Acoustic Wave Devices, Filters, and Multiplexers

Abstract

To provide an elastic wave device, a filter and a multiplexer that suppresses spurious.SOLUTION: An elastic wave device 100 has a piezoelectric layer 18, a comb-type electrode 53, a support substrate 10, and a boundary layer 12. The comb-type electrode 53 is provided on one side 19 of the piezoelectric layer 18 and has a plurality of electrode fingers 54 that excite elastic waves. The support substrate 10 is provided on the other side of the piezoelectric layer 18 and has a plurality of convex portions 30 on the piezoelectric layer 18 side in a shape having a plurality of linear inclines 32a, 32b inclined at different angles with respect to one side 19 of the piezoelectric layer 18 on each of the left and right sides when viewed in cross-section. The boundary layer 12 is provided between the piezoelectric layer 18 and the support substrate 10 on the side of the support substrate 10 where the convex portions 30 are formed.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to acoustic wave devices, filters, and multiplexers. [Background technology]

[0002] Surface acoustic wave resonators are known as acoustic wave resonators 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 an intermediate layer containing silica is provided between the piezoelectric substrate and the support substrate, and the interface between the intermediate layer and the piezoelectric substrate and the interface between the intermediate layer and the support substrate are made uneven (for example, Patent Document 1). It is known that an insulating layer is provided between the support substrate and the piezoelectric layer, and the interface between the insulating layer and the support substrate is made into a regular uneven pattern (for example, Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-061258 A [Patent Document 2] JP 2020-161899 A Summary of the Invention [Problem to be solved by the invention]

[0004] The spurious can be suppressed by providing a protrusion and / or a recess in the insulating layer below the piezoelectric layer. However, the suppression of the spurious is not sufficient and there is still room for improvement.

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

[0006] The present invention is an acoustic wave device comprising a piezoelectric layer, a pair of comb-shaped electrodes provided on one surface of the piezoelectric layer and having a plurality of electrode fingers that excite acoustic waves, a first insulating layer provided on the other surface of the piezoelectric layer and having a plurality of convex portions and / or concave portions on the piezoelectric layer side, the convex portions and / or concave portions having a shape with a plurality of linear inclinations inclined at different angles relative to the one surface of the piezoelectric layer, on each of the left and right side surfaces when viewed in cross section, and a second insulating layer provided between the piezoelectric layer and the first insulating layer on the surface of the first insulating layer on which the convex portions and / or concave portions are formed.

[0007] In the above configuration, when viewed in cross section, the angle corresponding to the first insulating layer side among the two angles that each of the multiple inclinations forms with the one surface of the piezoelectric layer can be greater than or equal to 45° and less than 90°.

[0008] In the above configuration, the angle of each of the plurality of inclinations corresponding to the first insulating layer side may be configured to increase in the order of the inclinations from the inclination closest to the piezoelectric layer to the inclination farthest from the piezoelectric layer.

[0009] In the above configuration, the second insulating layer may be configured to fill bottoms of the recesses and / or bottoms formed between adjacent protrusions when viewed in cross section.

[0010] In the above configuration, the second insulating layer can be configured to have a gap arranged adjacent to the inclination that is located closest to the piezoelectric layer among the multiple inclinations that form the convex portion and / or concave portion when viewed in cross section.

[0011] The present invention is an acoustic wave device comprising a piezoelectric layer, a pair of comb-shaped electrodes provided on one surface of the piezoelectric layer and having a plurality of electrode fingers for exciting acoustic waves, a first insulating layer provided on the other surface of the piezoelectric layer and having a plurality of first recesses on each of its left and right side surfaces when viewed in cross section, the first recesses having a shape that has a linear first slope inclined relative to the one surface of the piezoelectric layer, and a second insulating layer provided between the piezoelectric layer and the first insulating layer, the second recesses having side surfaces continuous with the side surfaces of the first recesses and having a shape that has a linear second slope on each of its left and right side surfaces when viewed in cross section, the second recesses having a shape that has a linear second slope inclined at an angle different from the first slope relative to the one surface of the piezoelectric layer.

[0012] In the above configuration, the first insulating layer can be 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.

[0013] 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] In the above configuration, a third insulating layer mainly composed of silicon oxide may be provided between the second insulating layer and the piezoelectric layer, and the second insulating layer may be configured to have a bulk wave propagating therethrough at a faster sound speed than the third insulating layer.

[0015] The present invention is a filter including the above-described acoustic wave device.

[0016] The present invention is a multiplexer comprising the filter described above. Effect of the Invention

