Elastic wave device, filter, and multiplexer

Abstract

To provide an elastic wave device, a filter and a multiplexer, which suppress deterioration in characteristics.SOLUTION: An elastic wave device includes a piezoelectric layer 14, a support substrate 10, an insulating layer 15, a first comb-shaped electrode, and a second comb-shaped electrode. In the piezoelectric layer 14, a second surface 40b in a second area 50b is inclined with respect to a first surface 40a in a first area 50a, and a thickness in the first area 50a and the second area 50b is nearly uniform. The support substrate 10 is provided on the opposite side of the first surface and the second surface with respect to the piezoelectric layer 14, and has a piezoelectric layer side surface in the second area 50b which is not inclined with respect to a piezoelectric layer side surface in the first area 50a. The insulating layer 15 is provided between the piezoelectric layer 14 and the support substrate 10, and has a support substrate side surface in the first area 50a which is not inclined with respect to a support substrate side surface in the second area 50b. The first comb-shaped electrode is provided on the first surface of the piezoelectric layer 14, and the second comb-shaped electrode is provided on the second surface of the piezoelectric layer 14.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] As an elastic wave resonator used in communication devices such as smartphones, a surface acoustic wave resonator is known. When a piezoelectric layer forming a surface acoustic wave resonator is bonded 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 wave (for example, Patent Document 1). It is known to make the sum of the thickness of the temperature compensation film provided between the piezoelectric layer and the support substrate and the thickness of the piezoelectric layer equal to or less than twice the wavelength of the elastic wave (for example, Patent Document 2). It is known to provide a pair of comb-shaped electrodes on each of the flat portion and the inclined portion of the piezoelectric 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] In Patent Document 3, a pair of comb-shaped electrodes on the flat portion and a pair of comb-shaped electrodes on the inclined portion can each have suitable characteristics. However, since the thickness of the piezoelectric layer in the inclined portion becomes non-uniform, the characteristics deteriorate.

[0005] The present invention has been made in view of the above problems, and an object thereof is to suppress deterioration of characteristics.

Means for Solving the Problems

[0006] The present invention relates to an elastic wave device including a piezoelectric layer in which a second surface in a second region is inclined with respect to a first surface in a first region and which has a substantially uniform thickness in the first region and the second region, a support substrate provided on the opposite side of the piezoelectric layer from the first surface and the second surface, in which a surface on the piezoelectric layer side in the second region is not inclined with respect to a surface on the piezoelectric layer side in the first region, an insulating layer provided between the piezoelectric layer and the support substrate, a pair of first comb-shaped electrodes provided on the first surface, and a pair of second comb-shaped electrodes provided on the second surface.

[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 X propagation lithium niobate substrate.

[0008] In the above configuration, the Euler angles of the piezoelectric layer in the first region are (0°, θ1, 0°), and the Euler angles of the piezoelectric layer in the second region are (0°, θ2, 0°), and a configuration can be adopted in which θ1 and θ2 are different.

[0009] In the above configuration, the insulating layer can be configured to include a first insulating layer provided on the support substrate and a second insulating layer provided on the first insulating layer and having a substantially uniform thickness in the first region and the second region.

[0010] In the above configuration, the second insulating layer is mainly composed of silicon oxide, and the sound velocity of the bulk wave propagating through the first insulating layer is faster than the sound velocity of the bulk wave propagating through the second insulating layer.

[0011] In the above configuration, the total thickness of the piezoelectric layer and the second insulating layer is 4 times or less the average pitch of the electrode fingers of the first comb-shaped electrode and a pair of 4 times or less the average pitch of the electrode fingers of the second comb-shaped electrode. a pair of ​

[0012] The present invention is a filter including the above elastic wave device.

[0013] In the above configuration, an input terminal, an output terminal, and a pair of first comb electrodes provided in the first region and connected in series between the input terminal and the output terminal type electrodes including a resonator, and a pair of second comb electrodes provided in the second region, one end of which is connected to a path between the input terminal and the output terminal and the other end of which is grounded type electrodes including a resonator, and can be configured to include.

[0014] In the above configuration, the piezoelectric layer in the first region is a Y-cut X-propagating lithium tantalate layer rotated by 25° or more and 55° or less, and the piezoelectric layer in the second region can be configured to be a Y-cut X-propagating lithium tantalate layer rotated by -15° or more and 15° or less.

[0015] The present invention is a multiplexer including the above filter.

