Elastic wave device, wafer, filter and multiplexer

Abstract

To provide an elastic wave device that suppresses spurious.SOLUTION: An elastic wave device comprises a support substrate 10, a piezoelectric layer 14 provided on the support substrate 10, at least a pair of comb-type electrodes 20 provided on the piezoelectric layer 14 and provided with a plurality of electrode fingers 18, an insulating layer 15 provided between the support substrate 10 and the piezoelectric layer 14 and thicker than the piezoelectric layer 14, a void layer 30 provided between the support substrate 10 and the insulating layer 15, and that overlaps more than 70% in plan view with a crossing area 25 where one of the electrode fingers 18 of a pair of comb-type electrodes 20 overlaps with the other electrode finger 18 of the pair of comb-type electrodes 20, viewed from the array direction of the plurality of electrode fingers 18.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an elastic wave device, a wafer, a filter, and a multiplexer, and more particularly to an elastic wave device, a wafer, a filter, and a multiplexer having a pair of comb-shaped electrodes, for example.

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] By providing a high acoustic velocity film and a low acoustic velocity film between the piezoelectric layer and the support substrate, spurious can be suppressed. Further, spurious can be suppressed by providing a damping layer between the piezoelectric layer and the support substrate. However, further suppression of spurious is required.

[0005] The present invention has been made in view of the above problems, and aims to suppress spurious signals.

Means for Solving the Problems

[0006] The present invention includes a support substrate, a piezoelectric layer provided on the support substrate, at least a pair of comb-shaped electrodes provided on the piezoelectric layer and having a plurality of electrode fingers, an insulating layer provided between the support substrate and the piezoelectric layer and being thicker than the piezoelectric layer, and a void layer provided between the support substrate and the insulating layer and overlapping, in a plan view, by 70% or more an intersection region where one electrode finger of the pair of comb-shaped electrodes overlaps with the other electrode finger of the pair of comb-shaped electrodes as viewed from the arrangement direction of the plurality of electrode fingers. It is an elastic wave device.

[0007] In the above configuration, the piezoelectric layer can be configured as a rotated Y-cut X-propagation lithium tantalate substrate or a rotated Y-cut lithium niobate substrate.

[0008] In the above configuration, the insulating layer can be configured to include a first insulating layer provided on the void layer and a second insulating layer provided between the first insulating layer and the piezoelectric layer, having silicon oxide as a main component and having a sound velocity of a bulk wave propagating therein slower than that of the bulk wave propagating in the first insulating layer.

[0009] In the above configuration, the distance between the surface of the first insulating layer on the support substrate side and the surface of the piezoelectric layer on the pair of comb-shaped electrode side can be configured to be 4 times or less the average pitch of the plurality of electrode fingers.

[0010] In the above configuration, in the intersection region, the width of the void layer in the arrangement direction of the plurality of electrode fingers can be configured to be 10 times or more the average pitch of the plurality of electrode fingers.

[0011] In the above configuration, the void layer can be configured to overlap the intersection region by 90% or more in a plan view.

[0012] In the above configuration, in a plan view, a support layer that is surrounded by the void layer, overlaps the intersection region, and connects the support substrate and the insulating layer can be provided.

[0013] In the above configuration, another void layer provided in the insulating layer and overlapping 70% or more of the intersection region in a plan view can be provided.

[0014] The present invention is a wafer including a support substrate, a piezoelectric layer provided on the support substrate, an insulating layer provided between the support substrate and the piezoelectric layer and thicker than the piezoelectric layer, and a void layer provided between the support substrate and the insulating layer, having a shape similar to the planar shape of the support substrate, having the center of the planar shape of the support substrate coincide with the center, and overlapping 70% or more of a region having 64% of the planar area of the support substrate in a plan view.

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

[0016] The present invention is a multiplexer including the above-described filter.

Advantages of the Invention

[0017] According to the present invention, spurious can be suppressed.

Brief Description of the Drawings

[0018]

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Mode for Carrying Out the Invention

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

Embodiment

[0020] In Example 1, an example in which an elastic wave device has an elastic wave resonator will be described. FIGS. 1(a) and 1(b) are a plan view and a cross-sectional view of the elastic wave resonator in Example 1. The arrangement direction of the electrode fingers is the X direction, the extending direction of the electrode fingers is the Y direction, and the stacking direction of the support substrate and the piezoelectric layer is the Z direction. The X direction, Y direction, and Z direction do not necessarily correspond to the X-axis direction and Y-axis direction of the crystal orientation of the piezoelectric layer. When the piezoelectric layer is a rotation Y-cut X-propagation substrate, the X direction becomes the X-axis direction of the crystal orientation.

[0021] As shown in FIGS. 1(a) and 1(b), a piezoelectric layer 14 is provided on a support substrate 10. An insulating layer 15 is provided between the support substrate 10 and the piezoelectric layer 14. The insulating layer 15 includes a temperature compensation film 13 provided between the support substrate 10 and the piezoelectric layer 14, and a boundary layer 12 provided between the temperature compensation film 13 and the support substrate 10. A void layer 30 is provided between the insulating layer 15 and the support substrate 10. The void layer 30 is a layer made of a gas such as air and is formed by a depression 31 provided on the upper surface of the support substrate 10.

[0022] An elastic wave resonator 26 is provided on the piezoelectric layer 14. The elastic 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.