[0017] According to the present invention, spurious signals can be suppressed. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1A is a plan view of an acoustic wave device in accordance with a first embodiment, and FIG. 1B is a cross-sectional view thereof. [Diagram 2] FIG. 2 is an enlarged cross-sectional view of the vicinity of a protrusion provided on a support substrate in the first embodiment. [Diagram 3] 3(a) to 3(c) are cross-sectional views (part 1) illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Figure 4] 4(a) to 4(c) are cross-sectional views (part 2) illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Diagram 5] FIG. 5 is a cross-sectional view of an acoustic wave device according to a comparative example. [Figure 6] FIG. 6A is a cross-sectional view showing an example of the period of protrusions in an acoustic wave device according to a comparative example, and FIG. 6B is a cross-sectional view showing an example of the period of protrusions in an acoustic wave device according to Example 1. [Figure 7] FIG. 7(a) is a cross-sectional view of an acoustic wave device according to a first modification of the first embodiment, and FIG. 7(b) is an enlarged cross-sectional view of the vicinity of a protrusion provided on a support substrate in the first modification of the first embodiment. [Figure 8] FIG. 8A is a cross-sectional view of an acoustic wave device in accordance with a second modification of the first embodiment, and FIG. 8B is a cross-sectional view of an acoustic wave device in accordance with a third modification of the first embodiment. [Figure 9] FIG. 9(a) is a plan view showing a first arrangement example of the convex portions and the concave portions, and FIG. 9(b) and FIG. 9(c) are cross-sectional views taken along line AA of FIG. 9(a). [Figure 10] FIG. 10(a) is a plan view showing a second example of the arrangement of the convex portions and the concave portions, and FIG. 10(b) and FIG. 10(c) are cross-sectional views taken along the line AA of FIG. 10(a). [Figure 11] FIG. 11 is a cross-sectional view of an acoustic wave device in accordance with the second embodiment. [Figure 12] FIG. 12(a) is a cross-sectional view of an acoustic wave device in accordance with a third embodiment, and FIG. 12(b) is an enlarged cross-sectional view of the vicinity of a convex portion formed in a boundary layer in the third embodiment. [Figure 13]FIG. 13(a) is a cross-sectional view of an acoustic wave device in accordance with a fourth embodiment, and FIG. 13(b) is an enlarged cross-sectional view of the vicinity of a protrusion formed below a supporting substrate and a boundary layer in the fourth embodiment. [Figure 14] FIG. 14 is a circuit diagram of a filter in accordance with the fifth embodiment. [Figure 15] FIG. 15 is a block diagram of a duplexer in accordance with the sixth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0020] 1(a) is a plan view of an acoustic wave device 100 according to a first embodiment, and FIG. 1(b) is a cross-sectional view. 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 the Y-axis direction of the crystal orientation of the piezoelectric layer. When the piezoelectric layer is a rotated Y-cut X-propagation layer, the X direction is the X-axis direction of the crystal orientation.

[0021] 1(a) and 1(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, but the bonding layer 16 may not be provided.

[0022] The support substrate 10 has protrusions 30 formed on its upper surface. The protrusions 30 are regularly arranged. The boundary layer 12 is provided on the upper surface of the support substrate 10 so as to fill in the spaces between the protrusions 30. Therefore, the interface between the support substrate 10 and the boundary layer 12 is an uneven surface. The interface between the boundary layer 12 and the temperature compensating layer 14 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.

[0023] An acoustic wave resonator 50 is provided on the surface 19 of 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.

[0024] 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 an intersection region 56. The length of the intersection region 56 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 56. The acoustic wave excited by the plurality of electrode fingers 54 in the intersection region 56 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 56 of the IDT 51.

[0025] FIG. 2 is a cross-sectional view enlarging the vicinity of the protrusion 30 provided on the support substrate 10 in the first embodiment. As shown in FIG. 1(b) and FIG. 2, the protrusion 30 provided on the support substrate 10 has a shape symmetrical in a cross-sectional view. The protrusion 30 has a shape having a plurality of linear inclinations 32a, 32b inclined at different angles on each of the left and right sides of the protrusion 30 when viewed in a cross-sectional view with respect to the surface 19 on which the IDT 51 of the piezoelectric layer 18 is provided. The inclination 32a is an inclination that forms a step on the side closer to the apex of the protrusion 30, and the inclination 32b is an inclination that forms a step on the side farther from the apex of the protrusion 30. Each step may be formed only by the linear inclinations 32a, 32b, or may include a curved portion in part. The linear inclination is not limited to a completely straight line, and an approximately linear inclination having a curve or step of the order of a manufacturing error is allowed. The angles α1, α2 between a virtual straight line 80 parallel to the surface 19 of the piezoelectric layer 18 and the inclinations 32a, 32b are 45° or more and less than 90°. Angle α1 between virtual line 80 and inclination 32a is smaller than angle α2 between virtual line 80 and inclination 32b. Angle α1 corresponds to the angle corresponding to the supporting substrate 10 side of the two angles formed by inclination 32a with respect to surface 19 of piezoelectric layer 18, and angle α2 corresponds to the angle corresponding to the supporting substrate 10 side of the two angles formed by inclination 32b with respect to surface 19 of piezoelectric layer 18.

[0026] The period P of the protrusions 30 is, for example, 0.3λ or more (λ is the wavelength of the elastic wave). The height H1 of the protrusions 30 is, for example, 0.1λ or more. The height H2 of the lower tapered portion of the protrusions 30 is, for example, 0.01λ or more.

[0027] 1(b), the thicknesses of the boundary layer 12, the temperature compensating layer 14, the bonding layer 16, and the piezoelectric layer 18 are designated as T1, T2, T3, and T4, respectively. Note that the thickness of the boundary layer 12 is not uniform, so the average thickness is designated as thickness T1. For example, the thickness T1 of the boundary layer 12 can be determined by dividing the sum of the thickness of the boundary layer 12 from the apex of the convex portion 30 to the temperature compensating layer 14 and the thickness of the boundary layer 12 from the bottom surface between adjacent convex portions 30 to the temperature compensating layer 14 by 2.

[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.

