Acoustic wave devices, filters and multiplexers

Abstract

An acoustic wave device, a filter and a multiplexer. An acoustic wave device includes: a piezoelectric substrate; a pair of comb-shaped electrodes located on the piezoelectric substrate, each of the comb-shaped electrodes including a plurality of electrode fingers; a supporting substrate having convex portions and / or concave portions in a region overlapping with the pair of comb-shaped electrodes in a plan view, the convex portions and / or concave portions being regularly arranged; and an insulating layer directly or indirectly bonded between the piezoelectric substrate and the supporting substrate, a boundary surface between the insulating layer and the supporting substrate being arranged along the convex portions and / or concave portions.

Description

Technical Field

[0001] Some aspects of the present invention relate to an acoustic wave device, a filter, and a multiplexer. Background Art

[0002] As an acoustic wave resonator used in a communication device such as a smartphone, a surface acoustic wave resonator is known. It is known to bond a piezoelectric substrate on which a surface acoustic wave resonator is to be formed to a supporting substrate. It is known to roughen the upper surface of a supporting substrate as disclosed in, for example, Japanese Patent Laid-Open No. 2018-61258 (hereinafter, referred to as Patent Document 1). Summary of the invention

[0003] According to a first aspect of an embodiment, there is provided an acoustic wave device comprising: a piezoelectric substrate; a pair of comb-shaped electrodes located on the piezoelectric substrate, each of the comb-shaped electrodes comprising a plurality of electrode fingers; a supporting substrate having protrusions and / or recesses in an area overlapping with the pair of comb-shaped electrodes in a plan view, the protrusions and / or recesses being regularly arranged; and an insulating layer directly or indirectly bonded between the piezoelectric substrate and the supporting substrate, a boundary surface between the insulating layer and the supporting substrate being arranged along the protrusions and / or recesses.

[0004] According to a second aspect of the embodiment, there is provided a filter including the above acoustic wave device.

[0005] According to a third aspect of the embodiment, there is provided a multiplexer including the above filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1A is a plan view of the acoustic wave resonator in the first embodiment, and Figure 1B It is along Figure 1A A cross-sectional view taken along line AA;

[0007] FIG. 2A to FIG. 2D is a cross-sectional view (No. 1) illustrating a method for manufacturing an acoustic wave device according to a first embodiment;

[0008] FIG. 3A to FIG. 3C is a cross-sectional view (No. 2) illustrating a method for manufacturing an acoustic wave device according to a first embodiment;

[0009] FIG. 4A to FIG. 4M A first example of the three-dimensional shapes of the convex and concave portions in the first embodiment is illustrated;

[0010] Figure 5A is a plan view illustrating a first example of the arrangement of the convex and concave portions in the first embodiment, and Figure 5B and Figure 5C It is along Figure 5A A cross-sectional view taken along line AA;

[0011] Fig. 6A is a plan view illustrating a second example of the arrangement of the convex and concave portions in the first embodiment, and Figure 6B and Figure 6C It is along Fig. 6A A cross-sectional view taken along line AA in FIG.

[0012] Fig. 7A and Figure 7B are plan views respectively illustrating third and fourth examples of the arrangement of the convex and concave portions in the first embodiment;

[0013] Fig. 8A and Figure 8B are plan views respectively illustrating fifth and sixth examples of the arrangement of the convex and concave portions in the first embodiment;

[0014] 9A to 9C is a perspective view illustrating a second example of the three-dimensional shapes of the convex portion and the concave portion in the first embodiment;

[0015] Fig. 10A A plan view illustrating a seventh example of the arrangement of the convex and concave portions in the first embodiment, and Fig. 10B and Fig. 10C It is along Fig. 10A A cross-sectional view taken along line AA in FIG.

[0016] Fig.11A and Fig. 11B are plan views respectively illustrating an eighth example and a ninth example of the arrangement of the convex and concave portions in the first embodiment;

[0017] Fig.12 is a plan view illustrating a tenth example of the arrangement of the convex and concave portions in the first embodiment;

[0018] Fig.13 is a cross-sectional view of an acoustic wave device according to a first modification example of the first embodiment;

[0019] Fig.14 is a graph of the magnitude of admittance relative to frequency in simulation 1;

[0020] Fig.15 is a graph of the magnitude of admittance versus frequency in simulation 2;

[0021] Fig.16 is a graph of the real part and magnitude of the admittance versus frequency in Experiment 1; and

[0022] Fig.17A is a circuit diagram of a filter according to a second embodiment, and Fig. 17Bis a circuit diagram of a duplexer according to a first modification of the second embodiment. DETAILED DESCRIPTION

[0023] The stray emission can be reduced by roughening the upper surface of the support substrate. In Patent Document 1, the upper surface of the support substrate is roughened by grinding or wet etching the entire upper surface of the support substrate. The use of grinding or wet etching makes the rough surface irregularly (i.e., randomly) uneven. This leads to a large change in characteristics. For example, the size of the stray emission varies depending on the position.

[0024] Hereinafter, a description will be given of embodiments with reference to the accompanying drawings.

[0025] First embodiment

[0026] Figure 1A is a plan view of the acoustic wave resonator according to the first embodiment, and Figure 1B It is along Figure 1A The cross-sectional view taken along the line AA of FIG. The direction in which the electrode fingers are arranged (arrangement direction) is defined as the X direction, the direction in which the electrode fingers extend (extension direction) is defined as the Y direction, and the direction in which the support substrate and the piezoelectric substrate are stacked (stacking direction) is defined as the Z direction. The X direction, the Y direction, and the Z direction do not necessarily correspond to the X-axis orientation and the Y-axis orientation of the crystal orientation of the piezoelectric substrate. When the piezoelectric substrate is a rotated Y-cut X-propagation substrate, the X direction is the X-axis orientation of the crystal orientation.

