Acoustic wave device, wafer, and wafer manufacturing method

Abstract

To provide an acoustic wave device that reduces spurious while suppressing deterioration of main response.SOLUTION: An acoustic wave device includes a support substrate 10, a piezoelectric layer 15 provided on the support substrate 10, at least a pair of comb-shaped electrodes 20 provided on the piezoelectric layer 15 and having a plurality of electrode fingers 18, and an insulating layer 17 provided between the support substrate 10 and the piezoelectric layer 15, and having a plurality of void regions in which at least some of them have different orientations in the stretching direction, which is a direction having a width longer than the width in the orthogonal direction, viewed from the thickness direction of the support substrate 10.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Acoustic wave elements such as surface acoustic wave resonators are used in communication devices such as smartphones. It is known that a piezoelectric layer forming the acoustic wave element is bonded to a support substrate. It is also known that the upper surface of the support substrate is roughened (for example, Patent Document 1). It is also known that a layer having a cavity is provided between the support substrate and the piezoelectric layer (for example, Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-61258 [Patent Document 2] Special Publication No. 2020-510354 Summary of the Invention [Problem to be solved by the invention]

[0004] Spurious signals can be reduced by roughening the top surface of the support substrate. Also, spurious signals can be reduced by providing a layer with a cavity between the support substrate and the piezoelectric layer. However, there is still room for improvement in terms of reducing spurious signals while suppressing degradation of the main response.

[0005] The present invention has been made in view of the above-mentioned problems, and has as its object to reduce spurious signals. [Means for solving the problem]

[0006] The present invention provides an optical fiber having a piezoelectric element, the piezoelectric element comprising: a support substrate; a piezoelectric layer provided on the support substrate; at least one pair of comb-shaped electrodes provided on the piezoelectric layer and each having a plurality of electrode fingers; and an insulating layer provided between the support substrate and the piezoelectric layer, the insulating layer having a plurality of void regions whose extension directions, which are a direction having a width longer than a width in a direction perpendicular to the thickness direction of the support substrate, are different from each other in at least a part of the thickness direction of the support substrate; The interface between the support substrate and the insulating layer is an uneven surface, and the plurality of void regions overlap with the concave portions of the uneven surface. It is an acoustic wave device.

[0007] In the above configuration, a plurality of void regions having different stretching directions may be connected to each other to form one void region.

[0008] In the above configuration, the one void region may have a shape in which the void extends in a plurality of directions from one point when viewed in the thickness direction of the support substrate.

[0009] In the above configuration, the one void region may be configured to surround a part of the insulating layer when viewed in the thickness direction of the support substrate.

[0010] In the above configuration, In a cross section in the thickness direction of the support substrate, The area of ​​the plurality of void regions may be 1% or more of the area of ​​the insulating layer including the plurality of void regions.

[0013] In the above configuration, In the thickness direction of the support substrate The cross-sectional shape of the plurality of void regions may be configured such that the width on the piezoelectric layer side is narrower than the width on the support substrate side.

[0014] In the above configuration, the distance between the plurality of void regions and the piezoelectric layer may be equal to or greater than the average pitch of the plurality of electrode fingers.

[0015] In the above configuration, the insulating layer may include a first insulating layer provided on the support substrate, having the plurality of void regions and through which the plurality of void regions pass, and a second insulating layer provided on the first insulating layer and having no void regions.

[0016] The above-described configuration may further include a third insulating layer provided on the second insulating layer, the third insulating layer having a sound velocity slower than that of the first insulating layer and the second insulating layer.

[0017] The present invention provides a piezoelectric element comprising: a support substrate; a piezoelectric layer provided on the support substrate; and an insulating layer provided between the support substrate and the piezoelectric layer, the insulating layer having a plurality of void regions whose extension directions, which are a direction having a width longer than a width in a direction perpendicular to the thickness direction of the support substrate, are different from each other in at least a part of the thickness direction of the support substrate, The interface between the support substrate and the insulating layer is an uneven surface, and the plurality of void regions overlap with the concave portions of the uneven surface. It is a wafer.

[0018] The present invention is a method for manufacturing a wafer, including the steps of: forming an insulating layer on a support substrate having an uneven surface, the insulating layer having a plurality of first void regions that contact the recesses of the uneven surface; etching the insulating layer that contacts the plurality of first void regions to form in the insulating layer a plurality of second void regions that have different orientations in extension directions, which are directions that have a width longer than the width in a perpendicular direction, at least in a portion of the thickness direction of the support substrate; and forming a piezoelectric layer on the insulating layer. [Effects of the Invention]

[0019] According to the present invention, spurious signals can be reduced. [Brief explanation of the drawings]

[0020] [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 of the acoustic wave device in accordance with the first embodiment. [Figure 2] FIG. 2 is a plan view of the upper surface of the insulating layer 11 in the first embodiment. [Figure 3] 3A to 3C are cross-sectional views illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Figure 4] 4A to 4C are cross-sectional views illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Figure 5] FIG. 5 is a cross-sectional view of an acoustic wave device in accordance with Comparative Example 2. As shown in FIG. [Figure 6] FIG. 6 is a graph showing the admittance |Y| versus frequency for samples A1 and B1 in the experiment. [Figure 7] FIG. 7 is a graph showing the admittance |Y| versus frequency for samples A2 and B2 in the experiment. [Figure 8] FIG. 8 is a graph showing the admittance |Y| versus frequency for samples A3 and B3 in the experiment. [Figure 9] FIG. 9 is a graph showing the admittance |Y| versus frequency of sample C1 in the experiment. [Figure 10] FIG. 10 is a cross-sectional view of an acoustic wave device in accordance with a first modification of the first embodiment. [Figure 11] 11(a) and 11(b) are graphs showing admittance |Y| versus frequency for samples A1 and D1 in Experiment 2. FIG. [Figure 12] FIG. 12 is a cross-sectional view of an acoustic wave device in accordance with a second modification of the first embodiment. [Figure 13] FIG. 13 is a plan view of the upper surface of the insulating layer 11 according to the second modification of the first embodiment. [Figure 14] FIG. 14 is a plan view of the upper surface of the insulating layer 11 according to the third modification of the first embodiment. [Figure 15] 15(a) and 15(b) are cross-sectional views of acoustic wave devices according to fourth and fifth modifications of the first embodiment, respectively. [Figure 16] FIG. 16(a) is a circuit diagram of a filter according to the second embodiment, and FIG. 16(b) is a circuit diagram of a duplexer according to a first modification of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [Example]

[0022] 1(a) is a plan view of an acoustic wave device according to a first embodiment, and FIG. 1(b) is a cross-sectional view of the acoustic wave device according to the first embodiment. The arrangement direction of the electrode fingers is the X direction, the extension direction of the electrode fingers is the Y direction, and the stacking direction of the support substrate and the piezoelectric layer is the Z direction. The X direction, Y direction, and Z direction do not necessarily correspond to the X axis direction and Y axis direction of the crystal orientation of the piezoelectric layer. When the piezoelectric layer is a rotated Y-cut X-propagation substrate, the X direction is the X axis direction of the crystal orientation.