[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 silicon substrate, 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, 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 can 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 the opposite sign to that of the piezoelectric layer 18. For example, the temperature coefficient of elastic constant of the piezoelectric layer 18 is negative, and the temperature coefficient of elastic constant of the temperature compensating layer 14 is positive. The temperature compensating layer 14 is, for example, an insulating layer mainly composed of silicon oxide (SiO2), for example, a silicon oxide layer with no additives or containing an additive element such as fluorine, for example, an amorphous layer. When the temperature compensating layer 14 is an insulating layer mainly composed of silicon oxide, the sound velocity of the bulk wave propagating through the temperature compensating layer 14 is slower than the sound velocity of the bulk wave propagating through the piezoelectric layer 18.

[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 IDT 51 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 (T2+T3+T4) between the surface of the temperature compensating layer 14 on the support substrate 10 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 multiple electrode fingers 54. The average pitch D of the multiple electrode fingers 54 can be calculated by dividing the width of the IDT 51 in the X direction by the number of the electrode fingers 54.

[0032] In order to allow the energy of the surface acoustic wave to exist in the temperature compensating layer 14, the thickness T4 of the piezoelectric layer 18 is preferably equal to or less than twice (λ) the average pitch D of the electrode fingers 54, and more preferably equal to or less than 1.2 times (0.6λ). If the piezoelectric layer 18 is too thin, the acoustic wave is not excited. Therefore, the thickness T4 of the piezoelectric layer 18 is preferably equal to or more than 0.2 times (0.1λ) the average pitch D of the electrode fingers 54.

[0033] When exciting a surface acoustic wave, the IDT 51 also excites unwanted waves such as bulk waves. Unwanted waves such as bulk waves exist to a depth of 10λ or more from the top surface of the piezoelectric layer 18. When the unwanted waves propagate downward, the energy of the acoustic wave leaks and the loss increases. On the other hand, when the bulk waves are reflected at the interface to the support substrate 10 and return to the IDT 51, they cause spurious responses.

[0034] The sound velocity of the bulk wave propagating through the boundary layer 12 is faster than the sound velocity of the bulk wave propagating through the temperature compensating layer 14. This makes it easier to confine the elastic wave in the piezoelectric layer 18 and the temperature compensating layer 14. The sound velocity of the bulk 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, faster than the sound velocity of the bulk wave propagating through the temperature compensating layer 14. If the sound velocity of the bulk 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 sound velocity of the bulk wave propagating through the boundary layer 12 is preferably 2.0 times or less, more preferably 1.5 times or less, faster than the sound velocity of the bulk wave propagating through the temperature compensating layer 14.

[0035] The sound 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. This allows the bulk wave to be effectively scattered by the convex portion 30 provided on the support substrate 10, thereby reducing spurious signals. The sound velocity of the bulk wave propagating through the support substrate 10 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 sound velocity of the bulk wave propagating through the boundary layer 12. The sound velocity of the bulk wave propagating through the support substrate 10 is preferably 2.0 times or less of the sound velocity of the bulk 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, 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] If the thickness T1 of the boundary layer 12 is thin, spurious responses will increase, so the thickness T1 of the boundary layer 12 is preferably 0.6 times (0.3λ) or more of the average pitch D of the electrode fingers 54, more preferably 1.4 times (0.7λ) or more, even more preferably 2 times (λ) or more, and even more preferably 4 times (2λ) or more.

[0037] The sound velocity of the bulk waves propagating through the temperature compensating layer 14 may be faster than the sound velocity of the bulk waves propagating through the piezoelectric layer 18, but is preferably slower than the sound velocity of the bulk waves propagating through the piezoelectric layer 18, so that elastic waves are more likely to exist in the temperature compensating layer 14. The sound velocity of the bulk waves propagating through the temperature compensating layer 14 is preferably 0.99 times or less the sound velocity of the bulk waves propagating through the piezoelectric layer 18. If the sound velocity of the bulk waves propagating through the temperature compensating layer 14 is too slow, elastic waves are less likely to exist in the piezoelectric layer 18. Therefore, the sound velocity of the bulk waves propagating through the temperature compensating layer 14 is preferably 0.9 times or more the sound velocity of the bulk waves propagating through the piezoelectric layer 18.

[0038] The sound velocity of the bulk wave propagating through the bonding layer 16 is faster than the sound velocity of the bulk 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, 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 T3 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 T3 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 functions as a protective film or a temperature compensation film.

[0040] The wavelength λ of the elastic wave is, for example, 1 μm to 6 μm. When two electrode fingers 54 are considered as one pair, the number of pairs is, for example, 20 pairs to 300 pairs. The duty ratio (thickness of electrode fingers 54) / (pitch of electrode fingers 54) of the IDT 51 is, for example, 30% to 70%. The aperture length of the IDT 51 is, for example, 10λ to 50λ.

[0041] [Manufacturing method] 3(a) to 4(c) are cross-sectional views showing a manufacturing method of the acoustic wave device 100 in accordance with the first embodiment. As shown in Fig. 3(a), a support substrate 10 having a flat upper surface is prepared, and a mask layer 82 having an opening is formed on the support substrate 10. The arithmetic mean roughness Ra of the upper surface of the support substrate 10 is, for example, 1 nm or less. The mask layer 82 is, for example, a photoresist.

[0042] 3(b), the upper part of the support substrate 10 is removed by, for example, etching using the mask layer 82 as a mask. For example, when the support substrate 10 is a sapphire substrate, the upper part of the support substrate 10 is removed by dry etching using a chlorine-based gas. At this time, etching conditions are used that allow etching of the support substrate 10 in the thickness direction to proceed quickly. For example, etching is performed under conditions of high gas pressure and / or bias voltage.

