Acoustic wave device, filter, multiplexer, and method for manufacturing an acoustic wave device

Abstract

To suppress the characteristic deterioration of an acoustic wave in a primary mode.SOLUTION: An acoustic wave device 100 includes: a piezoelectric layer 18; a pair of comb-shaped electrodes 53 disposed on one surface of the piezoelectric layer 18, each of the pair of comb-shaped electrodes including a plurality of electrode fingers 54 and a bus bar 55 to which the electrode fingers 54 are coupled; a boundary layer 12 disposed at the other surface side of the piezoelectric layer 18, and having recessed portions 20 overlapping with the plurality of electrode fingers 54 in a pair of edge regions 32 that are regions located at both ends in an intersection region 30 where the plurality of electrode fingers 54 of the pair of comb-shaped electrodes 53 intersect with each other; and a temperature compensation layer 14 which is provided by embedding the recessed portions 20 between the piezoelectric layer 18 and the boundary layer 12, and in which the thickness at a position overlapping with the plurality of electrode fingers 54 in the edge region 32 is thicker than the thickness at a position overlapping with the plurality of electrode fingers 54 in a central region 31 located inside the edge region 32 in the intersection region 30, and the acoustic velocity of an acoustic wave propagating through the temperature compensation layer is less than the acoustic velocity of the acoustic wave propagating through the piezoelectric layer 18 and the boundary layer 12.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an acoustic wave device, a filter, a multiplexer, and a method for manufacturing an acoustic wave device. [Background technology]

[0002] Surface acoustic wave resonators are known as acoustic wave devices used in communication devices such as smartphones. It is known that a piezoelectric layer forming a surface acoustic wave resonator is attached to a support substrate. It is known that a film mainly composed of silicon oxide is provided between the support substrate and the piezoelectric layer (for example, Patent Document 1). It is also known that a piston mode that suppresses transverse mode spurious can be realized by making the sound speed in the edge region of an intersection region where multiple electrode fingers intersect slower than the sound speed in the central region (for example, Patent Documents 2 and 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-73331 A [Patent Document 2] International Publication No. 2020 / 209359 [Patent Document 3] International Publication No. 2020 / 184466 Summary of the Invention [Problem to be solved by the invention]

[0004] In Patent Document 2, the piston mode is realized by providing unevenness on the lower surface of the piezoelectric layer and making the thickness of the piezoelectric layer at the positions overlapping with the electrode fingers in the edge regions thinner than the thickness of the piezoelectric layer at the positions overlapping with the electrode fingers in the central region. In Patent Document 3, the piston mode is realized by providing a sound speed adjustment film on or near the lower surface of the piezoelectric layer at the positions overlapping with the electrode fingers in the edge regions. However, with such a structure, the characteristics of the elastic wave in the main mode may deteriorate.

[0005] The present invention has been made in consideration of the above-mentioned problems, and has an object to suppress deterioration of the characteristics of the main mode elastic wave. [Means for solving the problem]

[0006] The present invention relates to a piezoelectric layer, a pair of comb-shaped electrodes provided on one surface of the piezoelectric layer, the pair of comb-shaped electrodes having a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected, and a first insulating layer provided on the other surface of the piezoelectric layer, the first insulating layer having recesses that overlap the plurality of electrode fingers in a pair of edge regions that are regions at both ends of an intersection region where the plurality of electrode fingers of the pair of comb-shaped electrodes intersect; In both the central region located inside the edge region of the intersection region and the edge region, Between the piezoelectric layer and the first insulating layer It is provided, The recess is filled fruit The thickness of the edge region at the position where the edge region overlaps with the electrode fingers is In the notes The acoustic wave device comprises a second insulating layer that is thicker than the thickness of the central region at positions overlapping with the plurality of electrode fingers and through which acoustic waves propagate at a slower speed than in the piezoelectric layer and the first insulating layer.

[0007] The present invention provides a piezoelectric element comprising: a piezoelectric layer; a pair of comb electrodes provided on one surface of the piezoelectric layer, the pair of comb electrodes having a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected; a first insulating layer provided on the other surface of the piezoelectric layer, the first insulating layer having recesses overlapping the plurality of electrode fingers in a pair of edge regions which are regions located at both ends of an intersection region where the plurality of electrode fingers of the pair of comb electrodes intersect; and a second insulating layer provided between the piezoelectric layer and the first insulating layer to embed the recesses, the second insulating layer having a thickness at a position overlapping with the plurality of electrode fingers in the edge regions that is greater than a thickness at a position overlapping with the plurality of electrode fingers in a central region of the intersection region that is located more inward than the edge regions, and the second insulating layer has a slower acoustic velocity of an elastic wave propagating through it than the piezoelectric layer and the first insulating layer; The distance between the surface of the second insulating layer facing the first insulating layer and the one surface of the piezoelectric layer is four times or less the average pitch of the plurality of electrode fingers of the pair of comb-shaped electrodes. It is an acoustic wave device. .

[0009] The present invention provides a piezoelectric element comprising: a piezoelectric layer; a pair of comb electrodes provided on one surface of the piezoelectric layer, the pair of comb electrodes having a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected; a first insulating layer provided on the other surface of the piezoelectric layer, the first insulating layer having recesses overlapping the plurality of electrode fingers in a pair of edge regions which are regions located at both ends of an intersection region where the plurality of electrode fingers of the pair of comb electrodes intersect; and a second insulating layer provided between the piezoelectric layer and the first insulating layer to embed the recesses, the second insulating layer having a thickness at a position overlapping with the plurality of electrode fingers in the edge regions that is greater than a thickness at a position overlapping with the plurality of electrode fingers in a central region of the intersection region that is located more inward than the edge regions, and the second insulating layer has a slower acoustic velocity of an elastic wave propagating through it than the piezoelectric layer and the first insulating layer; A difference between the linear expansion coefficients of the first insulating layer and the second insulating layer is smaller than a maximum value of a difference between the linear expansion coefficients of the piezoelectric layer and the second insulating layer. It is an acoustic wave device. .

[0010] The present invention provides a piezoelectric element comprising: a piezoelectric layer; a pair of comb electrodes provided on one surface of the piezoelectric layer, the pair of comb electrodes having a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected; a first insulating layer provided on the other surface of the piezoelectric layer, the first insulating layer having recesses overlapping the plurality of electrode fingers in a pair of edge regions which are regions located at both ends of an intersection region where the plurality of electrode fingers of the pair of comb electrodes intersect; and a second insulating layer provided between the piezoelectric layer and the first insulating layer to embed the recesses, the second insulating layer having a thickness at a position overlapping with the plurality of electrode fingers in the edge regions that is greater than a thickness at a position overlapping with the plurality of electrode fingers in a central region of the intersection region that is located more inward than the edge regions, and the second insulating layer has a slower acoustic velocity of an elastic wave propagating through it than the piezoelectric layer and the first insulating layer; The piezoelectric layer is a rotated Y-cut X-propagation lithium tantalate layer or a rotated Y-cut X-propagation lithium niobate layer, and the second insulating layer is a layer mainly composed of silicon oxide. It is an acoustic wave device. . The present invention is an acoustic wave device comprising: a piezoelectric layer; a pair of comb electrodes provided on one surface of the piezoelectric layer, the pair of comb electrodes having a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected; a first insulating layer provided on the other surface of the piezoelectric layer, the first insulating layer having recesses overlapping the plurality of electrode fingers in a pair of edge regions, which are regions located at both ends of an intersection region where the plurality of electrode fingers of the pair of comb electrodes intersect; and a second insulating layer provided between the piezoelectric layer and the first insulating layer to embed the recesses, the second insulating layer having a thickness at a position overlapping with the plurality of electrode fingers in the edge regions that is greater than a thickness at a position overlapping with the plurality of electrode fingers in a central region of the intersection region that is located more inward than the edge regions, and the second insulating layer having a slower acoustic wave propagating speed than the piezoelectric layer and the first insulating layer, the first insulating layer being a support substrate made of a sapphire substrate, a silicon substrate, a spinel substrate, a quartz substrate, a crystal substrate, an alumina substrate, or a silicon carbide substrate.

