JP3608499B2 - Material constant measuring device for piezoelectric substrate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a material constant measuring apparatus for measuring a material constant of a piezoelectric substrate cut out from a piezoelectric single crystal.
[0002]
[Prior art]
It is well known that the material constants of a piezoelectric single crystal, such as density and sound velocity, depend on the crystal composition and growth conditions. Therefore, it is necessary to measure the material constant of a substrate cut out from each position of the piezoelectric single crystal (hereinafter referred to as a piezoelectric substrate) and evaluate the crystal uniformity.
[0003]
As a method for evaluating the uniformity, when the piezoelectric single crystal is a paraelectric material such as La ₃ Ga ₅ Si O ₁₄ (Langasite), a SAW device is provided on the piezoelectric substrate, and the center frequency is measured by measuring the center frequency. Uniformity evaluation is performed.
[0004]
By the way, when evaluating a dielectric piezoelectric single crystal, the measurement of the center frequency is easily influenced by the surface condition of the piezoelectric substrate, the design of the SAW device, the reproducibility of the evaluation process, and the like, so the reliability of the measurement results is low. . In addition, there are problems that the work time of the evaluation process is long and the work efficiency is low.
[0005]
Therefore, a method has been developed in which the resonance frequency of the thickness-shear vibration and the substrate thickness are measured for each part of the piezoelectric substrate, and the material constant of the piezoelectric substrate is obtained based on these measurement data. If this method is adopted, it is not necessary to install a SAW device as in the prior art, and the time required for measurement is greatly reduced. In addition, since the piezoelectric substrate is not destroyed by the installation of the SAW device, it is possible to carry out measurement even for products shipped as products.
[0006]
[Problems to be solved by the invention]
The following problems have been pointed out in conducting the material constant measurement as described above.
To measure the resonance frequency of a piezoelectric substrate, first place measurement probes on both sides of the piezoelectric substrate, bring the measurement electrodes of both probes into contact with the measurement points on the piezoelectric substrate, and then send an AC signal. Transmits to excite the piezoelectric substrate. Then, the frequency scan of the AC signal is performed to detect the frequency dependence between the impedance and the phase at the measurement location, and the waveform indicating the frequency dependence is analyzed to obtain the resonance frequency.
[0007]
However, when the piezoelectric substrate is excited as described above, excitation occurs also at a part other than the measurement location, and the resonance signal and noise generated at the measurement site are detected by the measurement probe. Therefore, accurate measurement can be performed. There is no.
[0008]
The present invention has been made in view of the above circumstances, and provides an apparatus for measuring the material constant of a piezoelectric substrate so that the uniformity evaluation of a piezoelectric single crystal can be performed accurately and in a short time. The purpose is to do.
[0009]
[Means for Solving the Problems]
As means for solving the above problems, a material constant measuring apparatus for a piezoelectric substrate having the following configuration is employed. In other words, the material constant measuring apparatus for a piezoelectric substrate according to claim 1 of the present invention includes two measuring probes individually disposed on the front and back sides of the piezoelectric substrate cut out from the piezoelectric single crystal body, A material constant measuring apparatus for a piezoelectric substrate comprising probe supporting means for supporting the piezoelectric substrate so as to be able to approach and separate, wherein the measuring probe has a measuring electrode in contact with the piezoelectric substrate, and is disposed around the measuring electrode. An elastic body that abuts against the piezoelectric substrate is provided.
[0010]
In this material constant measuring apparatus for a piezoelectric substrate, an elastic body that abuts the piezoelectric substrate is provided around the measurement electrode of the measurement probe, so that resonance signals and noise generated at portions other than the portion where the measurement electrode abuts are elastic. Since they are absorbed by the body, they are difficult to detect by the measurement probe.
[0011]
The piezoelectric substrate material constant measuring apparatus according to claim 2 is the piezoelectric substrate material constant measuring apparatus according to claim 1, wherein the elastic body is annular.
