JPH10178331A - Surface acoustic wave element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave element with a high degree of freedom of combination of an electromechanical coupling coefficient and a temperature dependency, especially with a high electromechanical coupling coefficient and a small temperature dependency. SOLUTION: Flat processing, mirror surface processing, cleaning processing, hydrophilic processing are applied to a single crystal piezoelectric substrate 10 and a single crystal piezoelectric thin plate 20, they are overlapped and heat-treated, then they are directly adhered and laminated, and a interdigital electrode 30 to stimulate a Rayleigh surface acoustic wave is provided onto the single crystal piezoelectric substrate 10 or the single crystal piezoelectric thin plate 20. Let a plate thickness of the single crystal piezoelectric thin plate 20 be H and a wavelength of the stimulated surface acoustic wave be A, then a relation of H/λ<0.5 is in existence.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device having excellent temperature dependency and excellent electromechanical coupling coefficient used for a filter, a resonator or the like.

[0002]

2. Description of the Related Art In recent years, with the advancement and development of mobile communication technology, communication devices have been reduced in size and frequency. These devices always require an oscillator and a high-frequency filter, and a surface acoustic wave element is often used for these oscillators and high-frequency filters. Conventional surface acoustic wave devices, such as surface acoustic wave filters and surface acoustic wave resonators, form a comb-shaped electrode on a piezoelectric substrate such as lithium niobate and excite the surface acoustic wave vibration by applying an alternating electric field to the electrode. ing.

For use in mobile communication equipment, a surface acoustic wave element having high frequency and good characteristics is required. What is important as the high frequency characteristics of a surface acoustic wave element is the insertion loss and its temperature dependence in the case of a filter, and the resonance Q and the ratio of resonance and antiresonance (capacitance ratio) and its temperature dependence in the case of a resonator. is there. The capacitance ratio is directly related to the pass band when used in a resonator type filter or the like. The insertion loss, the resonance Q, and the capacitance ratio depend on the electromechanical coupling coefficient of the piezoelectric body used, and the temperature dependence involves the temperature dependence of the sound speed of the piezoelectric body used. The electromechanical coupling coefficient and the temperature dependence (hereinafter, the delay time temperature coefficient is used as an index of the temperature dependence) greatly vary depending on the material used and its crystal orientation.

In the case of quartz, an electromechanical coupling coefficient is 0.12% and a delay time temperature coefficient is 0 ppm / in a 42.5-degree rotation Y-cut X-axis propagation with respect to a Rayleigh-type surface acoustic wave.
℃, 105 degree rotation Y about leaky type surface acoustic wave
In the case of cut X-axis propagation, the electromechanical coupling coefficient is 0.11%, the delay time temperature coefficient is 0 ppm / ° C., and lithium niobate is used.
The electromechanical coupling coefficient is 5.5% in the cut X-axis propagation, the delay time temperature coefficient is 72 ppm / ° C., the electromechanical coupling coefficient is 11.3% in the Y-cut X-axis propagation with a rotation of 64 degrees with respect to leaky surface acoustic waves, The delay time temperature coefficient is 70 ppm /
° C and lithium tantalate, the electromechanical coupling coefficient is 5.0%, the delay time temperature coefficient is 30 ppm /
In the case of ℃, lithium borate, the electromechanical coupling coefficient is about 1.0% with a 45 ° rotation X cut for Rayleigh type surface acoustic waves.

In terms of the electromechanical coupling coefficient, lithium niobate is generally desirable. However, the temperature dependency is inferior to quartz or the like. Quartz has a very small temperature dependence, but a very small electromechanical coupling coefficient.

From the viewpoint of design flexibility, it is preferable that the electromechanical coupling coefficient is large and the temperature dependence is small. However, these materials are not sufficient.
When a conventional piezoelectric substrate made of a single material is used, the combination of the electromechanical coupling coefficient and the temperature dependency is limited, and the degree of freedom in design is small. In addition, the electromechanical coupling coefficient is large,
There was a problem that there was no material having low temperature dependence. In order to solve these problems, a surface acoustic wave device having a laminated structure is known.

For example, a laminate structure of zinc oxide and lithium niobate, which is a laminate of piezoelectric bodies, has been reported by A. Armstrong et al. (Proc. 1972 IEEE Ultrasonic
s Symp. (IEEE, New York, 1972) p.370). With such a configuration, a surface acoustic wave device having an excellent electromechanical coupling coefficient can be obtained. Further, in order to improve the temperature characteristics, a method is known in which an aluminum nitride film, which is a piezoelectric material, is formed on a Si semiconductor substrate, and a silicon oxide film is formed thereon to improve the temperature characteristics (USP4). , 516,049). In recent years, a surface acoustic wave element having excellent temperature characteristics and a coupling coefficient, which is formed on a composite piezoelectric substrate in which a piezoelectric substrate or a non-piezoelectric substrate is bonded by a direct bonding method, has been attracting attention (Japanese Patent Laid-Open Publication No. Hei 6-1994).
326553).

