JP2007228120A - Surface acoustic wave device - Google Patents

Abstract

A low-cost surface acoustic wave device having a large electromechanical coupling coefficient, extremely good frequency-temperature characteristics, particularly high power durability, and an electrode that does not deteriorate even when a large amount of power is applied is provided with high productivity.
A surface acoustic wave element in which a metal electrode for exciting and detecting surface acoustic waves or leaky surface acoustic waves is formed on a piezoelectric substrate, and at least the piezoelectric substrate and a ceramic substrate are bonded via an adhesive. A composite piezoelectric chip obtained by processing a combined composite piezoelectric substrate into a chip shape, and a mounting substrate on which the composite piezoelectric chip is mounted by flip chip bonding, and the thickness of the metal electrode is specified by the wavelength of the leaky surface acoustic wave The expansion coefficient αc (ppm / ° C.) in the propagation direction of the surface acoustic wave or leakage surface acoustic wave on the surface of the piezoelectric substrate and the expansion coefficient α s (ppm / ° C.) of the mounting substrate Are surface acoustic wave elements mounted so as to satisfy the relationship of αs <αc <αs + 6.
[Selection] Figure 1

Description

  The present invention relates to a surface acoustic wave device using a composite piezoelectric substrate.

For example, a comb-shaped electrode for exciting a surface acoustic wave is formed on a piezoelectric substrate as a component for frequency adjustment / selection used in high-frequency communication such as a cellular phone, a local area network (LAN), and a personal area network (PAN). A surface acoustic wave (SAW) device is used. The piezoelectric substrate material used for this has a very high conversion efficiency (hereinafter referred to as an electromechanical coupling coefficient) from electrical signals to mechanical vibrations, and the center of a filter or the like determined by the electrode spacing of the comb-shaped electrodes and the acoustic velocity of elastic waves. It is required that the frequency does not vary with temperature (hereinafter referred to as frequency-temperature characteristics).
In other words, it is preferable to have a piezoelectric substrate having both a large electromechanical coupling coefficient and a small frequency temperature coefficient. An example of a piezoelectric substrate that realizes such characteristics is a composite piezoelectric substrate in which a piezoelectric substrate and another substrate are bonded.

As an example of such a composite piezoelectric substrate, an electrode for exciting and detecting an elastic wave is provided on the surface of the piezoelectric material, and the temperature stabilization is characterized in that a composite laminate is joined to the back surface of the piezoelectric material. A surface wave device is disclosed. This surface wave device is such that temperature correction is performed in the piezoelectric material by inducing a controlled stress change in the piezoelectric material (see Patent Document 1).
In this example, “the LiNbO ₃ (lithium niobate) substrate is firmly bonded to the composite laminate to generate a compressive force on the substrate as described above, and this compressive force increases as the temperature increases. It is possible to obtain a means for correcting the influence of temperature on the delay time and the filter center frequency. " This means that the expansion coefficient of the composite laminate as the support substrate is smaller than that of the surface acoustic wave propagation direction of the LiNbO ₃ substrate, which is a piezoelectric material, and stress is generated in the piezoelectric substrate in response to temperature changes. This means that the influence of temperature on the delay time and filter center frequency of the SAW device can be corrected.

Further, an electrical component is disclosed in which a functional element having an electrode provided on the surface of the piezoelectric plate is housed in a package by bonding a rigid plate and a piezoelectric plate using an adhesive (Patent Document). 2).
That is, a surface acoustic wave device using a composite piezoelectric substrate in which a piezoelectric material and a substrate having a smaller expansion coefficient are bonded has improved frequency temperature characteristics, and a rigid plate and a piezoelectric plate are bonded using an adhesive. It is a well-known technique to combine them into an integrated substrate.

Non-Patent Document 1 discloses that a 5 ° rotated Y-cut LiNbO ₃ substrate in which an Al or Cu electrode is formed on the surface and an SiO ₂ film is formed thereon has a large electromechanical coupling coefficient of about 25%, which is a primary factor. It is shown that the temperature characteristics of are almost zero.
Here, an example is shown in which the electrode thickness normalized by the wavelength of the leaky surface acoustic wave is 0.035.
However, in such a substrate, when the SiO ₂ film is thickened, the electromechanical coupling coefficient is reduced. Further, for example, in a wireless communication component used in a transmission stage, there is a problem that an electrode deteriorates when a large amount of power is applied.
Non-Patent Document 2 discloses a composite piezoelectric substrate in which a 64 ° rotated Y-cut LiNbO ₃ substrate and a quartz substrate are bonded together. However, Non-Patent Document 2 does not discuss the thickness of the electrode material.

Further, a surface acoustic wave device including a piezoelectric substrate and an interdigital transducer (IDT) formed on the piezoelectric substrate and having a plurality of electrode fingers and a bus bar that commonly connects the electrode fingers, A surface acoustic wave element mounting structure mounted on a mounting substrate by flip chip bonding, wherein the mounting substrate has a smaller linear expansion coefficient than the piezoelectric substrate, and the bumps are subject to temperature changes. A mounting structure for a surface acoustic wave element is disclosed, wherein the piezoelectric substrate is disposed so that thermal expansion and contraction of the piezoelectric substrate are suppressed by the mounting substrate (see Patent Document 3).
In the example of this example, LiTaO ₃ (expansion coefficient 16 ppm / ° C.) is used as the piezoelectric body, and alumina (expansion coefficient 7 ppm / ° C.) is used as the mounting base, and the chip is mounted on the mounting substrate by flip chip bonding via bumps. In the surface acoustic wave filter, it is disclosed that the frequency variation due to temperature is improved by −11 kHz / ° C. at an operating frequency of 1.9 GHz.
This improvement effect is preferable because it is improved by about 6 ppm / ° C. in terms of temperature coefficient.

On the other hand, in Non-Patent Document 3, 48 ° rotated Y-cut LiTaO ₃ is used as a piezoelectric body, and an elastic using a composite piezoelectric substrate in which a Si substrate as a supporting substrate is directly bonded to the piezoelectric body via a SiO ₂ layer. A surface wave device is disclosed. The temperature characteristics of the operating frequency of this surface acoustic wave device are as follows. When the composite piezoelectric chip is connected by the bonding wire method, the temperature characteristic of the operating frequency is −12 ppm / ° C., whereas the flip chip bonding method is −22 ppm / ° C. (−35 ppm / ° C.) and temperature characteristics are described as being deteriorated.

