Acoustic wave device

Abstract

An acoustic wave device includes a pair of comb electrodes disposed on a piezoelectric substrate, each of the pair of comb electrodes including electrode fingers and a metal portion disposed between the electrode fingers adjacent to each other, the metal portion having a shorter length than the electrode fingers, the electrode fingers of one comb-shaped electrode and the electrode fingers of the other comb-shaped electrode are alternately arranged at least partially; the sound velocity of sound waves propagating through the area where the metal part is located is higher than the sound velocity of sound waves propagating through the central area of the overlapping area where the electrode fingers of one comb-shaped electrode and the electrode fingers of the other comb-shaped electrode are overlapped. And the sound velocity of the sound wave propagating through the region where the metal portion is located is equal to or less than 1.10 times the sound velocity of the sound wave propagating through the central region.

Description

Technical Field

[0001] One aspect of the present disclosure relates to an acoustic wave device. Background Art

[0002] Acoustic wave devices are used in high-frequency communication systems typified by mobile phones. As an acoustic wave device, as disclosed, for example, in Japanese Patent Application Laid-Open Nos. 2007-68107 and 2003-218665 and the Japanese translation of PCT International Publication No. 2013-518455 (Patent Documents 1 to 3), an acoustic wave device including a pair of comb-shaped electrodes is known, each comb-shaped electrode including a plurality of electrode fingers, a plurality of dummy electrode fingers, and a bus bar connected to the electrode fingers and the dummy electrode fingers. Further, as a method for reducing spurious emissions without degrading the Q factor, as disclosed, for example, in Japanese Patent Application Laid-Open Nos. 2022-11770 and 2022-126852 (Patent Documents 4 and 5), an acoustic wave device using a piston mode is known. Summary of the Invention

[0003] The piston mode is used to reduce spurious emissions. However, there is still room for improvement in reducing spurious emissions.

[0004] An object of the present invention is to reduce spurious emissions.

[0005] In one aspect of the present disclosure, there is provided an acoustic wave device including: a piezoelectric substrate; and a pair of comb-shaped electrodes provided on the piezoelectric substrate, each of the pair of comb-shaped electrodes including a plurality of electrode fingers and a plurality of metal portions provided between the electrode fingers adjacent to each other in the short direction of the plurality of electrode fingers, the plurality of metal portions having a length shorter than that of the plurality of electrode fingers in the long direction, the plurality of electrode fingers of one of the pair of comb-shaped electrodes and the plurality of electrode fingers of the other of the pair of comb-shaped electrodes being at least partially alternately arranged, the sound velocity of the acoustic wave propagating through the region where the plurality of metal portions are located being higher than the sound velocity of the acoustic wave propagating through the central region of the overlapping region where the plurality of electrode fingers of one of the pair of comb-shaped electrodes and the plurality of electrode fingers of the other of the pair of comb-shaped electrodes overlap, and the sound velocity of the acoustic wave propagating through the region where the metal portions are located being equal to or less than 1.10 times the sound velocity of the acoustic wave propagating through the central region.

[0006] In another aspect of the present disclosure, there is provided an acoustic wave device, the acoustic wave device comprising: a piezoelectric substrate; and a pair of comb-shaped electrodes disposed on the piezoelectric substrate, each of the pair of comb-shaped electrodes including a plurality of electrode fingers and a plurality of metal portions, two or more of the plurality of metal portions being disposed between electrode fingers adjacent in a short direction of the plurality of electrode fingers, the plurality of metal portions having a width smaller than that of the plurality of electrode fingers in the short direction, and the plurality of electrode fingers of one of the pair of comb-shaped electrode fingers and the plurality of electrode fingers of the other of the pair of comb-shaped electrode fingers being at least partially alternately arranged.

[0007] In another aspect of the present disclosure, there is provided an acoustic wave device, the acoustic wave device comprising: a piezoelectric substrate; and a pair of comb-shaped electrodes disposed on the piezoelectric substrate, each of the pair of comb-shaped electrodes including a plurality of electrode fingers and a plurality of metal portions, the plurality of metal portions being disposed between electrode fingers adjacent in a short direction of the plurality of electrode fingers, the plurality of metal portions containing a material having a higher sound velocity than that of the acoustic wave of the plurality of electrode fingers as a main component, and the plurality of electrode fingers of one of the pair of comb-shaped electrodes and the plurality of electrode fingers of the other of the pair of comb-shaped electrodes being at least partially alternately arranged. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 (A) of is a plan view of an acoustic wave device according to a first embodiment, Figure 1 (B) of is along Figure 1 a cross-sectional view taken along line A-A in (A) of ;

[0009] Figure 2A is a plan view of an acoustic wave device according to a comparative example, Figure 2B is along Figure 2A a cross-sectional view taken along line A-A in ;

[0010] Figure 3A shows the sound velocity of the acoustic wave in the comparative example, Figure 3B shows the sound velocity of the acoustic wave in the first embodiment;

[0011] Figure 4A is a plan view of Model A and Model B used in Simulation 1, Figure 4B is along Figure 4A a cross-sectional view taken along line A-A in ; Figure 4C is a plan view of Model C used in Simulation 1, Figure 4D is along Figure 4C a cross-sectional view taken along line A-A in ;

[0012] Figure 5 is a graph showing the absolute value |Y| of the admittance with respect to frequency in Simulation 1;

[0013] Figure 6A and Figure 6B is a graph (No.1) showing the real part Real(Y) of the admittance versus frequency in Simulation 2; Figure 7A and Figure 7B is a graph (Part 2) showing the real part Real(Y) of the admittance versus frequency in Simulation 2;

