Acoustic Wave Devices, Filters, Multiplexers and Wafers

Abstract

To provide an elastic wave device that can increase the heat discharge property.SOLUTION: The elastic wave device includes: a first insulating layer having a plurality of recessed parts and a plurality of protruding parts in a surface; a second insulating layer 11 located on the first insulating layer; a metal layer 28 located between at least a part of the recessed parts and the second insulating layer 11 and not located between at least a part of the protruding parts and the second insulating layer 11; a dielectric layer 14 located on the second insulating layer 11; and a pair of comb-like electrodes 20 located on the dielectric layer 14.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an acoustic wave device, a filter, a multiplexer, and a wafer, and more particularly to an acoustic wave device, a filter, a multiplexer, and a wafer having a pair of interdigital transducers. [Background technology]

[0002] As an acoustic wave device used in communication devices such as smartphones, an acoustic wave device having an IDT (Interdigital Transducer) having a pair of comb electrodes on a piezoelectric substrate is known. It is known that the bonding surface of the support substrate is made uneven (for example, Patent Document 1). It is known that wiring is provided on the piezoelectric layer (for example, Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-161899 A [Patent Document 2] JP 2018-207144 A Summary of the Invention [Problem to be solved by the invention]

[0004] Spurious emissions can be suppressed by providing an insulating layer between the support substrate and the piezoelectric layer and making the interface between the support substrate and the insulating layer an uneven surface. However, if the thermal conductivity of the insulating layer is poor, heat dissipation is poor. This causes the temperature of the acoustic wave element to rise and the characteristics to fluctuate. There is also a possibility that the electrode fingers of the IDT may melt.

[0005] The present invention has been made in consideration of the above problems, and has an object to improve heat dissipation. [Means for solving the problem]

[0006] The present invention is an acoustic wave device comprising a first insulating layer having a plurality of recesses and a plurality of protrusions on a surface thereof, a second insulating layer provided on the surface, a metal layer provided between at least a portion of the plurality of recesses and the second insulating layer and not provided between at least a portion of the plurality of protrusions and the second insulating layer, a piezoelectric layer provided on the second insulating layer, and a pair of comb electrodes provided on the piezoelectric layer.

[0007] In the above configuration, the metal layer may be provided in an island shape in a plan view.

[0008] In the above configuration, the metal layer may have a higher thermal conductivity than the first insulating layer.

[0009] In the above configuration, the second insulating layer may have a higher thermal conductivity than the first insulating layer.

[0010] In the above configuration, the first insulating layer is a sapphire substrate, a silicon substrate or a silicon carbide substrate, the second insulating layer is a layer mainly composed of aluminum oxide, a layer mainly composed of silicon oxide, or a stack of a layer mainly composed of aluminum oxide and a layer mainly composed of silicon oxide, and the metal layer can be composed mainly of at least one of copper, gold, silver and aluminum.

[0011] The above-mentioned configuration may further include a support substrate provided under the first insulating layer.

[0012] In the above configuration, the thickness of the piezoelectric layer may be equal to or less than twice the average pitch of the electrode fingers of the pair of comb-shaped electrodes.

[0013] In the above configuration, the piezoelectric layer may be a lithium tantalate layer or a lithium niobate layer.

[0014] The present invention is a filter including the above acoustic wave device.

[0015] The present invention is a multiplexer including the above filter.

[0016] The present invention is a wafer comprising a first insulating layer having a plurality of recesses and a plurality of protrusions on a surface thereof, a second insulating layer provided on the surface, a metal layer provided between at least a portion of the plurality of recesses and the second insulating layer and not between at least a portion of the plurality of protrusions and the second insulating layer, and a piezoelectric layer provided on the second insulating layer. Effect of the Invention

[0017] According to the present invention, the heat dissipation performance can be improved. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1(a) is a plan view of an acoustic wave resonator in accordance with a first embodiment, and FIG. 1(b) is a cross-sectional view taken along line AA of FIG. 1(a). [Diagram 2] 2(a) to 2(e) are cross-sectional views illustrating a method for manufacturing the acoustic wave resonator in accordance with the first embodiment. [Diagram 3] 3(a) and 3(b) are enlarged cross-sectional views of acoustic wave devices according to Comparative Example 1 and Example 1, respectively. [Figure 4] FIG. 4(a) is a plan view of an acoustic wave resonator according to a first modification of the first embodiment, and FIG. 4(b) is a cross-sectional view taken along line AA of FIG. 4(a). [Diagram 5] FIG. 5 is an enlarged cross-sectional view of an acoustic wave device in accordance with a first modification of the first embodiment. [Figure 6] 6A to 6C are cross-sectional views of acoustic wave devices according to second to fourth modifications of the first embodiment, respectively. [Figure 7] FIG. 7(a) is a circuit diagram of a filter according to a second embodiment, and FIG. 7(b) is a circuit diagram of a duplexer according to a first modified example of the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. EXAMPLES

