Elastic wave device, filter, multiplexer, and wafer

Abstract

To suppress spurious responses and also suppress degradation of main responses.SOLUTION: An elastic wave device 100 includes: a supporting substrate 10; a piezoelectric layer 14 formed on the supporting substrate 10; a pair of comb-shaped electrodes 20 provided on the piezoelectric layer 14; a first insulation layer 11 formed between the supporting substrate 10 and the piezoelectric layer 14, the first insulation layer being made of one of polycrystal or amorphous oxide aluminum and polycrystal or amorphous polysilicon; and a second insulation layer 12 formed between the first insulating layer 11 and the piezoelectric layer 14, the second insulation layer being made of aluminum nitride, silicon nitride, silicon carbide, or diamond-like carbon and having a first surface 60 adjacent to the first insulation layer 11 and a second surface 61 adjacent to the piezoelectric layer 14, and the first surface being rougher than the second surface.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] An elastic surface wave resonator is known as an elastic wave device used in communication devices such as smartphones. It is known to bond a piezoelectric layer forming the elastic surface wave resonator to a support substrate. It is known to make the thickness of the piezoelectric layer equal to or less than the wavelength of the elastic surface 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).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Summary of the Invention

Problems to be Solved by the Invention

[0004] By providing a high-speed layer between the low-speed layer and the support substrate, the main response can be improved, but the spurious response may deteriorate.

[0005] 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.

Means for Solving the Problems

[0006] The present invention includes 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 being polycrystalline or amorphous aluminum oxide or polysilicon, and a second insulating layer provided between the first insulating layer and the piezoelectric layer and being aluminum nitride, silicon nitride, silicon carbide, or diamond-like carbon, wherein a first surface on the first insulating layer side is rougher than a second surface on the piezoelectric layer side, and is an elastic wave device.

[0007] In the above configuration, the average thickness of the second insulating layer can be set to 7.5 times or more the thickness of the piezoelectric layer.

[0008] In the above configuration, the second insulating layer is aluminum nitride or silicon nitride, and the average height of the unevenness of the first surface of the second insulating layer can be set to 3 times or more and 11 times or less the thickness of the piezoelectric layer.

[0009] In the above configuration, the average thickness of the second insulating layer can be set to 11.5 times or less the thickness of the piezoelectric layer.

[0010] In the above configuration, the second insulating layer is silicon carbide or diamond-like carbon, and the average height of the unevenness of the first surface of the second insulating layer can be set to 8 times or more and 13 times or less the thickness of the piezoelectric layer.

[0011] In the above configuration, the average thickness of the second insulating layer can be set to 10.5 times or less the thickness of the piezoelectric layer.

[0012] In the above configuration, the average pitch of the unevenness on the first surface of the second insulating layer can be set to 1 time or more and 20 times or less the thickness of the piezoelectric layer.

[0013] In the above configuration, a third insulating layer provided between the piezoelectric layer and the second insulating layer, which is silicon oxide or silicon oxide added with fluorine, phosphorus, or boron, is provided. The substrate is sapphire, the piezoelectric layer is rotated Y-cut X-propagation lithium tantalate, the first insulating layer is polycrystalline or amorphous aluminum oxide, 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 can be set to 2 times or less the thickness of the piezoelectric layer.

[0014] In the above configuration, the average thickness of the second insulating layer can be set to the average of the thicknesses at three points, namely, both ends and the center of the cross section within the region where the pair of comb-shaped electrodes are provided.

[0015] The present invention is an elastic wave device including 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 the bulk wave sound velocity 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 the bulk wave sound velocity of the first insulating layer, wherein the first surface on the first insulating layer side is rougher than the second surface on the piezoelectric layer side.

[0016] The present invention is a filter including the elastic wave device described above.

[0017] The present invention is a multiplexer including the filter described above.

[0018] The present invention relates to a wafer comprising a substrate, a piezoelectric layer provided on the substrate, a first insulating layer provided between the substrate and the piezoelectric layer and being polycrystalline or amorphous aluminum oxide or polysilicon, and a second insulating layer provided between the first insulating layer and the piezoelectric layer and being aluminum nitride, silicon nitride, silicon carbide, or diamond-like carbon, wherein a first surface on the first insulating layer side is rougher than a second surface on the piezoelectric layer side.

Advantages of the Invention

[0019] According to the present invention, spurious response can be suppressed and deterioration of the main response can be suppressed.

Brief Description of the Drawings

[0020]

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Mode for Carrying Out the Invention

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

Embodiment

[0022] In Example 1, an example in which an elastic wave device has an elastic wave resonator will be described. FIG. 1(a) is a plan view of an elastic wave device 100 according to Example 1, FIG. 1(b) is a cross-sectional view taken along line A-A of FIG. 1(a), and FIG. 1(c) is a plan view of the first surface 60 of the second insulating layer 12. The arrangement direction of the electrode fingers 18 is defined as the X direction, the extending direction of the electrode fingers 18 is defined as the Y direction, and the stacking direction of the support substrate 10 and the piezoelectric layer 14 is defined 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.