[0023] As shown in FIGS. 1(a) and 1(b), the acoustic wave device of Example 1 includes a piezoelectric layer 15 provided on a support substrate 10. An insulating layer 17 is provided between the support substrate 10 and the piezoelectric layer 15. The insulating layer 17 includes insulating layers 11 to 14 provided on the support substrate 10. A surface 31 of the support substrate 10 corresponds to the interface between the support substrate 10 and the insulating layer 11 and is an uneven surface. A surface 32 of the insulating layer 11 corresponds to the interface between the insulating layers 11 and 12 and is an uneven surface. A surface 33 of the insulating layer 12 corresponds to the interface between the insulating layer 12 and the insulating layer 13 and is a flat surface. A surface 34 of the insulating layer 13 corresponds to the interface between the insulating layer 13 and the insulating layer 14 or the piezoelectric layer 15 and is a flat surface. The thicknesses of the insulating layers 11 to 14 and the piezoelectric layer 15 are T1 to T5, respectively. Because surfaces 31 and 32 are uneven surfaces, the thicknesses of the insulating layers 11 and 12 are average thicknesses. The height H1 of the gap 30 is approximately equal to the thickness T1 of the insulating layer 11. The distance H2 between the tip of the gap 30 and the lower surface of the piezoelectric layer 15 is approximately equal to the total thickness of the insulating layers 12 to 14. T2+T3+T4 is.

[0024] Surface 31 has protrusions 31a and recesses 31b. The protrusions and recesses on surfaces 31 and 32 correspond to each other. The protrusions and recesses on surfaces 31 and 32 do not have to correspond to each other. Protrusions 31a and recesses 31b are arranged irregularly. Spacings D1a to D1c between protrusions 31a are different from one another. Insulating layer 11 has a plurality of voids 30 extending in the Z direction and penetrating insulating layer 11. Width W1 of voids 30 on the piezoelectric layer 15 side is narrower than width W2 of voids 30 on the support substrate 10 side. No voids are provided in insulating layers 12 to 14.

[0025] An acoustic wave resonator 26 is provided on the piezoelectric layer 15. The acoustic wave resonator 26 has an IDT 22 and a reflector 24. The reflectors 24 are provided on both sides of the IDT 22 in the X direction. The IDT 22 and the reflector 24 are formed by a metal film 16 on the piezoelectric layer 15.

[0026] The IDT 22 includes a pair of opposing comb electrodes 20. The comb electrodes 20 include a plurality of electrode fingers 18 and a bus bar 19 to which the plurality of electrode fingers 18 are connected. The region where the electrode fingers 18 of the pair of comb electrodes 20 intersect as viewed from the X direction is an intersection region 25. The length of the intersection region 25 is the aperture length. The pair of comb electrodes 20 have the electrode fingers 18 arranged alternately in at least a portion of the intersection region 25. Acoustic waves excited primarily by the plurality of electrode fingers 18 in the intersection region 25 propagate primarily in the X direction. The pitch of the electrode fingers 18 of one of the pair of comb electrodes 20 is approximately the wavelength λ of the acoustic wave. If the pitch of the plurality of electrode fingers 18 (the pitch between the centers of the electrode fingers 18) is D, the pitch of the electrode fingers 18 of one of the comb electrodes 20 is D, which is the pitch of two electrode fingers 18. The reflector 24 reflects the acoustic waves (surface acoustic waves) excited by the electrode fingers 18 of the IDT 22. As a result, the acoustic waves are confined within the crossing region 25 of the IDT 22.

[0027] The piezoelectric layer 15 is, for example, a single-crystal lithium tantalate (LiTaO3) layer or a single-crystal lithium niobate (LiNbO3) layer, such as a rotated Y-cut X-propagation lithium tantalate layer or a rotated Y-cut X-propagation lithium niobate layer. The thickness T5 of the piezoelectric layer 15 is preferably 1λ or less, more preferably 0.5λ or less, from the viewpoint of suppressing spurious and loss. If the piezoelectric layer 15 is too thin, it becomes difficult to excite an acoustic wave, so the thickness T5 is preferably 0.1λ or more.

[0028] The support substrate 10 may be, for example, a sapphire substrate, alumina substrate, silicon substrate, spinel substrate, quartz substrate, or silicon carbide substrate. The sapphire substrate is a single-crystal Al2O3 substrate, the alumina substrate is a polycrystalline or amorphous Al2O3 substrate, the silicon substrate is a single-crystal or polycrystalline silicon substrate, the spinel substrate is a polycrystalline or amorphous MgAl2O4 substrate, the quartz substrate is a single-crystal SiO2 substrate, the quartz substrate is a polycrystalline or amorphous 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 that of the piezoelectric layer 15 in the X direction. This reduces the frequency temperature dependence of the acoustic wave resonator. The acoustic velocity of bulk waves propagating through the support substrate 10 is faster than that of bulk waves propagating through the insulating layers 11 and 12. The acoustic velocity of the bulk waves propagating through the support substrate 10 may be slower than the acoustic velocity of the bulk waves propagating through the insulating layers 11 and 12 .

[0029] The acoustic velocity of bulk waves propagating through insulating layers 11 and 12 is faster than that of bulk waves propagating through insulating layer 13. This confines the energy of the main response elastic wave within piezoelectric layer 15 and insulating layer 13. Insulating layers 11 and 12 are, for example, polycrystalline or amorphous, and may be aluminum oxide, silicon nitride, aluminum nitride, silicon, or silicon carbide films. The thickness T1 of insulating layer 11 is preferably 0.2λ or greater, more preferably 0.5λ or greater, from the viewpoint of increasing the height of gap 30. The thickness T2 of insulating layer 12 is preferably 0.3λ or greater, more preferably 1λ or greater, from the viewpoint of confining the elastic wave within insulating layer 13 and piezoelectric layer 15. The main response may be degraded if insulating layer 11 is too close to piezoelectric layer 15. To improve performance, the thicknesses T1 and T2 are each preferably 10λ or less.