[0011] In the above configuration, the other surface of the piezoelectric layer may be a flat surface. In the above configuration, the recess may penetrate the first insulating layer.

[0012] In the above configuration, the first insulating layer may be provided on a surface opposite to the second insulating layer with a support substrate made of a sapphire substrate, a silicon substrate, a spinel substrate, a quartz substrate, a crystal substrate, an alumina substrate, or a silicon carbide substrate.

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

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

[0016] The present invention includes the steps of simultaneously forming a recess and an alignment marker in a first insulating layer, forming a second insulating layer on the first insulating layer by embedding the recess and having a slower acoustic wave propagation speed than the first insulating layer, forming a piezoelectric layer on the second insulating layer and having a faster acoustic wave propagation speed than the second insulating layer, and forming a pair of comb-shaped electrodes having a plurality of electrode fingers on the piezoelectric layer using the alignment markers such that the plurality of electrode fingers overlap the recess in a pair of edge regions that are regions located at both ends of an intersection region where each of a plurality of electrode fingers intersects with each other, the second insulating layer is provided in both a central region located inside the edge region of the intersection region and the edge region, and a thickness of the second insulating layer at a position overlapping with the plurality of electrode fingers in the edge region is greater than a thickness of the second insulating layer at a position overlapping with the plurality of electrode fingers in the central region. A method for manufacturing an acoustic wave device. Effect of the Invention

[0017] According to the present invention, deterioration of the characteristics of the main mode elastic wave can be suppressed. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1(a) is a plan view of an acoustic wave device in accordance with a first embodiment, and FIG. 1(b) is an enlarged plan view of an IDT (Interdigital Transducer) in FIG. 1(a). [Diagram 2] 2(a) is a cross-sectional view taken along line AA in FIG. 1(a), and FIG. 2(b) is a cross-sectional view taken along line BB in FIG. 1(a). [Diagram 3] FIG. 3 is a diagram showing the sound velocity of an acoustic wave in an IDT in the first embodiment. [Figure 4] 4(a) to 4(c) are cross-sectional views (part 1) illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Diagram 5] 5(a) to 5(c) are cross-sectional views (part 2) illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Figure 6] Figure 6(a) is a plan view showing an example of an alignment marker formed in the boundary layer, Figure 6(b) is a plan view showing an example of an alignment marker on a photomask, and Figure 6(c) is a plan view showing the alignment of the alignment marker. [Figure 7] FIG. 7(a) is a plan view of an acoustic wave device in accordance with Comparative Example 1, and FIG. 7(b) is a cross-sectional view taken along line AA of FIG. 7(a). [Figure 8] 8(a) is a plan view of an acoustic wave device in accordance with a first modified example of the first embodiment, FIG. 8(b) is a cross-sectional view taken along line AA in FIG. 8(a), and FIG. 8(c) is a cross-sectional view taken along line BB in FIG. 8(a). [Figure 9] 9A to 9C are cross-sectional views of acoustic wave devices according to Modifications 2 to 4 of the first embodiment. [Figure 10] FIG. 10(a) is a plan view of an acoustic wave device in accordance with a second embodiment, and FIG. 10(b) is an enlarged plan view of an IDT in FIG. 10(a). [Figure 11] 11(a) is a plan view of an acoustic wave device in accordance with a third embodiment, FIG. 11(b) is a cross-sectional view taken along line AA in FIG. 11(a), and FIG. 11(c) is a cross-sectional view taken along line BB in FIG. 11(a). [Figure 12] FIG. 12 shows simulation results of admittance Y versus frequency for the acoustic wave device in accordance with Example 3 and the acoustic wave device in accordance with Comparative Example 2. In FIG. [Figure 13] FIG. 13 is a circuit diagram of a filter in accordance with the fourth embodiment. [Figure 14] FIG. 14 is a block diagram of a duplexer in accordance with the fifth 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 device 100 according to a first embodiment, and FIG. 1(b) is an enlarged plan view of an IDT 51 in FIG. 1(a). FIG. 2(a) is an AA cross-sectional view of FIG. 1(a), and FIG. 2(b) is a BB cross-sectional view 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 thickness direction of 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 the Y-axis direction of the crystal orientation of the piezoelectric layer. When the piezoelectric layer is a rotated Y-cut X-propagation piezoelectric layer, the X direction is the X-axis direction of the crystal orientation.

[0021] As shown in Figures 1(a), 1(b), 2(a), and 2(b), an acoustic wave device 100 has a piezoelectric layer 18 provided on a support substrate 10. A temperature compensating layer 14 is provided between the support substrate 10 and the piezoelectric layer 18. A boundary layer 12 is provided between the temperature compensating layer 14 and the support substrate 10. A bonding layer 16 is provided between the temperature compensating layer 14 and the piezoelectric layer 18. Note that the bonding layer 16 may not be provided.

[0022] An acoustic wave resonator 50 is provided on the piezoelectric layer 18. The acoustic wave resonator 50 has an IDT (Interdigital Transducer) 51 and a reflector 52. The reflectors 52 are provided on both sides of the IDT 51 in the X direction. The IDT 51 and the reflector 52 are formed by a metal film 57 on the piezoelectric layer 18.

[0023] The IDT 51 includes a pair of comb electrodes 53. The comb electrodes 53 include a plurality of electrode fingers 54 and a bus bar 55 to which the plurality of electrode fingers 54 are connected. The region where the pair of comb electrodes 53 intersect is the intersection region 30. The length of the intersection region 30 is the aperture length. The pair of comb electrodes 53 are provided opposite each other so that the electrode fingers 54 are substantially alternated in at least a part of the intersection region 30. The acoustic wave excited by the plurality of electrode fingers 54 in the intersection region 30 propagates mainly in the X direction. The pitch of the electrode fingers 54 of one of the pair of comb electrodes 53 is substantially the wavelength λ of the acoustic wave. The pitch D of the plurality of electrode fingers 54 is twice the pitch of the electrode fingers 54 of the one comb electrode 53. The reflector 52 reflects the acoustic wave (surface acoustic wave) excited by the electrode fingers 54 of the IDT 51. As a result, the acoustic wave is confined within the intersection region 30 of the IDT 51.

[0024] Intersection region 30 has a pair of edge regions 32 that are regions located at the edges in the Y direction (regions where the tips of electrode fingers 54 are located), and a central region 31 that is a region located inside edge regions 32 in the Y direction. A region located between the tips of electrode fingers 54 of one comb electrode 53 and busbar 55 of the other comb electrode 53 is gap region 33. A region where busbar 55 is located is busbar region 34.

