Sound wave device

Abstract

An end-face reflection type acoustic wave device (10) comprising a rectangular-parallel-plane composite substrate (15) in which a supporting substrate (14) and a piezoelectric substrate (12) are bonded together with a pair of IDT electrodes (16, 18) provided on the piezoelectric substrate (12) in a manner to be intercalated with each other, wherein a fragmentation size in a first side surface (12a) of the piezoelectric substrate (12) is 1 / 10 of a wavelength λ of a sound wave or smaller, the first side surface (12a) extending orthogonal to a direction of sound wave propagation, and wherein a chipping size in a second side surface (12b) of the piezoelectric substrate (12) is larger than the chipping size in the first side surface (12a) and is 1 / 2 the wavelength λ of the sound wave or larger and 50 times the wavelength λ of the sound wave or smaller, the second side surface (12a) extending in the direction of sound wave propagation.

Description

Technical area

[0001] The present invention relates to a sound wave device. State of the art

[0002] Previously proposed acoustic wave devices include end-face reflection acoustic wave devices that utilize acoustic waves reflected by the edges of substrates. In such an end-face reflection acoustic wave device, an acoustic wave, or sound wave, excited by IDT (interdigital transducer) electrodes provided on a piezoelectric substrate propagates to the edges of the substrate and is reflected by the edges. The end-face reflection acoustic wave device is manufactured, for example, as follows. First, a disc-shaped piezoelectric wafer and a supporting wafer whose thermal expansion coefficient is smaller than that of the piezoelectric wafer are bonded together, thereby obtaining a disc-shaped composite wafer.Subsequently, the piezoelectric wafer included in the composite wafer is divided into a number of rectangular regions, each having a predetermined size, and IDT electrodes are formed on each rectangular region. Then, the composite wafer is cut into pieces of the rectangular regions using a cutting device such as a dicing saw. This provides acoustic wave devices, each comprising a rectangular-parallel-plane composite substrate in which a piezoelectric substrate and a supporting substrate are bonded together, with IDT electrodes provided on the piezoelectric substrate.The composite substrate is used for the purpose of reducing the change in the size of the piezoelectric substrate that may occur with the change in temperature, and accordingly, the change in the frequency characteristic of the acoustic wave device that may occur with the change in temperature is suppressed.

[0003] However, when the composite wafer is cut, chipping (splintering) may occur on the cut surfaces of the piezoelectric wafer. Such chipping was a reason for the increase in the number of spurious peaks (irrelevant small peaks that appear around resonance-related peaks). To suppress the occurrence of such spurious peaks, JP 2002-261559 A and JP 2002-9583 A employed the following manufacturing methods. The method according to JP 2002-261559 A comprises the following steps: (1) providing cutting grooves around rectangular portions with a dicing saw before forming IDT electrodes, (2) polishing the surface of a piezoelectric wafer and removing chips formed around the openings of the cutting grooves, (3) forming IDT electrodes, and (4) performing cutting with a dicing saw thinner than the cutting grooves and obtaining pieces of acoustic wave devices.The method according to JP 2002-9583 A comprises the following steps: (1) forming IDT electrodes on each of a number of rectangular regions defined on a piezoelectric wafer included in a composite wafer, (2) making cuts along rectangular regions from the side of a supporting wafer by laser cutting to a depth not reaching the piezoelectric wafer, and (3) applying a voltage that cuts the supporting wafer, thereby obtaining pieces of acoustic wave devices.

[0004] DE 102 41 981 A1 discloses a method for manufacturing an end-face reflection acoustic wave device, comprising the following steps: (1) forming IDT electrodes on the upper surface of a piezoelectric substrate, (2) a first half cut for forming first end face portions having a smooth surface, i.e., two opposite end faces functioning as reflection end faces, from the upper surface of the piezoelectric substrate, (3) a second half cut for forming second end face portions having a rough surface after the first cut, and (4) a full cut for cutting the piezoelectric substrate to reach the lower surface of the piezoelectric substrate outside the second end face portions in the propagation direction of a surface acoustic wave.