[0014] Figure 8A is a plan view of an acoustic wave device according to a first variant of the first embodiment, Figure 8B is along Figure 8A a cross-sectional view taken along line A-A in;

[0015] Figure 9 gives the experimental results of the real part Real(Y) of the admittance versus frequency in the first embodiment and the first variant of the first embodiment;

[0016] Figure 10A and Figure 10B are the experimental results of the real part Real(Y) of the admittance versus frequency when the multilayer structure of the substrate changes in the first embodiment and the first variant of the first embodiment;

[0017] Figure 11A is a plan view of an acoustic wave device according to a second variant of the first embodiment, Figure 11B is along Figure 11A a cross-sectional view taken along line A-A in;

[0018] Figure 12A is a plan view of an acoustic wave device according to a third variant of the first embodiment, Figure 12B is along Figure 12A a cross-sectional view taken along line A-A in;

[0019] Figure 13A is a plan view of the case where three dummy electrode fingers are provided between adjacent electrode fingers in the first embodiment, Figure 13B is along Figure 13A a cross-sectional view taken along line A-A in; and

[0020] Figure 14A is a circuit diagram of a filter according to the second embodiment, Figure 14B is a circuit diagram of a duplexer according to a variant of the second embodiment. Detailed Embodiments

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

[0022] First Embodiment

[0023] Figure 1 FIG. (A) is a plan view of the acoustic wave device 100 according to the first embodiment. Figure 1 FIG. (B) is along Figure 1 FIG. (A) is a cross-sectional view taken along line A-A in FIG. (A). The short direction of the electrode fingers 22 is defined as the X direction, the long direction of the electrode fingers 22 is defined as the Y direction, and the thickness direction of the piezoelectric substrate 12 is defined as the Z direction. The short direction of the electrode fingers 22 is also the arrangement direction of the electrode fingers 22. The X direction, Y direction, and Z direction do not necessarily correspond to the X-axis orientation and Y-axis orientation of the crystal orientation of the piezoelectric substrate 12. When the piezoelectric substrate 12 is a rotated Y-cut X-propagation piezoelectric substrate, the X direction is the X-axis orientation of the crystal orientation.

[0024] As Figure 1 FIG. (A) and Figure 1 FIG. (B) show, the piezoelectric substrate 12 is bonded to the support substrate 10. The support substrate 10 is, for example, a sapphire substrate, an alumina substrate, a spinel substrate, a quartz substrate, a crystal substrate, a silicon carbide substrate, or a silicon substrate. The piezoelectric substrate 12 is, for example, a single crystal lithium tantalate substrate or a single crystal lithium niobate 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 piezoelectric substrate 12 can be, for example, a 30° to 50° Y-cut X-propagation lithium tantalate substrate. An insulating layer made of silicon oxide, aluminum oxide, and / or aluminum nitride can be provided between the support substrate 10 and the piezoelectric substrate 12. As described above, the piezoelectric substrate 12 is directly or indirectly bonded to the support substrate 10.

[0025] A digital interdigitated transducer (IDT) 20 and a reflector 25 are provided on the piezoelectric substrate 12. The IDT 20 includes a pair of comb-shaped electrodes 21. The comb-shaped electrodes 21 include a plurality of electrode fingers 22, a plurality of virtual electrode fingers 23, and a bus bar 24 connected to the electrode fingers 22 and the virtual electrode fingers 23. Two or more virtual electrode fingers are provided between the electrode fingers 22 adjacent to each other in the X direction. Here, a case where two virtual electrode fingers 23 are provided between the electrode fingers 22 adjacent to each other in the X direction is shown as an example. In the X direction, the widths of the electrode fingers 22 and the virtual electrode fingers 23 are constant from one end connected to the bus bar 24 to the other end opposite thereto. The width of the virtual electrode fingers 23 in the X direction is smaller than the width of the electrode fingers 22 in the X direction. The thickness of the electrode fingers 22 is the same as the thickness of the virtual electrode fingers 23. The same thickness means that a difference of about the manufacturing error is acceptable. For example, a ratio of two thicknesses of 0.95 or greater and 1.05 or less is acceptable. The virtual electrode fingers 23 are an example of the metal part in the claims.

[0026] The IDT 20 and the reflector 25 are formed of a metal film 26 on the piezoelectric substrate 12. The metal film 26 is a film containing, for example, aluminum, copper, molybdenum, iridium, platinum, rhenium, rhodium, ruthenium, tantalum, or tungsten as a main component. An adhesion film made of titanium, chromium, etc. can be provided between the piezoelectric substrate 12 and the electrode fingers 22, between the piezoelectric substrate 12 and the virtual electrode fingers 23, and between the piezoelectric substrate 12 and the bus bar 24. The adhesion film is thinner than the electrode fingers 22, the virtual electrode fingers 23, and the bus bar 24.

[0027] The region where the electrode fingers 22 of one of the pair of comb-shaped electrodes 21 overlap with the electrode fingers 22 of the other of the pair of comb-shaped electrodes 21 is the overlap region 30. The length of the overlap region 30 in the Y direction is the aperture length. The pair of comb-shaped electrodes 21 face each other such that the electrode fingers 22 of one of the pair of comb-shaped electrodes 21 and the electrode fingers 22 of the other of the pair of comb-shaped electrodes 21 are arranged alternately in the X direction at least in a part of the overlap region 30. The acoustic wave (surface acoustic wave) of the main mode excited by the electrode fingers 22 in the overlap region 30 mainly propagates in the X direction. The pitch of the electrode fingers 22 of one comb-shaped electrode 21 is substantially equal to the wavelength λ of the surface acoustic wave. The wavelength λ is approximately twice the pitch D of the electrode fingers 22. The reflector 25 reflects the surface acoustic wave excited by the electrode fingers 22 of the IDT 20. Therefore, the surface acoustic wave is confined within the overlap region 30 of the IDT 20.