JP 51-25951 A JP-A-2-62108 JP 2003-324334 A Proceedings of Piezoelectric Materials and Devices Symposium 2005, pp.153-158 K. Yamanouchi et al., Proc. 1999 IEEE Ultrasonics Symp., Pp.239-242 BPAbbot, J. Caron, J. Chocola, K. Lin, S. Malocha, N. Naumenko and P. Welsh, "Advances in Rf SAW Substrates", 2nd International Symposium on AcousticWave Devices for Future Mobile Communication Systems, pp.233 -243,2003

  The present invention provides an inexpensive surface acoustic wave device with high productivity that has a large electromechanical coupling coefficient, extremely good frequency temperature characteristics, particularly high power resistance, and does not deteriorate even when large power is applied. With the goal.

In order to solve the above problems, the present invention provides a surface acoustic wave element in which a metal electrode for exciting and detecting a surface acoustic wave or a leaky surface acoustic wave is formed on a piezoelectric substrate, and includes at least a piezoelectric substrate and a ceramic substrate. And a mounting substrate on which the composite piezoelectric chip is mounted by flip chip bonding. The composite piezoelectric substrate is formed on the piezoelectric substrate. The thickness of the metal electrode is 0.04 or more as a value normalized by the wavelength of the leaky surface acoustic wave, and the expansion coefficient αc (ppm / ° C.) in the propagation direction of the surface acoustic wave or leaky surface acoustic wave on the surface of the piezoelectric substrate. ) And an expansion coefficient αs (ppm / ° C.) of the mounting substrate,
αs <αc <αs + 6
The surface acoustic wave device is provided so as to satisfy the following relationship (claim 1).

Thus, the surface acoustic wave device of the present invention uses a ceramic substrate as a substrate to be bonded to a piezoelectric substrate in a composite piezoelectric chip, and also bonds the piezoelectric substrate and the ceramic substrate through an adhesive. It can be made inexpensive and can have good temperature characteristics.
In addition, if the thickness of the metal electrode formed on the surface of the piezoelectric substrate is 0.04 or more in terms of the value normalized by the wavelength of the leaky surface acoustic wave propagating on the surface of the piezoelectric substrate, the power durability is high and the power is large. It can be assumed that the electrode is not deteriorated even if s is applied.
Furthermore, it comprises a composite piezoelectric chip obtained by processing a composite piezoelectric substrate obtained by bonding a piezoelectric substrate and a ceramic substrate into a chip shape, and a mounting substrate on which the composite piezoelectric chip is mounted by flip chip bonding. The surface acoustic wave device is mounted so that the expansion coefficient αc in the propagation direction of the wave or leaky surface acoustic wave and the expansion coefficient αs of the mounting substrate satisfy the above relationship, so that the productivity is high and the frequency temperature characteristic improvement effect is high. It can be.

Further, it is preferable that the piezoelectric substrate is a 35 ° ± 35 ° rotation Y-cut LiNbO ₃ substrate or LiTaO ₃ substrate (claim 2).
As described above, if the piezoelectric substrate is a 35 ° ± 35 ° rotated Y-cut LiNbO ₃ substrate or a LiTaO ₃ substrate, the surface temperature wave device can be a broadband surface acoustic wave device with excellent frequency-temperature characteristics and low loss.

In addition, a SiO _2−x N _x layer (where 0.01 <x <0.5) is formed on the surface of the piezoelectric substrate so as to cover the metal electrode, and the thickness of the SiO _2−x N _x layer The thickness is preferably 0.1 or less as a value normalized by the wavelength of the leaky surface acoustic wave.

Thus, if the SiO _2-x N _x layer is formed so as to cover the metal electrode on the surface of the piezoelectric substrate, the electrode on the substrate surface can be protected and the frequency temperature characteristics can be adjusted, and the leaky surface acoustic wave and When surface acoustic waves are mixed, surface acoustic waves with small coupling are attenuated by this film, and there is an effect of suppressing unnecessary modes (spurious modes). In addition, if the thickness is a value normalized to the wavelength of the leaky surface acoustic wave of 0.1 or less, particularly about 0.05, the sound velocity of the leaky surface acoustic wave and the coupling coefficient do not decrease. it can. If x is larger than 0.01, the elastic properties of the SiO ₂ -xN _x layer hardly change with time. If x is less than 0.5, the film quality is unlikely to deteriorate. If x is preferably about 0.1, the power durability of the layer itself is improved as compared with the case where N is not included.

  Such a surface acoustic wave device according to the present invention has high power resistance, and the electrode is not easily deteriorated even when a large amount of electric power is applied. Further, the productivity is high, and the frequency temperature characteristic is wide in a wide band. can do. In addition, since the substrate to be bonded to the piezoelectric substrate is a ceramic substrate and bonded with an adhesive, it can be made inexpensive.

Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited thereto.
FIG. 1 is a schematic cross-sectional view showing an example of an embodiment of a surface acoustic wave device according to the present invention.
The surface acoustic wave element 8 includes a composite piezoelectric chip 1 obtained by processing a composite piezoelectric substrate obtained by bonding a piezoelectric substrate 2 and a ceramic substrate 3 through an adhesive (adhesive layer) 4 into a chip shape, and the composite piezoelectric chip 1. And a mounting substrate 6 mounted by flip chip bonding via the bumps 5. Further, a metal electrode 7 for exciting and detecting a surface acoustic wave or a leaky surface acoustic wave is formed on the piezoelectric substrate 2, and the thickness of the metal electrode 7 is a value normalized by the wavelength of the leaky surface acoustic wave. 0.04 or more. Further, a SiO ₂ -xN _x layer 10 (where 0.01 <x <0.5) is formed so as to cover the metal electrode 7. However, only the extraction part of the metal electrode 7 is removed and the metal electrode 7 is mounted via the bumps 5 as described above.
The expansion coefficient αc (ppm / ° C.) in the propagation direction of the surface acoustic wave or leaky surface acoustic wave on the surface of the piezoelectric substrate 2 and the expansion coefficient αs (ppm / ° C.) of the mounting substrate 6 are αs <αc <αs + 6. It is implemented so as to satisfy the following relationship.

The surface acoustic wave element 8 of the present invention has a high power durability and a large electric power by setting the thickness of the metal electrode 7 to 0.04 or more as a value normalized by the wavelength of the leaky surface acoustic wave. It is hard to deteriorate even when applied.
Further, by adopting the configuration as described above, the productivity is high and the effect of improving the frequency temperature characteristics can be high. That is, as in the present invention, the expansion coefficient αc of the surface acoustic wave or leakage surface acoustic wave propagation direction of the piezoelectric substrate 2 and the expansion coefficient αs of the mounting substrate 6 satisfy the relationship of αs <αc <αs + 6. In the surface acoustic wave element 8 on which the composite piezoelectric substrate is mounted by flip chip bonding, the frequency temperature coefficient is improved by about several ppm / ° C. to several tens ppm / ° C. as compared with the case of mounting by the chip and wire method, for example. In addition, since it is mounted by flip chip bonding, productivity can be increased.