[0025] A plurality of recesses 20 are formed on the upper surface of the boundary layer 12. Each of the recesses 20 is located in the edge region 32 and directly below the electrode finger 54, and is separated from one another. The recesses 20 are provided, for example, so as to overlap the entire electrode finger 54 in the edge region 32. The length of the recesses 20 in the Y direction is, for example, about 0.1λ to 2.5λ (λ is the wavelength of the elastic wave). The length of the recesses 20 in the X direction is, for example, approximately the same as the width of the electrode finger 54, but may be longer than the electrode finger 54. The depth of the recesses 20 is, for example, about several hundred nm, for example, about 0.1λ to 1λ.

[0026] Temperature compensating layer 14 is provided on the upper surface of boundary layer 12 so as to fill recesses 20 formed in boundary layer 12. Therefore, thickness T1 of temperature compensating layer 14 immediately below electrode fingers 54 in edge region 32 is thicker than thickness T2 of temperature compensating layer 14 immediately below electrode fingers 54 in central region 31.

[0027] The interface between the support substrate 10 and the boundary layer 12 is a flat surface, and the interface between the temperature compensating layer 14 and the piezoelectric layer 18 or the bonding layer 16 is a flat surface. The interface between the support substrate 10 and the boundary layer 12 may be an uneven surface. The uneven surface may have regularly arranged concaves or convexities, or may have irregularly arranged concaves or convexities.

[0028] The piezoelectric layer 18 is, for example, a single crystal lithium tantalate (LiTaO3) layer or a single crystal lithium niobate (LiNbO3) layer, for example, a rotated Y-cut X-propagation lithium tantalate layer or a rotated Y-cut X-propagation lithium niobate layer. For example, the piezoelectric layer 18 is a 36° to 48° Y-cut X-propagation lithium tantalate layer.

[0029] The support substrate 10 is, for example, a sapphire substrate, a silicon substrate, a spinel substrate, a quartz substrate, a crystal substrate, an alumina substrate, or a silicon carbide substrate. The sapphire substrate is a single crystal Al2O3 substrate, the silicon substrate is a single crystal or polycrystalline Si substrate, and the spinel substrate is a polycrystalline MgAl2O4 substrate. The quartz substrate is an amorphous SiO2 substrate, the crystal substrate is a single crystal SiO2 substrate, the alumina substrate is a polycrystalline Al2O3 substrate, and the silicon carbide substrate is a polycrystalline or single crystal SiC 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 18 in the X direction. This makes it possible to reduce the frequency temperature dependency of the acoustic wave resonator 50.

[0030] The temperature compensating layer 14 has a temperature coefficient of elastic constant with an opposite sign to that of the piezoelectric layer 18. For example, the temperature coefficient of the elastic constant of the piezoelectric layer 18 is negative, and the temperature coefficient of the elastic constant of the temperature compensating layer 14 is positive. The temperature compensating layer 14 is an insulating layer mainly composed of silicon oxide, for example, a silicon oxide (SiO2) layer with no additives or containing an additive element such as fluorine, for example, an amorphous layer.

[0031] In order for the temperature compensating layer 14 to perform the temperature compensation function, it is required that the energy of the surface acoustic wave (main mode elastic wave) excited in the piezoelectric layer 18 by the electrode fingers 54 exists to a certain extent in the temperature compensating layer 14. The range in which the energy of the surface acoustic wave exists depends on the type of the surface acoustic wave, but is typically up to a depth of about 2λ (λ is the wavelength of the elastic wave) from the upper surface of the piezoelectric layer 18. In particular, the energy of the surface acoustic wave is concentrated in the range from the upper surface of the piezoelectric layer 18 to λ. Therefore, from the viewpoint of confining the energy of the surface acoustic wave within the piezoelectric layer 18 and the temperature compensating layer 14, the distance L between the surface of the temperature compensating layer 14 on the boundary layer 12 side and the surface of the piezoelectric layer 18 on the comb-shaped electrode 53 side is preferably four times (2λ) or less, more preferably three times (1.5λ) or less, of the average pitch D of the plurality of electrode fingers 54. The average pitch D of the plurality of electrode fingers 54 can be calculated by dividing the width of the IDT 51 in the X direction by the number of electrode fingers 54.

[0032] In order to cause the energy of the surface acoustic wave to exist in the temperature compensating layer 14, the thickness of the piezoelectric layer 18 is preferably 2 times (λ) or less, and more preferably 1.2 times (0.6λ) or less, the average pitch D of the electrode fingers 54. If the piezoelectric layer 18 is too thin, the acoustic wave is not excited. Therefore, the thickness of the piezoelectric layer 18 is preferably 0.2 times (0.1λ) or more the average pitch D of the electrode fingers 54.

[0033] When the temperature compensating layer 14 is an insulating layer mainly composed of silicon oxide, the acoustic velocity (shear wave acoustic velocity) of the elastic wave propagating through the temperature compensating layer 14 is slower than the acoustic velocity of the elastic wave propagating through the piezoelectric layer 18. Since the acoustic velocity of the elastic wave propagating through the temperature compensating layer 14 is slower than the acoustic velocity of the elastic wave propagating through the piezoelectric layer 18, the surface acoustic wave is likely to exist in the temperature compensating layer 14. The acoustic velocity of the elastic wave propagating through the temperature compensating layer 14 is preferably 0.99 times or less than the acoustic velocity of the elastic wave propagating through the piezoelectric layer 18. If the acoustic velocity of the elastic wave propagating through the temperature compensating layer 14 is too slow, the elastic wave is unlikely to exist in the piezoelectric layer 18. Therefore, the acoustic velocity of the elastic wave propagating through the temperature compensating layer 14 is preferably 0.9 times or more than the acoustic velocity of the elastic wave propagating through the piezoelectric layer 18.

[0034] The acoustic velocity of the elastic wave propagating through the boundary layer 12 is faster than the acoustic velocity of the elastic wave propagating through the piezoelectric layer 18 and the temperature compensating layer 14. This makes it easier to confine the elastic wave within the piezoelectric layer 18 and the temperature compensating layer 14. The acoustic velocity of the elastic wave propagating through the boundary layer 12 is preferably 1.1 times or more, more preferably 1.2 times or more, and even more preferably 1.3 times or more, of the acoustic velocity of the elastic wave propagating through the piezoelectric layer 18 and the temperature compensating layer 14. If the acoustic velocity of the elastic wave propagating through the boundary layer 12 is too fast, the bulk wave may be easily reflected at the interface between the boundary layer 12 and the temperature compensating layer 14, which may increase the spurious response. Therefore, the acoustic velocity of the elastic wave propagating through the boundary layer 12 is preferably 2.0 times or less, more preferably 1.5 times or less, of the acoustic velocity of the elastic wave propagating through the temperature compensating layer 14.

[0035] The acoustic velocity of the elastic wave propagating through the boundary layer 12 is slower than that of the elastic wave propagating through the support substrate 10. For example, the acoustic velocity of the elastic wave propagating through the support substrate 10 is 1.1 times or more that of the elastic wave propagating through the boundary layer 12. The acoustic velocity of the elastic wave propagating through the support substrate 10 is 2 times or less that of the elastic wave propagating through the boundary layer 12. The boundary layer 12 is, for example, a polycrystalline or amorphous insulating layer, such as an aluminum oxide layer, a silicon layer, an aluminum nitride layer, an aluminum oxynitride layer, a diamond-like carbon layer, a silicon nitride layer, or a silicon carbide layer. A plurality of layers made of different materials may be provided as the boundary layer 12.