Advantages of the Invention

[0016] According to the present invention, deterioration of characteristics can be suppressed.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

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BEST MODE FOR CARRYING OUT THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

EXAMPLE

[0019] In Example 1, an elastic wave device having an elastic wave resonator will be described as an example. Fig. 1 is a plan view of the elastic wave device in Example 1. Figs. 2(a) to 2(c) are the cross-sectional views taken along the lines A-A, B-B, and C-C of Fig. 1, respectively. The arrangement direction of the electrode fingers is defined as the X direction, the extending direction of the electrode fingers is defined as the Y direction, and the stacking direction of the support substrate and the piezoelectric layer is defined as the Z direction. The X direction, the Y direction, and the Z direction do not necessarily correspond to the X-axis direction and the Y-axis direction of the crystal orientation of the piezoelectric layer. When the piezoelectric layer is a rotated Y-cut X-propagation substrate, the X direction becomes the X-axis direction of the crystal orientation.

[0020] As shown in FIGS. 1 to 2(c), 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. Regions 50a and 50b are provided in plan view. The upper surfaces 40a and 40b of the piezoelectric layer 14 in the regions 50a and 50b are inclined with respect to the upper surface 43 of the support substrate 10. Further, the upper surface 40b of the piezoelectric layer 14 in the region 50b is inclined with respect to the upper surface 40a of the piezoelectric layer 14 in the region 50a. The upper surface 40a of the piezoelectric layer 14 in the region 50a is separated from the upper surface 43 of the support substrate 10 as it goes in the +Y direction, and the upper surface 40b of the piezoelectric layer 14 in the region 50b is separated from the upper surface 43 of the support substrate 10 as it goes in the -Y direction. The thickness T4 of the piezoelectric layer 14 in the regions 50a and 50b is substantially uniform. The lower surfaces 41a and 41b of the piezoelectric layer 14 in the regions 50a and 50b are inclined corresponding to the upper surfaces 40a and 40b.

[0021] The thickness T3 of the temperature compensation film 13 in the regions 50a and 50b is substantially uniform. The lower surface 42b of the temperature compensation film in the region 50b is inclined with respect to the lower surface 42a of the temperature compensation film 13 in the region 50a. The lower surface of the boundary layer 12 in the region 50b is not inclined and is substantially flat with respect to the lower surface of the boundary layer 12 in the region 50a. Thereby, the thickness T2 of the boundary layer 12 changes so as to correspond to the inclination of the lower surfaces 42a and 42b of the temperature compensation film 13. The thickness T0 of the support substrate 10 in the regions 50a and 50b is substantially uniform.

[0022] Surface acoustic wave resonators 26a and 26b are respectively provided on the piezoelectric layer 14 in the regions 50a and 50b. The surface acoustic wave resonators 26a and 26b have IDTs 22 and reflectors 24. The reflectors 24 are provided on both sides of the IDTs 22 in the X direction. The IDTs 22 and the reflectors 24 are formed by a metal film 16 on the piezoelectric layer 14.

[0023] The IDT22 includes a pair of comb-shaped electrodes 20 facing each other. 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. As a result, 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 dependency of the elastic wave resonator can be reduced. Further, when, for example, a hard material and / or a material having a high thermal conductivity is selected as the support substrate 10, the sound velocity of the bulk wave propagating through the support substrate 10 becomes faster than the sound velocity of the bulk wave propagating through the boundary layer 12. The sound velocity of the bulk wave propagating through the support substrate 10 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 the sign 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 containing no additive or an additive element such as fluorine, and is, for example, a polycrystalline phase or an amorphous layer. Thereby, the frequency temperature coefficient of the elastic 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] For the temperature compensation film 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 in the temperature compensation film 13. Although the range where the energy of the surface elastic wave is concentrated depends on the type of the surface elastic wave, typically, the energy of the surface elastic 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 thickness T4 of the piezoelectric layer 14 is preferably 2λ or less, more preferably λ or less, and even more preferably 0.6λ or less.