[0023] As shown in FIGS. 1(a) and 1(b), 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. The first surface 60 of the second insulating layer 12 on the first insulating layer 11 side is a rough surface with larger irregularities than the second surface 61 on the piezoelectric layer 14 side. The measurement of the irregularities may be performed at any location in the plane. As shown in FIG. 1(c), the first surface 60 of the second insulating layer 12 has irregularities regularly formed by, for example, ridges 80 extending in the Y direction and valleys 81 alternating in the X direction. Note that the irregularities may be regularly formed by the convex portions or the concave portions being formed in an island shape.

[0024] 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 unevenness of 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 unevenness of the first surface 60 and the second surface 61. The average thicknesses T1 and T2 may be the average thicknesses within a 200 μm square region where the pair of comb-shaped electrodes 20 of the surface acoustic wave resonator 26 are provided. The average of the thicknesses at three points, namely both ends and the center, of an arbitrary cross-section in the region where the pair of comb-shaped electrodes 20 are provided may be used 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 unevenness of 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.

[0025] 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 by a metal film 16 on the piezoelectric layer 14.

[0026] The IDT 22 includes a pair of opposing comb-shaped electrodes 20. The comb-shaped electrode 20 includes 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-shaped electrodes 20 intersect is the intersection region 25. The length of the intersection region 25 is the aperture length. In at least a part of the intersection region 25 of the pair of comb-shaped electrodes 20, the electrode fingers 18 are alternately provided one by one. The surface acoustic wave mainly excited by the plurality of electrode fingers 18 in the intersection region 25 propagates mainly in the X direction. The pitch (the pitch between the centers of the electrode fingers 18) of the electrode fingers 18 of one of the pair of comb-shaped electrodes 20 is approximately equal to the wavelength λ of the surface acoustic wave. If the pitch of the plurality of electrode fingers 18 is D, the pitch of the electrode fingers 18 of one of the pair of comb-shaped electrodes 20 is D / 2 of the pitch of the electrode fingers 18. The reflector 24 reflects the surface acoustic wave excited by the electrode fingers 18 of the IDT 22. As a result, the surface acoustic wave is confined within the intersection region 25 of the IDT 22.

[0027] The piezoelectric layer 14 is, for example, a single crystal lithium tantalate (LiTaO 3 ) layer or a single crystal lithium niobate (LiNbO 3 ) layer, and is, for example, a rotated Y-cut X-propagation lithium tantalate layer or a rotated Y-cut X-propagation lithium niobate layer. The thickness T4 of the piezoelectric layer 14 is preferably 1.0λ or less, more preferably 0.5λ or less, from the viewpoint of suppressing spurious and loss. If the piezoelectric layer 14 becomes too thin, it becomes difficult to excite elastic waves, and therefore the thickness T4 is preferably 0.1λ or more.

[0028] 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, and the silicon carbide substrate is a polycrystalline or single crystal SiC substrate. The linear expansion coefficient of the support substrate 10 in the X direction is smaller than the linear expansion coefficient of the piezoelectric layer 14 in the X direction. Thereby, the frequency temperature dependence of the elastic wave resonator can be reduced.

[0029] The sound velocity of the bulk wave propagating through the first insulating layer 11 and the second insulating layer 12 is faster than that of the bulk wave propagating through the third insulating layer 13 and the piezoelectric layer 14. As a result, the energy of the elastic wave of the main response is confined within the piezoelectric layer 14 and the third insulating layer 13. The first insulating layer 11 is, for example, polycrystalline or amorphous, and is an aluminum oxide layer, a silicon nitride layer, an aluminum nitride layer, a silicon carbide layer, or a polysilicon layer. From the viewpoint of confining the elastic wave within 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, and more preferably 1.0λ or more. From the viewpoint of improving the characteristics, the average thickness T1 is preferably 10.0λ or less. Note that the sound velocity of the bulk wave of each layer is the sound velocity V S of the shear wave. When the shear modulus is G and the density is ρ, it is represented by Equation (1).

Equation

Equation

[0030] 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 that is not added or contains an additive element such as fluorine, phosphorus, or boron, and is, for example, polycrystalline or amorphous. Thereby, 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 bulk wave propagating through the third insulating layer 13 becomes slower than that of the bulk wave propagating through the piezoelectric layer 14.

[0031] For the third insulating layer 13 to have the function of temperature compensation, it is required that the energy of the elastic wave of the main response exists to a certain extent within the third insulating layer 13. Although the range where the energy of the surface elastic wave concentrates depends on the type of the surface elastic wave, typically, the energy of the surface elastic wave concentrates in the range of 2.0λ from the upper surface of the piezoelectric layer 14, and particularly concentrates 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, and 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 the thickness of the piezoelectric layer 14, and more preferably 1 time or less.

[0032] The second insulating layer 12 is a reflection layer that reflects the elastic wave of the main response. The sound velocity of the bulk wave propagating through the second insulating layer 12 is faster than the sound velocity of the bulk wave propagating through 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.

