JP3915582B2 - 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 uniformity, when the piezoelectric single crystal is a ferroelectric such as Li Ta O ₃ , the Curie temperature of the crystal (the temperature at which the phase changes from the ferroelectric phase to the paraelectric phase) strongly depends on the composition. The uniformity of the crystal is evaluated by utilizing the properties of
[0004]
On the other hand, when the piezoelectric single crystal is a paraelectric material such as La ₃ Ga ₅ SiO ₁₄ (Langasite), it does not have a Curie temperature. Therefore, a SAW device is provided on the piezoelectric substrate, and the uniformity of the crystal is evaluated by measuring the center frequency.
[0005]
[Problems to be solved by the invention]
When the paraelectric piezoelectric single crystal is evaluated as described above, 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, etc. The reliability of the results is low. In addition, there is a problem that work time of the evaluation process is long and work efficiency is low.
[0006]
Furthermore, since this evaluation process causes the piezoelectric substrate to lose its value as a product by installing the SAW device, it is also problematic that it cannot be applied to the shipment inspection of the piezoelectric substrate.
[0007]
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 in order to accurately evaluate the uniformity of a piezoelectric single crystal in a short time. It is an object.
[0008]
[Means for Solving the Problems]
As a means for solving the above problems, adopting a material measuring apparatus of the piezoelectric substrate of the following configuration.
In other words, the material constant measuring apparatus for a piezoelectric substrate according to the present invention includes two frequency measurement probes individually disposed on both sides of a piezoelectric substrate cut out from a piezoelectric single crystal, and approaching and separating from each other with the piezoelectric substrate interposed therebetween. A frequency measuring unit that supports the two frequency measuring probes in contact with the piezoelectric substrate and measures a resonance frequency of thickness-shear vibration at an arbitrary position sandwiched between the two probes;
A thickness measuring unit for measuring the thickness of a substrate at an arbitrary position sandwiched between the two measuring elements by bringing two thickness measuring elements individually disposed on both sides of the piezoelectric substrate into contact with the piezoelectric substrate; A material constant measuring device for a piezoelectric substrate comprising:
The frequency measuring probe and the thickness measuring element disposed on the same side of the piezoelectric substrate are provided with a through-hole penetrating in the thickness direction of the piezoelectric substrate at the center of the frequency measuring probe. The thickness gauge is inserted in the cable .
[0009]
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) (1)
f: resonance frequency, t: substrate thickness, ρ: crystal density, E: elastic constant determined by crystal direction.
Here, when formula (1) is arranged,
f · t = (E / ρ) ^1/2 / 2 (2)
Thus, by obtaining the values of f and t and further obtaining the product, a material constant corresponding to the right side of the equation (2) can be obtained. Note that f · t can be regarded as the bulk wave velocity in the piezoelectric substrate.
[0010]
In this material constant measuring apparatus for a piezoelectric substrate, the resonance frequency of the thickness shear vibration is measured by a frequency measuring unit at any part of the piezoelectric substrate cut out from the piezoelectric single crystal, and the thickness of the substrate is measured by the thickness measuring unit. Measure and substitute the measurement results into the above equation (2) to calculate the material constants (bulk wave sound velocity) at each location, but it is not necessary to install a conventional SAW device, a frequency measurement probe and By performing the frequency measurement and the thickness measurement at the same time by integrating the thickness gauge, the time required for the measurement is greatly shortened. In addition, since the piezoelectric substrate is not destroyed by the installation of the SAW device, it is possible to perform measurement on the piezoelectric substrate shipped as a product.
[0012]
In the material constant measuring apparatus for a piezoelectric substrate according to the present invention, the frequency measurement probe includes a base portion that is supported so as to be able to approach and separate from a side surface of the piezoelectric substrate, and a probe body that is swingably attached to the base portion. Preferably, the probe main body is configured to include a biasing member that returns the probe main body to a predetermined position of the base.
[0013]
In the material constant measuring apparatus for a piezoelectric substrate according to the present invention, it is desirable that an annular elastic body that is in contact with the piezoelectric substrate is provided around the measurement electrode provided at the tip of the probe body.