[0027] like Figure 1A and Figure 1B As shown, the insulating layer 11 is located on the support substrate 10. The boundary surface 50 between the support substrate 10 and the insulating layer 11 is a rough surface and has a plurality of protrusions 51 and a plurality of recesses 52. The piezoelectric substrate 12 is located on the insulating layer 11. The acoustic wave resonator 20 is located on the piezoelectric substrate 12. The acoustic wave resonator 20 includes an interdigital transducer (IDT) 22 and a reflector 24. The reflector 24 is located on both sides of the IDT 22 in the X direction. The IDT 22 and the reflector 24 are formed on the piezoelectric substrate 12 by a metal film 14.

[0028] The IDT 22 includes a pair of comb electrodes 18 facing each other. The comb electrodes 18 include a plurality of electrode fingers 15 and bus bars 16 connected to the electrode fingers 15. The region where the electrode fingers 15 of one comb electrode 18 overlap with the electrode fingers 15 of another comb electrode 18 is an overlap region 25. The length of the overlap region 25 is a hole length. The comb electrodes 18 are positioned facing each other so that the electrode fingers 15 of one comb electrode 18 and the electrode fingers 15 of another comb electrode 18 are substantially alternately arranged in at least a portion of the overlap region 25. The acoustic wave excited by the electrode fingers 15 propagates mainly in the X direction in the overlap region 25. The pitch of the electrode fingers 15 of one of the comb electrodes 18 corresponds to the wavelength λ of the acoustic wave. The wavelength λ of the acoustic wave is substantially equal to twice the pitch of the electrode fingers 15. The reflector 24 reflects the acoustic wave (surface acoustic wave) excited by the electrode fingers 15 of the IDT 22. Therefore, the acoustic wave is confined in the overlap region 25 of the IDT 22.

[0029] The piezoelectric substrate 12 is a single crystal lithium tantalate (LiTaO3) substrate, a single crystal lithium niobate (LiNbO3) substrate or a single crystal crystal substrate, and is, for example, a rotated Y-cut X-propagation lithium tantalate substrate or a rotated Y-cut X-propagation lithium niobate substrate. The insulating layer 11 is an amorphous and / or polycrystalline layer mainly composed of, for example, silicon oxide (SiO2). The insulating layer 11 may be mainly composed of silicon oxide and contain impurities such as fluorine. The temperature coefficient of the elastic constant of the insulating layer 11 is opposite in sign to the temperature coefficient of the elastic constant of the piezoelectric substrate 12. Therefore, the frequency temperature coefficient of the acoustic wave resonator can be reduced.

[0030] The support substrate 10 has a linear expansion coefficient smaller than the linear expansion coefficient of the piezoelectric substrate 12 in the X direction. Therefore, the frequency temperature coefficient of the acoustic wave resonator can be reduced. The support substrate 10 is, for example, a sapphire substrate, an alumina substrate, a silicon substrate, or a silicon carbide substrate. The sapphire substrate is a single crystal alumina (Al2O3) substrate whose upper surface is an r-plane, a c-plane, or an a-plane. The alumina substrate is a polycrystalline alumina (Al2O3) substrate. The silicon substrate is a single crystal or polycrystalline silicon (Si) substrate. The silicon carbide substrate is a single crystal or polycrystalline silicon carbide (SiC) substrate.

[0031] The metal film 14 is a film mainly composed of, for example, aluminum (Al), copper (Cu) or molybdenum (Mo), and is, for example, an aluminum film, a copper film or a molybdenum film. An adhesive film such as a titanium (Ti) film or a chromium (Cr) film may be provided between the electrode finger 15 and the piezoelectric substrate 12. The adhesive film is thinner than the electrode finger 15. An insulating film may be provided to cover the electrode finger 15. The insulating film serves as a protective film or a temperature compensation layer.

[0032] The support substrate 10 has a thickness of, for example, 50 μm to 500 μm. The thickness of the insulating layer 11 is, for example, 0.1 μm to 10 μm, and is equal to or less than, for example, the wavelength λ of an acoustic wave. The thickness of the piezoelectric substrate 12 is, for example, 0.1 μm to 20 μm, and is equal to or less than, for example, the wavelength λ of an acoustic wave. The wavelength λ of an acoustic wave is, for example, 1 μm to 6 μm. When two electrode fingers 15 are defined as a pair, the number of pairs of electrode fingers 15 is, for example, 20 pairs to 300 pairs. The duty ratio of the IDT 22 is calculated by dividing the width of the electrode finger 15 by the pitch of the electrode finger 15, and is, for example, 30% to 80%. The hole length of the IDT 22 is, for example, 10λ to 50λ.

[0033] Manufacturing method of the first embodiment

[0034] Figures 2A to 3C 2 is a cross-sectional view illustrating a method for manufacturing an acoustic wave device according to a first embodiment. Figure 2A As shown, a support substrate 10 having a flat surface is prepared. The arithmetic mean roughness Ra of the surface of the support substrate 10 is, for example, 1 nm or less. Figure 2B As shown, a mask layer 44 having an opening is formed on the support substrate 10. The mask layer 44 is formed of, for example, a photoresist.