[0030] The insulating layer 13 is, for example, a temperature compensation film, and has a temperature coefficient of elastic constant with a sign opposite to that of the piezoelectric layer 15. For example, the temperature coefficient of elastic constant of the piezoelectric layer 15 is negative, while the temperature coefficient of elastic constant of the insulating layer 13 is positive. The insulating layer 13 is an insulating layer mainly composed of silicon oxide (SiO2), for example, a silicon oxide (SiO2) film with no additives or additives such as fluorine, and is, for example, polycrystalline or amorphous. Furthermore, the insulating layer 13 is not limited to a polycrystalline or amorphous silicon oxide film, but may also be single-crystal quartz (SiO2). This reduces the frequency temperature coefficient of the acoustic wave resonator. When the insulating layer 13 is a silicon oxide film, the sound velocity of the bulk wave propagating through the insulating layer 13 is slower than the sound velocity of the bulk wave propagating through the piezoelectric layer 15.

[0031] In order for insulating layer 13 to have a temperature compensation function, it is necessary that a certain amount of energy of the main response acoustic wave is present within insulating layer 13. Although the range in which the energy of the surface acoustic wave is concentrated depends on the type of surface acoustic wave, the energy of the surface acoustic wave is typically concentrated within a range of 2λ (λ is the wavelength of the acoustic wave) from the top surface of piezoelectric layer 15, and is particularly concentrated within a range of λ from the top surface of piezoelectric layer 15. Therefore, the distance from the bottom surface of insulating layer 13 to the top surface of piezoelectric layer 15 (thickness T3+T4+T5) is preferably 2λ or less, and more preferably 1λ or less.

[0032] The insulating layer 14 is, for example, a bonding layer that bonds the insulating layer 13 and the piezoelectric layer 15. If the insulating layer 13 is a silicon oxide film, it is difficult to directly bond the piezoelectric layer 15 and the insulating layer 13 using a surface activation method. In such a case, an insulating layer made of a material different from that of the insulating layer 13 is provided as the insulating layer 14. The insulating layer 14 is, for example, polycrystalline or amorphous, and is an aluminum oxide film, a silicon nitride film, an aluminum nitride film, a silicon film, or a silicon carbide film. To confine the energy of the elastic wave within the insulating layer 13, the thickness T4 of the insulating layer 14 is preferably 100 nm or less. To allow the insulating layer 14 to function as a bonding layer, the thickness T4 is preferably 1 nm or more.

[0033] The metal film 16 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 18 and the piezoelectric layer 15. The adhesive film is thinner than the electrode fingers 18. An insulating layer may be provided to cover the electrode fingers 18. The insulating layer functions as a protective film or a temperature compensation film.

[0034] The wavelength λ of the acoustic wave is, for example, 1 μm to 6 μm. When two electrode fingers 18 are considered as one pair, the number of pairs is, for example, 20 to 300 pairs. The duty ratio of the IDT 22 is (thickness of the electrode fingers 18) / (pitch of the electrode fingers 18), and is, for example, 30% to 70%. The aperture length of the IDT 22 is, for example, 10λ to 50λ. The wavelength λ of the acoustic wave is twice the average pitch D of the electrode fingers 18. The average pitch of the electrode fingers 18 can be calculated by dividing the width of the IDT 22 in the X direction by the number of electrode fingers 18.

[0035] FIG. 2 is a plan view of the upper surface of the insulating layer 11 in Example 1. As shown in FIG. 2, the planar shape of the voids 30 is irregular. In the void 30b, the multiple voids 36a to 36d each have center lines 35a to 35d that extend in different directions. For example, the center lines 35a to 35c extend in three different directions from a single point. In this way, in the void 30b, the multiple voids 36a to 36c extend radially from a single point. The voids 36a to 36d each have a planar shape in which the width in the extension direction is wider than the width perpendicular to the extension direction, and the extension directions of the voids 36a to 36d are different from one another.

[0036] In the voids 30c, the plurality of voids 36e-36i have center lines 35e-35i extending in different directions, and the plurality of voids 36e-36i are provided so as to surround a partial region 11a of the insulating layer 11. The voids 36e-36i each have a planar shape whose width in the extension direction is greater than the width perpendicular to the extension direction, and the extension directions of the voids 36e-36i are different from one another.

[0037] The voids 30a have a complex planar shape that includes a planar shape in which a plurality of voids extend radially from one point and a planar shape in which a portion of the insulating layer 11 is surrounded by a plurality of voids.

[0038] The voids 30d to 30f are single voids 36j to 36l, respectively, and the center lines 35j to 35l of the voids 36j to 36l extend in directions different from one another.

[0039] [Manufacturing method of Example 1] 3(a) to 4(c) are cross-sectional views illustrating a method for manufacturing an acoustic wave device according to Example 1. The manufacturing method illustrated in Fig. 3(a) to 4(c) is performed in a wafer state, and the acoustic wave device according to Example 1 is finally formed by singulating the wafer. Although multiple acoustic wave devices are formed on the wafer, Fig. 3(a) to 4(c) illustrate only one acoustic wave device.

[0040] As shown in FIG. 3(a), a wafer-shaped support substrate 10 is prepared. Before processing, the upper surface of the support substrate 10 is flat, and the arithmetic mean roughness Ra of the support substrate 10 is, for example, 1 nm or less. The surface 31 of the support substrate 10 is ground or polished to make the surface 31 a rough surface. The surface 31 may be roughened by, for example, etching. As a result, a plurality of protrusions 31a and a plurality of recesses 31b are formed on the surface 31. The arithmetic mean roughness Ra of the surface of the support substrate 10 is, for example, 0.1 μm or more.

[0041] As shown in FIG. 3(b), the insulating layer 11 is formed on the surface 31 of the support substrate 10 by, for example, sputtering. Sputtering does not provide good coverage for uneven surfaces. Therefore, by appropriately setting the sputtering deposition conditions, voids 30 extending from the recesses 31b in the Z direction are formed in the insulating layer 11. The width W3 of the voids 30 is, for example, 100 nm or less, such as 10 nm or less. The surface 32 of the insulating layer 11 has an uneven surface that reflects the unevenness of the surface 31 of the support substrate 10. The surface 32 may have an arithmetic mean roughness Ra similar to that of the surface 31, or may have an uneven surface that is smoother than the surface 31 (i.e., a smaller Ra than the surface 31). The insulating layer 11 may be formed by chemical vapor deposition (CVD) instead of sputtering.