[0020] Fig. 1(a) is a plan view of an acoustic wave resonator according to a first embodiment, and Fig. 1(b) is a cross-sectional view taken along line AA of Fig. 1(a). The arrangement direction of the electrode fingers is the X direction, the extension direction of the electrode fingers is the Y direction, and the lamination direction of the support substrate and the piezoelectric layer is the Z direction. The X direction, Y direction, and Z direction do not necessarily correspond to the X-axis direction and Y-axis direction of the crystal orientation of the piezoelectric layer. When the piezoelectric layer is a rotated Y-cut X-propagation substrate, the X direction is the X-axis direction of the crystal orientation.

[0021] As shown in Figures 1(a) and 1(b), an insulating layer 11 is provided on a support substrate 10, and a piezoelectric layer 14 is provided on the insulating layer 11. An interface 30 between the support substrate 10 and the insulating layer 11 is an uneven surface having irregular unevenness. A metal layer 28 is provided on a part of the interface 30. In a plan view, the metal layer 28 is provided in an island shape. The interface between the insulating layer 11 and the piezoelectric layer 14 is a mirror surface.

[0022] An acoustic wave resonator 26 is provided on the piezoelectric layer 14. The acoustic wave resonator 26 has an IDT 22 and a reflector 24. The reflectors 24 are provided on both sides of the IDT 22 in the X direction. The IDT 22 and the reflector 24 are formed by the metal film 16 on the piezoelectric layer 14.

[0023] The IDT 22 includes a pair of comb electrodes 20 facing each other. The comb electrodes 20 include a plurality of electrode fingers 18 and a bus bar 19 to which the plurality of electrode fingers 18 are connected. The region where the electrode fingers 18 of the pair of comb electrodes 20 intersect is an intersection region 25. The length of the intersection region 25 is the aperture length. The pair of comb electrodes 20 are provided facing each other such that the electrode fingers 18 are substantially alternated in at least a part of the intersection region 25. The acoustic wave excited by the plurality of electrode fingers 18 in the intersection region 25 propagates mainly in the X direction. The pitch of the electrode fingers 18 of one of the pair of comb electrodes 20 is substantially the wavelength λ of the acoustic wave. If the pitch of the plurality of electrode fingers 18 (the pitch between the centers of the electrode fingers 18) is D, the pitch of the electrode fingers 18 of one comb electrode 20 is the pitch D of two electrode fingers 18. The reflector 24 reflects the acoustic wave (surface acoustic wave) excited by the electrode fingers 18 of the IDT 22. As a result, the acoustic wave is confined within the intersection region 25 of the IDT 22.

[0024] The IDT 22 excites elastic waves such as bulk waves that are faster (i.e., have higher frequencies) than the elastic waves of the main mode, as well as elastic waves of the main mode (surface acoustic waves, for example, SH (Shear Horizontal) waves). The bulk waves are reflected at the interface 30 between the support substrate 10 and the insulating layer 11 and return to the IDT 22. This results in spurious signals. By making the interface 30 an uneven surface, the elastic waves such as bulk waves are scattered at the interface 30. In addition, by making the insulating layer 11 thick, the elastic waves are attenuated when propagating through the insulating layer 11. This can suppress spurious signals. To suppress spurious signals, the arithmetic mean roughness Ra of the interface 30 is, for example, 0.01 μm or more, and preferably 0.1 μm or more. The arithmetic mean roughness Ra of the interface 30 is 1 μm or less and 0.5 μm or less. The arithmetic mean roughness Ra of a mirror surface such as the interface between the insulating layer 11 and the piezoelectric layer 14 is, for example, less than 0.01 μm, 0.005 μm or less, or 0.001 μm or less.