[0043] As shown in Fig. 3(c), the etching conditions are changed so that etching in a direction perpendicular to the thickness direction of the support substrate 10 proceeds faster than in Fig. 3(b), and the upper part of the support substrate 10 is removed using the mask layer 82 as a mask. For example, etching is performed under conditions in which the gas pressure and / or bias voltage is lowered or the etching gas ratio is changed. Then, the mask layer 82 is removed. As a result, a protrusion 30 is formed on the upper surface of the support substrate 10, which has linear slopes 32a, 32b inclined at different angles on each of the left and right side surfaces when viewed in cross section.

[0044] 4(a), a boundary layer 12 is formed on a support substrate 10 by a CVD (Chemical Vapor Deposition) method. The boundary layer 12 is formed on the support substrate 10 so as to fill in spaces between the protrusions 30 formed on the upper surface of the support substrate 10. Thereafter, the upper surface of the boundary layer 12 is planarized by, for example, a CMP (Chemical Mechanical Polishing) method.

[0045] 4(b), the temperature compensating layer 14 is formed on the boundary layer 12 by, for example, sputtering or CVD. Then, 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.

[0046] 4(c), the upper surface of the piezoelectric substrate 17 is polished by, for example, a CMP method to form a thin piezoelectric layer 18. An acoustic wave resonator 50 made of a metal film 57 is formed on the piezoelectric layer 18. In this way, the acoustic wave device 100 in accordance with the first embodiment is obtained.

[0047] [Comparative Example] Fig. 5 is a cross-sectional view of an acoustic wave device 1000 according to a comparative example. As shown in Fig. 5, in the acoustic wave device 1000, a convex portion 530 formed on the upper surface of a support substrate 10 has left and right side surfaces each formed with a linear inclination 532 inclined at a constant angle with respect to an imaginary straight line 80 when viewed in cross section. That is, in the first embodiment, the convex portion 30 has a shape having a two-step tapered side surface with different angles, whereas in the comparative example, the convex portion 530 has a shape having a one-step tapered side surface with a constant angle. The other configurations are the same as those in the first embodiment, and therefore description thereof will be omitted.

[0048] [Explanation of reflected waves] In the comparative example, the entire side surface of the protrusion 530 is formed at a constant angle, so that the bulk wave is reflected by one reflective surface, and a constant reflected wave is generated. On the other hand, in the first embodiment, the side surfaces of the protrusion 30 have different angles, so that the bulk wave is reflected by multiple reflective surfaces, and a variety of reflected waves are generated. Therefore, in the first embodiment, the bulk wave can be effectively scattered by the protrusion 30 provided on the support substrate 10, and spurious waves can be suppressed.

[0049] In addition, in the first embodiment, when the slope 32b is closer to a vertical than the slope 32a, the bulk wave is first reflected by the slope 32b and then reflected by the adjacent slope 32b immediately thereafter, which makes it easier to generate more diverse reflected waves. Therefore, the bulk wave can be scattered more effectively.

[0050] [Explanation of the period of the protrusions] FIG. 6(a) is a cross-sectional view showing an example of the period P of the convex portion 530 in the acoustic wave device 1000 according to the comparative example, and FIG. 6(b) is a cross-sectional view showing an example of the period P of the convex portion 30 in the acoustic wave device 100 according to the first embodiment. As shown in FIG. 6(a), in the convex portion 530 whose entire side surface is formed at a constant angle, it is difficult to narrow the period P of the convex portion 530 and to manufacture the convex portion 530 with a high height H in terms of durability of the mask layer for forming the convex portion 530. On the other hand, as shown in FIG. 6(b), in the convex portion 30 whose side surface is formed at a plurality of different angles, the etching conditions are changed during the formation of the convex portion 30, so that the convex portion 30 with a narrow period P and a high height H can be formed. Therefore, in the first embodiment, the degree of freedom in designing the period P and the height H of the convex portion 30 is increased. Since the period P having the spurious suppression effect varies depending on the wavelength of the unwanted wave, the wavelength band in which the spurious can be suppressed is widened in the first embodiment. From the viewpoint of suppressing spurious, the period P of the protrusions 30 is preferably 0.2 times (0.1λ) or more, and more preferably 0.4 times (0.2λ) or more, the average pitch D of the electrode fingers 54. From the viewpoint of increasing the response of the main mode, the period P of the protrusions 30 is preferably 10 times (5λ) or less, and more preferably 4 times (2λ) or less, the average pitch D of the electrode fingers 54. In addition, since the appropriate height H of the protrusions 30 changes depending on the frequency band (low band, mid band, or high band) in which the acoustic wave device is used, the first embodiment can be applied to acoustic wave devices of a wide frequency band.

[0051] According to the first embodiment, as shown in FIG. 1(a), FIG. 1(b), and FIG. 2, the support substrate 10 (first insulating layer) has a convex portion 30 formed on the upper surface. The convex portion 30 has a shape having a plurality of linear inclinations 32a, 32b inclined at different angles on each of the left and right side surfaces when viewed in cross section with respect to the surface 19 on which the comb-shaped electrode 53 of the piezoelectric layer 18 is provided. A boundary layer 12 (second insulating layer) is provided on the upper surface of the support substrate 10, and the piezoelectric layer 18 is provided on the boundary layer 12. A pair of comb-shaped electrodes 53 having a plurality of electrode fingers 54 that excite elastic waves are provided on the surface 19 of the piezoelectric layer 18. In this way, by forming the convex portion 30 into a shape having a plurality of inclinations 32a, 32b inclined at different angles on each of the left and right side surfaces when viewed in cross section, the bulk wave can be effectively scattered. Therefore, the spurious can be suppressed.

