Elastic wave device, filter, multiplexer, and wafer

Abstract

The invention provides an elastic wave device, a filter, a multiplexer, and a wafer. The purpose of the present invention is to suppress stray response and main response deterioration. An elastic wave device (100) is provided with: a support substrate (10); a piezoelectric layer (14) provided on the support substrate (10); a pair of comb-type electrodes (20) that are provided on the piezoelectric layer (14); a first insulating layer (11) that is provided between the support substrate (10) and the piezoelectric layer (14) and is made of polycrystalline or amorphous aluminum oxide or polycrystalline silicon; and a second insulating layer (12) that is provided between the first insulating layer (11) and the piezoelectric layer (14) and is aluminum nitride, silicon nitride, silicon carbide, or diamond-like carbon, the first surface (60) of the second insulating layer (12) on the first insulating layer (11) side being rougher than the second surface (61) on the piezoelectric layer (14) side.

Description

Technical Field

[0001] The present invention relates to an elastic wave device, a filter, a multiplexer, and a wafer. Background Art

[0002] As an elastic wave device used in communication devices such as smartphones, a surface acoustic wave resonator is known. It is known to bond a piezoelectric layer forming a surface acoustic wave resonator to a support substrate. It is known to set the thickness of the piezoelectric layer to be less than the wavelength of the surface acoustic wave (for example, Patent Document 1). It is known to provide a low sound velocity layer having a lower sound velocity than the piezoelectric layer between the piezoelectric layer and the support substrate (for example, Patent Documents 2 to 7). It is known to provide a high sound velocity layer having a higher sound velocity than the piezoelectric layer between the low sound velocity layer and the support substrate (for example, Patent Documents 2 and 3).

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 2017-034363

[0004] Patent Document 2: Japanese Patent Application Laid-Open No. 2015-115870

[0005] Patent Document 3: Japanese Patent Application Laid-Open No. 2015-122566

[0006] Patent Document 4: Japanese Patent Application Laid-Open No. 2019-201345

[0007] Patent Document 5: Japanese Patent Application Laid-Open No. 2022-25374

[0008] Patent Document 6: US Patent No. 10020796 Specification

[0009] Patent Document 7: International Publication No. 2017 / 043427

[0010] By providing a high sound velocity layer between the low sound velocity layer and the support substrate, the main response can be improved, but the spurious response sometimes deteriorates. Summary of the Invention

[0011] The present invention has been made in view of the above problems, and an object thereof is to suppress spurious response and suppress deterioration of the main response.

[0012] The present invention is an elastic wave device having: a substrate; a piezoelectric layer provided on the substrate; a pair of comb-shaped electrodes provided on the piezoelectric layer; a first insulating layer provided between the substrate and the piezoelectric layer, which is polycrystalline or amorphous alumina or polysilicon; and a second insulating layer provided between the first insulating layer and the piezoelectric layer, which is aluminum nitride, silicon nitride, silicon carbide, or diamond-like carbon, and a first surface of the second insulating layer on the first insulating layer side is rougher than a second surface on the piezoelectric layer side.

[0013] In the above structure, it can be configured such that the average thickness of the second insulating layer is more than 7.5 times the thickness of the piezoelectric layer.

[0014] In the above structure, it can be configured such that the second insulating layer is aluminum nitride or silicon nitride, and the average height of the unevenness on the first surface of the second insulating layer is more than 3 times and less than 11 times the thickness of the piezoelectric layer.

[0015] In the above structure, it can be configured such that the average thickness of the second insulating layer is 11.5 times or less the thickness of the piezoelectric layer.

[0016] In the above structure, it can be configured such that the second insulating layer is silicon carbide or diamond-like carbon, and the average height of the unevenness on the first surface of the second insulating layer is more than 8 times and less than 13 times the thickness of the piezoelectric layer.

[0017] In the above structure, it can be configured such that the average thickness of the second insulating layer is 10.5 times or less the thickness of the piezoelectric layer.

[0018] In the above structure, it can be configured such that the average pitch of the unevenness on the first surface of the second insulating layer is more than 1 time and less than 20 times the thickness of the piezoelectric layer.

[0019] In the above structure, it can be configured such that the surface acoustic wave device has a third insulating layer provided between the piezoelectric layer and the second insulating layer, the third insulating layer being silicon oxide or silicon oxide doped with fluorine, phosphorus, or boron, the substrate being sapphire, the piezoelectric layer being rotated Y-cut X-propagating lithium tantalate, the first insulating layer being polycrystalline or amorphous alumina, and the distance between the interface between the second insulating layer and the third insulating layer and the interface between the piezoelectric layer and the pair of comb-shaped electrodes being 2 times or less the thickness of the piezoelectric layer.

[0020] In the above structure, it can be configured such that the average thickness of the second insulating layer is the average of the thicknesses at three points, namely, both end portions and the central portion of a cross section within the region where the pair of comb-shaped electrodes is provided.

[0021] The present invention is a surface acoustic wave device having: a substrate; a piezoelectric layer provided on the substrate; a pair of comb-shaped electrodes provided on the piezoelectric layer; a first insulating layer provided between the substrate and the piezoelectric layer and having a bulk wave sound velocity faster than that of the piezoelectric layer; and a second insulating layer provided between the first insulating layer and the piezoelectric layer and having a bulk wave sound velocity faster than that of the first insulating layer, the first surface on the first insulating layer side of the second insulating layer being rougher than the second surface of the piezoelectric layer.

[0022] The present invention is a filter having the elastic wave device described above.

[0023] The present invention is a multiplexer having the filter described above.

[0024] The present invention is a wafer having: a substrate; a piezoelectric layer provided on the substrate; a first insulating layer provided between the substrate and the piezoelectric layer, which is polycrystalline or amorphous alumina or polysilicon; and a second insulating layer provided between the first insulating layer and the piezoelectric layer, which is aluminum nitride, silicon nitride, silicon carbide or diamond-like carbon, and a first surface of the second insulating layer on the first insulating layer side is rougher than a second surface on the piezoelectric layer side.

[0025] According to the present invention, spurious responses can be suppressed and degradation of the main response can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 (a) of is a plan view of the elastic wave device of Example 1, Figure 1 (b) of is a cross-sectional view taken along line A-A of Figure 1 (a) of, Figure 1 (c) of is a plan view of the first surface of the second insulating layer.

[0027] Figure 2 (a) of is a cross-sectional view of the elastic wave resonator of Comparative Example 1, Figure 2 (b) of is a cross-sectional view of the elastic wave resonator of Comparative Example 2.

[0028] Figure 3 (a) of shows the absolute value |Y| of the admittance with respect to frequency in Simulation 1, Figure 3 (b) of is a graph showing ΔY with respect to Q1 / Q3.

[0029] Figure 4 (a) of shows the absolute value |Y| of the admittance with respect to frequency in Simulation 2, Figure 4 (b) of is a graph showing ΔY with respect to the sound velocity V1 of the bulk wave of the first insulating layer 11.

[0030] Figure 5 (a) of is a graph showing ΔY of the main response with respect to the thickness T2 of the second insulating layer in Simulation 3-1, Figure 5 (b) of and Figure 5 (c) of are graphs showing ΔY of the spurious responses of the B mode and the C mode.

[0031] Figure 6 (a) of is a graph showing ΔY of the main response with respect to the thickness T2 of the second insulating layer in Simulation 3-2, Figure 6 (b) of and Figure 6(c) is a graph of ΔY showing the spurious responses of the B mode and the C mode.

