Acoustic wave device, filter, and multiplexer

Abstract

To provide an acoustic wave device capable of suppressing spurious.SOLUTION: The acoustic wave device includes a piezoelectric layer 15, a pair of comb-shaped electrodes provided on the piezoelectric layer 15, each of the comb-shaped electrodes including a plurality of electrode fingers 22 and a bus bar to which the plurality of electrode fingers 22 are connected, the pair of comb-shaped electrodes including an overlap region in which the plurality of electrode fingers 22 overlap with each other and a gap region 33 located between the overlap region and the bus bar and adjacent to the overlap region. And an additional film 40 that is not located in the central region 31 and a second region 52 located further out than the first region 51 in the gap region 33, and has a thickness T2 in the first region 51 greater than a thickness T1 in a third region 53 located closer to the gap region 33 in the edge region 32.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to acoustic wave devices, filters, and multiplexers. [Background technology]

[0002] Acoustic wave devices are used in high-frequency communication systems, such as mobile phones. A known example of an acoustic wave device is one that includes a pair of interdigital transducers, each of which has a plurality of electrode fingers and a bus bar connecting the electrode fingers. To suppress spurious signals, an acoustic wave device that utilizes a piston mode is known (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-171054 [Patent Document 2] International Publication No. 2018 / 116680 Summary of the Invention [Problem to be solved by the invention]

[0004] In the piston mode, the acoustic wave velocity in the edge region, located at the longitudinal edge of the electrode fingers in the intersection region where multiple electrode fingers intersect, may be a low acoustic wave velocity region where the acoustic wave velocity is slower than that in the central region located inside the edge region, and the acoustic wave velocity in the gap region outside the edge region may be a high acoustic wave velocity region where the acoustic wave velocity is faster than that in the central region. To slow down the acoustic wave velocity in the edge region, an additional film may be provided in the edge region. The additional film may also be provided from the edge region to the gap region. However, there is still room for improvement in terms of suppressing spurious signals.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to suppress spurious signals. [Means for solving the problem]

[0006] The present invention provides an acoustic wave device comprising: a piezoelectric layer; a pair of comb-shaped electrodes provided on the piezoelectric layer, each having a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected, the pair of comb-shaped electrodes having an intersection region where the plurality of electrode fingers intersect with each other and a gap region located between the intersection region and the bus bar and adjacent to the intersection region, the intersection region including edge regions located at longitudinal edges of the plurality of electrode fingers and a central region located inside the edge regions; and an additional film provided on the piezoelectric layer in the edge regions and a first region of the gap region located on the edge region side, but not in the central region or a second region of the gap region outside the first region, the additional film having a first thickness in the first region that is greater than a second thickness in a third region of the edge region located on the gap region side.

[0007] In the above configuration, the additional film may be configured such that the first thickness is greater than the third thickness in a fourth region of the edge region that is located between the third region and the central region, and the third thickness is greater than the second thickness.

[0008] In the above configuration, the first thickness is T1, the second thickness is T2, the third thickness is T3, the thickness of the plurality of electrode fingers is T4, and the density of the plurality of electrode fingers is ρ a , the density of the additional film is ρ b In this case, 1.6T2≦T3≦3.2T2 is satisfied and T1=T4ρ a / 2ρ b +T3 can be satisfied.

[0009] In the above configuration, a second length of the third region in the longitudinal direction may be greater than a first length of the first region in the longitudinal direction and a third length of the fourth region in the longitudinal direction.

[0010] In the above configuration, the additional film may be configured such that the second thickness is the same as the third thickness in a fourth region of the edge region that is located between the third region and the central region, and the first thickness is greater than the second thickness and the third thickness.

[0011] In the above configuration, the first thickness is T1, the third thickness is T3, the thickness of the plurality of electrode fingers is T4, and the density of the plurality of electrode fingers is ρ a , the density of the additional film is ρ b In this case, 3T4ρ a / 2ρ b +2T3≦T1≦11T4ρ a / 2ρ b It is possible to create a configuration that satisfies +6T3.

[0012] In the above configuration, the additional film may have the first thickness over the entire length in the first region.

[0013] In the above-described structure, the additional film may be composed mainly of niobium oxide, silicon oxide, tantalum oxide, aluminum, titanium, or tungsten.

[0014] The present invention is a filter including the acoustic wave device described above.

[0015] The present invention is a multiplexer including the filter described above. [Effects of the Invention]

[0016] According to the present invention, spurious signals can be suppressed. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1(a) is a plan view of an acoustic wave device in accordance with a first embodiment, and FIG. 1(b) is a cross-sectional view taken along line AA of FIG. 1(a). [Figure 2] 2(a) and 2(b) are cross-sectional views of the vicinity of the additional film in Example 1. FIG. [Figure 3] FIG. 3 is a diagram showing the acoustic velocity of an elastic wave in Example 1. As shown in FIG. [Figure 4] FIG. 4 is a cross-sectional view of model A used in the simulation. [Figure 5] FIG. 5 is a cross-sectional view of model B used in the simulation. [Figure 6] 6(a) to 6(f) are diagrams showing the real part of the admittance Real(Y) versus frequency in Simulation 1. FIG. [Figure 7] FIG. 7 is a diagram showing the edge sound velocity ratio versus the thickness of the additional film in Simulation 2. [Figure 8] 8(a) to 8(e) are diagrams showing the real part of the admittance Real(Y) versus frequency in Simulation 3. FIG. [Figure 9] FIG. 9 is a diagram showing the reflection coefficient versus the acoustic velocity ratio of the elastic waves in the first and fourth regions in Simulation 3. In FIG. [Figure 10] FIG. 10(a) is a cross-sectional view of an acoustic wave device according to a first modification of the first embodiment, and FIG. 10(b) is a graph showing the acoustic velocity of an acoustic wave. [Figure 11] 11(a) to 11(c) are plan views of acoustic wave devices according to a first embodiment, a second modification of the first embodiment, and a third modification of the first embodiment. [Figure 12] 12A to 12C are cross-sectional views of acoustic wave devices according to fourth to sixth modifications of the first embodiment. [Figure 13] 13A to 13C are cross-sectional views of acoustic wave devices according to seventh to ninth modifications of the first embodiment. [Figure 14] FIG. 14(a) is a cross-sectional view of the acoustic wave device in accordance with Example 2, and FIG. 14(b) is a graph showing the acoustic velocity of an acoustic wave. [Figure 15] FIG. 15 is a cross-sectional view of model C used in the simulation. [Figure 16]16(a) to 16(f) are diagrams showing the real part of the admittance Real(Y) versus frequency in Simulation 4. FIG. [Figure 17] FIG. 17 is a diagram showing the reflection coefficient versus the acoustic velocity ratio of the elastic wave in the first region in Simulation 4. In FIG. [Figure 18] FIG. 18 is a plan view of an acoustic wave device in accordance with a third embodiment. [Figure 19] FIG. 19(a) is a circuit diagram of a filter according to the fourth embodiment, and FIG. 19(b) is a circuit diagram of a duplexer according to a modified example of the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