  Since the composite piezoelectric substrate used in the present invention has the adhesive layer 4 as described above, the stress on the surface of the composite piezoelectric substrate due to the heat of the piezoelectric substrate is relieved, but the composite piezoelectric substrate is flip-chip mounted as described above. Then, since the stress value and the stress distribution on the surface of the piezoelectric body are dramatically recovered, the frequency temperature characteristics can be greatly improved as compared with the case where the flip chip mounting is not performed.

  Here, when αc is smaller than αs, as in Non-Patent Document 1, the result is that the frequency temperature characteristics when mounted by flip-chip bonding are deteriorated compared to when mounted by the chip-and-wire method. In addition, both the frequency temperature characteristics improvement effect and high productivity cannot be achieved. When αc is larger than αs + 6 (ppm / ° C.), the effect of improving the frequency temperature coefficient is small. Therefore, both high frequency improvement effect and high productivity can be achieved by mounting so as to satisfy the relationship of αs <αc <αs + 6 as in the present invention. In order for the expansion coefficient to satisfy the above relationship, for example, the thickness of the piezoelectric substrate 2, the thickness of the adhesive layer 4 that bonds the piezoelectric substrate 2 and the ceramic substrate 3 that is the support substrate, the chip size, and the like are adjusted. That's fine.

Next, the components of the composite piezoelectric chip 1 will be specifically described.
The composite piezoelectric chip 1 shown in FIG. 1 is formed by processing a composite piezoelectric substrate in which a piezoelectric substrate 2 and a ceramic substrate 3 are bonded together with an adhesive 4 into a chip shape as described above.
Here, when the present inventor conducted earnest research on the composite piezoelectric substrate used for the surface acoustic wave element of the present invention, the present inventor found that the SAW device used for, for example, the wireless communication component in the transmission stage has a large power. Therefore, it is necessary to form a thick electrode material on the piezoelectric substrate so that the metal electrode for exciting the surface acoustic wave formed on the surface of the piezoelectric substrate of the SAW device is unlikely to deteriorate. It was thought that good power resistance could not be expected unless the film thickness was sufficiently thick. Until now, the thickness of the electrode material has not been sufficiently studied. However, the present inventor has determined that the thickness of the metal electrode is 0.04 or more as a value normalized by the wavelength of the leaky surface acoustic wave. It has been found that the power durability can be made sufficiently high.

FIG. 2 is a schematic cross-sectional view showing an example of an embodiment of a composite piezoelectric substrate used for the surface acoustic wave element 8 according to the present invention.
This composite piezoelectric substrate 9 is formed by bonding a piezoelectric substrate 2 and a ceramic substrate 3, and a metal electrode 7 for exciting a surface acoustic wave is formed on the surface of the piezoelectric substrate 2. The thickness of the metal electrode 7 is 0.04 or more as a value normalized by the wavelength of the leaky surface acoustic wave as described above. That is, for example, if the wavelength of the leaky surface acoustic wave is 2 μm, the thickness of the electrode is It is 0.08 μm or more, and the ceramic substrate 3 and the piezoelectric substrate 2 are bonded via an adhesive 4.
The thicker the metal electrode 7 is, the less likely it is to deteriorate, but it is sufficient if the normalized value is, for example, about 0.1.

Such a composite piezoelectric substrate 9 can be produced, for example, by applying an adhesive to one or both of the piezoelectric substrate 2 and the ceramic substrate 3 and bonding them firmly under vacuum to bond them firmly. It is preferable to clean the surface of each substrate before bonding so that no foreign matter is mixed into the bonding surface, and the surface is hydrophilized with an ammonia-hydrogen peroxide solution or the like, or plasma treated, For example, the adhesion may be increased by heating the substrate to 100 ° C. and pre-treating with short wave UV light having a wavelength of 200 nm or less and ozone (preferably high concentration ozone).
The size of the composite piezoelectric substrate 9 is not particularly limited, and can be, for example, 100 mm in diameter, but may be larger or smaller.

  In the present invention, the piezoelectric substrate 2 may have a thickness of 5 to 100 μm, and the bonded surface of the piezoelectric substrate 2 may be processed into a rough surface. Thus, if the thickness of the piezoelectric substrate 2 is 5 to 100 μm, preferably 5 to 30 μm, the warp due to heating is small and there is no crack. If the thickness of the piezoelectric substrate 2 is 5 μm or more, it is preferable that cracks hardly occur when the piezoelectric substrate 12 is processed to the above thickness. Moreover, if it is 100 micrometers or less, even when the composite piezoelectric substrate 9 is heated to about 250 ° C., the piezoelectric substrate 2 is not easily broken, which is preferable. In order to set the thickness of the piezoelectric substrate 2 to a desired value within the above range, for example, after the composite piezoelectric substrate 9 is formed, the piezoelectric substrate 2 may be ground, lapped, or polished (polished).

The piezoelectric substrate 2 is preferably a 35 ° ± 35 ° rotated Y-cut LiNbO ₃ substrate or a LiTaO ₃ substrate. Since these are crystal materials having a large electromechanical coupling coefficient, a composite piezoelectric substrate capable of manufacturing a SAW device having a wide bandwidth as a frequency selection filter and a small insertion loss can be obtained. Further, as will be described later, the propagation loss characteristic and the frequency temperature characteristic can also be improved. A piezoelectric substrate made of this piezoelectric crystal material can be obtained with a high quality by growing these single crystal rods by, for example, the Czochralski method and slicing them to a desired thickness.

  In the present invention, a ceramic substrate is used as a support substrate for the composite piezoelectric substrate 9. However, if a ceramic substrate is used in this way, the expansion coefficient can be made smaller than that of the piezoelectric substrate, and it is widely used as a package material. Therefore, it is possible to obtain a high performance composite piezoelectric substrate that is inexpensive and has improved frequency temperature characteristics and electrical insulation is ensured. Bonding via an adhesive is one factor that makes the composite piezoelectric substrate inexpensive, and has the advantage that it can be firmly bonded.

  The metal electrode 7 is preferably made of Al, Cu, an alloy thereof, or the like. The metal electrode 7 can be formed by forming a film of the metal material on the composite piezoelectric substrate 9 by a method such as vapor deposition, sputtering, or CVD, and patterning it by etching or the like.

Further, a SiO _2−x N _x layer 10 (where 0.01 <x <0.5) is formed on the surface of the piezoelectric substrate 2 so as to cover the metal electrode 7, and the SiO _2−x N _x layer 10 The thickness is preferably 0.1 or less as a value normalized by the wavelength of the leaky surface acoustic wave.
If the SiO ₂ -xN _x layer 10 is formed in this way, the metal electrode 7 on the substrate surface can be protected and the frequency-temperature characteristics can be adjusted. The surface acoustic wave having a small value is attenuated by this film and has the effect of suppressing unnecessary modes.