[0052] From the viewpoint of effectively scattering bulk waves, the height H2 (see FIG. 2) of the lower tapered portion of the protrusion 30 is preferably 10% or more, more preferably 30% or more, and even more preferably 50% of the height H1 (see FIG. 2) of the protrusion 30. The height H3 (see FIG. 2) of the upper tapered portion of the protrusion 30 is preferably 10% or more, more preferably 30% or more, and even more preferably 50% of the height H1 of the protrusion 30.

[0053] In the first embodiment, the angle (corresponding to α1 and α2 in FIG. 2) corresponding to the support substrate 10 side among the two angles formed by each of the multiple inclinations 32a and 32b with respect to the surface 19 of the piezoelectric layer 18 on which the comb-shaped electrode 53 is provided is 45° or more and less than 90°. As a result, the side surface of the protrusion 30 becomes close to vertical, so that the bulk wave reflected by the side surface of the protrusion 30 is prevented from returning to the IDT 51, and spurious can be suppressed. From the viewpoint of preventing the bulk wave reflected by the side surface of the protrusion 30 from returning to the IDT 51, the angle (corresponding to α1 and α2 in FIG. 2) corresponding to the support substrate 10 side among the two angles formed by each of the multiple inclinations 32a and 32b with respect to the surface 19 of the piezoelectric layer 18 is preferably 55° or more and less than 90°, more preferably 65° or more and less than 90°, and even more preferably 75° or more and less than 90°.

[0054] In addition, in the first embodiment, of the two angles each of the multiple slopes 32a, 32b forms with the surface 19 of the piezoelectric layer 18, the angle (corresponding to α1 and α2 in FIG. 2) corresponding to the supporting substrate 10 side increases in the order from the slope 32a closer to the piezoelectric layer 18 to the slope 32b farther from the piezoelectric layer 18. As a result, when a bulk wave is reflected at a portion of the side surface of the protrusion 30 that is located away from the piezoelectric layer 18, the bulk wave is immediately reflected by the adjacent side surface, which makes it easier to generate a variety of reflected waves, and therefore the bulk wave can be effectively scattered.

[0055] 1(b) and 2, in the first embodiment, the boundary layer 12 is filled in the bottom portion formed between adjacent convex portions 30 when viewed in cross section. This allows the bulk waves to be reflected by multiple surfaces of the convex portions 30 with different angles, thereby scattering the bulk waves effectively.

[0056] [Variations] FIG. 7(a) is a cross-sectional view of an acoustic wave device 110 according to a first modification of the first embodiment, and FIG. 7(b) is a cross-sectional view of an enlarged view of the vicinity of a protrusion 30 provided on a support substrate 10 in the first modification of the first embodiment. As shown in FIG. 7(a) and FIG. 7(b), in the acoustic wave device 110, the protrusion 30 provided on the support substrate 10 has a shape having a plurality of linear inclinations 32a, 32b, and 32c inclined at different angles on each of the left and right side surfaces when viewed in cross section. The angles α1, α2, and α3 between the virtual line 80 and the inclinations 32a, 32b, and 32c are 45° or more and less than 90°. The angle α1 between the virtual line 80 and the inclination 32a is smaller than the angle α2 between the virtual line 80 and the inclination 32b, and the angle α2 between the virtual line 80 and the inclination 32b is smaller than the angle α3 between the virtual line 80 and the inclination 32c. The angle α3 corresponds to the angle corresponding to the supporting substrate 10 side out of the two angles formed by the inclination 32c with the surface 19 of the piezoelectric layer 18. The other configurations are the same as those in the first embodiment, and therefore description thereof will be omitted.

[0057] In the first embodiment, the side surface of the protrusion 30 is inclined in two steps when viewed in cross section, but this is not limited to the above case. As in the first modified example of the first embodiment, the side surface of the protrusion 30 may be inclined in three steps when viewed in cross section. In this manner, the protrusion 30 formed on the upper surface of the support substrate 10 may have a shape with multiple linear inclinations inclined at different angles on each of the left and right side surfaces when viewed in cross section. Increasing the number of inclinations with different angles improves the scattering effect of the bulk wave, thereby improving the spurious suppression effect.

[0058] Fig. 8(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. 8(a), in the acoustic wave device 120, the boundary layer 12 is not embedded in the lower portion between adjacent convex portions 30. That is, the boundary layer 12 is embedded between the slopes 32a of the adjacent convex portions 30, but the boundary layer 12 is not embedded between the slopes 32b. Therefore, a gap 15 is formed in the lower portion between the adjacent convex portions 30. The other configurations are the same as those of the first embodiment, and therefore description thereof will be omitted.

[0059] Fig. 8(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. 8(b), in the acoustic wave device 130, the slopes 32b of the protrusions 30 are inversely tapered, and the gaps between the slopes 32b of adjacent protrusions 30 are not filled with the boundary layer 12 but form gaps 15. The other configurations are the same as those of the first embodiment, and therefore will not be described.

[0060] As in the second and third modified examples of the first embodiment, the lower portions between adjacent protrusions 30 may be gaps 15 .

[0061] [Example of arrangement of convex and concave parts] Fig. 9(a) is a plan view showing a first arrangement example of the convex portion 30 and the concave portion 31, and Fig. 9(b) and Fig. 9(c) are cross-sectional views taken along line AA in Fig. 9(a). Fig. 9(b) shows an example of the convex portion 30, and Fig. 9(c) shows an example of the concave portion 31.