[0035] like Figure 2C As shown, the upper portion of the support substrate 10 is removed using the mask layer 44 as a mask. The upper portion of the support substrate 10 is removed by, for example, etching or sandblasting. For example, when the support substrate 10 is a sapphire substrate, the support substrate 10 is removed by dry etching using a chlorine-based gas. The etching liquid and the etching gas are appropriately selected according to the material of the support substrate 10.

[0036] like Figure 2D As shown, the insulating layer 11 is formed on the support substrate 10 by, for example, chemical vapor deposition (CVD), sputtering, or vacuum evaporation. This process forms a concavo-convex boundary surface 50 between the support substrate 10 and the insulating layer 11.

[0037] like Figure 3A As shown, the upper surface of the insulating layer 11 is planarized by, for example, chemical mechanical polishing (CMP). Figure 3B As shown, the piezoelectric substrate 12 is bonded to the upper surface of the insulating layer 11 through a bonding layer 13. The bonding layer 13 is, for example, an aluminum oxide layer, an aluminum nitride layer, a diamond-like carbon layer, a silicon carbide layer, a silicon nitride layer, or a silicon layer. The bonding layer 13 has a thickness of, for example, 1 nm to 100 nm. The insulating layer 11 and the piezoelectric substrate 12 may not be bonded through the bonding layer 13. The insulating layer 11 and the piezoelectric substrate 12 are bonded by, for example, surface activation.

[0038] like Figure 3CAs shown, the upper surface of the piezoelectric substrate 12 is flattened by, for example, CMP. Through this process, a composite substrate including the support substrate 10, the insulating layer 11, and the piezoelectric substrate 12 is formed. The acoustic wave resonator formed by the metal film 14 is formed on the upper surface of the piezoelectric substrate 12. Through the above steps, the acoustic wave device of the first embodiment is manufactured.

[0039] First Example of Three-Dimensional Shape of Convex and Concave Parts

[0040] FIG. 4A to FIG. 4M The first example of the three-dimensional shapes of the convex and concave portions in the first embodiment is illustrated. Figures 4A to 4K It is a perspective view, and when the convex portion 51 is illustrated, as indicated by arrow 56a, the upward direction is the positive Z direction. When the concave portion 52 is illustrated, as indicated by arrow 56b, the upward direction is the negative Z direction. Figure 4L is a plan view, and Figure 4M is a cross-sectional view. FIG. 4A to FIG. 4M In the figure, the convex portion 51 and the concave portion 52 are in the form of islands or dots.

[0041] like Figure 4A As shown, the convex portion 51 has a conical shape including a vertex 51a, and the concave portion 52 has a conical shape including a vertex 52a. Figure 4B As shown, the convex portion 51 has a truncated cone shape including an upper surface 51b, and the concave portion 52 has a truncated cone shape including a lower surface 52b. Figure 4C As shown, the convex portion 51 and the concave portion 52 have a cylindrical shape.

[0042] like Figure 4D As shown, the convex portion 51 has a triangular pyramid shape including a vertex 51a, and the concave portion 52 has a triangular pyramid shape including a vertex 52a. Figure 4E As shown, the convex portion 51 has a triangular truncated pyramid shape including an upper surface 51b, and the concave portion 52 has a triangular truncated pyramid shape including a lower surface 52b. Figure 4F As shown, the convex portion 51 and the concave portion 52 have a triangular prism shape.

[0043] like Figure 4G As shown in FIG. 5 , the convex portion 51 has a quadrangular pyramid shape including a vertex 51 a, and the concave portion 52 has a quadrangular pyramid shape including a vertex 52 a. Figure 4H As shown in FIG. 5 , the convex portion 51 has a quadrangular pyramid shape including an upper surface 51 b, and the concave portion 52 has a quadrangular pyramid shape including a lower surface 52 b. Fig. 4I As shown, the convex portion 51 and the concave portion 52 have a quadrangular prism shape. As described above, the three-dimensional shape of the convex portion 51 and the concave portion 52 may be a cone, a polygonal cone, a truncated cone, a polygonal truncated cone, a cylinder, or a prism.

[0044] like Figure 4JAs shown, the convex portion 51 and the concave portion 52 have a hemispherical shape. Figure 4K As shown, the convex portion 51 has a shape obtained by removing the upper portion of a hemisphere along the upper surface 51b, and the concave portion 52 has a shape obtained by removing the lower portion of a hemisphere along the surface 52b. As described above, the three-dimensional shapes of the convex portion 51 and the concave portion 52 may be a part of a spherical shape. The three-dimensional shapes of the convex portion 51 and the concave portion 52 may be a part of a prolate ellipsoid shape or a part of an ellipsoid shape. Figure 4L and Figure 4M As shown, the convex portion 51 and the concave portion 52 have a shape formed by a portion of a circular ring shape. Figure 2B The planar shape of the mask layer 44 and Figure 2C By adjusting the etching conditions of the support substrate 10 in FIG. 5 , the three-dimensional shapes of the protrusions 51 and the recesses 52 can be set as desired.

[0045] First Example of Arrangement of Convex and Concave Parts

[0046] The three-dimensional shape of the convex part 51 and the concave part 52 is as follows Figure 4A The case of the illustrated shape describes an example of arrangement of the convex portion 51 and the concave portion 52 in the XY plane as an example. Figure 5A is a plan view illustrating a first example of the arrangement of the convex and concave portions in the first embodiment, and Figure 5B and Figure 5C It is along Figure 5A A cross-sectional view taken along line AA. Figure 5B The convex part is illustrated, and Figure 5C Recesses are exemplified.