[0032] Figure 7 (a) to Figure 7 (f) is a graph of the absolute value |Y| of the admittance with respect to the frequency in Simulation 4-1.

[0033] Figure 8 (a) is a graph of ΔY showing the main response with respect to the height H of the unevenness in Simulation 4-1, Figure 8 (b) and Figure 8 (c) is a graph of ΔY showing the spurious responses of the B mode and the C mode.

[0034] Figure 9 (a) is a graph of ΔY showing the main response with respect to the height H of the unevenness in Simulation 4-2, Figure 9 (b) and Figure 9 (c) is a graph of ΔY showing the spurious responses of the B mode and the C mode.

[0035] Figure 10 (a) to Figure 10 (d) is a graph of the absolute value |Y| of the admittance with respect to the frequency in Simulation 5-1.

[0036] Figure 11 (a) and Figure 11 (b) is a graph of ΔY showing the spurious responses of the B mode and the C mode with respect to the pitch P of the unevenness in Simulation 5-1.

[0037] Figure 12 (a) is a graph of ΔY showing the main response with respect to the pitch P of the unevenness in Simulation 5-2, Figure 12 (b) and Figure 12 (c) is a graph of ΔY showing the spurious responses of the B mode and the C mode.

[0038] Figure 13 (a) to Figure 13 (d) is a cross-sectional view of the elastic wave resonator of Modification 1 to Modification 4 of Example 1.

[0039] Figure 14 is a cross-sectional view of the wafer of Example 2.

[0040] Figure 15 (a) to Figure 15 (d) is a plan view of the filter of Example 3 to Modification 3 of Example 3.

[0041] Figure 16 is a circuit diagram of the duplexer of Example 4.

[0042] Reference Numeral Explanation

[0043] 10: Support substrate; 11: First insulating layer; 12: Second insulating layer; 13: Third insulating layer; 14: Piezoelectric layer; 15: Fourth insulating layer; 16: Metal film; 17: Fifth insulating layer; 18: Electrode finger; 19: Bus bar; 20: Comb-shaped electrode; 21: Gap; 22: IDT; 24: Reflector; 25: Crossing region; 26: Elastic wave resonator; 50: Surface acoustic wave; 52: Useless wave; 60: First surface; 61: Second surface; 62: Interface; 63: Interface; 64: Interface; 65: Region; 70: Transmit filter; 72: Receive filter; 80: Peak; 81: Trough; 100 - 140, 500, 600: Elastic wave device; 200: Wafer; 300 - 330: Filter; 400: Duplexer. Detailed implementation mode

[0044] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0045]

Embodiment 1

[0046] In Embodiment 1, an example in which the elastic wave device has an elastic wave resonator will be described. Figure 1 (a) of is a plan view of the elastic wave device 100 of Embodiment 1, Figure 1 (b) of is along Figure 1 (a) of is a cross-sectional view taken along line A - A, Figure 1 (c) of is a plan view of the first surface 60 of the second insulating layer 12. The arrangement direction of the electrode fingers 18 is set as the X direction, the extending direction of the electrode fingers 18 is set as the Y direction, and the stacking direction of the support substrate 10 and the piezoelectric layer 14 is set as the Z direction. The X direction and the Y direction do not necessarily correspond to the X-axis direction and the Y-axis direction of the crystal orientation of the piezoelectric layer 14. When the piezoelectric layer 14 is a rotated Y-cut X-propagation substrate, the X direction is the X-axis direction of the crystal orientation.

[0047] As Figure 1 (a) of and Figure 1 (b) of show, a piezoelectric layer 14 is provided on a support substrate 10 (substrate). A first insulating layer 11 is provided between the support substrate 10 and the piezoelectric layer 14. A second insulating layer 12 is provided between the first insulating layer 11 and the piezoelectric layer 14. A third insulating layer 13 is provided between the second insulating layer 12 and the piezoelectric layer 14. In the second insulating layer 12, the first surface 60 on the first insulating layer 11 side is a rough surface with a larger unevenness ratio than the second surface 61 on the piezoelectric layer 14 side. The measurement of the unevenness can be performed at any part in the plane. As Figure 1As shown in (c), the first surface 60 of the second insulating layer 12 is regularly formed with irregularities, for example, by alternately arranging peaks 80 and valleys 81 extending in the Y direction in the X direction. Alternatively, the irregularities can be regularly formed by forming the convex or concave portions in an island shape.

[0048] Let the average thickness of the first insulating layer 11 be T1, and the average thickness of the second insulating layer 12 be T2. The average thickness T1 is the thickness between the interface 62 between the first insulating layer 11 and the support substrate 10 and the middle of the irregularities at the interface between the first insulating layer 11 and the second insulating layer 12. The average thickness T2 is the thickness between the middle of the irregularities on the first surface 60 and the second surface 61. The average thicknesses T1 and T2 can be the average thicknesses within a 200 μm square region where a pair of comb-shaped electrodes 20 of the surface acoustic wave resonator 26 are provided. The average of the thicknesses at the two end portions and the central portion of any cross section in the region where the pair of comb-shaped electrodes 20 are provided can be set as the average thicknesses T1 and T2. Let the thickness of the third insulating layer 13 be T3, and the thickness of the piezoelectric layer 14 be T4. Let the height of the irregularities on the first surface 60 of the second insulating layer 12 be H, and the pitch be P. Let the minimum distance between the first surface 60 and the second surface 61 of the second insulating layer 12 be L.

[0049] A surface acoustic wave resonator 26 is provided on the piezoelectric layer 14. The surface acoustic wave resonator 26 has an IDT 22 and reflectors 24. The reflectors 24 are provided on both sides of the IDT 22 in the X direction. The IDT 22 and the reflectors 24 are formed of a metal film 16 on the piezoelectric layer 14.

[0050] The IDT 22 has a pair of opposed comb-shaped electrodes 20. The comb-shaped electrodes 20 have a plurality of electrode fingers 18 and bus bars 19 connected to the plurality of electrode fingers 18. The region where the electrode fingers 18 of the pair of comb-shaped electrodes 20 cross is the crossing region 25. The length of the crossing region 25 is the opening length. For the pair of comb-shaped electrodes 20, in at least a part of the crossing region 25, the electrode fingers 18 are alternately arranged one by one. In the crossing region 25, the surface acoustic wave mainly excited by the plurality of electrode fingers 18 propagates mainly in the X direction. The pitch of the electrode fingers 18 of one of the pair of comb-shaped electrodes 20 (the pitch between the centers of the electrode fingers 18) is approximately the wavelength λ of the surface acoustic wave. Let the pitch of the plurality of electrode fingers 18 be D, then the pitch of the electrode fingers 18 of one of the pair of comb-shaped electrodes 20 is twice the pitch D of the electrode fingers 18. The reflectors 24 reflect the surface acoustic wave excited by the electrode fingers 18 of the IDT 22. Thus, the surface acoustic wave is confined within the crossing region 25 of the IDT 22.

[0051] The piezoelectric layer 14 is, for example, a single crystal lithium tantalate (LiTaO 3 ) layer or a single crystal lithium niobate (LiNbO 3) layer, for example, is a rotation Y-cut X-propagation lithium tantalate layer or a rotation Y-cut X-propagation lithium niobate layer. From the viewpoint of suppressing spurious and loss, the thickness T4 of the piezoelectric layer 14 is preferably 1.0λ or less, more preferably 0.5λ or less. If the piezoelectric layer 14 is too thin, it is difficult to excite elastic waves, so the thickness T4 is preferably 0.1λ or more.