[0012]
In this material constant measuring apparatus for a piezoelectric substrate, by making the elastic body annular, even if a resonance signal or noise is transmitted from any surrounding direction to the place where the measurement electrode contacts, this is absorbed by the elastic body. Therefore, it is possible to capture only the resonance signal generated at the measurement location, and accurate measurement can be performed based on this.
[0013]
The piezoelectric substrate material constant measuring apparatus according to claim 3 is the piezoelectric substrate material constant measuring apparatus according to claim 1 or 2 , wherein biasing means for pressing the measurement probe in a direction substantially perpendicular to the piezoelectric substrate is provided. It is provided.
[0014]
In this material constant measuring device for a piezoelectric substrate, by providing a biasing means for pressing the measurement probe in a direction substantially perpendicular to the piezoelectric substrate, the pressure at which the measurement electrode contacts the piezoelectric substrate is uniform between the two measurement probes. As a result, the measurement conditions become equal, and more accurate measurement can be performed.
[0015]
The material constant measuring device for a piezoelectric substrate according to claim 4 is the material constant measuring device for a piezoelectric substrate according to claim 1, 2 or 3 , wherein the measuring electrode has a gold electrode portion attached to a base having elasticity. It is characterized by being.
[0016]
In this material constant measuring apparatus for a piezoelectric substrate, the measurement electrode is made by attaching a gold electrode portion to an elastic base portion, so that the conductivity is high and the elasticity of the base portion makes contact with the piezoelectric substrate. The entire electrode is satisfactorily made without deviation.
[0017]
6. The material constant measuring apparatus for a piezoelectric substrate according to claim 5, wherein two measuring probes individually arranged on both the front and back sides of the piezoelectric substrate cut out from the piezoelectric single crystal body, and the measuring probes approaching each other with the piezoelectric substrate interposed therebetween. Probe support means for supporting the separation of the piezoelectric substrate, a frequency measurement unit for measuring the resonance frequency of the thickness-shear vibration at each location of the piezoelectric substrate, and a thickness measurement unit for measuring the substrate thickness at each location. A material constant measuring device for a piezoelectric substrate,
An elastic body that abuts on the piezoelectric substrate is provided around the measurement electrode of the measurement probe.
[0018]
In this material constant measuring apparatus for a piezoelectric substrate, for a piezoelectric substrate cut out from a piezoelectric single crystal, the resonance frequency of the thickness-shear vibration and the substrate thickness are measured for each part of the piezoelectric substrate, and the measured values are multiplied. A material constant for each part of the piezoelectric substrate is calculated.
[0019]
The relationship between the resonance frequency of the thickness shear vibration and the material constant for the piezoelectric substrate is shown in the following equation.
f = (E / ρ) ^1/2 / (2t) (I)
f: resonance frequency, t: substrate thickness, ρ: crystal density, E: elastic constant determined by crystal direction. Here, when formula (I) is arranged,
f · t = (E / ρ) ^1/2/2 (I ′)
Thus, by obtaining the values of f and t and further obtaining the product, a material constant corresponding to the right side of the formula (I ′) can be obtained. Note that f · t can be regarded as the bulk wave velocity in the piezoelectric substrate.
[0020]
According to this material constant measuring apparatus for a piezoelectric substrate, since it is not necessary to install a SAW device as in the prior art, the time required for measurement is greatly reduced. In addition, since the piezoelectric substrate is not destroyed by the installation of the SAW device, it is possible to carry out measurement even for products shipped as products.
[0021]
The material constant measuring apparatus for a piezoelectric substrate according to claim 6 is the material constant measuring apparatus for a piezoelectric substrate according to claim 5, wherein the resonance frequency measured by the frequency measuring section and the substrate thickness measured by the thickness measuring section. And an arithmetic unit that calculates a material constant for each location.
[0022]
In this material constant measuring device for a piezoelectric substrate, the resonance frequency of the thickness shear vibration is measured by the frequency measuring unit and the substrate thickness is measured by the thickness measuring unit for each part of the piezoelectric substrate cut out from the piezoelectric single crystal. The calculation unit calculates the material constant by calculating the product of the resonance frequency and the substrate thickness for each part of the piezoelectric substrate.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment according to the present invention will be described with reference to FIGS.