[0047] like FIG. 5A to FIG. 5C As shown, the convex portions 51 and the concave portions 52 are arranged at a constant interval. The constant interval between the convex portions 51 or the constant interval between the concave portions 52 is the smallest in the three directions 54a to 54c (the smallest constant interval Pa). The angle between the directions 54a and 54b, the angle between the directions 54b and 54c, and the angle between the directions 54c and 54a are approximately 60°. The direction 54a is substantially parallel to the X direction. Figure 5B In the embodiment, the portion other than the protrusion 51 is flat. Figure 5C , the portion other than the recess 52 is flat. The constant interval Pa between the convex portions 51 and the constant interval Pa between the recesses 52 are substantially uniform, the widths W of the convex portions 51 and the recesses 52 in the directions 54a to 54c are substantially uniform, and the heights H of the convex portions 51 and the recesses 52 are substantially uniform. Note that the term "substantially uniform" means "uniform to the extent that an effect is achieved", and variations within the range of, for example, manufacturing errors are allowed.

[0048] Second Example of Arrangement of Convex and Concave Portions

[0049] Fig. 6A is a plan view illustrating a second example of the arrangement of the convex and concave portions in the first embodiment, and Figure 6B and Figure 6C It is along Fig. 6A The cross-sectional view extracted by line AA. FIG. 6A to FIG. 6C As shown, the constant interval between the protrusions 51 or the constant interval between the recesses 52 is the smallest in the two directions 54a and 54b (the smallest constant interval Pa). The angle between the directions 54a and 54b is about 90°. The direction 54a is substantially parallel to the X direction, and the direction 54b is substantially parallel to the Y direction. Figure 6B In the embodiment, the portion other than the protrusion 51 is flat. Figure 6C The portion other than the recess 52 is flat. The constant interval Pa between the protrusions 51 and the constant interval Pa between the recesses 52 are substantially uniform, the widths W of the protrusions 51 and the recesses 52 in the directions 54a and 54b are substantially uniform, and the heights H of the protrusions 51 and the recesses 52 are substantially uniform.

[0050] As in the first and second examples of the arrangement of the convex portions 51 and the concave portions 52, one direction 54a of the directions in which the constant interval between the convex portions 51 or the concave portions 52 is the constant interval Pa may be substantially parallel to the X direction. As in the second example of the arrangement of the convex portions 51 and the concave portions 52, one direction 54b of the directions in which the constant interval between the convex portions 51 or the concave portions 52 is the constant interval Pa may be substantially parallel to the extending direction of the electrode fingers 15.

[0051] Third Example of Arrangement of Convex and Concave Parts

[0052] Fig. 7A 1 is a plan view of a third example of the arrangement of the convex and concave portions in the first embodiment. Fig. 7A As shown, when the constant interval between the convex portions 51 or the constant interval between the concave portions 52 is the smallest in the three directions 54a to 54c, the convex portions 51 or the concave portions 52 may contact each other. Fig. 7A As shown, as the vertices 51a or 52a approach each other, the planar shape of the convex portion 51 or the concave portion 52 becomes a hexagon.

[0053] Fourth Example of Arrangement of Convex and Concave Parts

[0054] Figure 7B 1 is a plan view illustrating a fourth example of the arrangement of the convex and concave portions in the first embodiment. Figure 7B As shown, when the constant interval between the convex portions 51 or the constant interval between the concave portions 52 is the smallest in both directions 54a and 54b, the convex portions 51 or the concave portions 52 may contact each other. Figure 7BAs shown, when the vertices 51a or 52a are close to each other, the planar shape of the convex portion 51 or the concave portion 52 becomes a quadrilateral.

[0055] Fifth Example of Arrangement of Convex and Concave Portions

[0056] Fig. 8A is a plan view illustrating a fifth example of the arrangement of the convex and concave portions in the first embodiment. Fig. 8A , the electrode fingers 15 are illustrated as being superimposed on the convex portion and the concave portion. Fig. 8A As shown, the angle between the direction 54a and the X direction is θa, and the angle between the direction 54b and the X direction is θb. The angles θa and θb are about 45°. The directions 54a and 54b in which the constant interval between the convex portions 51 or the concave portions 52 is the minimum constant interval Pa are not the X direction or the Y direction. The directions 55a and 55b in which the constant interval between the convex portions 51 or the concave portions 52 is the second minimum constant interval Pb are substantially parallel to the X direction and the Y direction.

[0057] Sixth Example of Arrangement of Convex and Concave Portions

[0058] Figure 8B is a plan view illustrating a sixth example of the arrangement of the convex and concave portions in the first embodiment. Figure 8B , the electrode fingers 15 superimposed on the convex portion and the concave portion in the first embodiment are illustrated. Figure 8B As shown, the angle θa between direction 54a and the X direction and the angle θb between direction 54b and the X direction are different from 45°. Directions 54a and 54b with a minimum constant interval Pa and directions 55a and 55b with a second minimum constant interval Pb are not parallel to the X direction or the Y direction.

[0059] As in the first to fourth examples of the arrangement, the directions 54a to 54c in which the constant intervals between the convex portions 51 and the constant intervals between the concave portions 52 are the minimum constant intervals Pa may be substantially parallel to at least one of the X direction and the Y direction. As in the fifth and sixth examples of the arrangement, the directions 54a and 54b in which the constant intervals are the minimum constant intervals Pa are not necessarily parallel to the X direction or the Y direction.