[0028] The sound velocity of the bulk wave propagating in the boundary layer 12 is faster than the sound velocity of the bulk wave propagating in the temperature compensation film 13. Thereby, the bulk wave is confined in the piezoelectric layer 14 and the temperature compensation film 13. Further, the sound velocity of the bulk wave propagating in the boundary layer 12 is slower than the sound velocity of the bulk wave propagating in 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, for example, a film mainly composed of 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] [Manufacturing method of Example 1] Figs. 3(a) to 4(c) are cross-sectional views showing a method for manufacturing an elastic wave device according to Example 1. As shown in Fig. 3(a), a mask layer such as a photoresist is formed on the upper surface of the piezoelectric substrate 14a, and by performing, for example, chemical etching or ion milling, upper surfaces 40a and 40b with different inclinations are formed in regions 50a and 50b on the upper surface of the piezoelectric substrate 14a, respectively. By optimizing the conditions of chemical etching or ion milling, the upper surfaces 40a and 40b of the piezoelectric substrate 14a become specific crystal planes.

[0031] As shown in FIG. 3(b), a mask layer such as a photoresist is formed on the lower surface of the piezoelectric substrate 14a, and by performing, for example, chemical etching or ion milling, lower surfaces 41a and 41b with different inclinations are formed on the lower surface of the piezoelectric substrate 14a. At this time, the inclination of the upper surface 40a corresponds to the inclination of the lower surface 41a, the inclination of the upper surface 40b corresponds to the inclination of the lower surface 41b, and the thickness of the piezoelectric substrate 14a is made substantially uniform within a range allowing manufacturing errors in regions 50a and 50b.

[0032] As shown in FIG. 3(c), a temperature compensation film 13 is formed on the lower surface of the piezoelectric substrate 14a. For the formation of the temperature compensation film 13, for example, a CVD (Chemical Vapor Deposition) method, a vacuum evaporation method, or a sputtering method is used. The thickness of the temperature compensation film in regions 50a and 50b is substantially uniform within a range allowing manufacturing errors, and the inclinations of the lower surfaces 42a and 42b of the temperature compensation film 13 correspond to the inclinations of the lower surfaces 41a and 41b of the piezoelectric substrate 14a, respectively.

[0033] As shown in FIG. 3(d), a boundary layer 12 is formed on the lower surface of the temperature compensation film 13. For the formation of the boundary layer 12, for example, a CVD method, a vacuum evaporation method, or a sputtering method is used. The inclinations of the lower surfaces 43a and 43b of the boundary layer 12 correspond to the inclinations of the lower surfaces 42a and 42b of the temperature compensation film 13, respectively.

[0034] As shown in FIG. 3(e), the lower surface of the boundary layer 12 is polished using, for example, a CMP (Chemical Mechanical Polishing) method. As a result, the lower surface of the boundary layer 12 becomes substantially flat within a range allowing manufacturing errors. An insulating layer 15 is formed by the temperature compensation film 13 and the boundary layer 12.

[0035] As shown in FIG. 4(a), a support substrate 10 is bonded to the lower surface of the boundary layer 12. For the bonding, for example, a surface activation method is used. A bonding layer for bonding the boundary layer 12 and the support substrate 10 may be provided between the boundary layer 12 and the support substrate 10. The upper surface and the lower surface of the support substrate 10 are substantially flat within a range allowing manufacturing errors, and the thickness of the support substrate 10 is substantially uniform within a range allowing manufacturing errors.

[0036] As shown in FIG. 4(b), the piezoelectric substrate 14a is thinned by polishing the upper surface of the piezoelectric substrate 14a to form the piezoelectric layer 14. The inclinations of the upper surfaces 40a and 40b of the piezoelectric layer 14 respectively correspond to the inclinations of the lower surfaces 41a and 41b of the piezoelectric layer 14, and the thicknesses of the piezoelectric layer 14 in the regions 50a and 50b are substantially uniform within a range allowing manufacturing errors. For example, the CMP method is used to polish the upper surfaces 40a and 40b of the piezoelectric substrate 14a. By appropriately setting the CMP conditions, the piezoelectric substrate 14a can be thinned while maintaining the inclinations of the upper surfaces 40a and 40b of the piezoelectric substrate 14a.

[0037] As shown in FIG. 4(c), the surface acoustic wave resonators 26a and 26b are respectively formed on the upper surfaces 40a and 40b of the piezoelectric layer 14. The surface acoustic wave resonators 26a and 26b are formed by patterning the metal film 16 using the vacuum evaporation method and the lift-off method. The surface acoustic wave resonators 26a and 26b may also be formed using the sputtering method and the etching method. For forming the mask layer for patterning, the photolithography method may be used, but when it is difficult to focus, the electron beam exposure technique may also be used. Thus, the surface acoustic wave device according to Example 1 can be manufactured.