[0042] As shown in FIG. 3(c), the insulating layer 11 in contact with the void 30 is removed by etching. For example, wet etching is used as the etching method. When an etching solution penetrates into the void 30, the insulating layer 11 in contact with the void 30 is etched. For example, when the etching solution penetrates along the grain boundary, the insulating layer 11 near the grain boundary is etched, forming the void 30 with a complex planar shape as shown in FIG. 2. Furthermore, the insulating layer 11 tends to be sparse around the grain boundary near the support substrate 10. Therefore, the insulating layer 11 around the grain boundary near the support substrate 10 is more easily etched than the insulating layer 11 around the upper grain boundary. Therefore, the width W2 of the void 30 on the support substrate 10 side is larger than the width W1 of the void 30 on the upper surface side. The widths W1 and W2 of the void 30 are larger than the width W3 of the void 30 in FIG. 3(b), and are, for example, 100 nm or more.

[0043] As shown in FIG. 4(a), insulating layer 12 is formed on surface 32 of insulating layer 11. The upper surface of insulating layer 12 is planarized using, for example, CMP (Chemical Mechanical Polishing). Insulating layers 13 and 14 are formed on insulating layer 12. Insulating layers 12-14 are formed by, for example, sputtering, vacuum deposition, or CVD. When insulating layers 12 and 14 are aluminum oxide films, insulating layers 12 and 14 are formed by, for example, sputtering. When insulating layer 13 is a silicon oxide film, insulating layer 13 is formed by, for example, CVD. Insulating layer 17 is formed from insulating layers 11-14.

[0044] As shown in Fig. 4(b), the insulating layer 14 and the piezoelectric layer 15 are bonded together. The insulating layer 13 and the piezoelectric layer 15 may be bonded directly to each other without the insulating layer 14. For example, a surface activation method may be used for bonding. The insulating layer 14 may be made of an adhesive such as a resin, and the insulating layer 13 and the piezoelectric layer 15 may be bonded together via the adhesive.

[0045] As shown in FIG. 4(c), the upper surface of the piezoelectric layer 15 is planarized by, for example, CMP to thin the piezoelectric layer 15. This completes the manufacture of a wafer for manufacturing an acoustic wave device. Then, as shown in FIG. 1(b), an acoustic wave resonator 26 made of a metal film 16 is formed on the upper surface of the piezoelectric layer 15. Finally, the wafer is diced into individual pieces to manufacture the acoustic wave device 100 according to the first embodiment.

[0046] [Experiment 1] Seven samples A1 to A3, B1 to B3, and C1 were created and an experiment to evaluate spurious emissions was conducted under the following experimental conditions.

[0047] Sample A1 Elastic wave wavelength λ: 6.0 μm Support substrate 10: sapphire substrate Surface 31: Rough surface with arithmetic mean roughness Ra of 0.15 μm Insulating layer 11: Aluminum oxide layer with a thickness T1 of 0.5λ Width of the gap 30: 0.1 to several μm Insulating layer 12: Aluminum oxide layer with thickness T2 of 1.5λ Insulating layer 13: silicon oxide layer with a thickness T3 of 0.2λ Insulation layer 14: Yes Piezoelectric layer 15: 42° rotated Y-cut X-propagating lithium tantalate layer with a thickness T4 of 0.3λ Metal film 16: Aluminum film with a thickness of 0.1λ

[0048] Sample A2 Elastic wave wavelength λ: 2.0 μm Support substrate 10: sapphire substrate Surface 31: Rough surface with arithmetic mean roughness Ra of 0.15 μm Insulating layer 11: Aluminum oxide layer with thickness T1 of 1.5λ Width of the gap 30: 0.1 to several μm Insulating layer 12: Aluminum oxide layer with thickness T2 of 1.5λ Insulating layer 13: silicon oxide layer with a thickness T3 of 0.2λ Insulation layer 14: Yes Piezoelectric layer 15: 42° rotated Y-cut X-propagating lithium tantalate layer with a thickness T4 of 0.3λ Metal film 16: Aluminum film with a thickness of 0.1λ

[0049] Sample A3 Elastic wave wavelength λ: 1.5 μm Support substrate 10: sapphire substrate Surface 31: Rough surface with arithmetic mean roughness Ra of 0.15 μm Insulating layer 11: Aluminum oxide layer with a thickness T1 of 0.7λ Width of the gap 30: 0.1 to several μm Insulating layer 12: Aluminum oxide layer with a thickness T2 of 2.0λ Insulating layer 13: silicon oxide layer with a thickness T3 of 0.2λ Insulation layer 14: Yes Piezoelectric layer 15: 42° rotated Y-cut X-propagating lithium tantalate layer with a thickness T4 of 0.3λ Metal film 16: Aluminum film with a thickness of 0.1λ

[0050] Sample B1 Elastic wave wavelength λ: 6.0 μm Support substrate 10: sapphire substrate Surface 31: Rough surface with arithmetic mean roughness Ra of 0.15 μm Insulation layer 11: None Insulating layer 12: Aluminum oxide layer with thickness T2 of 1.5λ Insulating layer 13: silicon oxide layer with a thickness T3 of 0.2λ Insulation layer 14: Yes Piezoelectric layer 15: 42° rotated Y-cut X-propagating lithium tantalate layer with a thickness T4 of 0.3λ Metal film 16: Aluminum film with a thickness of 0.1λ

[0051] Sample B2 Elastic wave wavelength λ: 2.0 μm Support substrate 10: sapphire substrate Surface 31: Rough surface with arithmetic mean roughness Ra of 0.15 μm Insulation layer 11: None Insulating layer 12: Aluminum oxide layer with a thickness T2 of 3.0λ Insulating layer 13: silicon oxide layer with a thickness T3 of 0.2λ Insulation layer 14: Yes Piezoelectric layer 15: 42° rotated Y-cut X-propagating lithium tantalate layer with a thickness T4 of 0.3λ Metal film 16: Aluminum film with a thickness of 0.1λ

[0052] Sample B3 Elastic wave wavelength λ: 1.5 μm Support substrate 10: sapphire substrate Surface 31: Rough surface with arithmetic mean roughness Ra of 0.15 μm Insulation layer 11: None Insulating layer 12: Aluminum oxide layer with a thickness T2 of 6.0λ Insulating layer 13: silicon oxide layer with a thickness T3 of 0.2λ Insulation layer 14: Yes Piezoelectric layer 15: 42° rotated Y-cut X-propagating lithium tantalate layer with a thickness T4 of 0.3λ Metal film 16: Aluminum film with a thickness of 0.1λ

[0053] Samples A1 to A3 are Example 1, and Samples B1 to B3 are Comparative Example 1 in which no insulating layer 11 is provided and no voids 30 are provided. Samples A1 to A3 were produced by the method described with reference to FIGS. 3(a) to 4(c). In Samples A1 to A3, the area of ​​the voids 30 in a cross-sectional view was approximately 8% of the area of ​​the insulating layer 11 including the voids 30. Samples B1 to B3 were produced by the method described with reference to FIGS. 3(a) to 4(c) except that no insulating layer 11 was formed.