[0025] The piezoelectric layer 14 is a single crystal lithium tantalate (LiTaO3) substrate or a single crystal lithium niobate (LiNbO3) substrate, for example, a rotated Y-cut X-propagation lithium tantalate substrate or a rotated Y-cut X-propagation lithium niobate substrate. When the rotated Y-cut X-propagation lithium tantalate layer is 36° or more and 48° or less, the SH wave becomes the main mode of the elastic wave. In order to confine the main mode of the elastic wave in the piezoelectric layer 14, the thickness T4 of the piezoelectric layer 14 is preferably, for example, equal to or less than the wavelength λ (2D) of the elastic wave, more preferably equal to or less than 0.8λ (1.6D), and more preferably equal to or less than 0.6λ (1.2D). In order to excite the main mode of the elastic wave, the thickness T4 is preferably equal to or more than 0.1λ (0.2D).

[0026] The support substrate 10 is, for example, a silicon substrate, a sapphire substrate, an alumina substrate, a spinel substrate, a quartz substrate, a silicon carbide substrate, or a silicon nitride substrate. The silicon substrate is a single crystal or polycrystalline Si substrate, the sapphire substrate is a single crystal Al2O3 substrate, the alumina substrate is a polycrystalline or amorphous Al2O3 substrate, the spinel substrate is a polycrystalline MgAl2O4 substrate, the quartz substrate is a single crystal SiO2 substrate, the silicon carbide substrate is a single crystal, polycrystalline or amorphous SiC substrate, and the silicon nitride substrate is a polycrystalline or amorphous SiN substrate. The linear expansion coefficient of the support substrate 10 in the X direction is smaller than the linear expansion coefficient of the piezoelectric layer 14 in the X direction. This can reduce the frequency temperature dependency of the acoustic wave resonator.

[0027] The insulating layer 11 is, for example, a silicon oxide layer, a silicon nitride layer, a silicon nitride oxide layer, an aluminum oxide layer, an aluminum nitride layer, or an aluminum nitride oxide layer, or a laminated film thereof. When the piezoelectric layer 14 is a lithium tantalate layer or a lithium niobate layer, and the insulating layer 11 is a silicon nitride layer, a silicon nitride oxide layer, an aluminum oxide layer, an aluminum nitride layer, or an aluminum nitride oxide layer, the sound velocity of the bulk wave propagating through the insulating layer 11 is faster than the sound velocity of the bulk wave propagating through the piezoelectric layer 14. This allows the main mode elastic wave to be confined within the piezoelectric layer 14. From the viewpoint of suppressing spurious, the thickness T1 of the insulating layer 11 is, for example, preferably 1λ (2D) or more, more preferably 2λ (4D) or more. From the viewpoint of reducing the number of manufacturing steps, the thickness T1 is preferably 10λ (20D) or less, more preferably 5λ (10D) or less. Note that the thickness T1 is an average thickness.

[0028] The metal layer 28 is, for example, a copper layer, a gold layer, a silver layer, or an aluminum layer. The metal film 16 is, for example, a film containing aluminum (Al), copper (Cu), or molybdenum (Mo) as a main component. An adhesive film such as a titanium (Ti) film or a chromium (Cr) film may be provided between the electrode fingers 18 and the piezoelectric layer 14. The adhesive film is thinner than the electrode fingers 18. An insulating film may be provided so as to cover the electrode fingers 18. The insulating film functions as a protective film or a temperature compensation film.

[0029] The wavelength λ of the elastic wave is, for example, 1 μm to 6 μm. When two electrode fingers 18 are considered as one pair, the number of pairs is, for example, 20 to 300 pairs. The duty ratio of the IDT 22 is a value obtained by dividing the thickness of the electrode fingers 18 by the pitch of the electrode fingers 18, and is, for example, 30% to 70%. The aperture length of the IDT 22 is, for example, 10λ to 50λ.

[0030] [Production method of Example 1] 2(a) to 2(e) are cross-sectional views showing a method for manufacturing the acoustic wave resonator according to the first embodiment. As shown in FIG. 2(a), the upper surface of the support substrate 10 is made uneven or rough. When the upper surface 31 of the support substrate 10 is made to have an irregular rough surface, the upper surface 31 of the support substrate 10 is polished with a coarse abrasive to make the upper surface 31 of the support substrate 10 a rough surface. The arithmetic mean roughness Ra of the upper surface 31 is, for example, 0.15 μm.

[0031] As shown in FIG. 2(b), a metal layer 28 is formed on the support substrate 10. The metal layer 28 is formed, for example, by plating. The metal layer 28 is formed so as to completely cover the upper surface 31 of the support substrate 10. As shown in FIG. 2(c), the upper surface of the metal layer 28 is polished, for example, by CMP (Chemical Mechanical Polishing). By adjusting the amount of polishing, the metal layer 28 remains in the recesses on the upper surface of the support substrate 10. The amount of remaining metal layer 28 can be adjusted by the roughness of the upper surface 31 and the amount of polishing.