[0036] The sound velocity V of the elastic wave propagating in each layer can be calculated by the following formula 1, when each layer is made of an isotropic material. In formula 1, V is the sound velocity, E is Young's modulus, ρ is density, and ν is Poisson's ratio.

number

[0037] The linear expansion coefficient of the temperature compensating layer 14 is closer to the linear expansion coefficient of the boundary layer 12 than to the linear expansion coefficient of the piezoelectric layer 18. That is, the difference between the linear expansion coefficients of the boundary layer 12 and the temperature compensating layer 14 is smaller than the difference between the linear expansion coefficients of the piezoelectric layer 18 and the temperature compensating layer 14. When the linear expansion coefficient of the piezoelectric layer 18 varies depending on the crystal orientation, the difference between the linear expansion coefficients of the boundary layer 12 and the temperature compensating layer 14 is smaller than the maximum difference between the linear expansion coefficients of the piezoelectric layer 18 and the temperature compensating layer 14. For example, when the piezoelectric layer 18 is a rotated Y-cut X-propagation lithium tantalate layer, the linear expansion coefficients of the piezoelectric layer 18 are α11 of 16.1 ppm / K and α33 of 4.1 ppm / K. When the temperature compensating layer 14 is a silicon oxide layer, the linear expansion coefficient is 0.5 ppm / K. When boundary layer 12 is an aluminum oxide layer, the linear expansion coefficient is 7.7 ppm / K. In this case, the difference in the linear expansion coefficient between boundary layer 12 and temperature compensating layer 14 is 7.2 ppm / K, and the maximum difference in the linear expansion coefficient between piezoelectric layer 18 and temperature compensating layer 14 is 15.6 ppm / K. Therefore, the difference in the linear expansion coefficient between boundary layer 12 and temperature compensating layer 14 is smaller than the maximum difference in the linear expansion coefficient between piezoelectric layer 18 and temperature compensating layer 14.

[0038] The acoustic velocity of the elastic wave propagating through the bonding layer 16 is faster than the acoustic velocity of the elastic wave propagating through the temperature compensating layer 14. The bonding layer 16 is, for example, polycrystalline or amorphous, and is, for example, an aluminum oxide layer, a silicon layer, an aluminum nitride layer, an aluminum oxynitride layer, a diamond-like carbon layer, a silicon nitride layer, or a silicon carbide layer. From the viewpoint of not impairing the functions of the piezoelectric layer 18 and the temperature compensating layer 14, the thickness of the bonding layer 16 is preferably 20 nm or less, and more preferably 10 nm or less. From the viewpoint of not impairing the function of the bonding layer 16, the thickness of the bonding layer 16 is preferably 1 nm or more, and more preferably 2 nm or more.

[0039] The metal film 57 is a film whose main component is, for example, aluminum (Al), copper (Cu), or molybdenum (Mo). An adhesive film such as a titanium (Ti) film or a chromium (Cr) film may be provided between the electrode fingers 54 and the piezoelectric layer 18. The adhesive film is thinner than the electrode fingers 54. An insulating film may be provided so as to cover the electrode fingers 54. The insulating film may function as a protective film or a temperature compensation film.

[0040] FIG. 3 is a diagram showing the acoustic velocity of an acoustic wave in the IDT 51 in the first embodiment. As shown in FIG. 1(b) and FIG. 2(a), a recess 20 is provided on the upper surface of the boundary layer 12, located immediately below the electrode fingers 54 in the edge region 32. The temperature compensating layer 14 is provided on the upper surface of the boundary layer 12 so as to fill the recess 20. Therefore, the thickness T1 of the temperature compensating layer 14 immediately below the electrode fingers 54 in the edge region 32 is thicker than the thickness T2 of the temperature compensating layer 14 immediately below the electrode fingers 54 in the central region 31. Since the acoustic velocity of the acoustic wave propagating through the temperature compensating layer 14 is slower than the acoustic velocity of the acoustic wave propagating through the piezoelectric layer 18 and the boundary layer 12, as shown in FIG. 3, the acoustic velocity of the surface acoustic wave (the main mode acoustic wave) propagating through the edge region 32 is slower than the acoustic velocity of the surface acoustic wave propagating through the central region 31. Moreover, the acoustic velocity of the surface acoustic wave propagating through the gap region 33 is faster than the acoustic velocity of the surface acoustic wave propagating through the central region 31. This realizes a piston mode and suppresses transverse mode spurious emissions.

[0041] [Manufacturing method] 4(a) to 5(c) are cross-sectional views showing a manufacturing method of the acoustic wave device 100 according to the first embodiment. In FIG. 4(a) to FIG. 5(c), the left diagram is a cross-sectional view of a region where an IDT 51 is formed, and the right diagram is a cross-sectional view of a region where an alignment marker is formed. As shown in FIG. 4(a), a boundary layer 12 is formed on a support substrate 10 by a sputtering method, a CVD (Chemical Mechanical Polishing) method, or a vacuum deposition method. When making the upper surface of the support substrate 10 into an uneven surface, an irregular uneven surface may be formed by grinding the upper surface of the support substrate 10, or a regular uneven surface may be formed by using a photolithography technique and an etching technique.

[0042] 4(b), a mask layer 80 having an opening 82 at a position corresponding to the recess 20 to be formed in the boundary layer 12 and an opening 84 at a position where the alignment marker is to be formed is formed on the boundary layer 12. The mask layer 80 is, for example, a photoresist.

[0043] As shown in FIG. 4(c), the upper part of the boundary layer 12 is removed by, for example, etching using the mask layer 80 as a mask. For example, when the boundary layer 12 is an aluminum oxide layer, the upper part of the boundary layer 12 is removed by dry etching using a chlorine-based gas. Note that sandblasting may be used instead of etching. As a result, the recess 20 is formed on the upper surface of the boundary layer 12, and at the same time as the recess 20, an alignment marker 70 is formed on the upper surface of the boundary layer 12. FIG. 6(a) is a plan view showing an example of the alignment marker 70 formed on the boundary layer 12. As shown in FIG. 6(a), the alignment marker 70 has, for example, a cross shape in a plan view.

[0044] As shown in FIG. 5(a), after removing the mask layer 80, the temperature compensating layer 14 is formed on the boundary layer 12 by, for example, sputtering, CVD, or vacuum deposition. The temperature compensating layer 14 is formed so as to fill the recesses 20. The upper surface of the temperature compensating layer 14 is planarized by, for example, CMP (Chemical Mechanical Polishing). Thereafter, the piezoelectric substrate 17 is bonded to the temperature compensating layer 14 via the bonding layer 16. The temperature compensating layer 14 and the piezoelectric substrate 17 may be bonded together without the bonding layer 16. For example, a surface activation method is used for bonding.

[0045] As shown in FIG. 5(b), the upper surface of the piezoelectric substrate 17 is polished by, for example, a CMP method to form a thin piezoelectric layer 18. A metal film 57 is formed on the piezoelectric layer 18 by, for example, a sputtering method, a CVD method, or a vacuum deposition method, and a mask layer 86 is formed on the metal film 57. Thereafter, an opening 88 is formed in the mask layer 86 for patterning the metal film 57 into the IDT 51 and the reflector 52. When forming the opening 88 in the mask layer 86, the formation position of the opening 88 is adjusted using an alignment marker 70 formed in the boundary layer 12. The mask layer 86 is, for example, a photoresist.

[0046] Fig. 6(b) is a plan view showing an example of an alignment marker 92 of a photomask 90, and Fig. 6(c) is a plan view showing the alignment of the alignment markers 70 and 92. As shown in Fig. 6(b), the alignment markers 92 are formed on a photomask 90 used when forming an opening 88 in a mask layer 86. As shown in Fig. 6(c), the alignment markers 92 formed on the photomask 90 are aligned with the alignment markers 70 formed on the boundary layer 12, exposed, and then developed. As a result, the openings 88 are formed at the desired positions of the mask layer 86.