[0054] FIG. 5 is a cross-sectional view of an acoustic wave device according to Comparative Example 2. As shown in FIG. 5, a surface 31 has multiple protrusions 31a and multiple recesses 31b regularly arranged at a constant period D1. The recesses 31b are flat, and the width of the flat surface is W4. The insulating layer 11 has multiple voids 30 that penetrate the insulating layer 11 from the recesses 31b. The width W1 of the voids 30 is constant in the Z direction. Insulating layers 12 and 14 are not provided. The other configurations are the same as in Example 1. The manufacturing method for Comparative Example 2 is as follows. In FIG. 3(a), a regularly textured surface is formed on the upper surface of the support substrate 10. In FIG. 3(b), an insulating layer 11 is formed. Thereafter, an insulating layer 13 is formed as shown in FIG. 4(a) without performing etching to widen the voids 30 as shown in FIG. 3(c). The subsequent manufacturing method for Comparative Example 2 is the same as in Example 1.

[0055] Sample C1 Elastic wave wavelength λ: 5.0 μm Support substrate 10: sapphire substrate Surface 31: D1=0.8λ, W4=0.4λ Insulating layer 11: Aluminum oxide layer with a thickness T1 of 0.3λ Width W1 of the gap 30: approximately 0.025λ Insulation layer 12: None Insulating layer 13: silicon oxide layer with a thickness T3 of 0.4λ Insulation layer 14: Yes Piezoelectric layer 15: 42° rotated Y-cut X-propagating lithium tantalate layer with a thickness T4 of 0.4λ Metal film 16: Aluminum film with a thickness of 0.1λ The insulating layer 11 of sample C1 has a void 30, but unlike Example 1, there are not multiple voids 30 with different extension directions in a planar view, but voids that extend in one direction (Y direction) in a planar view.

[0056] FIG. 6 shows the admittance |Y| versus frequency for samples A1 and B1 in Experiment 1. FIG. 7 shows the admittance |Y| versus frequency for samples A2 and B2 in Experiment 1. FIG. 8 shows the admittance |Y| versus frequency for samples A3 and B3 in Experiment 1. As shown in FIGS. 6 to 8, a main response with peaks and troughs at the resonant frequency fr and the antiresonant frequency fa due to the surface acoustic wave in the main mode is observed. The main response does not differ significantly between samples A1 to A3 and B1 to B3. A spurious response Sp due to bulk waves is observed at a frequency higher than the main response. The difference ΔY between the maximum and minimum of |Y| in the spurious response Sp was calculated. Furthermore, in the spurious response, the reflection coefficient (absolute value of S11) varies significantly with frequency. The minimum value of the reflection coefficient in the spurious response was defined as the reflection coefficient Γ. It is preferable that the reflection coefficient Γ be close to 1.

[0057] The ΔY and Γ of samples A1 to A3 and B1 to B3 are shown below. Sample A1: ΔY=4dB Γ=0.7 Sample B1: ΔY=20dB Γ=0.1 Sample A2: ΔY=2dB Γ=0.8 Sample B2: ΔY=10dB Γ=0.3 Sample A3: ΔY=2dB Γ=0.8 Sample B3: ΔY=5dB Γ=0.6 Regardless of the wavelength of the elastic wave, samples A1 to A3 have smaller ΔY than samples B1 to B3, and the reflection coefficient Γ is closer to 1. In this way, samples A1 to A3 of Example 1 can suppress spurious responses more than samples B1 to B3 of Comparative Example 1 in which the air gap 30 is not provided.

[0058] Fig. 9 is a diagram showing the admittance |Y| versus frequency for sample C1 in experiment 1. As shown in Fig. 9, ΔY of the spurious response Sp in sample C1 is smaller than that in samples B1 to B3, but larger than that in samples A1 to A3. Thus, the spurious response Sp in sample C1 is not as small as that in samples A1 to A3.

[0059] The reason why spurious responses were reduced in Samples A1 to A3 of Example 1 is believed to be as follows: The main response is primarily due to surface acoustic waves (e.g., SH (Shear Horizontal) waves), and the spurious responses are primarily due to bulk waves. A spurious response occurs when a bulk wave excited by the IDT 22 is reflected at the interface between the support substrate 10 and the insulating layer 17 and returns to the IDT 22. By making the surface 31 of the support substrate 10 uneven, the bulk wave is scattered, suppressing the spurious response. However, this does not sufficiently suppress the spurious response. The voids 30 attenuate bulk waves that cannot be scattered by the unevenness of the surface 31 alone. The propagation direction of bulk waves in a planar view is not limited to the X direction. Therefore, multiple voids 30 are provided in different directions that intersect the extension direction. This allows the voids 30 to attenuate bulk waves propagating in various directions. This is believed to enhance the spurious suppression effect.

[0060] Although sample C1 also has voids 30 in the insulating layer 11, the voids 30 in sample C1 extend in the same direction in a plan view. On the other hand, samples A1 to A3 have voids 30 extending in different directions, as shown in Fig. 2. This is thought to result in greater attenuation of bulk waves propagating through the insulating layer 11, and thus spurious responses being suppressed in samples A1 to A3 more than in sample C1.