[0033] The metal film 16 is a film mainly composed of, for example, aluminum (Al), copper (Cu), or molybdenum (Mo). An adhesion film such as a titanium (Ti) film, a chromium (Cr) film, or a titanium nitride (TiN) film may be provided between the electrode finger 18 and the piezoelectric layer 14. The adhesion film is thinner than the electrode finger 18. An insulating layer may be provided so as to cover the electrode finger 18. The insulating layer functions as a protective film or a temperature compensation film.

[0034] 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 taken as a pair is, for example, from 20 pairs to 300 pairs. The duty ratio of the IDT22 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 IDT22 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 IDT22 in the X direction by the number of the electrode fingers 18.

[0035] [Comparative Example] Fig. 2(a) is a cross-sectional view of the elastic wave device 500 according to Comparative Example 1, and Fig. 2(b) is a cross-sectional view of the elastic wave device 600 according to Comparative Example 2. As shown in Fig. 2(a), 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 configurations are the same as those in Example 1 and will not be described. As shown in Fig. 2(b), in Comparative Example 2, the first surface 60 of the second insulating layer 12 is a flat surface without unevenness. Other configurations are the same as those in Example 1 and will not be described.

[0036] [Simulation 1] Regarding the elastic wave device 500 of Comparative Example 1, simulation 1 of the main response and spurious response was performed by changing the Q value of the first insulating layer 11. The conditions of simulation 1 are as follows. Support substrate 10: Sapphire substrate, Q value = 500 First insulating layer 11: Aluminum oxide layer, thickness T1 = 2.7λ, Q value = Q1 Third insulating layer 13: Silicon oxide layer, thickness T3 = 0.2λ, Q value = Q3 = 500 Piezoelectric layer 14: 42° rotated Y-cut X-propagating lithium tantalate substrate, T4 = 0.3λ, Q value = 2000 Metal film 16: Aluminum film, thickness is 0.07λ Wavelength λ (2×D) of elastic wave: 2.2μm The sound velocities of the bulk waves propagating through each layer are as follows. Support substrate 10: V0 = 7068.2m / s First insulating layer 11: V1 = 4581.8m / s Third insulating layer 13: V3 = 3683.5m / s Piezoelectric layer 14: V4 = 3750.8m / s The Q value is the Q value of vibration and is the reciprocal of the attenuation constant of the elastic wave.

[0037] First, the sound velocity V1 of the bulk wave of the first insulating layer 11 was set to 4581.8m / s, and the Q value Q1 of the first insulating layer 11 was changed to 1 time, 0.5 times, and 0.2 times with respect to the Q value Q3 of the third insulating layer 13.

[0038] Fig. 3(a) shows the absolute value |Y| of the admittance with respect to the frequency in Simulation 1, and Fig. 3(b) is a diagram showing ΔY with respect to Q1 / Q3. In Fig. 3(b), the dots indicate the simulation points and the curve is an approximate curve. The dashed line indicates the main response ΔY, and the solid line indicates the spurious response ΔY. The main response ΔY is the difference between |Y| at the resonance frequency fr and |Y| at the anti-resonance frequency fa in the main response Mn. The spurious response ΔY is the difference between the |Y| values of the response where the difference in |Y| in the spurious response SP is the largest.

[0039] As shown in Fig. 3(a), when Q1 = 0.2×Q3, although the spurious response SP is smaller than when Q1 = Q3, the difference between |Y| at the resonance frequency fr and |Y| at the anti-resonance frequency fa in the main response Mn is also smaller. As shown in Fig. 3(b), when Q1 / Q3 is decreased, the spurious response ΔY decreases, but the main response ΔY also decreases. Thus, when the Q value Q1 of the first insulating layer 11 is lowered and the attenuation constant is increased, the spurious response ΔY becomes smaller, but the main response ΔY also becomes smaller.

[0040] [Simulation 2] Regarding 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. First insulating layer 11: Aluminum oxide layer, thickness T1 = 2.7λ, Q value = 0.5×Q3 Sound velocity of the bulk wave of the first insulating layer 11: V1 The other simulation conditions are the same as those in Simulation 1.

[0041] Fig. 4(a) shows the absolute value |Y| of the admittance with respect to the frequency in Simulation 2, and Fig. 4(b) is a diagram showing ΔY with respect to the sound velocity V1 of the bulk wave of the first insulating layer 11. In Fig. 4(b), the dots indicate the simulation points and the curve is an approximate curve. The dashed line indicates the main response ΔY, and the solid line indicates the spurious response ΔY.

[0042] As shown in FIGS. 4(a) and 4(b), 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.

[0043] In Comparative Example 1, the reason why the main response deteriorates when trying to suppress the spurious response will be described with reference to FIG. 2(a). The electrode finger 18 excites the elastic surface wave 50 of the main response and the unwanted wave 52 of the spurious response. The elastic surface wave 50 is, for example, an SH (Shear Horizontal) wave, and the unwanted wave 52 is, for example, a bulk wave. As in Patent Document 4, the elastic surface wave 50 propagates in the range up to about 2.0λ from the upper surface of the piezoelectric layer 14. Therefore, when 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 (that is, when 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 total 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 elastic surface wave 50 and the attenuation of the unwanted wave 52 are considered.