FIG. 1 is a diagram showing a schematic configuration of a bulk wave measurement unit 1 constituting a frequency measurement unit. As shown in the figure, the bulk wave measurement unit 1 includes a substrate support mechanism 11 that supports the piezoelectric substrate P, measurement probes 12 and 13 that are individually disposed on both sides of the piezoelectric substrate P, and measurement probes 12 and 13. A probe support mechanism (probe support means) 14 that supports the impedance, an impedance analyzer 15 that drives the measurement probes 12 and 13 to measure the impedance of the piezoelectric substrate P and the frequency dependence of the phase, the substrate support mechanism 11 and the probe And a control device 16 for controlling the driving of the support mechanism 14.
[0024]
The substrate support mechanism 11 supports the supported piezoelectric substrate P so as to be movable in two directions parallel to and orthogonal to the substrate surface (these are the X direction and the Y direction). Measuring probes 12 and 13 can be arranged at various places.
[0025]
The probe support mechanism 14 supports the supported measurement probes 12 and 13 so as to be close to and away from the direction perpendicular to the substrate surface (this is the Z direction) with the piezoelectric substrate P interposed therebetween. When probing is performed, the measurement probes 12 and 13 can be brought close to the front and back surfaces of the piezoelectric substrate P, respectively.
[0026]
FIG. 2 is a diagram showing the structures of the measurement probes 12 and 13 and their surroundings. In the figure, reference numerals 12a and 13a denote measurement electrodes of the probes, 17 denotes a shaft body to which the measurement electrodes 12a and 13a are attached, 18 denotes a cylinder that supports the shaft body 17, and 19 biases the shaft body 17 against the cylinder 18. A spring (biasing means) 20 is an absorption ring made of an elastic body.
[0027]
Each of the measurement electrodes 12a and 13a has a structure in which gold electrode portions 12c and 13c are attached to the base portions 12b and 13b having elasticity, and is formed at one end of the shaft body 17 in parallel with the substrate surface of the piezoelectric substrate P. The plate-like portion 17a is attached so as to face the front and back substrate surfaces.
[0028]
The cylinder 18 is fixed to an arm constituting the probe support mechanism 14 and supports the shaft body 17 so as to be movable in the Z direction. The spring 19 is interposed between the cylinder 18 and the shaft body 17, and biases the shaft body 17 (that is, the measurement electrodes 12a and 13a) in the Z direction (or -Z direction). A bulging portion 17b is provided at the other end of the shaft body 17, and has a function as a stopper for regulating the movement range in the Z direction of the measurement probes 12, 13 together with the plate-like portion 17a at one end. .
[0029]
The absorbing ring 20 is made of an elastic material such as rubber that can be easily deformed, and is arranged in an annular shape so as to surround the measurement electrodes 12a and 13a on the plate-like portion 17a.
[0030]
FIG. 3 is a diagram showing a schematic configuration of the thickness distribution measuring unit 2 constituting the thickness measuring unit. As shown in the figure, the thickness distribution measuring unit 2 includes a light source 21 that emits a He—Ne laser, an optical element 22 that converts laser light into parallel light, and transmits the laser light from one surface to the other surface. The semi-reflective mirror 23 to be reflected, the substrate support 24 for supporting the piezoelectric substrate P so as to be perpendicular to the laser light at a position facing the light source 21 with the semi-reflective mirror 23 interposed therebetween, A screen 25 on which reflected light reflected on the surface of the image is projected, a digital camera 26 that captures interference fringes of the reflected light projected on the screen 25, and an image analysis device 27 that analyzes the digital image captured by the digital camera 26. And.
[0031]
The impedance analyzer 15 and the control device 16 in the bulk wave measurement unit 1 and the digital camera 26 in the thickness distribution measurement unit 2 are connected to a main computer 31 having a calculation unit 30 that controls and controls all of them.
[0032]
An operation procedure for measuring the material constant of the piezoelectric substrate P using the piezoelectric substrate material constant measuring apparatus including the bulk wave measuring unit 1, the thickness distribution measuring unit 2, and the main computer 31 will be described.