[0061] [Modification 1 of Example 1] 10 is a cross-sectional view of an acoustic wave device according to a first modification of the first embodiment. As shown in FIG. 10 , in the first modification of the first embodiment, an insulating layer 12a is provided between insulating layer 11 and insulating layer 12. The insulating layer 12a functions as a barrier layer for preventing voids 30 from being formed in insulating layer 12 when insulating layer 12 is formed on insulating layer 11. A surface 32a between insulating layers 11 and 12a is an uneven surface having an arithmetic mean roughness Ra similar to that of surface 31 or a surface having an arithmetic mean roughness Ra smaller than that of surface 31. A surface 32b between insulating layers 12a and 12b is an uneven surface having an arithmetic mean roughness Ra similar to that of surface 32a or a surface having an arithmetic mean roughness Ra smaller than that of surface 31.

[0062] [Experiment 2] A sample A1 corresponding to Example 1 and a sample D1 corresponding to Modification 1 of Example 1 were prepared, and an experiment to evaluate spurious emissions was carried out under the following experimental conditions.

[0063] Sample A1 Elastic wave wavelength λ: 6.0 μm Support substrate 10: sapphire substrate Surface 31: Rough surface with arithmetic mean roughness Ra of 0.15 μm Insulating layer 11: Aluminum oxide layer with a thickness T1 of 0.5λ Width of the gap 30: 0.1 to several μm Insulating layer 12a: None Insulating layer 12: Aluminum oxide layer with thickness T2 of 1.5λ Insulating layer 13: silicon oxide layer with a thickness T3 of 0.2λ Insulation layer 14: Yes Piezoelectric layer 15: 42° rotated Y-cut X-propagating lithium tantalate layer with a thickness T4 of 0.3λ Metal film 16: Aluminum film with a thickness of 0.1λ

[0064] Sample D1 Elastic wave wavelength λ: 6.0 μm Support substrate 10: sapphire substrate Surface 31: Rough surface with arithmetic mean roughness Ra of 0.15 μm Insulating layer 11: Aluminum oxide layer with a thickness T1 of 0.3λ Width of the gap 30: 0.1 to several μm Insulating layer 12a: silicon oxide layer with a thickness of 0.75 μm Insulating layer 12: Aluminum oxide layer with a thickness T2 of 1.0λ Insulating layer 13: silicon oxide layer with a thickness T3 of 0.1λ Insulation layer 14: Yes Piezoelectric layer 15: 42° rotated Y-cut X-propagating lithium tantalate layer with a thickness T4 of 0.2λ Metal film 16: Aluminum film with a thickness of 0.1λ

[0065] Figures 11(a) and 11(b) show the admittance |Y| versus frequency for samples A1 and D1 in experiment 2. Comparing Figures 11(a) and 11(b), sample D1 has a larger main response due to the surface acoustic wave in the principal mode than sample A1. The spurious responses are comparable for samples A1 and D1. The ΔY of the main response and the ΔY of the spurious response are as follows: Sample A1: Main ΔY=67dB, Spurious ΔY=2dB Sample D1: Main ΔY=82dB, Spurious ΔY=2dB

[0066] In Example 1, when insulating layer 12 is formed on insulating layer 11 in FIG. 4(a), voids 30 may extend into insulating layer 12. If voids 30 extend to the vicinity of surface 33, the surface acoustic waves of the main mode may be attenuated by voids 30. This may result in a deterioration of the main response. In Modification 1 of Example 1, insulating layer 12a is provided between insulating layer 11 and insulating layer 12, functioning as a barrier layer that suppresses the extension of voids 30. This suppresses the extension of voids 30 into insulating layer 12, thereby suppressing the deterioration of the main response.

[0067] [Modification 2 of Example 1] FIG. 12 is a cross-sectional view of an acoustic wave device according to a second modification of the first embodiment. As shown in FIG. 12, an uneven surface is provided on a surface 31 of a support substrate 10. A plurality of protrusions 31a on the surface 31 are regularly arranged, and a plurality of recesses 31b are also regularly arranged. The period of the protrusions 31a (or recesses 31b) is constant, D1. The recesses 31b are flat. The voids 30 are provided on the recesses 31b, and the period of the voids 30 is also constant, D1.

[0068] FIG. 13 is a plan view of the upper surface of the insulating layer 11 according to Modification 2 of Example 1. The protrusions 31a are indicated by dashed lines, and the vertices 31c of the protrusions 31a are indicated by black dots. As shown in FIG. 13, the protrusions 31a are conical and circular in plan view. The vertices 31c are located at the centers of the circles. The areas between the protrusions 31a are flat recesses 31b. The period D1 of the protrusions 31a is constant. Voids 30 are formed on the recesses 31b. The planar shape of the voids 30 is a honeycomb structure formed by connecting regular hexagons. Of the voids 30, center lines 35x to 35z of the voids 36x to 36z extend in different directions. The rest of the configuration is the same as in Example 1, and therefore a description thereof will be omitted.

[0069] [Modification 3 of Example 1] Fig. 14 is a plan view of the upper surface of the insulating layer 11 according to the third modification of the first embodiment. As shown in Fig. 14, the voids 36x to 36z are separated from one another. The other configurations are the same as those of the second modification of the first embodiment, and therefore, description thereof will be omitted.

[0070] As in Modifications 2 and 3 of Example 1, the unevenness of the surface 31 of the support substrate 10 may be regular, and the voids 30 may be regularly arranged. As in Modification 2 of Example 1, the voids 36x to 36z may be connected to one another, or as in Modification 3 of Example 1, the voids 36x to 36z may be separated from one another. The convex portion 31a may be a polygonal pyramid shape other than a cone shape, or may be a cylindrical shape or a polygonal prism shape.

[0071] [Modification 3 of Example 1] Fig. 15(a) is a cross-sectional view of an acoustic wave device according to a fourth modification of the first embodiment. As shown in Fig. 15(a), the surface 31 of the support substrate 10 may be a flat surface. In this case, the surfaces 31 to 34 are flat surfaces. The other configurations are the same as those of the first embodiment, and therefore a description thereof will be omitted.

[0072] [Modification 5 of Example 1] 15(b) is a cross-sectional view of an acoustic wave device according to a fifth modification of the first embodiment. As shown in FIG. 15(b), insulating layers 12 and 14 are not provided. As in the fifth modification of the first embodiment, insulating layer 17 may be one or more insulating layers. As insulating layer 17, for example, one or more insulating layers of a silicon oxide film, a silicon nitride film, a silicon nitride oxide film, an aluminum oxide film, an aluminum nitride film, an aluminum nitride oxide film, or a silicon carbide film can be used.