[0060] In the first to sixth examples of arrangement, it is described that the three-dimensional shapes of the convex portion 51 and the concave portion 52 are Figure 4A However, the three-dimensional shapes of the convex portion 51 and the concave portion 52 may be FIG. 4B to FIG. 4M Any of the shapes shown, or other three-dimensional shapes.

[0061] Second example of the concave portion and the three-dimensional shape of the concave portion

[0062] 9A to 9C2 is a perspective view illustrating a second example of the three-dimensional shape of the convex and concave parts in the first embodiment. When the convex part 51 is illustrated, as shown by arrow 56a, the upward direction is the positive Z direction. When the concave part 52 is illustrated, as shown by arrow 56b, the upward direction is the negative Z direction. 9A to 9C In the embodiment, the convex portion 51 and the concave portion 52 are in the shape of lines or strips.

[0063] like Fig. 9A As shown in FIG. 1 , the convex portion 51 and the concave portion 52 may be in the shape of a line having a triangular cross section. Lines 51c and 52c are lines connecting the vertices of the triangles in the convex portion 51 and the concave portion 52, respectively. Fig. 9B As shown, the convex portion 51 and the concave portion 52 may be in the shape of a line having a semicircular cross section. Fig. 9C As shown, the convex portion 51 and the concave portion 52 may be in the shape of a line having a quadrilateral cross section. As described above, the convex portion 51 and the concave portion 52 may extend linearly or in a curved line.

[0064] Seventh Example of Arrangement of Convex and Concave Portions

[0065] The three-dimensional shape of the convex part 51 and the concave part 52 is Fig. 9A Taking the case of the illustrated shape as an example, an example of arrangement of the convex portion 51 and the concave portion 52 in the XY plane will be described. Fig. 10A is a plan view illustrating a seventh example of the arrangement of the convex and concave portions in the first embodiment, and Fig. 10B and Fig. 10C It is along Fig. 10A A cross-sectional view taken along line AA in FIG. Fig. 10B The convex part is illustrated, and Fig. 10C Recesses are exemplified.

[0066] like FIG. 10A to FIG. 10C As shown, the convex portions 51 and the concave portions 52 are arranged at a constant interval. The constant interval between the convex portions 51 or the concave portions 52 is a direction 54 of the minimum constant interval Pa and is substantially parallel to the X direction. Fig. 10B In the embodiment, the portion other than the protrusion 51 is flat. Fig. 10C The portion other than the recess 52 is flat. The constant interval Pa is substantially uniform, the width W of the convex portion 51 and the recess 52 in the direction 54 is substantially uniform, and the height H of the convex portion 51 and the recess 52 is substantially uniform.

[0067] Eighth and Ninth Examples of Arrangement of Convex and Concave Portions

[0068] Fig.11A 1 is a plan view illustrating an eighth example of the arrangement of the convex and concave portions in the first embodiment. Fig.11AAs shown, the direction 54 in which the constant interval is the minimum constant interval Pa is the Y direction. As in the seventh and eighth examples of arrangement of convex and concave portions, the direction 54 in which the constant interval is the minimum constant interval Pa may be substantially parallel to the X direction or the Y direction.

[0069] Fig. 11B 1 is a plan view illustrating a ninth example of the arrangement of the convex and concave portions in the first embodiment. Fig. 11B As shown, direction 54 is different from the X direction and the Y direction. That is, direction 54 is inclined relative to the X direction and the Y direction. As seen above, direction 54 is not necessarily parallel to the X direction or the Y direction.

[0070] In the seventh to ninth examples of arrangement, it is described that the three-dimensional shapes of the convex portion 51 and the concave portion 52 are Fig. 9A , but the three-dimensional shapes of the convex portion 51 and the concave portion 52 may be Fig. 9B and Fig. 9C Any of the shapes shown, or may be other three-dimensional shapes. In the seventh to ninth examples of arrangement, the case where the convex portions 51 or the concave portions 52 are away from each other is described, but the convex portions 51 or the concave portions 52 may be in contact with each other.

[0071] Tenth Example of Arrangement of Convex and Concave Portions

[0072] Fig.12 1 is a plan view illustrating a tenth example of the arrangement of the convex and concave portions in the first embodiment. Fig.12 As shown, in each region 58, the convex portions 51 and the concave portions 52 are arranged irregularly, and the sizes of the convex portions 51 and the concave portions 52 are not uniform. The regions 58 are periodically arranged in the X direction and the Y direction. The constant intervals Pa and Pb of the region 58 are substantially uniform. The constant interval Pa is the smallest constant interval among the constant intervals between the convex portions 51 and the constant intervals between the concave portions 52, and the constant interval Pb is the second smallest constant interval.

[0073] As in the tenth example of the arrangement of the convex and concave portions, a group including a plurality of convex portions 51 or a plurality of concave portions 52 may be regularly arranged. It has been described that the three-dimensional shapes of the convex portions 51 and the concave portions 52 are Figure 4A The shape shown in the figure is the case, but the three-dimensional shape of the protrusion 51 and the recess 52 can be any one of the first example and the second example of the three-dimensional shape, or can be other three-dimensional shapes. The protrusion 51 with different three-dimensional shapes or the recess 52 with different three-dimensional shapes can be set in the area 58.