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

[0019] 1(a) is a plan view of an acoustic wave device 100 according to a first embodiment, and FIG. 1(b) is a cross-sectional view taken along line AA of FIG. 1(a). The short-side direction of the electrode fingers 22 is the X-direction, the long-side direction of the electrode fingers 22 is the Y-direction, and the stacking direction of the substrate 10 and the piezoelectric layer 15 is the Z-direction. The X-direction, Y-direction, and Z-direction do not necessarily correspond to the X-axis direction of the crystal orientation of the piezoelectric layer 15. When the piezoelectric layer 15 is a rotated Y-cut X-propagation piezoelectric layer, the X-direction corresponds to the X-axis direction of the crystal orientation.

[0020] As shown in FIGS. 1(a) and 1(b), a piezoelectric layer 15 is provided on a substrate 10. The substrate 10 is, for example, a sapphire substrate, an alumina substrate, a silicon substrate, a spinel substrate, a quartz substrate, or a silicon carbide substrate. The piezoelectric layer 15 is, for example, a single-crystal lithium tantalate layer, a single-crystal lithium niobate layer, or a single-crystal quartz layer. The piezoelectric layer 15 may be, for example, a rotated Y-cut X-propagation lithium tantalate layer or a rotated Y-cut X-propagation lithium niobate layer, or may be, for example, a 30° to 50° rotated Y-cut X-propagation lithium tantalate layer. An insulating film such as a silicon oxide film, an aluminum oxide film, and / or an aluminum nitride film may be provided between the substrate 10 and the piezoelectric layer 15.

[0021] An IDT (Interdigital Transducer) 20 and a reflector 25 are provided on the piezoelectric layer 15. The IDT 20 includes a pair of comb electrodes 21. The comb electrode 21 has a plurality of electrode fingers 22, a plurality of dummy electrode fingers 23, and a bus bar 24 to which the plurality of electrode fingers 22 and the plurality of dummy electrode fingers 23 are connected. The tips of the electrode fingers 22 of one comb electrode 21 face the tips of the dummy electrode fingers 23 of the other comb electrode 21. The IDT 20 and the reflector 25 are formed by a metal film 26 on the piezoelectric layer 15. The metal film 26 is a film mainly composed of, for example, aluminum (Al), copper (Cu), or molybdenum (Mo). An adhesive layer of titanium (Ti), chromium (Cr), or the like may be provided between the piezoelectric layer 15 and the metal film 26.

[0022] The region where the electrode fingers 22 of each of the pair of comb electrodes 21 intersect is the intersection region 30. The pair of comb electrodes 21 face each other so that the electrode fingers 22 are alternately arranged in the X direction in at least a portion of the intersection region 30. The main-mode acoustic waves (surface acoustic waves) excited by the electrode fingers 22 in the intersection region 30 propagate primarily in the X direction. The pitch of the electrode fingers 22 of one comb electrode 21 is approximately equal to the wavelength λ of the surface acoustic waves. The wavelength λ is approximately twice the average pitch D of the multiple electrode fingers 22. The average pitch D can be calculated by dividing the length of the IDT 20 in the X direction by the number of electrode fingers 22. Reflectors 25 are provided on either side of the IDT 20 in the X direction and reflect the surface acoustic waves excited by the electrode fingers 22. This confines the surface acoustic waves within the intersection region 30 of the IDT 20.

[0023] Intersection region 30 has edge region 32 located at the edge in the Y direction, and central region 31 located inside edge region 32 in the Y direction. A region located between the tips of electrode fingers 22 of one comb electrode 21 and the tips of dummy electrode fingers 23 of the other comb electrode 21 is gap region 33. A region where dummy electrode fingers 23 are located is dummy region 34. A region where busbars 24 are located is busbar region 35.

[0024] An additional film 40 is provided on the piezoelectric layer 15 from the edge region 32 to a part of the gap region 33. The additional film 40 is provided extending in a strip shape in the X direction in a plan view, and covers the electrode fingers 22 located in the edge region 32.

[0025] 2(a) and 2(b) are cross-sectional views of the vicinity of the additional film 40 in Example 1. As shown in FIGS. 2(a) and 2(b), an insulating film 27 may be provided on the piezoelectric layer 15 to cover the electrode fingers 22 and the dummy electrode fingers 23, and the additional film 40 may be provided on the insulating film 27. The insulating film 27 may be a film mainly composed of silicon oxide (SiO2), for example. The gap region 33 includes a first region 51 located on the edge region 32 side and a second region 52 located on the opposite side of the edge region 32. That is, the first region 51 is located between the edge region 32 and the second region 52. The second region 52 is located between the dummy region 34 and the first region 51. The edge region 32 includes a third region 53 located on the gap region 33 side and a fourth region 54 located on the central region 31 side. That is, the third region 53 is located between the gap region 33 and the fourth region 54. The fourth region 54 is located between the central region 31 and the third region 53.