[0028] The overlap region 30 includes an edge region 32 and a central region 31. The edge region 32 is the region located at each edge in the Y direction, and the central region 31 is the region located more internally than the edge region 32 in the Y direction. The edge region 32 can also be said to be the region of the overlap region 30 where the ends of the electrode fingers 22 are located. The region located between the end of the electrode finger 22 of one comb-shaped electrode 21 and the end of the virtual electrode finger 23 of the other comb-shaped electrode 21 is the gap region 33. The region where the virtual electrode fingers 23 are located is the virtual region 34. The region where the bus bar 24 is located is the bus bar region 35. The virtual region 34 is an example of the region where multiple metal parts are located in the claims.

[0029] An additional film 40 is provided on the piezoelectric substrate 12 in the edge region 32. The additional film 40 covers the electrode fingers 22 located in each of the edge regions 32. The additional film 40 is also provided in a part of the edge region 32 where the electrode fingers 22 are not provided. The additional film 40 is not provided in the central region 31, the gap region 33, the virtual region 34, and the bus bar region 35.

[0030] The additional film 40 is an insulating film containing, for example, silicon oxide, tantalum oxide, or niobium oxide as a main component, but as long as the sound velocity of the acoustic wave propagating through the edge region 32 can be adjusted, it can be a film containing another material as a main component.

[0031] Here, when a film contains an element as its main component, the film may contain intentional or unintentional impurities other than the main component. When a certain element is the main component of a certain film, the concentration of the certain element is, for example, 50 at% (atomic percentage) or higher, or for example, 80 at% or higher. In the case where two elements are the main components, such as in the case of silicon oxide, the sum of the concentration of silicon and the concentration of oxygen is, for example, 50 at% or higher, for example, 80 at% or higher, and the concentration of silicon and the concentration of oxygen are each, for example, 10 at% or higher.

[0032] Manufacturing method

[0033] A method of manufacturing the acoustic wave device 100 according to the first embodiment will be described. First, the piezoelectric substrate 12 is bonded to the support substrate 10 using, for example, a surface activation method. Then, the piezoelectric substrate 12 is polished to a desired thickness using, for example, a chemical mechanical polishing (CMP) method. Then, a metal film 26 is formed on the piezoelectric substrate 12 and then patterned into a desired shape. This forms the IDT 20 including a pair of comb-shaped electrodes 21, and a reflector 25 is formed on the piezoelectric substrate 12. Each comb-shaped electrode 21 includes electrode fingers 22, dummy electrode fingers 23, and a bus bar 24. The metal film 26 is formed by, for example, sputtering, vacuum evaporation, or chemical vapor deposition (CVD). The metal film 26 is patterned by, for example, photolithography and etching.

[0034] Then, an additional film 40 is formed so as to cover the electrode fingers 22 in each of the edge regions 32. The additional film 40 is formed by, for example, forming a mask layer having an opening on the edge region 32 of the piezoelectric substrate 12, using the mask layer as a mask to form the additional film 40, and then removing the mask layer. The mask layer is formed of, for example, a photoresist. The additional film 40 is formed by, for example, sputtering, vacuum evaporation, or CVD. Through the above processes, the acoustic wave device 100 according to the first embodiment is formed.

[0035] Comparative example

[0036] Figure 2A is a plan view of the acoustic wave device 500 according to the comparative example, Figure 2B is a cross-sectional view taken along the line A-A in Figure 2A . As shown in Figure 2A and Figure 2B , in the comparative example, one dummy electrode finger 23 of one comb-shaped electrode 21 faces the end of the electrode finger 22 of the other comb-shaped electrode 21 and is located between the electrode fingers 22 adjacent to each other in the X direction of one comb-shaped electrode 21. The width of the dummy electrode finger 23 in the X direction is the same as the width of the electrode finger 22 in the X direction. Other configurations are the same as those of the first embodiment, and thus the description thereof will be omitted.

[0037] Sound velocity of acoustic wave

[0038] Figure 3A The sound velocity of the acoustic wave in the comparative example is shown. Figure 3B The sound velocity of the acoustic wave in the first embodiment is shown. As Figure 3A shown, in the acoustic wave device 500 according to the comparative example, the virtual electrode fingers 23 have the same width and thickness as the electrode fingers 22. Therefore, the sound velocity of the acoustic wave propagating through the virtual region 34 is the same as the sound velocity of the acoustic wave propagating through the central region 31. Since the additional film 40 is provided in the edge region 32, the sound velocity of the acoustic wave propagating through the edge region 32 is lower than the sound velocity of the acoustic wave propagating through the central region 31. The piston mode can be achieved by adjusting the sound velocity of the acoustic wave propagating through the edge region 32 to be lower than the sound velocity of the acoustic wave propagating through the central region 31. The sound velocity of the acoustic wave propagating through the gap region 33 is higher than the sound velocity of the acoustic wave propagating through the central region 31 and the virtual region 34. The sound velocity of the acoustic wave is the sound velocity of the surface acoustic wave (e.g., SH wave) propagating on the surface of the piezoelectric substrate 12.

[0039] As Figure 3B shown, in the acoustic wave device 100 according to the first embodiment, two virtual electrode fingers 23 having a width smaller than that of the electrode fingers 22 are provided between the electrode fingers 22 adjacent to each other in the X direction in one comb-shaped electrode 21. The provision of such virtual electrode fingers 23 makes the sound velocity of the acoustic wave propagating through the virtual region 34 higher than the sound velocity of the acoustic wave propagating through the central region 31. The sound velocity of the acoustic wave propagating through the virtual region 34 is, for example, equal to or less than 1.10 times the sound velocity of the acoustic wave propagating through the central region 31. The other configurations are the same as those in Figure 3A , and thus the description thereof will be omitted.