[0032] As shown in FIG. 2(d), the insulating layer 11 is formed on the support substrate 10 and the metal layer 28 by, for example, CVD (Chemical Vapor Deposition), sputtering, or vacuum deposition. As a result, the upper surface 31 becomes the interface 30 between the support substrate 10 and the insulating layer 11. The upper surface of the insulating layer 11 is planarized by, for example, CMP. As shown in FIG. 2(e), the upper surface of the insulating layer 11 is bonded to the piezoelectric layer 14. For example, a surface activation method is used to bond the insulating layer 11 and the piezoelectric layer 14. The upper surface of the piezoelectric layer 14 is polished by, for example, CMP. As a result, the wafer 44 is completed. Thereafter, the metal film 16 is formed on the piezoelectric layer 14, thereby forming the IDT 22 and the reflector 24 on the piezoelectric layer 14. The wafer 44 is divided into individual pieces to complete the acoustic wave devices.

[0033] The thermal conductivities of the materials used for the support substrate 10, the insulating layer 11, the piezoelectric layer 14 and the metal layer 28 are shown below. Piezoelectric layer 14 Lithium tantalate: 2W / m / K Insulating layer 11 Silicon oxide: 1.5W / m / K Silicon nitride: 27W / m / K Aluminum oxide: 32W / m / K Aluminum nitride: 150W / m / K Support substrate 10 Sapphire: 42W / m / K Silicon: 149W / m / K Silicon carbide: 200W / m / K Spinel: 14W / m / K metal layer 28 Copper: 398W / m / K Gold:320W / m / K Silver:420W / m / K Aluminum: 236W / m / K

[0034] 3(a) and 3(b) are enlarged cross-sectional views of acoustic wave devices according to Comparative Example 1 and Example 1, respectively. As shown in FIG. 3(a), Comparative Example 1 does not include a metal layer 28. The interface 30 includes a recess 34 recessed in the -Z direction and a protrusion 36 protruding in the +Z direction. The unevenness of the interface 30 is irregular, and the heights of adjacent recesses 34 and protrusions 36 vary. Height H2 is smaller than height H1. A thickness T1a of the insulating layer 11 at the bottom of the recess 34 that constitutes the large height H2 is larger than a thickness T1b of the insulating layer 11 at the protrusion 36.

[0035] When acoustic wave resonator 26 operates, heat is generated near piezoelectric layer 14. The heat is dissipated from support substrate 10 via insulating layer 11. In convex portion 36, the heat dissipation path through insulating layer 11 is short as indicated by arrow 50b, and the heat that has passed through insulating layer 11 is dissipated via support substrate 10 as indicated by arrow 52b. In concave portion 34, the heat dissipation path through insulating layer 11 is long as indicated by arrow 50a, and the heat that has passed through insulating layer 11 is dissipated via support substrate 10 as indicated by arrow 52a. Insulating layer 11 and support substrate 10 have low thermal conductivity. This results in poor heat dissipation and an increase in the temperature of piezoelectric layer 14.

[0036] As shown in FIG. 3(b), in the first embodiment, a part of the recess 34 of the interface 30 is embedded in the metal layer 28. The height H3 of the metal layer 28 is smaller than the height H1. Therefore, as shown in FIG. 1(a), the metal layer 28 is provided in a scattered manner in a plan view. The density and width W of the metal layer 28 in a plan view can be set by the roughness of the upper surface 31 of the support substrate 10 in FIG. 2(c) and the amount of polishing of the metal layer 28. If the height of the metal layer 28 in the height H1 is H3, the thickness of the insulating layer 11 is T1a-H3. As a result, the heat dissipation path of the insulating layer 11 indicated by the arrow 50a is shorter than that of the first comparative example. As indicated by the arrow 54, heat passes through the metal layer 28, and as indicated by the arrow 52a, the heat is dissipated to the support substrate 10. Since the metal layer 28 has a higher thermal conductivity than the insulating layer 11 and the support substrate 10, the first embodiment has improved heat dissipation performance compared to the first comparative example. As a result, the temperature rise of the acoustic wave resonator 26 is suppressed. This suppresses fluctuations in the characteristics of acoustic wave resonator 26. Furthermore, melting of electrode fingers 18 can be suppressed.