[0026] The additional film 40 is provided from the fourth region 54 through the third region 53 to the first region 51. The additional film 40 is not provided in the central region 31, the second region 52, the dummy region 34, and the busbar region 35 (see also FIGS. 1(a) and 1(b)).

[0027] The thickness of the additional film 40 in the first region 51 is T1, the thickness of the additional film 40 in the third region 53 is T2, and the thickness of the additional film 40 in the fourth region 54 is T3. Thicknesses T1 and T3 are greater than thickness T2. Thickness T1 is greater than thickness T3. The length of the first region 51 in the Y direction is L1, the length of the third region 53 in the Y direction is L2, and the length of the fourth region 54 in the Y direction is L3. Length L2 is greater than lengths L1 and L3. For example, lengths L1 and L3 may be greater than or equal to 1 / 4 and less than or equal to 1 / 2 of length L2. Lengths L1 and L3 may be the same or different. "The same lengths" means that a difference of the order of manufacturing error is allowed, for example, a difference of ±3% or less between lengths L1 and L3 relative to length L1 is allowed.

[0028] The additional film 40 is a film whose main component is, for example, silicon oxide (SiO2), tantalum oxide (Ta2O5), niobium oxide (Nb2O5), aluminum (Al), titanium (Ti), or tungsten (W). The additional film 40 may be a single-layer or multilayer film whose main component is another material, as long as it is capable of adjusting the acoustic velocity of the elastic wave.

[0029] Here, when a film is primarily composed of a certain element, it is acceptable for the film to contain intentional or unintentional impurities other than the primary component. When a film is primarily composed of a certain element, the concentration of the element is, for example, 80 atomic % or more, for example, 90 atomic % or more. For example, when the additional film 40 is primarily composed of aluminum, the aluminum content is 80 atomic % or more, for example, 90 atomic % or more. When the additional film 40 is primarily composed of two or more elements, the total concentration of the two or more elements is 80 atomic % or more, for example, 90 atomic % or more. Each of the two or more elements is 10 atomic % or more or 20 atomic % or more. For example, when the additional film 40 is primarily composed of niobium oxide, the total of the niobium content and the oxygen content is 80 atomic % or more or 90 atomic % or more. The niobium content and the oxygen content are each 10 atomic % or more or 20 atomic % or more.

[0030] FIG. 3 is a diagram showing the acoustic velocity of elastic waves in Example 1. As shown in FIG. 3, because the additional film 40 is provided in the edge region 32, the acoustic velocity of elastic waves propagating through the edge region 32 is slower than the acoustic velocity of elastic waves propagating through the central region 31. Because the thickness T3 of the additional film 40 in the fourth region 54 is greater than the thickness T2 of the additional film 40 in the third region 53, the acoustic velocity of elastic waves propagating through the fourth region 54 is slower than the acoustic velocity of elastic waves propagating through the third region 53. By making the thickness T1 of the additional film 40 in the first region 51 greater than the thickness T3 of the additional film 40 in the fourth region 54, the acoustic velocity of elastic waves propagating through the first region 51 and the fourth region 54 is made the same. The acoustic velocities do not necessarily have to be completely the same; for example, a difference of ±3% or less between the acoustic velocity in the first region 51 and the acoustic velocity in the fourth region 54 relative to the acoustic velocity in the first region 51 is allowed. The acoustic velocity of the elastic waves propagating through the dummy region 34 is the same as the acoustic velocity of the elastic waves propagating through the central region 31. The acoustic velocity of the elastic waves propagating through the second region 52 is faster than the acoustic velocity of the elastic waves propagating through the central region 31 and the dummy region 34. The acoustic velocity of the elastic waves propagating through the edge region 32 and the first region 51 of the gap region 33 is slower than the acoustic velocity of the elastic waves propagating through the central region 31, and the acoustic velocity of the elastic waves propagating through the second region 52 of the gap region 33 is faster than the acoustic velocity of the elastic waves propagating through the central region 31, thereby realizing a piston mode.

[0031] [Manufacturing method] A manufacturing method of the acoustic wave device 100 according to the first embodiment will be described. After bonding the piezoelectric layer 15 to the substrate 10 using, for example, a surface activation method, the piezoelectric layer 15 is polished to a desired thickness using, for example, a CMP (Chemical Mechanical Polishing) method. Next, a metal film 26 is formed on the piezoelectric layer 15 using, for example, a sputtering method, a CVD (Chemical Vapor Deposition) method, or a vacuum deposition method, and the metal film 26 is patterned into a desired shape using, for example, a photolithography method and an etching method. This results in the IDT 20 and the reflector 25 being formed on the piezoelectric layer 15. Next, an additional film 40 is formed on the piezoelectric layer 15 in the edge region 32 and the first region 51 of the gap region 33. The additional film 40 is formed using, for example, a lift-off method. This results in the acoustic wave device 100 according to the first embodiment.

[0032] [Simulation 1] Fig. 4 is a cross-sectional view of model A used in the simulation. Fig. 5 is a cross-sectional view of model B used in the simulation. Although not shown, in models A and B, an IDT 20 including electrode fingers 22 and dummy electrode fingers 23 and a reflector 25 are provided on a piezoelectric layer 15, similar to Fig. 1(a).