[0062] As shown in FIG. 9(a) to FIG. 9(c), a plurality of convex portions 30 may be formed on the upper surface of the support substrate 10, or a plurality of concave portions 31 may be formed. Like the convex portions 30, the concave portions 31 are also symmetrical in cross section. The convex portions 30 and the concave portions 31 are periodically arranged. The three-dimensional shape of the convex portions 30 and the concave portions 31 is a substantially conical shape with a varying angle of the side surface. The points 30a and 31a are the apexes of the substantially conical shape. As shown in FIG. 9(b), the convex portions 30 are provided on a plane 60. As shown in FIG. 9(c), the concave portions 31 are provided on a plane 60. The directions of the closest period P among the periods of the convex portions 30 or the concave portions 31 are the three directions 62a, 62b, and 62c. The angle between the directions 62a to 62c is about 60°. The direction 62a is substantially parallel to the X direction. The period P of the protrusions 30 and the recesses 31 is approximately uniform, the interval W between the protrusions 30 and the recesses 31 in the directions 62a to 62c is approximately uniform, and the height H of the protrusions 30 and the recesses 31 is approximately uniform. The three-dimensional shape of the protrusions 30 and the recesses 31 may be, for example, an approximately cone shape such as an approximately conical or polygonal pyramid, an approximately truncated cone or an approximately truncated polygonal pyramid, etc. The plane 60 may not be provided between the protrusions 30 and the recesses 31.

[0063] Fig. 10(a) is a plan view showing a second arrangement example of the convex portion 30 and the concave portion 31, and Fig. 10(b) and Fig. 10(c) are cross-sectional views taken along line AA of Fig. 10(a). Fig. 10(b) shows an example of the convex portion 30, and Fig. 10(c) shows an example of the concave portion 31. In Fig. 10(a), the plane 60 is hatched for clarity.

[0064] As shown in FIG. 10(a) to FIG. 10(c), the convex portions 30 and the concave portions 31 are arranged periodically. The convex portions 30 and the concave portions 31 are linear or striped. The cross-sectional shape of the convex portions 30 and the concave portions 31 is a substantially triangular shape with a varying angle of the side surface. The lines 30b and 31b are lines connecting the vertices of the substantially triangular shapes of the convex portions 30 and the concave portions 31, respectively. The direction 62 of the smallest period P among the periods of the convex portions 30 and the concave portions 31 is substantially parallel to the X direction. The period P of the convex portions 30 and the concave portions 31 is substantially uniform, the interval W of the convex portions 30 and the concave portions 31 in the direction 62 is substantially uniform, and the height H of the convex portions 30 and the concave portions 31 is substantially uniform. The lines 30b and 31b may be straight or curved. The plane 60 may not be provided between the convex portions 30 and the concave portions 31.

[0065] In addition to the case where convex portions 30 or concave portions 31 are formed on the upper surface of the support substrate 10, both convex portions 30 and concave portions 31 may be formed. Furthermore, when concave portions 31 are formed on the upper surface of the support substrate 10, it is preferable that the boundary layer 12 fills the bottom of the concave portions 31 when viewed in cross section, from the viewpoint of effectively scattering bulk waves. EXAMPLES

[0066] FIG. 11 is a cross-sectional view of an acoustic wave device 200 according to a second embodiment. As shown in FIG. 11, in the acoustic wave device 200, a gap 40 is formed in the boundary layer 12 between adjacent convex portions 30, and between the inclination 32a located closest to the apex of the convex portion 30 among the multiple inclinations 32a, 32b. The other configurations are the same as those of the first embodiment, and therefore a description thereof will be omitted. The gap 40 is formed by depositing the boundary layer 12 using, for example, a sputtering method and appropriately setting the deposition conditions of the sputtering method at this time. Note that the boundary layer 12 having the gap 40 may be formed by depositing the film using other methods.

[0067] According to the second embodiment, a void 40 is formed in the boundary layer 12, adjacent to the void 32a located closest to the piezoelectric layer 18 among the multiple slants 32a, 32b forming the convex portion 30 in cross section. By forming the void 40 in the boundary layer 12, in addition to the bulk waves being scattered by the convex portion 30 formed on the support substrate 10, the bulk waves are also scattered by the void 40. Therefore, the bulk waves can be effectively scattered, and spurious emissions can be suppressed.

[0068] In Examples 1 and 2, an example was shown in which three insulating layers, namely, a boundary layer 12, a temperature compensation layer 14, and a bonding layer 16, are provided between the support substrate 10 and the piezoelectric layer 18, but it is also possible that only one insulating layer is provided. EXAMPLES

[0069] FIG. 12(a) is a cross-sectional view of an acoustic wave device 300 in accordance with a third embodiment, and FIG. 12(b) is an enlarged cross-sectional view of the vicinity of a protrusion 34 formed on the boundary layer 12. As shown in FIGS. 12(a) and 12(b), in the acoustic wave device 300, the boundary layer 12 includes a lower layer 12a and an upper layer 12b. The interface between the lower layer 12a and the support substrate 10 is a flat surface. The interface between the lower layer 12a and the upper layer 12b is an uneven surface. A plurality of protrusions 34 are formed on the upper surface of the lower layer 12a. The protrusions 34 are regularly arranged.