[0037] For example, the piezoelectric layer 14 is made of lithium tantalate, the insulating layer 11 is made of aluminum oxide, the support substrate 10 is made of sapphire, and the metal layer 28 is made of copper. The piezoelectric layer 14 has the lowest thermal conductivity. However, the thickness T4 of the piezoelectric layer 14 is thin, less than λ. Therefore, the heat in the piezoelectric layer 14 is easily dissipated to the insulating layer 11. Since the thermal conductivity of the insulating layer 11 is lower than that of the support substrate 10, when the heat dissipation path of the arrow 50a is long as in Comparative Example 1, the heat dissipation performance is deteriorated. Therefore, in Example 1, the metal layer 28 is provided in the recess 34 of the interface 30, thereby shortening the heat dissipation path of the arrow 50a, and the shortened portion becomes the heat dissipation path of the arrow 54 via the metal layer 28. Therefore, the heat dissipation performance can be improved.

[0038] Incidentally, by providing the metal layer 28 on the entire surface of the intersection region 25, it is possible to improve the heat dissipation. However, if the metal layer 28 is provided on the entire surface, the bulk wave will be reflected by the upper surface of the metal layer 28, and it will be impossible to suppress spurious. Therefore, the metal layer 28 is provided on at least a portion of the plurality of recesses 34, but not on at least a portion of the plurality of protrusions 36.

[0039] From the viewpoint of suppressing spurious, the arithmetic mean roughness Ra of the interface 30 is, for example, 0.01 μm or more, and preferably 0.1 μm or more. In this case, the height H1 is, for example, 0.1λ to 2λ (0.2D to 4D). The wavelength λ of the elastic wave is 1 μm to 6 μm, and H1 is, for example, 0.1 μm to 12 μm. From the viewpoint of improving heat dissipation, H3 / H1 is preferably 1 / 10 or more, and more preferably 1 / 4 or more. From the viewpoint of suppressing spurious, H3 / H1 is, for example, preferably 9 / 10 or less, and more preferably 3 / 4 or less. The width W of the metal layer 28 is, for example, 1 μm to 20 μm. From the viewpoint of improving heat dissipation, the ratio of the total planar area of ​​the metal layer 28 in the intersection region 25 to the planar area of ​​the intersection region 25 is preferably 0.01 or more, and more preferably 0.05 or more. In order to suppress spurious signals, the ratio of the total planar area of ​​the metal layers 28 in the intersection region 25 to the planar area of ​​the intersection region 25 is preferably equal to or less than 0.8, and more preferably equal to or less than 0.5.

[0040] [Modification 1 of Example 1] FIG. 4(a) is a plan view of an acoustic wave resonator according to a first modified example of the first embodiment, and FIG. 4(b) is a cross-sectional view taken along line AA of FIG. 4(a). FIG. 5 is an enlarged cross-sectional view of an acoustic wave device according to a first modified example of the first embodiment. As shown in FIGS. 4(a) to 5, recesses 34 and protrusions 36 at an interface 30 between a support substrate 10 and an insulating layer 11 are provided periodically and regularly. The height H1 of adjacent recesses 34 and protrusions 36 is approximately uniform. The width W of the metal layer 28 is approximately uniform. In a plan view, the metal layer 28 is provided regularly.

[0041] The regular uneven surface is formed by providing a mask layer having regular openings on the upper surface of the support substrate 10 as in Patent Document 1, and etching the upper surface of the support substrate 10 using the mask layer as a mask. The three-dimensional shape of the recesses 34 or the protrusions 36 may be a cone shape, a polygonal pyramid shape such as a triangular pyramid shape or a square pyramid shape, a cylindrical shape or a polygonal column shape, or may be a straight line or a curved line. From the viewpoint of suppressing spurious, the period of the recesses 34 or the protrusions 36 is preferably 0.1λ (0.2D) or more, more preferably 0.5λ (1D) or more, preferably 5λ (10D) or less, and more preferably 2λ (4D) or less. The preferred ranges of H1 and H3 / H1 are the same as those in Example 1. The other configurations are the same as those in Example 1, and description thereof will be omitted.

[0042] [Modification 2 of Example 1] Fig. 6(a) is a cross-sectional view of an acoustic wave device according to Modification 2 of Example 1. As shown in Fig. 6(a), an insulating layer 11 includes a boundary layer 12 provided on a support substrate 10 and a temperature compensation film 13 provided on the boundary layer 12.