[0052] The support substrate 10 is, for example, a sapphire substrate, an alumina substrate, a silicon substrate, a spinel substrate, a quartz substrate, a quartz substrate, or a silicon carbide substrate. The sapphire substrate is a single crystal Al 2 O 3 substrate, the alumina substrate is a polycrystalline or amorphous Al 2 O 3 substrate, the silicon substrate is a single crystal or polycrystalline silicon substrate. The spinel substrate is a polycrystalline or amorphous MgAl 2 O 4 substrate, the quartz substrate is a single crystal SiO 2 substrate, the quartz substrate is a polycrystalline or amorphous SiO 2 substrate, 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 14 in the X direction. Thereby, the frequency temperature dependence of the elastic wave resonator can be reduced.

[0053] The sound velocity of the body wave propagating in the first insulating layer 11 and the second insulating layer 12 is faster than the sound velocity of the body wave propagating in the third insulating layer 13 and the piezoelectric layer 14. Thereby, the energy of the elastic wave of the main response is enclosed in the piezoelectric layer 14 and the third insulating layer 13. The first insulating layer 11 is, for example, polycrystalline or amorphous, and is an alumina layer, a silicon nitride layer, an aluminum nitride layer, a silicon carbide layer, or a polycrystalline silicon layer. From the viewpoint of enclosing the elastic wave in the third insulating layer 13 and the piezoelectric layer 14, the average thickness T1 of the first insulating layer 11 is preferably 0.3λ or more, more preferably 1.0λ or more. From the viewpoint of improving characteristics, the average thickness T1 is preferably 10.0λ or less. In addition, the sound velocity of the body wave of each layer is the sound velocity V S , and in the case where the rigidity modulus is G and the density is ρ, it is represented by Mathematical formula 1.

[0054]

Mathematical formula 1

[0055]

[0056] In the case where the Young's modulus is E and the Poisson's ratio is ν, the rigidity modulus G is represented by Mathematical formula 2.

[0057]

Mathematical formula 2

[0058]

[0059] The Poisson's ratio ν is from 0.2 to 0.3, typically 0.25. Thus, by measuring the Young's modulus and density of each layer, the sound velocity of the body wave of each layer can be calculated.

[0060] The third 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 temperature coefficient of the elastic constant of the piezoelectric layer 14. For example, the temperature coefficient of the elastic constant of the piezoelectric layer 14 is negative, and the temperature coefficient of the elastic constant of the third insulating layer 13 is positive. The third insulating layer 13 is, for example, a silicon oxide (SiO 2 ) layer without addition or containing additive elements such as fluorine, phosphorus, or boron, and is, for example, polycrystalline or amorphous. Thus, the frequency temperature coefficient of the elastic wave resonator can be reduced. When the third insulating layer 13 is a silicon oxide layer, the sound velocity of the body wave propagating in the third insulating layer 13 is slower than the sound velocity of the body wave propagating in the piezoelectric layer 14.

[0061] In order for the third insulating layer 13 to have a temperature compensation function, it is required that the energy of the elastic wave of the main response exists to some extent within the third insulating layer 13. The range where the energy of the surface acoustic wave is concentrated depends on the type of the surface acoustic wave, but typically, the energy of the surface acoustic wave is concentrated in the range of 2.0λ from the upper surface of the piezoelectric layer 14, particularly concentrated in the range of 1.0λ from the upper surface of the piezoelectric layer 14. Therefore, the distance (thickness T3 + T4) from the lower surface of the third insulating layer 13 to the upper surface of the piezoelectric layer 14 is preferably 2.0λ or less, more preferably 1.0λ or less. In other words, since the maximum thickness of the piezoelectric layer 14 is 1.0λ, the thickness T3 + T4 is preferably 2 times or less, more preferably 1 time or less, of the thickness of the piezoelectric layer 14.

[0062] The second insulating layer 12 is a reflection layer that reflects the elastic wave of the main response. The sound velocity of the body wave propagating in the second insulating layer 12 is faster than the sound velocity of the body wave propagating in the first insulating layer 11. The second insulating layer 12 is, for example, polycrystalline or amorphous, and is an aluminum nitride layer, a silicon nitride layer, a silicon carbide layer, or a diamond-like carbon (DLC) layer.

[0063] The metal film 16 is, for example, a film mainly composed of aluminum (Al), copper (Cu), or molybdenum (Mo). A bonding film such as a titanium (Ti) film, a chromium (Cr) film, or a titanium nitride (TiN) film may be provided between the electrode fingers 18 and the piezoelectric layer 14. The bonding film is thinner than the electrode fingers 18. An insulating layer may be provided so as to cover the electrode fingers 18. The insulating layer functions as a protective film or a temperature compensation film.

[0064] The wavelength λ of the elastic wave is, for example, from 1 μm to 6 μm. The number of pairs when two electrode fingers 18 are set as a pair is, for example, from 20 pairs to 300 pairs. The duty ratio of the IDT 22 is (the thickness of the electrode finger 18) / (the pitch of the electrode finger 18), and is, for example, from 30% to 70%. The aperture length of the IDT 22 is, for example, from 10λ to 50λ. The wavelength λ of the elastic 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 the electrode fingers 18.

[0065] [Comparative Example]

[0066] Figure 2 (a) of is a cross-sectional view of the elastic wave device 500 of Comparative Example 1. Figure 2 (b) of is a cross-sectional view of the elastic wave device 600 of Comparative Example 2. As Figure 2 shown in (a) of, in Comparative Example 1, the second insulating layer 12 is not provided. The interface 63 between the first insulating layer 11 and the third insulating layer 13 is a flat surface. Other structures are the same as those in Embodiment 1, and the description thereof is omitted. As Figure 2 shown in (b) of, in Comparative Example 2, the first surface 60 of the second insulating layer 12 is not formed with irregularities and is a flat surface. Other structures are the same as those in Embodiment 1, and the description thereof is omitted.

[0067] [Simulation 1]

[0068] For the elastic wave device 500 of Comparative Example 1, Simulation 1 of the main response and the spurious response was performed while changing the Q value of the first insulating layer 11. The conditions of Simulation 1 are as follows.

[0069] Support substrate 10: Sapphire substrate, Q value = 500

[0070] First insulating layer 11: Alumina layer, thickness T1 = 2.7λ, Q value = Q1

[0071] Third insulating layer 13: Silicon oxide layer, thickness T3 = 0.2λ, Q value = Q3 = 500

[0072] Piezoelectric layer 14: 42° rotated Y-cut X-propagating lithium tantalate substrate, T4 = 0.3λ, Q value = 2000

[0073] Metal film 16: Aluminum film, thickness 0.07λ

[0074] Wavelength λ (2×D) of the elastic wave: 2.2 μm

[0075] The sound velocities of the bulk waves propagating in each layer are as follows.

[0076] Support substrate 10: V0 = 7068.2 m / s

[0077] The first insulating layer 11: V1 = 4581.8 m / s

[0078] The third insulating layer 13: V3 = 3683.5 m / s

[0079] The piezoelectric layer 14: V4 = 3750.8 m / s

[0080] The Q value is the Q value of vibration and is the reciprocal of the attenuation constant of the elastic wave.

[0081] First, the sound velocity V1 of the bulk wave of the first insulating layer 11 is set to 4581.8 m / s, and the Q value Q1 of the first insulating layer 11 is changed by 1 time, 0.5 times, and 0.2 times with respect to the Q value Q3 of the third insulating layer 13.