[0044] The unwanted wave 52 is reflected at the interface 62 with the support substrate 10 to become a spurious response. The sound velocity V1 of the bulk wave of the first insulating layer 11 is made 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 elastic surface wave 50 with a low frequency is likely to be reflected at the interface 63 between the first insulating layer 11 and the third insulating layer 13. The unwanted wave 52 with a high frequency (for example, a bulk wave) is likely to transmit through the interface 63. The unwanted wave 52 that has transmitted through 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 Q value Q1, etc. of the first insulating layer 11, the unwanted wave 52 passing through the first insulating layer 11 can be attenuated. Thereby, the spurious response can be suppressed. On the other hand, since the elastic surface wave 50 is reflected at the interface 63 and confined in the piezoelectric layer 14 and the third insulating layer 13, the main response is less likely to deteriorate.

[0045] However, at the interface 63, in order for the surface acoustic wave 50 to be reflected and the unwanted wave 52 to be transmitted, it is a condition 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 confinement effect of the surface acoustic wave 50 is not sufficient, and a part of the surface acoustic wave 50 penetrates into the first insulating layer 11. For this reason, the surface acoustic wave 50 is attenuated and the main response deteriorates.

[0046] In Simulation 1, by lowering the Q value Q1 of the first insulating layer 11, spurious response can be suppressed. However, since the surface acoustic wave 50 that has penetrated into the first insulating layer 11 is attenuated, the main response deteriorates. In Simulation 2, by increasing the sound velocity V1 of the bulk wave of the first insulating layer 11, penetration of the surface acoustic wave 50 into the first insulating layer 11 can be suppressed, and 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 likely to be reflected at the interface 63, so the spurious response increases.

[0047] In Comparative Example 2, as shown in Fig. 2(b), 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. Thereby, the surface acoustic wave 50 is likely to be reflected at the interface 64 between the second insulating layer 12 and the third insulating layer 13 and is less likely to penetrate into the first insulating layer 11. Thereby, deterioration of the main response can be suppressed. Also, the unwanted wave 52 penetrates through the interface 64 and enters the first insulating layer 11. Thereby, the unwanted wave 52 is attenuated in the first insulating layer 11, and spurious response can be suppressed.

[0048] [Simulations 3-1, 3-2] Regarding the elastic wave device 600 of Comparative Example 2, simulations 3-1 and 3-2 of the main response and spurious response were performed by changing the thickness T2 of the second insulating layer 12. The conditions of Simulation 3-1 are as follows. Support substrate 10: Sapphire substrate, Q value = 500 First insulating layer 11: Aluminum oxide layer, thickness T1 = 3.5λ, Q value = Q1 = 250 Second insulating layer 12: Aluminum nitride layer, thickness T2, Q value = Q2 = 500 Third insulating layer 13: Silicon oxide layer, thickness T3 = 0.2λ, Q value = Q3 = 500 Piezoelectric layer 14: 42° rotated Y-cut X-propagating lithium tantalate substrate, T4 = 0.3λ, Q value = 2000 Metal film 16: Aluminum film, thickness is 0.07λ Wavelength λ (2×D) of elastic wave: 2.0 μm The sound velocities of bulk waves propagating through each layer are as follows. Support substrate 10: V0 = 7068.2 m / s First insulating layer 11: V1 = 4581.8 m / s Second insulating layer 12: V2 = 6029 m / s Third insulating layer 13: V3 = 3683.5 m / s Piezoelectric layer 14: V4 = 3750.8 m / s

[0049] FIG. 5(a) is a diagram showing ΔY of the main response with respect to the thickness T2 of the second insulating layer 12 in Simulation 3-1. FIGS. 5(b) and 5(c) are diagrams 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 ΔY of the spurious response that occurs at a frequency close to the main response, shown in region A of FIG. 7(a). The spurious response of the C mode is ΔY of the spurious response that occurs at a frequency higher than the spurious response of the B mode, shown in region B of FIG. 7(a).

[0050] As shown in Fig. 5(a), as the thickness T2 of the second insulating layer 12 increases, the main response ΔY increases, but it saturates at about 0.75λ and does not change much even if it becomes thicker. As shown in Figs. 5(b) and 5(c), when the thickness T2 of the second insulating layer 12 is 0.75λ or more, the spurious response ΔY increases.

[0051] Simulation 3-2 is the same as the conditions of Simulation 3-1 except that the second insulating layer 12 is a silicon carbide layer, the thickness T2 is 0.75λ, the Q value Q2 is 500, and the sound velocity V2 is 6983 m / s.

[0052] Fig. 6(a) is a diagram showing ΔY of the main response with respect to the thickness T2 of the second insulating layer 12 in Simulation 3-2. Figs. 6(b) and 6(c) are diagrams showing ΔY of the spurious responses in the B mode and the C mode with respect to the thickness T2 of the second insulating layer 12 in Simulation 3-2. As shown in Fig. 6(a), even when the second insulating layer 12 is a silicon carbide layer, as the thickness T2 of the second insulating layer 12 increases, the main response ΔY increases, but it saturates at about 0.75λ and does not change much even if it becomes thicker. As shown in Figs. 6(b) and 6(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 increases. Thus, in the elastic 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, but when the thickness T2 becomes 0.75λ or more, the spurious response ΔY increases.