[0043] The temperature compensation film 13 has a temperature coefficient of elastic constant with the opposite sign to that of the piezoelectric layer 14. For example, the temperature coefficient of the elastic constant of the piezoelectric layer 14 is negative, and the temperature coefficient of the elastic constant of the temperature compensation film 13 is positive. The temperature compensation film 13 is an insulating film mainly composed of silicon oxide (SiO2), for example, a silicon oxide (SiO2) film with no additives or with an additive element such as fluorine, and is, for example, polycrystalline or amorphous. This makes it possible to reduce the frequency temperature coefficient of the elastic wave resonator. When the temperature compensation film 13 is a silicon oxide film, the sound velocity of the bulk wave propagating through the temperature compensation film 13 is slower than the sound velocity of the bulk propagating through the piezoelectric layer 14.

[0044] In order for the temperature compensation film 13 to have a temperature compensation function, it is required that the energy of the main mode elastic wave is present to a certain extent within the temperature compensation film 13. Although the range in which the energy of the surface acoustic wave is concentrated depends on the type of the surface acoustic wave, typically, the energy of the surface acoustic wave is concentrated within a range of 2λ (λ is the wavelength of the elastic wave) from the upper surface of the piezoelectric layer 14, and particularly within a range of λ from the upper surface of the piezoelectric layer 14. Therefore, the distance from the lower surface of the temperature compensation film 1 to the upper surface of the piezoelectric layer 14 is preferably 2λ (4D) or less, more preferably 1λ (2D) or less, and even more preferably 0.6λ (1.2D) or less. The thickness T3 of the temperature compensation film 13 is preferably 0.75λ (1.5D) or less, and more preferably 0.5λ (1D) or less. From the viewpoint of exerting the temperature compensation function of the temperature compensation film 13, the thickness T3 is preferably 0.1λ (0.2D) or more, and more preferably 0.2λ (0.4D) or more.

[0045] The acoustic velocity of the bulk wave propagating through the boundary layer 12 is faster than that of the bulk wave propagating through the temperature compensation film 13. This causes the energy of the elastic wave of the main mode to be trapped in the piezoelectric layer 14 and the temperature compensation film 13. Furthermore, the acoustic velocity of the bulk wave propagating through the boundary layer 12 is slower than that of the bulk wave propagating through the support substrate 10. The boundary layer 12 is, for example, polycrystalline or amorphous, and is an aluminum oxide film, a silicon nitride film, an aluminum nitride film, or a silicon film. The boundary layer 12 may be a laminate of multiple layers made of different materials. When the boundary layer 12 is thinner, the elastic wave of the main mode is less likely to be trapped in the piezoelectric layer 14 and the temperature compensation film 13. From this viewpoint, the thickness T2 of the boundary layer 12 is preferably 2.2 times (1.1λ) or more of the average pitch D of the electrode fingers 18, and more preferably 3.0 times (1.5λ) or more. When the boundary layer 12 is thicker, the number of manufacturing steps increases and the difficulty of the manufacturing process increases. From this viewpoint, thickness T2 of boundary layer 12 is preferably equal to or less than 10 times (5λ) the average pitch D of electrode fingers 18, and more preferably equal to or less than 8 times (4λ).

[0046] [Modification 3 of Example 1] Fig. 6(b) is a cross-sectional view of an acoustic wave device according to Modification 3 of Example 1. As shown in Fig. 6(b), a bonding layer 15 may be provided between the temperature compensation film 13 and the piezoelectric layer 14. The bonding layer 15 is a layer for bonding the piezoelectric layer 14 and the temperature compensation film 13 by a surface activation method. The bonding layer 15 is, for example, an aluminum oxide layer or an aluminum oxynitride film having a thickness T5 of 1 nm to 20 nm. The other configurations are the same as those of Modification 2 of Example 1, and therefore description thereof will be omitted.

[0047] [Variation 4 of Example 1] Fig. 6(c) is a cross-sectional view of an acoustic wave device according to Modification 4 of Example 1. As shown in Fig. 6(c), the interface between the support substrate 10 and the boundary layer 12 is a mirror surface. The interface 32 between the boundary layer 12 and the temperature compensation film 13 is an uneven surface, and a metal layer 28 is provided at the interface 32. The other configurations are the same as those of Modification 2 of Example 1, and a description thereof will be omitted. As in Modification 4 of Example 1, the insulating layer 11 may include a plurality of laminated insulating layers, and the metal layer 28 may be provided between the insulating layers.

