostatic capacitance) is measured on the assumption that the equivalent circuit of the ferroelectric substance is a parallel circuit of a capacitor and a resistor.

(1) When the bias voltage is changed from 0V to 10V (FIG. 16). (2) When the bias voltage is changed from 10V to 0V (FIG. 17). (3) When the bias voltage is changed from 0V to −10V (FIG. 18). (4) When the bias voltage is changed from −10V to 0V (FIG. 19).

As is apparent from FIGS. 16 to 19, it can be seen that the resonance frequency is shifted with respect to the bias voltage. Also, for a bias voltage change from 10V to 0V and a bias voltage change from -10V to 0V,
The resonance frequency rises uniformly, but for the bias voltage conversion from 0V to 10V and the bias voltage change from 0V to -10V, the resonance frequency once rises and then falls. FIG. 20 shows a plot of the change in frequency at the resonance point against the bias voltage. A hysteresis with two peaks is drawn, and the appearance is C-V shown in Fig. 21.
It can be seen that the change is similar to the curve.

In this way, the resonance frequency can be adjusted by applying the bias voltage. As described above, during the measurement operation of the ultrasonic sensor element 20, a bias voltage that may damage the ferroelectric is not used, and a predetermined bias voltage is applied between the two electrodes 16 and 18. By applying, the resonance frequency of the ultrasonic sensor element 20 can be changed. In addition, as shown in FIG. 2, in the ultrasonic array sensor device 30 in which a plurality of ultrasonic sensor elements 20 are arranged side by side, during the measurement operation of the plurality of ultrasonic sensor elements 20, 2 By applying a predetermined bias voltage between the two electrodes 16 and 18, the resonance frequencies of the ultrasonic sensor elements 20 can be changed so as to substantially match each other. That is, according to the present embodiment, the resonance frequencies of the ultrasonic sensor elements 20 can be changed very easily and highly accurately, and the resonance frequencies of the plurality of ultrasonic sensor elements 20 can be substantially matched with each other. In the object position measuring device including the ultrasonic array sensor device 30 described above, the sensitivity of the sensor can be increased, and the object recognition including the position measurement of the measured objects 51 and 52 can be performed. It will be possible to do.

In the above embodiment, when the ultrasonic array sensor device 30, which is an array sensor, is used with the bias voltage applied during the measurement, the measuring circuit system for the output signal from each ultrasonic sensor element 20 is used. Complicates
Moreover, the application of the DC electric field for a long time causes a new problem that the PZT ceramic thin film layer 17 is damaged.

In order to solve this, the same effect as when a bias electric field is applied is obtained by a poling process for the ultrasonic sensor element 20 (a process in which a ferroelectric substance is in a remanent polarization state to orient molecules and fix an electric dipole). Tried to get by. By applying a predetermined DC voltage to the ferroelectric substance of each ultrasonic sensor element 20 and applying a DC electric field,
After performing polling for 1 minute in each electric field, a pulse ultrasonic wave was irradiated and the output signal was Fourier-transformed to calculate the resonance frequency of the ultrasonic sensor element 20 from the peak frequency. FIG. 22 shows the dependence of the mechanical resonance frequency of the ultrasonic sensor element 20 on the poling electric field. Figure 2
As is clear from 2, it is understood that a curve similar to the bias electric field dependency is drawn. Thereby, the resonance frequency can be tuned to a predetermined frequency without continuously applying the DC electric field.

Using this method, tuning is performed so that the resonance frequencies of the ultrasonic sensor elements 20 in the ultrasonic array sensor device 30 which is actually an array sensor substantially match each other, and the resonance frequencies are aligned. An ultrasonic array sensor device 30 which is an array sensor was formed, and an electronic scanning by delay addition similar to the conventional technique was tried. The arrangement of the elements is the same as that in FIG. 6A, and the arrangement of the ultrasonic sensor element 20, the ultrasonic sound source 40, and the measured objects 51 and 52 is also the same as that in FIG. 7.

