JP2003273691A - Surface acoustic wave device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave (SAW) device in which a degree of freedom in the combination of an electro-mechanical coupling coefficient, a sonic velocity, and temperature dependency is high, particularly, the electro- mechanical coupling coefficient is high and the temperature dependency is low. <P>SOLUTION: At least two single crystal piezoelectric substrates of mutually different SAW propagation characteristics or a single crystal piezoelectric substrate and a non-piezoelectric substrate are directly bonded by piling heat treatment while applying flattening, making into mirror surface, cleaning and making hydrophilic to respective substrate surfaces. Then, the thickness of one piezoelectric substrate is defined as a thickness suitable for the wavelength of a sonic wave to be used, and the piezoelectric substrate is equipped with a surface wave exciting interdigital electrode. <P>COPYRIGHT: (C)2003,JPO

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 used for filters, resonators and the like.

[0002]

2. Description of the Related Art In recent years, with the progress and development of mobile communication technology, the size and frequency of communication equipment have been increasing. An oscillator and a high frequency filter are always required for these devices, and surface acoustic wave devices are often used for these oscillators and high frequency filters.

A conventional surface acoustic wave device, such as a surface acoustic wave filter or a surface acoustic wave resonator, has a comb-shaped electrode formed on a piezoelectric substrate of lithium niobate and the like, and an alternating electric field is applied to the electrode to vibrate the surface acoustic wave. Are excited. A surface acoustic wave device having high frequency characteristics is required for use in mobile communication equipment. In the case of a filter, the important high-frequency characteristics of the surface acoustic wave element are the insertion loss and its temperature dependence. In the case of a resonator, the resonance Q (corresponding to the reciprocal of the loss) and the resonance / anti-resonance ratio (capacitance ratio). ) And its temperature dependence. The capacitance ratio is directly related to the pass band when used in a resonator type filter or the like. Insertion loss,
The Q of resonance 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 speed of sound of the piezoelectric body used.

From a manufacturing point of view, since the line width of the comb-shaped electrodes varies depending on the acoustic velocity of the piezoelectric substrate, the acoustic velocity of the piezoelectric substrate is also important from the viewpoint of ease of fine processing such as photolithography.

The electromechanical coupling coefficient, temperature dependence, and sound velocity are
It depends largely on the material used and its crystal orientation.
In the case of lithium niobate, 64 degree Y-cut X-axis propagation,
Electromechanical coupling coefficient 11.3%, temperature dependence 70pp
m / ° C, sound velocity 4742 m / sec, 128 degree Y-cut X-axis propagation, electromechanical coupling coefficient 5.5%, temperature dependence 7
5 ppm / ° C, sound velocity 3980 m / sec, lithium tantalate, 36 degree Y-cut X-axis propagation, electromechanical coupling coefficient 5.0%, temperature dependence 30 ppm / ° C, sound velocity 4160 m / sec, crystal In the case of 42.5 degrees Y-cut X-axis propagation, electromechanical coupling coefficient 0.15%, temperature dependence 0 ppm / ° C, sound velocity 3158 m / sec, in the case of lithium borate, 45 degrees X-cut, electrical Mechanical coupling coefficient is 1.0
%, The sound velocity is about 3401 m / sec.

From the viewpoint of electromechanical coupling coefficient, lithium niobate is generally desirable. However, the temperature dependence is inferior to that of quartz. Quartz has extremely low temperature dependence, but has a small electromechanical coupling coefficient. Regarding the speed of sound, when using it for a resonator or filter at high frequencies,
The faster the line width of the comb-shaped electrode, the greater the width of 64 degrees Y.
Cut X-axis propagating lithium niobate is preferred.

From the viewpoint of design flexibility, it is preferable that the electromechanical coupling coefficient is large, the temperature dependence is small, and the sound velocity is fast. However, the above materials are not sufficient.

When the conventional piezoelectric substrate made of a single material is used, the combination of the electromechanical coupling coefficient and the temperature dependence is limited, and the degree of freedom in design is small. In addition, there is a problem that there is no material having a large electromechanical coupling coefficient and a small temperature dependence, and there is no piezoelectric substrate having a high acoustic velocity.

In order to solve these problems, a surface acoustic wave device having a laminated structure is known. For example, in order to obtain a surface acoustic wave substrate having a high acoustic velocity, a configuration in which a piezoelectric film is laminated on a non-piezoelectric substrate having a high acoustic velocity such as sapphire or diamond has been reported. (For example, refer to Patent Document 1). The piezoelectric film may be formed by sputtering or chemical vapor deposition (CV).
ZnO or AlN formed by a thin film forming technique such as D)
Is used.

A laminated structure of ZnO and lithium niobate, which is a laminated structure of piezoelectric materials, has been reported by A. Armstrong et al. (See Non-Patent Document 1, for example). With this structure, a surface acoustic wave device having an excellent electromechanical coupling coefficient can be obtained.

In order to improve temperature characteristics, a method is known in which an AlN film which is a piezoelectric material is formed on a Si semiconductor substrate and a silicon oxide film is formed on the AlN film to improve the temperature characteristics. (For example, refer to Patent Document 2).

[0012]

[Patent Document 1] JP-A-64-62911

[Patent Document 2] US Pat. No. 4,516,049

[Non-Patent Document 1] Proc. 1972 IEEE Ultrasonics Symp.
(IEEE, New York, 1972) p.370

[0013]

The above-mentioned conventional stacking techniques are all stacked structures using various thin film forming techniques such as sputtering and CVD. In that case, there are severe restrictions on the combination of substrate and material. For example, a piezoelectric film formed by sputtering or the like has inferior piezoelectric characteristics to a bulk single crystal. Further, in order to obtain the piezoelectric characteristics, it is necessary to orient at least the crystal direction uniformly, but the combination of the substrate and the film is extremely limited for the orientation. Further, it is preferable to form the single crystal thin film by the epitaxial growth technique, but in this case, the combination of the substrate and the film is further limited. For example, in piezoelectric materials such as quartz, lithium niobate, lithium tantalate, and lithium borate, which are usually used for surface acoustic wave devices, good epitaxial films have not been obtained when the substrate materials are different. Therefore, even in this case, the degree of freedom in design is poor,
There is a problem that there are few materials that have a large electromechanical coupling coefficient, excellent temperature dependence, and excellent sound speed.

Characteristically, it is known that if a piezoelectric material having a large electromechanical coupling coefficient, such as PZT, can be laminated on a substrate such as a dielectric or a semiconductor, a substrate having a large electromechanical coupling coefficient can be obtained. Has no means of achieving it. When the thin film technique is used, it is necessary to orient the piezoelectric material in a predetermined direction. However, since the combination with the substrate is extremely limited, a practical material has not been obtained. If various adhesives are used, the adhesive enters the interface of surface acoustic wave propagation and the surface acoustic waves are attenuated,
The desired characteristics cannot be obtained.

[0015]

In order to solve the above problems, a surface acoustic wave device of the present invention is provided with at least two single crystal piezoelectric substrates having different surface acoustic wave propagation characteristics, and the single crystal piezoelectric substrate. And a comb-shaped electrode for exciting the surface acoustic wave generated, flattening each substrate surface,
It is a product that is directly bonded and laminated by being mirror-finished, cleaned, hydrophilized, and heat-treated for superposition.

Further, since the acoustic velocities of the single crystal piezoelectric substrates are different from each other, a composite single crystal piezoelectric substrate having piezoelectric characteristics and acoustic velocity which cannot be obtained by the single single crystal piezoelectric substrate can be obtained.

Further, since the electromechanical coupling coefficient between the single crystal piezoelectric substrates is different, a composite single crystal piezoelectric substrate having piezoelectric characteristics which cannot be obtained by the single single crystal piezoelectric substrate can be obtained.

Particularly, of the single crystal piezoelectric substrates, the electromechanical coupling coefficient of the single crystal piezoelectric substrate at the surface acoustic wave excitation portion is larger than the electromechanical coupling coefficient of the other single crystal piezoelectric substrate. It is possible to obtain a composite single crystal piezoelectric substrate having piezoelectric characteristics that cannot be obtained with a crystalline piezoelectric substrate.

The single crystal piezoelectric substrate is preferably lithium niobate, lithium tantalate, lithium borate, or quartz.

The single crystal piezoelectric substrate for exciting the surface acoustic wave may be lithium niobate, and the other single crystal piezoelectric substrate may be quartz.

The thickness of the single crystal piezoelectric substrate for exciting the surface acoustic wave is preferably 3 wavelengths or less of the wavelength of the surface acoustic wave used.

Further, at least one single crystal piezoelectric substrate, at least one non-piezoelectric substrate having a surface acoustic wave propagation characteristic different from that of the single crystal piezoelectric substrate, and surface acoustic waves provided on the single crystal piezoelectric substrate are excited. The single crystal piezoelectric substrate and the non-piezoelectric substrate are directly bonded by subjecting their respective substrate surfaces to flattening, mirror finishing, cleaning, hydrophilic treatment, and heat treatment for superposition. Are stacked.

At that time, since the acoustic velocities of the single crystal piezoelectric substrate and the non-piezoelectric substrate are different, a composite single crystal piezoelectric substrate having piezoelectric characteristics and acoustic velocity which cannot be obtained by the single single crystal piezoelectric substrate can be obtained.

In particular, even if the speed of sound of the single crystal piezoelectric substrate is slow, if the speed of sound of the non-piezoelectric substrate is high, a composite single crystal piezoelectric substrate which is advantageous for manufacturing photolithography or the like can be obtained as a high frequency surface acoustic wave device.

The single crystal piezoelectric substrate is preferably lithium niobate, lithium tantalate, lithium borate, or quartz.

The thickness of the single crystal piezoelectric substrate is preferably one wavelength or less of the surface acoustic wave used.