[0048] According to the first embodiment and its first to third modifications, the support substrate 10 (first insulating layer) has a plurality of recesses 34 and a plurality of protrusions 36 on the surface (interface 30) on the insulating layer 11 (second insulating layer) side. The metal layer 28 is provided between at least some of the recesses 34 and the insulating layer 11, but is not provided between at least some of the protrusions 36 and the insulating layer 11. This improves heat dissipation because heat is dissipated via the metal layer 28, as shown in FIG. 3(b). Also, because the metal layer 28 is not provided on the entire surface, spurious emissions can be suppressed.

[0049] 1(a) and 4(a), the metal layer 28 is provided in an island shape in plan view, which improves heat dissipation and suppresses spurious emissions.

[0050] The thermal conductivity of the metal layer 28 is higher than that of the insulating layer 11. As a result, as shown in FIG. 3(b), the thermal conductivity is higher at height H3 where the metal layer 28 is provided within the distance (corresponding to thickness T1a) between the bottom of the recess 34 and the upper surface of the insulating layer 11. This improves heat dissipation. The thermal conductivity of the metal layer 28 is preferably at least twice as high as the thermal conductivity of the insulating layer 11, and more preferably at least five times as high.

[0051] The thermal conductivity of the support substrate 10 and that of the metal layer 28 are higher than that of the insulating layer 11. As a result, in FIG. 3(a) of Comparative Example 1, at the bottom of the recess 34 where the heat dissipation path of the insulating layer 11, which has a lower thermal conductivity than the support substrate 10, is longer, a metal layer 28 with high thermal conductivity can be provided as shown in FIG. 3(b). This improves heat dissipation. The thermal conductivity of the support substrate 10 is preferably 1.2 times or more, more preferably 2 times or more, of the thermal conductivity of the insulating layer 11.

[0052] The thermal conductivity of the metal layer 28 is higher than that of the support substrate 10 and that of the insulating layer 11. This allows the metal layer 28, which has high thermal conductivity, to be provided in the heat dissipation path via the insulating layer 11 and the support substrate 10. This improves heat dissipation. The thermal conductivity of the metal layer 28 is preferably 1.5 times or more, more preferably 5 times or more, the thermal conductivity of the support substrate 10.

[0053] The material for the metal layer 28 having a higher thermal conductivity than the insulating layer 11 and the support substrate 10, and the support substrate 10 having a higher thermal conductivity than the insulating layer 11, is a sapphire substrate, a silicon substrate, or a silicon carbide substrate. The insulating layer 11 is a layer mainly made of aluminum oxide, a layer mainly made of silicon oxide, or a laminate of a layer mainly made of aluminum oxide and a layer mainly made of silicon oxide. The metal layer 28 is mainly made of at least one of copper, gold, silver, and aluminum. This can improve heat dissipation. Note that a certain layer being mainly made of a certain material allows for intentional or unintentional addition of impurities to the certain layer. The concentration of a certain material in a certain layer is, for example, 50 atomic % or more, 80 atomic % or more, 90 atomic % or more. For example, when insulating layer 11 is mainly composed of silicon oxide (or aluminum oxide), the sum of the silicon concentration (or aluminum concentration) and oxygen concentration in insulating layer 11 is, for example, 50 atomic % or more, 80 atomic % or more, or 90 atomic % or more. Both the silicon concentration (or aluminum concentration) and oxygen concentration are 10 atomic % or more or 20 atomic % or more.

[0054] As in the fourth modification of the first embodiment, the interface 32 between the boundary layer 12 and the temperature compensation film 13 may be an uneven surface, and the metal layer 28 may be provided at the interface 32. That is, the first insulating layer may be the boundary layer 12, the second insulating layer may be the temperature compensation film 13, and the support substrate 10 may be provided below the boundary layer 12.

[0055] The thickness T4 of the piezoelectric layer 14 is equal to or less than twice the average pitch D of the electrode fingers 18 of the pair of comb-shaped electrodes 20. Although the thermal conductivity of the piezoelectric layer 14 is low, by reducing the thickness T4 of the piezoelectric layer 14, heat dissipation through the insulating layer 11 and the support substrate 10 is possible. The thickness T4 is more preferably equal to or less than 1.6D, and even more preferably equal to or less than 1.2D. When the insulating layer 11 includes an insulating layer 11 mainly composed of silicon oxide such as the temperature compensation film 13, the thermal conductivity of silicon oxide is low, so that the thickness T3 of the temperature compensation film 13 is preferably equal to or less than twice the average pitch D of the electrode fingers 18, more preferably equal to or less than 1.5D, and even more preferably equal to or less than 1D. This enables heat dissipation through the insulating layer 11 and the support substrate 10. The average pitch of the electrode fingers 18 can be calculated by dividing the width of the IDT 22 in the X direction by the number of the electrode fingers 18.