[0053] In Simulation 3-1, an aluminum nitride layer was used for the second insulating layer 12, and in Simulation 3-2, a silicon carbide layer was used. However, it is considered that the same results can be obtained when using a silicon nitride layer having a sound velocity similar to that of aluminum nitride or a diamond-like carbon (DLC) layer having a sound velocity similar to that of silicon carbide.

[0054] Therefore, in Example 1, as shown in Fig. 1(b), the second insulating layer 12 provided between the first insulating layer 11 and the piezoelectric layer 14 has a bulk wave sound velocity faster than that of the bulk 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 bulk wave sound velocity of the second insulating layer 12 is faster than that of the bulk wave of the first insulating layer 11, the surface acoustic wave 50 is likely to be reflected at the interface 64 between the second insulating layer 12 and the third insulating layer 13 and is less likely to 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 unwanted wave 52 that has penetrated into the second insulating layer 12 is scattered at the first surface 60. Thereby, spurious response can be suppressed.

[0055] When the bulk wave sound velocity V0 of the support substrate 10 is high, the unwanted wave 52 is likely to be reflected at the interface 62 between the support substrate 10 and the first insulating layer 11, and spurious response is likely to occur. On the other hand, for the viewpoint of supporting each layer, a hard material may be used for the support substrate 10. When the bulk wave sound velocity V0 of the support substrate 10 is faster than the bulk wave sound velocity V2 of the second insulating layer 12, it is preferable to provide the first insulating layer 11 and the second insulating layer 12. The bulk wave sound velocity V0 of the support substrate 10 is, for example, 1.1 times or more, and 1.2 times or more of the bulk wave sound velocity V2 of the second insulating layer 12.

[0056] If the bulk wave sound velocity V2 of the second insulating layer 12 is too fast, the unwanted wave 52 is likely to be reflected at the interface 64 of the second insulating layer 12. From this viewpoint, the bulk wave sound velocity V2 of the second insulating layer 12 is preferably 1.5 times or less, more preferably 1.4 times or less, still more preferably 1.2 times or less, and still more preferably 1.1 times or less of the bulk wave sound velocity V1 of the first insulating layer 11. From the viewpoint of making it easy to reflect 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 of the sound velocity V1.

[0057] If the sound velocity V1 of the bulk wave of the first insulating layer 11 is too fast, the unwanted wave 52 is less likely to penetrate into the first insulating layer 11. From this perspective, the sound velocity V1 of the bulk wave of the first insulating layer 11 is preferably 1.5 times or less, more preferably 1.3 times or less, of 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. If the sound velocity V1 of the bulk wave of the first insulating layer 11 is too slow, the surface acoustic wave 50 will penetrate into the first insulating layer 11. From this perspective, the sound velocity V1 is preferably 1.05 times or more, more preferably 1.2 times or more, of the sound velocity V4 and the sound velocity V3.

[0058] [Simulations 4-1, 4-2] Regarding 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 for Simulation 4-1 are as follows. First insulating layer 11; aluminum oxide layer, average thickness T1 = 3.5λ, Q value = Q1 = 250 Second insulating layer 12 layer: aluminum nitride layer, average thickness T2 = 0.75λ, Q value = Q2 = 500 Height H of the unevenness on the first surface 60 of the second insulating layer 12 Pitch P of the unevenness on the first surface 60 of the second insulating layer 12: 0.5λ Other simulation conditions are the same as those in Simulation 3-1.

[0059] Figures 7(a) to 7(f) are diagrams showing the absolute value |Y| of the admittance with respect to the frequency in Simulation 4-1. Figures 7(a) to 7(f) are diagrams for the cases where the height H of the unevenness is 0λ, 0.1λ, 0.3λ, 0.45λ, 0.7λ, and 1.3λ, respectively. As shown in Figures 7(a) to 7(f), the magnitude of the spurious response changes as the height H of the unevenness changes.

[0060] FIG. 8(a) is a diagram showing ΔY of the main response with respect to the height H of the unevenness in Simulation 4-1. FIGS. 8(b) and 8(c) are diagrams showing ΔY of the spurious responses in the B mode and the C mode with respect to the height H of the unevenness in Simulation 4-1. As shown in FIG. 8(a), 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 shown in FIGS. 8(b) and 8(c), when the height H of the unevenness is 0.3λ or more, ΔY of the spurious responses in the B mode and the C mode decreases compared to the case where the height H of the unevenness is 0λ.

[0061] From 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 set to 7.5 times or more the thickness of the piezoelectric layer 14. Thereby, as shown in FIGS. 5(a) and 6(a), the main response can be increased.