[0008]

Among the above conventional lamination techniques, when a lamination structure is formed by using a thin film formation technique such as a sputtering method, a chemical vapor deposition method, or a vacuum deposition method,
There are severe restrictions on substrate and material combinations. For example, a piezoelectric film formed by a sputtering method or the like has lower piezoelectric characteristics than a bulk single crystal. Further, in order to obtain the piezoelectric characteristics, it is necessary to at least uniformly orient the crystal direction. However, in order to achieve the orientation, the combination of the substrate and the film is extremely limited. Preferably, a single crystal thin film is preferably formed by an epitaxial growth technique. In this case, the combination of the substrate and the film is further limited. For example, in the case of a piezoelectric material such as quartz, lithium niobate, lithium tantalate, and lithium borate, which is usually used for a surface acoustic wave device, a good epitaxial film cannot be obtained when the substrate material is different. Therefore, also in this case, there is a problem that the degree of freedom in design is poor, and the material having a large electromechanical coupling coefficient and excellent in temperature dependency is poor.

In the case of the above-mentioned thin film technology, it is necessary to orient the piezoelectric material in a predetermined direction. However, a practical material has not been obtained because the combination with the substrate is extremely limited. . When various adhesives are used, the adhesive enters the interface of surface acoustic wave propagation, and the surface acoustic waves are attenuated.
Preferred characteristics cannot be obtained.

In view of the above-mentioned problems of the conventional method of manufacturing a surface acoustic wave element, the present invention greatly increases the degree of freedom of the combination of the electromechanical coupling coefficient and the temperature dependence, and in particular, the elasticity having a small temperature dependence. It is an object to provide a surface acoustic wave element.

[0011]

Means for Solving the Problems To solve the above problems, a surface acoustic wave device according to the present invention comprises a single crystal piezoelectric substrate,
A surface acoustic wave element including a single-crystal piezoelectric thin plate and a comb-shaped electrode provided on at least one of the single-crystal piezoelectric substrate and the single-crystal piezoelectric thin plate for exciting a surface acoustic wave; The substrate and the single-crystal piezoelectric thin plate are respectively flattened, mirror-finished, cleaned, hydrophilized, and directly bonded and laminated by heat treatment for superposition, and the surface acoustic wave is a Rayleigh-type surface acoustic wave. When the thickness of the single-crystal piezoelectric thin plate is H and the wavelength of the surface acoustic wave to be excited is λ, H / λ is H /
λ <0.5.

The delay time temperature coefficient of the single crystal piezoelectric substrate in the direction in which the surface acoustic wave propagates is smaller than the delay time temperature coefficient of the single crystal piezoelectric thin plate in the direction in which the surface acoustic wave propagates. Temperature characteristics that cannot be obtained with a single single-crystal piezoelectric substrate, specifically, a surface acoustic wave element having a small delay time temperature coefficient can be obtained.

The single-crystal piezoelectric substrate is preferably made of quartz or langasite, and the single-crystal piezoelectric thin plate is preferably made of lithium niobate, lithium tantalate or lithium borate.

The single-crystal piezoelectric substrate may be made of quartz, and the single-crystal piezoelectric thin plate may be made of lithium niobate.

With the above-described structure, the surface acoustic wave propagates in the vicinity of the laminated interface, so that the sound velocity, the electromechanical coupling coefficient, and the temperature dependency of the laminated substrate are independent of the sound velocity and the electromechanical coupling, respectively. Coefficients and temperature dependence are obtained.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of a surface acoustic wave device according to an embodiment of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 shows a first embodiment of the structure of a surface acoustic wave device according to the present invention.

In FIG. 1, reference numeral 10 denotes a single crystal piezoelectric substrate;
Is a single-crystal piezoelectric thin plate, and 30 and 30 'are comb-shaped electrodes provided on the single-crystal piezoelectric thin plate. The comb electrodes are shown here in a simplified manner.

The single-crystal piezoelectric substrate 10 and the single-crystal piezoelectric thin plate 20 are flattened, mirror-finished, cleaned, and hydrophilized, and are directly joined and laminated by heat treatment for superposition.

As the single-crystal piezoelectric substrate 10, for example, quartz which is a single-crystal piezoelectric body, and as the single-crystal piezoelectric thin plate 20, for example, lithium niobate which is a single-crystal piezoelectric body are suitable.

A function as a surface acoustic wave element is to apply a high-frequency signal to the comb-shaped electrode 30 so that a surface acoustic wave is excited in a piezoelectric portion near the comb-shaped electrode 30, and this is passed through a laminated structure to form the other comb-shaped electrode 30 ′. And is converted again into an electric signal by the piezoelectric portion below the comb-shaped electrode 30 '. Here, the basic configuration of a surface acoustic wave element using a comb-shaped electrode is shown, and when actually forming a filter or a resonator,
Increase the number of comb electrodes or change the configuration.