FIG. 23 shows the waveform of the output signal from each ultrasonic sensor element 20 after tuning the resonance frequency. As is clear from FIG. 23, the reflected waves from the two measured objects 51 and 52 are clearly captured as in the past. Next, FIG. 24 shows a signal waveform obtained by performing delay addition using these waveforms. Since the resonance frequencies of the ultrasonic sensor elements 20 are the same, a "beat" does not occur, and the signal waveform indicates the presence of an object as in the case of the pseudo array.

Further, FIG. 25 shows the maximum amplitude and delay time of the waveform for each scanning angle. Two measured objects 51, 52
It is possible to clearly confirm the peak of the maximum amplitude value that indicates the presence of, and it is possible to easily determine the threshold value with 80% of the maximum value. FIG. 26 shows the result of reconstructing the object arrangement using the above-mentioned object position measuring device based on FIG.
As is apparent from FIG. 26, it can be seen that the object arrangement in the measurement system is reconstructed correctly, as in the case of the pseudo array.

As described above, according to this embodiment, before the measurement operation of the ultrasonic sensor element 20, a predetermined period between the two electrodes 16 and 18 is maintained for a predetermined period of time, for example, 1 second to 1 hour. By applying a voltage, a predetermined electric field is applied, and by polling the ultrasonic sensor element 20, the resonance frequency of the ultrasonic sensor element 20 can be changed. In addition, in the ultrasonic array sensor device 30, a plurality of ultrasonic sensor elements 20
Before the measurement operation of 1., a predetermined electric field is applied by applying a predetermined voltage between the two electrodes 16 and 18 of each ultrasonic sensor element 20 for a predetermined time of, for example, 1 second to 1 hour. By polling the plurality of ultrasonic sensor elements 20, the resonance frequencies of the ultrasonic sensor elements 20 can be changed so as to substantially match each other. That is, according to the present embodiment, the resonance frequencies of the ultrasonic sensor elements 20 can be changed very easily and highly accurately, and the resonance frequencies of the plurality of ultrasonic sensor elements 20 can be substantially matched with each other. In the object position measuring device including the ultrasonic array sensor device 30 described above, the sensitivity of the sensor can be increased, and the object recognition including the position measurement of the measured objects 51 and 52 can be performed. It will be possible to do.

In the above embodiment, the poling time may be a required time for completing polarization in a shorter time, but for example, preferably 1 second to 1 hour, more preferably 1 second to 10 minutes. , And even more preferably 1
Set to seconds to 1 minute. Note that it may be 1 second or less, for example, 10 seconds to 30 seconds.

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

In the above embodiment, the two electrodes 1
The electric field in the vertical direction (thickness direction) is applied to the ferroelectric substance by using the piezoelectric sensor made of the ferroelectric substance sandwiched by 6, 18; however, the present invention is not limited to this. First, by applying a bias voltage or a poling voltage to the two electrodes formed on the ferroelectric substance at a predetermined interval,
An electric field in the lateral direction (parallel plate direction) may be applied to the ferroelectric substance.

[0076]

As described above, according to the method of adjusting the resonance frequency of the ultrasonic sensor element according to the first invention of the present application, the ferroelectric substance is sandwiched between the two electrodes, and the predetermined resonance is achieved. A method of adjusting a resonance frequency of an ultrasonic sensor element, which comprises a piezoelectric sensor having a frequency to detect an ultrasonic wave, wherein a predetermined bias voltage is applied between the two electrodes during operation of the ultrasonic sensor element. Changing the resonance frequency of the ultrasonic sensor element by applying.
Therefore, by applying a predetermined bias voltage between the two electrodes during the operation of the ultrasonic sensor element,
The resonance frequency of each ultrasonic sensor element can be changed very easily and highly accurately.

Further, according to the method of adjusting the resonance frequency of the ultrasonic array sensor device according to the second invention of the present application, the ferroelectric substance is sandwiched between the two electrodes and has a predetermined resonance frequency. A method for adjusting an ultrasonic array sensor device, comprising a plurality of ultrasonic sensor elements, each of which is composed of a piezoelectric sensor for detecting ultrasonic waves, and arranged side by side. 2 of ultrasonic sensor element
A step of applying a predetermined bias voltage between the two electrodes to change the resonance frequencies of the ultrasonic sensor elements to substantially match each other.
Therefore, the resonance frequency of each ultrasonic sensor element can be changed very easily and highly accurately, and the resonance frequencies of a plurality of ultrasonic sensor elements can be substantially matched with each other (can be aligned). In the object position measuring device equipped with the ultrasonic array sensor device, the sensitivity of the sensor can be increased and the object recognition including the position measurement of the measured object can be performed.