[0062] Further, 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 on 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. Thereby, as shown in FIGS. 8(a) to 8(c), the spurious response can be suppressed while suppressing the decrease in the main response. From the viewpoint of suppressing the decrease in the main response and suppressing the spurious response, the height H of the unevenness may be 0.35λ or more and 1.0λ or less, or 0.4λ or more and 0.9λ or less, or 0.45λ or more and 0.8λ or less. The height H of the unevenness may be the height of the unevenness within a 200 μm square region where the elastic wave resonator 26 is provided.

[0063] Simulation 4-2 is the same as the conditions of Simulation 4-1 except that the second insulating layer 12 is a silicon carbide layer, the average thickness T2 is 0.75λ, the Q value Q2 is 500, and the sound velocity V2 is 6983 m / s.

[0064] FIG. 9(a) is a diagram showing ΔY of the main response with respect to the height H of the unevenness in Simulation 4-2. FIGS. 9(b) and 9(c) are diagrams showing ΔY of the spurious responses in the B mode and the C mode with respect to the height H of the unevenness in Simulation 4-2. As shown in FIG. 9(a), when the height H of the unevenness is 1.3λ 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 shown in FIGS. 9(b) and 9(c), when the height H of the unevenness is 0.8λ or more, ΔY of the spurious responses in the B mode and the C mode decreases compared to the case where the height H of the unevenness is 0λ.

[0065] From this, in Example 1, when the second insulating layer 12 is a silicon carbide layer or a diamond-like carbon layer having a sound velocity comparable to that of silicon carbide, the height H of the unevenness on the first surface 60 is set to be 0.8λ or more and 1.3λ or less. In other words, the height H of the unevenness is set to be 8 times or more and 13 times or less the thickness of the piezoelectric layer 14. Thereby, as shown in FIGS. 9(a) to 9(c), it is possible to suppress the spurious response while suppressing the decrease in the main response. From the viewpoint of suppressing the decrease in the main response and suppressing the spurious response, the height H of the unevenness may be 0.85λ or more and 1.2λ or less, or 0.9λ or more and 1.15λ or less, or 0.95λ or more and 1.1λ or less.

[0066] [Simulations 5-1, 5-2] 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 on the first surface 60 of the second insulating layer 12. The conditions for Simulation 5-1 are as follows. First insulating layer 11; aluminum oxide layer, average thickness T1 = 3.5λ, Q value = Q1 = 250 Second insulating layer 12: aluminum nitride layer, average thickness T2 = 0.75λ, Q value = Q2 = 500 Height H of the unevenness on the first surface 60 of the second insulating layer 12: 0.5λ Pitch P of the unevenness on the first surface 60 of the second insulating layer 12 Other simulation conditions are the same as those in Simulation 3-1.

[0067] Figures 10(a) to 10(d) are diagrams showing the absolute value |Y| of admittance with respect to frequency in Simulation 5-1. Figures 10(a) to 10(d) are diagrams for the cases where the pitch P of the unevenness is 0.3λ, 0.5λ, 0.7λ, and 0.8λ, respectively. As shown in Figures 10(a) to 10(d), the magnitude of the spurious response changes as the pitch P of the unevenness changes.

[0068] Figures 11(a) and 11(b) are diagrams showing ΔY of the spurious responses in the B mode and the C mode with respect to the pitch P of the unevenness in Simulation 5-1. As shown in Figures 11(a) and 11(b), in the range where the pitch P of the unevenness is 0.1λ or more and 2.0λ or less, ΔY of the spurious responses in the B mode and the C mode is lower than that in the case where there is no unevenness (0λ).

[0069] Therefore, in Example 1, when the second insulating layer 12 is an aluminum nitride layer or a silicon nitride layer having the same sound velocity as that of aluminum nitride, 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, the spurious response can be suppressed. From the viewpoint of suppressing the spurious response, the pitch P of the unevenness may be 0.2λ or more and 1.8λ or less, may be 0.3λ or more and 1.6λ or less, or may be 0.4λ or more and 1.4λ or less. The pitch P of the unevenness may be the pitch of the unevenness within a 200-μm square region where the elastic wave resonator 26 is provided.

[0070] Simulation 5-2 is the same as the conditions of Simulation 5-1 except that the second insulating layer 12 is a silicon carbide layer, the average thickness T2 is 0.75λ, and the Q value Q2 is 500.

[0071] Fig. 12(a) is a diagram showing ΔY of the main response with respect to the pitch P of the unevenness in Simulation 5-2, and Figs. 12(b) and 12(c) are diagrams showing ΔY of the spurious responses in the B mode and the C mode with respect to the pitch P of the unevenness. As shown in Figs. 12(b) and 12(c), in the range where the pitch P of the unevenness is 0.1λ or more and 2.0λ or less, the ΔY of the spurious responses in the B mode and the C mode is lower than that in the case where there is no unevenness (0λ). Further, as shown in Fig. 12(a), in the range where the pitch P of the unevenness is 0.1λ or more and 2.0λ or less, the decrease in ΔY of the main response is within 0.1 dB compared to the case where there is no unevenness (0λ).

[0072] Therefore, in Example 1, when the second insulating layer 12 is a silicon carbide layer or a diamond-like carbon layer having a sound velocity comparable 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 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 may be 0.2λ or more and 1.8λ or less, or 0.3λ or more and 1.6λ or less, or 0.4λ or more and 1.4λ or less.