Here, the propagation characteristics of the Rayleigh-type surface acoustic wave in the laminated substrate will be examined by calculation. Hereinafter, a method of calculating the propagation characteristics of the Rayleigh-type surface acoustic wave propagating through the laminated substrate and the result thereof will be described. First, the Rayleigh wave theory will be described. The characteristics of the Rayleigh-type surface acoustic wave propagating through the layered substrate can be calculated from the relational expression described below. FIG. 2 shows a model and a coordinate system used for the calculation. The Rayleigh-type surface acoustic wave propagates in the X1 direction. In both the single-crystal piezoelectric substrate 10 and the single-crystal piezoelectric thin plate 20, the following basic piezoelectric formula, equation of motion, and Maxwell's equation approximating the quasi-electrostatic field hold. The piezoelectric basic equation, the equation of motion, and the Maxwell's equation of the quasi-electrostatic field approximation are given as follows.

[0023]

(Equation 1)

[0024]

(Equation 2)

[0025]

(Equation 3)

Here, cij, eijk, and εij are tensors of the elastic constant, the piezoelectric constant, and the dielectric constant after the coordinate rotation, respectively, and ρ is the density. It is sufficient to find a sound velocity that satisfies the boundary conditions at the boundaries between the single crystal substrate, the single crystal thin plate, and the surface of the single crystal thin plate. The boundary condition is, specifically, the stress X at each boundary.
That is, the three-directional components are continuous, the X3-direction component of the electric flux density is continuous, and the particle displacement is continuous.

From the sound velocity v obtained by the above procedure, the electromechanical coupling coefficient k2 and the delay time temperature coefficient (TCD) are obtained as follows.

[0028]

(Equation 4)

[0029]

(Equation 5)

Here, vf and vm are the sound velocities in the X1 direction where the surfaces are electrically open and electrically short, respectively, and α indicates the thermal expansion coefficient in the X1 direction.

The calculation was performed by changing the cutout angle and propagation direction of the quartz single crystal substrate and the propagation characteristics of the Rayleigh wave propagating through the composite substrate when the cutout angle, the propagation direction and the thickness of the lithium niobate single crystal substrate were changed. In particular, the purpose was to determine sound velocity, electromechanical coupling coefficient, and delay time temperature coefficient.

The calculation result will be described with reference to FIGS. FIG. 3 to FIG. 5 show that the propagation direction of the surface acoustic wave in quartz is Euler angle display (0 °, 90 °, θ1), and the ray propagates in the same direction as the Rayleigh-type surface acoustic wave when the angle θ1 is changed. It is a calculation result of the sound velocity, electromechanical coupling coefficient, and delay time coupling coefficient of a slow transverse wave.
FIGS. 6 to 8 show the Rayleigh-type surface acoustic wave and the same direction when the angle θ2 is changed when the propagation direction of the surface acoustic wave is represented by Euler angles (0 °, 90 °, θ2) in lithium niobate. The speed of sound of the slow transverse waves propagating,
It is a calculation result of an electromechanical coupling coefficient and a delay time temperature coefficient. As shown in FIGS. 3 to 5, when 0 ° ≦ θ1 ≦ 180 °, the sound speed of the Rayleigh-type surface acoustic wave is 3160 m / s to 3810 m / s, the sound speed of the slow transverse wave is 3300 m / s to 4675 m / s, and the electromechanical coupling The coefficient is 0.18% or less, and the delay time temperature coefficient is from -23 ppm / ° C to 69 pp.
m / ° C. As shown in FIG. 6, when θ2 = 0 °, the sound speed of the Rayleigh-type surface acoustic wave is 3440 m / s to 3743 m / s, the sound speed of the slow transverse wave is 3534 m / s to 3910 m / s, and the electromechanical coupling coefficient is 1. 5% to 5.0%, lag time temperature coefficient 75 ppm / ° C to 94%
ppm / ° C. The delay time temperature coefficient of the Rayleigh-type surface acoustic wave of quartz is smaller than the delay time temperature coefficient of the Rayleigh-type surface acoustic wave of lithium niobate. The delay time temperature coefficient of Rayleigh-type surface acoustic waves of quartz is
It has a negative value at 0 ° ≦ θ1 ≦ 35 ° and 145 ° ≦ θ1 ≦ 180 °.