[0073] According to the first embodiment and its modifications, the insulating layer 17 is provided between the support substrate 10 and the piezoelectric layer 15. As shown in FIGS. 2, 13, and 14, the insulating layer 17 has multiple voids 30. The multiple voids 30 (void regions) have a width in the extension direction longer than the width in the direction perpendicular to the extension direction, as viewed from the thickness direction of the support substrate 10, and extend in different directions that intersect with the extension direction. At least some of the multiple voids 30 (void regions) have different extension directions, i.e., directions in which the width is longer than the width in the direction perpendicular to the extension direction. The propagation direction of the bulk waves is not limited to the X direction in which the electrode fingers 18 are arranged. The different extension directions of the voids 30 allow the voids 30 to attenuate bulk waves propagating in various directions, thereby suppressing spurious signals. The maximum crossing angle at which the extension directions of two of the multiple voids 30 intersect is preferably 30° or greater, more preferably 45° or greater.

[0074] A plurality of voids having different extension directions are connected to each other to form a single void region. For example, void 30b in FIG. 2 is formed by connecting a plurality of voids 36a to 36d. void 30c is formed by connecting a plurality of voids 36e to 36i. In FIG. 13, void 30 is formed by connecting voids 36x to 36y. This allows void 30 and voids 30a to 30c to further suppress bulk waves. As shown in FIG. 14, voids 36x to 36z having different extension directions may be separated from each other.

[0075] As shown in FIG. 2, the void 30b, in which multiple voids 36a-36c are connected, may have a shape in which the voids 36a-36c extend in multiple directions from a single point when viewed in the thickness direction of the support substrate 10. As shown in FIG. 2, the void 30b may have a shape in which multiple voids 36e-36i surround a portion of the insulating layer 11 when viewed in the thickness direction of the support substrate 10. This configuration can further suppress bulk waves. Furthermore, as shown in FIG. 2, the insulating layer 11 may have multiple individual voids 30d-30f extending in a single direction in addition to the voids 30a-30c in which multiple voids are connected. Thus, the insulating layer 11 may have various voids 30a-30f with different planar shapes, thereby further suppressing bulk waves propagating in various directions.

[0076] In samples A1 to A3, the area of ​​the plurality of voids 30 in a cross-sectional view is approximately 8% of the area including the plurality of voids 30 in the insulating layer 11. Thus, the area of ​​the plurality of voids 30 in a cross-sectional view is preferably 1% or more of the area including the plurality of voids 30 in the insulating layer 11, more preferably 2% or more, and even more preferably 5% or more. From the viewpoint of ensuring the strength of the insulating layer 11 and attenuating bulk waves on the surface 31, the area of ​​the plurality of voids 30 in a cross-sectional view is preferably 20% or less of the area including the plurality of voids 30 in the insulating layer 11.

[0077] From the viewpoint of attenuating bulk waves, the height of the void 30 is preferably 0.2λ or more, more preferably 0.5λ or more. From the viewpoint of ensuring the strength of the insulating layer 11, the height of the void 30 is preferably 10λ or less. From the viewpoint of attenuating bulk waves, the widths W1 and W2 of the void 30 are preferably 0.01λ or more, more preferably 0.1λ or more. The widths W1 and W2 are, for example, 100 nm or more. From the viewpoint of ensuring the strength of the insulating layer 11, the widths W1 and W2 of the void 30 are preferably 2λ or less.

[0078] As in Example 1 and its Modifications 1, 2, 4, and 5, the interface 31 between the support substrate 10 and the insulating layer 11 is an uneven surface. This allows the bulk waves to be scattered at the interface, thereby further suppressing spurious emissions. As in Modification 3 of Example 1, the interface between the support substrate 10 and the insulating layer 11 may be a flat surface.

[0079] In order to scatter bulk waves and suppress spurious signals, if surface 31 of support substrate 10 is a rough surface, the arithmetic mean roughness Ra is preferably 100 nm or more, more preferably 150 nm or more. It is preferable that bulk waves are not reflected at the interface between piezoelectric layer 15 and insulating layer 13 and the interface between insulating layers 12 and 13. From this perspective, the arithmetic mean roughness Ra of surfaces 33 and 34 is preferably 10 nm or less, more preferably 1 nm or less. Modification of Example 1 2 When the unevenness is regular, the convex portions 31a and the concave portions 31b height is preferably 0.1λ or more, more preferably 0.3λ or more, and even more preferably 1λ or more. Height of the convex portion 31a and the concave portion 31b is preferably 2λ or less. From the viewpoint of suppressing spurious responses, the period D1 of the convex portions 31a or concave portions 31b of the surface 31 is preferably 0.8λ or more, and more preferably 1.0λ or more. From the viewpoint of increasing the main response, the period D1 of the surface 31 is preferably 2.4λ or less, and more preferably 1.6λ or less.

[0080] The plurality of voids 30 overlap the recesses 31b of the uneven surface, thereby forming the voids 30 as shown in Figures 3(b) and 3(c).

[0081] The cross-sectional shape of the plurality of voids 30 is such that the width on the piezoelectric layer 15 side is narrower than the width on the support substrate 10 side. This allows the voids 30 to attenuate bulk waves more effectively.

[0082] If the upper ends of the multiple voids 30 are close to the lower surface of the piezoelectric layer 15, the surface acoustic waves will be affected by the voids 30. From this perspective, the distance H2 between the voids 30 and the piezoelectric layer 15 is preferably 0.5λ or more, and more preferably 1λ or more. The distance H2 is preferably 10λ or less.

[0083] The insulating layer 17 includes an insulating layer 11 (first insulating layer) provided on the support substrate 10 and having a plurality of voids 30 through which the voids 30 pass, and an insulating layer 12 (second insulating layer) provided on the insulating layer 11 and having no voids 30. This makes it possible to suppress the influence of the voids 30 on the surface acoustic wave.

[0084] Insulating layer 17 is provided on insulating layer 12 and includes insulating layer 13 (third insulating layer) whose bulk wave acoustic velocity is slower than that of insulating layers 11 and 12. This allows surface acoustic waves to be confined within insulating layer 13 and piezoelectric layer 15, thereby increasing the main response. Using insulating layer 13 as a temperature compensation film improves the temperature characteristics of the acoustic wave device. The bulk wave acoustic velocity of insulating layer 13 is preferably 0.9 times or less, more preferably 0.8 times or less, of the bulk wave acoustic velocity of insulating layers 11 and 12.