Since the coefficient of thermal expansion of the single crystal piezoelectric substrate is larger than that of the non-piezoelectric substrate, a composite single crystal piezoelectric substrate having excellent temperature dependence can be obtained.

With the above structure, the surface acoustic wave propagates in the vicinity of the laminated interfaces, so that the electromechanical coupling coefficient, sound velocity, and temperature dependence of the composite single crystal piezoelectric substrate are independent of each substrate. Different electromechanical coupling coefficient, sound velocity, and temperature dependence are obtained.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION The structure of a surface acoustic wave device according to an embodiment of the present invention and its manufacturing method will be described below with reference to the drawings.

(Embodiment 1) A perspective view of a first embodiment of the structure of the surface acoustic wave device of the present invention is shown in FIG.
FIG. 1B shows a cross-sectional structure taken along the line AA ′ of (a).

In FIG. 1, 10 is a single crystal piezoelectric substrate, 2
0 is a single crystal piezoelectric thin plate (a single crystal piezoelectric substrate is used, but the substrate that excites surface acoustic waves is used as a thin plate, and is hereinafter referred to as a single crystal piezoelectric thin plate in order to distinguish it from the single crystal piezoelectric substrate 10. , 30 and 30 ′ are comb-shaped electrodes provided on the single crystal piezoelectric thin plate 20. The comb-shaped electrodes are shown here in a simplified manner.

Single crystal piezoelectric substrate 10 and single crystal piezoelectric thin plate 20
For example, single crystal piezoelectric materials such as lithium niobate, lithium tantalate, lithium borate, and quartz are suitable.

The function as a surface acoustic wave element is that when a high frequency signal is applied to the comb-shaped electrode 30, the surface acoustic wave is excited in the piezoelectric portion in the vicinity of the comb-shaped electrode 30, and the surface acoustic wave is laminated to the other comb-shaped electrode 30 '. It propagates and is converted into an electric signal again in the piezoelectric portion below the comb-shaped electrode 30 '. Here, the basic structure of the surface acoustic wave device using the comb-shaped electrodes is shown, and when actually forming a high frequency filter or a resonator, the number of the comb-shaped electrodes is increased or the structure is changed.

Single crystal piezoelectric substrate 10 and single crystal piezoelectric thin plate 20
Prepares a single crystal piezoelectric substrate with a thickness that is easy to handle.
The surfaces of the respective substrates are flattened, mirror-finished, cleaned, hydrophilized, and laminated and heat-treated to be directly bonded and laminated, and then the single crystal piezoelectric thin plate 20 side is polished and thinned to a predetermined thickness. It is a thing.

The meaning of the direct bonding used here will be described.

First, the manufacturing process of direct bonding will be described.

Specifically, for example, a case where a single crystal of lithium niobate, lithium tantalate, lithium borate, or quartz is used as the piezoelectric material will be described.

First, the surfaces of the two piezoelectric bodies to be directly bonded are flattened, then mirror-polished and washed. If necessary, the surface layer is removed by etching. A hydrofluoric acid-based etching solution is used for etching lithium niobate, lithium tantalate, and quartz. In the case of lithium borate, a weak acid may be used. Next, the surface is hydrophilized. In particular,
For example, by immersing in ammonia-hydrogen peroxide solution,
Hydroxyl groups easily attach to the surface and are made hydrophilic. Then, it is thoroughly washed with pure water. As a result, hydroxyl groups are attached to the surface of each single crystal piezoelectric substrate. When two single crystal piezoelectric substrates are stacked in this state, the two substrates are adsorbed mainly by the van der Waals force of the hydroxyl group. Even in this state, a strong adhesive state is obtained, but in this state, 1
By performing heat treatment at a temperature of 00 ° C. or higher for several tens of minutes to several tens of hours, water constituent components gradually escape from the interface.
Along with this, bonds relating to oxygen, hydrogen, and substrate-constituting atoms progress from the bond of hydrogen-bonding group of hydroxyl group, and the joining of the substrate-constituting atoms gradually starts to be strengthened. Especially in the presence of silicon and oxygen, covalent bonding proceeds and the bonding is strengthened.

The heat treatment temperature is, in particular, 200-100.
A range of 0 ° C. in which the piezoelectric characteristics of the piezoelectric body used are not lost is preferable.

FIG. 2 shows a transmission electron microscope (TEM) photograph of a direct bonding interface in which lithium niobate and lithium tantalate were directly bonded by the above-mentioned method. The heat treatment temperature is 400 ° C. for 1 hour. In the TEM image, the lines seen on the respective substrate sides are so-called atomic lattice images. Since the distance between these lines corresponds to the lattice distance, the junction has a lattice, that is, atomic order (about 1 nm) accuracy. You can see that they are joined with.
As described above, since the bonding can be performed with high accuracy and without inclusions at the interface, the loss for surface acoustic wave propagation is extremely small.

In the case of bonding with an ordinary adhesive, it is difficult to reduce the thickness of the adhesive to a few μm or less, and therefore, the surface acoustic wave is significantly attenuated, which is not practical.

When a piezoelectric body is formed by using a thin film technique such as sputtering, chemical vapor deposition, vacuum deposition, etc., a fairly good joint interface can be obtained, but the piezoelectric characteristic of the obtained piezoelectric body is that of a bulk. It is far inferior to the above, and the types of piezoelectric bodies obtained are limited to ZnO, AlN, and the like. The crystal orientation is also limited by the crystal orientation of the substrate, and the specific orientation, for example, the orientation that facilitates growth such as the C-axis direction is limited.

If the direct bonding technique of this embodiment is used, the composite piezoelectric substrate can be formed in any crystal orientation while maintaining the bulk property in the single crystal piezoelectric materials lithium niobate, lithium tantalate, lithium borate, and quartz. Is obtained.

Also, before or after direct bonding, one of the piezoelectric bodies can be easily thinned by processing such as polishing. Usually, after direct bonding, one of the piezoelectric bodies is made thinner by polishing or the like to a thickness suitable for the wavelength of the surface acoustic wave using the piezoelectric body, and then the comb-shaped electrode is formed. If it is a thickness that can be handled, it may be set to that thickness in advance and then directly bonded. However, when it is difficult to handle, ordinarily from about 50 μm to the following, it is better to directly bond and then polish to make a thin plate.

When the direct bonding according to the present embodiment is used, since the interface is bonded with the flatness of atomic order, it is possible to highly accurately make the thin plate uniform. Specifically, 3 μm +
It is possible to reduce the thickness to about 0.01 μm. This is also an advantage of direct bonding.

In the configuration of FIG. 1, the single crystal piezoelectric substrate 10
And piezoelectric characteristics of the single crystal piezoelectric thin plate 20, sound velocity, temperature dependence,
By appropriately combining the coefficients of thermal expansion, it is possible to obtain a surface acoustic wave element composed of various composite single crystal piezoelectric substrates having a high degree of freedom in design.

The characteristics of the surface acoustic wave device are mainly determined by the electromechanical coupling coefficient, the speed of sound, and the temperature dependence of the speed of sound. When applied to a filter or the like, the electromechanical coupling coefficient is related to insertion loss and pass band width. Generally, the larger the electromechanical coupling coefficient, the smaller the insertion loss and the wider the pass band width. Depending on the application, the wider passband may be better,
On the contrary, sometimes it is better to be narrow.

The speed of sound determines the electrode width of the comb-shaped electrode. Since the electrode width of the comb-shaped electrodes and the distance between them are usually set to about 1/4 wavelength, in high frequency applications, the faster the speed of sound, the easier microfabrication such as photolithography in manufacturing, which is preferable.

On the other hand, in low frequency applications, or in applications such as signal delay lines, the slower the speed of sound, the smaller the element size, which is preferable.

Generally, the smaller the temperature dependence, the better.

(Embodiment 1-1) FIG. 3 shows the structure of the first specific embodiment of the first embodiment. Lithium tantalate is used for the single crystal piezoelectric substrate and niobate is used for the single crystal piezoelectric thin plate. This is an example using lithium.

In FIG. 3, 11 is a single crystal piezoelectric substrate made of 36 ° Y-cut, X-axis propagating single crystal lithium tantalate, and 21 is 41 ° Y-cut, X-axis propagating single crystal niobate. In the single crystal piezoelectric thin plate made of lithium, the single crystal piezoelectric substrate 11 and the single crystal piezoelectric thin plate 21 are combined by the above-mentioned direct bonding.

Reference numerals 30 and 30 ′ are comb-shaped electrodes provided on the single crystal piezoelectric thin plate 21. Here, the display is simplified.

The electromechanical coupling coefficient of 41 ° Y-cut, X-axis propagating single crystal lithium niobate is 17.2%, the speed of sound is 4792 m / sec, 36 ° Y-cut, X-axis propagating single crystal lithium tantalate. Has an electromechanical coupling coefficient of 5-7% and a sound velocity of 4160 m / sec.

However, in the composite single crystal piezoelectric substrate composited by direct bonding in this way, the thickness of the single crystal piezoelectric thin plate 21 is set to an appropriate thickness according to the wavelength of the surface acoustic wave to be used. The electromechanical coupling coefficient and the sound velocity are different from those of the piezoelectric bodies.

For example, when the comb electrodes are excited at about 200 MHz, the interval between the comb electrodes is set to about 5 μm at 1/4 wavelength (the sound velocity is considered to be 4160 m / sec), and the single crystal piezoelectric thin plate 21 is used.
By setting the thickness of the single-crystal piezoelectric thin plate 21 to 36 ° Y-cut and X-axis propagating single-crystal tantalic acid, the electromechanical coupling coefficient and the sound velocity are both set to 5-60 μm, which is from ¼ wavelength to 3 wavelengths. With respect to the value of lithium, a value different from the 41 ° Y-cut of the single crystal piezoelectric substrate 11 and the single crystal lithium niobate of X axis propagation is obtained.