[0038] [Another manufacturing method of Example 1] FIGS. 5(a) to 5(d) are cross-sectional views showing another manufacturing method of the surface acoustic wave device according to Example 1. As shown in FIG. 5(a), in the step of FIG. 3(a), the lower surfaces 41a and 41b that are inclined with respect to each other are formed on the lower surface (the upper surface in FIG. 5(a)) of the piezoelectric substrate 14a. The method of forming the lower surfaces 41a and 41b is the same as the method of forming the upper surfaces 40a and 40b in FIG. 3(a). A temperature compensation film 13 is formed on the lower surface (the upper surface in FIG. 5(a)) of the piezoelectric substrate 14a. The method of forming the temperature compensation film 13 is the same as that in FIG. 3(c). As shown in FIG. 5(b), a boundary layer 12 is formed on the lower surface of the temperature compensation film 13. The method of forming the boundary layer 12 is the same as that in FIG. 3(d).

[0039] As shown in FIG. 5(c), by polishing the lower surface of the boundary layer 12 using, for example, the CMP method, the lower surface of the boundary layer 12 is made into a substantially flat surface within a range allowing manufacturing errors. The polishing method for the lower surface of the boundary layer 12 is the same as that in FIG. 3(e). The support substrate 10 is bonded to the lower surface of the boundary layer 12. The bonding method is the same as that in FIG. 4(a). As shown in FIG. 5(d), by polishing the upper surface of the piezoelectric substrate 14a, the piezoelectric substrate 14a is thinned to form the piezoelectric layer 14. The method for thinning the piezoelectric substrate 14a is the same as that in FIG. 4(b). Thereafter, as in FIG. 4(c), the surface acoustic wave resonators 26a and 26b are formed on the upper surfaces 40a and 40b of the piezoelectric layer 14.

[0040] [Modification Example 1 of Example 1] FIG. 6 is a plan view of the surface acoustic wave device in Modification Example 1 of Example 1. FIGS. 7(a) to 7(c) are the A-A cross-sectional view, B-B cross-sectional view, and C-C cross-sectional view of FIG. 6, respectively. As shown in FIGS. 6 to 7(c), the upper surface 40a of the piezoelectric layer 14 in the region 50a is inclined with respect to the upper surface 43 of the support substrate 10. The upper surface 40b of the piezoelectric layer 14 in the region 50b is not inclined with respect to the upper surface 43 of the support substrate 10. That is, the upper surface 40b of the piezoelectric layer 14 in the region 50b and the upper surface 30 of the support substrate 10 are substantially parallel. The thickness T2 of the boundary layer 12 in the region 50b is substantially uniform. Other configurations are the same as those in Example 1 and the description thereof is omitted.

[0041] [Simulation] The characteristics of the surface acoustic wave resonator when the rotation Y cut angle changes were simulated using a lithium tantalate substrate as the piezoelectric layer 14. The simulation conditions are as follows. Wavelength λ of surface acoustic wave: 5.0 μm Piezoelectric layer 14: Rotated Y cut X propagation lithium tantalate substrate with a thickness T4 of 0.4λ Temperature compensation film 13: Silicon oxide (SiO2) film with a thickness T3 of 0.4λ Boundary layer 12: Not provided Support substrate 10: Sapphire substrate Metal film 16: Aluminum film with a thickness of 0.1λ

[0042] Fig. 8(a) is a diagram showing the TCV (Temperature Coefficient of Velocity) at the resonance frequency fr and the anti-resonance frequency fa with respect to the cut angle θ in the simulation, and Fig. 8(b) is a diagram showing the resonance frequency fr, the anti-resonance frequency fa, and the electromechanical coupling coefficient k with respect to the cut angle θ. 2 The TCV is the temperature coefficient of the velocity of the elastic wave and corresponds to the TCF (Temperature Coefficient of Frequency) of the resonance frequency fr and the anti-resonance frequency fa.

[0043] As shown in Fig. 8(a), when θ is in the range of 0° to 70° and 130° to 180°, the TCV of fr is larger than that of fa. When θ is in the range of 70° to 130°, the TCVs of fr and fa are almost the same. As shown in Fig. 8(b), except for the range where θ is in the range of 120° to 130°, the anti-resonance frequency fa is higher than the resonance frequency fr. fa and fr are the highest when θ is around 40°, and fa and fr are the lowest when θ is around 130°. The electromechanical coupling coefficient k 2 is the largest when θ is 20° and the lowest when θ is 120°.