[0033] As shown in FIG. 4, model A has an insulating film 12 provided on a substrate 10. A piezoelectric layer 15 is provided on the insulating film 12. An IDT 20 including electrode fingers 22 and dummy electrode fingers 23, and a reflector 25 are provided on the piezoelectric layer 15. An additional film 40 is provided on the piezoelectric layer 15 from the edge region 32 to a first region 51 of the gap region 33. The additional film 40 has a thickness of T a , the thickness in the third region 53 is T b , the thickness in the fourth region 54 is T c The length of the first region 51 in the Y direction is L a , the length of the third region 53 in the Y direction is L b , the length of the fourth region 54 in the Y direction is L c Let's say.

[0034] 5, model B differs from model A in that the additional film 40 is provided only in the edge region 32 and not in the gap region 33. The other configurations are the same as model A, so a description thereof will be omitted.

[0035] The simulation conditions are as follows: Common conditions for Model A and Model B Wavelength of surface acoustic wave λ: 2.2 μm Substrate 10: sapphire substrate Insulating film 12: silicon oxide (SiO2) film with a thickness of 0.2λ Piezoelectric layer 15: 42° rotated Y-cut X-propagating lithium tantalate layer with a thickness of 0.3λ IDT 20 and reflector 25: Aluminum film with a thickness of 0.096λ IDT20 duty ratio: 50% Additional film 40: Niobium oxide (Nb2O5) film Length of gap region 33 in the Y direction: 2.2 μm Model A Conditions Length L of the first region 51 a :0.1λ Length L of the third region 53 b :0.3λ Length L of the fourth region 54 c :0.1λ Model B Conditions Length L of the third region 53 b :0.3λ Length L of the fourth region 54 c :0.1λ

[0036] Simulations were performed to evaluate spurious responses for models A-1, A-2, A-3, B-1, B-2, and B-3, in which the acoustic velocities of the elastic waves in the first region 51 and the fourth region 54 were made different from each other for model A and model B. Table 1 shows the acoustic velocity ratios of the elastic waves in the first region 51, the third region 53, and the fourth region 54 in models A-1, A-2, A-3, B-1, B-2, and B-3. The acoustic velocity ratio of the elastic waves is (V IDT -V R ) / V IDT It was calculated by V IDTis the acoustic velocity of the elastic wave in the central region 31. R is the acoustic velocity of the elastic wave in the first region 51, the third region 53, or the fourth region 54. The acoustic velocity of the elastic wave in the first region 51, the third region 53, and the fourth region 54 can be controlled by the thickness of the additional film 40 in the first region 51, the third region 53, and the fourth region 54. In Model B, the additional film 40 is not provided in the gap region 33, so the acoustic velocity ratio of the elastic wave in the first region 51 is represented as "-". [Table 1] As shown in Table 1, in Model A-1, the sound velocity ratios of the elastic waves in the first region 51, the third region 53, and the fourth region 54 were set to -0.5%, -1.5%, and -0.5%. In Model A-2, they were set to -1.5%, -1.5%, and -1.5%, and in Model A-3, they were set to -2.5%, -1.5%, and -2.5%. In Model B-1, the sound velocity ratios of the elastic waves in the third region 53 and the fourth region 54 were set to -1.5% and -0.5%. In Model B-2, they were set to -1.5% and -1.5%, and in Model B-3, they were set to -1.5% and -2.5%.

[0037] Figures 6(a) to 6(f) show the real part of the admittance, Real(Y), versus frequency in Simulation 1. Figures 6(a) to 6(c) show the simulation results for models A-1, A-2, and A-3, and Figures 6(d) to 6(f) show the simulation results for models B-1, B-2, and B-3. Large spurious responses are observed in the real part of the admittance, Real(Y).

[0038] As shown in Figures 6(a) and 6(d), Model A-1 had reduced spurious responses compared to Model B-1. As shown in Figures 6(b) and 6(e), Model A-2 had reduced spurious responses compared to Model B-2. As shown in Figures 6(c) and 6(f), Model A-3 had reduced spurious responses compared to Model B-3. Models A-1 and B-1, Model A-2 and B-2, and Model A-3 and B-3 differ in whether or not the additional film 40 is provided in the first region 51 of the gap region 33. Therefore, providing the additional film 40 in the first region 51 reduced spurious responses compared to when the additional film 40 was not provided in the first region 51. As shown in Model A-3 in Figure 6(c), spurious responses were suppressed when the acoustic velocity of the elastic wave in the first region 51 and the acoustic velocity of the elastic wave in the fourth region 54 were slower than the acoustic velocity of the elastic wave in the third region 53.

[0039] The reason why spurious responses are suppressed in model A-3 is not clear, but the following may be considered: In model A-3, the acoustic velocity ratios of the first region 51, the third region 53, and the fourth region 54 are -2.5%, -1.5%, and -2.5%, respectively, which is similar to the acoustic velocity graph of the acoustic wave in Figure 3. The thickness T of the additional film 40 in the first region 51 a is the thickness T of the additional film 40 in the fourth region 54 c The acoustic wave is reflected at the tip of the electrode finger 22, but the thickness T a It is considered that the provision of the additional film 40 with a large thickness further reduces the acoustic velocity of the elastic waves due to attenuation of the acoustic velocity and / or a change in the reflection phase. This increases the difference in acoustic velocity of the elastic waves between the central region 31 and the edge region 32 and the first region 51 of the gap region 33, thereby suppressing spurious emissions.

[0040] [Simulation 2] In the model B of FIG. 5, the thickness T b and T c A simulation was performed on the acoustic velocity of the elastic wave in the edge region 32 when the acoustic velocity was changed while keeping the same. The acoustic velocity of the elastic wave in the edge region 32 was IDT-V E ) / V IDT The evaluation was performed using the edge sound velocity ratio calculated by V IDT is the acoustic velocity of the elastic wave in the central region 31. E is the acoustic velocity of the elastic wave in the edge region 32. The simulation conditions are the thickness T b and thickness T c This is the same as Simulation 1 except that the same value was used.