[0047] 5(c), the mask layer 86 is used as a mask to remove and pattern the metal film 57 by, for example, an etching method, thereby forming an acoustic wave resonator 50 including an IDT 51 and a reflector 52. Since the recess 20 and the alignment marker 70 are formed simultaneously in the boundary layer 12, the alignment marker 70 is used to form an opening 88 in the mask layer 86, and the IDT 51 and the reflector 52 are formed using the mask layer 86 as a mask, whereby the tip portions of the electrode fingers 54 can be formed precisely directly above the recess 20. After the metal film 57 is patterned, the mask layer 86 is removed. In this way, the acoustic wave device 100 in accordance with the first embodiment is obtained.

[0048] [Comparative Example] FIG. 7(a) is a plan view of an acoustic wave device 1000 according to Comparative Example 1, and FIG. 7(b) is a cross-sectional view taken along line AA of FIG. 7(a). As shown in FIGS. 7(a) and 7(b), in the acoustic wave device 1000, the interface between the support substrate 10 and the boundary layer 12 and the interface between the boundary layer 12 and the temperature compensating layer 14 are flat. A recess 94 is formed on the lower surface of the piezoelectric layer 18, located in the edge region 32 and directly below the electrode fingers 54. The temperature compensating layer 14 is provided so as to fill the recess 94 formed in the piezoelectric layer 18. Therefore, the thickness T3 of the temperature compensating layer 14 directly below the electrode fingers 54 in the edge region 32 is thicker than the thickness T4 of the temperature compensating layer 14 directly below the electrode fingers 54 in the central region 31. The other configurations are the same as those in Example 1, and therefore will not be described.

[0049] In Comparative Example 1, similarly to Example 1, the thickness T3 of the temperature compensating layer 14 immediately below the electrode fingers 54 in the edge region 32 is greater than the thickness T4 of the temperature compensating layer 14 immediately below the electrode fingers 54 in the central region 31. Therefore, the acoustic velocity of the acoustic wave in the IDT 51 is the same as that in Fig. 2. Therefore, the piston mode is realized.

[0050] However, as described above, the piezoelectric layer 18 is thinned to allow the temperature compensating layer 14 to exhibit the temperature compensation function, and therefore the recess 94 provided on the lower surface of the piezoelectric layer 18 is located near the IDT 51. Strain stress is likely to occur in the recess 94 in which the temperature compensating layer 14 is embedded. Since the recess 94 is located near the IDT 51, when strain stress occurs in the recess 94, the IDT 51 is affected by the strain stress, which may result in deterioration of the characteristics of the elastic wave in the main mode.

[0051] When the piezoelectric layer 18 is a rotated Y-cut X-propagation lithium tantalate layer and the temperature compensating layer 14 is a silicon oxide layer, the maximum difference in the linear expansion coefficient between the piezoelectric layer 18 and the temperature compensating layer 14 is as large as 15.6 ppm / K as described above. In this case, when a temperature change occurs in the acoustic wave device 1000, a large thermal stress is generated in the recess 94. This thermal stress may cause a gap to be generated between the piezoelectric layer 18 and the temperature compensating layer 14 in the recess 94, or a crack may be generated in the piezoelectric layer 18 and / or the temperature compensating layer 14. In this case, the characteristics of the acoustic wave in the main mode are deteriorated.

[0052] On the other hand, according to the first embodiment, as shown in FIG. 1(b) and FIG. 2(a), the upper surface of the boundary layer 12 (first insulating layer) is provided with recesses 20 that overlap the electrode fingers 54 in a pair of edge regions 32, which are regions located at both ends of the intersection region 30. A temperature compensating layer 14 (second insulating layer) in which the acoustic velocity of the elastic wave propagating therethrough is slower than that of the boundary layer 12 and the piezoelectric layer 18 is provided on the upper surface of the boundary layer 12 by embedding the recesses 20. The temperature compensating layer 14 has a thickness T1 at a position where it overlaps with the electrode fingers 54 in the edge regions 32 that is thicker than a thickness T2 at a position where it overlaps with the electrode fingers 54 in the central region 31 located inside the edge regions 32 of the intersection region 30. As a result, as shown in FIG. 3, the acoustic velocity of the elastic wave propagating in the edge regions 32 becomes slower than that of the elastic wave propagating in the central region 31, realizing a piston mode, and thus suppressing transverse mode spurious. In addition, since the recess 20 is provided in the boundary layer 12, the distance between the recess 20 and the IDT 51 is long, and even if a strain stress occurs in the recess 20, the effect on the IDT 51 can be suppressed to a small extent. Therefore, the deterioration of the characteristics of the main mode elastic wave can be suppressed.

[0053] In order to realize the piston mode, it is preferable that the Y-direction length of the central region 31 and the Y-direction length of the edge region 32 satisfy a certain relationship. For example, it is preferable that the Y-direction length of the central region 31 is longer than the total Y-direction length of the edge region 32. The total Y-direction length of the edge region 32 is preferably 5λ or less (e.g., ¼ or less of the aperture length), more preferably 2λ or less (e.g., 1 / 10 or less of the aperture length). The Y-direction length of each edge region 32 is preferably 0.1λ or more (e.g., 1 / 200 or more of the aperture length), more preferably 0.5λ or more (e.g., 1 / 40 or more of the aperture length). In other words, the Y-direction length of the recess 20 is preferably 0.1λ or more, more preferably 0.5λ or more. The length of recess 20 in the X direction may be approximately the same as the length of electrode finger 54 in the X direction, but is preferably longer than the length of electrode finger 54 in the X direction, and is preferably at least 1.1 times, and more preferably at least 1.2 times, the length of electrode finger 54 in the X direction. "Approximately the same" means that a difference of the order of manufacturing error is allowed. Recess 20 preferably overlaps with the entire portion of electrode finger 54 located in edge region 32 in plan view, but may overlap with 90% or more, or may overlap with 95% or more of the portion of electrode finger 54 located in edge region 32.

[0054] In order to realize the piston mode, the thickness T1 of the temperature compensating layer 14 at the position overlapping the electrode finger 54 in the edge region 32 is preferably 1.5 times or more, more preferably 2 times or more, than the thickness T2 of the temperature compensating layer 14 at the position overlapping the electrode finger 54 in the central region 31. If the recess 20 is too deep, the embedding property of the temperature compensating layer 14 is deteriorated. Therefore, the thickness T1 of the temperature compensating layer 14 at the position overlapping the electrode finger 54 in the edge region 32 is preferably 3 times or less, more preferably 2.5 times or less than the thickness T2 of the temperature compensating layer 14 at the position overlapping the electrode finger 54 in the central region 31. The depth of the recess 20 is preferably 0.1λ or more, more preferably 0.3λ or more. The depth of the recess 20 is preferably 1λ or less, more preferably 0.8λ or less. The edge region 32 may be provided only on one side of the central region 31. The total length of the gap region 33 in the Y direction is preferably 5λ or less, more preferably 2λ or less. The length of each of the gap regions 33 in the Y direction is preferably 0.1λ or more, and more preferably 0.5λ or more.