[0082] Figure 3 (a) of shows the absolute value |Y| of the admittance with respect to the frequency in Simulation 1. Figure 3 (b) of is a graph showing ΔY with respect to Q1 / Q3. In Figure 3 (b) of, the dots represent the simulation points and the curve is an approximate curve. The dashed line represents the main response ΔY, and the solid line represents the spurious response ΔY. The main response ΔY is the difference between |Y| at the resonance frequency fr of the main response Mn and |Y| at the anti-resonance frequency fa. The spurious response ΔY is the difference between |Y| of the response with the largest difference in |Y| of the spurious response SP.

[0083] As Figure 3 shown in (a) of, when Q1 = 0.2 × Q3, compared with the case of Q1 = Q3, the spurious response SP becomes smaller, but the difference between |Y| at the resonance frequency fr of the main response Mn and |Y| at the anti-resonance frequency fa also becomes smaller. As Figure 3 shown in (b) of, when Q1 / Q3 becomes smaller, the spurious response ΔY becomes smaller, but the main response ΔY also becomes smaller. Thus, when the Q value Q1 of the first insulating layer 11 is decreased and the attenuation constant is increased, the spurious response ΔY becomes smaller, but the main response ΔY also becomes smaller.

[0084] [Simulation 2]

[0085] For the elastic wave device 500 of Comparative Example 1, Simulation 2 of the main response and the spurious response was performed by changing the sound velocity V1 of the bulk wave of the first insulating layer 11.

[0086] The first insulating layer 11: alumina layer, thickness T1 = 2.7λ, Q value = 0.5 × Q3

[0087] The sound velocity of the bulk wave of the first insulating layer 11: V1

[0088] Other simulation conditions are the same as those in Simulation 1.

[0089] Figure 4(a) of shows the absolute value |Y| of the admittance with respect to frequency in Simulation 2. Figure 4 (b) of is a graph showing ΔY with respect to the sound velocity V1 of the bulk wave with respect to the first insulating layer 11. In Figure 4 (b) of, the dots represent the simulation points, and the curve is an approximate curve. The dashed line represents the main response ΔY, and the solid line represents the spurious response ΔY.

[0090] As Figure 4 (a) of and Figure 4 (b) of show, when the sound velocity V1 of the bulk wave of the first insulating layer 11 is increased, the main response ΔY increases, but the spurious response ΔY also increases.

[0091] Using Figure 2 (a) of to explain the reason for the deterioration of the main response in Comparative Example 1 when the spurious response is desired to be suppressed. The electrode finger 18 excites the surface acoustic wave 50 of the main response and the useless wave 52 of the spurious response. The surface acoustic wave 50 is, for example, an SH (Shear Horizontal) wave, and the useless wave 52 is, for example, a bulk wave. As in Patent Document 4, the surface acoustic wave 50 propagates in the range of about 2.0λ from the upper surface of the piezoelectric layer 14. Thus, for the case where the thickness T4 of the piezoelectric layer 14 is, for example, 2 times (λ) or less of the average pitch D of the electrode fingers 18 (i.e., the case where the average pitch D of the electrode fingers 18 is 0.5 times or more of the thickness T4 of the piezoelectric layer 14) and the sum of the thickness T3 of the third insulating layer 13 and the thickness T4 of the piezoelectric layer 14 is, for example, 4 times (2.0λ) or less of the average pitch D of the electrode fingers 18, the confinement of the surface acoustic wave 50 and the attenuation of the useless wave 52 are considered.

[0092] The useless wave 52 becomes a spurious response by being reflected at the interface 62 with the support substrate 10. The sound velocity V1 of the bulk wave of the first insulating layer 11 is faster than the sound velocity V4 of the bulk wave of the piezoelectric layer 14 and the sound velocity V3 of the bulk wave of the third insulating layer 13. The surface acoustic wave 50 with a low frequency is easily reflected at the interface 63 between the first insulating layer 11 and the third insulating layer 13. The useless wave 52 with a high frequency (e.g., bulk wave) easily penetrates the interface 63. The useless wave 52 that has penetrated the interface 63 is reflected at the interface 62 between the support substrate 10 and the first insulating layer 11 and returns to the electrode finger 18 to become a spurious response. By appropriately setting the thickness T1 and the Q value Q1 of the first insulating layer 11, etc., the useless wave 52 passing through the first insulating layer 11 can be attenuated. Thus, the spurious response can be suppressed. On the other hand, since the surface acoustic wave 50 is reflected at the interface 63 and is confined within the piezoelectric layer 14 and the third insulating layer 13, the main response is not easily deteriorated.

[0093] However, in order to reflect the surface acoustic wave 50 at the interface 63 and allow the unwanted wave 52 to pass through, the condition is that the sound velocity V1 of the bulk wave of the first insulating layer 11 is not too fast compared to the sound velocity V4 of the bulk wave of the piezoelectric layer 14 and the sound velocity V3 of the bulk wave of the third insulating layer 13. For example, in Simulation 1, the sound velocity V1 of the bulk wave of the first insulating layer 11 is 1.22 times the sound velocity V4 of the bulk wave of the piezoelectric layer 14 and 1.24 times the sound velocity V3 of the bulk wave of the third insulating layer 13. In this case, the blocking effect of the surface acoustic wave 50 is insufficient, and a part of the surface acoustic wave 50 penetrates into the first insulating layer 11. Therefore, the surface acoustic wave 50 attenuates and the main response deteriorates.

[0094] In Simulation 1, by reducing the Q value Q1 of the first insulating layer 11, the spurious response can be suppressed. However, the surface acoustic wave 50 that penetrates into the first insulating layer 11 attenuates, so the main response deteriorates. In Simulation 2, by increasing the sound velocity V1 of the bulk wave of the first insulating layer 11, the penetration of the surface acoustic wave 50 into the first insulating layer 11 can be suppressed, and the deterioration of the main response can be suppressed. However, when the sound velocity V1 of the bulk wave of the first insulating layer 11 increases, the unwanted wave 52 is easily reflected at the interface 63, so the spurious response becomes larger.

[0095] In Comparative Example 2, as Figure 2 (b) shows, the second insulating layer 12 is provided between the first insulating layer 11 and the piezoelectric layer 14. The sound velocity V2 of the bulk wave of the second insulating layer 12 is faster than the sound velocity V1 of the bulk wave of the first insulating layer 11. As a result, the surface acoustic wave 50 is easily reflected at the interface 64 between the second insulating layer 12 and the third insulating layer 13 and does not easily penetrate into the first insulating layer 11. As a result, the deterioration of the main response can be suppressed. And, the unwanted wave 52 penetrates through the interface 64 and enters the first insulating layer 11. As a result, the unwanted wave 52 attenuates in the first insulating layer 11, and the spurious response can be suppressed.

[0096] [Simulation 3-1, Simulation 3-2]

[0097] For the elastic wave device 600 of Comparative Example 2, Simulations 3-1 and 3-2 of the main response and the spurious response were performed by changing the thickness T2 of the second insulating layer 12. The conditions of Simulation 3-1 are as follows.

[0098] Support substrate 10: Sapphire substrate, Q value = 500

[0099] First insulating layer 11: Alumina layer, thickness T1 = 3.5λ, Q value = Q1 = 250

[0100] Second insulating layer 12: Aluminum nitride layer, thickness T2, Q value = Q2 = 500

[0101] Third insulating layer 13: Silicon oxide layer, thickness T3 = 0.2λ, Q value = Q3 = 500

[0102] Piezoelectric layer 14: 42° rotated Y-cut X-propagating lithium tantalate substrate, T4 = 0.3λ, Q value = 2000

[0103] Metal film 16: Aluminum film, thickness 0.07λ

[0104] Wavelength λ(2×D) of elastic wave: 2.0 μm

[0105] The sound velocities of the body waves propagating in each layer are as follows.