Further, according to the method of adjusting the resonance frequency of the ultrasonic sensor element according to the third aspect of the present invention, the ferroelectric substance is sandwiched between the two electrodes, and the ultrasonic wave has a predetermined resonance frequency. A method of adjusting a resonance frequency of an ultrasonic sensor element including a piezoelectric sensor that detects a sound wave, wherein a predetermined voltage is applied between the two electrodes for a predetermined time before the operation of the ultrasonic sensor element. Thus, a step of applying a predetermined electric field to polling the ultrasonic sensor element to change the resonance frequency of the ultrasonic sensor element is included. Therefore, before the operation of the ultrasonic sensor element, by applying a predetermined bias voltage between the two electrodes without using a bias voltage that may damage the ferroelectric substance, it is possible to achieve extremely high voltage. The resonance frequency of each ultrasonic sensor element can be changed with accuracy.

Furthermore, according to the resonance frequency adjusting method of the ultrasonic array sensor device in the fourth aspect of the present invention,
An ultrasonic array sensor device in which a ferroelectric material is sandwiched between two electrodes, and a plurality of ultrasonic sensor elements each having a predetermined resonance frequency and configured to detect ultrasonic waves are arranged side by side. And a predetermined electric field by applying a predetermined voltage between two electrodes of each of the ultrasonic sensor elements for a predetermined time before the plurality of ultrasonic sensor elements operate. Applying and polling the plurality of ultrasonic sensor elements to change the resonance frequencies of the ultrasonic sensor elements to substantially match each other. Therefore, before the operation of the ultrasonic sensor element, it is possible to change the resonance frequency of each ultrasonic sensor element very easily and highly accurately without using the bias voltage that may damage the ferroelectric substance. It is possible to make the resonance frequencies of the plurality of ultrasonic sensor elements substantially coincide with each other (can be aligned), and to enhance the sensitivity of the sensor in the object position measuring device equipped with the ultrasonic array sensor device. Therefore, it is possible to perform object recognition including position measurement of the measured object.

According to the ultrasonic sensor element of the fifth invention of the present application, the resonance frequency of the ultrasonic sensor element is adjusted to a predetermined resonance by using the method of adjusting the resonance frequency of the ultrasonic sensor element of the first invention. Set to frequency. Therefore, it is possible to provide an ultrasonic sensor element capable of changing the resonance frequency of each ultrasonic sensor element very easily and highly accurately.

Further, according to the ultrasonic array sensor device of the sixth invention of the present application, a plurality of ultrasonic sensor elements are formed by using the resonance frequency adjusting method of the ultrasonic array sensor device of the second invention. The resonance frequency was set to a predetermined same resonance frequency. Therefore, it is possible to provide an ultrasonic array sensor device capable of changing the resonance frequency of each ultrasonic sensor element very easily and with high accuracy and aligning the resonance frequencies of a plurality of ultrasonic sensor elements.

Further, according to the ultrasonic sensor element of the seventh invention of the present application, the resonance frequency of the ultrasonic sensor element is set to a predetermined value by using the method of adjusting the resonance frequency of the ultrasonic sensor element of the third invention. Set to the resonance frequency of. Therefore,
Before operating the ultrasonic sensor elements, it is possible to change the resonance frequency of each ultrasonic sensor element very easily and with high accuracy without using a bias voltage that may damage the ferroelectric substance. A sound wave sensor element can be provided.

Furthermore, according to the ultrasonic array sensor device of the eighth invention of the present application, a plurality of ultrasonic sensor elements are formed by using the resonance frequency adjusting method of the ultrasonic array sensor device of the fourth invention. The resonance frequency of 1 was set to a predetermined same resonance frequency. Therefore, the resonance frequency of each ultrasonic sensor element can be changed very easily and with high accuracy without using the bias voltage that may damage the ferroelectric substance. An ultrasonic array sensor device that can be aligned can be provided.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of an ultrasonic sensor element 20 according to an embodiment of the present invention.