FIGS. 9 to 11 show that in the case of a laminated substrate in which quartz is a substrate and lithium niobate is a thin plate, the propagation direction of the surface acoustic wave in the quartz is represented by Euler angles (0 °, 9).
0 °, θ1), and when the propagation direction of the surface acoustic wave in lithium niobate is represented by Euler angles (0 °, 90 °, θ2), θ1 is set to 0 ° and θ2 is set in the range of 0 ° ≦ θ2 ≦ 90 °. Calculation results of the sound velocity, electromechanical coupling coefficient, and delay time temperature coefficient of a Rayleigh-type surface acoustic wave when the value H / λ obtained by normalizing the thickness H of the thin plate with the wavelength λ of the Rayleigh-type surface acoustic wave is changed It is. As shown in FIG. 9, in the range of change of θ2, the sound speed of the Rayleigh-type surface acoustic wave of quartz is lower than the sound speed of the Rayleigh-type surface acoustic wave of lithium niobate. There is a Rayleigh-type surface acoustic wave propagating through the substrate, and the sound speed propagating through the composite substrate takes an intermediate value between the sound speeds of the quartz and lithium niobate alone. As shown in FIG. 10, the electromechanical coupling coefficient of the composite substrate also takes an intermediate value between the electromechanical coupling coefficients of quartz and lithium niobate alone. Further, as shown in FIG. 11, the delay time temperature coefficient of the composite substrate also takes an intermediate value between the delay time temperature coefficients of the quartz and lithium niobate alone. As the delay time temperature coefficient increases as H / λ increases, the value changes from negative to positive, so that H / λ having a zero temperature coefficient exists, and good temperature characteristics can be obtained. In the range of the changed θ2, it has a zero temperature coefficient at H / λ = 0.2 to 0.3.

FIGS. 12 to 14 show that when (θ1, θ2) = (15 °, θ2) in a laminated substrate in which the piezoelectric substrate is quartz and the piezoelectric thin plate is lithium niobate,
2 is in the range of 0 ° ≦ θ1 ≦ 90 °, and the thickness H of the thin plate is a value H / normalized by the wavelength λ of the Rayleigh-type surface acoustic wave.
10 shows calculation results of the sound velocity, electromechanical coupling coefficient, and delay time temperature coefficient of a Rayleigh-type surface acoustic wave and a slow transverse wave propagating in the same direction when λ is changed. As shown in FIG. 12, the sound speed of the Rayleigh-type surface acoustic wave of quartz is lower than the sound speed of the Rayleigh-type surface acoustic wave of lithium niobate. The sound velocity that exists and propagates through the composite substrate takes an intermediate value between the sound velocities of the quartz and lithium niobate alone. As shown in FIG. 13, the electromechanical coupling coefficient of the composite substrate also takes an intermediate value between the electromechanical coupling coefficients of quartz and lithium niobate alone. As shown in FIG. 14, the delay time temperature coefficient of the composite substrate also takes an intermediate value between the delay time temperature coefficients of the quartz and lithium niobate alone. In the range of the changed θ2, it has a zero temperature coefficient at H / λ = 0.2 to 0.3.

FIGS. 15 to 17 show the case where (θ1, θ2) = (30 °, θ2) in a laminated substrate in which the piezoelectric substrate is quartz and the piezoelectric thin plate is lithium niobate.
2 is in the range of 0 ° ≦ θ2 ≦ 90 °, and the thickness H of the thin plate is a value H / normalized by the wavelength λ of the Rayleigh-type surface acoustic wave.
10 shows calculation results of the sound velocity, electromechanical coupling coefficient, and delay time temperature coefficient of a Rayleigh-type surface acoustic wave and a slow transverse wave propagating in the same direction when λ is changed. As shown in FIG. 16, the electromechanical coupling coefficient of the composite substrate also takes an intermediate value between the electromechanical coupling coefficients of quartz and lithium niobate alone. As shown in FIG. 17, the delay time temperature coefficient of the composite substrate also takes an intermediate value between the delay time temperature coefficients of the quartz and lithium niobate alone. In the range of the changed θ2, it has a zero temperature coefficient at H / λ = 0.20 to 0.25.

FIGS. 18 to 20 show that when (θ1, θ2) = (45 °, θ2) in a laminated substrate in which the piezoelectric substrate is quartz and the piezoelectric thin plate is lithium niobate,
2 is in the range of 0 ° ≦ θ1 ≦ 90 °, and the thickness H of the thin plate is a value H / normalized by the wavelength λ of the Rayleigh-type surface acoustic wave.
10 shows calculation results of the sound velocity, electromechanical coupling coefficient, and delay time temperature coefficient of a Rayleigh-type surface acoustic wave and a slow transverse wave propagating in the same direction when λ is changed. Changed θ
In the range of 2, there is no range where the delay time time temperature coefficient becomes zero. This is due to the non-negative delay time temperature coefficient of the thin veneer.