[0014]
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 material constant measuring apparatus for a piezoelectric substrate. As shown in the figure, a frequency measuring unit 1 that measures the resonance frequency of thickness-shear vibration of the piezoelectric substrate P, a thickness measuring unit 2 that measures the substrate thickness of the piezoelectric substrate P, the frequency measuring unit 1 and the thickness measurement. And a control device 3 that controls driving of each unit of the unit 2.
The frequency measurement unit 1 includes a substrate support mechanism 11 that supports the piezoelectric substrate P, two frequency measurement probes 12 and 13 that are individually disposed on both upper and lower sides of the piezoelectric substrate P, and frequency measurement probes that are disposed to face each other. And a probe support mechanism 14 for supporting 12 and 13 and an impedance analyzer 15 for driving the frequency measurement probes 12 and 13 to measure the impedance of the piezoelectric substrate P and the frequency dependence of the phase.
[0015]
The substrate support mechanism 11 supports the supported piezoelectric substrate P so as to be movable in two directions parallel to or orthogonal to the surface direction (they are referred to as the X direction and the Y direction). A stage is used. The substrate support mechanism 11 can arrange the frequency measurement probes 12 and 13 so as to face each other at any location on the piezoelectric substrate P.
[0016]
The probe support mechanism 14 includes an upper boom 17 projecting from the support column 16 on the upper surface side of the piezoelectric substrate P supported by the substrate support mechanism 11, a lower boom 18 projecting from the support column 16 on the lower surface side of the piezoelectric substrate P, and an upper portion. An elevating unit 19 provided at the tip of the boom 17 moves one frequency measuring probe 12 in the thickness direction of the piezoelectric substrate P, and the other frequency measuring probe 13 provided at the tip of the lower boom 18 is attached to the piezoelectric substrate P. And an elevating unit 20 that moves in the thickness direction. The frequency measuring probes 12 and 13 are operated in synchronization with opposite directions of the elevating units 19 and 20 to approach and separate in a direction perpendicular to the substrate surface (this is referred to as Z direction) with the piezoelectric substrate P interposed therebetween. Supported as possible.
[0017]
The thickness measuring unit 2 includes an upper displacement meter 21 provided at the tip of the upper boom 17 and a lower displacement meter 22 provided at the tip of the lower boom 18. The upper displacement meter 21 is provided with a spindle (thickness measuring element) 21a that protrudes and protrudes in the Z direction toward the piezoelectric substrate P supported below, and the lower displacement meter 22 includes the piezoelectric substrate P supported upward. A spindle (thickness measuring element) 22a protruding and protruding in the Z direction is provided. The upper displacement meter 21 has a structure for measuring the distance by the difference in the protruding length of the spindle 21a. The lower displacement meter 22 has a similar structure.
[0018]
FIG. 2 is a diagram showing the structure of the frequency measuring probes 12 and 13 and the upper and lower displacement meters 21 and 22 and their surroundings.
The frequency measurement probe 12 includes a base portion 23a that is lifted and lowered by a lift portion 19, a probe main body 24a that is swingably attached to the base portion 23a, a measurement electrode 12a that is attached to the tip (lower end) of the probe main body 24a, a probe The main body 24a includes an absorption ring 25a disposed so as to surround the measurement electrode 12a.
[0019]
A circular hole 26a is formed through the base portion 23a in the Z direction, and a mortar-shaped enlarged diameter portion (engaged portion) 27a is formed in the upper opening of the circular hole 26a by aligning the central axis of the circular hole 26a. Has been. A cylindrical portion 28a having a smaller diameter than the circular hole 26a is provided at the center of the probe main body 24a so as to protrude to the opposite side of the measurement electrode 12a. At the tip of the cylindrical portion 28a (that is, the upper end of the probe main body 24a), an inverted conical flange portion (engagement portion) 29a is formed by aligning the central axis line with the cylindrical portion 28a.