FIG. 2 is a top view showing an ultrasonic array sensor device 30 showing an element arrangement when a plurality of ultrasonic sensor elements 20 shown in FIG. 1 are arranged in an array.

FIG. 3 is a schematic diagram showing a method for measuring the position of an object using ultrasonic waves in the related art.

FIG. 4 is a block diagram showing a circuit portion of an object position measuring device using the object position measuring method of FIG.

5 is a waveform diagram showing signal waveforms at various portions in the circuit portion of the object position measuring device shown in FIG.

6A is a top view showing an arrangement and an azimuth angle of an ultrasonic sensor element 20 in a 4-element linear pseudo array when the position measuring method of FIG. 3 is used, and FIG. 4 is a graph showing directional characteristics in the 4-element linear pseudo array of FIG.

7 is a schematic block diagram showing the configuration of an object position measuring device by electronic scanning using the 4-element linear pseudo array of FIG. 6 (a).

8 is a waveform diagram showing a received waveform of each ultrasonic sensor element in the object position measuring device by electronic scanning in FIG.

9 is a waveform diagram showing each signal waveform after delay addition in a four-element linear pseudo array in the object position measuring device by electronic scanning in FIG. 7.

10 is a waveform diagram showing a reference for measuring an object position from a signal waveform after delay addition in the waveform diagram of FIG.

11 is a graph showing the electronic scanning azimuth angle dependence characteristics of the maximum amplitude of the reflection waveform and the delay time in the electronic position measuring device by electronic scanning of FIG.

12 is a top view showing an object arrangement measured by the electronic position measuring device by electronic scanning shown in FIG. 7. FIG.

13 is a waveform diagram showing a reception waveform of each ultrasonic sensor element 20 in a linear array in the object position measuring device by electronic scanning in FIG.

14 is a waveform diagram showing each signal waveform after delay addition in a linear array in the object position measuring device by electronic scanning in FIG.

15 is a graph showing an electronic scanning azimuth angle dependence characteristic of a maximum amplitude and a delay time in a linear array in the object position measuring device by electronic scanning in FIG.

16 is a diagram showing an ultrasonic sensor device 20 used in the electronic scanning object position measuring apparatus of FIG.
It is a graph which shows the bias voltage dependence characteristic of the frequency characteristic of capacitance when changing from V to 10V.

17 is a diagram showing an ultrasonic sensor element 20 used in the electronic scanning object position measuring apparatus of FIG.
It is a graph which shows the bias voltage dependence characteristic of the frequency characteristic of capacitance when changing from 0V to 0V.

18 is a diagram showing an ultrasonic sensor element 20 used in the object position measuring apparatus using electronic scanning shown in FIG.
It is a graph which shows the bias voltage dependence characteristic of the frequency characteristic of capacitance when changing from V to -10V.

FIG. 19 shows a bias voltage of − in the ultrasonic sensor element 20 used in the object position measuring apparatus by electronic scanning in FIG.
It is a graph which shows the bias voltage dependence characteristic of the frequency characteristic of a capacitance when changing from 10V to 0V.

20 is a graph showing a bias voltage dependence characteristic of a resonance frequency in the ultrasonic sensor element 20 used in the object position measuring device by electronic scanning in FIG. 7. FIG.

21 is a graph showing a bias voltage dependence characteristic of capacitance in the ultrasonic sensor element 20 used in the object position measuring apparatus by electronic scanning in FIG. 7. FIG.

22 is a graph showing a polling voltage dependence characteristic of a resonance frequency in the ultrasonic sensor element 20 used in the object position measuring device by electronic scanning in FIG. 7. FIG.

FIG. 23 is a waveform diagram showing a reception waveform of each ultrasonic sensor element 20 in the frequency-tuned linear array ultrasonic sensor device 30 according to the present embodiment.

FIG. 24 is a waveform diagram showing a signal waveform after delay addition in the linear array ultrasonic sensor device 30 with frequency tuning according to the present embodiment.

FIG. 25 is a graph showing the electronic scanning azimuth angle dependence characteristics of the maximum amplitude of the reflected waveform and the delay time in the frequency-tuned linear array ultrasonic sensor device 30 according to the present embodiment.