Specifically, for example, intermediate values are obtained. When the thickness of the single crystal piezoelectric thin plate 21 is set to about 1 wavelength to about 1 wavelength, the electromechanical coupling coefficient is 10%.
Thus, a sound velocity of about 4500 m / sec can be obtained. In this case, since both the electromechanical coupling coefficient and the sound velocity have intermediate values of the original piezoelectric bodies, for example, the surface acoustic wave element is suitable for a filter having a high frequency and a narrow band.

The effect of such a combination is remarkable when the thickness of the single crystal piezoelectric thin plate 21 is particularly between 1/4 wavelength and one wavelength, but the effect is recognized even when the thickness of the single crystal piezoelectric thin plate is about 3 wavelengths.

This embodiment mainly shows the effect on the electromechanical coupling coefficient and the speed of sound.

(Embodiment 1-2) FIG. 4 shows the structure of the second specific embodiment of the first embodiment, in which a single crystal piezoelectric substrate is made of quartz (single crystal) and a single crystal piezoelectric thin plate is made of quartz. This is an example using lithium niobate.

In FIG. 4, 12 is a 43 ° Y-cut, X-axis propagating single crystal piezoelectric substrate made of quartz, and 21 is 41 ° Y-cut, X-axis propagating as in (Example 1-1). A single crystal piezoelectric thin plate made of single crystal lithium niobate,
The single crystal piezoelectric substrate 12 and the single crystal piezoelectric thin plate 21 are combined by the above-mentioned direct bonding.

Reference numerals 30 and 30 ′ are comb-shaped electrodes provided on the single crystal piezoelectric thin plate 21. Here, the display is simplified.

The electromechanical coupling coefficient of 41 ° Y-cut, X-axis propagating single crystal lithium niobate is 17.2%, the speed of sound is 4792 m / sec, and the temperature dependence is about 50 ppm / ° C., 4
The electromechanical coupling coefficient of 3 degree Y-cut, X-axis propagating crystal is 0.16%, the speed of sound is 3158 m / sec, and the temperature dependence is 0 p.
pm / ° C.

Also in this case, as in (Example 1-1), by setting the thickness of the single crystal piezoelectric thin plate to an appropriate thickness according to the wavelength of the surface acoustic wave used, a substantial electromechanical coupling coefficient is obtained. It is possible to obtain characteristics in which the speed of sound and the temperature dependence are different from those of the piezoelectric bodies.

For example, when the comb-shaped electrodes are excited at about 200 MHz, the interval between the comb-shaped electrodes is set to about 4 μm at 1/4 wavelength (sound velocity is considered to be 3158 m / sec), and the single crystal piezoelectric thin plate 21 is used.
Of the electromechanical coupling coefficient, sonic velocity, and temperature dependency of the single crystal piezoelectric thin plate 21 by 41 degrees Y-cut, X by setting the thickness of the single crystal piezoelectric thin plate 21 to 4 to 48 μm, which is three wavelengths from ¼ wavelength.
A value different from that of the axial-propagation single crystal lithium niobate and a value of 43 ° Y-cut of the single-crystal piezoelectric substrate 12 and X-axis propagation crystal is obtained.

For example, intermediate values are obtained. When the thickness of the single-crystal piezoelectric thin plate 21 is set to about 1/2 wavelength to about 1 wavelength, the electromechanical coupling coefficient is 5% and the sound velocity is 33%.
A value of 00 m / sec and a temperature dependence of about 30 ppm / ° C. can be obtained. In this case, since the electromechanical coupling coefficient, the sound velocity, and the temperature dependence have intermediate values of the original piezoelectric materials, the surface acoustic wave device is suitable for a filter having very little temperature dependence.

The effect of such compounding is remarkable when the thickness of the single crystal piezoelectric thin plate 21 is particularly between 1/4 wavelength and 1 wavelength, but the effect is recognized even when the thickness of the single crystal piezoelectric thin plate is about 3 wavelengths.

The present example mainly shows the effect on the temperature dependence.

(Embodiment 1-3) FIG. 5 shows the structure of the third specific embodiment of the first embodiment, in which a single crystal piezoelectric substrate is made of quartz (single crystal) and a single crystal piezoelectric thin plate is made of quartz. This is an example using lithium tantalate.

In FIG. 5, numeral 12 indicates (Example 1-1).
Similarly, a single crystal piezoelectric substrate made of 43 ° Y-cut, X-axis propagating quartz, 22 is a single crystal piezoelectric thin plate made of 36 ° Y-cut, X-axis propagating single crystal lithium tantalate. The piezoelectric substrate 12 and the single crystal piezoelectric thin plate 22 are combined by the above-mentioned direct bonding.

Reference numerals 30 and 30 ′ are comb-shaped electrodes provided on the single crystal piezoelectric thin plate 22. Here, the display is simplified.

The electromechanical coupling coefficient of 36 ° Y-cut, X-axis propagating single crystal lithium tantalate is 5-7%, the speed of sound is 4160 m / sec, and the temperature dependence is about 30 ppm / ° C.
The electromechanical coupling coefficient of 3 degree Y-cut, X-axis propagating crystal is 0.16%, the speed of sound is 3158 m / sec, and the temperature dependence is 0 p.
pm / ° C.

Also in this case, as in (Example 1-1), the thickness of the single crystal piezoelectric thin plate is set to an appropriate thickness according to the wavelength of the surface acoustic wave to be used, so that a substantial electromechanical coupling coefficient is obtained. It is possible to obtain characteristics in which the speed of sound and the temperature dependence are different from those of the piezoelectric bodies.

For example, when the comb-shaped electrodes are excited at about 200 MHz, the interval between the comb-shaped electrodes is set to about 4 μm at 1/4 wavelength (the sound velocity is considered to be 3158 m / sec), and the single crystal piezoelectric thin plate 21 is used.
Of the electromechanical coupling coefficient, sonic velocity, and temperature dependency of the monocrystalline piezoelectric thin plate 22 by 36 degrees Y-cut, X by setting the thickness of the single crystal piezoelectric thin plate 22 to 4 to 48 μm, which is from ¼ wavelength to 3 wavelengths.
A value different from that of the axially propagated single crystal lithium tantalate and a value of 43 ° Y-cut of the single crystal piezoelectric substrate 12 and that of the X axis propagated crystal are obtained.

For example, intermediate values are obtained. When the thickness of the single crystal piezoelectric thin plate 22 is set to about 1/2 wavelength to about 1 wavelength, the electromechanical coupling coefficient is 2% and the sound velocity is 33%.
A value of 00 m / sec and a temperature dependence of about 20 ppm / ° C. can be obtained. In this case, since the electromechanical coupling coefficient, the sound velocity, and the temperature dependence have intermediate values of the original piezoelectric materials, the surface acoustic wave device is suitable for a filter having very little temperature dependence.

The effect of such combination is remarkable when the thickness of the single crystal piezoelectric thin plate 21 is particularly between 1/4 wavelength and one wavelength, but the effect is recognized even when the thickness of the single crystal piezoelectric thin plate is about 3 wavelengths.

The present example mainly shows the effect on the temperature dependence.

(Embodiment 1-4) FIG. 6 shows the structure of the fourth concrete embodiment of the embodiment 1, in which a single crystal piezoelectric substrate is made of single crystal lithium borate and a single crystal piezoelectric thin plate is made of niobium. This is an example using lithium acid.

In FIG. 6, 13 is a 45 ° X-cut single crystal piezoelectric substrate made of Z-axis propagating single crystal lithium borate, and 21 is 41 ° Y-, as in (Example 1-1).
A single crystal piezoelectric thin plate made of cut and X-axis propagating single crystal lithium niobate. The single crystal piezoelectric substrate 13 and the single crystal piezoelectric thin plate 21 are combined by the above-mentioned direct bonding.

Reference numerals 30 and 30 ′ are comb-shaped electrodes provided on the single crystal piezoelectric thin plate 21. Here, the display is simplified.

The electromechanical coupling coefficient of 41 ° Y-cut, X-axis propagating single crystal lithium niobate is 17.2%, the speed of sound is 4792 m / sec, and the temperature dependence is about 50 ppm / ° C., 4
The electromechanical coupling coefficient of 5 ° X-cut, Z-axis propagating single crystal lithium borate is 1%, the speed of sound is 3401 m / sec, and the temperature dependence is 0 ppm / ° C.

Also in this case, as in (Example 1-1), the thickness of the single crystal piezoelectric thin plate is set to an appropriate thickness according to the wavelength of the surface acoustic wave to be used, so that a substantial electromechanical coupling coefficient is obtained. It is possible to obtain characteristics in which the speed of sound and the temperature dependence are different from those of the piezoelectric bodies.

For example, when the comb-shaped electrodes are excited at about 200 MHz, the interval between the comb-shaped electrodes is set to about 4 μm at 1/4 wavelength (sound velocity is considered to be 3401 m / sec), and the single crystal piezoelectric thin plate 21 is used.
Of the electromechanical coupling coefficient, sonic velocity, and temperature dependency of the single crystal piezoelectric thin plate 21 by 41 degrees Y-cut, X by setting the thickness of the single crystal piezoelectric thin plate 21 to 4 to 48 μm, which is three wavelengths from ¼ wavelength.
A value different from the axial propagation single crystal lithium niobate and the 45 ° X-cut of the single crystal piezoelectric substrate 13 and the Z axis propagation single crystal lithium borate is obtained.

For example, intermediate values are obtained. When the thickness of the single-crystal piezoelectric thin plate 21 is set to about 1/2 wavelength to 1 wavelength, the electromechanical coupling coefficient is 5% and the sound velocity is 35%.
A value of 00 m / sec and a temperature dependence of about 30 ppm / ° C. can be obtained. In this case, since the electromechanical coupling coefficient, the sound velocity, and the temperature dependence have intermediate values of the original piezoelectric materials, the surface acoustic wave device is suitable for a filter having very little temperature dependence.