[0023] The IDT22 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 when viewed from the X direction 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. The elastic wave mainly excited by the plurality of electrode fingers 18 in the intersection region 25 propagates mainly in the X direction. The pitch of the electrode fingers 18 of one of the pair of comb-shaped electrodes 20 is approximately equal to the wavelength λ of the elastic wave. If the pitch of the plurality of electrode fingers 18 (the pitch between the centers of the electrode fingers 18) is D, the pitch of the electrode fingers 18 of one of the comb-shaped electrodes 20 is D / 2 of the electrode fingers 18. The reflector 24 reflects the elastic wave (surface elastic wave) excited by the electrode fingers 18 of the IDT22. Thereby, the elastic wave is confined within the intersection region 25 of the IDT22.

[0024] The piezoelectric layer 14 is, for example, a single crystal lithium tantalate (LiTaO3) layer or a single crystal lithium niobate (LiNbO3) layer, and is, for example, a rotated Y-cut X-propagating lithium tantalate layer or a rotated Y-cut X-propagating lithium niobate layer.

[0025] 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 Al2O3 substrate, the alumina substrate is a polycrystalline or amorphous Al2O3 substrate, the silicon substrate is a single crystal or polycrystalline silicon substrate, the spinel substrate is a polycrystalline or amorphous MgAl2O4 substrate, the quartz substrate is a single crystal SiO2 substrate, the quartz substrate is a polycrystalline or amorphous SiO2 substrate, and the silicon carbide substrate is a polycrystalline or single crystal SiC substrate. The linear expansion coefficient of the support substrate 10 in the X direction is smaller than 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. The sound velocity of the bulk wave propagating through the support substrate 10 is faster than the sound velocity of the bulk wave propagating through the boundary layer 12. Note that the sound velocity of the bulk wave propagating through the support substrate 10 may be slower than the sound velocity of the bulk wave propagating through the boundary layer 12.

[0026] The temperature compensation film 13 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 temperature compensation film 13 is positive. The temperature compensation film 13 is an insulating film mainly composed of silicon oxide (SiO2), for example, a silicon oxide (SiO2) film without addition or containing an additive element such as fluorine, and is, for example, polycrystalline or amorphous. Thereby, the frequency temperature coefficient of the surface acoustic wave resonator can be reduced. When the temperature compensation film 13 is a silicon oxide film, the sound velocity of the bulk wave propagating through the temperature compensation film 13 becomes slower than the sound velocity of the bulk wave propagating through the piezoelectric layer 14.

[0027] In order for the temperature compensation film 13 to have a temperature compensation function, it is required that the energy of the elastic wave of the main response exists to a certain extent in the temperature compensation film 13. Although the range in which the energy of the surface acoustic wave is concentrated depends on the type of the surface acoustic wave, typically, the energy of the surface acoustic wave is concentrated in the range of 2λ (λ is the wavelength of the elastic wave) from the upper surface of the piezoelectric layer 14, and particularly concentrated in the range of λ from the upper surface of the piezoelectric layer 14. Therefore, the distance from the lower surface of the temperature compensation film 1 to the upper surface of the piezoelectric layer 14 is preferably 2λ or less, more preferably 1λ or less, and even more preferably 0.6λ or less.

[0028] The sound velocity of the bulk wave propagating through the boundary layer 12 is faster than the sound velocity of the bulk wave propagating through the temperature compensation film 13. Thereby, the energy of the elastic wave of the main response is confined in the piezoelectric layer 14 and the temperature compensation film 13. Further, the sound velocity of the bulk wave propagating through the boundary layer 12 is slower than the sound velocity of the bulk wave propagating through the support substrate 10. The boundary layer 12 is, for example, polycrystalline or amorphous, and is an aluminum oxide film, a silicon nitride film, an aluminum nitride film, or a silicon film. The boundary layer 12 may be formed by laminating a plurality of layers made of different materials.

[0029] 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 or a chromium (Cr) 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 film may be provided so as to cover the electrode finger 18. The insulating film functions as a protective film or a temperature compensation film.

[0030] Figures 2(a) to 3(c) are cross-sectional views showing a method for manufacturing an elastic wave device according to Example 1. As shown in Figure 2(a), a depression 31 is formed on the upper surface of the support substrate 10. For the formation of the depression 31, for example, photolithography and etching methods are used. As shown in Figure 2(b), a sacrificial layer 38 is formed on the support substrate 10 so as to be embedded in the depression 31. The sacrificial layer 38 is preferably a material with selectivity in etching with respect to the support substrate 10 and the boundary layer 12, and is, for example, magnesium oxide.

[0031] As shown in Figure 2(c), the upper surface of the sacrificial layer 38 is polished. For example, the CMP (Chemical Mechanical Polishing) method is used for polishing the sacrificial layer 38. Thereby, the sacrificial layer 38 on the support substrate 10 in the region other than the depression 31 is removed, and the depression 31 is filled with the sacrificial layer 38. The upper surface of the sacrificial layer 38 and the upper surface of the support substrate 10 in the region other than the depression 31 become substantially flat. As shown in Figure 2(d), an insulating layer 12a is formed on the support substrate 10 and the sacrificial layer 38. For the formation of the insulating layer 12a, for example, the CVD (Chemical Vapor Deposition) method, vacuum evaporation method, or sputtering method is used. A through-hole 32 is formed in the insulating layer 12a using photolithography and etching methods. As shown in Figure 2(e), the sacrificial layer 38 in the depression 31 is removed by introducing an etching solution from the through-hole 32. Thereby, a void layer 30 is formed in the depression 31.