[0044] As in the above simulation, the upper surface 40a (the first surface) of the piezoelectric layer 14 in the region 50a (the first region) is inclined with respect to the upper surface 40b (the second surface) of the piezoelectric layer 14 in the region 50b (the second region). Thereby, the characteristics of the elastic wave resonator 26a having the pair of comb-shaped electrodes 20 (the first comb-shaped electrodes) provided on the upper surface 40a in the region 50a can be made different from the characteristics of the elastic wave resonator 26b having the pair of comb-shaped electrodes 20 (the second comb-shaped electrodes) provided on the upper surface 40b in the region 50b.

[0045] [Comparative Example 1] A comparative example 1 will be described in which the thickness T4 of the piezoelectric layer 14 is changed and the upper surfaces 40a and 40b (surfaces) of the piezoelectric layer 14 have different inclinations. FIG. 9(a) is a cross-sectional view of the elastic wave device according to the comparative example 1. As shown in FIG. 9(a), in the comparative example 1, in the regions 50a and 50b, the thickness T2 of the boundary layer 12 is substantially uniform, and the thickness T3 of the temperature compensation film 13 is substantially uniform. The thickness T4 of the piezoelectric layer 14 changes corresponding to the inclinations of the upper surfaces 40a and 40b. If the thickness T4 of the piezoelectric layer 14 is different within the elastic wave resonators 26a and 26b, the characteristics will deteriorate. For example, as in Patent Document 1, when the piezoelectric layer 14 becomes thicker, the loss increases and the spurious becomes larger.

[0046] According to the first embodiment, in the regions 50a and 50b, the piezoelectric layer 14 has a substantially uniform thickness in the regions 50a and 50b. The upper surface of the support substrate 10 in the region 50b is not inclined with respect to the upper surface (the surface on the piezoelectric layer 14 side) of the support substrate 10 in the region 50a. Thereby, since the thickness of the piezoelectric layer 14 is uniform, deterioration of the characteristics of the elastic wave resonators 26a and 26b can be suppressed.

[0047] The substantially uniform thickness means uniform to the extent that manufacturing errors are tolerated. For example, a thickness variation of about ±10% is tolerated. That is, assuming that the maximum value of the thickness is Tmax, the minimum value of the thickness is Tmin, and the average value of the thickness is Tave, 2(Tmax - Tmin) / (Tmax + Tmin) ≤ 0.1 is tolerated. 2(Tmax - Tmin) / (Tmax + Tmin) ≤ 0.05 is preferable. That the second surface is not inclined with respect to the first surface means that it is not inclined to the extent of manufacturing errors. The angle of the second surface with respect to the first surface is, for example, 5° or less, and preferably 1° or less. Further, when the first surface and the second surface are uneven surfaces or rough surfaces, it is sufficient that the planes approximated by the first surface and the second surface are not inclined to each other.

[0048] From the viewpoint of making the characteristics of the elastic wave resonators 26a and 26b different, the inclination angle of the upper surface 40b with respect to the upper surface 40a of the piezoelectric layer 14 is preferably 5° or more, and more preferably 10° or more. From the viewpoint of manufacturing the elastic wave resonators 26a and 26b, the inclination angle of the upper surface 40b with respect to the upper surface 40a is preferably 60° or less.

[0049] The piezoelectric layer 14 is a rotated Y-cut X-propagation lithium tantalate substrate or a rotated Y-cut lithium niobate substrate. In this case, the Euler angles of the piezoelectric layer 14 in the region 50a are (0°, θ1, 0°), and the Euler angles of the piezoelectric layer 14 in the region 50b are (0°, θ2, 0°), where θ1 and θ2 are different. Thereby, since the rotation cut angles of the regions 50a and 50b are different, the characteristics of the elastic wave resonators 26a and 26b can be made different.

[0050] [Modification Example 2 of Example 1] FIG. 9(b) is a cross-sectional view of an elastic wave device according to Modification Example 2 of Example 1. As shown in FIG. 9(b), in Modification Example 2 of Example 1, in the regions 50a and 50b, the thickness T4 of the piezoelectric layer 14 is substantially uniform, and the thickness of the boundary layer 12 is substantially uniform. The thickness T3 of the temperature compensation film 13 changes corresponding to the inclinations of the upper surfaces 40a and 40b of the piezoelectric layer 14. Other configurations are the same as those in Example 1 and the description thereof is omitted. As in Modification Example 2 of Example 1, the thickness T3 of the temperature compensation film 13 may be changed.