[0040] The sound velocity of the acoustic wave can be obtained, for example, by Equation (1). In Equation (1), V represents the sound velocity, ρ represents the density, E represents the Young's modulus, and ν represents the Poisson's ratio.

[0041]

[0042] To achieve the piston mode, the length of the central region 31 in the Y direction and the length of the edge region 32 in the Y direction preferably satisfy a certain relationship. For example, the length of the central region 31 in the Y direction is preferably longer than the total length of the edge region 32 in the Y direction. The length of each of the edge regions 32 in the Y direction is preferably 1λ or less (e.g., equal to or less than 1 / 20 of the aperture length), more preferably 0.5λ or less (e.g., equal to or less than 1 / 40 of the opening length). The length of each of the edge regions 32 in the Y direction is preferably 0.05λ or more (e.g., equal to or greater than 1 / 400 of the aperture length), more preferably 0.1λ or more (e.g., equal to or greater than 1 / 200 of the aperture length). The edge regions 32 can be provided only on one side of the central region 31. The length of the gap region 33 in the Y direction is preferably 2λ or less (e.g., equal to or less than 1 / 10 of the aperture length), more preferably 1λ or less (e.g., equal to or less than 1 / 20 of the aperture length). The length of each of the gap regions 33 in the Y direction is preferably 0.1λ or more (e.g., equal to or greater than 1 / 200 of the aperture length), more preferably 0.2λ or more (e.g., equal to or greater than 1 / 100 of the aperture length).

[0043] Simulation 1

[0044] Simulation 1 regarding the higher sound velocity of the acoustic wave propagating through the virtual region 34 in the first embodiment will be described. Figure 4A are the plan views of Model A and Model B on which Simulation 1 is performed, Figure 4B is along Figure 4A the cross-sectional view taken along line A - A in Figure 4C is the plan view of Model C on which Simulation 1 is performed, Figure 4D is along Figure 4C the cross-sectional view taken along line A - A in. Although reflectors 25 sandwiching the IDT 20 are provided, for clarity, these reflectors are not shown in Figure 4A and Figure 4C . As shown in Figure 4B and Figure 4D , in all of Model A, B, and C, the piezoelectric substrate 12 is bonded to the support substrate 10 with an insulating layer 13 and an insulating layer 14 interposed therebetween. As shown in Figure 4A and Figure 4C , additional films 40 are provided in the edge regions 32 in all of Model A, B, and C.

[0045] As Figure 4AAs shown, in Model A and Model B, a dummy electrode finger 23 is provided between electrode fingers 22 adjacent to each other in the X direction in a comb-shaped electrode 21. In Model A, the width of the dummy electrode finger 23 is the same as that of the electrode finger 22. In Model B, the width of the dummy electrode finger 23 is smaller than that of the electrode finger 22. As Figure 4C shown, in Model C, two dummy electrode fingers 23 having a width smaller than that of the electrode finger 22 are provided between electrode fingers 22 adjacent to each other in the X direction in a comb-shaped electrode 21.

[0046] The simulation conditions are as follows.

[0047] Common conditions for Models A, B, and C

[0048] Wavelength λ of surface acoustic wave: 2.2 μm

[0049] Support substrate 10: Sapphire substrate

[0050] Insulating layer 13: Aluminum oxide layer with a thickness of 2.72λ

[0051] Insulating layer 14: Silicon oxide layer with a thickness of 0.2λ

[0052] Piezoelectric substrate 12: 42° Y-cut X-propagating lithium tantalate substrate with a thickness of 0.3λ

[0053] Electrode fingers 22, dummy electrode fingers 23, and bus bar 24: Aluminum film with a thickness of 0.07λ

[0054] Additional film 40: Niobium oxide film with a thickness of 0.01λ

[0055] Width W1 of electrode finger 22: 0.55 μm

[0056] Pitch D between electrode fingers 22: 1.1 μm

[0057] Conditions for Model A

[0058] Width W2 of dummy electrode finger 23: 0.55 μm

[0059] Distance L1 between electrode finger 22 and dummy electrode finger 23: 0.55 μm

[0060] Conditions for Model B

[0061] Width W2 of dummy electrode finger 23: 0.33 μm

[0062] Distance L1 between electrode finger 22 and dummy electrode finger 23: 0.66 μm

[0063] Conditions for Model C

[0064] Width W2 of dummy electrode finger 23: 0.33 μm

[0065] The distances L2 between the electrode fingers 22 and the dummy electrode fingers 23 and L3 between the dummy electrode fingers 23: 0.33 μm

[0066] Figure 5 is a graph showing the absolute value |Y| of the admittance with respect to the frequency in Simulation 1. In the absolute value |Y| of the admittance, peaks of the resonance frequency fr and the anti-resonance frequency fa are observed. As Figure 5 shown, the resonance frequency fr of Model B is shifted to a higher frequency than that of Model A. In Model C, the resonance frequency fr is shifted to a higher frequency than that of Model B. Compared with the case where the width W2 of the dummy electrode fingers 23 is the same as the width W1 of the electrode fingers 22 in Model A, by narrowing the width W2 of the dummy electrode fingers 23 as in Model B, the sound velocity of the acoustic wave propagating through the dummy region 34 is increased. In this case, the resonance frequency fr of Model B is shifted to a higher frequency than that of Model A. The resonance frequency fr of Model C is shifted to a higher frequency than that of Model B. This indicates that the sound velocity of the acoustic wave propagating through the dummy region is higher in Model C than in Model B. Therefore, in the first embodiment, as Figure 3B shown, the sound velocity of the acoustic wave propagating through the dummy region 34 is increased.