The effect of such a combination is remarkable when the thickness of the single crystal piezoelectric thin plate 21 is particularly between 1/4 wavelength and one wavelength, but the effect is recognized even when the thickness of the single crystal piezoelectric thin plate is about 3 wavelengths.

The present example mainly shows the effect on the temperature dependence.

Although only specific combinations of lithium niobate, lithium tantalate, lithium borate, and quartz have been shown as the single-crystal piezoelectric body, various combinations other than this, various electric machines according to the combination are also shown. Coupling coefficient,
A composite single crystal piezoelectric substrate having sonic velocity and temperature dependency can be obtained.

Reference Example 1 A perspective view of a second embodiment of the structure of the surface acoustic wave device of the present invention is shown in FIG. 7A, and a sectional view taken along the line AA ′ in FIG. 7A. Is shown in FIG.

In FIG. 7, 10, 20, 30, 30 '
Are the comb-shaped electrodes formed on the single crystal piezoelectric substrate, the single crystal piezoelectric thin plate, and the single crystal piezoelectric thin plate 20, respectively, as in the first embodiment. Here again, the comb-shaped electrodes are shown in a simplified manner. Reference numeral 40 denotes the single crystal piezoelectric substrate 10 and the single crystal piezoelectric thin plate 2.
It is an inorganic thin film layer formed between 0.

Single crystal piezoelectric substrate 10 and single crystal piezoelectric thin plate 20
In the same manner as in Example 1, for example, single crystal piezoelectric materials such as lithium niobate, lithium tantalate, lithium borate, and quartz are suitable.

Suitable inorganic thin film layers are silicon compounds such as silicon, silicon oxide and silicon nitride, and silicic acid compounds such as borosilicate compounds. The thickness of the inorganic thin film layer is preferably sufficiently thin with respect to the wavelength of the surface acoustic wave used, and specifically, it is preferably ½ wavelength or less.

The function as the surface acoustic wave device is the same as that of the first embodiment.
Similarly, by applying a high frequency signal to the comb-shaped electrode 30, a surface acoustic wave is excited in the piezoelectric portion in the vicinity of the comb-shaped electrode 30 and propagates to the other comb-shaped electrode 30 'through the laminated structure to form a lower part of the comb-shaped electrode 30'. It is converted back into an electric signal by the piezoelectric section of.

Here, the basic structure of the surface acoustic wave device using the comb-shaped electrodes is shown, and when actually forming a high frequency filter or a resonator, the number of the comb-shaped electrodes is increased or the structure is changed.

Single crystal piezoelectric substrate 10 and single crystal piezoelectric thin plate 20
Has an inorganic thin film layer on at least one substrate surface of the piezoelectric body, and each inorganic thin film layer and the substrate surface are flattened, mirror-finished, cleaned, hydrophilized, and heat-treated by superposition. It is directly joined and laminated.

The meaning of the direct bonding used here is that of Example 1.
Is the same as.

A manufacturing process of direct bonding in this embodiment will be described.

Specifically, for example, the case where a single crystal of lithium niobate, lithium tantalate, lithium borate, or quartz is used as the piezoelectric body will be described.

As the inorganic thin film layer, silicon, silicon oxide,
The case where silicon nitride or borosilicate glass is used will be described.

First, the surfaces of the two piezoelectric bodies to be directly bonded are flattened, mirror-finished, and washed. If necessary, the surface layer is removed by etching.

Next, an inorganic thin film layer is formed by a thin film technique on the surface to be bonded of at least one of the two piezoelectric bodies. The inorganic thin film layer can be formed of any of the above materials by sputtering, chemical vapor deposition, or vacuum vapor deposition. The film thickness is made sufficiently thinner than the wavelength of the surface acoustic wave used. Specifically, it is 1/2 wavelength or less of the surface acoustic wave to be used, more preferably 1/10 wavelength or less, for example 0.1.
It is about -1 μm.

Next, the surface of the piezoelectric body or the inorganic thin film layer to be joined is, if necessary (flattened, mirror-finished, and cleaned before the formation of the inorganic thin film layer, so that the inorganic thin film layer is well formed). (It is unnecessary if necessary.) After flattening and mirror-finishing, apply hydrophilic treatment. The subsequent processing is the same as in the first embodiment.

Specifically, by immersing in, for example, an ammonia-hydrogen peroxide solution, hydroxyl groups easily adhere to the surface and are made hydrophilic. Then, it is thoroughly washed with pure water.
As a result, hydroxyl groups are attached to the surface of each substrate. When the two substrates are superposed in this state, the two substrates are adsorbed mainly by the van der Waals force of the hydroxyl group. Even in this state, it will be a strong adhesion state, but in this state,
By performing heat treatment at a temperature of 100 ° C. or higher for several tens of minutes to several tens of hours, water constituent components gradually escape from the interface. Along with this, bonds relating to oxygen, hydrogen, and substrate-constituting atoms progress from the bond of hydrogen-bonding group of hydroxyl group, and the joining of the substrate-constituting atoms gradually starts to be strengthened. In particular, since the inorganic thin film layer contains silicon and oxygen is sufficiently present in the periphery, covalent bonding proceeds,
The bond is strengthened.

The heat treatment temperature is, in particular, 200-100.
A range of 0 ° C. in which the characteristics of the piezoelectric body used are not lost is preferable.

The direct joining in this case is also the same as in the first embodiment.
Since the joining is performed with the accuracy of atomic order, the loss for the propagation of the surface acoustic wave is extremely small. Further, when the thickness of the inorganic thin film layer is made sufficiently thin as compared with the wavelength of the surface acoustic wave to be used, the loss of the surface acoustic wave in the inorganic thin film layer is extremely small, and there is practically no problem. Therefore, the advantage of direct bonding is similar to that of the first embodiment.

The feature of this embodiment is that an inorganic thin film layer is present at the direct bonding interface as compared with the first embodiment. This has two advantages.

The first advantage is that even if there is some dust on the interface during joining, the dust is taken into this inorganic thin film layer during direct joining, so the manufacturing yield during joining is improved.

The second advantage is that the electrode can be easily embedded in the inorganic thin film layer, which further increases the degree of freedom in designing the surface acoustic wave element.

FIG. 8 shows an embodiment having a structure in which an electrode is embedded in an inorganic thin film layer.

In FIG. 8A, reference numerals 10 and 20 denote a single crystal piezoelectric substrate and a single crystal piezoelectric thin plate, respectively. Three
Reference numerals 1 and 31 ′ are comb electrodes embedded in the inorganic thin film layer 40. The comb-shaped electrode is formed on the lower substrate side. Although not shown, the ends of the comb electrodes are exposed so that they can be connected to an external circuit.

FIG. 8B shows an example in which a comb-shaped electrode is formed on the single crystal piezoelectric thin plate side.

FIG. 8C is an example in which the ground electrode 35 is provided on the upper surface of the single crystal piezoelectric thin plate in the configuration of FIG. 8A.

FIG. 8D is an example in which the ground electrode 35 is provided on the upper surface of the single crystal piezoelectric thin plate in the configuration of FIG. 8B.

FIG. 8E shows an example in which the ground electrode 35 'is formed in the inorganic thin film layer in the structure of FIG.

The difference in characteristics due to such an electrode structure is as follows.
Qualitatively it is as follows. Basically, it depends on where the electric field is concentrated on the upper and lower substrates. FIG. 8 shows the order in which electric fields are easily concentrated on the single crystal piezoelectric thin plate.
(E), FIG. 7, FIG. 8 (d) (c), FIG. 8 (b) (a). Qualitatively, in almost this order, the piezoelectric characteristics obtained by mixing the characteristics of the upper and lower substrates are obtained as the piezoelectric characteristics of the laminated structure.

Therefore, in the case of such an electrode structure, even if the same piezoelectric body and thickness as those in FIG. 7 are used, the way in which surface acoustic wave is excited is different, and naturally, piezoelectric characteristics different from those in FIG. 7 are obtained. To be Specifically, for example, the effect of increasing the electromechanical coupling coefficient can be obtained.

In order to obtain the structure of FIG. 8, the surface of the single crystal piezoelectric substrate is flattened, mirror-finished, and cleaned, and then a comb-shaped electrode is formed. It can be obtained by forming an inorganic thin film layer and directly bonding it by the above-described manufacturing process. When embedding the comb-shaped electrodes, the inorganic thin film layer must have sufficiently high resistance.

Also in the configuration of FIG. 7 or FIG. 8, the piezoelectric characteristics of the single crystal piezoelectric substrate 10 and the single crystal piezoelectric thin plate 20, the sound velocity,
By appropriately combining the temperature dependence and the coefficient of thermal expansion, a surface acoustic wave device composed of various composite single crystal piezoelectric substrates having a high degree of design freedom can be obtained.

Reference Example 1-1 FIG. 9 shows the structure of the first specific example of Reference Example 1. Lithium tantalate is used for the single crystal piezoelectric substrate and niobate is used for the single crystal piezoelectric thin plate. In this example, lithium is used and silicon is used for the inorganic thin film layer.

In FIG. 9, similar to (Example 1-1),
11 is a 36 degree Y-cut, X-axis propagating single crystal lithium tantalate single crystal piezoelectric substrate, 21 is a 41 degree Y-cut, X-axis propagating single crystal lithium niobate single crystal piezoelectric thin plate. Is. Reference numeral 41 is a silicon (amorphous or polycrystalline) layer formed on the single crystal piezoelectric substrate 11 by sputtering, chemical vapor deposition or vacuum deposition.