FIG. 26 is a top view showing an object position reconstructed and measured by electronic scanning in the frequency-tuned linear array ultrasonic sensor device 30 according to the present embodiment.

[Explanation of symbols]

10 ... Semiconductor chip wafer, 11 ... Semiconductor substrate, 12, 13, 15, 25 ... Insulating film layer, 14 ... Semiconductor active layer, 16, 18 ... Electrode layer, 17 ... PZT ceramic thin film layer 19 ... Bonding, 20, 20-1 to 20-5 ... Ultrasonic sensor element, 21, 22 ... Lead wire, 30 ... Ultrasonic array sensor device, 31-1 to 31-5 ... Variable delay device, 32 ... adder, 40 ... Ultrasonic sound source, 51, 52 ... Object to be measured, 60 ... computer, T1, T2 ... terminals.

Front page continuation (51) Int.Cl. ⁷ identification code FI theme code (reference) H04R 1/22 330 G01S 7/52 A 17/00 332 H01L 41/08 Z

Claims (8)

[Claims] 1. A ferroelectric material sandwiched between two electrodes,
A method of adjusting the resonance frequency of an ultrasonic sensor element, which comprises a piezoelectric sensor having a predetermined resonance frequency and detecting ultrasonic waves, comprising:
A method of adjusting the resonance frequency of an ultrasonic sensor element, comprising the step of changing the resonance frequency of the ultrasonic sensor element by applying a predetermined bias voltage between two electrodes. 2. A ferroelectric material sandwiched between two electrodes,
A method for adjusting an ultrasonic array sensor device comprising a plurality of ultrasonic sensor elements arranged side by side, each of which is a piezoelectric sensor for detecting ultrasonic waves having a predetermined resonance frequency.
By applying a predetermined bias voltage between the two electrodes of each of the ultrasonic sensor elements during the operation of the plurality of ultrasonic sensor elements, the resonance frequencies of the ultrasonic sensor elements substantially match each other. A method of adjusting the resonance frequency of an ultrasonic array sensor device, comprising the step of: 3. A ferroelectric material sandwiched between two electrodes,
A method for adjusting a resonance frequency of an ultrasonic sensor element, which comprises a piezoelectric sensor having a predetermined resonance frequency for detecting an ultrasonic wave, comprising the steps of: A predetermined electric field is applied by applying a predetermined voltage between the electrodes, and the resonance frequency of the ultrasonic sensor element is changed by performing polling on the ultrasonic sensor element. Method for adjusting resonance frequency of ultrasonic sensor element. 4. A ferroelectric is sandwiched between two electrodes,
A method for adjusting an ultrasonic array sensor device comprising a plurality of ultrasonic sensor elements arranged side by side, each of which is a piezoelectric sensor for detecting ultrasonic waves having a predetermined resonance frequency.
Prior to the operation of the plurality of ultrasonic sensor elements, a predetermined electric field is applied by applying a predetermined voltage between the two electrodes of each of the ultrasonic sensor elements for a predetermined time, thereby applying a plurality of ultrasonic waves to the plurality of ultrasonic sensors. A method of adjusting the resonance frequency of an ultrasonic array sensor device, comprising the step of changing the resonance frequencies of the ultrasonic sensor elements so as to substantially match each other by polling the ultrasonic sensor elements. . 5. An ultrasonic sensor element, wherein the resonant frequency of the ultrasonic sensor element is set to a predetermined resonant frequency by using the method for adjusting the resonant frequency of the ultrasonic sensor element according to claim 1. 6. An ultrasonic wave wherein the resonance frequency of a plurality of ultrasonic sensor elements is set to a predetermined same resonance frequency by using the method of adjusting the resonance frequency of an ultrasonic array sensor device according to claim 2. Array sensor device. 7. An ultrasonic sensor element, wherein the resonant frequency of the ultrasonic sensor element is set to a predetermined resonant frequency by using the method for adjusting the resonant frequency of the ultrasonic sensor element according to claim 3. 8. An ultrasonic wave, wherein the resonance frequency of a plurality of ultrasonic sensor elements is set to a predetermined same resonance frequency by using the resonance frequency adjusting method of the ultrasonic array sensor device according to claim 4. Array sensor device.