[0106] Support substrate 10: V0 = 7068.2 m / s

[0107] First insulating layer 11: V1 = 4581.8 m / s

[0108] Second insulating layer 12: V2 = 6029 m / s

[0109] Third insulating layer 13: V3 = 3683.5 m / s

[0110] Piezoelectric layer 14: V4 = 3750.8 m / s

[0111] Figure 5 (a) of is a graph showing ΔY of the main response with respect to the thickness T2 of the second insulating layer 12 in Simulation 3-1. Figure 5 (b) of and Figure 5 (c) of are graphs showing ΔY of the spurious responses of the B mode and C mode with respect to the thickness T2 of the second insulating layer 12 in Simulation 3-1. The spurious response of the B mode is Figure 7 ΔY of the spurious response generated at a frequency close to the main response, shown by region A in (a) of. The spurious response of the C mode is Figure 7 ΔY of the spurious response generated at a frequency higher than the spurious response of the B mode, shown by region B in (a) of.

[0112] As Figure 5 shown in (a) of, when the thickness T2 of the second insulating layer 12 becomes thicker, the main response ΔY becomes larger, but saturates at around 0.75λ and hardly changes even if it becomes thicker further. As Figure 5 shown in (b) of and Figure 5 shown in (c) of, when the thickness T2 of the second insulating layer 12 is 0.75λ or more, the spurious response ΔY becomes larger.

[0113] In Simulation 3-2, the second insulating layer 12 is set as a silicon carbide layer, the thickness T2 is set as 0.75λ, the Q value Q2 is set as 500, the sound velocity V2 is set as 6983 m / s, and the other conditions are the same as those in Simulation 3-1.

[0114] Figure 6Fig. (a) is a graph showing ΔY of the main response with respect to the thickness T2 of the second insulating layer 12 in Simulation 3-2. Figure 6 Figs. (b) and Figure 6 Figs. (c) are graphs showing ΔY of the spurious responses of the B mode and C mode with respect to the thickness T2 of the second insulating layer 12 in Simulation 3-2. As Figure 6 shown in Fig. (a), even when the second insulating layer 12 is a silicon carbide layer, when the thickness T2 of the second insulating layer 12 becomes thicker, the main response ΔY becomes larger, but saturates at around 0.75λ and hardly changes even if it becomes thicker further. As Figure 6 shown in Figs. (b) and Figure 6 Figs. (c), even when the second insulating layer 12 is a silicon carbide layer, when the thickness T2 of the second insulating layer 12 is 0.75λ or more, the spurious response ΔY becomes larger. Thus, in the surface acoustic wave device 600 of Comparative Example 2, from the viewpoint of increasing the main response ΔY, the thickness T2 of the second insulating layer 12 is preferably 0.75λ or more. However, when the thickness T2 is 0.75λ or more, the spurious response ΔY becomes larger.

[0115] In Simulation 3-1, the second insulating layer 12 used an aluminum nitride layer, and in Simulation 3-2, a silicon carbide layer was used. However, it can be considered that the same results can be obtained when using a silicon nitride layer having the same sound velocity as that of aluminum nitride and when using a diamond-like carbon (DLC) layer having the same sound velocity as that of silicon carbide.

[0116] Therefore, in Embodiment 1, as Figure 1 shown in Fig. (b), the second insulating layer 12 provided between the first insulating layer 11 and the piezoelectric layer 14 has a body wave sound velocity faster than that of the body wave of the first insulating layer 11, and the first surface 60 on the first insulating layer 11 side is rougher than the second surface 61 on the piezoelectric layer 14 side. Since the body wave sound velocity of the second insulating layer 12 is faster than that of the body wave of the first insulating layer 11, the surface acoustic wave 50 is easily reflected at the interface 64 between the second insulating layer 12 and the third insulating layer 13 and does not easily penetrate into the first insulating layer 11. Thereby, deterioration of the main response can be suppressed. Since the first surface 60 of the second insulating layer 12 is rougher than the second surface 61, the useless wave 52 penetrating into the second insulating layer 12 is scattered at the first surface 60. Thereby, the spurious response can be suppressed.

[0117] When the sound velocity V0 of the bulk wave in the support substrate 10 is high, the useless wave 52 is likely to be reflected at the interface 62 between the support substrate 10 and the first insulating layer 11, and spurious responses are likely to occur. On the other hand, from the viewpoint of supporting each layer, a relatively hard material is sometimes used for the support substrate 10. When the sound velocity V0 of the bulk wave in the support substrate 10 is higher than the sound velocity V2 of the bulk wave in the second insulating layer 12, it is preferable to provide the first insulating layer 11 and the second insulating layer 12. The sound velocity V0 of the bulk wave in the support substrate 10 is, for example, 1.1 times or more, and 1.2 times or more the sound velocity V2 of the bulk wave in the second insulating layer 12.

[0118] When the sound velocity V2 of the bulk wave in the second insulating layer 12 is too high, the useless wave 52 is likely to be reflected at the interface 64 of the second insulating layer 12. From this viewpoint, the sound velocity V2 of the bulk wave in the second insulating layer 12 is preferably 1.5 times or less, more preferably 1.4 times or less, further preferably 1.2 times or less, and further preferably 1.1 times or less the sound velocity V1 of the bulk wave in the first insulating layer 11. From the viewpoint of easily reflecting the surface acoustic wave 50 at the interface 64, the sound velocity V2 is preferably 1.01 times or more, and more preferably 1.02 times or more the sound velocity V1.

[0119] When the sound velocity V1 of the bulk wave in the first insulating layer 11 is too high, the useless wave 52 is difficult to penetrate into the first insulating layer 11. From this viewpoint, the sound velocity V1 of the bulk wave in the first insulating layer 11 is preferably 1.5 times or less, more preferably 1.3 times or less the sound velocity V4 of the bulk wave in the piezoelectric layer 14 and the sound velocity V3 of the bulk wave in the third insulating layer 13. When the sound velocity V1 of the bulk wave in the first insulating layer 11 is too low, the surface acoustic wave 50 penetrates into the first insulating layer 11. From this viewpoint, the sound velocity V1 is preferably 1.05 times or more, and more preferably 1.2 times or more the sound velocities V4 and V3.

[0120] [Simulation 4-1, Simulation 4-2]

[0121] For the elastic wave device 100 of Example 1, simulations 4-1 and 4-2 of the main response and the spurious response were performed by changing the height H of the unevenness on the first surface 60 of the second insulating layer 12. The conditions of Simulation 4-1 are as follows.

[0122] First insulating layer 11: Alumina layer, average thickness T1 = 3.5λ, Q value = Q1 = 250

[0123] Second insulating layer 12: Aluminum nitride layer, average thickness T2 = 0.75λ, Q value = Q2 = 500

[0124] Height of the unevenness on the first surface 60 of the second insulating layer 12: H

[0125] Pitch P of the unevenness on the first surface 60 of the second insulating layer 12: 0.5λ

[0126] Other simulation conditions are the same as those in Simulation 3-1.