[0005] DE 696 27 757 T2 discloses a method for manufacturing an end-face reflection acoustic wave device, comprising the steps of: (1) forming IDT electrodes on a piezoelectric substrate, and (2) cutting the piezoelectric substrate in a direction parallel to the outermost electrode fingers of the IDT electrodes within a target area extending from the outer edges of the outermost electrodes to a position λ / 8 outward therefrom, where λ is the wavelength of the surface acoustic wave generated by the IDT electrodes, to form opposite end faces of the end-face reflection acoustic wave device. Summary of the inventionTechnical problem

[0006] JP 2002-261559 A and JP 2002-9583 A, as mentioned above, describe suppressing the occurrence of noise peaks by removing splinters in the edges that reflect the sound wave, i.e., the edges that extend orthogonally to the direction of sound wave propagation. However, JP 2002-261559 A and JP 2002-9583 A do not consider edges that extend in the direction of sound wave propagation. The inventors have found that edges that extend in the direction of sound wave propagation and are uniform without splintering reflect irrelevant sound waves, and such reflection is one of the reasons for the increase in the number of noise peaks.

[0007] The present invention is intended to solve the foregoing problem and mainly aims to more surely suppress the occurrence of noise peaks in an end-face reflection acoustic wave device. Solution to the problem

[0008] The sound wave device according to the present invention has the features specified in claim 1.

[0009] In the acoustic wave device according to the present invention, the chipping size in the first side surface that reflects a sound wave at a desired wavelength is 1 / 10 of the wavelength λ of the sound wave or less. Therefore, the amount of reflection by the first side surface is satisfactorily large. Furthermore, changes in the phase of the sound wave due to changes in the position of the first side surface are less likely to occur. Therefore, the occurrence of noise peaks accompanying such changes in phase can be suppressed. On the other hand, the chipping size in the second side surface is larger than the chipping size in the first side surface, specifically, 1 / 2 of the wavelength λ of the sound wave or more and 50 times the wavelength λ of the sound wave or less. Therefore, any sound waves at irrelevant wavelengths are less likely to be reflected by the second side surface.In this regard, the occurrence of noise peaks can also be suppressed. If the fragmentation size in the second side surface is less than 1 / 2 the wavelength λ, any sound waves at irrelevant wavelengths are less likely to be reflected by the second side surface. Accordingly, noise peaks are less likely to occur, which is undesirable. If the fragmentation size in the second side surface is greater than 50 times the wavelength λ, the Q factor of the resonator is lowered, which is undesirable.

[0010] In the acoustic wave device according to the present invention, it is desirable that the fragmentation size in the second side surface be 12.5 times the wavelength λ of the acoustic wave or greater and 50 times the wavelength λ of the acoustic wave or less. If so, the occurrence of noise peaks can be more reliably suppressed.

[0011] In the acoustic wave device according to the present invention, it is desirable that the supporting substrate has a smaller thermal expansion coefficient than the piezoelectric substrate. If so, the change in the size of the piezoelectric substrate that may occur with the change in temperature can be reduced, and the change in the frequency characteristics of the acoustic wave device that may occur with the change in temperature can be reduced. Short description of the drawings Fig. 1 is a perspective view of a sound wave device 10. Fig. 2 is a plan view of a sound wave device 10. Fig. 3 is a sectional view taken along a line AA shown in Fig. 2 is shown. Fig.4 includes perspective views illustrating the process of manufacturing the sound wave device 10. Fig. 5 includes diagrams illustrating cutting and sawing. Description of embodiments

[0012] An embodiment of the present invention will now be described with reference to the drawings. Fig. 1 and Fig. 2 are a perspective view and a plan view of a sound wave device 10 according to the embodiment, respectively. Fig. 3 is a sectional view taken along a line AA shown in Fig. 2 is shown.

[0013] The acoustic wave device 10 is an edge reflection type acoustic wave device and comprises a rectangular-parallel-plane composite substrate 15 in which a piezoelectric substrate 12 and a supporting substrate 14 are bonded together with a pair of IDT electrodes 16 and 18 provided on the piezoelectric substrate 12 in such a manner as to be intercalated with each other.