FIGS. 21 to 23 show that when (θ1, θ2) = (60 °, θ2) in a laminated substrate in which the piezoelectric substrate is quartz and the piezoelectric thin plate is lithium niobate,
2 is in the range of 0 ° ≦ θ1 ≦ 90 °, and the thickness H of the thin plate is a value H / normalized by the wavelength λ of the Rayleigh-type surface acoustic wave.
10 shows calculation results of the sound velocity, electromechanical coupling coefficient, and delay time temperature coefficient of a Rayleigh-type surface acoustic wave and a slow transverse wave propagating in the same direction when λ is changed. Changed θ
In the range of 2, there is no range where the delay time time temperature coefficient becomes zero. This is due to the non-negative delay time temperature coefficient of the thin veneer.

FIGS. 24 to 26 show that when (θ1, θ2) = (75 °, θ2) in a laminated substrate in which the piezoelectric substrate is quartz and the piezoelectric thin plate is lithium niobate,
2 is in the range of 0 ° ≦ θ1 ≦ 90 °, and the thickness H of the thin plate is a value H / normalized by the wavelength λ of the Rayleigh-type surface acoustic wave.
10 shows calculation results of the sound velocity, electromechanical coupling coefficient, and delay time temperature coefficient of a Rayleigh-type surface acoustic wave and a slow transverse wave propagating in the same direction when λ is changed. There is no range where the delay time temperature coefficient of the laminated substrate becomes zero. This is due to the non-negative delay time temperature coefficient of the thin veneer.

In a laminated substrate in which the piezoelectric substrate is quartz and the piezoelectric thin plate is lithium niobate, (θ1, θ2)
= (90 °, θ2), θ2 is 0 ° ≦ θ1 ≦ 9
The surface acoustic wave considered in the present invention in the range of 0 ° could not be obtained by calculation.

Considering the symmetry, 0 ° ≦ θ1 ≦ 90 ° and 0 ° ≦ θ2 with respect to the combination of Y-cut plates.
It is sufficient to study the propagation characteristics of the surface acoustic wave when ≦ 90 °.

To summarize the above, in a laminated substrate in which the piezoelectric substrate is quartz and the piezoelectric thin plate is lithium niobate, the sound speed of Rayleigh-type surface acoustic waves of quartz is the same as that of lithium niobate. When it is slower than the above, there is a surface acoustic wave propagating through the laminated substrate. Also, when the delay time temperature coefficient of the piezoelectric substrate in the direction in which the surface acoustic wave propagates is smaller than the delay time temperature coefficient of the surface acoustic wave of the piezoelectric thin plate and the value is negative, the laminated substrate is excellent. It can be seen that it has a temperature dependency.

The examination by the numerical calculation so far is as follows.
Although shown in the case of quartz and lithium niobate in a Y-cut plate, similar conditions are satisfied for the main cut, the cut other than the propagation direction, the propagation direction, and the combination of a single crystal substrate and a single crystal thin plate material. It is clear that things have similar effects.

[0043]

EXAMPLE FIG. 27 shows the structure of a specific example of the first embodiment, in which quartz is used for a single-crystal piezoelectric substrate and lithium niobate is used for a single-crystal piezoelectric thin plate. In FIG. 27, reference numeral 11 denotes a crystal in which the cut-out angle and the propagation method of the surface acoustic wave are represented by Euler angles (0 °, 90 °, 0 °) (hereinafter, referred to as a Y-cut X-axis propagating crystal).
The single-crystal piezoelectric substrate 21 is made up of a cutout angle and a propagation method of a surface acoustic wave in Euler angles (0 °, 90 °,
0 °), which is a single crystal piezoelectric thin plate made of lithium niobate (hereinafter, referred to as Y-cut X-axis propagating lithium niobate), wherein the single crystal piezoelectric substrate 11 and the single crystal piezoelectric thin plate 21 are directly bonded as described above. Are combined. Reference numeral 31 denotes a comb-shaped electrode provided on the single-crystal piezoelectric thin plate 21. Here, the display is simplified.

For Rayleigh-type surface acoustic waves, Y-
The sound velocity in the crystal of the cut X-axis propagation is 3160 m / sec,
The electromechanical coupling coefficient is 0.19% and the delay time temperature coefficient is-
The sound velocity of single-crystal lithium niobate of 23 ppm / ° C and Y-cut X-axis propagation is 3744 m / sec, the electromechanical coupling coefficient is 1.5%, and the delay time temperature coefficient is 76 ppm / ° C.

However, in the case of the laminated substrate formed by the direct bonding as described above, by setting the thickness of the single-crystal piezoelectric substrate 21 to an appropriate thickness in accordance with the wavelength of the Rayleigh-type surface acoustic wave to be used, the substantial sound velocity can be obtained. In addition, characteristics different from those of the piezoelectric substance alone can be obtained with respect to the piezoelectric material and the electromechanical coupling coefficient and the delay time temperature coefficient.