Further, if the thickness of the SiO ₂ -xN _x layer 10 is a value normalized by the wavelength of the leaky surface acoustic wave is 0.1 or less, particularly about 0.05, the sound velocity of the leaky surface acoustic wave is reduced. It is possible to prevent the coupling coefficient from being lowered. If x is greater than 0.01, the elastic properties of the SiO ₂ -xN _x layer 10 are unlikely to change over time, and if x is less than 0.5, the film quality is unlikely to deteriorate. If x is preferably about 0.1, the power durability of the layer itself is improved as compared with the case where N is not included.

FIG. 3 is a graph showing a frequency temperature characteristic of the composite piezoelectric substrate used in the present invention obtained by simulation. The horizontal axis represents the Y-cut rotation angle of the piezoelectric substrate, and the vertical axis represents the frequency temperature characteristic (TCF). The piezoelectric substrate is a LiNbO ₃ substrate having a thickness of 20 μm, the supporting substrate is a low expansion ceramic substrate (expansion coefficient 5.5 ppm / ° C.), and the total thickness of the composite piezoelectric substrate is 0.2 mm. The electrode thickness normalized by the wavelength of the surface acoustic wave (leakage surface acoustic wave) is 0.06. The electrode material is an alloy of Al and Cu, and the ratio of Al: Cu is 2: 1. For comparison, the calculated values in the case of a single LiNbO ₃ substrate are also shown in FIG. The frequency-temperature characteristics are shown for the resonant frequency and anti-resonant frequency. In the composite piezoelectric substrate used in the present invention, the frequency temperature characteristic is greatly improved from −20 ppm / ° C. to about −40 ppm / ° C. over a wide Y-cut rotation angle as compared with the case of the piezoelectric substrate alone. The Y-cut rotation angle is preferably 35 ° ± 35 °, particularly preferably 20 ° to 70 °.
The TCF corresponds to a case where the composite piezoelectric substrate is mounted by a chip and wire method.

Here, as described above, the surface acoustic wave device in which the composite piezoelectric substrate is mounted by flip chip bonding so as to satisfy the relationship of αs <αc <αs + 6, as in the surface acoustic wave device of the present invention, is, for example, Compared with the case of mounting by the wire method, the frequency temperature coefficient is improved by about several ppm / ° C. to about several tens ppm / ° C.
Therefore, when a simulation was performed when the chip was mounted by flip chip bonding while satisfying the above relationship as in the present invention, the frequency temperature characteristic was 5 to 10 ppm / cm more than the simulation result of the chip and wire method shown in FIG. It was found that the temperature was improved by about 0 ° C., and similarly, the Y-cut rotation angle was preferably 35 ° ± 35 °, and 20 ° to 70 ° was particularly preferable.

FIG. 4 shows the calculated values of the propagation loss of the leaky surface acoustic wave when the thickness of the metal electrode normalized by the wavelength of the leaky surface acoustic wave is used as a parameter for the same composite piezoelectric substrate shown in FIG. It is a graph to show. The horizontal axis represents the Y-cut rotation angle, and the vertical axis represents the propagation loss (attenuation constant).
The propagation loss is preferably less than 0.15 dB / wavelength, particularly preferably less than 0.01 dB / wavelength. In this case, the Y-cut rotation angle is preferably 35 ° ± 35 °, particularly preferably 20 ° to 70 °. If the thickness of the metal electrode between these Y cut rotation angles is 0.04 or more as a value normalized by the wavelength of the leaky surface acoustic wave, the propagation loss can be made less than 0.15 dB / wavelength. . Depending on the Y-cut rotation angle, if the metal electrode is thick, the propagation loss may increase. From the point of propagation loss, the thickness of the metal electrode is a value normalized by the wavelength of the leaky surface acoustic wave. And preferably 0.1 or less.

FIG. 5 is a graph showing the calculated value of the coupling coefficient (k ² ) for the same composite piezoelectric substrate as shown in FIG. From FIG. 5, it is more preferable if the Y-cut rotation angle in LiNbO ₃ is 35 ° ± 35 ° and the bond is large, and the Y-cut rotation angle is 0 ° to 40 °.
From the above points, the Y-cut rotation angle of the LiNbO ₃ substrate used in the present invention is preferably 35 ° ± 35 °, particularly preferably 20 ° to 40 °.

  Then, the composite piezoelectric substrate 9 as described above is diced and cut into a chip shape to obtain a composite piezoelectric chip 1. The surface acoustic wave element 8 of the present invention uses such a composite piezoelectric chip 1, for example, Au It is mounted on the mounting substrate 6 by conventional flip chip bonding via bumps 5 made of Sn or Sn. If the mounting substrate 6 is made of alumina (expansion coefficient 8 ppm / ° C.) or low expansion ceramic (expansion coefficient 5.5 ppm / ° C.), the expansion coefficient is an appropriate value, and the expansion coefficients αc and αs are the above-mentioned values. It is easy to adjust and mount so as to satisfy the above relationship, but a mounting substrate made of other materials may be used.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.
Example 1
The diameter is 4 inches (100 mm), the thickness is 290 μm, the surface roughness Ra of the bonding surface and the opposite surface is both 0.3 μm, the porosity is 2%, the Young's modulus is 380 GPa, An alumina substrate having a resistivity of 10 ¹⁵ Ωcm was prepared.
Further, a 25-degree rotated Y-cut LiNbO ₃ substrate having a diameter of 4 inches (100 mm) as a piezoelectric substrate was finished by double-side polishing so as to have a thickness of 0.15 mm (150 μm). At this time, a LiNbO ₃ substrate having no pyroelectricity was used. Each of the substrates was pretreated with short-wave UV light having a wavelength of 200 nm or less and high-concentration ozone while being heated to 100 ° C.

The alumina substrate was spin-coated with an ultraviolet curable adhesive mainly composed of epoxy methacrylate and applied uniformly on the bonding surface.
Also, the adhesive is similarly applied to the bonding surface of the LiNbO ₃ substrate, and the adhesive application surface of the alumina substrate and the adhesive application surface of the LiNbOL ₃ substrate are applied under a vacuum of 1 × 10 ⁻³ mbar. Pasted together.
Next, the bonded composite piezoelectric substrate was irradiated with ultraviolet rays having an illuminance of 50 mW / cm ² for 10 minutes to cure the adhesive. At this time, the adhesive layer was uniformly 5 μm in thickness within the bonded substrate surface.
Thereafter, this bonded substrate was cured at a temperature of 130 ° C. for 2 hours in an N ₂ atmosphere.