The single crystal piezoelectric thin plate 21 is compounded at the interface with the silicon layer 41 by the direct bonding described above. 30,
30 'is the single crystal piezoelectric thin plate 2 as in (Example 1-1).
It is a comb-shaped electrode provided on top of 1. Here, the display is simplified.

Also in this embodiment, the thickness of the inorganic thin film layer is sufficiently thin (1/2 wavelength or less, more preferably 1/10).
By setting the wavelength to the wavelength or less), the degree of freedom in designing the piezoelectric characteristics is substantially the same as that in (Example 1-1).

Further, in the case of the present embodiment, the presence of the inorganic thin film layer is advantageous in manufacturing as described above, and the degree of freedom in the arrangement of electrodes is increased.

Reference Example 1-2 FIG. 10 shows the structure of the second specific example of Reference Example 1, in which a single crystal piezoelectric substrate is made of quartz (single crystal), and a single crystal piezoelectric thin plate is made of quartz. This is an example in which lithium niobate is used and silicon oxide or silicon nitride is used for the inorganic thin film layer.

In FIG. 10, reference numeral 12 is a single crystal piezoelectric substrate made of crystal of 43 ° Y-cut and X-axis propagation, and 21.
Is a single crystal piezoelectric thin plate made of 41 ° Y-cut, X-axis propagating single crystal lithium niobate. Also, 42 is formed by sputtering, chemical vapor deposition or vacuum deposition,
Silicon oxide (amorphous) formed on single crystal piezoelectric substrate 12
Alternatively, it is a silicon nitride (amorphous) layer.

The single crystal piezoelectric thin plate 21 is compounded at the interface with the silicon oxide or silicon nitride layer 42 by the above-mentioned direct bonding. Reference numerals 30 and 30 ′ are comb-shaped electrodes provided on the single crystal piezoelectric thin plate 21 as in (Reference Example 1-1).
Here, the display is simplified.

Also in this embodiment, the thickness of the inorganic thin film layer is sufficiently thin (1/2 wavelength or less, more preferably 1/10).
By setting the wavelength to the wavelength or less), as the degree of freedom in designing the piezoelectric characteristic, an effect substantially similar to that of (Example 1-2) can be obtained.

Further, in the case of the present embodiment, the presence of the inorganic thin film layer is advantageous in manufacturing as described above, and the degree of freedom in the arrangement of electrodes is increased.

Reference Example 1-3 FIG. 11 shows the structure of the third specific example in Reference Example 1, in which a single crystal piezoelectric substrate is made of quartz (single crystal) and a single crystal piezoelectric thin plate is made of quartz. This is an example in which lithium tantalate is used and borosilicate glass is used for the inorganic thin film layer.

In FIG. 11, reference numeral 12 indicates (reference example 1-
Similar to 1), a single crystal piezoelectric substrate made of 43 ° Y-cut, X-axis propagating quartz, and 22 is a single crystal piezoelectric thin plate made of 36 ° Y-cut, X-axis propagating single crystal lithium tantalate. . Reference numeral 43 is a borosilicate glass layer formed on the single crystal piezoelectric substrate 12 by sputtering, chemical vapor deposition or vacuum deposition.

The single crystal piezoelectric thin plate 22 is compounded at the interface with the borosilicate glass layer 43 by the above-mentioned direct bonding. Reference numerals 30 and 30 ′ are comb-shaped electrodes provided on the single crystal piezoelectric thin plate 22 as in (Reference Example 1-1). Here, the display is simplified.

Also in this embodiment, the thickness of the inorganic thin film layer is sufficiently thin (1/2 wavelength or less, more preferably 1/10).
By setting the wavelength to the wavelength or less), the degree of freedom in designing the piezoelectric characteristics is substantially the same as that in (Example 1-3).

Further, in the case of the present embodiment, the presence of the inorganic thin film layer is advantageous in manufacturing as described above, and the degree of freedom of the electrode arrangement is increased.

Reference Example 1-4 FIG. 12 shows the structure of the fourth specific example of Reference Example 1, in which a single crystal piezoelectric substrate is provided with single crystal lithium borate and a single crystal piezoelectric thin plate is provided with a single crystal. In this example, crystalline lithium niobate is used as the inorganic thin film layer using a silicon oxide or silicon nitride layer.

In FIG. 12, 13 is a 45 ° X-cut, Z-axis propagating single crystal lithium borate single crystal piezoelectric substrate, and 21 is 41 ° Y-cut, X-axis propagating single crystal lithium niobate. Is a single crystal piezoelectric thin plate.

Reference numeral 42 is a silicon oxide (amorphous) or silicon nitride (amorphous) layer formed on the single crystal piezoelectric substrate 13 by sputtering, chemical vapor deposition or vacuum deposition.

The single crystal piezoelectric thin plate 21 is compounded at the interface with the silicon oxide or silicon nitride layer 42 by the above-mentioned direct bonding. Reference numerals 30 and 30 ′ are comb-shaped electrodes provided on the single crystal piezoelectric thin plate 21 as in (Reference Example 1-1).
Here, the display is simplified.

Also in this example, the thickness of the inorganic thin film layer was made sufficiently thin (1/2 wavelength or less, more preferably 1/10).
By setting the wavelength to the wavelength or less), the degree of freedom in designing the piezoelectric characteristics is substantially the same as that in (Example 1-4).

Further, in the case of the present embodiment, the presence of the inorganic thin film layer is advantageous in manufacturing as described above, and the degree of freedom of electrode arrangement is increased.

As the single crystal piezoelectric body, lithium niobate, lithium tantalate, lithium borate, quartz, and the inorganic thin film layer are shown only for a specific combination of silicon, silicon oxide, silicon nitride, and borosilicate glass. Even in various combinations other than this, a composite single crystal piezoelectric substrate having various electromechanical coupling coefficients, sonic velocities, and temperature dependences can be obtained according to the combinations.

(Embodiment 2) A perspective view of a third embodiment of the structure of the surface acoustic wave device of the present invention is shown in FIG. 13 (a), and a sectional view taken along the line AA 'in FIG. 13 (a). Fig. 13 (b)
Shown in.

In FIG. 13, reference numeral 50 denotes a non-piezoelectric substrate, 20
Is a single crystal piezoelectric thin plate, and 30 and 30 'are single crystal piezoelectric thin plates 20.
It is a comb-shaped electrode provided on the top. The comb-shaped electrodes are shown here in a simplified manner.

The non-piezoelectric substrate 50 is, for example, a substrate having a low sound velocity such as glass, a substrate having a small coefficient of thermal expansion, or a substrate having a high sound velocity such as boron, amorphous carbon or graphite, and the single crystal piezoelectric thin plate 20. For example, single crystal piezoelectric materials such as lithium niobate, lithium tantalate, lithium borate, and quartz are suitable.

The function as the surface acoustic wave device is the same as that of the first embodiment.
Similarly, by applying a high frequency signal to the comb-shaped electrode 30, a surface acoustic wave is excited in the piezoelectric portion in the vicinity of the comb-shaped electrode 30 and propagates to the other comb-shaped electrode 30 'through the laminated structure to form a lower part of the comb-shaped electrode 30'. It is converted back into an electric signal by the piezoelectric section of.

Here, the basic structure of the surface acoustic wave device using the comb-shaped electrodes is shown, and when actually forming a high frequency filter or a resonator, the number of the comb-shaped electrodes is increased or the structure is changed.

The non-piezoelectric substrate 50 and the single crystal piezoelectric thin plate 20 are
The respective surfaces are flattened, mirror-finished, cleaned, hydrophilized, and subjected to a heat treatment for superposition to be directly bonded and laminated.

The meaning of the direct bonding used here is that of Example 1.
Is the same as.

Next, the manufacturing process in this embodiment will be described.

Specifically, for example, as a non-piezoelectric substrate,
Glass, boron, amorphous carbon, graphite,
A case where single crystal lithium niobate, lithium tantalate, lithium borate, or quartz is used as the piezoelectric body will be described.

First, the non-piezoelectric substrate to be directly bonded and the surface of the piezoelectric body are flattened, mirror-polished, and washed. If necessary, the surface layer is removed by etching. A hydrofluoric acid-based etching solution is used for etching lithium niobate, lithium tantalate, and quartz. In the case of lithium borate, a weak acid may be used. The surface of the non-piezoelectric substrate is also washed with a hydrofluoric acid solution.

Next, the surface is hydrophilized. The following process is similar to that of the first embodiment.

Specifically, by immersing in, for example, an ammonia-hydrogen peroxide solution, hydroxyl groups easily adhere to the surface and are made hydrophilic. Then, it is thoroughly washed with pure water.
As a result, hydroxyl groups are attached to the surface of each substrate. When the two substrates are superposed in this state, the two substrates are adsorbed mainly by the van der Waals force of the hydroxyl group. Even in this state, it will be a strong adhesion state, but in this state,
By performing heat treatment at a temperature of 100 ° C. or higher for several tens of minutes to several tens of hours, water constituent components gradually escape from the interface. Along with this, bonds relating to oxygen, hydrogen, and substrate-constituting atoms progress from the bond of hydrogen-bonding group of hydroxyl group, and the joining of the substrate-constituting atoms gradually starts to be strengthened. In particular, when silicon, carbon, or oxygen is present, the covalent bond proceeds and the bond is strengthened.

The heat treatment temperature is, in particular, 200-100.
A range of 0 ° C. in which the characteristics of the piezoelectric body used are not lost is preferable. In the case of an easily oxidizable material, it is necessary to perform heat treatment in a non-oxidizing atmosphere.

As in the case of the first embodiment, the junction in this case has a very small loss in propagation of surface acoustic waves because the junction is made with a lattice, that is, with atomic order accuracy.

Boron, amorphous carbon and graphite may be formed on various substrates by a thin film technique.
It suffices that the film thickness is sufficiently thicker than the wavelength of the surface acoustic wave used.