[0032] As shown in Fig. 3(a), an insulating layer 12b is formed on the insulating layer 12a. A temperature compensation film 13 is formed on the insulating layer 12b. For the formation of the insulating layer 12b and the temperature compensation film 13, for example, the CVD method, the vacuum evaporation method, or the sputtering method is used. The boundary layer 12 is formed by the insulating layers 12a and 12b, and the insulating layer 15 is formed by the boundary layer 12 and the temperature compensation film 13. The insulating layers 12a and 12b may be insulating layers mainly composed of the same material, or insulating layers with different main components. As shown in Fig. 3(b), a piezoelectric layer 14 is bonded onto the temperature compensation film 13. For the bonding of the piezoelectric layer 14, for example, the surface activation method is used. As shown in Fig. 3(c), the upper surface of the piezoelectric layer 14 is polished to thin the piezoelectric layer 14. For the polishing of the piezoelectric layer 14, for example, the CMP method is used. Thereby, the wafer 48 is completed. Thereafter, an elastic wave resonator 26 is formed on the piezoelectric layer 14. Thereby, an elastic wave device is manufactured.

[0033] [Simulation] For resonators A to C, the admittance characteristics were two-dimensionally simulated. Figs. 4(a) to 4(c) are cross-sectional views of resonators A to C in the simulation. In Figs. 4(a) to 4(c), one wavelength is illustrated. As shown in Fig. 4(a), in resonator A, an intermediate layer 11 is provided between the support substrate 10 and the boundary layer 12. The thicknesses of the intermediate layer 11, the boundary layer 12, the temperature compensation film 13, and the piezoelectric layer 14 are T1, T2, T3, and T4, respectively. The other configurations are the same as the layer configuration in Fig. 1(b).

[0034] As shown in Fig. 4(b), in resonator B, a cavity 33 is provided in the intermediate layer 11. The cavity 33 is circular, and the centers of the two cavities 33 are located on the center line 33a of a straight line that passes through the center in the X direction of the electrode finger 18 and extends in the Z direction. Let the distance between the upper surface of the intermediate layer 11 and the center of the upper cavity 33 be D1, the distance between the centers of the cavities 33 be D2, and the distance between the lower surface of the intermediate layer 11 and the center of the lower cavity 33 be D3. The other configurations are the same as those of resonator A.

[0035] As shown in Fig. 4(c), in resonator C, a void layer 30 is provided between the intermediate layer 11 and the support substrate 10. The thickness of the void layer 30 is T30. Other configurations are the same as those of resonator C.

[0036] The simulation conditions are as follows. Wavelength λ of elastic wave: 2 μm Piezoelectric layer 14: 42° Y-cut X-propagating lithium tantalate (LiTaO3) substrate with a thickness T4 of 0.6 μm (0.3λ) Temperature compensation film 13: Silicon oxide (SiO2) film with a thickness T3 of 0.4 μm (0.2λ) Boundary layer 12: Aluminum oxide (Al2O3) film with a thickness T2 of 5 μm (2.5λ) Intermediate layer 11: Silicon oxide film with a thickness T1 of 2 μm (1λ) Void layer 30: Air layer with a thickness T30 of 0.25 μm (0.125λ) Hole 33: Air layer with a radius D4 of 0.25 μm (0.125λ) Position of holes: D1 = D3 = 0.5 μm, D2 = 1.0 μm Support substrate 10: Sapphire substrate The simulation was performed for 100 pairs of resonators. The sound velocities of bulk waves of each material used in the simulation were as follows. Support substrate 10: 7068.2 m / s Intermediate layer 11: 3683.5 m / s Boundary layer 12: 4581.8 m / s Temperature compensation film 13: 3683.5 m / s Piezoelectric layer 14: 3750.8 m / s

[0037] Resonator A corresponds to providing an intermediate layer 11 with a slower sound velocity of bulk wave than that of the boundary layer 12 between the boundary layer 12 and the support substrate 10. Resonator B corresponds to providing a porous layer as the intermediate layer. Resonator C corresponds to the embodiment having a void layer 30.

[0038] Figures 5(a) to 5(d) are diagrams showing the magnitude of admittance |Y| with respect to the frequency of resonators A to C in the simulation. Figures 5(a) to 5(c) are the admittances of resonators A to C respectively, and Figure 5(d) is an enlarged view near the spurious response of Figures 5(a) to 5(c).

[0039] As shown in Figures 5(a) to 5(c), the main response 58 is observed near 1900 MHz. A spurious response 59 is observed at 2300 MHz to 3300 MHz on the high-frequency side of the main response 58. The difference between |Y| at the resonance frequency and |Y| at the anti-resonance frequency in the main response 58 in resonators A to C is the magnitude of the main response main ΔY. The main ΔY of resonators A to C is all 88.18 dB and there is no difference. The spurious response 59 is large at 2700 MHz to 2900 MHz out of 2300 MHz to 3300 MHz.