[0056] When the piezoelectric layer 14 is a lithium tantalate layer or a lithium niobate layer, the thermal conductivity is low, so it is preferable to make the piezoelectric layer 14 thin. EXAMPLES

[0057] FIG. 7(a) is a circuit diagram of a filter according to a second embodiment. As shown in FIG. 7(a), one or more series resonators S1 to S3 are connected in series between an input terminal Tin and an output terminal Tout. One or more parallel resonators P1 and P2 are connected in parallel between the input terminal Tin and the output terminal Tout. The acoustic wave resonators according to the first embodiment and its modified examples can be used for at least one of the one or more series resonators S1 to S3 and the one or more parallel resonators P1 and P2. The number of resonators of the ladder filter can be set as appropriate. The filter may be a multimode filter.

[0058] [Modification 1 of Example 2] FIG. 7(b) is a circuit diagram of a duplexer according to a first modified example of the second embodiment. As shown in FIG. 7(b), a transmission filter 40 is connected between a common terminal Ant and a transmission terminal Tx. A reception filter 42 is connected between the common terminal Ant and a reception terminal Rx. The transmission filter 40 passes a signal in a transmission band among high-frequency signals input from the transmission terminal Tx to the common terminal Ant as a transmission signal, and suppresses signals of other frequencies. The reception filter 42 passes a signal in a reception band among high-frequency signals input from the common terminal Ant to the reception terminal Rx as a reception signal, and suppresses signals of other frequencies. At least one of the transmission filter 40 and the reception filter 42 can be the filter of the second embodiment.

[0059] Although a duplexer has been described as an example of a multiplexer, a triplexer or a quadplexer may also be used.

[0060] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0061] 10 Support substrate 11 Insulating layer 12 Boundary layer 13 Temperature compensation membrane 14 Piezoelectric layer 15 Bonding layer 18 electrode fingers 20 comb electrode 22 IDT 26 Elastic Wave Resonator 28 Metal layer 30, 32 interface 34 Recess 36 Convex 40 Transmission Filter 42 Receiving Filter 44 Wafers

Claims

1. a first insulating layer having a plurality of recesses and a plurality of protrusions on a surface thereof; A second insulating layer provided on the surface; a metal layer provided between at least some of the recesses and the second insulating layer, but not between at least some of the protrusions and the second insulating layer; a piezoelectric layer provided on the second insulating layer; A pair of comb-shaped electrodes provided on the piezoelectric layer; 1. An acoustic wave device comprising:

2. The acoustic wave device according to claim 1 , wherein the metal layer is provided in an island shape in a plan view.

3. The acoustic wave device according to claim 1 , wherein the thermal conductivity of the metal layer is higher than the thermal conductivity of the first insulating layer.

4. The acoustic wave device according to claim 3 , wherein the second insulating layer has a higher thermal conductivity than the first insulating layer.

5. the first insulating layer is a sapphire substrate, a silicon substrate or a silicon carbide substrate; the second insulating layer is a layer mainly made of aluminum oxide, a layer mainly made of silicon oxide, or a laminate of a layer mainly made of aluminum oxide and a layer mainly made of silicon oxide, The acoustic wave device according to claim 1 , wherein the metal layer is mainly composed of at least one of copper, gold, silver, and aluminum.

6. The acoustic wave device according to claim 1 , further comprising a support substrate provided under the first insulating layer.

7. The acoustic wave device according to claim 1 , wherein the thickness of the piezoelectric layer is equal to or less than twice the average pitch of the electrode fingers of the pair of comb-shaped electrodes.

8. The acoustic wave device according to claim 1 , wherein the piezoelectric layer is a lithium tantalate layer or a lithium niobate layer.

9. A filter comprising an acoustic wave device according to any one of claims 1 to 8.

10. A multiplexer including a filter according to claim 9.

11. a first insulating layer having a plurality of recesses and a plurality of protrusions on a surface thereof; A second insulating layer provided on the surface; a metal layer provided between at least some of the recesses and the second insulating layer, but not between at least some of the protrusions and the second insulating layer; a piezoelectric layer provided on the second insulating layer; A wafer comprising:

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