In the structure shown in FIG. 13, the sonic velocity and thermal expansion coefficient of the non-piezoelectric substrate 50 and the piezoelectric characteristics, sonic velocity, temperature dependence, and thermal expansion coefficient of the single crystal piezoelectric thin plate 20 are appropriately combined to provide a degree of freedom in design. A surface acoustic wave device composed of various large composite piezoelectric substrates can be obtained.

(Embodiment 2-1) FIG. 14 shows the structure of the first specific embodiment of the second embodiment, in which a non-piezoelectric substrate is made of glass having a slow sound velocity and a single crystal piezoelectric thin plate is made of a single crystal. This is an example using lithium niobate.

In FIG. 14, 21 is a 41 ° Y-cut, X-axis-propagating single crystal piezoelectric substrate made of single crystal lithium niobate, and 51 is lead borosilicate glass, which is a non-piezoelectric substrate 51 and a single crystal. The piezoelectric thin plate 21 is compounded by the above-mentioned direct bonding.

Reference numerals 30 and 30 'are comb-shaped electrodes for exciting a surface wave, and show the same basic structure as that of the first embodiment.

41 ° Y-cut, X-axis propagation single crystal lithium niobate has an electromechanical coupling coefficient of 17.2%, a sound velocity of 4792 m / sec, and a lead borosilicate glass substrate has a sound velocity of 10%.
00-2000 m / sec.

Also in this case, as in (Example 1-1), by setting the thickness of the single crystal piezoelectric thin plate to an appropriate thickness according to the wavelength of the surface acoustic wave used, a substantial electromechanical coupling coefficient is obtained. A characteristic in which the speed of sound is different from that of the piezoelectric body used can be obtained.

For example, when the comb-shaped electrodes are excited at about 200 MHz, the distance between the comb-shaped electrodes is about 2.5 μm at a quarter wavelength.
(Consider the sound velocity is 2000 m / sec), and the thickness of the single crystal piezoelectric thin plate 21 is from 1/4 wavelength to 1 wavelength, 2.5-
By setting the thickness to 10 μm, both the electromechanical coupling coefficient and the sound velocity, the 41 ° Y-cut of the single crystal piezoelectric thin plate 21, the value of the single crystal lithium niobate propagating in the X axis, and the non-piezoelectric substrate 5 are set.
A value different from that of the lead borosilicate glass substrate of 1 is obtained.

For example, intermediate values are obtained. When the thickness of the single crystal piezoelectric thin plate 21 is set to about 1/2 wavelength to about 1 wavelength, the electromechanical coupling coefficient is 1-5% and the sound velocity is 1500-2500 m / sec. In this case, since both the electromechanical coupling coefficient and the sound velocity are intermediate values of the original substrates, the electromechanical coupling coefficient is relatively large and the sound velocity is relatively slow. The surface acoustic wave device is suitable for a frequency filter and a delay line.

The effect of such combination is remarkable when the thickness of the single crystal piezoelectric thin plate 21 is particularly between ½ wavelength and one wavelength.

The present example mainly shows the effect on the speed of sound.

(Embodiment 2-2) FIG. 15 shows the structure of the second specific embodiment of the second embodiment, in which a non-piezoelectric substrate is made of boron or amorphous carbon having a high speed of sound or This is an example of using graphite and a single crystal piezoelectric thin plate made of lithium niobate.

In FIG. 15, reference numeral 21 is a single crystal piezoelectric substrate made of 41 ° Y-cut, X-axis propagating single crystal lithium niobate, and 52 is a non-piezoelectric substrate, which is boron or amorphous carbon or graphite. Is. The non-piezoelectric substrate 52 and the single crystal piezoelectric thin plate 21 are combined by the above-mentioned direct bonding.

Reference numerals 30 and 30 'are comb-shaped electrodes for exciting a surface wave, and show the same basic structure as that of the first embodiment.

The electromechanical coupling coefficient of 41 ° Y-cut, X-axis propagating single crystal lithium niobate was 17.2%, the speed of sound was 4792 m / sec, and the speed of sound of the non-piezoelectric substrate was 10 for boron.
000 m / sec, amorphous carbon is about 10,000 m / sec, and graphite is 10,000-15,000 m / sec.

Also in this case, as in the case of (Example 1-1), by setting the thickness of the single crystal piezoelectric thin plate to an appropriate thickness according to the wavelength of the surface acoustic wave used, a substantial electromechanical coupling coefficient is obtained. A characteristic in which the speed of sound is different from that of the piezoelectric body used can be obtained.

For example, when the comb-shaped electrodes are excited at about 200 MHz, the distance between the comb-shaped electrodes is 1/4 of the speed of sound of each non-piezoelectric substrate.
By setting the wavelength and the thickness of the single crystal piezoelectric thin plate 21 from 1/4 wavelength to 1 wavelength, the electromechanical coupling coefficient and the sound velocity are 41 degrees Y-cut of the single crystal piezoelectric thin plate 21 and a single crystal of X-axis propagation. Both the value of lithium niobate and the non-piezoelectric substrate 52
Different values are obtained.

For example, intermediate values can be obtained. When the thickness of the single crystal piezoelectric thin plate 21 is set to about 1/2 wavelength to about 1 wavelength, the electromechanical coupling coefficient is 1-5%, and the sound velocity is about 5000-12000 m / sec. In this case, since both the electromechanical coupling coefficient and the sound velocity have intermediate values of the original substrates, the electromechanical coupling coefficient is relatively large and a high sound velocity characteristic is obtained. The surface acoustic wave device is suitable for.

The effect of such compounding is remarkable when the thickness of the single crystal piezoelectric thin plate 21 is particularly between 1/4 wavelength and 1 wavelength.

The present example mainly shows the effect on the speed of sound.

(Embodiment 2-3) FIG. 16 shows the structure of the third concrete embodiment of the second embodiment. The single crystal piezoelectric thin plate is made of lithium niobate, and the non-piezoelectric substrate is made of thermal expansion. This is an example of using a glass having a rate smaller than that of a single crystal piezoelectric thin plate.

In FIG. 16, 21 is a single crystal piezoelectric substrate made of 41 ° Y-cut, X-axis propagating single crystal lithium niobate, and 53 is a non-piezoelectric substrate, which is glass having a small coefficient of thermal expansion. Non-piezoelectric substrate 53 and single crystal piezoelectric thin plate 21
Are compounded by the above-mentioned direct bonding.

Reference numerals 30 and 30 'are comb-shaped electrodes for exciting surface waves, and show the same basic construction as that of the first embodiment.

In the case of this embodiment, the single crystal piezoelectric thin plate 21 may be thicker than the wavelength of the surface wave used.

In such a structure, the non-piezoelectric substrate 53
The thermal expansion coefficient of the material used for is selected to be smaller than the thermal expansion coefficient of the material used for the single crystal piezoelectric thin plate 21,
A surface acoustic wave device having excellent temperature dependence can be obtained.

For example, a single crystal piezoelectric substrate having a thickness of 100
By using lithium niobate of μm (the coefficient of thermal expansion is 7.5-15 ppm / ° C. depending on the crystal orientation), a glass substrate having a thickness of 1 mm and a coefficient of thermal expansion of 4 ppm / ° C. Even if the thickness is several times the wavelength of the surface acoustic wave to be used, the temperature dependence can be improved by 10 to 20% without lowering the electromechanical coupling coefficient.

Since the single crystal piezoelectric thin plate 21 and the non-piezoelectric substrate 53 are directly bonded to each other at the atomic order level, the compressive stress due to the difference in the coefficient of thermal expansion is increased by the temperature rise. It is considered that the temperature dependency was improved by adding No. 21.

Therefore, by using the holding substrate having a smaller coefficient of thermal expansion than that of the single crystal piezoelectric thin plate, it is possible to obtain a surface acoustic wave device having improved temperature characteristics while having substantially the same electromechanical coupling coefficient.

For example, the coefficient of thermal expansion of lithium tantalate is
4-16 ppm / ° C, the coefficient of thermal expansion of lithium borate is 4
-13ppm / ℃, the coefficient of thermal expansion of quartz is 7.5-14p
pm / ° C. On the other hand, a glass substrate having a coefficient of thermal expansion of 4-10 ppm / ° C can be freely selected. Therefore, by using a single crystal piezoelectric substrate, such as lithium tantalate, lithium borate, and crystal oriented in a specific crystal orientation, and by using a glass substrate having a thermal expansion coefficient smaller than that of the crystal orientation, The same effect as can be obtained. The substrate on the holding side does not need to be a non-piezoelectric substrate to obtain the above effect.

Lithium niobate, lithium tantalate, lithium borate and quartz are used as the single crystal piezoelectric body, and glass, boron and amorphous carbon are used as the non-piezoelectric substrate.
Although only a specific combination of graphite is shown, a composite single crystal piezoelectric substrate having various electromechanical coupling coefficients, sonic velocities, and temperature dependences can be obtained in various combinations other than this.

Reference Example 2 A perspective view of a fourth embodiment of the structure of the surface acoustic wave device of the present invention is shown in FIG. 17A, and a sectional view taken along the line AA ′ in FIG. 17A. 17 (b)
Shown in.

In FIG. 17, 20, 30, 30 ', 5
Similarly to the second embodiment, reference numeral 0 denotes a single crystal piezoelectric thin plate, a comb-shaped electrode formed on the single crystal piezoelectric thin plate 20, and a non-piezoelectric substrate. Here again, the comb-shaped electrodes are shown in a simplified manner. Reference numeral 40 is an inorganic thin film layer formed between the non-piezoelectric substrate 50 and the single crystal piezoelectric thin plate 20.