[0074] First Modification of the First Embodiment

[0075] Fig.13 is a cross-sectional view of an acoustic wave device according to a first modification example of the first embodiment. Fig.13 As shown, an additional film 53 is provided to the boundary surface 50 between the support substrate 10 and the insulating layer 11. The roughness of the upper surface of the additional film 53 is less than the roughness of the upper surface of the support substrate 10. The additional film 53 is, for example, an aluminum oxide film, an aluminum nitride film, or a silicon nitride film, and the acoustic impedance of the additional film 53 is greater than the acoustic impedance of the insulating layer 11. The thickness of the additional film 53 is, for example, 0.1 μm or less. This configuration causes the sound waves to be scattered more on the boundary surface 50. The additional film 53 may be provided in an island pattern, or may have a structure in which the additional film 53 is formed by a single-layer film having multiple portions with different thicknesses. The other structures are the same as those in the first embodiment, and therefore their description is omitted. As in the first variant of the first embodiment, the insulating layer 11 may be indirectly bonded to the support substrate 10.

[0076] Simulation 1

[0077] The first embodiment and the first comparative example were simulated. For the first comparative example, it was assumed that the boundary surface 50 between the support substrate 10 and the insulating layer 11 was flat. The simulation conditions were as follows.

[0078] Support substrate 10: sapphire substrate

[0079] Insulating layer 11: Silicon oxide film with an average thickness of 2 μm (0.4λ)

[0080] Piezoelectric substrate 12: 42° rotated Y-cut X-propagated lithium tantalate substrate with a thickness of 2 μm (0.4λ)

[0081] Electrode finger 15: Aluminum film with a thickness of 500 nm

[0082] Pitch λ of electrode fingers 15: 5 μm

[0083] Number of pairs of electrode fingers 15: 10 pairs

[0084] Convex part 51: having Figure 5B The cross-sectional shape shown in the cross-sectional view of FIG. 1 , wherein Pa=3 μm, W=2.7 μm, and H=1.65 μm

[0085] The admittance was simulated using a 2.5-dimensional finite element method under the premise that the width in the Y direction was λ / 32. The simulation result of the admittance was converted into the admittance of an acoustic wave resonator in which the number of pairs of electrode fingers 15 was 100 pairs and the hole length was 25λ.

[0086] Fig.14 is a graph of the magnitude of the admittance relative to the frequency in simulation 1. Fig.14As shown, spurious emission 64 is generated at a frequency higher than the resonance frequency fr and the anti-resonance frequency fa. The spurious emission 64 is caused by the body wave excited together with the acoustic wave in the main mode excited by the electrode finger 15. When the support substrate 10 is a hard substrate, the acoustic velocity in the support substrate 10 is faster than the acoustic velocity in the insulating layer 11 and the piezoelectric substrate 12. That is, the acoustic impedance of the support substrate 10 is higher than the acoustic impedance of the insulating layer 11 and the acoustic impedance of the piezoelectric substrate 12. When the boundary surface 50 between the support substrate 10 and the insulating layer 11 is flat as in the first comparative example, the body wave excited by the electrode finger 15 is reflected by the boundary surface 50. The spurious emission 64 is generated due to the reflected body wave. In the first embodiment, since the boundary surface 50 is rough, the body wave is scattered by the boundary surface or absorbed in the support substrate 10. Therefore, the spurious emission 64 is smaller than the spurious emission in the first comparative example. As described above, the first embodiment can reduce the spurious emission.

[0087] Simulation 2

[0088] The simulation was performed on the premise that the boundary surface 50 between the support substrate 10 and the insulating layer 11 is an irregular rough surface. The difference D between the maximum value and the minimum value of the boundary surface 50 in the Z direction changes as follows.

[0089] Sample A: D = 1 μm

[0090] Sample B: D = 2 μm

[0091] Sample C: D = 4 μm

[0092] The other simulation conditions are the same as those in Simulation 1.

[0093] Fig.15 is a graph of the magnitude of the admittance relative to the frequency in simulation 2. The frequency band of the spurious emission 64 formed by the body wave is widened. Fig.15 As shown, the magnitude of the stray emission of sample A is substantially the same as that of the first comparative example. The stray emission of sample B is smaller than that of sample A, and the stray emission of sample C is smaller than that of sample B. As described above, the magnitude of the stray emission varies depending on the roughness of the rough surface.

[0094] The roughness of the rough surface having irregular concavoconvexities is different depending on the position in the XY plane. Therefore, in a microscopic sense, characteristics such as the size of stray emission are different depending on the position. For example, even if the roughness of the rough surface is made to be a roughness at which the stray emission becomes minimum, since the size of the stray emission is different depending on the position, the size of the stray emission becomes larger than the optimal stray emission in a macroscopic sense.

[0095] In the first embodiment, the convex portions 51 and / or concave portions 52 are regularly arranged. This structure makes characteristics such as the magnitude of stray emission uniform.

[0096] Experiment 1

[0097] The acoustic wave resonators of the first embodiment and the first comparative example were manufactured under the following manufacturing conditions.

[0098] Support substrate 10: 500 μm thick sapphire substrate

[0099] Insulating layer 11: Silicon oxide film with an average thickness of 2.8 μm (0.4λ)

[0100] Bonding layer 13: 10 nm thick aluminum oxide film

[0101] Piezoelectric substrate 12: 42° rotated Y-cut X-propagated lithium tantalate substrate with a thickness of 2 μm (0.4λ)

[0102] Electrode finger 15: A titanium film with a thickness of 160 nm and an aluminum film with a thickness of 268 nm are stacked in this order from the piezoelectric substrate 12 side.