For example, when exciting the comb electrodes 30 at 80 MHz, the interval between the comb electrodes 30 is set to about 40 μm at 0.5 wavelength.
And the thickness of the single-crystal piezoelectric thin plate 21 is set to 1 at about 0.26 wavelength.
By setting the thickness to 0 μm, the sound velocity, the electromechanical coupling coefficient, and the delay time temperature coefficient both of the values of Y-cut and X-axis propagating single-crystal lithium niobate propagating through the single-crystal piezoelectric thin plate 21 and the single-crystal piezoelectric substrate 11 And a value different from the value of the single-crystal quartz crystal propagated in the Y-cut and X-axis directions.

Specifically, when the thickness of the single-crystal piezoelectric thin plate 21 is set to 0.26 wavelength, the sound velocity is 3222 m / sec, the electromechanical coupling coefficient is 1.5%, and the delay time coupling coefficient is 0 pp.
A value of about m / ｍC is obtained. In this case, by obtaining intermediate values of the sound velocity, the electromechanical coupling coefficient, and the delay time temperature coefficient between the respective piezoelectric materials, a surface acoustic wave element suitable for, for example, a high-frequency band filter is obtained.

When the temperature change of the surface acoustic wave velocity in the first specific example of this embodiment in the range of −20 ° C. to + 80 ° C. was measured, the temperature change was 100 ppm or less, and the temperature change was extremely small. The result was close to the calculation.

[0049]

According to the above configuration, the degree of freedom of the combination of the electromechanical coupling coefficient and the temperature dependence is greatly increased, and a surface acoustic wave element having a small temperature dependence can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is a diagram showing a numerical analysis model of a surface acoustic wave and a coordinate system;

FIG. 3 shows a cutout angle of a quartz single crystal substrate and a propagation direction of a wave in Euler angles (0 °, 90 °, θ1), and θ
The figure which shows the result by numerical calculation of the sound speed of a surface acoustic wave and the sound speed of a slow transverse wave when changing 1

FIG. 4 shows the cut-out angle of the quartz single crystal substrate and the wave propagation direction as Euler angles (0 °, 90 °, θ1), and θ
The figure which shows the result by numerical calculation of the electromechanical coupling coefficient of a surface acoustic wave and the electromechanical coupling coefficient of a slow transverse wave when 1 is changed.

FIG. 5 shows the cutout angle and the wave propagation direction of the quartz single crystal substrate as Euler angles (0 °, 90 °, θ1), and θ
The figure which shows the result by numerical calculation of the delay time temperature coefficient of a surface acoustic wave and the delay time temperature coefficient of a slow shear wave when 1 is changed.

FIG. 6 shows the cutout angle and wave propagation direction of a lithium niobate single crystal substrate in Euler angles (0 °, 90 °, θ).
2) is a diagram showing the results of numerical calculations of the sound speed of a surface acoustic wave and the sound speed of a slow transverse wave when θ2 is changed.

FIG. 7 shows the cutout angle and wave propagation direction of a lithium niobate single crystal substrate in Euler angles (0 °, 90 °, θ).
2) is a diagram showing the results of numerical calculation of the electromechanical coupling coefficient of the surface acoustic wave and the electromechanical coupling coefficient of the slow transverse wave when θ2 is changed.

FIG. 8 shows the cutout angle and wave propagation direction of a lithium niobate single crystal substrate in Euler angles (0 °, 90 °, θ).
2) is a diagram showing the results of numerical calculation of the delay time temperature coefficient of the surface acoustic wave and the delay time temperature coefficient of the slow transverse wave when θ2 is changed.

FIG. 9 shows the cutout angle of the quartz single crystal substrate and the propagation direction of the surface acoustic wave in Euler angles (0 °, 90 °, 0 °).
゜), and the cutout angle and the propagation direction of the surface acoustic wave of the lithium niobate single crystal thin plate are represented by Euler angles (0 °,
90 °, θ2), showing the results of numerical calculation of the sound velocity of surface acoustic waves when θ2 and the normalized plate thickness H / λ are changed.

FIG. 10 shows the cutout angle of the quartz single crystal substrate and the propagation direction of the surface acoustic wave in Euler angles (0 °, 90 °, 0 °).
゜), and the cutout angle and the propagation direction of the surface acoustic wave of the lithium niobate single crystal thin plate are represented by Euler angles (0 °,
90 °, θ2), showing the results of numerical calculation of the electromechanical coupling coefficient of the surface acoustic wave when θ2 and the normalized plate thickness H / λ are changed.

FIG. 11 shows the cutout angle of the quartz single crystal substrate and the propagation direction of the surface acoustic wave in Euler angles (0 °, 90 °, 0 °).
゜), and the cutout angle and the propagation direction of the surface acoustic wave of the lithium niobate single crystal thin plate are represented by Euler angles (0 °,
90 °, θ2), showing the results of numerical calculation of the delay time temperature coefficient of the surface acoustic wave when θ2 and the normalized plate thickness H / λ are changed.