[0014] The piezoelectric substrate 12 is capable of propagating surface acoustic waves (SAWs). The piezoelectric substrate 12 is made of any one of lithium tantalate (LT), lithium niobate (LN), a single crystal of lithium niobate and lithium tantalate, a single crystal, lithium borate, zinc oxide, aluminum nitride, langasite (LGS), langalate (LGT), and the like. Among the foregoing materials, LT or LN is preferred. LT and LN each propagate SAWs at a high speed and each have a high electromechanical coupling coefficient. Therefore, LT and LN are each suitable for a high-frequency broadband acoustic wave device. The thickness of the piezoelectric substrate 12 is not particularly limited and may be, for example, 0.2 to 50 μm. The piezoelectric substrate 12 has first side surfaces 12a each orthogonal to a direction of acoustic wave propagation.Acoustic wave propagation (a direction of SAW propagation), and second side surfaces 12b each extending in the direction of SAW propagation. Let the wavelength of the SAW being excited be λ, and the distance between the first side surfaces 12a, which are opposite to each other, be L (see . Fig. 3), then L is designed to be an integer multiple of λ / 2.

[0015] The supporting substrate 14 has a smaller thermal expansion coefficient than the piezoelectric substrate 12 and is bonded to the back surface of the piezoelectric substrate 12 directly or with an organic adhesive layer therebetween. Since the supporting substrate 12 has a smaller thermal expansion coefficient than the piezoelectric substrate 12, the change in the size of the piezoelectric substrate 12 that may occur with the change in temperature is reduced. Therefore, in a case where the composite substrate 15 is used to form the acoustic wave device 10, the change in the frequency characteristic that may occur with the change in temperature can be reduced. The supporting substrate 14 is made of any of silicon, sapphire, aluminum nitride, alumina, borosilicate glass, quartz glass, and the like. Silicon or sapphire is preferred.The thickness of the supporting substrate 14 is not particularly limited and may be, for example, 200 to 1200 µm.

[0016] The composite substrate 15 is formed from the piezoelectric substrate 12 and the supporting substrate 14, which are joined together. The joining can be either direct joining or indirect joining using an organic adhesive layer. The composite substrate 15 obtained in this manner is a rectangular parallelepiped. The size of the composite substrate 15 is not particularly limited and can be, for example, 1 mm by 2 mm or 2 mm by 2.5 mm in length by width.

[0017] The IDT electrode 16 includes a base portion 16a extending in the direction of SAW propagation, wide electrode fingers 16b extending from the base portion 16a in the direction orthogonal to the direction of SAW propagation, respectively, and a narrow electrode finger 16c extending from the base portion 16a in the direction orthogonal to the direction of SAW propagation and provided at one end in the direction of SAW propagation. Similarly, the IDT electrode 18 includes a base portion 18a, wide electrode fingers 18b, and a narrow electrode finger 18c. The two IDT electrodes 16 and 18 are spaced apart from each other so as not to contact each other.Specifically, one of the two wide electrode fingers 16b of the IDT electrode 16 extends into a space between the two adjacent wide electrode fingers 18b of the IDT electrode 18, while the other extends into a space between one of the wide electrode fingers 18b and the narrow electrode fingers 18c. Referring to FIG. Fig. 3, the wavelength of the surface acoustic wave to be excited shall be λ, where the width of each of the wide electrode fingers 16b and 18b is λ / 4, the width of the gap between adjacent ones of the electrode fingers is also λ / 4, and the width of each of the narrow electrode fingers 16c and 18c is λ / 8.

[0018] In the acoustic wave device 10 configured as described above, a SAW excited by the IDT electrodes 16 and 18 and having the wavelength λ propagates toward each of the first side surfaces 12a of the piezoelectric substrate 12 and is reflected by the first side surface 12a. In the embodiment, the chipping amount in the first side surface 12a is 1 / 10 of the wavelength λ of the SAW or smaller. Therefore, the amount of reflection by the first side surface 12a is satisfactorily large. Furthermore, since the profile accuracy of the first side surface 12a is high, changes in the phase of the SAW due to changes in the position of the first side surface 12a are less likely to occur. Therefore, the occurrence of spurious peaks accompanying such changes in phase can be suppressed.On the other hand, the splintering size in each of the second side surfaces 12b is larger than the splintering size in the first side surface 12a, specifically, 1 / 2 the wavelength λ or greater and 50 times the wavelength λ or less. Therefore, any SAWs at irrelevant wavelengths are less likely to be reflected by the second side surface 12b. In this respect, too, the occurrence of spurious peaks can be suppressed.

[0019] Now, a method of manufacturing the acoustic wave device 10 will be described with reference to Fig. 4 described. Fig. 4 has perspective views illustrating the process of manufacturing the sound wave device 10.