[0103] Pitch λ of electrode fingers 15: 5 μm

[0104] Number of pairs of electrode fingers 15: 100 pairs

[0105] The three-dimensional shape of the protrusion 51 is: Figure 4A The cone shape shown.

[0106] Arrangement of the protrusion 51: Figure 8B Arrangement shown, where Pa = 3 μm, W = 2.7 μm, and H = 1.65 μm

[0107] Fig.16 This is a graph of the real part and magnitude of the admittance in Experiment 1 versus frequency. Fig.16 This is an enlarged view of the vicinity of the resonant frequency fr and the anti-resonant frequency fa. Fig.16 As shown in FIG. 1 , the stray emission 66 in the first embodiment is smaller than the stray emission in the first comparative example. The stray emission 66 is not caused by body waves, but is a transverse mode stray emission caused by acoustic waves propagating in the Y direction. Fig.16 As shown in , in the first embodiment, the transverse mode spurious emission is reduced. Specifically, by Figure 8B Directions 54a and 54b are shown to be different from both the X-direction and the Y-direction to reduce transverse mode spurious emissions.

[0108] In the first embodiment, a pair of comb-shaped electrodes 18 are located on the piezoelectric substrate 12 and include a plurality of electrode fingers 15. The support substrate 10 has regularly arranged convex portions 51 and / or concave portions 52. The insulating layer 11 is directly or indirectly bonded between the piezoelectric substrate 12 and the support substrate 10, and a boundary surface between the insulating layer 11 and the support substrate 10 is provided along the convex portions 51 and / or concave portions 52. This structure improves the uniformity of characteristics such as the size of stray emissions.

[0109] The insulating layer 11 is in contact with the upper surface of the support substrate 10. This structure causes the bulk wave to be scattered on the boundary surface 50 or absorbed in the support substrate 10, thereby reducing the stray emission 64.

[0110] The arithmetic mean roughness Ra of the boundary surface 50 is preferably not less than 10 nm and not more than 1000 nm, more preferably not less than 50 nm and not more than 500 nm, and further preferably not less than 100 nm and not more than 300 nm. The arithmetic mean roughness of the boundary surface 50 is preferably equal to or greater than 10 times the arithmetic mean roughness of the boundary surface between the insulating layer 11 and the piezoelectric substrate 12 and / or the arithmetic mean roughness of the surface of the piezoelectric substrate 12, and more preferably equal to or greater than 100 times the arithmetic mean roughness of the boundary surface between the insulating layer 11 and the piezoelectric substrate 12 and / or the arithmetic mean roughness of the surface of the piezoelectric substrate 12.

[0111] As in the fifth example, the sixth example, and the ninth example of the arrangement of the recesses and recesses, the directions 54, 54a, and 54b in which the constant interval between the convex portions 51 and / or between the concave portions 52 is the minimum constant interval Pa are directions different from the arrangement direction (X direction) of the electrode fingers 15. This structure makes the phases of the body waves propagating in the X direction and reflected by the concave portions 52 or the convex portions 51 different. Therefore, the stray emission due to the body waves is reduced. The angle between each of the directions 54, 54a, and 54b and the X direction is preferably 10° or more, more preferably 20° or more, and further preferably 30° or more.

[0112] The directions 54, 54a and 54b in which the constant interval is the minimum constant interval Pa are different from the extending direction (Y direction) of the electrode finger 15. This structure makes the phases of the acoustic waves propagating in the Y direction and reflected by the concave portion 52 or the convex portion 51 different. Therefore, the transverse mode spurious emission is reduced. The angle between each of the directions 54, 54a and 54b and the Y direction is preferably 10° or more, more preferably 20° or more, and further preferably 30° or more.

[0113] As in the sixth example of the arrangement of the convex and concave portions, the directions 54a and 54b in which the constant interval between the convex portions 51 and / or between the concave portions 52 is the minimum constant interval Pa and the directions 55a and 55b in which the constant interval between the convex portions 51 and / or between the concave portions 52 is the second minimum constant interval Pb are directions different from both the X direction and the Y direction. This structure further reduces the spurious emission due to body waves and transverse mode spurious emission. The angle between each of the directions 55a and 55b and the X direction and the angle between each of the directions 55a and 55b and the Y direction are preferably 10° or more, more preferably 20° or more, and further preferably 30° or more.

[0114] When the wavelength of the acoustic wave is represented by λ, the constant interval Pa is preferably equal to or greater than λ / 16 and less than λ. That is, the minimum constant interval Pa is preferably equal to or greater than 1 / 8 times the pitch of the electrode fingers 15 and less than twice the pitch of the electrode fingers 15. This configuration can make the phase of the body wave propagating in the X direction and / or the phase of the acoustic wave propagating in the Y direction different. Therefore, stray emissions are further reduced. The constant interval Pa is more preferably equal to or greater than 0.15 times the pitch of the electrode fingers 15 and equal to or less than 1.8 times the pitch of the electrode fingers 15, and further preferably equal to or greater than 1 / 4 times the pitch of the electrode fingers 15 and equal to or less than 3 / 4 times the pitch of the electrode fingers 15. The average pitch of the electrode fingers 15 is calculated by dividing the length of the IDT 22 in the X direction by the number of electrode fingers 15.

[0115] As shown in the first example of the three-dimensional shape FIG. 4A to FIG. 4I As shown, the convex portion 51, the concave portion 52, or the convex portion 51 and the concave portion 52 are island-shaped. 9A to 9C As shown in , the convex portion 51 , the concave portion 52 , or the convex portion 51 and the concave portion 52 may have a shape extending in one direction in the planar direction.