[0070] The convex portion 34 provided on the lower layer 12a has a shape in which, when viewed in cross section, the left and right side surfaces have linear inclinations 36a and 36b inclined at different angles with respect to the surface 19 on which the comb-shaped electrode 53 of the piezoelectric layer 18 is provided. The inclination 36a is an inclination that forms a step on the side closer to the apex of the convex portion 34, and the inclination 36b is an inclination that forms a step on the side farther from the apex of the convex portion 34. Each step may be formed only by the linear inclinations 32a and 32b, or may include a curved line in part. The linear inclination is not limited to a completely straight line, but allows an approximately linear inclination having a curve or step of the order of manufacturing error. The angles β1 and β2 formed by the virtual straight line 80 and the inclinations 36a and 36b are 45° or more and less than 90°. The angle β1 formed by the virtual straight line 80 and the inclination 36a is smaller than the angle β2 formed by the virtual straight line 80 and the inclination 36b. The angle β1 corresponds to the angle corresponding to the lower layer 12a side of the two angles that the slope 36a forms with the surface 19 of the piezoelectric layer 18, and the angle β2 corresponds to the angle corresponding to the lower layer 12a side of the two angles that the slope 36b forms with the surface 19 of the piezoelectric layer 18. The other configurations are the same as those in the first embodiment, and therefore description thereof will be omitted. The protrusions 34 formed on the lower layer 12a are formed by the same method as the protrusions 30 formed on the support substrate 10 in the first embodiment.

[0071] According to the third embodiment, a lower layer 12a (first insulating layer) of the boundary layer 12 has a convex portion 34 formed on the upper surface. The convex portion 34 has a shape with a plurality of linear inclinations 36a, 36b inclined at different angles with respect to the surface 19 of the piezoelectric layer 18 on each of the left and right side surfaces when viewed in cross section. An upper layer 12b (second insulating layer) of the boundary layer 12 is provided on the upper surface of the lower layer 12a, and the piezoelectric layer 18 is provided on the upper layer 12b. A pair of comb-shaped electrodes 53 having a plurality of electrode fingers 54 that excite elastic waves are provided on the piezoelectric layer 18. Therefore, similar to the first embodiment, the bulk wave can be effectively scattered, and spurious can be suppressed.

[0072] In the third embodiment, similarly to the first embodiment, a convex portion 34 may be formed on the upper surface of the lower layer 12a, or a concave portion may be formed. The convex portion 34 and the concave portion may be arranged in the same manner as in Fig. 9(a) to Fig. 9(c) or Fig. 10(a) to Fig. 10(c). Also, in the third embodiment, the arrangement between the lower layer 12a of the boundary layer 12 and the piezoelectric layer 18 is not limited to the arrangement in which three insulating layers, the upper layer 12b of the boundary layer 12, the temperature compensation layer 14, and the bonding layer 16, are provided, and one insulating layer may be provided. EXAMPLES

[0073] FIG. 13(a) is a cross-sectional view of an acoustic wave device 400 according to a fourth embodiment, and FIG. 13(b) is a cross-sectional view enlarging the vicinity of recesses 42, 46 formed in the support substrate 10 and the lower layer 12c of the boundary layer 12 in the fourth embodiment. As shown in FIG. 13(a) and FIG. 13(b), the acoustic wave device 400 has a recess 42 formed in the support substrate 10. The recess 42 has a shape having a linear inclination 44 inclined at a certain angle with respect to the surface 19 on which the comb-shaped electrode 53 of the piezoelectric layer 18 is provided on each of the left and right sides when viewed in cross section. The boundary layer 12 formed on the upper surface of the support substrate 10 includes a lower layer 12c and an upper layer 12d. The lower layer 12c is formed on the upper surface of the support substrate 10 so as to fill at least a part of the recess 42 formed in the support substrate 10, and a recess 46 is formed. The side surface of the recess 46 is continuous with the side surface of the recess 42. When viewed in cross section, the recess 46 has a shape with linear inclinations 48 on each of the left and right side surfaces that are inclined at an angle different from the inclination 44 of the recess 42 relative to the surface 19 on which the comb-shaped electrodes 53 of the piezoelectric layer 18 are provided.

[0074] The angles γ1 and γ2 between the virtual line 80 and the inclinations 44 and 48 are 45° or more and less than 90°. The angle γ1 between the virtual line 80 and the inclination 44 is smaller than the angle γ2 between the virtual line 80 and the inclination 48. The angle γ1 corresponds to the angle corresponding to the support substrate 10 side of the two angles formed by the inclination 44 with respect to the surface 19 of the piezoelectric layer 18, and the angle γ2 corresponds to the angle corresponding to the lower layer 12c side of the two angles formed by the inclination 48 with respect to the surface 19 of the piezoelectric layer 18. The upper layer 12d is provided on the lower layer 12c so as to fill the recess 46. The other configurations are the same as those of the first embodiment, so a description thereof will be omitted. The recess 46 in the lower layer 12c is formed by forming the lower layer 12c on the supporting substrate 10 so as to fill the recess 42 formed in the supporting substrate 10, planarizing the lower layer 12c by a CMP method or the like, and then removing the lower layer 12c above the recess 42 by an etching method or the like.

[0075] According to the fourth embodiment, the support substrate 10 (first insulating layer) has a recess 42 formed on the upper surface thereof, the recess 42 having a linear inclination 44 (first straight line) inclined with respect to the surface 19 of the piezoelectric layer 18 on each of the left and right side surfaces when viewed in cross section. The lower layer 12c (second insulating layer) of the boundary layer 12 is provided on the upper surface of the support substrate 10, and a recess 46 having a side surface continuous with the side surface of the recess 42 is formed. The recess 46 has a linear inclination 48 (second straight line) inclined at an angle different from the inclination 44 on each of the left and right side surfaces when viewed in cross section. The piezoelectric layer 18 is provided on the upper layer 12d, and a pair of comb-shaped electrodes 53 having a plurality of electrode fingers 54 for exciting an elastic wave is provided on the piezoelectric layer 18. As a result, the recess 42 and the recess 46 form a recess having a shape having a plurality of inclinations 44, 48 with different angles on each of the left and right side surfaces when viewed in cross section, so that the bulk wave can be effectively scattered and spurious can be suppressed.