[0067] Simulation 2

[0068] In the dummy region 34, Simulation 2 was performed on the sound velocity and the spurious emission. Simulations 2 were performed using Models D, E, F, G, and H having the structures shown in Figure 4A and Figure 4B . The simulation conditions are as follows.

[0069] General conditions for Models D, E, F, G, and H

[0070] Wavelength λ of the surface acoustic wave: 5.0 μm

[0071] Support substrate 10: Sapphire substrate

[0072] Insulating layer 13: Aluminum oxide layer with a thickness of 2.72λ

[0073] Insulating layer 14: Silicon oxide layer with a thickness of 0.2λ

[0074] Piezoelectric substrate 12: 42° Y-cut X-propagating lithium tantalate substrate with a thickness of 0.3λ

[0075] Electrode fingers 22, dummy electrode fingers 23, and bus bar 24: Aluminum film with a thickness of 0.1λ

[0076] Additional film 40: Niobium oxide film with a thickness of 0.01λ

[0077] Width W1 of the electrode finger 22: 1.25 μm

[0078] Pitch D between the electrode fingers 22: 2.5 μm

[0079] Sound velocity in the central region 31: 3750 m / s

[0080] Sound velocity in the edge region 32: 3675 m / s

[0081] Sound velocity in the gap region 33: 4200 m / s

[0082] Conditions of Model D

[0083] Sound velocity in the virtual region 34: the same as the sound velocity in the central region 31 (3750 m / s)

[0084] Conditions of Model E

[0085] Sound velocity in the virtual region 34: 1.03 times the sound velocity in the central region 31 (3862.5 m / s)

[0086] Conditions of Model F

[0087] Sound velocity in the virtual region 34: 1.05 times the sound velocity in the central region 31 (3937.5 m / s)

[0088] Conditions of Model G

[0089] Sound velocity in the virtual region 34: 1.08 times the sound velocity in the central region 31 (4050 m / s)

[0090] Conditions of Model H

[0091] Sound velocity in the virtual region 34: 1.10 times the sound velocity in the central region 31 (4125 m / s)

[0092] Figures 6A to 7B is the graph presenting the real part Real(Y) of the admittance versus frequency in Simulation 2. In the real part Real(Y) of the admittance, more spurious responses are observed than in the absolute value Y. As Figure 6A presented, the spurious emissions are reduced in Model E compared to Model D. As Figure 6B presented, the spurious emissions are reduced in Model F compared to Model E. As Figure 7A and Figure 7B presented, the spurious emissions at approximately 780 MHz are larger in Model G and Model H than in Model F, but the spurious emissions in Model G and Model H are smaller than in Model D.

[0093] The results of Simulation 2 show that, as shown in Models E to H, spurious emissions can be reduced by adjusting the sound velocity of the sound wave in the virtual region 34 to be higher than the sound velocity of the sound wave in the central region 31. Additionally, since the spurious emissions are greater in Models G and H than in Model F, an upper limit was found to exist for the sound velocity of the sound wave in the virtual region 34. To reduce spurious emissions, for example, the sound velocity of the sound wave in the virtual region 34 is preferably equal to or less than 1.10 times, more preferably equal to or less than 1.08 times, and even more preferably equal to or less than 1.06 times the sound velocity of the sound wave in the central region 31.

[0094] When the standing wave displacement generated in the Y direction in the IDT 20 is completely canceled out in the positive and negative directions, no spurious emissions are generated, but the portion that cannot be canceled out appears as spurious emissions. When the sound velocity of the sound wave in the virtual region 34 becomes higher than the sound velocity of the sound wave in the central region 31, the shape of the standing wave changes due to the enhanced confinement effect. It is considered that the change in the standing wave shape reduces the displacement of the standing wave that cannot be canceled between the positive and negative directions. Therefore, in Models E to H, the spurious emissions are reduced.

[0095] First Variant

[0096] Figure 8A is a plan view of the acoustic wave device 110 according to the first variant of the first embodiment. Figure 8B is along Figure 8A the cross-sectional view taken along line A-A in. As Figure 8A and Figure 8B shown, in the first variant of the first embodiment, a virtual electrode finger 23 is provided between the electrode fingers 22 adjacent to each other in the X direction in one comb-shaped electrode 21. The end portions of the virtual electrode fingers 23 of one of the comb-shaped electrodes 21 face the end portions of the electrode fingers 22 of the other comb-shaped electrode 21. The width of the virtual electrode finger 23 in the X direction is smaller than the width of the electrode finger 22 in the X direction. Other configurations are the same as those of the first embodiment, and thus the description thereof will be omitted. In the first variant of the first embodiment, the sound velocity of the sound wave in the virtual region 34 is higher than the sound velocity of the sound wave in the central region 31. The sound velocity of the sound wave propagating through the virtual region 34 is, for example, equal to or less than 1.10 times the sound velocity of the sound wave propagating through the central region 31.

[0097] Experiment

[0098] Acoustic wave devices according to the first embodiment and the first variant of the first embodiment were fabricated, and an experiment for evaluating spurious emissions was conducted. The experimental conditions are as follows.