[0020] First, a disk-shaped piezoelectric wafer 22 having an orientation flat (OF) and a supporting wafer 24 having the same shape as the piezoelectric wafer 22 are provided (see Fig. 4(a)). Subsequently, the wing surfaces of the respective wafers 22 and 24 are cleaned so that any dirt on the wing surfaces is removed. Subsequently, an ion beam of an inert gas, such as argon, is applied to the wing surfaces of the respective wafers 22 and 24, thereby removing any contaminants (oxide films and other adherent substances) remaining thereon, and the wing surfaces are activated. Subsequently, in a vacuum and at room temperature, the wafers 22 and 24 are positioned such that the OFs of the two coincide with each other, and the wafers 22 and 24 are joined or bonded together (see Fig. 4(b)).

[0021] Specifically, the front surface of the piezoelectric wafer 22 is polished to a predetermined thickness. Accordingly, a composite wafer 25 is completed (see Fig. 4(c)). Subsequently, electrodes intended for acoustic wave devices are formed on the front surface of the piezoelectric wafer 22 contained in the composite wafer 25. The front surface of the piezoelectric wafer 22 is divided such that a number of acoustic wave devices are obtained. The above-described IDT electrodes 16 and 18 are photolithographically formed at positions corresponding to each of the acoustic wave devices. Finally, the composite wafer 25 is separated along the division lines. Accordingly, a number of acoustic wave devices 10 are obtained (see Fig. 4(d)).

[0022] Fig.5 includes diagrams illustrating the cutting. Part (a) is a plan view of the composite wafer 25, and part (b) is an enlarged view of the area enclosed by a dotted line in part (a). Before cutting the composite wafer 25, a blade is selected such that cut surfaces to be obtained along cutting lines CLa provided to form the first side surfaces 12a of the acoustic wave devices 10 have a chipping of 1 / 10 of the wavelength λ or less.Further, the number of revolutions and the feed rate of the blade are adjusted, or blades of different roughness or different thicknesses are selectively used so that cut surfaces to be obtained along cutting lines CLb intended to form the second side surfaces 12b of the acoustic wave devices 10 have a chipping of 1 / 2 the wavelength λ or greater and 50 times the wavelength λ or less. Note that the chipping size refers to the size of the largest of concavities or convexities formed in the cut surface.

[0023] In the acoustic wave device 10 according to the above-described embodiment, the chipping size in the first side surface 12a that reflects a SAW at a certain wavelength λ is 1 / 10 of the wavelength λ of the SAW or less. Therefore, the amount of reflection by the first side surface 12a is satisfactorily large. Furthermore, changes in the phase of the SAW due to changes in the position of the first side surface 12a are less likely to occur. Therefore, the occurrence of spurious peaks accompanying such a change in phase can be suppressed. On the other hand, the chipping size in the second side surface 12b is larger than the chipping size in the first side surface 12a (specifically, 1 / 2 of the wavelength λ or greater and 50 times the wavelength λ or less). Therefore, any SAWs at irrelevant wavelengths are less likely to be reflected by the second side surface 12b.In this respect, the occurrence of interference peaks can also be kept down or suppressed.

[0024] It is needless to say that the present invention is not limited to the foregoing embodiment in any way and may be embodied in various other ways within the technical scope of the present invention.

[0025] For example, the cutting along the cutting lines CLa and the cutting lines CLb performed with blades in the foregoing embodiment may be performed by laser cutting. In this case, laser irradiation conditions may be adjusted in accordance with the chipping sizes specified for the respective cutting lines CLa and CLb. Alternatively, after cutting along the cutting lines CLa and CLb is performed under laser irradiation conditions that form uniform cutting surfaces, the chipping size in the cutting surfaces obtained along the cutting lines CLb may be increased by roughening the cutting surfaces with a file or the like.

[0026] In the previous embodiment, the piezoelectric wafer 22 and the supporting wafer 24 are bonded by directly joining the two with an ion beam. Instead of using an ion beam, a method using a plasma or a neutral atom beam may be employed.