[Measurement of resonance frequency]
The piezoelectric substrate P cut out from the piezoelectric single crystal is set on the substrate support mechanism 11 and fixed so as not to be displaced. When the substrate support mechanism 11 is driven from this state, the piezoelectric substrate P is moved stepwise in the X / Y direction, and the measurement probes 12 and 13 for each of a plurality of measurement points provided on the piezoelectric substrate P. Are arranged in order, and probing is performed at each location.
[0033]
When the measurement probes 12 and 13 are arranged on both the front and back sides of the piezoelectric substrate P across a certain measurement location, the probe support mechanism 14 is driven, and the measurement probes 12 and 13 move in the Z direction (or -Z direction). It approaches in synchronism with the front and back surfaces of the piezoelectric substrate P.
[0034]
When the measurement electrodes 12a and 13a of the measurement probes 12 and 13 are both in contact with the piezoelectric substrate P, an AC signal is emitted from the impedance analyzer 15, and the piezoelectric substrate P is excited through the measurement electrodes 12a and 13a.
[0035]
Therefore, the frequency dependence of the impedance and phase at the measurement location is detected by frequency scanning of the AC signal. This measurement data is input to the main computer 31. In the main computer 31, the calculation unit 30 analyzes a waveform indicating frequency dependence to obtain the resonance frequency.
[0036]
When the information on the resonance frequency is obtained, the measurement probes 12 and 13 move in the opposite direction and are separated from the piezoelectric substrate P. In synchronization with this, the substrate support mechanism 11 is driven in the X / Y direction, and the piezoelectric substrate P is moved to place the next measurement location between the measurement probes 12 and 13.
Thereafter, the above procedure is repeated, and the resonance frequency is obtained for all measurement points on the piezoelectric substrate P.
[0037]
[Measurement of substrate thickness]
The piezoelectric substrate P is fixed to the substrate support 24 so as not to be displaced. From this state, when laser light is emitted from the light source 21 toward the optical element 22, the laser light is converted into parallel light, which passes through the semi-reflective mirror 23 and is irradiated onto the piezoelectric substrate P.
[0038]
A part of the irradiated laser light is reflected on the surface of the piezoelectric substrate P, and the rest is reflected on the back surface of the piezoelectric substrate P. At this time, the thickness of the piezoelectric substrate P is twice between the laser light reflected on the front surface (hereinafter referred to as front surface reflected light) and the laser light reflected on the back surface (hereinafter referred to as back surface reflected light). An optical path length difference corresponding to this occurs.
[0039]
The front surface reflected light and the back surface reflected light are reflected by the other surface of the semi-reflective mirror 23 while interfering with each other, and are projected on the screen 25, so that interference fringes depending on the optical path length difference are generated on the screen 25. One interference fringe can be regarded as a contour line representing the same thickness on the piezoelectric substrate P. The difference in thickness between adjacent interference fringes is expressed by λ ₀ / (2n) (λ ₀ ; wavelength of laser light in vacuum, n: refractive index of piezoelectric substrate P).
[0040]
When the incident angle of the front / back surface reflected light is changed, a change occurs in the interference fringes, and this is photographed by the digital camera 26. When the photographed digital image is analyzed by the image analyzer 27, the thick part and the thin part of the piezoelectric substrate P can be grasped relatively. These analysis data are input to the main computer 31 and based on the thickness of a representative portion of the piezoelectric substrate P measured in advance with a precise micrometer, the arithmetic unit 30 determines the thickness of the entire piezoelectric substrate P. Distribution is obtained.
[0041]
Once the thickness distribution information is obtained, the material constants for each measurement point on the piezoelectric substrate P are calculated in combination with the previously obtained resonance frequency information. Based on this, the material constants are evaluated. Do.
[0042]
Since the measurement can be performed without providing a SAW device, the time required to manufacture the SAW device can be shortened, so that the uniformity evaluation of the piezoelectric single crystal can be performed in a short time. can do. In addition, since the piezoelectric substrate is not destroyed by the installation of the SAW device, it is possible to carry out measurement even for products shipped as products.