[0041] FIG. 7 shows the thickness T b and T c 7 is a graph showing the edge sound velocity ratio with respect to the thickness T of the additional film 40. The black circles indicate the simulation results, and the dashed lines indicate the approximate straight lines. b and T c The thickness T of the additional film 40 is approximately proportional to the edge sound velocity ratio. b and T c The edge acoustic velocity ratio was −0.83% when the thickness was 8 nm, and −1.63% when the thickness was 16 nm. From this, it can be said that in the edge region 32, the ratio of the thickness of the additional film 40 to the acoustic velocity is almost equal. For example, in model A-3 of the above simulation 1, the ratio of the acoustic velocity of the elastic wave in the third region 53 to the acoustic velocity of the elastic wave in the fourth region 54 is −1.5:−2.5, so the thickness T of the additional film 40 in the third region 53 is −0.83% when the thickness was 8 nm, and −1.63% when the thickness was 16 nm. b and the thickness T of the additional film 40 in the fourth region 54 c The ratio is about 1.5:2.5.

[0042] [Simulation 3] In model A of Figure 4, simulations were performed to evaluate spurious emissions for models A-11, A-12, A-13, A-14, A-15, A-16, A-17, and A-18, in which the acoustic velocities of the elastic waves in the first region 51 and the fourth region 54 were made different from each other. Table 2 shows the acoustic velocity ratios of the elastic waves in the first region 51, the third region 53, and the fourth region 54 in models A-11, A-12, A-13, A-14, A-15, A-16, A-17, and A-18. The acoustic velocity ratios of the elastic waves were calculated in the same manner as in Table 1. The other simulation conditions were the same as in Simulation 1. [Table 2] As shown in Table 2, the acoustic velocity ratios of the elastic waves in the first region 51, the third region 53, and the fourth region 54 were set to -0.5%, -1.5%, and -0.5% for Model A-11, -1.0%, -1.5%, and -1.0% for Model A-12, -1.5%, -1.5%, and -1.5% for Model A-13, -2.0%, -1.5%, and -2.0% for Model A-14, -2.5%, -1.5%, and -2.5% for Model A-15, -3.0%, -1.5%, and -3.0% for Model A-16, -4.5%, -1.5%, and -4.5% for Model A-17, and -6.0%, -1.5%, and -6.0% for Model A-18.

[0043] Figures 8(a) to 8(e) show the real part of the admittance (Real(Y)) versus frequency in Simulation 3. Figures 8(a) to 8(e) show the simulation results for Models A-11, A-13, A-15, A-17, and A-18. As shown in Figures 8(a) to 8(e), spurious signals were generated in Models A-11, A-13, and A-18, whereas spurious signals were suppressed in Models A-15 and A-17. The reflection coefficients were 0.85 for Model A-11, 0.88 for Model A-13, 0.94 for Model A-15, 0.95 for Model A-17, and 0.87 for Model A-18. The reflection coefficient is related to the magnitude of transverse-mode spurious signals; the smaller the reflection coefficient, the larger the transverse-mode spurious signals. This indicates that spurious signals can be suppressed when the reflection coefficient is 0.94 or higher.

[0044] FIG. 9 shows the reflection coefficient versus the acoustic velocity ratio of the elastic waves in the first region 51 and the fourth region 54 in Simulation 3. The black circles represent the simulation results, and the dashed line represents an approximation curve. The acoustic velocity ratio of the elastic waves in the first region 51 and the fourth region 54 on the horizontal axis is the value listed in Table 2, and is the value when the acoustic velocity ratio of the elastic waves in the third region 53 is −1.5%. Since the reflection coefficient is preferably 0.94 or higher to suppress spurious signals, as shown in FIG. 9, the acoustic velocity ratio of the elastic waves in the first region 51 and the fourth region 54 is preferably −4.7% or higher and −2.5% or lower when the acoustic velocity ratio of the elastic waves in the third region 53 is −1.5%. In other words, the acoustic velocity of the elastic waves in the first region 51 and the fourth region 54 is preferably 1.6 times or higher and 3.2 times or lower than the acoustic velocity of the elastic waves in the third region 53. As described in FIG. 7, the thickness ratio of the additional film 40 and the acoustic velocity ratio are approximately equal in the edge region 32. Therefore, the thickness T of the additional film 40 in the fourth region 54 c is the thickness T of the additional film 40 in the third region 53 b It is preferable that the ratio is 1.6 times or more and 3.2 times or less.

[0045] The reason why spurious responses occur when the acoustic velocity of the elastic waves in the first region 51 and the fourth region 54 is too slow or too fast, resulting in a small reflection coefficient, is not clear, but the following is one possible reason: When the acoustic velocity of the elastic waves in the first region 51 and the fourth region 54 is too slow or too fast, the difference in acoustic velocity of the elastic waves between the central region 31 and the first region 51 of the edge region 32 and gap region 33 is not appropriate for establishing a piston mode, resulting in a small reflection coefficient and causing spurious responses.

[0046] In Simulation 3, as shown in Table 2, the acoustic velocity of the acoustic wave in the first region 51 is the same as that in the fourth region 54. In this case, the total weight of the electrode fingers 22 and the additional film 40 in the first region 51 is the same as that of the electrode fingers 22 and the additional film 40 in the fourth region 54. If the mass of the additional film 40 in the first region 51 is M a , the mass of the additional film 40 in the fourth region 54 is M c , the mass of the electrode fingers 22 in the first region 51 and the fourth region 54 is M d Then, the length L of the first region 51 a and the length L of the fourth region 54 c are the same, so M a =M d / 2+M c It can be said that the relationship (1) holds. Note that the additional film 40 is provided in a strip shape in the first region 51 and the fourth region 54 and is therefore also present between the electrode fingers 22, but in this calculation, it is sufficient to consider the additional film 40 other than between the electrode fingers 22.