[0085] As in the first modification of the first embodiment, insulating layer 17 has insulating layer 12a between insulating layers 11 and 12, which has a bulk wave acoustic velocity equal to or lower than the bulk wave acoustic velocity of insulating layer 12, and insulating layer 12a does not have voids 30. In this way, by providing insulating layer 12a that prevents voids 30 from extending into insulating layer 12, it is possible to prevent voids 30 from extending into insulating layer 12 and thereby suppress deterioration of the main response.

[0086] In a wafer manufacturing method for an acoustic wave device according to the first embodiment and its modified examples, as shown in FIG. 3(b), an insulating layer 11 having a plurality of first voids 30 contacting the recesses 31b of the uneven surface is formed on a support substrate 10 having an uneven surface. As shown in FIG. 3(b), the insulating layer 11 contacting the plurality of first voids 30 is etched to form a plurality of second voids 30 in the insulating layer 11, the second voids 30 being longer in the extension direction than in the direction perpendicular to the extension direction, as viewed from the thickness direction of the support substrate 10, and extending in a different direction that intersects with the extension direction. As shown in FIGS. 4(b) and 4(c), a piezoelectric layer 15 is formed on the insulating layer 11. This allows the acoustic wave devices according to the first embodiment and its modified examples to be easily manufactured.

[0087] When the acoustic waves excited primarily by the pair of interdigital transducers 20 are SH waves, bulk waves are likely to be excited. When the piezoelectric layer 15 is a Y-cut, X-propagation lithium tantalate layer rotated at an angle of 36° or more and 50° or less, SH waves are excited. Therefore, in this case, it is preferable to provide a gap 30 in the insulating layer 17.

[0088] Although the acoustic wave device has been mainly described as a surface acoustic wave (SAW) device, the acoustic wave device may be a bulk acoustic wave (BAW) device or a Lamb wave device. [Example]

[0089] FIG. 16(a) is a circuit diagram of a filter according to a second embodiment. As shown in FIG. 16(a), one or more series resonators S1 to S3 are connected in series between an input terminal Tin and an output terminal Tout. One or more parallel resonators P1 and P2 are connected in parallel between the input terminal Tin and the output terminal Tout. The acoustic wave resonators according to the first embodiment and its modifications 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 in the ladder filter can be set as appropriate. The filter may be a multimode filter having two or more pairs of comb electrodes.

[0090] [Modification 1 of Example 2] FIG. 16(b) is a circuit diagram of a duplexer according to a first modification of the second embodiment. As shown in FIG. 16(b), a transmit filter 40 is connected between a common terminal Ant and a transmit terminal Tx. A receive filter 42 is connected between the common terminal Ant and a receive terminal Rx. The transmit filter 40 passes, to the common terminal Ant, signals in the transmit band among the high-frequency signals input from the transmit terminal Tx as transmit signals, and suppresses signals of other frequencies. The receive filter 42 passes, to the receive terminal Rx, signals in the receive band among the high-frequency signals input from the common terminal Ant as receive signals, and suppresses signals of other frequencies. At least one of the transmit filter 40 and the receive filter 42 can be the filter of the second embodiment.

[0091] Although a duplexer has been described as an example of a multiplexer, a triplexer or a quadplexer may also be used.

[0092] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims. [Explanation of symbols]

[0093] 10 Support substrate 11-14, 17 Insulating layer 15 Piezoelectric layer 18 electrode fingers 20 comb electrode 26 Acoustic Wave Resonator 35a~35i, 35x~35z center line 30, 30a~30f, 36a~36i, 36x~36z void 31~34 sides 40 Transmission Filter 42 Receive Filter

Claims

1. A support substrate; a piezoelectric layer provided on the support substrate; At least one pair of comb-shaped electrodes provided on the piezoelectric layer and having a plurality of electrode fingers; an insulating layer provided between the support substrate and the piezoelectric layer, the insulating layer having, at least in a part thereof, a plurality of void regions whose extension directions, which are a direction having a width longer than a width in a direction orthogonal to the thickness direction of the support substrate, are different from each other; Equipped with the interface between the support substrate and the insulating layer is an uneven surface; The acoustic wave device, wherein the plurality of void regions overlap the recesses of the uneven surface.

2. The acoustic wave device according to claim 1 , wherein a plurality of void regions having different extension directions are connected to each other to form a single void region.

3. The acoustic wave device according to claim 2 , wherein the one void region has a shape in which the void region extends in a plurality of directions from one point when viewed in the thickness direction of the support substrate.

4. The acoustic wave device according to claim 2 , wherein the one void region is shaped to surround a part of the insulating layer when viewed in the thickness direction of the support substrate.

5. An elastic wave device described in any one of claims 1 to 4, wherein in a cross section in the thickness direction of the support substrate, the area of ​​the multiple void regions is 1% or more of the area including the multiple void regions of the insulating layer.

6. An elastic wave device described in any one of claims 1 to 5, wherein the cross-sectional shape of the multiple void regions in the thickness direction of the support substrate is such that the width on the piezoelectric layer side is narrower than the width on the support substrate side.

7. The acoustic wave device according to claim 1 , wherein a distance between the plurality of void regions and the piezoelectric layer is equal to or greater than an average pitch of the plurality of electrode fingers.

8. 8. The acoustic wave device according to claim 1, wherein the insulating layer comprises: a first insulating layer provided on the support substrate and having the plurality of void regions, the first insulating layer having the plurality of void regions passing therethrough; and a second insulating layer provided on the first insulating layer and having no void regions.

9. The acoustic wave device according to claim 8 , further comprising a third insulating layer provided on the second insulating layer, the third insulating layer having a sound velocity slower than that of the first insulating layer and the second insulating layer.

10. A support substrate; a piezoelectric layer provided on the support substrate; an insulating layer provided between the support substrate and the piezoelectric layer, the insulating layer having, at least in a part thereof, a plurality of void regions whose extension directions, which are a direction having a width longer than a width in a direction orthogonal to the thickness direction of the support substrate, are different from each other; Equipped with the interface between the support substrate and the insulating layer is an uneven surface; The plurality of void regions overlap the recesses of the uneven surface of the wafer.

11. forming an insulating layer on a support substrate having an uneven surface, the insulating layer having a plurality of first void regions contacting the concave portions of the uneven surface; forming a plurality of second void regions in the insulating layer, the second void regions having different extension directions, which are directions having a width longer than a width in a direction perpendicular to the thickness direction of the support substrate, in at least a part of the insulating layer by etching the insulating layer in contact with the plurality of first void regions; forming a piezoelectric layer on the insulating layer; A method for manufacturing a wafer, comprising:

Images