[0051] However, when the insulating layer 15 includes the boundary layer 12 (first insulating layer) provided on the support substrate 10 and the temperature compensation film 13 (second insulating layer) provided on the boundary layer 12, if the thickness T3 of the temperature compensation film 13 close to the piezoelectric layer 14 changes within the regions 50a and 50b, the characteristics of the elastic wave resonators 26a and 26b deteriorate. Therefore, as in Example 1, it is preferable that the temperature compensation film 13 has a substantially uniform thickness in the regions 50a and 50b.

[0052] The temperature compensation film 13 is mainly composed of silicon oxide, and the sound velocity of the bulk wave propagating through the boundary layer 12 is faster than that of the bulk wave propagating through the temperature compensation film 13. As a result, the elastic wave of the main mode (elastic surface wave, for example, SH (Shear Horizontal) wave) is mainly reflected at the interface between the temperature compensation film 13 and the boundary layer 12 and confined in the piezoelectric layer 14 and the temperature compensation film 13. Therefore, the frequency temperature characteristics of the elastic wave resonators 26a and 26b can be reduced, and the elastic wave of the main mode can be confined in the piezoelectric layer 14 and the temperature compensation film 13, and the loss can be suppressed. As shown in FIGS. 2(a), 2(b), 7(a), and 7(b), the elastic wave 46 such as the bulk wave faster than the elastic wave of the main mode is reflected at the interface between the boundary layer 12 and the support substrate 10 and returns to the IDT22. As a result, spurious signals are generated. As shown in FIG. 2(c), when the upper surfaces 40a and 40b of the piezoelectric layer 14 are inclined with respect to the upper surface of the support substrate 10, the elastic wave 46 goes out of the elastic wave resonators 26a and 26b by repeating reflections. Thereby, spurious signals can be suppressed. As shown in FIG. 7(c), in Modification 1 of Example 1, in the elastic wave resonator 26a, the elastic wave 46 goes out of the elastic wave resonator 26a by repeating reflections, and spurious signals can be suppressed.

[0053] The total thickness T4 + T3 of the piezoelectric layer 14 and the temperature compensation film 13 is preferably 4 times (2λ) or less, more preferably 3 times (1.5λ) or less, and even more preferably 2 times (1λ) or less of the average pitch D of the electrode fingers 18 of the comb-shaped electrodes 20 of the elastic wave resonators 26a and 26b. Thereby, as in Patent Document 2, the frequency temperature characteristics can be reduced and the loss can be suppressed. Since the thicknesses T4 and T3 of the piezoelectric layer 14 and the temperature compensation film 13 are thin, if the thicknesses T4 and T3 of the piezoelectric layer 14 and the temperature compensation film 13 change in the elastic wave resonators 26a and 26b, the temperature characteristics and the resonance characteristics deteriorate. Therefore, in the regions 50a and 50b, it is preferable that the thickness T4 of the piezoelectric layer 14 is substantially uniform and the thickness T3 of the temperature compensation film 13 is substantially uniform. The average pitch D 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.

[0054] Here, it is acceptable 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 or 80 atomic% or more. For example, when the temperature compensation film 13 has silicon oxide as the main component, it is acceptable 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 or 80 atomic% or more, and the oxygen concentration and the silicon concentration are each 10 atomic% or more or 20 atomic% or more. Also, when the boundary layer 12 has aluminum oxide as the main component, it is acceptable that the boundary layer 12 contains impurities, and the total of the oxygen concentration and the aluminum concentration in the boundary layer 12 is 50 atomic% or more or 80 atomic% or more, and the oxygen concentration and the aluminum concentration are each 10 atomic% or more or 20 atomic% or more.

[0055] When the boundary layer 12 becomes thinner, the elastic wave of the main mode becomes difficult 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 level 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.

[0056] From the viewpoint of passing the elastic wave 46 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.

[0057] From the perspective of causing the energy of the elastic wave of the main response to exist within the temperature compensation film 13, the thickness T4 of the piezoelectric layer 14 is preferably 2 times (1λ) or less, more preferably 1 time (0.5λ) or less, of the average pitch D of the plurality of electrode fingers 18. From the perspective of enabling the piezoelectric layer 14 to function, the thickness T4 of the piezoelectric layer 14 is preferably 0.05 times (0.1λ) or more, more preferably 0.1 times (0.2λ) or more, of the average pitch D of the plurality of electrode fingers 18.