[0073] Also, 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, and the preferable range of the height H of the unevenness on the first surface 60 is 0.3λ to 1.1λ from FIGS. 8(a) to 8(c). 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, a decrease in the main response can be suppressed. Since the shortest distance L between the first surface 60 and the second surface 61 of the second insulating layer 12 can be calculated as L = T2 - (H / 2), when the height H of the unevenness is 0.3λ, the shortest distance L is 0.6λ. That is, considering that the shortest distance L capable of suppressing spurious response is 0.6λ or less and the height H of the unevenness capable of suppressing a decrease in the main response is 1.1λ or less, the average thickness T2 of the second insulating layer 12 is 1.15λ or less. Therefore, 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.

[0074] Also, in Example 1, when the second insulating layer 12 is a silicon carbide layer or a carbonaceous layer containing carbon nanotubes, 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 in Simulation 4-2, when the average thickness T2 of the second insulating layer 12 is 0.75λ, and the preferable range of the height H of the unevenness on the first surface 60 is 0.7λ to 1.3λ from FIGS. 9(a) to 9(c), when calculated in the same manner as above, the average thickness T2 of the second insulating layer 12 is 1.05λ or less. Therefore, 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.

[0075] In Simulations 4-1, 4-2, 5-1, and 5-2, a 42° rotated Y-cut X-propagating lithium tantalate layer was used as the piezoelectric layer 14. However, for any 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. Therefore, the results of Simulations 4-1, 4-2, 5-1, and 5-2 can be applied when the piezoelectric layer 14 is a rotated Y-cut X-propagating lithium tantalate layer. Also, a 30° to 60° rotated Y-cut X-propagating lithium tantalate layer has an SH wave as the main mode. Therefore, when the piezoelectric layer 14 is a 30° to 60° (or 36° to 50°) rotated Y-cut X-propagating lithium tantalate layer, the simulation results can be more applicable. Note that the elastic wave may be a Lamb wave or the like.

[0076] In Simulations 4-1, 4-2, 5-1, and 5-2, an undoped silicon oxide layer was used as the third insulating layer 13. 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 in the third insulating layer 13 does not change significantly. Therefore, the simulation results can be applied when the third insulating layer 13 is a silicon oxide layer or a silicon oxide layer doped with other elements such as fluorine, phosphorus, or boron. That is, in Example 1, the third insulating layer 13 may be a silicon oxide layer or a silicon oxide layer doped with fluorine, phosphorus, or boron.

[0077] In Simulations 4-1, 4-2, 5-1, and 5-2, a polycrystalline or amorphous aluminum oxide layer was used as the first insulating layer 11. However, the simulation results can also be applied in 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. Therefore, in Example 1, in addition to a polycrystalline or amorphous aluminum oxide layer, the first insulating layer 11 may be a polycrystalline or amorphous silicon nitride layer, a polycrystalline or amorphous aluminum nitride layer, or a polycrystalline or amorphous silicon carbide layer.

[0078] Note that the "material name + layer" allows for the intentional or unintentional inclusion of impurities in addition to the elements constituting the material in the layer. For example, the total of the elements constituting the material is 80 atomic % or more, or 90 atomic % or more. For example, in the aluminum nitride layer, the total of the aluminum and nitrogen contents is 80 atomic % or more, or 90 atomic % or more.

[0079] [Modification Example] Figs. 13(a) to 13(d) are cross-sectional views of the elastic wave devices 110 to 140 according to Modification Example 1 to Modification Example 4 of Example 1. Even when the interface 62 between the support substrate 10 and the first insulating layer 11 has regular irregularities as in the elastic wave device 110 shown in Fig. 13(a), it may be acceptable. Since the unnecessary wave 52 is scattered at the interface 62 due to the irregularities of the interface 62 between the support substrate 10 and the first insulating layer 11, spurious response can be more effectively suppressed. Note that the irregularities of the interface 62 are not limited to the regular case and may be irregular.

[0080] Even when a fourth insulating layer 15 is provided between the support substrate 10 and the first insulating layer 11 as in the elastic wave device 120 shown in Fig. 13(b), it may be acceptable. The fourth insulating layer 15 is, for example, a damping 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 unnecessary wave 52 can be more effectively attenuated in the fourth insulating layer 15, so that spurious response can be more effectively suppressed. The fourth insulating layer 15 may be an insulating layer other than the damping layer. The Q value of the fourth insulating layer 15 is preferably 0.5 times or less, and more preferably 0.2 times or less, of the Q value of the first insulating layer 11.

[0081] Even when a fifth insulating layer 17 having columnar voids 21 is provided between the support substrate 10 and the first insulating layer 11 as in the elastic wave device 130 shown in Fig. 13(c), it may be acceptable. Since the unnecessary wave 52 is scattered by the voids 21, spurious response can be more effectively suppressed.

[0082] Even when the first surface 60 of the second insulating layer 12 has a rough surface with irregular irregularities as in the elastic wave device 140 shown in Fig. 13(d), it may be acceptable.