FIG. 12 shows the cutout angle of the quartz single crystal substrate and the propagation direction of the surface acoustic wave in Euler angles (0 °, 90 °, 15 °).
゜), and the cutout angle and the propagation direction of the surface acoustic wave of the lithium niobate single crystal thin plate are represented by Euler angles (0 °,
90 °, θ2), showing the results of numerical calculation of the sound velocity of surface acoustic waves when θ2 and the normalized plate thickness H / λ are changed.

FIG. 13 shows the cutout angle of the quartz single crystal substrate and the propagation direction of the surface acoustic wave in Euler angles (0 °, 90 °, 15 °).
゜), and the cutout angle and the propagation direction of the surface acoustic wave of the lithium niobate single crystal thin plate are represented by Euler angles (0 °,
90 °, θ2), showing the results of numerical calculation of the electromechanical coupling coefficient of the surface acoustic wave when θ2 and the normalized plate thickness H / λ are changed.

FIG. 14 shows the cutout angle of the quartz single crystal substrate and the propagation direction of the surface acoustic wave in Euler angles (0 °, 90 °, 15 °).
゜), and the cutout angle and the propagation direction of the surface acoustic wave of the lithium niobate single crystal thin plate are represented by Euler angles (0 °,
90 °, θ2), showing the results of numerical calculation of the delay time temperature coefficient of the surface acoustic wave when θ2 and the normalized plate thickness H / λ are changed.

FIG. 15 shows the cutout angle of the quartz single crystal substrate and the propagation direction of the surface acoustic wave in Euler angles (0 °, 90 °, 30 °).
゜), and the cutout angle and the propagation direction of the surface acoustic wave of the lithium niobate single crystal thin plate are represented by Euler angles (0 °,
90 °, θ2), showing the results of numerical calculation of the sound velocity of surface acoustic waves when θ2 and the normalized plate thickness H / λ are changed.

FIG. 16 shows the cutout angle of the quartz single crystal substrate and the propagation direction of the surface acoustic wave in Euler angles (0 °, 90 °, 30 °).
゜), and the cutout angle and the propagation direction of the surface acoustic wave of the lithium niobate single crystal thin plate are represented by Euler angles (0 °,
90 °, θ2), showing the results of numerical calculation of the electromechanical coupling coefficient of the surface acoustic wave when θ2 is changed.

FIG. 17 shows the cutout angle of the quartz single crystal substrate and the propagation direction of the surface acoustic wave in Euler angles (0 °, 90 °, 30 °).
゜), and the cutout angle and the propagation direction of the surface acoustic wave of the lithium niobate single crystal thin plate are represented by Euler angles (0 °,
90 °, θ2), showing the results of numerical calculation of the delay time temperature coefficient of the surface acoustic wave when θ2 and the normalized plate thickness H / λ are changed.

FIG. 18 shows the cutout angle of the quartz single crystal substrate and the propagation direction of the surface acoustic wave in Euler angles (0 °, 90 °, 45 °).
゜), and the cutout angle and the propagation direction of the surface acoustic wave of the lithium niobate single crystal thin plate are represented by Euler angles (0 °,
90 °, θ2), showing the results of numerical calculation of the sound velocity of surface acoustic waves when θ2 and the normalized plate thickness H / λ are changed.

FIG. 19 shows the cutout angle of the quartz single crystal substrate and the propagation direction of the surface acoustic wave in Euler angles (0 °, 90 °, 45 °).
゜), and the cutout angle and the propagation direction of the surface acoustic wave of the lithium niobate single crystal thin plate are represented by Euler angles (0 °,
90 °, θ2), showing the results of numerical calculation of the electromechanical coupling coefficient of the surface acoustic wave when θ2 and the normalized plate thickness H / λ are changed.

FIG. 20 shows the cutout angle of the quartz single crystal substrate and the propagation direction of the surface acoustic wave in Euler angles (0 °, 90 °, 45 °).
゜), and the cutout angle and the propagation direction of the surface acoustic wave of the lithium niobate single crystal thin plate are represented by Euler angles (0 °,
90 °, θ2), showing the results of numerical calculation of the delay time temperature coefficient of the surface acoustic wave when θ2 and the normalized plate thickness H / λ are changed.

FIG. 21 shows the cutout angle of the quartz single crystal substrate and the propagation direction of the surface acoustic wave in Euler angles (0 °, 90 °, 60 °).
゜), and the cutout angle and the propagation direction of the surface acoustic wave of the lithium niobate single crystal thin plate are represented by Euler angles (0 °,
90 °, θ2), showing the results of numerical calculation of the sound velocity of surface acoustic waves when θ2 and the normalized plate thickness H / λ are changed.