[0055] Furthermore, according to the first embodiment, the distance L between the surface of the temperature compensating layer 14 on the boundary layer 12 side and the surface of the piezoelectric layer 18 on which the pair of comb electrodes 53 are provided is equal to or less than four times (2λ) the average pitch D of the multiple electrode fingers 54. As a result, as described above, the energy of the surface acoustic wave excited by the electrode fingers 54 is present in the temperature compensating layer 14, and the effect of temperature compensation by the temperature compensating layer 14 is obtained.

[0056] Furthermore, according to the first embodiment, the surface of the piezoelectric layer 18 facing the temperature compensating layer 14 is flat. This prevents distortion stress from occurring in the piezoelectric layer 18, and can prevent deterioration of the characteristics of the main mode elastic wave.

[0057] Furthermore, according to the first embodiment, the difference in the linear expansion coefficient between the boundary layer 12 and the temperature compensating layer 14 is smaller than the maximum difference in the linear expansion coefficient between the piezoelectric layer 18 and the temperature compensating layer 14. This reduces the thermal stress generated in the recess 20 even when a temperature change occurs in the acoustic wave device 100. This prevents a gap from being generated between the boundary layer 12 and the temperature compensating layer 14 in the recess 20 and prevents cracks from being generated in the boundary layer 12 and / or the temperature compensating layer 14.

[0058] Table 1 provides examples of materials that may be used for piezoelectric layer 18, temperature compensating layer 14, and boundary layer 12. [Table 1] As shown in Table 1, a rotated Y-cut X-propagation lithium tantalate layer or a rotated Y-cut X-propagation lithium niobate layer is used for the piezoelectric layer 18. A silicon oxide layer is used for the temperature compensating layer 14. An aluminum oxide layer, an aluminum nitride layer, a diamond-like carbon layer, a silicon carbide layer, a silicon nitride layer, or a silicon layer is used for the boundary layer 12. In such a case, the difference in linear expansion coefficient between the boundary layer 12 and the temperature compensating layer 14 is smaller than the maximum difference in linear expansion coefficient between the piezoelectric layer 18 and the temperature compensating layer 14. Suitable combinations of the piezoelectric layer 18, the temperature compensating layer 14, and the boundary layer 12 include a rotated Y-cut X-propagation lithium tantalate layer / silicon oxide layer / aluminum oxide layer, a rotated Y-cut X-propagation lithium tantalate layer / silicon oxide layer / silicon, and a rotated Y-cut X-propagation lithium tantalate layer / silicon oxide layer / silicon nitride layer.

[0059] In the first embodiment, the piezoelectric layer 18 is a rotated Y-cut X-propagation lithium tantalate layer or a rotated Y-cut X-propagation lithium niobate layer. The temperature compensating layer 14 is a layer mainly made of silicon oxide. This can reduce the frequency temperature dependency of the acoustic wave resonator 50. The acoustic velocity of the acoustic wave propagating through the temperature compensating layer 14 is slower than that of the acoustic wave propagating through the piezoelectric layer 18. The main component means that the total ratio of oxygen and silicon to the total of the elements contained in the temperature compensating layer 14 is 50 at% (atomic %) or more, and may be 80 at% or more. The respective ratios of oxygen and silicon are 10 at% or more, and may be 20 at% or more.

[0060] In addition, in the first embodiment, as shown in FIG. 4(c), the recesses 20 and the alignment markers 70 are simultaneously formed in the boundary layer 12 (first insulating layer). As shown in FIG. 5(a), the recesses 20 are embedded on the boundary layer 12 to form the temperature compensating layer 14 (second insulating layer). As shown in FIG. 5(b), the piezoelectric layer 18 is formed on the temperature compensating layer 14. As shown in FIGS. 5(b) and 5(c), using the alignment markers 70, a pair of comb-shaped electrodes 53 is formed on the piezoelectric layer 18 so that the electrode fingers 54 overlap the recesses 20 in the edge region 32. This allows the electrode fingers 54 to be accurately overlapped with the recesses 20 in the edge region 32.

[0061] [Variations] Fig. 8(a) is a plan view of an acoustic wave device 110 according to a first modified example of the first embodiment, Fig. 8(b) is an AA cross-sectional view of Fig. 8(a), and Fig. 8(c) is a BB cross-sectional view of Fig. 8(a). As shown in Figs. 8(a) to 8(c), in the acoustic wave device 110, a recess 20a formed in the boundary layer 12 extends in the X direction and is provided across two or more of the multiple electrode fingers 54. For example, the recess 20 is provided across all of the electrode fingers 54. The other configurations are the same as those of the first embodiment, and therefore description thereof will be omitted.

[0062] In the first embodiment, the recesses 20 are provided immediately below the plurality of electrode fingers 54 in the edge region 32 and are separated from each other. However, the present invention is not limited to this. As in the first modified example of the first embodiment, the recesses 20 may be provided immediately below two or more of the plurality of electrode fingers 54 in the edge region 32. Providing the recesses 20 across two or more electrode fingers 54 facilitates alignment of the recesses 20 with the electrode fingers 54. From the viewpoint of alignment, the recesses 20 are preferably provided across half or more of the plurality of electrode fingers 54, more preferably across two-thirds or more of the electrode fingers 54, and even more preferably across all of the electrode fingers 54.

[0063] Fig. 9(a) is a cross-sectional view of an acoustic wave device 120 according to a second modification of the first embodiment. As shown in Fig. 9(a), in the acoustic wave device 120, a recess 20b formed in a boundary layer 12 has a shape in which the width narrows toward the support substrate 10. The other configurations are the same as those in the first embodiment, and therefore description thereof will be omitted.

[0064] Fig. 9(b) is a cross-sectional view of an acoustic wave device 130 according to a third modification of the first embodiment. As shown in Fig. 9(b), in the acoustic wave device 130, the bottom surface of the recess 20c formed in the boundary layer 12 has a curved shape. The other configurations are the same as those in the first embodiment, and therefore description thereof will be omitted.

[0065] Fig. 9(c) is a cross-sectional view of an acoustic wave device 140 according to a fourth modification of the first embodiment. As shown in Fig. 9(c), in the acoustic wave device 140, a recess 20d formed in the boundary layer 12 penetrates the boundary layer 12. The other configurations are the same as those in the first embodiment, and therefore description thereof will be omitted.

[0066] The recesses formed in the boundary layer 12 may be recesses 20 having a substantially rectangular shape in a cross section in the Y direction as in the first embodiment, recesses 20b having a shape in which the width becomes narrower as the depth increases as in the second modification of the first embodiment, or recesses 20c having a curved bottom as in the third modification of the first embodiment. Also, recesses 20d penetrating the boundary layer 12 as in the fourth modification of the first embodiment may be used. In the recesses 20d penetrating the boundary layer 12, the depth of the recesses 20d can be controlled with high precision. EXAMPLES

[0067] FIG. 10(a) is a plan view of an acoustic wave device 200 according to a second embodiment, and FIG. 10(b) is an enlarged plan view of an IDT 51 in FIG. 10(a). As shown in FIG. 10(a) and FIG. 10(b), in the acoustic wave device 200, a comb-shaped electrode 53 includes a plurality of electrode fingers 54, a plurality of dummy electrode fingers 56, and a bus bar 55 to which the plurality of electrode fingers 54 and the plurality of dummy electrode fingers 56 are connected. The tip of the electrode finger 54 of one comb-shaped electrode 53 faces the tip of the dummy electrode finger 56 of the other comb-shaped electrode 53. The acoustic wave resonator 50 includes an intersection region 30 having a central region 31 and an edge region 32, a gap region 33, a bus bar region 34, and a dummy region 35 between the gap region 33 and the bus bar region 34, in which the dummy electrode finger 56 is located. The other configurations are the same as those of the first embodiment, and therefore description thereof will be omitted.