The non-piezoelectric substrate 50 is, for example, a substrate having a high sound velocity such as boron, amorphous carbon or graphite, a substrate having a slow sound velocity such as glass, or a substrate having a small coefficient of thermal expansion, as in the second embodiment. Example 2 of the single crystal piezoelectric thin plate 20
Similarly to, for example, lithium niobate which is a single crystal piezoelectric material,
Lithium tantalate, lithium borate and quartz are suitable.

As in the case of Reference Example 1, silicon compounds such as silicon, silicon oxide and silicon nitride, and silicic acid compounds such as borosilicate compounds are suitable for the inorganic thin film layer. The thickness of the inorganic thin film layer is preferably sufficiently thin with respect to the wavelength of the surface acoustic wave used, and specifically, it is preferably 1 wavelength or less, particularly 1/10 wavelength or less.

The function as the surface acoustic wave device is the same as that of the first embodiment.
Similarly, by applying a high frequency signal to the comb-shaped electrode 30, a surface acoustic wave is excited in the piezoelectric portion in the vicinity of the comb-shaped electrode 30 and propagates to the other comb-shaped electrode 30 'through the laminated structure to form a lower part of the comb-shaped electrode 30'. It is converted back into an electric signal by the piezoelectric section of.

Here, the basic structure of the surface acoustic wave device using the comb-shaped electrodes is shown, and when actually forming a high frequency filter or a resonator, the number of comb-shaped electrodes is increased or the structure is changed.

The non-piezoelectric substrate 10 and the single crystal piezoelectric thin plate 20 are
At least one surface of the substrate has an inorganic thin film layer, each inorganic thin film layer and the substrate surface is flattened,
It is a product that is directly bonded and laminated by being mirror-finished, cleaned, hydrophilized, and heat-treated for superposition.

The meaning of the direct bonding used here is that of Example 1.
Is the same as.

A manufacturing process of direct bonding in this embodiment will be described.

Specifically, for example, as the piezoelectric material, single crystal lithium niobate, lithium tantalate, lithium borate, and quartz are used, and as the insulator, glass, boron, amorphous carbon, graphite, and the inorganic material are used. The case where silicon, silicon oxide, silicon nitride, or borosilicate glass is used as the thin film layer will be described.

First, the surfaces of the piezoelectric body and the non-piezoelectric substrate to be directly bonded are flattened, mirror-polished, and washed. If necessary, the surface layer is removed by etching. A hydrofluoric acid-based etching solution is used for etching lithium niobate, lithium tantalate, and quartz. In the case of lithium borate, a weak acid may be used. Hydrofluoric acid is used for glass, boron, amorphous carbon, and graphite.

Next, an inorganic thin film layer is formed by a thin film technique on the surface to be joined of at least one of the two substrates. The inorganic thin film layer can be formed of any of the above materials by sputtering, chemical vapor deposition, or vacuum vapor deposition. The film thickness is made sufficiently thinner than the wavelength of the surface acoustic wave used (1/2 wavelength or less, more preferably 1/10 wavelength or less). For example, it is about 0.1-1 μm.

Next, the surface of the piezoelectric or inorganic thin film layer to be joined is flattened, mirror-finished, and cleaned. If the surface state of the substrate before the formation of the inorganic thin film layer is sufficiently flat, mirror-finished, and clean, it is not always necessary to treat it again. Then, each surface is hydrophilized. The following processing is performed in the second embodiment.
Is the same as.

Specifically, by immersing in, for example, an ammonia-hydrogen peroxide solution, hydroxyl groups easily adhere to the surface and are made hydrophilic. Then, it is thoroughly washed with pure water.
As a result, hydroxyl groups are attached to the surface of each substrate. When the two substrates are superposed in this state, the two substrates are adsorbed mainly by the van der Waals force of the hydroxyl group. Even in this state, it will be a strong adhesion state, but in this state,
By performing heat treatment at a temperature of 100 ° C. or higher for several tens of minutes to several tens of hours, water constituent components gradually escape from the interface. Along with this, bonds relating to oxygen, hydrogen, and substrate-constituting atoms progress from the bond of hydrogen-bonding group of hydroxyl group, and the joining of the substrate-constituting atoms gradually starts to be strengthened. In particular, since the inorganic thin film layer contains silicon and oxygen is sufficiently present in the periphery, covalent bonding proceeds,
The bond is strengthened.

The heat treatment temperature is, in particular, 200-100.
A range of 0 ° C. in which the characteristics of the piezoelectric body used are not lost is preferable.

The direct joining in this case is the same as in the first embodiment.
Since the joining is performed with the accuracy of atomic order, the loss for the propagation of the surface acoustic wave is extremely small. Further, since the thickness of the inorganic thin film layer is sufficiently smaller than the wavelength of the surface acoustic wave to be used, the loss of the surface acoustic wave in the inorganic thin film layer is extremely small, and there is practically no problem. Therefore, the advantage of direct bonding is similar to that of the first embodiment.

The feature of this embodiment is that an inorganic thin film layer is present at the direct bonding interface as compared with the second embodiment. As a result, two advantages are obtained as in Reference Example 1.

The first advantage is that even if there is some dust on the interface at the time of joining, the dust is taken into this inorganic thin film layer at the time of direct joining, so that the manufacturing yield at the time of joining is improved.

The second advantage is that the electrodes can be easily embedded in the inorganic thin film layer, which further increases the degree of freedom in designing the surface acoustic wave device.

FIG. 18 shows an embodiment having a structure in which an electrode is embedded in an inorganic thin film layer.

In FIG. 18A, reference numerals 50 and 20 denote a non-piezoelectric substrate and a single crystal piezoelectric thin plate, respectively. 31,
31 'is a comb-shaped electrode embedded in the inorganic thin film layer 40. The comb-shaped electrode is formed on the lower substrate side. Although not shown, the ends of the comb electrodes are exposed so that they can be connected to an external circuit.

FIG. 18B shows an example in which a comb-shaped electrode is formed on the single crystal piezoelectric thin plate side.

FIG. 18C shows an example in which the ground electrode 35 is provided on the upper surface of the single crystal piezoelectric thin plate in the structure of FIG. 18A.

FIG. 18D shows an example in which the ground electrode 35 is provided on the upper surface of the single crystal piezoelectric thin plate in the structure of FIG. 18B.

FIG. 18 (e) shows the configuration of FIG.
This is an example in which the ground electrode 35 'is formed in the inorganic thin film layer.

The difference in the characteristics due to the electrode structure is as follows.
It is similar to Reference Example 1 and is qualitatively as follows.
Basically, it depends on where the electric field is concentrated on the upper and lower substrates. FIG. 18E, FIG. 17 and FIG. 18D show the single crystal piezoelectric thin plates in the order in which the electric field tends to concentrate.
The order of (c) and FIG. Qualitatively,
In almost this order, the piezoelectric characteristics obtained by mixing the characteristics of the upper and lower substrates are obtained as the piezoelectric characteristics of the laminated structure.

Therefore, in the case of such an electrode structure, even if the same piezoelectric body and thickness as those in FIG. 17 are used, the way in which surface acoustic wave is excited is different, and naturally, piezoelectric characteristics different from those in FIG. 17 are obtained. To be Specifically, for example, the effect of increasing the electromechanical coupling coefficient can be obtained.

In order to obtain the structure shown in FIG. 18, the surface of the non-piezoelectric substrate or the single crystal piezoelectric substrate is flattened, mirror-polished and cleaned, and then a comb-shaped electrode is formed on the surface thereof, as described above. , Forming an inorganic thin film layer by various thin film technologies,
It can be obtained by directly joining by the above manufacturing process.

Also in the configuration of FIG. 17 or 18, the piezoelectric characteristics of the non-piezoelectric substrate 50 and the single crystal piezoelectric thin plate 20, the speed of sound,
By appropriately combining the temperature dependence and the coefficient of thermal expansion, a surface acoustic wave device composed of various composite single crystal piezoelectric substrates having a high degree of design freedom can be obtained.

Reference Example 2-1 FIG. 19 shows the structure of the first specific example of Reference Example 2, in which a non-piezoelectric substrate is made of glass with a slow sound velocity and a single crystal piezoelectric thin plate is made of a single crystal. In this example, lithium niobate is used and silicon is used for the inorganic thin film layer.

In FIG. 19, 21 is a 41 ° Y-cut, X-axis propagating single crystal piezoelectric thin plate made of single crystal lithium niobate, and 51 is lead borosilicate glass. 41
Is silicon (amorphous or polycrystalline) formed on the non-piezoelectric substrate 51 by sputtering, chemical vapor deposition or vacuum deposition.

The non-piezoelectric substrate 51 is combined with the single crystal piezoelectric thin plate 21 at the interface with the silicon layer 41 by the direct bonding described above.

Reference numerals 30 and 30 'are comb-shaped electrodes for exciting a surface wave, and show the same basic structure as that of the first embodiment.

Even in such a structure, if the thickness of the inorganic thin film layer is sufficiently thin as compared with the wavelength of the surface acoustic wave to be used (1/2 wavelength or less, more preferably 1/10 wavelength or less), An effect similar to that of the example (3-1) can be obtained.

Reference Example 2-2 FIG. 20 shows the structure of the second specific example of Reference Example 2, in which a non-piezoelectric substrate is provided with boron or amorphous carbon or graphite having a high sound velocity. Is an example in which single crystal lithium niobate is used for the single crystal piezoelectric thin plate and silicon oxide or silicon nitride is used for the inorganic thin film layer.

In FIG. 20, 21 is a single crystal piezoelectric substrate made of 41 ° Y-cut, X-axis propagating single crystal lithium niobate, 52 is a non-piezoelectric substrate, and boron or amorphous carbon or graphite. , 42 are non-piezoelectric substrates 5 formed by sputtering, chemical vapor deposition or vacuum deposition.
2 is a silicon oxide (amorphous) layer or a silicon nitride (amorphous) layer formed on the second layer.