[0047] Since mass is volume × density, the volume of the additional film 40 in the first region 51 is V a , the volume of the additional film 40 in the fourth region 54 is V c , the volume of the electrode fingers 22 in the first region 51 and the fourth region 54 is V d , the density of the electrode fingers 22 is ρ a , the density of the additional film 40 is ρ b , then the above equation (1) becomes: V a ρ b =V d ρa / 2+V c ρ b ...can be transformed into (2).

[0048] Since the volume is the bottom area x thickness, the thickness of the additional film 40 in the first region 51 is T a , the thickness of the additional film 40 in the fourth region 54 is T c , the thickness of the electrode finger 22 is T d , the bottom area of ​​the additional film 40 in the first region 51 is S a , the bottom area of ​​the additional film 40 in the fourth region 54 is S c , the bottom area of ​​the electrode finger 22 in the first region 51 and the fourth region 54 is S d Then, the above equation (2) becomes: T a S a ρ b =T d S d ρ a / 2+T c S c ρ b ...can be transformed into (3).

[0049] Since the additional film 40 between the electrode fingers 22 is not taken into consideration, S a =S b =S c Therefore, the above equation (3) can be expressed as T a ρ b =T d ρ a / 2+T c ρ b ...can be transformed into (4). Transforming the above equation (4) gives: T a =T d ρ a / 2ρ b +T c It becomes (5).

[0050] From the simulation results of FIG. 9, in order to suppress spurious by making the reflection coefficient 0.94 or more, the thickness T c is the thickness T of the additional film 40 in the third region 53b Furthermore, from the viewpoint of suppressing spurious by making the reflection coefficient 0.94 or more, the thickness T a It is preferable that satisfies the above formula (5).

[0051] 2(a) and 2(b), in order to suppress spurious signals, the thickness T3 of the additional film 40 in the fourth region 54 is set to be 1.6 times or more and 3.2 times or less the thickness T2 of the additional film 40 in the third region 53. The thickness T1 of the additional film 40 in the first region 51 is set to be T1=T4ρ a / 2ρ b +T3 is satisfied, where T4 is the thickness of the electrode finger 22. T3 is the thickness of the additional film 40 in the fourth region 54. ρ a is the density of the electrode fingers 22. b is the density of the additional film 40.

[0052] [Variations] FIG. 10(a) is a cross-sectional view of an acoustic wave device according to a first modification of the first embodiment, and FIG. 10(b) is a diagram illustrating the acoustic velocity of an acoustic wave. As shown in FIG. 10(a), in the first modification of the first embodiment, the thickness T1 of the additional film 40 provided in the fifth region 55 located on the second region 52 side of the first region 51 is greater than the thickness T2 in the third region 53 and the thickness T3 in the fourth region 54. On the other hand, the thickness T5 of the additional film 40 provided in the sixth region 56 located on the edge region 32 side of the first region 51 is equal to or less than the thickness T2 in the third region 53. The length L5 of the sixth region 56 in the Y direction is equal to or less than 1.0λ, and may be equal to or less than 0.5λ. The other configurations are the same as those of the first embodiment, and therefore, description thereof will be omitted.

[0053] 10(b), since the thickness T5 of the additional film 40 in the sixth region 56 is smaller than the thickness T1 of the additional film 40 in the fifth region 55, the acoustic velocity of the elastic wave in the sixth region 56 is faster than the acoustic velocity of the elastic wave in the fifth region 55. The rest is the same as in FIG. 3 of Example 1, and therefore a description thereof will be omitted.

[0054] Even when the thickness T5 of the additional film 40 in the sixth region 56 is equal to or less than the thickness T2 of the additional film 40 in the third region 53, if the length L5 of the sixth region 56 is equal to or less than 1.0λ, it is considered that the acoustic wave penetrates to the fifth region 55 by the tunnel effect. Therefore, since the fifth region 55 functions as a low sound velocity region in the piston mode, it is considered that the same effect as in Example 1 can be obtained and spurious can be suppressed.

[0055] FIG. 11(a) is a plan view of an acoustic wave device according to Example 1, and FIGS. 11(b) and 11(c) are plan views of acoustic wave devices according to Modifications 2 and 3 of Example 1. In FIGS. 11(a) to 11(c), thick portions of the additional film 40 having thicknesses T1 and T3 are indicated by fine hatching, and thin portions of the additional film 40 having thickness T2 are indicated by coarse hatching. As shown in FIG. 11(a), Example 1 illustrates an example in which both side surfaces of the thick portion (finely hatched portion) and the thin portion (coarsely hatched portion) of the additional film 40 extend linearly in the X direction. As shown in FIGS. 11(b) and 11(c), both side surfaces of the thick portion (finely hatched portion) and the thin portion (coarsely hatched portion) of the additional film 40 may protrude or recess between the electrode fingers 22.

[0056] 12(a) to 13(c) are cross-sectional views of acoustic wave devices according to Modifications 4 to 9 of Example 1. Both side surfaces of the additional film 40 may be inclined in an inverse tapered manner as shown in FIG. 12(a) or in a forward tapered manner as shown in FIG. 12(b). As shown in FIGS. 12(c) and 13(a), one of the two side surfaces of the additional film 40 may be inclined in an inverse tapered manner and the other inclined in a forward tapered manner. As shown in FIG. 13(b), the additional film 40 may be a laminated film of a first film 41 and a second film 42. The number of laminated layers is not limited to two, and may be three or more. As shown in FIG. 13(c), the taper angles of both side surfaces of the additional film 40 may be different from each other.