[0040] As shown in Figure 5(d), the magnitude of the largest spurious response among the spurious responses 59 is spurious ΔY. The spurious ΔY of resonators A to C is as follows. Resonator A: 23.76 dB Resonator B: 23.33 dB Resonator C: 19.51 dB As in the above simulation, even if the void layer 30 is provided, the main ΔY hardly changes. Resonator B with the intermediate layer 11 being a porous layer has a smaller spurious ΔY than resonator A. Resonator C with the void layer 30 provided has an even smaller spurious ΔY than resonator B. Thus, providing the void layer 30 can suppress spurious.

[0041] The reason why spurious signals can be suppressed by providing the void layer 30 will be explained. FIG. 6(a) is a cross-sectional view of the elastic wave resonator of Comparative Example 1, and FIG. 6(b) is an enlarged view of the support substrate 10 and the boundary layer 12. As shown in FIG. 6(a), in Comparative Example 1, the void layer 30 is not provided. Other configurations are the same as those in FIG. 1(b) of Example 1. The sound velocity of the bulk wave in the boundary layer 12 is faster than the sound velocities of the bulk waves in the temperature compensation film 13 and the piezoelectric layer 14. Therefore, the slow elastic wave 50 including the elastic wave which is the main mode is reflected at the interface 35 between the temperature compensation film 13 and the boundary layer 12. Thereby, the main ΔY can be increased.

[0042] The elastic wave 52 including a bulk wave faster than the elastic wave 50 passes through the interface 35. The sound velocity of the bulk wave in the support substrate 10 is faster than the sound velocity of the bulk wave in the boundary layer 12. Therefore, the elastic wave 52 including a bulk wave faster than the elastic wave 50 is reflected at the interface 36 between the boundary layer 12 and the support substrate 10 and returns to the IDT22. Thereby, the high-frequency spurious ΔY becomes large. By increasing the thickness of the boundary layer 12, the elastic wave 52 is attenuated by passing through the boundary layer 12. However, the attenuation of the elastic wave 52 is not sufficient.

[0043] In FIG. 6(b), the displacement of the elastic wave 52 is schematically shown. When the intermediate layer 11 is displaced, if a hard (i.e., the sound velocity of the bulk wave is fast) support substrate 10 is provided under the intermediate layer 11, the displacement is strongly reflected. Thereby, the reflection of the elastic wave 52 at the interface 36 becomes large. Therefore, the spurious signals become large.

[0044] FIG. 7(a) is a cross-sectional view of the elastic wave resonator of Example 1, and FIG. 7(b) is an enlarged view of the support substrate 10 and the boundary layer 12. As shown in FIG. 7(a), in Example 1, the elastic wave 52 is reflected at the interface 37 between the boundary layer 12 and the void layer 30. At this time, the reflection of the elastic wave 52 at the interface 37 is smaller than that of Comparative Example 1 in FIG. 6(a).

[0045] As shown in FIG. 7(b), in Example 1, when the intermediate layer 11 is displaced by the elastic wave 52, since there is a void layer 30 under the intermediate layer 11, the reflection of the displacement is small. As a result, the reflection of the elastic wave 52 at the interface 36 becomes small. Therefore, spurious caused by the elastic wave 52 can be reduced.

[0046] According to Example 1, Example 2, and their modified examples, an insulating layer 15 is provided between the support substrate 10 and the piezoelectric layer 14. A void layer 30 is provided between the support substrate 10 and the insulating layer 15. Thereby, spurious can be suppressed.

[0047] The difference between the void layer 30 and the damping layer in Patent Document 3 will be described. In Patent Document 3, a porous material is used as the damping layer. This corresponds to the resonator B. However, the suppression of spurious in the resonator B is insufficient.

[0048] On the other hand, in Example 1, all of the intersection regions 25 in the IDT 22 overlap with the void layer 30. Thereby, the reflection of the elastic wave 52 at the interface 37 between the void layer 30 and the boundary layer 12 can be suppressed. Therefore, spurious can be suppressed. The void layer 30 does not have to overlap 100% with the intersection region 25 in plan view. The void layer 30 preferably overlaps 70% or more, more preferably 80% or more, and even more preferably 90% or more with the intersection region 25 in plan view. Also, in the intersection region 25, the width of the void layer 30 in the X direction is preferably 10 times (5λ) or more, more preferably 20 times (10λ) or more of the average pitch D of the plurality of electrode fingers. If the void layer 30 is thick, the manufacturing man-hours increase. From this viewpoint, the thickness T30 of the void layer 30 is preferably 10λ or less, more preferably 2λ or less, and even more preferably 1λ or less. If the void layer 30 is thin, the support substrate 10 and the insulating layer 15 may come into contact. From this viewpoint, the thickness T30 of the void layer 30 is preferably 0.01λ or more, more preferably 0.1λ or more.

[0049] An elastic wave device that provides a void layer between a piezoelectric layer 14 and a support substrate 10 will be described, which is different from Lamb waves. In a Lamb wave device, the elastic wave reflected on the lower surface of the piezoelectric layer 14 is the main mode. Therefore, an insulating layer is not provided on the lower surface of the piezoelectric layer 14. Even if an insulating layer is provided, it is thinner than the piezoelectric layer 14. Further, the thickness of the piezoelectric layer 14 is 0.1λ to 0.2λ. Furthermore, for Lamb waves, a rotated Z-cut lithium niobate substrate is used. Since elastic waves other than Lamb waves (e.g., SH (Shear Horizontal) waves) are dominant in a lithium tantalate substrate, a lithium tantalate substrate is not used for a Lamb wave device.