[0058] 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 it becomes easier for the elastic wave to exist within 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 better 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 the elastic wave to exist within 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.

[0059] 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 46 including the bulk wave is reflected at the interface between the boundary layer 12 and the temperature compensation film 13. From this perspective, 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.

[0060] The insulating layer 15 may be a single layer made of a uniform material such as a silicon oxide layer, a silicon nitride layer, or an aluminum oxide layer.

Example

[0061] Example 2 is an example in which Example 1 and its modified examples are used as filters. FIGS. 10(a) and 10(b) are a circuit diagram and a plan view, respectively, of the filter according to Example 2. As shown in FIG. 10(a), series resonators S1 to S3 are connected in series between an input terminal Tin and an output terminal Tout. Parallel resonators P1 and P2 are connected in parallel between the input terminal Tin and the output terminal Tout. One ends of the parallel resonators P1 and P2 are connected to a path between the input terminal Tin and the output terminal Tout, and the other ends are connected to a ground terminal Gnd and grounded.

[0062] As shown in FIG. 10(b), surface acoustic wave resonators 26a, 26b, and wiring 44 are provided on a support substrate 10 and a piezoelectric layer 14. The surface acoustic wave resonators 26a and 26b each have an IDT 22 and a reflector 24. The wiring 44 electrically connects the surface acoustic wave resonators 26a and 26b. The wiring 44 is a metal layer including a gold layer, a copper layer, or an aluminum layer. The plurality of surface acoustic wave resonators 26a includes the series resonators S1 to S3, and the surface acoustic wave resonator 26b includes the parallel resonators P1 and P2. A part of the wiring 44 includes the input terminal Tin, the output terminal Tout, and the ground terminal Gnd.

[0063] According to Example 2, the series resonators S1 to S3 are provided in a region 50a, and the parallel resonators P1 and P2 are provided in a region 50b. Thereby, as shown in FIGS. 8(a) and 8(b), the series resonators S1 to S3 and the parallel resonators P1 and P2 can have different frequency temperature coefficients. Further, even if the pitch D of the electrode fingers 18 is the same, the resonance frequency fr can be made different, and the anti-resonance frequency fa can be made different.

[0064] The piezoelectric layer 14 is a rotated Y-cut X-propagation lithium tantalate substrate, the cut angle θ of the region 50a is 40°, and the cut angle θ of the region 50b is 0°. Thereby, as shown in FIG. 8(b), the electromechanical coupling coefficient k between the series resonators S1 to S3 and the parallel resonators P1 and P2 2can be made substantially the same. As shown in Fig. 8(a), when the cut angle θ is 40°, the TCV of the anti-resonant frequency fa is -34 ppm / K, the TCV of the resonant frequency fr is -18 ppm / K, and the difference is 16 ppm / K. The anti-resonant frequencies fa of the series resonators S1 to S3 form the high-frequency end of the passband, and the low-frequency ends of the parallel resonators P1 and P2 are formed. Therefore, if the difference in TCV between fa and fr is large, the temperature coefficient of the passband width will increase. When the cut angle θ of region 50a is 40° and the cut angle θ of region 50b is 0°, the TCV of the anti-resonant frequency fa of the series resonators S1 to S3 is -34 ppm / K, the TCV of the resonant frequency fr of the parallel resonators P1 and P2 is -24 ppm / K, and the difference is 9 ppm / K. Therefore, the temperature coefficient of the passband width can be reduced.

[0065] Also, as shown in Fig. 8(b), when the cut angle θ is 40°, the anti-resonant frequency fa is approximately 790 MHz, the resonant frequency fr is approximately 755 MHz, and the difference is approximately 35 MHz. When the cut angle θ of region 50a is 40° and the cut angle θ of region 50b is 0°, the anti-resonant frequency fa of the series resonators S1 to S3 is approximately 790 MHz, the resonant frequency fr of the parallel resonators P1 and P2 is approximately 712 MHz, and the difference is 78 MHz. Therefore, even if the pitch D of the electrode fingers 18 of the series resonators S1 to S3 and the pitch D of the parallel resonators P1 and P2 are made substantially the same, the passband width can be ensured.