Then, after chamfering the composite piezoelectric substrate, the outer periphery of about 0.5 mm of the LiNbO ₃ substrate which is a piezoelectric substrate was scraped off with a special chamfering wheel. Then, scraping 130 .mu.m LiNbO ₃ surface side of the substrate (bonding surface opposite) by lap and grinding, the thickness of the LiNbO ₃ substrate was set to 20μm by further polishing.
The thickness of the alumina substrate has less extremely variations and 290μm ± 0.5μm, LiNbO ₃ substrate of a thickness of the composite piezoelectric substrate was very small and 20 ± 0.5 [mu] m. Further, no processing strain or cracks were observed on the LiNbO ₃ substrate.

Next, an alloy of Al and Cu was deposited to a thickness of 0.12 μm by sputtering on the surface side of the LiNbO ₃ substrate of the composite piezoelectric substrate. At this time, the target composition was selected so that the Al: Cu ratio was 2: 1.
Next, a part of the metal material on the surface was melted by plasma etching and patterned to form a metal electrode, thereby producing a 1-port leaky surface acoustic wave resonator (wavelength: 2 μm). That is, the thickness of the metal electrode was 0.06 as a value normalized by the wavelength of the leaky surface acoustic wave.

In the composite piezoelectric chip obtained by dicing the composite piezoelectric substrate on which the metal electrode is formed and processing it into a chip shape, the expansion in the X direction that is the leakage surface acoustic wave propagation direction of the surface on which the electrode of the LiNbO ₃ substrate is formed The coefficient was determined by in-situ observation and found to be αc = 10 ppm / ° C.
Next, the composite piezoelectric chip on which the electrodes were formed was flip-chip connected to a mounting substrate made of an alumina ceramic substrate (expansion coefficient αs = 8 ppm / ° C.) via solder bumps made of Ag and Sn, and packaging was performed. .
When the resonator characteristics at 2 GHz of the 1-port resonator in which the composite piezoelectric chip is flip-chip connected are evaluated, the specific bandwidth ((fa−fr) / fa, fa is the antiresonance frequency, and fr is the resonance frequency) is 11. % And broadband.

Further, when the frequency temperature characteristics of this resonator were obtained, the anti-resonance frequency was as low as −20 ppm / ° C. and the resonance frequency was as small as −35 ppm / ° C., and the effect of improving the frequency temperature characteristics was high.
Furthermore, when 2 GHz and 1 W of electric power were continuously supplied to this resonator, it was confirmed that there was no deterioration of the resonance characteristics even after 2000 hours and that the power durability was high.

(Example 2)
A composite piezoelectric substrate (thickness 0.2 mm) was produced in the same procedure as in Example 1 except that the cut angle of the LiNbO ₃ substrate was changed to 41 ° rotation Y cut. The thickness of the LiNbO ₃ substrate was 20 μm.

Next, an alloy of Al and Cu was deposited to a thickness of 0.125 μm on the surface side of the LiNbO ₃ substrate of the composite piezoelectric substrate by sputtering. At this time, the target composition was selected so that the Al: Cu ratio was 2: 1.
Next, a part of the metal material on the surface was melted by plasma etching and patterned to form a metal electrode, thereby producing a 1-port leaky surface acoustic wave resonator (wavelength: 2.1 μm). That is, the thickness of the metal electrode was 0.06 as a value normalized by the wavelength of the leaky surface acoustic wave. This composite piezoelectric substrate was diced and processed into a chip shape.

At this time, the coefficient of expansion in the X direction, which is the leaky surface acoustic wave propagation direction, of the surface on which the electrode of the LiNbO ₃ substrate was formed was determined by in-situ observation, and αc = 10 ppm / ° C.
Next, the composite piezoelectric chip on which the electrodes were formed was flip-chip connected to a mounting substrate made of an alumina ceramic substrate (expansion coefficient αs = 8 ppm / ° C.) via solder bumps made of Ag and Sn, and packaging was performed. .
When the resonator characteristics at 2 GHz of the 1-port resonator in which the composite piezoelectric chip is flip-chip connected are evaluated, the specific bandwidth ((fa−fr) / fa, fa is the antiresonance frequency, and fr is the resonance frequency) is 9%. And it was broadband.

Further, when the frequency temperature characteristics of the resonator were obtained, the anti-resonance frequency was -18 ppm / ° C. and the resonance frequency was a small temperature coefficient of −33 ppm / ° C., and the effect of improving the frequency temperature characteristics was high.
Furthermore, when 2 GHz and 1 W of electric power were continuously supplied to this resonator, it was confirmed that there was no deterioration of the resonance characteristics even after 2000 hours and that the power durability was high.

(Example 3)
A composite piezoelectric substrate (thickness 0.2 mm) was prepared in the same procedure as in Example 1 except that the cut angle of the LiNbO ₃ substrate in Example 1 was changed to a 5 ° rotation Y cut.
Next, an alloy of Al and Cu was deposited to a thickness of 0.18 μm on the surface side of the LiNbO ₃ substrate of the composite piezoelectric substrate by sputtering. At this time, the target composition was selected so that the Al: Cu ratio was 2: 1.
Next, a part of the metal material on the surface was melted by plasma etching and patterned to form a metal electrode, thereby producing a 1-port leaky surface acoustic wave resonator (wavelength: 1.8 μm). That is, the thickness of the metal electrode was set to 0.1 as a value normalized by the wavelength of the leaky surface acoustic wave.

Next, a protective film of SiO _1.8 N _0.2 was deposited to a thickness of 0.1 μm by plasma CVD on the composite piezoelectric substrate on which the metal electrode was formed. That is, the thickness of the protective film was 0.06 as a value normalized by the wavelength of the leaky surface acoustic wave.
At this time, the coefficient of expansion in the X direction, which is the leaky surface acoustic wave propagation direction, of the surface on which the electrode of the LiNbO ₃ substrate was formed was determined by in-situ observation, and αc = 10 ppm / ° C.

Only the SiO _1.8 N _0.2 protective film portion of the resonator electrode extraction portion formed on the composite piezoelectric substrate is dry-etched and then diced into a chip shape to form this electrode. Further, the composite piezoelectric chip was flip-chip connected to a mounting substrate made of an alumina ceramic substrate (expansion coefficient αs = 8 ppm / ° C.) via solder bumps made of Ag and Sn for packaging.
When the resonator characteristics at 2 GHz of the 1-port resonator in which the composite piezoelectric chip is flip-chip connected are evaluated, the specific bandwidth ((fa−fr) / fa, fa is the antiresonance frequency, and fr is the resonance frequency) is 12. % And broadband.

Further, when the frequency temperature characteristics of this resonator were obtained, the anti-resonance frequency was -5 ppm / ° C. and the resonance frequency was a small temperature coefficient of −20 ppm / ° C., and the effect of improving the frequency temperature characteristics was high.
Furthermore, when 2 GHz and 1 W of electric power were continuously supplied to this resonator, it was confirmed that there was no deterioration of the resonance characteristics even after 2000 hours and that the power durability was high.