[0020]
The probe main body 24a is engaged with the base portion 23a so that the cylindrical portion 28a passes through the circular hole 26a and the flange portion 29a is fitted to the enlarged diameter portion 27a. The enlarged diameter portion 27a and the flange portion 29a have the same maximum diameter and the same inclination angle of the inclined surface, and when they are properly engaged, the circular hole 26a and the cylindrical portion 28a come to coincide with the central axis. ing. A spring body 30a is interposed between the base 23a and the probe main body 24a to urge the probe main body 24a in the direction of moving downward from the base 23a.
[0021]
The absorption ring 25a is made of an elastic material such as rubber, and is bonded to the lower surface of a disk-shaped flange 31a formed on the probe body 24a with the measurement electrode 12a as the center. The absorption ring 25a is disposed so as to contact the upper surface of the piezoelectric substrate P together with the measurement electrode 12a and surround the measurement location.
[0022]
The hole 32a inside the cylindrical portion 28a is formed so as to penetrate the probe main body 24a and the measurement electrode 12a, and the spindle 21a of the upper displacement meter 21 is inserted into the hole 31a. The spindle 21a is thinner than the hole 32a, and does not come into contact with the spindle 22a even if the probe body 24a swings.
[0023]
The frequency measurement probe 13 includes a base portion 23b that is lifted and lowered by the lift portion 20, a probe body 24b that is swingably attached to the base portion 23b, a measurement electrode 12b that is attached to the tip (upper end) of the probe body 24b, and a probe. The main body 24b includes a rubber absorption ring 25b disposed so as to surround the measurement electrode 13a.
[0024]
A circular hole 26b is formed through the base portion 23b in the Z direction, and a mortar-shaped diameter-enlarged portion (engaged portion) 27b is formed in the lower opening of the circular hole 26b by aligning the central axis of the circular hole 26b. Has been. A cylindrical portion 28b having a smaller diameter than the circular hole 26b is provided at the center of the probe main body 24b so as to protrude to the opposite side of the measurement electrode 12b. At the tip of the cylindrical portion 28b (that is, the lower end of the probe main body 24a), an inverted conical flange portion (engagement portion) 29b is formed by aligning the central axis line with the cylindrical portion 28b.
[0025]
The probe body 24b is engaged with the base portion 23b so that the cylindrical portion 28b passes through the circular hole 26b and the flange portion 29b is fitted to the enlarged diameter portion 27b. The enlarged diameter portion 27b and the flange portion 29b have the same maximum diameter and the same inclined angle of the inclined surface, and when they are properly engaged, the circular hole 26b and the cylindrical portion 28b come to coincide with the central axis. ing. In addition, a spring body 30b that biases the probe body 24b in the direction of separating upward from the base portion 23b is interposed between the base portion 23b and the probe body 24b.
[0026]
The absorption ring 25b is made of an elastic material such as rubber, and is bonded to the lower surface of a disk-shaped flange 31b formed on the probe body 24b with the measurement electrode 12a as the center. The absorption ring 25b is in contact with the lower surface of the piezoelectric substrate P together with the measurement electrode 13a and is disposed so as to surround the measurement location.
[0027]
The hole 32b inside the cylindrical portion 28b is formed so as to penetrate the probe body 24b and the measurement electrode 12b, and the spindle 22a of the lower displacement meter 22 is inserted into the hole 31b. The spindle 22a is thinner than the hole 32b, and does not come into contact with the spindle 22a even if the probe main body 23b swings.
[0028]
The control device 3 and the impedance analyzer 15 are connected to a computer 33 that controls and controls them all and calculates material constants based on information from the impedance analyzer 15.
[0029]
A procedure for measuring the material constant of the piezoelectric substrate P using the material constant measuring apparatus configured as described above will be described.
First, 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 frequency measurement probes 12 and 13 are applied to each of a plurality of measurement points set on the piezoelectric substrate P. They are arranged in order and probing is performed at each location.