The non-piezoelectric substrate 52 and the single crystal piezoelectric thin plate 21 are
It is compounded by the above-mentioned direct bonding through the inorganic thin film layer 42.

Reference numerals 30 and 30 ′ are comb-shaped electrodes for exciting surface waves, and show the same basic constitution example as that of the first embodiment.

Even in such a structure, if the thickness of the inorganic thin film layer is sufficiently smaller than the wavelength of the surface acoustic wave used (1/2 wavelength or less, more preferably 1/10 wavelength or less), An effect similar to that of the example (3-2) can be obtained.

Reference Example 2-3 FIG. 21 shows the structure of the third specific example of Reference Example 2, in which lithium niobate is applied to a single crystal piezoelectric thin plate and a non-piezoelectric substrate is subjected to thermal expansion. This is an example in which glass whose ratio is smaller than that of a single crystal piezoelectric thin plate and a borosilicate compound is used in the inorganic thin film layer.

In FIG. 21, reference numeral 21 is a single crystal piezoelectric substrate made of 41 ° Y-cut, X-axis propagating single crystal lithium niobate, and 53 is a non-piezoelectric substrate having a small coefficient of thermal expansion. Reference numeral 43 is a borosilicate glass layer formed on the non-piezoelectric substrate 53 by sputtering, chemical vapor deposition or vacuum deposition.

The non-piezoelectric substrate 53 and the single crystal piezoelectric thin plate 21 are
The borosilicate glass layer 43 is used to form a composite by the direct bonding described above.

Reference numerals 30 and 30 'are comb-shaped electrodes for exciting surface waves, and show the same basic constitution example as that of the first embodiment.

Even in such a structure, if the thickness of the inorganic thin film layer is sufficiently smaller than the wavelength of the surface acoustic wave to be used (1/2 wavelength or less, more preferably 1/10 wavelength or less), the operation is carried out. The same effect as in Example (3-3) can be obtained. The substrate on the holding side does not need to be a non-piezoelectric substrate to obtain the above effect.

Lithium niobate, lithium tantalate, lithium borate and quartz are used as the single crystal piezoelectric body, and glass, boron and amorphous carbon are used as the non-piezoelectric substrate.
Only specific combinations of silicon, silicon oxide, silicon nitride and other silicon compounds have been shown as graphite and inorganic thin film layers.
Even in various combinations other than this, a composite single crystal piezoelectric substrate having various electromechanical coupling coefficients, sonic velocities, and temperature dependences can be obtained according to the combinations.

In each of the above embodiments, the direct bonding of the two substrates has been described, but the same effect can be obtained even if the number of substrates is further increased.

Further, in Reference Examples 1 and 2, an example in which the inorganic thin film layer is formed only on one substrate side has been described, but it may be formed on both substrate surfaces.

As the electrode material, an ordinary metal material such as aluminum or gold can be used.

[0232]

With the above-mentioned structure, the degree of freedom in the combination of the electromechanical coupling coefficient, the speed of sound, and the temperature dependency is greatly increased, and in particular, the surface having a large electromechanical coupling coefficient and a small temperature dependency. An elastic wave device is obtained.

By interposing the inorganic thin film layer at the direct bonding interface, the manufacturing yield is improved, and the degree of freedom in the arrangement of the electrodes is increased, so that the degree of freedom in designing the piezoelectric characteristics is further increased.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a transmission electron micrograph showing a grain structure at an interface of a composite piezoelectric substrate directly bonded according to the present invention.

FIG. 3 is a configuration diagram of a first concrete example of the first embodiment of the present invention.

FIG. 4 is a configuration diagram of a second specific example of the first embodiment of the present invention.

FIG. 5 is a configuration diagram of a third example of the first embodiment of the present invention.

FIG. 6 is a configuration diagram of a fourth specific example of the first embodiment of the present invention.

FIG. 7 is a configuration diagram of a first reference example of the present invention.

FIG. 8 is a configuration diagram of a specific example of electrode arrangement according to the first reference example of the present invention.

FIG. 9 is a configuration diagram of a first specific example of the first reference example of the present invention.

FIG. 10 is a configuration diagram of a second specific example of the first reference example of the present invention.

FIG. 11 is a configuration diagram of a third specific example of the first reference example of the present invention.

FIG. 12 is a configuration diagram of a fourth specific example of the first reference example of the present invention.

FIG. 13 is a configuration diagram of a second embodiment of the present invention.

FIG. 14 is a configuration diagram of a first specific example of the second embodiment of the present invention.

FIG. 15 is a configuration diagram of a second specific example of the second embodiment of the present invention.

FIG. 16 is a configuration diagram of a third example of the second embodiment of the present invention.

FIG. 17 is a configuration diagram of a second reference example of the present invention.

FIG. 18 is a configuration diagram of a specific example of electrode arrangement according to a second reference example of the present invention.

FIG. 19 is a configuration diagram of a first specific example of a second reference example of the present invention.

FIG. 20 is a configuration diagram of a second specific example of the second reference example of the present invention.

FIG. 21 is a configuration diagram of a third specific example of the second reference example of the present invention.

[Explanation of symbols]

10 Single crystal piezoelectric substrate 20 Single crystal piezoelectric thin plate 30 comb-shaped electrode 30 'comb electrode 11 Single crystal piezoelectric substrate (lithium niobate) 12 Single crystal piezoelectric substrate (lithium tantalate) 13 Single crystal piezoelectric substrate (crystal) 21 Single crystal piezoelectric thin plate (lithium niobate) 22 Single crystal piezoelectric thin plate (lithium tantalate) 31 Comb-shaped electrode (embedded) 31 'comb-shaped electrode (embedded) 32 comb-shaped electrode (embedded) 32 'comb-shaped electrode (embedded) 33 Ground electrode (surface) 34 Ground electrode (embedded) 40 Inorganic thin film layer 41 Inorganic thin film layer (silicon) 42 Inorganic thin film layer (silicon oxide or silicon nitride) 43 Inorganic thin film layer (silica oxide) 50 Non-piezoelectric substrate 51 Non-piezoelectric substrate (glass; low sonic velocity) 52 Non-piezoelectric substrate (boron or amorphous carbon; high sound velocity) 53 Non-piezoelectric substrate (glass; low coefficient of thermal expansion)

Continued front page    (72) Inventor Keiji Onishi             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Shunichi Seki             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F term (reference) 5J097 AA06 AA32 EE08 EE09 FF01                       GG01 GG02 GG03 GG04 HA03

Claims (14)

[Claims] 1. A single crystal piezoelectric substrate comprising: at least two single crystal piezoelectric substrates having surface acoustic wave propagation characteristics different from each other; and comb-shaped electrodes provided on the single crystal piezoelectric substrate for exciting surface acoustic waves. A surface acoustic wave device characterized in that the respective substrates are directly bonded and laminated by flattening, mirror-finishing, cleaning, and hydrophilizing the respective substrate surfaces, and subjecting them to superposition heat treatment. 2. The surface acoustic wave device according to claim 1, wherein the laminated single crystal piezoelectric substrates have different sound velocities. 3. The temperature dependence of the sound velocity of the single crystal piezoelectric substrate in the surface acoustic wave excited portion of the single crystal piezoelectric substrate is larger than the temperature dependence of the sound velocity of the other single crystal piezoelectric substrate. The surface acoustic wave device according to claim 1. 4. The electromechanical coupling coefficient of the single crystal piezoelectric substrate in the surface acoustic wave excitation portion of the single crystal piezoelectric substrate is larger than the electromechanical coupling coefficient of the other single crystal piezoelectric substrate. Item 2. The surface acoustic wave device according to item 1. 5. The single crystal piezoelectric substrate is a combination selected from the group consisting of lithium niobate, lithium tantalate, lithium borate, and quartz.
5. The surface acoustic wave device according to any one of 1 to 4. 6. The surface acoustic wave device according to claim 5, wherein the single crystal piezoelectric substrate for exciting the surface acoustic wave is lithium niobate, and the other single crystal piezoelectric substrate is quartz. 7. The surface according to claim 1, wherein the thickness of the single crystal piezoelectric substrate for exciting the surface acoustic wave is 3 wavelengths or less of the wavelength of the surface acoustic wave used. Elastic wave device. 8. A surface acoustic wave provided on at least one single crystal piezoelectric substrate, at least one non-piezoelectric substrate having a surface acoustic wave propagation characteristic different from that of the single crystal piezoelectric substrate, and a surface acoustic wave provided on the single crystal piezoelectric substrate. A comb-shaped electrode for, the single-crystal piezoelectric substrate and the non-piezoelectric substrate, the respective substrate surface is subjected to flattening, mirroring, cleaning, hydrophilic treatment,
A surface acoustic wave device characterized in that it is directly joined and laminated by heat treatment by superposition. 9. The surface acoustic wave device according to claim 8, wherein the acoustic velocity of the single crystal piezoelectric substrate is slower than that of the non-piezoelectric substrate. 10. The surface acoustic wave device according to claim 8, wherein the acoustic velocity of the single crystal piezoelectric substrate is higher than that of the non-piezoelectric substrate. 11. The surface acoustic wave device according to claim 8, wherein the single crystal piezoelectric substrate is lithium niobate, lithium tantalate, lithium borate, or quartz. 12. The surface acoustic wave device according to claim 8, wherein the single crystal piezoelectric substrate is lithium tantalate. 13. The surface acoustic wave device according to claim 8, wherein the thickness of the single crystal piezoelectric substrate is not more than one wavelength of the surface acoustic wave used. 14. The single crystal piezoelectric substrate has a coefficient of thermal expansion higher than that of the non-piezoelectric substrate.
3. The surface acoustic wave device according to any one of 3 above.