Example 4
A low expansion ceramic substrate (expansion coefficient 5.5 ppm / ° C.) having a diameter of 4 inches (100 mm) and a thickness of 190 μm was prepared, and then 15 inches having a diameter of 4 inches (100 mm) and a thickness of 0.15 mm (150 μm). A rotating Y-cut LiNbO ₃ substrate was processed by double-sided lapping so that the surface Ra was 0.12 μm.

Next, the surface of the ceramic substrate is washed, pretreated with short-wave UV light having a wavelength of 200 nm or less and high-concentration ozone while being heated to 100 ° C., and an ultraviolet curable adhesive mainly composed of epoxy methacrylate is formed on one surface. Spin-coated and applied uniformly. Next, the back surface of the LiNbO ₃ substrate is washed, and the adhesive is applied in the same manner. The adhesive-coated surface of the ceramic substrate and the adhesive-coated surface of the LiNbO ₃ substrate are subjected to a vacuum of 1 × 10 ⁻³ mbar. We pasted together.

Next, the bonded composite piezoelectric substrate was irradiated with ultraviolet rays having an illuminance of 50 mW / cm ² for 10 minutes to cure the adhesive. At this time, the adhesive layer was uniformly 5 μm thick within the substrate surface. Then, after processing chamfering the composite piezoelectric substrate, off 120μm shaving by wrap and grinding the surface of the LiNbO ₃ substrate, and as the thickness of the LiNbO ₃ substrate is 10μm by further polishing.

Next, an alloy of Al and Cu was deposited to a thickness of 0.2 μm on the surface side of the LiNbO ₃ substrate of the composite piezoelectric substrate by sputtering. At this time, the target composition was selected so that the Al: Cu ratio was 2: 1.
Next, a part of the metal material on the surface was melted by plasma etching and patterned to form a metal electrode, thereby producing a 1-port leaky surface acoustic wave resonator (wavelength 1.8 μm). That is, the thickness of the metal electrode was set to 0.11 as a value normalized by the wavelength of the leaky surface acoustic wave. This composite piezoelectric substrate was diced and processed into a chip shape.

At this time, the coefficient of expansion in the X direction, which is the leaky surface acoustic wave propagation direction, of the surface on which the electrode of the LiNbO ₃ substrate was formed was determined by in-situ observation, and αc = 9 ppm / ° C.
Next, the composite piezoelectric chip on which the electrodes were formed was flip-chip connected to a mounting substrate made of an alumina ceramic substrate (expansion coefficient αs = 8 ppm / ° C.) via solder bumps made of Ag and Sn, and packaging was performed. .
When the resonator characteristics at 2 GHz of the 1-port resonator in which the composite piezoelectric chip is flip-chip connected are evaluated, the specific bandwidth ((fa−fr) / fa, fa is the antiresonance frequency, and fr is the resonance frequency) is 12. % And broadband.

Further, when the frequency temperature characteristics of the resonator were obtained, the anti-resonance frequency was -27 ppm / ° C., and the resonance frequency was a low temperature coefficient of −29 ppm / ° C., and the effect of improving the frequency temperature characteristics was high.
Furthermore, when 2 GHz and 1 W of electric power were continuously supplied to this resonator, it was confirmed that there was no deterioration of the resonance characteristics even after 2000 hours and that the power durability was high.

(Example 5)
An alumina substrate similar to that in Example 1 was prepared. Next diameter of 4 inches 36 ° rotated Y-cut LiTaO ₃ substrate thickness (100 mm) were finished by double side polishing to a 0.15 mm (150 [mu] m). At this time, a LiTaO ₃ substrate having no pyroelectricity was used. Each of the substrates was pretreated with short-wave UV light having a wavelength of 200 nm or less and high-concentration ozone while being heated to 100 ° C.
The alumina substrate was spin-coated with an ultraviolet curable adhesive mainly composed of epoxy methacrylate and applied uniformly on the bonding surface.
Further, the adhesive is similarly applied to the bonding surface of the LiTaO ₃ L substrate, and the adhesive application surface of the alumina substrate and the adhesive application surface of the LiTaO ₃ substrate are subjected to a vacuum of 1 × 10 ⁻³ mbar. We pasted together.
Next, the bonded composite piezoelectric substrate was irradiated with ultraviolet rays having an illuminance of 50 mW / cm ² for 10 minutes to cure the adhesive. At this time, the adhesive layer was uniformly 5 μm in thickness within the bonded substrate surface.
Thereafter, this bonded substrate was cured at a temperature of 130 ° C. for 2 hours in an N ₂ atmosphere.

Then, after chamfering the composite piezoelectric substrate, about 0.5 mm of the outer periphery of the LiTaO ₃ substrate which is a piezoelectric substrate was scraped off with a special chamfering wheel. Next, the surface side (the side opposite to the bonding surface) of the LiTaO ₃ substrate was scraped off by 130 μm by lapping and grinding, and the thickness of the substrate was adjusted to 20 μm by polishing.

The thickness of the alumina substrate was very small as 290 μm ± 0.5 μm, and the thickness of the LiTaO ₃ substrate of the composite piezoelectric substrate was as extremely small as 20 ± 0.5 μm. Further, no processing strain or cracks were observed in the LiTaO ₃ substrate.
Next, an alloy of Al and Cu was deposited to a thickness of 0.12 μm by sputtering on the surface side of the LiTaO ₃ substrate of the composite piezoelectric substrate. At this time, the target composition was selected so that the Al: Cu ratio was 2: 1.
Next, a part of the metal material on the surface was melted by plasma etching and patterned to form a metal electrode, thereby producing a 1-port leaky surface acoustic wave resonator (wavelength: 2 μm). That is, the thickness of the metal electrode was 0.06 as a value normalized by the wavelength of the leaky surface acoustic wave. This composite piezoelectric substrate was diced and processed into a chip shape.

At this time, αc = 10 ppm / ° C. was obtained by in-situ observation of the expansion coefficient in the X direction, which is the leaky surface acoustic wave propagation direction, of the surface on which the electrode of the LiTaO ₃ substrate was formed.
Next, the composite piezoelectric chip on which the electrodes were formed was flip-chip connected to a mounting substrate made of an alumina ceramic substrate (expansion coefficient αs = 8 ppm / ° C.) via solder bumps made of Ag and Sn, and packaging was performed. .
When the resonator characteristics at 2 GHz of the 1-port resonator in which the composite piezoelectric chip is flip-chip connected are evaluated, the specific bandwidth ((fa−fr) / fa, fa is the antiresonance frequency, and fr is the resonance frequency) is 3. % Was a relatively wide band.