[0127] Figure 7 from (a) to Figure 7 (f) of is a graph showing the absolute value |Y| of the admittance with respect to frequency in Simulation 4-1. Figure 7 from (a) to Figure 7 (f) of are graphs of the cases where the height H of the unevenness is 0λ, 0.1λ, 0.3λ, 0.45λ, 0.7λ, and 1.3λ, respectively. As Figure 7 from (a) to Figure 7 (f) shows that by changing the height H of the unevenness, the magnitude of the spurious response changes.

[0128] Figure 8 (a) of is a graph showing ΔY of the main response with respect to the height H of the unevenness in Simulation 4-1. Figure 8 (b) of and Figure 8 (c) of are graphs showing ΔY of the spurious responses of the B mode and the C mode with respect to the height H of the unevenness in Simulation 4-1. As Figure 8 (a) shows that when the height H of the unevenness is 1.1λ or less, the decrease in ΔY of the main response is suppressed to 0.1 dB or less compared to the case where the height H of the unevenness is 0λ. As Figure 8 (b) of and Figure 8 (c) show that when the height H of the unevenness is 0.3λ or more, the ΔY of the spurious responses of the B mode and the C mode decreases compared to the case where the height H of the unevenness is 0λ.

[0129] Based on the above, in Example 1, the average thickness T2 of the second insulating layer 12 is set to 0.75λ or more. In other words, since the minimum thickness of the piezoelectric layer 14 is 0.1λ, the average thickness T2 is 7.5 times or more the thickness of the piezoelectric layer 14. Thus, as Figure 5 (a) of and Figure 6 (a) show that the main response can be increased.

[0130] Also, in Example 1, when the second insulating layer 12 is an aluminum nitride layer or a silicon nitride layer having a sound velocity similar to that of aluminum nitride, the height H of the unevenness of the first surface 60 of the second insulating layer 12 is set to 0.3λ or more and 1.1λ or less. In other words, the height H of the unevenness is set to 3 times or more and 11 times or less the thickness of the piezoelectric layer 14. Therefore, as Figure 8 from (a) to Figure 8As in (c) thereof, it is possible to suppress the reduction of the main response and suppress the spurious response. From the viewpoint of suppressing the reduction of the main response and suppressing the spurious response, the height H of the unevenness can be 0.35λ or more and 1.0λ or less, can be 0.4λ or more and 0.9λ or less, and can be 0.45λ or more and 0.8λ or less. The height H of the unevenness can be the height of the unevenness within a 200-μm square region where the elastic wave resonator 26 is provided.

[0131] In Simulation 4-2, the second insulating layer 12 was a silicon carbide layer, the average thickness T2 was 0.75λ, the Q value Q2 was 500, and the sound velocity V2 was 6983 m / s. Other than this, the conditions were the same as those in Simulation 4-1.

[0132] Figure 9 (a) thereof is a graph showing ΔY of the main response with respect to the height H of the unevenness in Simulation 4-2. Figure 9 and (b) thereof Figure 9 and (c) thereof are graphs showing ΔY of the spurious responses of the B mode and the C mode with respect to the height H of the unevenness in Simulation 4-2. As Figure 9 shown in (a) thereof, when the height H of the unevenness is 1.3λ or less, the reduction of ΔY of the main response is suppressed to 0.1 dB or less compared with the case where the height H of the unevenness is 0λ. As Figure 9 shown in (b) thereof Figure 9 and (c) thereof, when the height H of the unevenness is 0.8λ or more, ΔY of the spurious responses of the B mode and the C mode decreases compared with the case where the height H of the unevenness is 0λ.

[0133] Accordingly, in Example 1, when the second insulating layer 12 is a silicon carbide layer or a diamond-like carbon layer having a sound velocity similar to that of silicon carbide, the height H of the unevenness of the first surface 60 is set to 0.8λ or more and 1.3λ or less. In other words, the height H of the unevenness is set to 8 times or more and 13 times or less the thickness of the piezoelectric layer 14. Accordingly, as Figure 9 shown in (a) thereof to Figure 9 (c) thereof, it is possible to suppress the reduction of the main response and suppress the spurious response. From the viewpoint of suppressing the reduction of the main response and suppressing the spurious response, the height H of the unevenness can be 0.85λ or more and 1.2λ or less, can be 0.9λ or more and 1.15λ or less, and can be 0.95λ or more and 1.1λ or less.

[0134] [Simulation 5-1, Simulation 5-2]

[0135] Regarding the elastic wave device 100 of Example 1, simulations 5-1 and 5-2 of the main response and the spurious response were performed by changing the pitch P of the unevenness of the first surface 60 of the second insulating layer 12. The conditions of Simulation 5-1 are as follows.

[0136] The first insulating layer 11: an alumina layer with an average thickness T1 = 3.5λ and a Q value = Q1 = 250

[0137] The second insulating layer 12: an aluminum nitride layer with an average thickness T2 = 0.75λ and a Q value = Q2 = 500

[0138] The height H of the unevenness on the first surface 60 of the second insulating layer 12: 0.5λ

[0139] The pitch of the unevenness on the first surface 60 of the second insulating layer 12: P

[0140] Other simulation conditions are the same as those in Simulation 3-1.

[0141] Figure 10 (a) to Figure 10 (d) of are graphs showing the absolute value |Y| of the admittance with respect to frequency in Simulation 5-1. Figure 10 (a) to Figure 10 (d) of are graphs of the cases where the pitch P of the unevenness is 0.3λ, 0.5λ, 0.7λ, and 0.8λ, respectively. As Figure 10 (a) to Figure 10 shown in (d) of, by changing the pitch P of the unevenness, the magnitude of the spurious response changes.

[0142] Figure 11 (a) and Figure 11 (b) of are graphs showing ΔY of the spurious responses of the B mode and the C mode with respect to the pitch P of the unevenness in Simulation 5-1. As Figure 11 (a) and Figure 11 (b) of show that when the pitch P of the unevenness is in the range of 0.1λ or more and 2.0λ or less, the ΔY of the spurious responses of the B mode and the C mode is reduced compared to the case without unevenness (0λ).

[0143] Therefore, in Embodiment 1, when the second insulating layer 12 is an aluminum nitride layer or a silicon nitride layer having a sound velocity similar to that of aluminum nitride, the pitch P of the unevenness on the first surface 60 of the second insulating layer 12 is set to be 0.1λ or more and 2.0λ or less. In other words, the pitch P of the unevenness is set to be 1 time or more and 20 times or less the thickness of the piezoelectric layer 14. Thereby, the spurious response can be suppressed. From the viewpoint of suppressing the spurious response, the pitch P of the unevenness can be 0.2λ or more and 1.8λ or less, can be 0.3λ or more and 1.6λ or less, or can be 0.4λ or more and 1.4λ or less. The pitch P of the unevenness can be the pitch of the unevenness within a 200-μm square region where the elastic wave resonator 26 is provided.

[0144] In Simulation 5-2, the second insulating layer 12 is a silicon carbide layer, the average thickness T2 is set to 0.75λ, and the Q value Q2 is set to 500. Other conditions are the same as those in Simulation 5-1.

[0145] Figure 12 (a) of FIG. shows the ΔY of the main response with respect to the pitch P of the unevenness in Simulation 5-2. Figure 12 (b) of FIG. and Figure 12 FIG. (c) shows the ΔY of the spurious responses of the B mode and C mode with respect to the pitch P of the unevenness. As Figure 12 (b) of FIG. and Figure 12 (c) of FIG. show, when the pitch P of the unevenness is in the range of 0.1λ or more and 2.0λ or less, the ΔY of the spurious responses of the B mode and C mode is reduced compared to the case without unevenness (0λ). And, as Figure 12 (a) of FIG. shows, when the pitch P of the unevenness is in the range of 0.1λ or more and 2.0λ or less, the reduction of the ΔY of the main response converges to 0.1 dB or less compared to the case without unevenness (0λ).