[0076] In the fourth embodiment, the recess 42 is formed in the support substrate 10, and the recess 46 is formed in the lower layer 12c of the boundary layer 12. However, the upper surface of the support substrate 10 may be flat, the recess 42 is formed in the lower layer 12c of the boundary layer 12, and the recess 46 is formed in the upper layer 12d of the boundary layer 12. In this case, it is preferable that the boundary layer 12 has a top layer with a flat upper surface on the upper layer 12d. In the fourth embodiment, the gap between the lower layer 12c of the boundary layer 12 and the piezoelectric layer 18 is not limited to three insulating layers, namely, the upper layer 12d of the boundary layer 12, the temperature compensation layer 14, and the bonding layer 16, and may be one insulating layer. EXAMPLES

[0077] FIG. 14 is a circuit diagram of a filter 500 according to a fifth embodiment. As shown in FIG. 14, in the filter 500, 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 device according to the first to fourth embodiments 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. EXAMPLES

[0078] FIG. 15 is a block diagram of a duplexer 600 according to a sixth embodiment. As shown in FIG. 15, in the duplexer 600, a transmission filter 70 is connected between a common terminal Ant and a transmission terminal Tx, and a reception filter 72 is connected between the common terminal Ant and a reception terminal Rx. The transmission filter 70 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 72 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 70 and the reception filter 72 can be the filter of the fifth embodiment.

[0079] Although a duplexer has been described as an example of a multiplexer, a triplexer or a quadplexer may also be used.

[0080] 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]

[0081] 10 Support substrate 12 Boundary layer 12a, 12c lower layer 12b, 12d upper layer 14 Temperature compensation layer 15 void 16 Bonding layer 18 Piezoelectric layer 19 sides 30 Convex 31 Recess 32a, 32b, 32c slope 34 Convex 36a, 36b slope 40 void 42, 46 Recess 44, 48 incline 50 Elastic Wave Resonator 51 IDT 52 Reflector 53 Comb-shaped electrode 54 Electrode finger 55 Busbar 70 Transmission Filter 72 Receiving Filter 80 Imaginary Line 530 Convex 532 Incline 100, 110, 120, 130, 200, 300, 400, 1000 Acoustic Wave Devices 500 Filters 600 Duplexer

Claims

1. A piezoelectric layer; a pair of comb-shaped electrodes provided on one surface of the piezoelectric layer and having a plurality of electrode fingers for exciting an acoustic wave; a first insulating layer provided on the other surface side of the piezoelectric layer, the first insulating layer having a plurality of linearly inclined convex portions and / or concave portions on each of left and right side surfaces on the piezoelectric layer side when viewed in cross section, the convex portions and / or concave portions having a shape inclined at different angles with respect to the one surface of the piezoelectric layer; A second insulating layer is provided between the piezoelectric layer and the first insulating layer on the surface of the first insulating layer on which the convex portions and / or concave portions are formed.

2. The acoustic wave device of claim 1 , wherein when viewed in cross section, one of the two angles formed by each of the multiple inclinations with respect to the one surface of the piezoelectric layer is an angle corresponding to the first insulating layer side that is greater than or equal to 45° and less than 90°.

3. The acoustic wave device according to claim 2 , wherein the angle of each of the plurality of inclinations corresponding to the first insulating layer side increases in the order of the inclinations from the inclination closer to the piezoelectric layer to the inclinations farther from the piezoelectric layer.

4. The acoustic wave device according to claim 1 , wherein the second insulating layer is filled in a bottom of the recess and / or a bottom formed between adjacent ones of the protrusions when viewed in cross section.

5. 5. The elastic wave device according to claim 1, wherein the second insulating layer has a gap arranged adjacent to the slope that is closest to the piezoelectric layer among the plurality of slopes that form the convex portion and / or concave portion when viewed in cross section.

6. A piezoelectric layer; a pair of comb-shaped electrodes provided on one surface of the piezoelectric layer and having a plurality of electrode fingers for exciting an acoustic wave; a first insulating layer provided on the other surface side of the piezoelectric layer, the first insulating layer having a plurality of first recesses on the left and right side surfaces on the piezoelectric layer side when viewed in cross section, the first recesses having a shape with a linear first inclination inclined with respect to the one surface of the piezoelectric layer; an elastic wave device comprising: a second insulating layer provided between the piezoelectric layer and the first insulating layer, having a side surface continuous with a side surface of the first recess, and having a second recess on each of the left and right side surfaces when viewed in cross section, the second recess having a shape having a linear second inclination inclined at an angle different from the first inclination relative to the one surface of the piezoelectric layer.

7. The acoustic wave device according to claim 1 , 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.

8. 7. 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 third insulating layer mainly composed of silicon oxide is provided between the second insulating layer and the piezoelectric layer; The acoustic wave device according to claim 1 , wherein a bulk wave propagates through the second insulating layer at a faster acoustic velocity than through the third insulating layer.

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

11. A multiplexer comprising the filter of claim 10.

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