[0027] In the foregoing embodiment, the piezoelectric wafer 22 and the supporting wafer 24 are bonded together by directly joining the two. Alternatively, the piezoelectric wafer 22 and the supporting wafer 24 may be bonded together with an organic adhesive layer interposed therebetween. In this case, an organic adhesive is evenly applied to one or both of the front surface of the supporting substrate 14 and the back surface of the piezoelectric substrate 12, and the organic adhesive is solidified with the two substrates superimposed, thereby bonding the two substrates together. EXAMPLES[EXAMPLE 1]

[0028] A disc-shaped, 42° Y-cut, X-propagation LT substrate (with a thickness of 250 µm) was provided as a piezoelectric wafer in which the direction of SAW propagation was the X direction and a rotated Y-cut substrate had a cut angle. Furthermore, a disc-shaped Si(111) substrate (with a thickness of 230 µm) was provided as a supporting wafer. The two wafers were placed in a vacuum chamber maintained at 2 × 10 -6(Pa), and an argon beam was applied to the corresponding surfaces for 60 seconds. Subsequently, the surfaces of the two wafers to which the beam was applied were brought into contact with each other, and the two wafers were pressed together at 2000 kg. Thus, the two wafers were directly bonded together. The bonded body was removed from the vacuum chamber, and the LT surface was ground to 30 µm. Subsequently, the bonded body was polished to 25 µm with a tin disc while diamond slurry (with a particle size of 1 µm) was applied thereon. Further, the bonded body was ground to 20 µm with a urethane pad while colloidal silicon (with a particle size of 20 nm) was applied thereon. Thus, a composite wafer intended for acoustic wave devices was obtained.Subsequently, IDT electrodes were photolithographically formed on each of a number of rectangular regions (2 mm by 1 mm) divided on the LT surface of the composite wafer, and the composite wafer was cut into pieces of the rectangular regions. Accordingly, a number of acoustic wave devices were obtained. The design value of the longitudinal wavelength λ of the SAW was set to 4 μm. Cutting was performed using blades. The blade, which was used in a cutting direction (along the cutting lines CLa shown in . Fig. 5) which is orthogonal to the direction of SAW propagation, had a thickness of 0.05 mm and was made of #2000. Cutting was carried out at a rotational speed of 29000 rpm and at a feed rate of 20 mm / s. The blade, which was used in a cutting operation in the direction of SAW propagation (along the cutting lines CLb shown in Fig.5) had a thickness of 0.1 mm and was made of #500. Cutting was performed at a rotational speed of 29,000 rpm and at a feed rate of 50 mm / s. In each of the acoustic wave devices thus obtained, the chipping size in the first side surface extending orthogonal to the direction of SAW propagation was 0.4 µm (0.1 of λ), and the chipping size in the second side surface extending in the direction of SAW propagation was 50 µm (12.5 times λ). Data regarding Example 1 are summarized in Table 1. [EXAMPLE 2]

[0029] As in Working Example 1, a composite wafer on which IDT electrodes were formed was prepared and was cut under processing conditions for Example 2, which are summarized in Table 1. In each of the acoustic wave devices obtained accordingly, the chipping size in the first side surface was 0.4 µm (0.1 of λ), and the chipping size in the second side surface was 2 µm (0.5 of λ). [EXAMPLE 3]

[0030] As in Working Example 1, a composite wafer on which IDT electrodes were formed was prepared and was cut under processing conditions for Example 3 summarized in Table 1. In each of the acoustic wave devices obtained accordingly, the chipping size in the first side surface was 0.4 µm (0.1 of λ), and the chipping size in the second side surface was 200 µm (50 times λ). [COMPARISON EXAMPLE 1]

[0031] As in Working Example 1, a composite wafer on which IDT electrodes were formed was prepared and was cut under processing conditions for Comparative Example 1 summarized in Table 1. In each of the acoustic wave devices obtained accordingly, the chipping size in the first and second side surfaces was 10 µm or smaller both times, specifically, 0.4 µm (0.1 of λ). [COMPARISON EXAMPLE 2]

[0032] As in Working Example 1, a composite wafer on which IDT electrodes were formed was prepared and was cut under processing conditions for Comparative Example 2 summarized in Table 1. In each of the acoustic wave devices obtained accordingly, the chipping size in the first side surface was 0.4 µm (0.1 of λ), and the chipping size in the second side surface was 240 µm (60 times λ). [COMPARISON EXAMPLE 3]