[0099] General Conditions

[0100] Wavelength λ of surface acoustic wave: 3 μm

[0101] Support substrate 10: Sapphire substrate

[0102] Piezoelectric substrate 12: 42° Y-cut X-propagation lithium tantalate substrate with a thickness of 0.15λ

[0103] Electrode fingers 22, dummy electrode fingers 23, and bus bar 24: Aluminum film with a thickness of 0.03λ

[0104] Additional film 40: Niobium oxide film with a thickness of 0.007λ

[0105] Width of electrode finger 22: 0.76 μm

[0106] Duty ratio of electrode finger 22: 50%

[0107] Conditions of the first embodiment

[0108] Width of dummy electrode finger 23: 0.5 μm

[0109] Duty ratio of dummy electrode finger 23: 50%

[0110] Sound velocity in virtual region 34: 1.05 times the sound velocity in central region 31

[0111] Conditions of the first modification of the first embodiment

[0112] Width of dummy electrode finger 23: 0.5 μm

[0113] Duty ratio of dummy electrode finger 23: 30%

[0114] Sound velocity in virtual region 34: 1.03 times the sound velocity in central region 31

[0115] Figure 9 Experimental results of the real part Real(Y) of admittance versus frequency in the first embodiment and the first modification of the first embodiment are given. As Figure 9 shown, the experimental results of the first embodiment where the sound velocity in virtual region 34 is 1.05 times the sound velocity in central region 31 and the experimental results of the first modification of the first embodiment where the sound velocity in virtual region 34 is 1.03 times the sound velocity in central region 31 are respectively similar to Figure 6B the simulation results of model F where the sound velocity in virtual region 34 is 1.05 times the sound velocity in central region 31 and the simulation results of model E where the sound velocity in virtual region 34 is 1.03 times the sound velocity in central region 31 shown in

[0116] Figure 10A and Figure 10B Experimental results of the real part Real(Y) of admittance versus frequency are given in the first embodiment and the first modification of the first embodiment when the layer structure of the substrate changes. Figure 10B Given in addition toFigure 10A In addition to the results shown, experimental results when a high sound velocity film with a thickness of 0.25λ is provided between the support substrate 10 and the piezoelectric substrate 12. As Figure 10A and Figure 10B shown, even when the stacked structure of the substrates is different, results similar to those of Figure 9 are obtained. This indicates that the influence of the stacked structure of the substrates is small.

[0117] Second variant and third variant

[0118] Figure 11A is a plan view of the acoustic wave device 120 according to the second variant of the first embodiment, Figure 11B is a cross-sectional view taken along line A-A in Figure 11A . As Figure 11A and Figure 11B shown, in the second variant of the first embodiment, a virtual electrode finger 23 having the same width as the electrode fingers 22 is provided between the electrode fingers 22 adjacent to each other in the X direction in one comb-shaped electrode 21. The virtual electrode fingers 23 face the ends of the electrode fingers 22 of the other comb-shaped electrode 21 respectively, and are mainly formed of a material having a higher sound velocity than the electrode fingers 22. For example, when the electrode fingers 22 are mainly formed of aluminum, the virtual electrode fingers 23 are mainly formed of beryllium or sodium. When the electrode fingers 22 are mainly formed of gold, molybdenum or tungsten, the virtual electrode fingers 23 are mainly formed of aluminum. Here, in order to compare the sound velocities, the sound velocities obtained from the above equation (1) can be compared. Other configurations are the same as those of the first embodiment, so the description thereof will be omitted. In the second variant of the first embodiment, the sound velocity of the acoustic wave in the virtual region 34 is higher than the sound velocity of the acoustic wave in the central region 31. The sound velocity of the acoustic wave propagating through the virtual region 34 is, for example, equal to or less than 1.10 times the sound velocity of the acoustic wave propagating through the central region 31.

[0119] Figure 12A is a plan view of the acoustic wave device 130 according to the third variant of the first embodiment, Figure 12B is a cross-sectional view taken along line A-A in Figure 12A . As Figure 12A and Figure 12BAs shown, in the third modification of the first embodiment, a virtual electrode finger 23 having the same width as the electrode fingers 22 is provided between the electrode fingers 22 adjacent to each other in the X direction in one comb-shaped electrode 21. The virtual electrode finger 23 faces the end of the electrode finger 22 of the other comb-shaped electrode 21 and is formed mainly of the same material as the electrode fingers 22. A protective film 42 is provided on the piezoelectric substrate 12 in the overlapping region 30, the gap region 33, and the bus bar region 35 to cover the electrode fingers 22 and the bus bar 24. A protective film 44 is provided on the piezoelectric substrate 12 in the virtual region 34. The protective film 44 is mainly composed of a material having a higher sound velocity than the protective film 42 to cover the virtual electrode finger 23. For example, when the protective film 42 is formed mainly of silicon oxide, the protective film 44 is formed mainly of silicon nitride. The protective film 42 and the protective film 44 have the same thickness. The sound velocities can be compared by comparing the sound velocities obtained from the above equation (1). Other configurations are the same as those of the first embodiment, and thus their descriptions will be omitted. In the third modification of the first embodiment, the sound velocity of the sound wave in the virtual region 34 is higher than the sound velocity of the sound wave in the central region 31. The sound velocity of the sound wave propagating through the virtual region 34 is, for example, equal to or less than 1.10 times the sound velocity of the sound wave propagating through the central region 31.

[0120] As described above, in the first embodiment and its modifications, the sound velocity of the sound wave propagating through the virtual region 34 is higher than the sound velocity of the sound wave propagating through the central region 31 and is equal to or less than 1.10 times the sound velocity of the sound wave propagating through the central region 31. Therefore, as Figures 6A to 7B shown, spurious emissions can be reduced. To reduce spurious emissions, for example, the sound velocity of the sound wave propagating through the virtual region 34 is preferably equal to or less than 1.09 times, more preferably equal to or less than 1.08 times, and further preferably equal to or less than 1.07 times the sound velocity of the sound wave propagating through the central region 31.