Further, the frequency temperature characteristics of the resonator were obtained. As a result, the anti-resonance frequency was as low as −15 ppm / ° C., and the resonance frequency was as low as −5 ppm / ° C., and the effect of improving the frequency temperature characteristics was high.
Furthermore, when 2 GHz and 1 W of electric power were continuously supplied to this resonator, it was confirmed that there was no deterioration of the resonance characteristics even after 2000 hours and that the power durability was high.

(Comparative Example 1)
A 1-port leaky surface acoustic wave resonator was fabricated in the same manner as in Example 1, mounted in a chip-and-wire manner, and the frequency-temperature characteristics of the resonator were examined. The anti-resonance frequency was -23 ppm / ° C. The resonance frequency was a temperature coefficient of -38 ppm / ° C.

(Comparative Example 2)
A 1-port leaky surface acoustic wave resonator was produced in the same manner as in Example 2, mounted in a chip-and-wire system, and the frequency-temperature characteristics of the resonator were examined. The anti-resonance frequency was −21 ppm / ° C., The resonance frequency was a temperature coefficient of −36 ppm / ° C.

(Comparative Example 3)
A 1-port leaky surface acoustic wave resonator was manufactured by the same method as in Example 3, and mounted by the chip-and-wire method. When the frequency-temperature characteristics of the resonator were examined, the antiresonance frequency was -8 ppm / ° C. The resonance frequency was a temperature coefficient of −23 ppm / ° C.

(Comparative Example 4)
A one-port leaky surface acoustic wave resonator was fabricated by the same method as in Example 4, mounted by the chip-and-wire method, and the frequency-temperature characteristics of the resonator were examined. The anti-resonance frequency was -31 ppm / The temperature coefficient of ° C. and the resonance frequency was −36 ppm / ° C.

Thus, compared with Example 1-4, Comparative Example 1-4 has a large value for the temperature coefficient of the antiresonance frequency and the resonance frequency, respectively. Thus, as described above, the one mounted by flip chip bonding so as to satisfy the relationship of αs <αc <αs + 6 as in the present invention is mounted by the chip and wire method as in Comparative Example 1-4. It can be seen that the frequency temperature characteristic is more effectively improved than that.
Moreover, in the mounting by the chip and wire method as in Comparative Example 1-4, the mounting work is complicated and the productivity is not high.

(Comparative Example 5)
A composite piezoelectric substrate was produced by the same method as in Example 1, and an alloy of Al and Cu was deposited to a thickness of 0.06 μm on the surface side of the LiNbO ₃ substrate of the composite piezoelectric substrate by a sputtering method. At this time, the target composition was selected so that the Al: Cu ratio was 2: 1.
Next, a part of the metal material on the surface was melted by plasma etching and patterned to form a metal electrode, thereby producing a 1-port leaky surface acoustic wave resonator (wavelength: 2 μm). That is, the thickness of the metal electrode was 0.03 as a value normalized by the wavelength of the leaky surface acoustic wave. This is different from the feature of the present invention in which the thickness of the metal electrode is 0.04 or more as a value normalized by the wavelength of the leaky surface acoustic wave.
A composite piezoelectric chip obtained by dicing the composite piezoelectric substrate formed with the metal electrodes into a chip shape is flip-chip connected to a mounting substrate made of an alumina ceramic substrate via solder bumps made of Ag and Sn. I did packaging.
When power of 2 GHz and 1 W was continuously applied to a 1-port resonator in which the composite piezoelectric chip was flip-chip connected, the metal electrode deteriorated in about 10 hours.

(Comparative Example 6)
A 25-degree rotated Y-cut LiNbO ₃ substrate having a diameter of 4 inches (100 mm) was finished to a thickness of 0.15 mm (150 μm).
An alloy of Al and Cu was deposited on the surface of this LiNbO ₃ substrate to a thickness of 0.06 μm by sputtering. At this time, the target composition was selected so that the Al: Cu ratio was 2: 1.
Next, a part of the metal material on the surface was melted by plasma etching, and patterned to form a metal electrode, thereby producing a 1-port leaky surface acoustic wave resonator (wavelength: 2 μm). That is, the thickness of the metal electrode was 0.03 as a value normalized by the wavelength of the leaky surface acoustic wave.

In the piezoelectric chip obtained by dicing the piezoelectric substrate on which the metal electrode is formed and processing it into a chip shape, an expansion coefficient in the X direction, which is a leakage surface acoustic wave propagation direction, of the surface on which the electrode of the LiNbO ₃ substrate is formed. As a result of in-situ observation, αc = 15 ppm / ° C.
Next, the piezoelectric chip on which the electrodes were formed was flip-chip connected to a mounting substrate made of an alumina ceramic substrate (expansion coefficient αs = 8 ppm / ° C.) via solder bumps made of Ag and Sn, and packaging was performed.
When the frequency temperature characteristics of the 1-port resonator in which the piezoelectric chip was flip-chip connected were obtained, the anti-resonance frequency was as high as −60 pm / ° C., and the resonance frequency was −83 ppm / ° C ..
Furthermore, when 2 GHz and 1 W of electric power were continuously applied to the resonator, the metal electrode deteriorated in about 10 hours.

(Comparative Example 7)
A 25-degree rotated Y-cut LiNbO ₃ substrate having a diameter of 4 inches (100 mm) was finished to a thickness of 0.15 mm (150 μm).
An alloy of Al and Cu was deposited on the surface of this LiNbO ₃ substrate to a thickness of 0.06 μm by sputtering. At this time, the target composition was selected so that the Al: Cu ratio was 2: 1.
Next, a part of the metal material on the surface was melted by plasma etching, and patterned to form a metal electrode, thereby producing a 1-port leaky surface acoustic wave resonator (wavelength: 2 μm). That is, the thickness of the metal electrode was 0.03 as a value normalized by the wavelength of the leaky surface acoustic wave.
Next, a SiO _1.8 N _0.2 protective film was deposited to a thickness of 0.2 μm by plasma CVD on the piezoelectric substrate on which the metal electrode was formed.

In the piezoelectric chip obtained by dicing the piezoelectric substrate on which the metal electrode is formed and processing it into a chip shape, an expansion coefficient in the X direction, which is a leakage surface acoustic wave propagation direction, of the surface on which the electrode of the LiNbO ₃ substrate is formed. As a result of in-situ observation, αc = 15 ppm / ° C.
Next, the piezoelectric chip on which the electrodes were formed was flip-chip connected to a mounting substrate made of an alumina ceramic substrate (expansion coefficient αs = 8 ppm / ° C.) via solder bumps made of Ag and Sn, and packaging was performed.
When the frequency-temperature characteristics of the 1-port resonator in which the piezoelectric chip was flip-chip connected were obtained, the anti-resonance frequency had a large temperature coefficient of −50 pm / ° C. and the resonance frequency was −70 ppm / ° C.
Furthermore, when 2 GHz and 1 W of electric power were continuously applied to the resonator, the metal electrode deteriorated in about 10 hours.