[0066] The piezoelectric layer 14 in region 50a is preferably a Y-cut X-propagating lithium tantalate layer rotated by 25° or more and 55° or less, more preferably a Y-cut X-propagating lithium tantalate layer rotated by 30° or more and 50° or less, and even more preferably a Y-cut X-propagating lithium tantalate layer rotated by 35° or more and 45° or less. The piezoelectric layer 14 in region 50b is preferably a Y-cut X-propagating lithium tantalate layer rotated by -15° or more and 15° or less, more preferably a Y-cut X-propagating lithium tantalate layer rotated by -10° or more and 10° or less, and even more preferably a Y-cut X-propagating lithium tantalate layer rotated by -5° or more and 5° or less.

[0067] The elastic wave resonators of Example 1 and its modifications may be used for at least one of the series resonators S1 to S3 and the parallel resonators P1 and P2. The number of resonators of the ladder-type filter and the like can be set as appropriate. The filter may be a multiplex mode filter.

[0068] [Modification Example 1 of Example 2] FIG. 11 is a circuit diagram of a duplexer according to Modification Example 1 of Example 2. As shown in FIG. 11, a transmission filter 60 is connected between the common terminal Ant and the transmission terminal Tx. A reception filter 62 is connected between the common terminal Ant and the reception terminal Rx. The transmission filter 60 passes the signal in the transmission band among the high-frequency signals input from the transmission terminal Tx as a transmission signal to the common terminal Ant and suppresses signals of other frequencies. The reception filter 62 passes the signal in the reception band among the high-frequency signals input from the common terminal Ant as a reception signal to the reception terminal Rx and suppresses signals of other frequencies. At least one of the transmission filter 60 and the reception filter 62 can be the filter of Example 2.

[0069] Although the duplexer has been described as an example of the multiplexer, a triplexer or a quadplexer may also be used.

[0070] As described above in detail for 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

[0071] 10 Support substrate 12 Boundary layer 13 Temperature compensation film 14 Piezoelectric layer 15 Insulating layer 16 Metal film 18 Electrode finger 20 Comb-shaped electrode 22 IDT 25 Crossing region 26a, 26b Elastic wave resonator 40a, 40b Upper surface of piezoelectric layer Regions 50a and 50b Transmission filter 60 Receiving filter 62

Claims

1. A piezoelectric layer in which a second surface in a second region is inclined with respect to a first surface in a first region, and which has a substantially uniform thickness in the first region and the second region; A support substrate provided on the opposite side of the piezoelectric layer from the first surface and the second surface, and in which a surface on the piezoelectric layer side in the second region is not inclined with respect to a surface on the piezoelectric layer side in the first region; An insulating layer provided between the piezoelectric layer and the support substrate; A pair of first comb-shaped electrodes provided on the first surface; A pair of second comb-shaped electrodes provided on the second surface; An elastic wave device comprising the above.

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 X-propagation lithium niobate substrate.

3. The elastic wave device according to claim 2, wherein the Euler angle of the piezoelectric layer in the first region is (0°, θ1, 0°), the Euler angle of the piezoelectric layer in the second region is (0°, θ2, 0°), and θ1 and θ2 are different.

4. The elastic wave device according to any one of claims 1 to 3, wherein the insulating layer includes a first insulating layer provided on the support substrate and a second insulating layer provided on the first insulating layer and having a substantially uniform thickness in the first region and the second region.

5. The second insulating layer contains silicon oxide as a main component, The elastic wave device according to claim 4, wherein the sound velocity of the bulk wave propagating through the first insulating layer is faster than the sound velocity of the bulk wave propagating through the second insulating layer.

6. The elastic wave device according to claim 4, wherein the total thickness of the piezoelectric layer and the second insulating layer is 4 times or less the average pitch of the electrode fingers of the pair of first comb-shaped electrodes and 4 times or less the average pitch of the electrode fingers of the pair of second comb-shaped electrodes.

7. A filter including the elastic wave device according to any one of claims 1 to 6.

8. An input terminal; An output terminal; A resonator connected in series between the input terminal and the output terminal and including the pair of first comb-shaped electrodes provided in the first region; A resonator having one end connected to a path between the input terminal and the output terminal and the other end grounded and including the pair of second comb-shaped electrodes provided in the second region; The filter according to claim 7, comprising the above.

9. The piezoelectric layer in the first region is a rotated Y-cut X-propagation lithium tantalate layer of 25° or more and 55° or less, The piezoelectric layer in the second region is a lithium tantalate layer with a rotation of Y-cut X-propagation of -15° or more and 15° or less. The filter according to claim 8.

10. A multiplexer comprising the filter according to any one of claims 7 to 9.

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