[0121] In the first embodiment and its modifications, the sound velocity of the sound wave propagating through the virtual region 34 is equal to or greater than 1.03 times the sound velocity of the sound wave propagating through the central region 31. Therefore, as Figures 6A to 7A shown, spurious emissions can be reduced. To reduce spurious emissions, for example, the sound velocity of the sound wave propagating through the virtual region 34 is preferably equal to or greater than 1.04 times, and more preferably equal to or greater than 1.05 times the sound velocity of the sound wave propagating through the central region 31.

[0122] In the first embodiment, as Figure 1As shown in (A) of FIG. 0, in a comb-shaped electrode 21, two dummy electrode fingers 23 are provided between electrode fingers 22 adjacent to each other in the X direction of the electrode fingers 22. The width of the dummy electrode fingers 23 in the X direction is smaller than the width of the electrode fingers 22 in the X direction. Providing such dummy electrode fingers 23 increases the sound velocity of the acoustic wave propagating through the dummy region 34 to be higher than the sound velocity of the acoustic wave propagating through the central region 31. Therefore, spurious emissions can be reduced.

[0123] When two dummy electrode fingers 23 are provided between electrode fingers 22 adjacent to each other in the X direction, the width of the dummy electrode fingers 23 in the short direction (X direction) can be equal to or greater than 0.56 times, and equal to or less than 0.64 times the width of the electrode fingers 22 in the short direction (X direction). In this case, the duty ratios of the electrode fingers 22 and the dummy electrode fingers 23 can be set within the range of 30% to 70% to improve the manufacturability. The sound velocity of the acoustic wave in the dummy region 34 is equal to or greater than 1.03 times the sound velocity of the acoustic wave in the central region 31, and equal to or less than 1.10 times the sound velocity of the acoustic wave in the central region 31. The widths of the dummy electrode fingers 23 in the short direction are preferably equal to each other. Equal widths mean that differences in manufacturing errors are acceptable. For example, a ratio of the two widths of 0.95 or more and 1.05 or less is acceptable.

[0124] Figure 13A FIG. is a plan view showing the case where three dummy electrode fingers 23 are provided between adjacent electrode fingers 22 in the first embodiment, Figure 13B is along Figure 13A the cross-sectional view taken along line A-A in Figure 13A and Figure 13B As shown in FIG. and FIG., three dummy electrode fingers 23 can be provided between electrode fingers 22 adjacent to each other in the X direction. In this case, the width of the dummy electrode fingers 23 in the short direction (X direction) can be equal to or greater than 0.39 times the width of the electrode fingers 22 in the short direction (X direction), and equal to or less than 0.45 times the width of the electrode fingers 22 in the short direction (X direction). In this case, the duty ratios of the electrode fingers 22 and the dummy electrode fingers 23 can be set within the range of 30% to 70% to improve the manufacturability. The sound velocity of the acoustic wave in the dummy region 34 is equal to or greater than 1.03 times the sound velocity of the acoustic wave in the central region 31, and equal to or less than 1.10 times the sound velocity of the acoustic wave in the central region 31. The widths of the dummy electrode fingers 23 in the short direction are preferably equal to each other.

[0125] The number of dummy electrode fingers 23 provided between electrode fingers 22 adjacent to each other in the X direction is not limited to two or three, and is two or more.

[0126] In the first modification of the first embodiment, asFigure 8A As shown, the dummy electrode finger 23 of one of the comb electrodes 21 faces the electrode finger 22 of the other comb electrode 21, and the width of the dummy electrode finger 23 in the short direction (X direction) is smaller than the width of the electrode finger 22 in the short direction (X direction). Therefore, the sound velocity of the acoustic wave propagating through the dummy region 34 is higher than the sound velocity of the acoustic wave propagating through the central region 31. Accordingly, spurious emissions can be reduced.

[0127] In a second modification of the first embodiment, as Figure 11A and Figure 11B shown, the dummy electrode finger 23 is mainly composed of a material having a higher sound velocity of acoustic waves than the electrode finger 22. Therefore, the sound velocity of the acoustic wave propagating through the dummy region 34 is higher than the sound velocity of the acoustic wave propagating through the central region 31. Accordingly, spurious emissions can be reduced.

[0128] In a third modification of the first embodiment, as Figure 12B shown, a protective film 42 (first insulating film) is provided on the piezoelectric substrate 12 to cover the electrode finger 22 in the central region 31. A protective film 44 (second insulating film) containing a material having a higher sound velocity of acoustic waves than the protective film 42 as a main component is provided on the piezoelectric substrate 12 to cover the dummy electrode finger 23 in the dummy region 34. Therefore, the sound velocity of the acoustic wave propagating through the dummy region 34 is higher than the sound velocity of the acoustic wave propagating through the central region 31. Accordingly, spurious emissions can be reduced.

[0129] As a method of making the sound velocity of the acoustic wave propagating through the dummy region 34 higher than the sound velocity of the acoustic wave propagating through the central region 31, a method different from the above method can be used. For example, the thickness of the dummy electrode finger 23 can be smaller than the thickness of the electrode finger 22. For example, the thickness of the piezoelectric substrate 12 in the dummy region 34 can be made smaller than the thickness of the piezoelectric substrate 12 in the central region 31. For example, a material having a higher sound velocity of acoustic waves than the piezoelectric substrate 12 can be provided in the dummy region 34.