[0030]
When the frequency measurement probes 12 and 13 are arranged on both sides of the piezoelectric substrate P across a certain measurement location, the upper displacement meter 21 first contacts the spindle 21a with the piezoelectric substrate P, and the upper displacement meter 21 starts the piezoelectric substrate. Measure the distance to the top surface of P. At the same time, the lower displacement meter 22 brings the spindle 22a into contact with the piezoelectric substrate P and measures the distance from the upper displacement meter 22 to the piezoelectric substrate P. These measurement data are input to the computer 33, and the distance between the upper and lower displacement gauges 21 and 22 without the piezoelectric substrate P measured in advance is measured from the upper displacement meter 21 to the upper surface of the piezoelectric substrate P. The substrate thickness of the piezoelectric substrate P is obtained by subtracting the sum of the distance and the distance from the lower displacement gauge 22 to the lower surface of the piezoelectric substrate P.
[0031]
The probe support mechanism 14 is operated slightly after the upper and lower displacement gauges 21 and 22 bring the respective spindles 21a and 22a into contact with the piezoelectric substrate P, and the frequency measurement probes 12 and 13 are moved in the Z direction (or -Z). Direction) and approaches the upper and lower side surfaces of the piezoelectric substrate P in synchronization.
[0032]
When the measurement electrodes 12a and 13a of the frequency measurement probes 12 and 13 are both in contact with the piezoelectric substrate P and the spring bodies 30a and 30b both exert an urging force to press the measurement electrodes 12a and 13a against the piezoelectric substrate P, the frequency measurement is performed. The probes 12 and 13 are stopped (see FIG. 3). At this time, the flange portions 29a and 29b of the probe main bodies 24a and 24b are separated from the enlarged diameter portions 27a and 27b on the base portions 23a and 23b side.
[0033]
Subsequently, an AC signal is emitted from the impedance analyzer 15 and the piezoelectric substrate P is excited via the measurement electrodes 12a and 13a. Therefore, the frequency scan of the AC signal is performed, and the frequency dependence of the impedance and phase at the measurement location is measured. Detect sex. This measurement data is input to the computer 33, and the resonance frequency is obtained by analyzing the waveform showing the frequency dependence.
[0034]
When the substrate thickness and the resonance frequency are obtained as described above, the computer 33 processes these pieces of information to calculate the material constant of a certain measurement location on the piezoelectric substrate P.
[0035]
When the measurement at the measurement location is completed, the spindles 21a and 22a are retracted and the frequency measurement probes 12 and 13 are retracted to return to their original positions. When the measurement electrodes 12a and 13a are separated from the piezoelectric substrate P, the flange portions 29a and 29b are engaged with the enlarged diameter portions 27a and 27b by the urging force of the spring bodies 30a and 30b, and the circular hole 26b and the cylindrical portion 28b are centered. The probe bodies 24a and 24b and the measurement electrodes 12a and 13a are returned to the fixed positions by matching the axes of the two.
Thereafter, the above procedure is repeated, and the material constants are calculated for all the measurement points set on the piezoelectric substrate P. Based on this, the material constants are evaluated.
[0036]
If it carries out as mentioned above, it will be unnecessary to install a SAW device, and frequency measurement and thickness measurement will be carried out at the same time by integrating frequency measurement probes 12 and 13 and a thickness gauge, thereby greatly increasing the time required for measurement. Shortened to In addition, since the piezoelectric substrate is not destroyed by the installation of the SAW device, it is possible to perform measurement on the piezoelectric substrate shipped as a product.
[0037]
Since the spindles 21a and 22a as thickness gauges are arranged in the center of the frequency measurement probes 12 and 13, the frequency measurement location and the substrate thickness measurement location are exactly the same, so there is no error. Can be measured.