[0050] On the other hand, in Example 1, the insulating layer 15 is thicker than the piezoelectric layer 14. This is because the insulating layer has functions such as a temperature compensation film function and / or an elastic wave attenuation function. The thickness T2 + T3 of the insulating layer 15 is preferably 1.5 times or more, more preferably 2.0 times or more, the thickness T4 of the piezoelectric layer 14. The piezoelectric layer 14 is a rotated Y-cut X-propagating lithium tantalate substrate or a rotated Y-cut lithium niobate substrate. Thereby, the IDT22 mainly excites an elastic surface wave. When the elastic wave mainly excited by the pair of comb-shaped electrodes 20 is an SH wave, a bulk wave is likely to be excited as an unnecessary wave. When the piezoelectric layer 14 is a rotated Y-cut X-propagating lithium tantalate layer of 36° or more and 48° or less, an SH wave is excited.

[0051] Although an example of two layers, i.e., the temperature compensation film 13 and the boundary layer 12, has been described as the insulating layer 15, the insulating layer 15 may be a single-layer insulating layer of a uniform material such as a silicon oxide layer, an aluminum oxide layer, or an aluminum nitride layer. In Example 1, the boundary layer 12 (the first insulating layer) is provided on the void layer 30, and the temperature compensation film 13 (the second insulating layer) is provided on the boundary layer 12. The temperature compensation film 13 is mainly composed of silicon oxide. Thereby, the sign of the temperature coefficient of the elastic constant of the temperature compensation film 13 becomes opposite to the sign of the temperature coefficient of the elastic constant of the piezoelectric layer 14, and the frequency temperature coefficient can be reduced. The sound velocity of the bulk wave propagating through the temperature compensation film 13 is made slower than the sound velocity of the bulk wave propagating through the boundary layer 12. Thereby, the elastic surface wave is confined in the piezoelectric layer 14 and the temperature compensation film 13, and the loss is suppressed. Further, the boundary layer 12 attenuates the elastic wave with the unnecessary bulk wave. The boundary layer 12 is mainly composed of aluminum oxide, for example.

[0052] Here, it is allowed that a certain layer has a certain component as the main component, a certain layer contains impurities intentionally or unintentionally added in addition to a certain component, and the atomic concentration of a certain component in a certain layer is, for example, 50 atomic % or more, 80 atomic % or more, or 90 atomic % or more. For example, when the temperature compensation film 13 has silicon oxide as the main component, it is allowed that the temperature compensation film 13 contains impurities such as fluorine, and the total of the oxygen concentration and the silicon concentration in the temperature compensation film 13 is 50 atomic % or more, 80 atomic % or more, or 90 atomic % or more, and the oxygen concentration and the silicon concentration are each 10 atomic % or more or 20 atomic % or more. Further, when the boundary layer 12 has aluminum oxide as the main component, it is allowed that the boundary layer 12 contains impurities, and the total of the oxygen concentration and the aluminum concentration in the boundary layer 13 is 50 atomic % or more, 80 atomic % or more, or 90 atomic % or more, and the oxygen concentration and the aluminum concentration are each 10 atomic % or more or 20 atomic % or more.

[0053] In FIGS. 6(a) and 7(a), when the boundary layer 12 becomes thin, the elastic wave 50 is less likely to be confined in the piezoelectric layer 14 and the temperature compensation film 13, and the main response deteriorates. From this viewpoint, the thickness T2 of the boundary layer 12 is preferably 2.2 times (1.1λ) or more of the average pitch D of the electrode fingers 18, and more preferably 3.0 times (1.5λ) or more. When the boundary layer 12 is thickened, the manufacturing process increases and the difficulty of the manufacturing process rises. From this viewpoint, the thickness T2 of the boundary layer 12 is preferably 10 times (5λ) or less of the average pitch D of the electrode fingers 18, and more preferably 8 times (4λ) or less.

[0054] From the viewpoint of passing the elastic wave 52 including the bulk wave through the boundary layer 12, the thickness T3 of the temperature compensation film 13 is preferably 1.5 times (0.75λ) or less of the average pitch D of the electrode fingers 18, and more preferably 1 time (0.5λ) or less. From the viewpoint of exerting the temperature compensation function of the temperature compensation film 13, the thickness T3 is preferably 0.05 times (0.1λ) or more of the average pitch D of the electrode fingers 18, and more preferably 0.1 times (0.2λ) or more.

[0055] From the viewpoint of making the energy of the elastic wave of the main response exist in the temperature compensation film 13, the thickness T4 of the piezoelectric layer 14 is preferably 2 times (1λ) or less of the average pitch D of the plurality of electrode fingers 18, and more preferably 1 time (0.5λ) or less. From the viewpoint of functioning the piezoelectric layer 14, the thickness T4 of the piezoelectric layer 14 is preferably 0.05 times (0.1λ) or more of the average pitch D of the plurality of electrode fingers 18, and more preferably 0.1 times (0.2λ) or more.