[0116] In the third example illustrating the arrangement of the convex and concave portions Fig. 7A , the direction 54a in which the constant interval is the minimum constant interval Pa is the X direction, but the directions 54b and 54c are not parallel to the Y direction. The X direction and the Y direction are along the side surface of the support substrate 10. In this case, as indicated by the thick line 57, the support substrate 10 may be unevenly divided. Therefore, cracks starting from the convex portion or the concave portion may be introduced into the support substrate 10.

[0117] On the other hand, in the fourth example illustrating the arrangement of the convex and concave portions, Figure 7B, directions 54a and 54b in which the constant interval is the minimum constant interval Pa are substantially parallel to the X direction and the Y direction, respectively. When the support substrate 10 is cut, the support substrate 10 is linearly divided as indicated by the thick line 57. Therefore, the formation of cracks in the support substrate 10 is suppressed.

[0118] When the IDT 22 excites a shear horizontal wave (SH), a body wave tends to be generated. When the piezoelectric substrate 12 is a Y-cut lithium tantalate substrate rotated by 36° or more and 48° or less, an SH wave is excited. Therefore, in this case, it is preferable to set the convex portion 51 and the concave portion 52 of the interface 50. When the thickness of the piezoelectric substrate 12 is equal to or less than the wavelength λ of the acoustic wave, that is, when the thickness of the piezoelectric substrate 12 is equal to or less than twice the average value of the pitch of the electrode fingers 15, the loss is reduced. When the distance from the upper surface of the support substrate 10 to the upper surface of the piezoelectric substrate 12 is equal to or less than four times the average value of the pitch of the electrode fingers 15, the loss is reduced.

[0119] In order to prevent the sound wave from leaking to the support substrate 10, it is preferable that the acoustic impedance of the support substrate 10 is higher than the acoustic impedance of the piezoelectric substrate 12 (i.e., the acoustic velocity in the support substrate 10 is faster than the acoustic velocity in the piezoelectric substrate 12). Since the sound wave propagates in the insulating layer 11, it is preferable that the acoustic impedance of the insulating layer 11 is lower than the acoustic impedance of the piezoelectric substrate 12 and the support substrate 10 (i.e., the acoustic velocity in the insulating layer 11 is lower than the acoustic velocity in the piezoelectric substrate 12 and the support substrate 10).

[0120] Second embodiment

[0121] Fig.17A is a circuit diagram of a filter according to the second embodiment. Fig.17A As shown, one or more series resonators S1 to S3 are connected in series between the input terminal Tin and the output terminal Tout. One or more parallel resonators P1 and P2 are connected in parallel between the input terminal Tin and the output terminal Tout. The acoustic wave resonator of the first embodiment can be used for at least one of the one or more series resonators S1 to S3 and the one or more parallel resonators P1 and P2. The number of resonators in the ladder filter can be freely selected. The filter can be a multi-mode type filter.

[0122] First Modification of the Second Embodiment

[0123] Fig. 17B is a circuit diagram of a duplexer according to a first variation of the second embodiment. Fig. 17BAs shown, the transmission filter 40 is connected between the common terminal Ant and the transmission terminal Tx. The receiving filter 42 is connected between the common terminal Ant and the receiving terminal Rx. The transmission filter 40 sends the signal in the transmission frequency band to the common terminal Ant as a transmission signal among the high-frequency signals input from the transmission terminal Tx, and suppresses signals of other frequencies. The receiving filter 42 sends the signal in the reception frequency band to the receiving terminal Rx as a reception signal among the high-frequency signals input from the common terminal Ant, and suppresses signals of other frequencies. At least one of the transmission filter 40 and the receiving filter 42 can be a filter of the second embodiment.

[0124] A duplexer has been described as an example of a multiplexer, but the multiplexer may be a triplexer or a quadplexer.

[0125] Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.

Claims

1. An acoustic wave device, comprising: Piezoelectric substrate; a pair of comb-shaped electrodes, the pair of comb-shaped electrodes being located on the piezoelectric substrate, each of the comb-shaped electrodes comprising a plurality of electrode fingers; a supporting substrate having convex portions and / or concave portions in a region overlapping with the pair of comb-shaped electrodes in a plan view, the convex portions and / or the concave portions being regularly arranged; as well as an insulating layer, the insulating layer being directly or indirectly bonded between the piezoelectric substrate and the supporting substrate, wherein a boundary surface between the insulating layer and the supporting substrate is arranged along the convex portion and / or the concave portion, Among them, the two directions of the minimum constant interval among the constant intervals between the protrusions and / or the constant intervals between the recesses, and the other two directions of the second minimum constant interval among the constant intervals between the protrusions and / or the constant intervals between the recesses, which are different from the two directions, are different from both the arrangement direction and the extension direction of the electrode fingers.

2. The acoustic wave device according to claim 1, wherein The minimum constant interval among the constant intervals between the convex portions and / or the constant intervals between the concave portions is equal to or greater than 1 / 4 times the pitch of the electrode fingers and less than 2 times the pitch of the electrode fingers.

3. The acoustic wave device according to claim 1, wherein The convex portion, the concave portion, or the convex portion and the concave portion are island-shaped.

4. The acoustic wave device according to claim 1, wherein: The convex portion, the concave portion, or the convex portion and the concave portion extend in one direction among planar directions.

5. A filter, comprising: The acoustic wave device according to claim 1.

6. A multiplexer, the multiplexer comprising: The filter according to claim 5.

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