[0038]
In the frequency measurement, the absorption rings 25a and 25b together with the measurement electrodes 12a and 13a contact the piezoelectric substrate P to surround the measurement part from above and below, and absorb unnecessary vibration generated at the measurement part, so that the resonance frequency can be set with higher accuracy. Can be identified. When an AC signal is passed through the piezoelectric substrate P, a number of sub-vibrations close to the main vibration are excited along with the main vibration constituted by the basic and higher-order thickness vibrations. The sub-vibration is vibration generated when an elastic wave propagates in the lateral direction while being reflected by the upper and lower boundary surfaces in the piezoelectric substrate P and is reflected by the end surface of the piezoelectric substrate P to become a stationary wave. Although this noise is undesirable for the measurement of the main vibration that is essentially necessary for the secondary vibration, it may be stronger than the main vibration depending on the measurement location set on the piezoelectric substrate P, and is a major factor that hinders the measurement of the main vibration. It has become. Since the absorption rings 25a and 25b absorb the elastic wave and leave only the main vibration, a waveform with less noise can be obtained and high-precision measurement can be performed.
[0039]
The spring bodies 30a and 30b exert an urging force to press the measurement electrodes 12a and 13a against the piezoelectric substrate P, so that the pressure when the measurement electrodes 12a and 13a contact the piezoelectric substrate P causes the two frequency measurement probes 12 and 13 to be in contact with each other. Since the measurement conditions are equalized, the measurement conditions are equal and high-precision measurement is possible.
[0040]
The probe main bodies 24a and 24b can be swung with respect to the base portions 23a and 23b, and the measurement surfaces of the measurement electrodes 12a and 13a are given a degree of freedom to be tilted by a small amount. Since it is made uniform between the two frequency measurement probes 12 and 13, the measurement can be performed with higher accuracy.
[0041]
【The invention's effect】
As described above, according to the present invention, it is not necessary to install a conventional SAW device, and by performing frequency measurement and thickness measurement simultaneously with a frequency measurement probe and a thickness gauge as one body, 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 perform measurement on the piezoelectric substrate shipped as a product.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment according to the present invention, and is an overall view of a material constant measuring apparatus.
FIG. 2 is a diagram illustrating a main part of the material constant measuring apparatus in FIG. 1, and is a state explanatory diagram illustrating a state in which a frequency measurement probe and a spindle are separated from a piezoelectric substrate.
3 is a view showing the main part of the material constant measuring apparatus of FIG. 1 and is a state explanatory view showing a state in which the frequency measuring probe and the spindle are in contact with the piezoelectric substrate. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Frequency measurement part 2 Thickness measurement part 12, 13 Frequency measurement probe 21 Upper displacement meter 22 Lower displacement meter 21a, 22a Spindle (thickness measuring element)
27a, 27b Expanded portion (engaged portion)
29a, 29b collar part (engagement part)
30a, 30b Spring bodies 12a, 13a Measuring electrodes 25a, 25b Absorption ring P Piezoelectric substrate

Claims (3)

Two frequency measurement probes individually arranged on both sides of the piezoelectric substrate cut out from the piezoelectric single crystal body are supported so as to be close to and away from each other with the piezoelectric substrate interposed therebetween, and these two frequency measurement probes are supported by the piezoelectric substrate. A frequency measurement unit that measures the resonance frequency of thickness-shear vibration at an arbitrary location sandwiched between both probes in contact with
A thickness measuring unit for measuring the thickness of a substrate at an arbitrary position sandwiched between the two measuring elements by bringing two thickness measuring elements individually disposed on both sides of the piezoelectric substrate into contact with the piezoelectric substrate; A material constant measuring device for a piezoelectric substrate comprising:
The frequency measuring probe and the thickness measuring element disposed on the same side of the piezoelectric substrate are provided with a through-hole penetrating in the thickness direction of the piezoelectric substrate at the center of the frequency measuring probe. A material constant measuring apparatus for a piezoelectric substrate , wherein the thickness gauge is inserted in the piezoelectric substrate. The frequency measurement probe includes a base portion that is supported on the side surface of the piezoelectric substrate so as to be able to approach and separate, a probe body that is swingably attached to the base portion, and a probe body that returns the probe body to a predetermined position of the base portion. material constant measuring apparatus for a piezoelectric substrate according to claim 1 Symbol mounting, characterized in that it comprises a-energizing member. 3. The material constant measuring apparatus for a piezoelectric substrate according to claim 2 , wherein an annular elastic body that is in contact with the piezoelectric substrate is provided around a measurement electrode provided at a tip of the probe main body.

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