[0130] Second Embodiment

[0131] In the first embodiment, the acoustic wave device is an acoustic wave resonator. In the second embodiment and modifications of the second embodiment, cases where the acoustic wave device is a filter and a duplexer will be described. Figure 14A is a circuit diagram of a filter 200 according to the second embodiment. As Figure 14AAs shown, one or more series resonators S1 to S4 are connected in series between an input terminal Tin and an output terminal Tout. One or more parallel resonators P1 to P3 are connected in parallel between the input terminal Tin and the output terminal Tout. The acoustic wave resonator of the first embodiment or its modification can be used for at least one of the following resonators: the series resonators S1 to S4 and the parallel resonators P1 to P3. The number of the series resonators and the parallel resonators can be set appropriately. Although the ladder filter is described as an example of the filter, the filter can be a multi-mode filter.

[0132] Figure 14B is a circuit diagram of a duplexer 210 according to a modification of the second embodiment. As Figure 14B shown, a transmit filter 70 is connected between a common terminal Ant and a transmit terminal Tx. A receive filter 72 is connected between the common terminal Ant and a receive terminal Rx. The transmit filter 70 transmits a signal within a transmit frequency band as a transmission signal in a high-frequency signal input from the transmit terminal Tx to the common terminal Ant and suppresses signals of other frequencies. The receive filter 72 transmits a signal within a receive frequency band as a receive signal in a high-frequency signal input from the common terminal Ant to the receive terminal Rx and suppresses signals of other frequencies. One or both of the transmit filter 70 and the receive filter 72 can be the filter of the second embodiment. Although the duplexer is exemplified as a multiplexer, the multiplexer can be a triplexer or a quadruplexer.

[0133] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims.

Claims

1. An acoustic wave device, comprising: Piezoelectric substrate; as well as A pair of comb electrodes are arranged on the piezoelectric substrate, each of the pair of comb electrodes includes a plurality of electrode fingers and a plurality of metal parts, the plurality of metal parts are arranged between electrode fingers adjacent to each other in the short direction of the plurality of electrode fingers, the plurality of metal parts have a length shorter than the plurality of electrode fingers in the long direction, the plurality of electrode fingers of one of the pair of comb electrodes and the plurality of electrode fingers of the other of the pair of comb electrodes are at least partially arranged alternately, the sound velocity of sound waves propagating through the area where the plurality of metal parts are arranged is higher than the sound velocity of sound waves propagating through the central area of ​​the overlapping area where the plurality of electrode fingers of one of the pair of comb electrodes and the plurality of electrode fingers of the other of the pair of comb electrodes overlap, and the sound velocity of sound waves propagating through the area where the plurality of metal parts are arranged is equal to or less than 1.10 times the sound velocity of sound waves propagating through the central area.

2. The acoustic wave device according to claim 1, wherein: A sound velocity of a sound wave propagating through a region where the plurality of metal portions are provided is equal to or greater than 1.03 times a sound velocity of a sound wave propagating through the central region.

3. The acoustic wave device according to claim 1 or 2, in, The plurality of metal portions of one of the pair of comb-shaped electrodes face the plurality of electrode fingers of the other of the pair of comb-shaped electrodes, and Wherein, the width of the plurality of metal parts in the short direction is smaller than the width of the plurality of electrode fingers in the short direction.

4. The acoustic wave device according to claim 1 or 2, further comprising: a first insulating film provided on the piezoelectric substrate to cover the plurality of electrode fingers in the central region; as well as a second insulating film provided on the piezoelectric substrate to cover the plurality of metal portions in a region where the plurality of metal portions are provided, the second insulating film containing as a main component a material having a higher acoustic velocity of acoustic waves than the first insulating film. 5 . The acoustic wave device according to claim 1 , further comprising an additional film provided at an end portion of each of the plurality of electrode fingers in the long direction.

6. An acoustic wave device, comprising: Piezoelectric substrate; as well as A pair of comb electrodes are arranged on the piezoelectric substrate, each of the pair of comb electrodes includes a plurality of electrode fingers and a plurality of metal parts, two or more of the plurality of metal parts are arranged between electrode fingers adjacent to each other in the short direction of the plurality of electrode fingers, the plurality of metal parts have a width smaller than that of the plurality of electrode fingers in the short direction, and the plurality of electrode fingers of one of the pair of comb electrodes and the plurality of electrode fingers of the other of the pair of comb electrodes are at least partially arranged alternately.

7. The acoustic wave device according to claim 6, in, Two of the plurality of metal portions are disposed between the adjacent electrode fingers, and The width of the plurality of metal portions in the short direction is equal to or greater than 0.56 times the width of the plurality of electrode fingers in the short direction and equal to or less than 0.64 times the width of the plurality of electrode fingers in the short direction.

8. The acoustic wave device according to claim 6, in, three of the plurality of metal portions are disposed between the adjacent electrode fingers, and The width of the plurality of metal portions in the short direction is equal to or greater than 0.39 times the width of the plurality of electrode fingers in the short direction and equal to or less than 0.45 times the width of the plurality of electrode fingers in the short direction.

9. The acoustic wave device according to claim 7 or 8, in, The widths of the plurality of electrode fingers in the short direction are equal from one end connected to the bus bar to the other end on the opposite side, and Wherein, the widths of the plurality of metal portions in the short direction are equal to each other.

10. An acoustic wave device, comprising: Piezoelectric substrate; as well as A pair of comb-shaped electrodes are arranged on the piezoelectric substrate, each of the pair of comb-shaped electrodes includes a plurality of electrode fingers and a plurality of metal parts, the plurality of metal parts are arranged between the plurality of electrode fingers adjacent to each other in the short direction of the plurality of electrode fingers, the plurality of metal parts contain a material having a higher sound velocity than that of the sound waves of the plurality of electrode fingers as a main component, and the plurality of electrode fingers of one of the pair of comb-shaped electrodes and the plurality of electrode fingers of the other of the pair of comb-shaped electrodes are at least partially arranged alternately.

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