[0146] Therefore, in Example 1, when the second insulating layer 12 is a silicon carbide layer or a diamond-like carbon layer with a sound velocity similar to that of silicon carbide, the pitch P of the unevenness on the first surface 60 of the second insulating layer 12 is set to 0.1λ or more and 2.0λ or less. In other words, the pitch P of the unevenness is set to 1 time or more and 20 times or less the thickness of the piezoelectric layer 14. Thereby, spurious responses can be suppressed. From the viewpoint of suppressing spurious responses, the pitch P of the unevenness can be 0.2λ or more and 1.8λ or less, can be 0.3λ or more and 1.6λ or less, or can be 0.4λ or more and 1.4λ or less.

[0147] And, in Example 1, when the second insulating layer 12 is an aluminum oxide layer or an aluminum nitride layer, the average thickness T2 of the second insulating layer 12 is preferably 1.15λ or less. In other words, the average thickness T2 is preferably 11.5 times or less the thickness of the piezoelectric layer 14. This is for the following reason. Simulation 4-1 is the case where the average thickness T2 of the second insulating layer 12 is 0.75λ. According to Figure 8 (a) to Figure 8In (c), the preferred range of the height H of the unevenness on the first surface 60 is 0.3λ to 1.1λ. By setting the height H of the unevenness to 0.3λ or more, spurious response can be suppressed, and by setting it to 1.1λ or less, reduction of the main response can be suppressed. The shortest distance L between the first surface 60 and the second surface 61 of the second insulating layer 12 can be calculated by L = T2 - (H / 2). Therefore, when the height H of the unevenness is 0.3λ, the shortest distance L is 0.6λ. That is, the shortest distance L that can suppress spurious response is 0.6λ or less. Based on the fact that the height H of the unevenness that can suppress reduction of the main response is 1.1λ or less, the average thickness T2 of the second insulating layer 12 is 1.15λ or less. Thus, by setting the average thickness T2 of the second insulating layer 12 to 1.15λ or less, spurious response can be suppressed. From the viewpoint of suppressing spurious response, the average thickness T2 of the second insulating layer 12 is preferably 1.10λ or less, more preferably 1.05λ or less, and still more preferably 1.00λ or less.

[0148] Moreover, in Example 1, when the second insulating layer 12 is a silicon carbide layer or a diamond-like carbon layer, the average thickness T2 of the second insulating layer 12 is preferably 1.05λ or less. In other words, the average thickness T2 is preferably 10.5 times or less the thickness of the piezoelectric layer 14. This is because Simulation 4-2 is a case where the average thickness T2 of the second insulating layer 12 is 0.75λ. According to Figure 9 of (a) to Figure 9 of (c), the preferred range of the height H of the unevenness on the first surface 60 is 0.7λ to 1.3λ. Therefore, if calculated in the same manner as above, the average thickness T2 of the second insulating layer 12 is 1.05λ or less. Thus, by setting the average thickness T2 of the second insulating layer 12 to 1.05λ or less, the effect of suppressing spurious response can be obtained. From the viewpoint of suppressing spurious response, the average thickness T2 of the second insulating layer 12 is preferably 1.00λ or less, more preferably 0.95λ or less, and still more preferably 0.90λ or less.

[0149] In Simulations 4-1, 4-2, 5-1, and 5-2, as the piezoelectric layer 14, a 42° rotated Y-cut X-propagating lithium tantalate layer was used. However, if it is a rotated Y-cut X-propagating lithium tantalate layer, the main propagation direction of the elastic wave is the X-axis direction of the crystal orientation, which is the same as in the simulation. Thus, the results of Simulations 4-1, 4-2, 5-1, and 5-2 can be applied to the case where the piezoelectric layer 14 is a rotated Y-cut X-propagating lithium tantalate layer. Moreover, for a 30° to 60° rotated Y-cut X-propagating lithium tantalate layer, the SH wave is the main mode. Thus, in the case where the piezoelectric layer 14 is a 30° to 60° (or 36° to 50°) rotated Y-cut X-propagating lithium tantalate layer, the results of the simulation can be further applied. Additionally, the elastic wave can also be a Lamb wave or the like.

[0150] In Simulations 4-1, 4-2, 5-1, and 5-2, as the third insulating layer 13, a silicon oxide layer without addition was used. However, even if other elements such as fluorine, phosphorus, or boron are added to the silicon oxide layer, the sound velocity of the bulk wave of the third insulating layer 13 does not change significantly. Thus, the results of the simulation can be applied to the case where the third insulating layer 13 is a silicon oxide layer or a silicon oxide layer added with other elements such as fluorine, phosphorus, or boron. That is, in Example 1, the third insulating layer 13 can also be set as a silicon oxide layer or a silicon oxide layer added with fluorine, phosphorus, or boron.

[0151] In Simulations 4-1, 4-2, 5-1, and 5-2, as the first insulating layer 11, a polycrystalline or amorphous aluminum oxide layer was used. However, the results of the simulation can also be applied to the case of a polycrystalline or amorphous silicon nitride layer, a polycrystalline or amorphous aluminum nitride layer, or a polycrystalline or amorphous silicon carbide layer. Thus, in Example 1, in addition to setting the first insulating layer 11 as a polycrystalline or amorphous aluminum oxide layer, the first insulating layer 11 can also be set as a polycrystalline or amorphous silicon nitride layer, a polycrystalline or amorphous aluminum nitride layer, or a polycrystalline or amorphous silicon carbide layer.

[0152] In addition, "material name + layer" means that impurities may be intentionally or unintentionally contained in the layer in addition to the elements constituting the material, for example, the total of the elements constituting the material is 80 atomic% or more or 90 atomic% or more. For example, in the case of an aluminum nitride layer, the total content rate of aluminum and nitrogen is 80 atomic% or more or 90 atomic% or more.

[0153] [Modified Example]

[0154] Figure 13 of (a) to Figure 13 of (d) are cross-sectional views of the elastic wave devices 110 to 140 of Modified Example 1 to Modified Example 4 of Example 1. It can be like Figure 13 the elastic wave device 110 shown in (a) of. That is, the interface 62 between the support substrate 10 and the first insulating layer 11 is in the case of regular unevenness. Since the useless wave 52 is scattered at the interface 62 due to the unevenness of the interface 62 between the support substrate 10 and the first insulating layer 11, the spurious response can be further suppressed. In addition, the unevenness of the interface 62 is not limited to the regular case and can also be an irregular case.

[0155] It can be like Figure 13As in the case of the elastic wave device 120 shown in (b), a fourth insulating layer 15 is provided between the support substrate 10 and the first insulating layer 11. The fourth insulating layer 15 is, for example, an attenuation layer having a lower Q value than the first insulating layer 11. By providing the fourth insulating layer 15 with a low Q value, the unwanted wave 52 can be further attenuated in the fourth insulating layer 15, and thus spurious response can be further suppressed. The fourth insulating layer 15 may also be an insulating layer other than the attenuation layer. The Q value of the fourth insulating layer 15 is preferably 0.5 times or less, more preferably 0.2 times or less, of the Q value of the first insulating layer 11.