[0068] As in the second embodiment, comb-shaped electrode 53 may include a plurality of electrode fingers 54, a plurality of dummy electrode fingers 56, and bus bar 55 connecting the plurality of electrode fingers 54 and the plurality of dummy electrode fingers 56. EXAMPLES

[0069] FIG. 11(a) is a plan view of an acoustic wave device 300 according to a third embodiment, FIG. 11(b) is an AA cross-sectional view of FIG. 11(a), and FIG. 11(c) is a BB cross-sectional view of FIG. 11(a). As shown in FIG. 11(a) to FIG. 11(c), in the acoustic wave device 300, the boundary layer 12 is not provided between the support substrate 10 and the temperature compensating layer 14, and the bonding layer 16 is not provided between the temperature compensating layer 14 and the piezoelectric layer 18. A plurality of recesses 22 are formed on the upper surface of the support substrate 10. Each of the plurality of recesses 22 is located in the edge region 32 and directly below the electrode finger 54, and is separated from each other. The recesses 22 are provided, for example, so as to overlap the entire electrode finger 54 in the edge region 32 in a plan view. The length of the recesses 22 in the Y direction is the same as that of the recesses 20 in the first embodiment, and is, for example, about 0.1λ to 2.5λ (λ is the wavelength of the acoustic wave). The length of the recess 22 in the X direction is similar to that of the recess 20 in Example 1, and is, for example, approximately the same as the width of the electrode finger 54, but may be longer than the electrode finger 54. The depth of the recess 22 is similar to that of the recess 20 in Example 1, and is, for example, approximately several hundred nm, for example, approximately 0.1λ to 1λ.

[0070] Temperature compensating layer 14 is provided on the upper surface of supporting substrate 10 so as to fill recesses 22 formed in supporting substrate 10. Therefore, thickness T1 of temperature compensating layer 14 directly under electrode fingers 54 in edge region 32 is thicker than thickness T2 of temperature compensating layer 14 directly under electrode fingers 54 in central region 31. The other configurations are the same as in Example 1, so descriptions thereof will be omitted.

[0071] In the third embodiment, similarly to the first embodiment, the thickness T1 of the temperature compensating layer 14 at the position overlapping with the electrode fingers 54 in the edge region 32 is greater than the thickness T2 of the temperature compensating layer 14 at the position overlapping with the electrode fingers 54 in the central region 31. Therefore, the acoustic velocity of the acoustic wave in the IDT 51 is the same as that in Fig. 3. Therefore, the piston mode is realized.

[0072] [simulation] A simulation was performed to evaluate the spurious response of the acoustic wave device 300 in accordance with Example 3. The simulation conditions were as follows. Support substrate 10: sapphire substrate Temperature compensation layer 14: a silicon oxide layer with an average thickness of 0.2λ Piezoelectric layer 18: 42° Y-cut X-propagation lithium tantalate layer with a thickness of 0.2λ IDT51 and reflector 52: Aluminum film with a thickness of 0.1λ Elastic wave wavelength λ: 1.5 μm Number of pairs of electrode fingers 54: 1 pair Length of the recess 22 in the X direction: 0.75λ Depth of the recess 22: 0.2λ Opening length: 15λ Under these conditions, the admittance was simulated using a three-dimensional finite element method, and the admittance of the acoustic wave device 300 when the number of pairs of electrode fingers 54 was 100 was calculated from the results. For comparison, the admittance was also simulated by the same method for the acoustic wave device according to Comparative Example 2, which has the same structure as Example 3 except that the recesses 22 are not formed in the supporting substrate 10.

[0073] 12 shows simulation results of admittance Y versus frequency for acoustic wave device 300 according to Example 3 and acoustic wave device according to Comparative Example 2. As shown in Fig. 12, acoustic wave device 300 according to Example 3 exhibits suppressed transverse mode spurious. This is believed to be because recess 22 is provided on the upper surface of supporting substrate 10, and thickness T1 of temperature compensating layer 14 at the position overlapping electrode finger 54 in edge region 32 is thicker than thickness T2 of temperature compensating layer 14 at the position overlapping electrode finger 54 in central region 31, thereby realizing a piston mode.

[0074] According to the third embodiment, as shown in Figs. 11(a) to 11(c), the recess 22 overlapping the electrode finger 54 in the edge region 32 is provided on the upper surface of the support substrate 10 (first insulating layer). The temperature compensating layer 14 (second insulating layer) through which the acoustic velocity of the elastic wave propagating from the support substrate 10 and the piezoelectric layer 18 is slow is provided on the upper surface of the support substrate 10 by embedding the recess 22. The temperature compensating layer 14 has a thickness T1 at the position where it overlaps with the electrode finger 54 in the edge region 32 that is thicker than a thickness T2 at the position where it overlaps with the electrode finger 54 in the central region 31. This realizes a piston mode as in the first embodiment, so that the transverse mode spurious can be suppressed. In addition, since the recess 22 is provided on the support substrate 10, the distance between the recess 22 and the IDT 51 is long, and even if a strain stress occurs in the recess 22, the effect on the IDT 51 can be suppressed to a small extent. This makes it possible to suppress the deterioration of the characteristics of the elastic wave in the main mode.

[0075] In the third embodiment, similarly to the first modification of the first embodiment shown in Figs. 8(a) to 8(c), the recess 22 may be provided in the edge region 32 to extend directly below two or more of the electrode fingers 54. In Fig. 11(b), the recess 22 has a substantially rectangular shape in a cross section in the Y direction, but similarly to the second modification of the first embodiment shown in Fig. 9(a), the recess 22 may have a shape in which the width becomes narrower as the recess 22 becomes deeper in a cross section in the Y direction, or similarly to the third modification of the first embodiment shown in Fig. 9(b), the bottom surface may be curved. Also, in the third embodiment, the comb-shaped electrode 53 may include a plurality of electrode fingers 54, a plurality of dummy electrode fingers 56, and a bus bar 55 to which the plurality of electrode fingers 54 and the plurality of dummy electrode fingers 56 are connected, similarly to the second embodiment. EXAMPLES

[0076] Fig. 13 is a circuit diagram of a filter 400 according to a fourth embodiment. As shown in Fig. 13, the filter 400 has one or more series resonators S1 to S4 connected in series and one or more parallel resonators P1 to P3 connected in parallel between an input terminal Tin and an output terminal Tout. The acoustic wave device according to the first to third embodiments can be used for at least one of the one or more series resonators S1 to S4 and the one or more parallel resonators P1 to P3. The number of resonators of the ladder filter can be set as appropriate. The filter may be a multimode filter. EXAMPLES

[0077] FIG. 14 is a block diagram of a duplexer 500 according to a fifth embodiment. As shown in FIG. 14, in the duplexer 500, a transmission filter 60 is connected between a common terminal Ant and a transmission terminal Tx, and a reception filter 62 is connected between the common terminal Ant and a reception terminal Rx. The transmission filter 60 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 62 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 60 and the reception filter 62 can be the filter 400 according to the fourth embodiment.

[0078] Although a duplexer has been shown as an example of a multiplexer, a triplexer or a quadplexer may also be used.