[0043]
Further, when the measurement probes 12 and 13 are pressed in a direction substantially perpendicular to the piezoelectric substrate P by the action of the spring 20, the pressure when the measurement electrodes 12 a and 13 a are in contact with the piezoelectric substrate P is increased. 13 is uniformized, the measurement conditions are equal, and more accurate measurement can be performed.
[0044]
Furthermore, the measurement electrodes 12a and 13a have a structure in which the gold electrode portions 12c and 13c are attached to the base portions 12b and 13b having elasticity, so that the conductivity is high and the contact with the piezoelectric substrate is achieved by the elasticity of the base portion. The entire electrode is satisfactorily made without unevenness.
[0045]
In this embodiment, the control device 16 in the bulk wave measurement unit 1 and the image analysis device 27 in the thickness distribution measurement unit 2 are provided separately from the main computer 31, but these functions are provided in the main computer 31. You may comprise so that it may be performed.
[0046]
【The invention's effect】
As described above, according to the present invention, by providing an elastic body that comes into contact with the piezoelectric substrate around the measurement electrode of the measurement probe, resonance signals and noise generated in parts other than the place where the measurement electrode comes into contact can be prevented. Since it is absorbed by the elastic body, it is possible to capture only the resonance signal generated at the measurement location, and accurate measurement can be performed based on this. As a result, the uniformity evaluation of the piezoelectric single crystal can be performed accurately and in a short time.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an embodiment according to the present invention, and is a diagram illustrating a schematic configuration of a bulk wave measurement unit constituting a frequency measurement unit.
FIG. 2 is a diagram showing a measurement probe and its surrounding structure.
FIG. 3 is a diagram showing a schematic configuration of a thickness distribution measuring unit constituting a thickness measuring unit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Bulk wave measurement unit 11 Substrate support mechanism 12, 13 Measurement probe 14 Probe support mechanism 15 Impedance analyzer 20 Spring (biasing means)
30 arithmetic unit 31 main computer P piezoelectric substrate

Claims (6)

Two measurement probes individually disposed on both sides of the piezoelectric substrate cut out from the piezoelectric single crystal;
A material constant measuring device for a piezoelectric substrate, comprising probe support means for supporting the measurement probe so as to be able to approach and separate with the piezoelectric substrate interposed therebetween,
The measurement probe has a measurement electrode in contact with the piezoelectric substrate;
An apparatus for measuring a material constant of a piezoelectric substrate, wherein an elastic body that contacts the piezoelectric substrate is provided around the measurement electrode. 2. The material constant measuring apparatus for a piezoelectric substrate according to claim 1, wherein the elastic body is annular. 3. An apparatus for measuring a material constant of a piezoelectric substrate according to claim 1 , further comprising biasing means for pressing the measurement probe in a direction substantially perpendicular to the piezoelectric substrate. 4. The material constant measuring apparatus for a piezoelectric substrate according to claim 1, wherein the measurement electrode is a base having elasticity and a gold electrode part pasted thereon. Two measurement probes individually disposed on the front and back sides of the piezoelectric substrate cut out from the piezoelectric single crystal body, and probe support means for supporting the measurement probes so that they can be approached and separated with the piezoelectric substrate interposed therebetween, A frequency measurement unit that measures the resonance frequency of thickness-shear vibration for each part of the piezoelectric substrate;
A material constant measuring device for a piezoelectric substrate comprising a thickness measuring unit for measuring a substrate thickness for each of the above-mentioned locations,
An apparatus for measuring a material constant of a piezoelectric substrate, wherein an elastic body that contacts the piezoelectric substrate is provided around a measurement electrode of the measurement probe. 6. The piezoelectric device according to claim 5, further comprising an arithmetic unit that calculates a material constant for each part by multiplying a resonance frequency measured by the frequency measuring unit and a substrate thickness measured by the thickness measuring unit. Equipment for measuring substrate material constants.

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