Example

[0083] Example 2 is an example of a wafer. FIG. 14 is a cross-sectional view of a wafer 200 according to Example 2. As shown in FIG. 14, the wafer 200 is not provided with the surface acoustic wave resonator 26. Other configurations are the same as those in FIG. 1(b) of Example 1 and the description thereof is omitted. The wafer 200 of Example 2 may be a wafer in which the surface acoustic wave resonator 26 is not provided in each modification of Example 1.

Example

[0084] FIGS. 15(a) to 15(d) are plan views of filters 300 to 330 according to Example 3 and Modification 3 of Example 3. As shown in FIGS. 13(a) to 13(d), 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 surface acoustic wave resonators 26 shown in FIG. 1(a) of Example 1. The number of resonators of the ladder type filter and the like can be set as appropriate. Note that the filter may be a multi-mode type filter.

[0085] As in the filter 300 shown in FIG. 15(a), the region 65 (hatched portion) where irregularities are formed on the first surface 60 of the second insulating layer 12 and which is a rough surface may be the entire support substrate 10. As in the filter 310 shown in FIG. 15(b) and the filter 320 shown in FIG. 15(c), the region 65 where the first surface 60 is a rough surface is divided into a plurality of parts, and two or more of the series resonators S1 to S4 and the parallel resonators P1 to P3 may be arranged in each part. As in the filter 330 shown in FIG. 15(d), the region 65 where the first surface 60 is a rough surface is divided into a plurality of parts, and each of the series resonators S1 to S4 and the parallel resonators P1 to P3 may be arranged in each part.

[0086] The region 65 where the first surface 60 is a rough surface may be provided in any manner as long as it overlaps the whole in all resonators.

Example

[0087] FIG. 16 is a circuit diagram of a duplexer 400 according to Embodiment 4. As shown in FIG. 16, in the duplexer 400, a transmission filter 70 is connected between a common terminal Ant and a transmission terminal Tx. A reception filter 72 is connected between the common terminal Ant and a reception terminal Rx. The transmission filter 70 passes, as a transmission signal, a signal in a transmission band among high-frequency signals input from the transmission terminal Tx to the common terminal Ant, and suppresses signals of other frequencies. The reception filter 72 passes, as a reception signal, a signal in a reception band among high-frequency signals input from the common terminal Ant to the reception terminal Rx, and suppresses signals of other frequencies. At least one of the transmission filter 70 and the reception filter 72 can be the filter of Embodiment 3 and its modified examples. Although a duplexer is shown as an example of the multiplexer, a triplexer or a quadplexer may also be used.

[0088] As described above in detail with respect to the embodiments of the present invention, the present invention is not limited to such specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

Explanation of Reference Numerals

[0089] 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... intersection region, 26... surface acoustic wave resonator, 50... surface acoustic wave, 52... unwanted wave, 60... first surface, 61... second surface, 62... interface, 63... interface, 64... interface, 65... region, 70... transmission filter, 72... reception filter, 80... peak portion, 81... valley portion, 100 to 140, 500, 600... surface acoustic wave device, 200... wafer, 300 to 330... filter, 400... duplexer

Claims

1. 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 aluminum oxide or polysilicon; 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 on the first insulating layer side is rougher than a second surface on the piezoelectric layer side, an elastic wave device comprising the same.

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

3. The second insulating layer is aluminum nitride or silicon nitride, The elastic wave device according to claim 2, wherein an average height of unevenness of the first surface of the second insulating layer is 3 times or more and 11 times or less 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 the thickness of the piezoelectric layer.

5. The second insulating layer is silicon carbide or diamond-like carbon, The elastic wave device according to claim 2, wherein an average height of unevenness of the first surface of the second insulating layer is 8 times or more and 13 times or less 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 10.5 times or less the thickness of the piezoelectric layer.

7. The elastic wave device according to claim 3 or 5, wherein an average pitch of unevenness of the first surface of the second insulating layer is 1 time or more and 20 times or less the thickness of the piezoelectric layer.

8. comprising a third insulating layer provided between the piezoelectric layer and the second insulating layer, which is silicon oxide, or silicon oxide added with fluorine, phosphorus, or boron, the substrate is sapphire, the piezoelectric layer is rotated Y-cut X-propagation lithium tantalate, the first insulating layer is polycrystalline or amorphous aluminum oxide, The elastic wave device according to claim 3 or 5, wherein 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 2 times or less the thickness of the piezoelectric layer.

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

10. 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, having a bulk wave sound velocity faster than that of the bulk wave of the piezoelectric layer; An elastic wave device comprising: a second insulating layer provided between the first insulating layer and the piezoelectric layer, having a bulk wave sound velocity faster than that of the bulk wave of the first insulating layer, and a first surface on the first insulating layer side being rougher than a second surface on the piezoelectric layer side.

11. A filter comprising the elastic wave device according to claim 1 or claim 10.

12. A multiplexer comprising the filter according to claim 11.

13. 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 aluminum oxide or polysilicon; A wafer comprising: 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 on the first insulating layer side being rougher than a second surface on the piezoelectric layer side.

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