[0056] When most of the energy of the surface elastic wave exists in the range from the surface of the piezoelectric layer 14 to 2λ, from the viewpoint of confining the energy of the elastic wave of the main response in the piezoelectric layer 14 and the temperature compensation film 13 and suppressing the spurious response, the distance (T3 + T4) between the surface of the temperature compensation film 13 on the support substrate 10 side and the surface of the piezoelectric layer 14 on the side of the comb-shaped electrode 20 is preferably 4 times (2λ) or less of the average pitch D of the plurality of electrode fingers 18, more preferably 3 times (1.5λ) or less, and even more preferably 2 times (1λ) or less.

[0057] The sound velocity of the bulk wave propagating through the temperature compensation film 13 may be faster than the sound velocity of the bulk wave propagating through the piezoelectric layer 14, but since elastic waves are likely to exist in the temperature compensation film 13, it is preferable that the sound velocity of the bulk wave propagating through the temperature compensation film 13 is slower than the sound velocity of the bulk wave propagating through the piezoelectric layer 14. Thereby, it can function more effectively as the temperature compensation film 13. The sound velocity of the bulk wave propagating through the temperature compensation film 13 is preferably 0.99 times or less of the sound velocity of the bulk wave propagating through the piezoelectric layer 14. If the sound velocity of the bulk wave propagating through the temperature compensation film 13 is too slow, it becomes difficult for elastic waves to exist in the piezoelectric layer 14. Therefore, the sound velocity of the bulk wave propagating through the temperature compensation film 13 is preferably 0.9 times or more of the sound velocity of the bulk wave propagating through the piezoelectric layer 14.

[0058] The sound velocity of the bulk wave propagating through the boundary layer 12 is preferably 1.1 times or more, more preferably 1.2 times or more, of the sound velocity of the bulk wave propagating through the temperature compensation film 13. Also, the sound velocity of the bulk wave propagating through the boundary layer 12 is preferably greater than the sound velocity of the bulk wave propagating through the piezoelectric layer 14. If the sound velocity of the bulk wave propagating through the boundary layer 12 is too fast, the elastic wave 52 including the bulk wave is reflected at the interface 35 between the boundary layer 12 and the temperature compensation film 13. From this viewpoint, the sound velocity of the bulk wave propagating through the boundary layer 12 is preferably 2.0 times or less, more preferably 1.5 times or less, of the sound velocity of the bulk wave propagating through the temperature compensation film 13.

[0059] [Modification Example 1 of Example 1] FIG. 8(a) is a cross-sectional view of the elastic wave resonator according to Modification Example 1 of Example 1. As shown in FIG. 8(a), the upper surface of the support substrate 10 may be a rough surface or an uneven surface. Since elastic waves hardly propagate through the void layer 30, the material of the support substrate 10 and the state of the upper surface of the support substrate 10 do not affect spuriousness much. However, when a portion 10a of the support substrate 10 where the void layer 30 is not formed in the region overlapping the IDT 22 is provided, it is preferable that the interface 36 between the portion 10a and the boundary layer 12 is a rough surface or an uneven surface. Thereby, since elastic waves are scattered at the interface 36, spuriousness can be suppressed. Other configurations are the same as those in Example 1 and the description thereof is omitted.

[0060] [Modification Example 2 of Example 1] FIG. 8(b) is a cross-sectional view of the surface acoustic wave resonator according to Modification 2 of Example 1. As shown in FIG. 8(b), the interface 35 between the temperature compensation film 13 and the boundary layer 12 may be a rough surface or an uneven surface. Since the surface acoustic wave is scattered at the interface 35, spurious can be suppressed. Other configurations are the same as those in Example 1 and the description thereof is omitted.

[0061] [Modification 3 of Example 1] FIG. 8(c) is a cross-sectional view of the surface acoustic wave resonator according to Modification 3 of Example 1. As shown in FIG. 8(c), a bonding layer 21 is provided between the piezoelectric layer 14 and the temperature compensation film 13. The bonding layer 21 bonds the piezoelectric layer 14 and the temperature compensation film 13. When it is difficult to directly bond the piezoelectric layer 14 and the temperature compensation film 13, the bonding layer 21 may be provided. The bonding layer 21 is, for example, an aluminum oxide film, a silicon film, an aluminum nitride film, a silicon nitride film, or a silicon carbide film. From the viewpoint of not impairing the functions of the piezoelectric layer 14 and the temperature compensation film 13, the thickness of the bonding layer 21 is preferably 20 nm or less, more preferably 10 nm or less. From the viewpoint of not impairing the function as the bonding layer 21, the thickness of the bonding layer 15 is preferably 1 nm or more, more preferably 2 nm or more. From the viewpoint of confining the surface acoustic wave of the main response in the piezoelectric layer 14, the sound velocity of the bulk wave propagating through the bonding layer 21 is preferably faster than the sound velocity of the bulk wave propagating through the temperature compensation film 13. Other configurations are the same as those in Example 1 and the description thereof is omitted.

[0062] [Modification 4 of Example 1] FIGS. 9(a) and 9(b) are plan views of the surface acoustic wave resonator according to Modification 4 of Example 1. FIG. 10(a) is a cross-sectional view of the surface acoustic wave resonator according to Modification 4 of Example 1 and is a cross-sectional view taken along line A-A of FIGS. 9(a) and 9(b). As shown in FIGS. 9(a) to 10(a), a support layer 34 that does not overlap the void layer 30 may be provided in a region overlapping the intersection region 25. As shown in FIG. 9(a), the support layer 34 may be provided in an island shape so as to be surrounded by the void layer 30 in a plan view. As shown in FIG. 9(b), the support layer 34 may be provided between a plurality of void layers 30 arranged in a plane direction. The support layer 34 may be a part of the support substrate 10 or may be formed of a material different from the support substrate 10.