(Comparative Example 8)
An alumina substrate similar to the alumina substrate prepared in Example 1 was prepared as a ceramic substrate as a support substrate. Then, a surface acoustic wave element is manufactured in the same procedure as in Example 1 except that a substrate different from that in Example 1 is prepared as the mounting substrate and the thickness of the metal electrode formed on the piezoelectric substrate is changed. did.
The thickness of the metal electrode was 0.03, which was a value normalized by the wavelength of the leaky surface acoustic wave.
Further, when the expansion coefficient in the X direction, which is the leakage acoustic surface wave propagation direction, of the surface on which the electrode of the LiTaO ₃ substrate is formed was determined by in-situ observation, αc = 10 ppm / ° C., and the expansion coefficient αs of the mounting substrate was It was 12 ppm / ° C. That is, unlike the relationship between αs and αc (αs <αc <αs + 6) in the present invention, αs> αc.

The temperature coefficient of the antiresonance frequency of the 1-port resonator in which the composite piezoelectric chip was flip-chip connected was -41 ppm / ° C, and the temperature coefficient of the resonance frequency was -38 ppm / ° C.
Further, when 2 GHz and 1 W of power were continuously applied to the resonator composed of the composite piezoelectric substrate, the metal electrode deteriorated in about 10 hours.
Thus, compared with the example, in the surface acoustic wave device of Comparative Example 8, the metal electrode was easily deteriorated, and the temperature characteristics were also poor.

(Comparative Example 9)
A gadolinium gallium garnet (GGG) substrate having a diameter of 4 inches (100 mm) and a thickness of 200 μm was prepared. Next, a 36-degree rotated Y-cut lithium tantalate (LiTaO ₃ ) substrate having a diameter of 4 inches (100 mm) was processed to have a thickness of 0.2 mm (200 μm) and a surface Ra of 0.12 μm by double-sided lapping.

Next, the surface of the GGG substrate is cleaned, and the substrate is further pretreated with short-wave UV light having a wavelength of 200 nm or less and high-concentration ozone while being heated to 100 ° C., and an ultraviolet curable adhesive mainly composed of epoxy methacrylate is spin-coated. Then, it was uniformly applied on one surface. Next, the back surface of the LiTaO ₃ substrate is washed, and the adhesive is applied in the same manner. The adhesive application surface of the GGG substrate and the adhesive application surface of the LiTaO ₃ substrate are subjected to a vacuum of 1 × 10 ⁻³ mbar. We pasted together.

Next, an alloy of Al and Cu was deposited to a thickness of 0.06 μm on the surface side of the LiNbO ₃ substrate of the composite piezoelectric substrate by sputtering. At this time, the target composition was selected so that the Al: Cu ratio was 2: 1.
Next, a part of the metal material on the surface was melted by plasma etching and patterned to form a metal electrode, thereby producing a 1-port leaky surface acoustic wave resonator (wavelength: 2 μm). That is, the thickness of the metal electrode was 0.03 as a value normalized by the wavelength of the leaky surface acoustic wave.

In the composite piezoelectric chip obtained by dicing the composite piezoelectric substrate on which the metal electrode is formed and processing it into a chip shape, the expansion in the X direction that is the leakage surface acoustic wave propagation direction of the surface on which the electrode of the LiNbO ₃ substrate is formed When the coefficient was determined by in-situ observation, αc = 16 ppm / ° C.

Next, this composite piezoelectric chip was flip-chip connected to a mounting substrate made of an alumina ceramic substrate (expansion coefficient αs = 8 ppm / ° C.) via a solder bump made of Sn to perform packaging. That is, unlike the relationship between αs and αc (αs <αc <αs + 6) in the present invention, αc> αs + 6.
The temperature coefficient of the antiresonance frequency of the one-port resonator in which the composite piezoelectric chip is flip-chip connected is −40 ppm / ° C., and the temperature coefficient of the resonance frequency is −39 ppm / ° C., which is a relatively large temperature coefficient. .
Further, when 2 GHz and 1 W of power were continuously applied to the resonator composed of the composite piezoelectric substrate, the metal electrode deteriorated in about 10 hours.

1 is a schematic cross-sectional view showing an example of an embodiment of a surface acoustic wave element according to the present invention. It is the schematic sectional drawing which showed an example of the composite piezoelectric substrate used for the surface acoustic wave element concerning this invention. It is a graph which shows what calculated | required the frequency temperature characteristic of the composite piezoelectric substrate which concerns on this invention by simulation. FIG. 4 is a graph showing calculated values of leakage surface acoustic wave propagation loss when the thickness of the metal electrode normalized by the wavelength of the leakage surface acoustic wave is used as a parameter for the composite piezoelectric substrate shown in FIG. 3. . About the same as the composite piezoelectric substrate shown in FIG. 3 is a graph showing the calculated value of the coupling coefficient (k ^2).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Composite piezoelectric chip, 2 ... Piezoelectric substrate, 3 ... Ceramic substrate,
4 ... Adhesive (adhesive layer), 5 ... Bump, 6 ... Mounting substrate, 7 ... Metal electrode,
8 ... Surface acoustic wave element, 9 ... Composite piezoelectric substrate, 10 ... SiO2 _{- xNx} layer.

Claims (3)

A surface acoustic wave element in which a metal electrode that excites and detects surface acoustic waves or leaky surface acoustic waves is formed on a piezoelectric substrate, and is a composite piezoelectric device in which at least a piezoelectric substrate and a ceramic substrate are bonded via an adhesive A composite piezoelectric chip obtained by processing the substrate into a chip shape; and a mounting substrate on which the composite piezoelectric chip is mounted by flip chip bonding. A thickness of the metal electrode formed on the piezoelectric substrate is determined by a surface acoustic wave leakage. The value normalized by the wavelength is 0.04 or more, and the expansion coefficient αc (ppm / ° C.) in the propagation direction of the surface acoustic wave or leaky surface acoustic wave on the surface of the piezoelectric substrate and the expansion coefficient αs (ppm) of the mounting substrate / ℃)
αs <αc <αs + 6
The surface acoustic wave device is mounted so as to satisfy the following relationship. 2. The surface acoustic wave device according to claim 1, wherein the piezoelectric substrate is a 35 ° ± 35 ° rotated Y-cut LiNbO ₃ substrate or a LiTaO ₃ substrate. 3. The surface acoustic wave device according to claim 1, wherein a SiO _2−x N _x layer (where 0.01 <x <0.5) is formed on the surface of the piezoelectric substrate so as to cover the metal electrode. The surface acoustic wave device is characterized in that the thickness of the SiO ₂ -xN _x layer is 0.1 or less as a value normalized by the wavelength of the leaky surface acoustic wave.

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