[0057] According to Example 1 and its modifications, an additional film 40 is provided on the piezoelectric layer 15 in the edge region 32 and the first region 51 of the gap region 33. The additional film 40 is not provided in the central region 31 or the second region 52 of the gap region 33. The additional film 40 has a thickness T1 (first thickness) in the first region 51 that is greater than a thickness T2 (second thickness) in the third region 53 of the edge region 32. This makes it possible to suppress spurious emissions, as shown in Simulations 1 and 3.

[0058] Furthermore, in Example 1 and its modified example, the additional film 40 has a thickness T1 (first thickness) in the first region 51 that is greater than a thickness T3 (third thickness) in the fourth region 54, and the thickness T3 is greater than a thickness T2 (second thickness) in the third region 53. This makes it possible to suppress spurious emissions, as in Simulations 1 and 3.

[0059] In Example 1 and its modified examples, the thickness T3 of the additional film 40 in the fourth region 54 is 1.6 times or more and 3.2 times or less than the thickness T2 of the additional film 40 in the third region 53, that is, 1.6T2≦T3≦3.2T2 is satisfied. Furthermore, the thickness T1 of the additional film 40 in the first region 51 is T1=T4ρ a / 2ρ b +T3, where T4 is the thickness of the electrode finger 22, T3 is the thickness of the additional film 40 in the fourth region 54, and ρ a is the density of the electrode fingers 22, ρ b is the density of the additional film 40. This increases the reflection coefficient, as in Simulation 3, and makes it possible to suppress spurious emissions. From the viewpoint of suppressing spurious emissions, the thickness T3 is preferably 1.8 to 3.0 times the thickness T2, more preferably 2.0 to 2.8 times, and even more preferably 2.2 to 2.6 times.

[0060] Furthermore, in Example 1 and its modified examples, the length L2 (second length) in the Y direction of the third region 53 is greater than the length L1 (first length) in the Y direction of the first region 51 and the length L3 (third length) in the Y direction of the fourth region 54. This makes it possible to increase the reflection coefficient and suppress spurious emissions, as in Simulation 3.

[0061] In addition, in the first embodiment, the additional film 40 has a thickness of T1 in the entire Y direction in the first region 51. This simplifies the shape of the additional film 40, making it possible to suppress spurious responses.

[0062] In the first embodiment and its modifications, the additional film 40 is mainly composed of niobium oxide, silicon oxide, tantalum oxide, aluminum, titanium, or tungsten, which effectively changes the acoustic velocity of the elastic wave, making it easier to realize the piston mode.

[0063] In addition, in Example 1 and its modified examples, comb electrode 21 includes electrode fingers 22, dummy electrode fingers 23, and bus bar 24. Electrode fingers 22 of one comb electrode 21 and dummy electrode fingers 23 of the other comb electrode 21 face each other, forming gap region 33 therebetween. In this way, provision of dummy electrode fingers 23 can suppress leakage of acoustic waves. [Example]

[0064] FIG. 14(a) is a cross-sectional view of an acoustic wave device 200 according to a second embodiment, and FIG. 14(b) is a graph illustrating the acoustic velocity of an acoustic wave. Although not shown, in the second embodiment, similarly to FIG. 1(a), an IDT 20 including electrode fingers 22 and dummy electrode fingers 23 and a reflector 25 are provided on a piezoelectric layer 15. As shown in FIG. 14(a), in the second embodiment, the thickness T3 of the additional film 40 in the fourth region 54 of the edge region 32 is the same as the thickness T2 of the additional film 40 in the third region 53. The thicknesses being the same means that a difference of the order of a manufacturing error is allowed, for example, a ratio of the difference between the thicknesses T3 and T2 to the thickness T3 being ±3% or less. The thickness T1 of the additional film 40 in the first region 51 of the gap region 33 is greater than the thicknesses T2 and T3. The other configurations are the same as those in the first embodiment, and therefore description thereof will be omitted.

[0065] 14(b), the thickness T2 of the additional film 40 in the third region 53 is the same as the thickness T3 of the additional film 40 in the fourth region 54, and therefore the acoustic velocity of the elastic wave in the third region 53 is the same as the acoustic velocity of the elastic wave in the fourth region 54. The rest is the same as in FIG. 3 of Example 1, and therefore a description thereof will be omitted.

[0066] [Simulation 4] FIG. 15 is a cross-sectional view of model C used in the simulation. Although not shown, model C also has an IDT 20 including electrode fingers 22 and dummy electrode fingers 23 and a reflector 25 provided on a piezoelectric layer 15, similar to FIG. 1(a). As shown in FIG. 15, model C has an insulating film 12 provided on a substrate 10. A piezoelectric layer 15 is provided on the insulating film 12. An IDT 20 including electrode fingers 22 and dummy electrode fingers 23 and a reflector 25 are provided on the piezoelectric layer 15. An additional film 40 is provided on the piezoelectric layer 15 from the edge region 32 to a first region 51 of the gap region 33. The additional film 40 has a thickness of T a , the thickness in the third region 53 is T b , the thickness in the fourth region 54 is T c The length of the first region 51 in the Y direction is L a , the length of the third region 53 in the Y direction is L b , the length of the fourth region 54 in the Y direction is L c Let's say.