[0079] Although the embodiment of the present invention has been described in detail above, the present invention is not limited to such specific embodiment, and various modifications and variations are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0080] 10 Support substrate 12 Boundary layer 14 Temperature compensation layer 16 Bonding layer 17 Piezoelectric Substrate 18 Piezoelectric layer 20, 20a, 20b, 20c, 20d recess 22 Recess 30 Intersection Area 31 Central area 32 Edge Area 33 Gap Region 34 Busbar Area 35 Dummy Area 50 Elastic Wave Resonator 51 IDT 52 Reflector 53 Comb-shaped electrode 54 Electrode finger 55 Busbar 56 Dummy electrode finger 57 Metal Film 60 Transmission Filter 62 Receiving Filter 70 Alignment Marker 80 Mask Layers 82, 84 aperture 86 Mask Layer 88 Aperture 90 Photomask 92 Alignment Marker 94 Recess 100, 110, 120, 130, 140, 200, 300, 1000 Acoustic Wave Devices 400 Filters 500 Duplexer

Claims

1. A piezoelectric layer; a pair of comb-shaped electrodes provided on one surface of the piezoelectric layer, the comb-shaped electrodes having a plurality of electrode fingers and a bus bar connecting the plurality of electrode fingers; a first insulating layer provided on the other surface side of the piezoelectric layer, the first insulating layer having recesses overlapping the electrode fingers in a pair of edge regions that are regions at both ends of an intersection region where the electrode fingers of the pair of comb-shaped electrodes intersect; an insulating layer provided between the piezoelectric layer and the first insulating layer in both a central region of the intersection region located inside the edge region and the edge region, filling the recesses, having a thickness greater at a position overlapping with the multiple electrode fingers in the edge region than a thickness greater at a position overlapping with the multiple electrode fingers in the central region, and having a slower acoustic wave propagation speed than the piezoelectric layer and the first insulating layer.

2. A piezoelectric layer, a pair of comb-shaped electrodes provided on one surface of the piezoelectric layer, the comb-shaped electrodes having a plurality of electrode fingers and a bus bar connecting the plurality of electrode fingers; a first insulating layer provided on the other surface side of the piezoelectric layer, the first insulating layer having recesses overlapping the electrode fingers in a pair of edge regions that are regions at both ends of an intersection region where the electrode fingers of the pair of comb-shaped electrodes intersect; a second insulating layer provided between the piezoelectric layer and the first insulating layer and filling the recess, the second insulating layer having a thickness greater at a position overlapping with the plurality of electrode fingers in the edge region than a thickness at a position overlapping with the plurality of electrode fingers in a central region of the intersection region that is located inside the edge region, and an acoustic velocity of an elastic wave propagating through the second insulating layer is slower than that of the piezoelectric layer and the first insulating layer; An acoustic wave device in which the distance between the surface of the second insulating layer facing the first insulating layer and the one surface of the piezoelectric layer is four times or less the average pitch of the multiple electrode fingers of the pair of comb electrodes.

3. A piezoelectric layer, a pair of comb-shaped electrodes provided on one surface of the piezoelectric layer, the comb-shaped electrodes having a plurality of electrode fingers and a bus bar connecting the plurality of electrode fingers; a first insulating layer provided on the other surface side of the piezoelectric layer, the first insulating layer having recesses overlapping the electrode fingers in a pair of edge regions that are regions at both ends of an intersection region where the electrode fingers of the pair of comb-shaped electrodes intersect; a second insulating layer provided between the piezoelectric layer and the first insulating layer and filling the recess, the second insulating layer having a thickness greater at a position overlapping with the plurality of electrode fingers in the edge region than a thickness at a position overlapping with the plurality of electrode fingers in a central region of the intersection region that is located inside the edge region, and an acoustic velocity of an elastic wave propagating through the second insulating layer is slower than that of the piezoelectric layer and the first insulating layer; An acoustic wave device in which a difference between the linear expansion coefficients of the first insulating layer and the second insulating layer is smaller than a maximum difference between the linear expansion coefficients of the piezoelectric layer and the second insulating layer.

4. A piezoelectric layer; a pair of comb-shaped electrodes provided on one surface of the piezoelectric layer, the comb-shaped electrodes having a plurality of electrode fingers and a bus bar connecting the plurality of electrode fingers; a first insulating layer provided on the other surface side of the piezoelectric layer, the first insulating layer having recesses overlapping the electrode fingers in a pair of edge regions that are regions at both ends of an intersection region where the electrode fingers of the pair of comb-shaped electrodes intersect; a second insulating layer provided between the piezoelectric layer and the first insulating layer and filling the recess, the second insulating layer having a thickness greater at a position overlapping with the plurality of electrode fingers in the edge region than a thickness at a position overlapping with the plurality of electrode fingers in a central region of the intersection region that is located inside the edge region, and an acoustic velocity of an elastic wave propagating through the second insulating layer is slower than that of the piezoelectric layer and the first insulating layer; the piezoelectric layer is a rotated Y-cut X-propagation lithium tantalate layer or a rotated Y-cut X-propagation lithium niobate layer; The second insulating layer is a layer mainly composed of silicon oxide.

5. A piezoelectric layer; a pair of comb-shaped electrodes provided on one surface of the piezoelectric layer, the comb-shaped electrodes having a plurality of electrode fingers and a bus bar connecting the plurality of electrode fingers; a first insulating layer provided on the other surface side of the piezoelectric layer, the first insulating layer having recesses overlapping the electrode fingers in a pair of edge regions that are regions at both ends of an intersection region where the electrode fingers of the pair of comb-shaped electrodes intersect; a second insulating layer provided between the piezoelectric layer and the first insulating layer and filling the recess, the second insulating layer having a thickness greater at a position overlapping with the plurality of electrode fingers in the edge region than a thickness at a position overlapping with the plurality of electrode fingers in a central region of the intersection region that is located inside the edge region, and an acoustic velocity of an elastic wave propagating through the second insulating layer is slower than that of the piezoelectric layer and the first insulating layer; The acoustic wave device, wherein the first insulating layer is a support substrate made of a sapphire substrate, a silicon substrate, a spinel substrate, a quartz substrate, a crystal substrate, an alumina substrate, or a silicon carbide substrate.

6. The acoustic wave device according to claim 1 , wherein the other surface of the piezoelectric layer is a flat surface.

7. The acoustic wave device according to claim 1 , wherein the recess penetrates the first insulating layer.

8. 5. The acoustic wave device according to claim 1, further comprising a support substrate, the support substrate being made of a sapphire substrate, a silicon substrate, a spinel substrate, a quartz substrate, a crystal substrate, an alumina substrate, or a silicon carbide substrate, on a surface of the first insulating layer opposite to the second insulating 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. Simultaneously forming a recess and an alignment marker in a first insulating layer; forming a second insulating layer on the first insulating layer by filling the recess, the second insulating layer having a slower acoustic wave propagation speed than the first insulating layer; forming a piezoelectric layer on the second insulating layer, the piezoelectric layer having a faster acoustic velocity of an elastic wave propagating therethrough than the second insulating layer; forming, on the piezoelectric layer, a pair of comb-shaped electrodes having the plurality of electrode fingers, using the alignment markers, such that the plurality of electrode fingers overlap the recesses in a pair of edge regions that are regions located at both ends of an intersection region where each of the plurality of electrode fingers intersects; A method for manufacturing an acoustic wave device, wherein the second insulating layer is provided in both a central region of the intersection region that is located inside the edge region and the edge region, and the thickness at the position overlapping with the multiple electrode fingers in the edge region is thicker than the thickness at the position overlapping with the multiple electrode fingers in the central region.

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