[0063] If the planar area of the void layer 30 is large, the laminated film on the void layer 30 may be bent or damaged. By connecting the support layer 34 to the boundary layer 12 and supporting the boundary layer 12 on the support substrate 10, bending or damage of the laminated film on the void layer 30 can be suppressed. If the planar area of the support layer 34 is too large, elastic waves are reflected at the interface between the support layer 34 and the boundary layer 12. Therefore, the area of the void layer 30 overlapping the intersection region 25 in the IDT 22 in plan view in terms of the planar area of the intersection region 25 in the IDT 22 is preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more. The spurious ΔY of the resonator C in the simulation is 4 dB smaller than the spurious ΔY of the resonators A and B. When the ratio of the void layer 30 overlapping the intersection region 25 in the IDT 22 is 91.6%, the improvement of the spurious ΔYn is 3.5 dB, which is fully acceptable.

[0064] [Modification Example 5 of Example 1] FIGS. 10(b) and 10(c) are cross-sectional views of the surface acoustic wave resonator according to Modification Example 5 of Example 1. As shown in FIGS. 10(b) and 10(c), an insulating layer 12c may be provided on the insulating layer 12a, and a void layer 30a may be provided between the insulating layers 12a and 12b. The insulating layers 12a and 12b may have the same material as the main component or different materials as the main component. A support layer 34a may be provided in the void layer 30a. The support layer 34a may be a part of the insulating layer 12a or may be formed of a material different from the insulating layer 12a. As shown in FIG. 10(b), the support layer 34 and the support layer 34a may overlap in plan view. As shown in FIG. 10(c), the support layers 34 and 34a may not overlap in plan view.

[0065] In Modification Example 4 of Example 1, since the elastic wave is reflected at the interface between the support layer 34 and the boundary layer 12, the spurious is larger than that in Example 1. According to Modification Example 5 of Example 1, the void layer 30a (another void layer) is provided in the insulating layer 15 and overlaps the intersection region 25 by 70% or more in plan view. By providing the void layer 30a, the elastic wave is attenuated in either the void layer 30 or 30a. Therefore, even if the support layer 34 is provided, the spurious can be suppressed. Three or more void layers overlapping the intersection region 25 by 70% or more may be provided in the Z direction. As shown in FIG. 10(b), when the support layers 34 and 34a overlap in plan view, the elastic wave passing through the support layer 34a may be reflected at the interface between the insulating layer 12a and the support layer 34 and reach the IDT22 through the support layer 34a. In FIG. 10(c), since the support layers 34 and 34a do not overlap in plan view, reflection of the elastic wave passing through the support layer 34a at the interface between the insulating layer 12a and the support layer 34 is suppressed, and the spurious can be further suppressed.

Example

[0066] Example 2 is an example in which the elastic wave resonator according to Example 1 and its modification is used in a filter. FIG. 11 is a circuit diagram of the filter according to Example 2. As shown in FIG. 11, series resonators S1 to S4 are connected in series between the input terminal Tin and the output terminal Tout. Parallel resonators P1 to P3 are connected in parallel between the input terminal Tin and the output terminal Tout. One end of the parallel resonators P1 to P3 is connected to the path between the input terminal Tin and the output terminal Tout, and the other end is connected to the ground terminal Gnd.

[0067] Figs. 12(a) to 13(b) are plan views of the filter according to Example 2. As shown in Figs. 12(a) to 13(b), an elastic wave resonator 26, wirings 44, and pads 45 are provided on a support substrate 10 and a piezoelectric layer 14. The elastic wave resonator 26 has an IDT 22 and a reflector 24. The wirings 44 electrically connect between the elastic wave resonators 26 and between the elastic wave resonator 26 and the pad 45. The pad 45 is electrically connected to the outside through a via wiring (not shown) penetrating the support substrate 10 or a bump (not shown) provided on the pad 45. The wirings 44 and the pads 45 are metal layers including a gold layer, a copper layer, or an aluminum layer. The plurality of elastic wave resonators 26 include series resonators S1 to S4 and parallel resonators P1 to P3. The plurality of pads 45 include an input terminal Tin, an output terminal Tout, and a ground terminal Gnd.

[0068] As shown in Fig. 12(a), a plurality of void layers 30 may be provided corresponding to the plurality of elastic wave resonators 26 respectively. As shown in Fig. 12(b), three void layers 30 are provided, and the series resonator S1 and the parallel resonator P1 may overlap one void layer 30, the series resonators S2, S3, and the parallel resonator P2 may overlap one void layer 30, and the series resonator S4 and the parallel resonator P3 may overlap one void layer. As shown in Fig. 13(a), two void layers 30 are provided, and the series resonators S1 to S4 may overlap one void layer 30, and the parallel resonators P1 to P3 may overlap one void layer 30. As shown in Fig. 13(b), one void layer 30 is provided, and the series resonators S1 to S4 and the parallel resonators P1 to P3 may overlap one void layer 30.