[0156] It can be as Figure 13 As in the case of the elastic wave device 130 shown in (c), a fifth insulating layer 17 having columnar voids 21 is provided between the support substrate 10 and the first insulating layer 11. The unwanted wave 52 is scattered at the voids 21, and thus spurious response can be further suppressed.

[0157] It can be as Figure 13 As in the case of the elastic wave device 140 shown in (d), the first surface 60 of the second insulating layer 12 is a rough surface having irregular unevenness.

[0158]

Example 2

[0159] Example 2 is an example of a wafer. Figure 14 It is a cross-sectional view of the wafer 200 of Example 2. As Figure 14 shown, the wafer 200 is not provided with the elastic wave resonator 26. Other structures are the same as those in (b) of Example 1, and the description thereof is omitted. The wafer 200 of Example 2 may also be a wafer in which the elastic wave resonator 26 is not provided in each modification of Example 1. Figure 1

[0160]

Example 3

[0161] Figure 15 From (a) to Figure 15 From (a) to (d) of Figure 15 are plan views of filters 300 to 330 of Example 3 to Modification 3 of Example 3. As Figure 13 From (a) to Figure 13 From (a) to (d) of Figure 13 shown, in the filters 300 to 330, one or more series resonators S1 to S4 are connected in series between the input terminal Tin and the output terminal Tout. One or more parallel resonators P1 to P3 are connected in parallel between the input terminal Tin and the output terminal Tout. The series resonators S1 to S4 and the parallel resonators P1 to P3 are the elastic wave resonators 26 shown in (a) of Example 1. The number of resonators of the ladder filter and the like can be appropriately set. In addition, the filter may also be a multi-mode filter. Figure 1

[0162] ​​It can be like Figure 15 In the case of the filter 300 shown in (a) of Figure 15 , the entire support substrate 10 is the region 65 (shaded portion) where the first surface 60 of the second insulating layer 12 is formed with irregularities and is a rough surface. It can be like Figure 15 In the case of the filter 310 shown in (b) of Figure 15 and Figure 15 In the case of the filter 320 shown in (c) of Figure 15 , the region 65 where the first surface 60 is a rough surface is divided into a plurality of parts, and two or more resonators among the series resonators S1 to S4 and the parallel resonators P1 to P3 are respectively arranged therein. It can be like Figure 15 In the case of the filter 330 shown in (d) of Figure 15 , the region 65 where the first surface 60 is a rough surface is divided into a plurality of parts, and one of the series resonators S1 to S4 and the parallel resonators P1 to P3 is respectively arranged therein.

[0163] The region 65 where the first surface 60 is a rough surface can be set in any manner as long as it is set to overlap with the entire body of all the resonators.

[0164]

Embodiment 4

[0165] Figure 16 is a circuit diagram of the duplexer 400 according to Embodiment 4. As shown in Figure 16 , in the duplexer 400, a transmit filter 70 is connected between the common terminal Ant and the transmit terminal Tx. A receive filter 72 is connected between the common terminal Ant and the receive terminal Rx. The transmit filter 70 allows the signal in the transmit band among the high-frequency signals input from the transmit terminal Tx to pass through the common terminal Ant as a transmit signal, and suppresses signals of other frequencies. The receive filter 72 allows the signal in the receive band among the high-frequency signals input from the common terminal Ant to pass through the receive terminal Rx as a receive signal, and suppresses signals of other frequencies. At least one of the transmit filter 70 and the receive filter 72 can be the filter according to Embodiment 3 and its modified examples. In addition, as the multiplexer, a duplexer is exemplified, but it can also be a triplexer or a quadruplexer.

[0166] As described above, the embodiments of the present invention have been described in detail, but the present invention is not limited to the specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims.

Claims

1. An elastic wave device, comprising: substrate; a piezoelectric layer disposed on the substrate; a pair of comb-shaped electrodes, the pair of comb-shaped electrodes being arranged on the piezoelectric layer; a first insulating layer, which is disposed between the substrate and the piezoelectric layer and is polycrystalline or amorphous aluminum oxide or polycrystalline silicon; and The second insulating layer is provided between the first insulating layer and the piezoelectric layer and is made of aluminum nitride, silicon nitride, silicon carbide or diamond-like carbon. The first surface of the second insulating layer on the first insulating layer side is rougher than the second surface on the piezoelectric layer side.

2. The elastic wave device according to claim 1, wherein: The average thickness of the second insulating layer is 7.5 times or more the thickness of the piezoelectric layer.

3. The elastic wave device according to claim 2, wherein: The second insulating layer is aluminum nitride or silicon nitride, An average height of the concavities and convexities on the first surface of the second insulating layer is not less than 3 times and not more than 11 times the thickness of the piezoelectric layer.

4. The elastic wave device according to claim 3, wherein: An average thickness of the second insulating layer is 11.5 times or less of a thickness of the piezoelectric layer.

5. The elastic wave device according to claim 2, wherein: The second insulating layer is silicon carbide or diamond-like carbon, An average height of the concavities and convexities on the first surface of the second insulating layer is not less than 8 times and not more than 13 times the thickness of the piezoelectric layer.

6. The elastic wave device according to claim 5, wherein: An average thickness of the second insulating layer is not more than 10.5 times the thickness of the piezoelectric layer.

7. The elastic wave device according to claim 3 or 5, wherein: An average pitch of the concavities and convexities on the first surface of the second insulating layer is not less than 1 time and not more than 20 times the thickness of the piezoelectric layer.

8. The elastic wave device according to claim 3 or 5, wherein: The elastic wave device has a third insulating layer, which is provided between the piezoelectric layer and the second insulating layer and is made of silicon oxide or silicon oxide to which fluorine, phosphorus or boron is added. The substrate is sapphire, The piezoelectric layer is a rotating Y-cut X-spread lithium tantalate, The first insulating layer is polycrystalline or amorphous aluminum oxide. A distance between an interface between the second insulating layer and the third insulating layer and an interface between the piezoelectric layer and the pair of comb-shaped electrodes is less than or equal to twice the thickness of the piezoelectric layer.

9. The elastic wave device according to claim 2, 4 or 6, wherein: The average thickness of the second insulating layer is an average of thicknesses at three points, namely, both end portions and a center portion of a cross section in a region where the pair of comb-shaped electrodes are provided.

10. An elastic wave device, comprising: substrate; a piezoelectric layer disposed on the substrate; a pair of comb-shaped electrodes, the pair of comb-shaped electrodes being arranged on the piezoelectric layer; a first insulating layer provided between the substrate and the piezoelectric layer and having a body wave acoustic velocity faster than a body wave acoustic velocity of the piezoelectric layer; and The second insulating layer is provided between the first insulating layer and the piezoelectric layer and has a body wave acoustic velocity faster than that of the first insulating layer. The first surface of the second insulating layer on the first insulating layer side is rougher than the second surface on the piezoelectric layer side.

11. A filter, wherein: The filter includes the elastic wave device according to claim 1 or 10.

12. A multiplexer, wherein: The multiplexer has the filter according to claim 11.

13. A wafer comprising: substrate; a piezoelectric layer disposed on the substrate; a first insulating layer, which is disposed between the substrate and the piezoelectric layer and is polycrystalline or amorphous aluminum oxide or polycrystalline silicon; and The second insulating layer is provided between the first insulating layer and the piezoelectric layer and is made of aluminum nitride, silicon nitride, silicon carbide or diamond-like carbon. The first surface of the second insulating layer on the first insulating layer side is rougher than the second surface on the piezoelectric layer side.

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