FIG. 22 shows the cutout angle of the quartz single crystal substrate and the propagation direction of the surface acoustic wave in Euler angles (0 °, 90 °, 60 °).
゜), and the cutout angle and the propagation direction of the surface acoustic wave of the lithium niobate single crystal thin plate are represented by Euler angles (0 °,
90 °, θ2), showing the results of numerical calculation of the electromechanical coupling coefficient of the surface acoustic wave when θ2 and the normalized plate thickness H / λ are changed.

FIG. 23 shows the cutout angle of the quartz single crystal substrate and the propagation direction of the surface acoustic wave in Euler angles (0 °, 90 °, 60 °).
゜), and the cutout angle and the propagation direction of the surface acoustic wave of the lithium niobate single crystal thin plate are represented by Euler angles (0 °,
90 °, θ2), showing the results of numerical calculation of the delay time temperature coefficient of the surface acoustic wave when θ2 and the normalized plate thickness H / λ are changed.

FIG. 24 shows the cutout angle of the quartz single crystal substrate and the propagation direction of the surface acoustic wave in Euler angles (0 °, 90 °, 75 °).
゜), and the cutout angle and the propagation direction of the surface acoustic wave of the lithium niobate single crystal thin plate are represented by Euler angles (0 °,
90 °, θ2), showing the results of numerical calculation of the sound velocity of surface acoustic waves when θ2 and the normalized plate thickness H / λ are changed.

FIG. 25 shows the cutout angle of the quartz single crystal substrate and the propagation direction of the surface acoustic wave in Euler angles (0 °, 90 °, 75 °).
゜), and the cutout angle and the propagation direction of the surface acoustic wave of the lithium niobate single crystal thin plate are represented by Euler angles (0 °,
90 °, θ2), showing the results of numerical calculation of the electromechanical coupling coefficient of the surface acoustic wave when θ2 and the normalized plate thickness H / λ are changed.

FIG. 26 shows the cutout angle of the quartz single crystal substrate and the propagation direction of the surface acoustic wave in Euler angles (0 °, 90 °, 75 °).
゜), and the cutout angle and the propagation direction of the surface acoustic wave of the lithium niobate single crystal thin plate are represented by Euler angles (0 °,
90 °, θ2), showing the results of numerical calculation of the delay time temperature coefficient of the surface acoustic wave when θ2 and the normalized plate thickness H / λ are changed.

FIG. 27 is a configuration diagram of an example according to the first embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Single crystal piezoelectric substrate 20 Single crystal piezoelectric thin plate 30 Comb electrode 30 'Comb electrode 11 Single crystal piezoelectric substrate (quartz) 21 Single crystal piezoelectric thin plate (lithium niobate) 31 Comb electrode

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Osamu Kawasaki, Inventor 1006 Ojidoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (7)

[Claims] 1. A single-crystal piezoelectric substrate, a single-crystal piezoelectric thin plate, and a comb-shaped electrode provided on at least one of the single-crystal piezoelectric substrate and the single-crystal piezoelectric thin plate for exciting surface acoustic waves. In the surface acoustic wave element including, the single crystal piezoelectric substrate and the single crystal piezoelectric thin plate are directly bonded and laminated, and the surface acoustic wave is a Rayleigh type surface acoustic wave, and the single crystal piezoelectric thin plate H / λ is in the range of H / λ <0.5, where H is the plate thickness and λ is the wavelength of the surface acoustic wave to be excited. 2. The direct bonding method according to claim 1, wherein the single-crystal piezoelectric substrate and the single-crystal piezoelectric thin plate are respectively flattened, mirror-finished, and cleaned.
2. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is directly bonded by performing a hydrophilization treatment and a superposition heat treatment. 3. The sound velocity of the surface acoustic wave in the propagation direction of the surface acoustic wave of the single crystal piezoelectric thin plate is lower than the sound velocity of the surface acoustic wave in the propagation direction of the surface acoustic wave of the single crystal piezoelectric substrate. The surface acoustic wave device according to claim 1 or 2, wherein: 4. A delay time temperature coefficient of the surface acoustic wave in a direction in which the surface acoustic wave of the single crystal piezoelectric substrate propagates,
4. The surface acoustic wave device according to claim 3, wherein a delay time temperature coefficient of the surface acoustic wave in the direction of the single crystal piezoelectric thin plate is smaller. 5. The surface acoustic wave has a negative delay time temperature coefficient in a direction in which the surface acoustic wave of the single crystal piezoelectric substrate propagates, and the surface acoustic wave in the direction of the single crystal piezoelectric thin plate has a negative value. 4. The surface acoustic wave device according to claim 3, wherein the delay time temperature coefficient has a positive value. 6. The single crystal piezoelectric substrate is quartz or langasite, and the single crystal piezoelectric thin plate is lithium niobate, lithium tantalate or lithium borate. The surface acoustic wave device as described in the above. 7. The surface acoustic wave device according to claim 6, wherein the single-crystal piezoelectric substrate is quartz and the single-crystal piezoelectric thin plate is lithium niobate.