[0069] When the laminated film on the void layer 30 is likely to be bent or damaged, as shown in Fig. 12(a), it is preferable to provide a large number of void layers 30. When the laminated film on the void layer 30 is unlikely to be bent or damaged, as shown in Fig. 13(b), one void layer 30 may be provided. The number of void layers 30 can be set as appropriate. As in Modifications 4 and 5 of Example 1, a support layer 34 may be provided in the void layer 30. The elastic wave resonators of Example 1 and its modifications may be used for at least one of the series resonators S1 to S4 and the parallel resonators P1 to P3. The number of resonators of the ladder-type filter, etc. can be set as appropriate. The filter may be a multi-mode type filter.

[0070] Fig. 14 is a plan view of a wafer for forming the filter of Fig. 13(b). As shown in Fig. 14, the void layer 30 is provided in a matrix pattern on the wafer 48. The cutting line 49 for cutting the wafer 48 is not provided with the void layer 30. The elastic wave device is not formed in the peripheral region of the wafer 48. A region 47 having a center that coincides with the center 46 of the wafer 48 and is similar to the planar shape of the wafer 48 (i.e., the planar shape of the support substrate 10) is defined. Let the diameter of the wafer 48 be R1 and the diameter of the region 47 be R2. If R2 = 0.8×R1 (i.e., the planar area of the region 47 is 64% of the planar area of the support substrate 10), the peripheral region where the elastic wave device is not formed is hardly included in the region 47. Therefore, the void layer 30 overlaps the region 47 by 70% or more in plan view. R2 = 0.7×R1 (i.e., the planar area of the region 47 is 49% of the planar area of the support substrate 10) may be used, or R2 = 0.6×R1 (i.e., the planar area of the region 47 is 36% of the planar area of the support substrate 10) may be used.

[0071] [Modification 1 of Example 2] FIG. 15 is a circuit diagram of a duplexer according to Modification 1 of Example 2. As shown in FIG. 15, a transmission filter 40 is connected between the common terminal Ant and the transmission terminal Tx. A reception filter 42 is connected between the common terminal Ant and the reception terminal Rx. The transmission filter 40 passes, as a transmission signal, a signal in the transmission band among the high-frequency signals input from the transmission terminal Tx to the common terminal Ant, and suppresses signals of other frequencies. The reception filter 42 passes, as a reception signal, a signal in the reception band among the 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 40 and the reception filter 42 can be the filter of Example 2.

[0072] Although the duplexer has been described as an example of the multiplexer, a triplexer or a quadplexer may also be used.

[0073] As described above in detail with reference 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.

Description of Reference Numerals

[0074] 10 Support substrate 11 Intermediate layer 12 Boundary layer 12a, 12b, 15 Insulating layer 13 Temperature compensation film 14 Piezoelectric layer 16 Metal film 18 Electrode finger 20 Comb-shaped electrode 21 Bonding layer 22 IDT 25 Intersection region 26 Surface acoustic wave resonator 30, 30a Void layer 34, 34a Support layer 40 Transmission filter 42 Reception filter 46 Center 47 Region 48 Wafer

Claims

1. A support substrate, a piezoelectric layer provided on the support substrate, at least a pair of comb-shaped electrodes provided on the piezoelectric layer, having a plurality of electrode fingers and mainly exciting surface acoustic waves (SAWs) of SH waves, an insulating layer provided between the support substrate and the piezoelectric layer and thicker than the piezoelectric layer, a void layer provided between the support substrate and the insulating layer and overlapping, in a plan view, by 70% or more with an intersection region where one electrode finger of the pair of comb-shaped electrodes and the other electrode finger of the pair of comb-shaped electrodes overlap when viewed from the arrangement direction of the plurality of electrode fingers, An elastic wave device comprising the above components.

2. The elastic wave device according to claim 1, wherein the piezoelectric layer is a rotated Y-cut X-propagation lithium tantalate substrate or a rotated Y-cut lithium niobate substrate.

3. The elastic wave device according to claim 1 or 2, wherein the insulating layer includes a first insulating layer provided on the void layer and a second insulating layer provided between the first insulating layer and the piezoelectric layer, the second insulating layer being mainly composed of silicon oxide and having a slower sound velocity of the bulk wave propagating therethrough than that of the bulk wave propagating through the first insulating layer.

4. The elastic wave device according to claim 3, wherein the distance between the surface of the second insulating layer on the support substrate side and the surface of the piezoelectric layer on the side of the pair of comb-shaped electrodes is 4 times or less the average pitch of the plurality of electrode fingers.

5. The elastic wave device according to any one of claims 1 to 4, wherein in the intersection region, the width of the void layer in the arrangement direction of the plurality of electrode fingers is 10 times or more the average pitch of the plurality of electrode fingers.

6. The elastic wave device according to any one of claims 1 to 5, wherein the void layer overlaps the intersection region by 90% or more in a plan view.

7. The elastic wave device according to any one of claims 1 to 6, comprising a support layer surrounded by the void layer and overlapping the intersection region in a plan view and connecting the support substrate and the insulating layer.

8. The elastic wave device according to any one of claims 1 to 7, comprising another void layer provided in the insulating layer and overlapping the intersection region by 70% or more in a plan view.

9. A wafer comprising a plurality of void layers according to claim 1.

10. A filter comprising the elastic wave device according to any one of claims 1 to 8.

11. A multiplexer comprising the filter according to claim 10.

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