[0033] As in Working Example 1, a composite wafer on which IDT electrodes were formed was prepared and was cut under processing conditions for Comparative Example 3 summarized in Table 1. In each of the acoustic wave devices obtained accordingly, the chipping size in the first side surface was 2.0 µm (0.5 of λ), and the chipping size in the second side surface was 50 µm (12.5 times λ). Table 1 Wavelength λ Processing conditions Splitting amount Disturbance intensities Processing area Blade thickness Particle size speed feed rate Example 1 4 µm first side surface 0.05 mm #2000 29000 rpm 20 mm / s 0.4 µm (0.1 λ) 2 dB second side surface 0.1 mm #500 29000 rpm 50 mm / s 50 µm (12.5 λ) Example 2 4 µm first side surface 0.05 mm #2000 29000 rpm 20 mm / s 0.4 µm (0.1 λ) 2.7 dB second side surface 0.05 mm #1500 29000 rpm 20 mm / s 2 µm (0.5 λ) Example 3 4 µm first side surface 0.05 mm #2000 29000 rpm 20 mm / s 0.4 µm (0.1 λ) 2.5 dB second side surface 0.1 mm #300 29000 rpm 50 mm / s 200 µm (50 λ) Comparison example 1 4 µm first side surface 0.05 mm #2000 29000 rpm 20 mm / s 0.4 µm (0.1 λ) 5 dB second side surface 0.05 mm #2000 29000 rpm 20 mm / s 0.4 µm (0.1 λ) Comparison example 2 4 µm first side surface 0.05 mm #2000 29000 rpm 20 mm / s 0.4 µm (0.1 λ) 7 dB second side surface 0.1 mm #300 29000 rpm 100 mm / s 240 µm (60 1) Comparison example 3 4 µm first side surface 0.05 mm #1500 29000 rpm 20 mm / s 2.0 µm (0.5 λ) 7 dB second side surface 0.1 mm #500 29000 rpm 50 mm / s 50 µm (12.5 l) [Evaluation]

[0034] Characteristics of single-port resonators according to Working Examples 1 to 3 and Comparative Examples 1 to 3 were evaluated. As summarized in Table 1, the intensity of noise peaks ranged from 2 to 2.7 dB in Working Examples 1 to 3, but ranged from 5 to 7 dB in Comparative Examples 1 to 3. The results show that, in terms of suppressing the occurrence of noise peaks, it is desirable to set the chipping size in the first side surface to 1 / 10 of the length λ of the acoustic wave or sound wave or smaller, and the chipping size in the second side surface to 1 / 2 of the wavelength λ of the acoustic wave or sound wave or larger and 50 times the wavelength λ or smaller (specifically, 12.5 times the wavelength λ or larger and 50 times the wavelength λ or smaller).

[0035] Needless to say, the foregoing working examples do not limit the present invention in any way. Commercial applicability

[0036] The present invention can be applied to an acoustic wave device such as a SAW filter. List of reference symbols

[0037] Acoustic wave device 10, piezoelectric substrate 12, first side surface 12a, second side surface 12b, supporting substrate 14, composite substrate 15, IDT electrodes 16 and 18, base portion 16a and 18a, wide electrode fingers 16b and 18b, narrow electrode fingers 16c and 18c, piezoelectric wafer 22, supporting wafer 24, and composite wafer 25.

Claims

An end-face reflection type acoustic wave device (10) comprising a rectangular-parallel-plane composite substrate (15) in which a supporting substrate (14) and a piezoelectric substrate (12) are bonded to each other with a pair of IDT electrodes (16, 18) provided on the piezoelectric substrate (12) in a manner to be intercalated with each other, wherein a chipping size in a first side surface (12a) of the piezoelectric substrate (12) is 1 / 10 of a wavelength λ of an acoustic wave or smaller, the first side surface (12a) extending orthogonally to a direction of acoustic wave propagation, and wherein a chipping size in a second side surface (12b) of the piezoelectric substrate (12) is larger than the chipping size in the first side surface (12a) and 1 / 2 of the wavelength λ of the acoustic wave or larger, and 50 times the wavelength λ of the sound wave or less,wherein the second side surface (12a) extends in the direction of sound wave propagation., The acoustic wave device (10) according to claim 1, wherein the fragmentation size in the second side surface (12b) is 12.5 times the wavelength λ of the acoustic wave or greater and 50 times the wavelength λ of the acoustic wave or less. Acoustic wave device (10) according to claim 1 or 2, wherein the supporting substrate (14) has a smaller thermal expansion coefficient than the piezoelectric substrate (12).

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