[0067] The simulation conditions are as follows: Wavelength of surface acoustic wave λ: 2.2 μm Substrate 10: sapphire substrate Insulating film 12: silicon oxide (SiO2) film with a thickness of 0.2λ Piezoelectric layer 15: 42° rotated Y-cut X-propagating lithium tantalate layer with a thickness of 0.3λ IDT 20 and reflector 25: Aluminum film with a thickness of 0.096λ IDT20 duty ratio: 50% Additional film 40: Niobium oxide (Nb2O5) film Length of gap region 33 in the Y direction: 2.2 μm Length L of the first region 51 a :0.1λ Length L of the third region 53 b :0.3λ Length L of the fourth region 54 c :0.1λ

[0068] Simulations were performed to evaluate spurious responses for models C-1, C-2, C-3, C-4, C-5, C-6, C-7, C-8, C-9, and C-10 in which the acoustic velocity of the elastic wave in the first region 51 was made different from one another in model C. Table 3 shows the acoustic velocity ratios of the elastic waves in the first region 51, the third region 53, and the fourth region 54 in models C-1, C-2, C-3, C-4, C-5, C-6, C-7, C-8, C-9, and C-10. The acoustic velocity ratios of the elastic waves were calculated in the same manner as in Table 1. [Table 3] As shown in Table 3, the acoustic velocity ratios of the elastic waves in the first region 51, the third region 53, and the fourth region 54 were set to -0.5%, -1.5%, and -1.5% in Model C-1, -1.0%, -1.5%, and -1.5% in Model C-2, -1.5%, -1.5%, and -1.5% in Model C-3, -1.5%, -1.5%, and -1.5% in Model C-4, -3.0%, -1.5%, and -1.5% in Model C-5, -4.5%, -1.5%, and -1.5% in Model C-6, -6.0%, -1.5%, and -1.5% in Model C-7, and -7.5%, -1.5%, and -1.5% in Model C-8. For model C-8, the values ​​were -9.0%, -1.5%, and -1.5%, for model C-9, -15.0%, -1.5%, and -1.5%, and for model C-10, the values ​​were -20.0%, -1.5%, and -1.5%.

[0069] 16(a) to 16(f) are diagrams showing the real part of the admittance Real(Y) versus frequency in Simulation 4. 16(a) to 16(f) show the simulation results for models C-1, C-2, C-3, C-4, C-6, and C-9.

[0070] As shown in Figures 16(a) to 16(f), spurious signals occurred in models C-1, C-2, C-3, and C-9, but were suppressed in models C-4 and C-6. The reflection coefficients were 0.85 for model C-1, 0.85 for model C-2, 0.88 for model C-3, 0.94 for model C-4, 0.95 for model C-6, and 0.72 for model C-9. Therefore, spurious signals can be suppressed when the reflection coefficient is 0.94 or higher.

[0071] FIG. 17 is a diagram showing the reflection coefficient versus the acoustic velocity ratio of the elastic waves in the first region 51 in Simulation 4. The black circles represent the simulation results, and the dashed line represents an approximation curve. The acoustic velocity ratio of the elastic waves in the first region 51 on the horizontal axis is the value listed in Table 3, and is the value when the acoustic velocity ratio of the elastic waves in the third region 53 and the fourth region 54 is -1.5%. Since the reflection coefficient is preferably 0.94 or higher to suppress spurious signals, as shown in FIG. 17, the acoustic velocity ratio of the elastic waves in the first region 51 is preferably -9.0% or higher and -3.0% or lower when the acoustic velocity ratio of the elastic waves in the third region 53 and the fourth region 54 is -1.5%. In other words, the acoustic velocity of the elastic waves in the first region 51 is preferably 2.0 times or higher and 6.0 times or lower than the acoustic velocity of the elastic waves in the third region 53 and the fourth region 54.

[0072] T shown in Example 1 a =T d ρ a / 2ρ b +T c From the above formula, when the acoustic velocity of the elastic wave in the first region 51 is n times the acoustic velocity of the elastic wave in the fourth region 54, T a =(2n-1)T d ρ a / 2ρ b +nT c It can be said that (6) is satisfied. Therefore, in the simulation 4, in order to suppress spurious by making the reflection coefficient 0.94 or more, the thickness T a It is preferable that the thickness T satisfies the above formula (6) when n is 2 to 6.a is 3T d ρ a / 2ρ b +2T c ≦T a ≦11T d ρ a / 2ρ b +6T c It is preferable that the following is satisfied.

[0073] Therefore, in Example 2 of FIG. 14(a), in order to suppress spurious, the thickness T1 of the additional film 40 in the first region 51 is set to 3T4ρ a / 2ρ b +2T3≦T1≦11T4ρ a / 2ρ b +6T3 is satisfied, where T4 is the thickness of the electrode finger 22, T3 is the thickness of the additional film 40 in the fourth region 54, and ρ a is the density of the electrode fingers 22, ρ b is the density of the additional film 40.

[0074] In Simulation 4, it is not clear why spurious responses were suppressed when the acoustic velocity of the elastic wave in the first region 51 was made faster than the acoustic velocity of the elastic wave in the third region 53 and the fourth region 54, but this is thought to be due to the reasons described in Simulation 1. In addition, it is also not clear why the reflection coefficient became small and spurious responses occurred when the acoustic velocity of the elastic wave in the first region 51 was too slow or too fast, but this is thought to be due to the reasons described in Simulation 3.

[0075] According to Example 2, an additional film 40 is provided on the piezoelectric layer 15 in the edge region 32 and the first region 51 of the gap region 33. The additional film 40 is not provided in the central region 31 or the second region 52 of the gap region 33. The additional film 40 has a thickness T1 (first thickness) in the first region 51 that is greater than a thickness T2 (second thickness) in the third region 53 of the edge region 32. This makes it possible to suppress spurious emissions, as in Simulations 1 and 4.

[0076] In Example 2, the additional film 40 has a thickness T2 (second thickness) in the third region 53 and a thickness T3 (third thickness) in the fourth region 54 that are the same, and a thickness T1 (first thickness) in the first region 51 that is greater than the thicknesses T2 and T3. This makes it possible to suppress spurious emissions, as in Simulation 4.

[0077] In Example 2, the thickness T1 of the additional film 40 in the first region 51 is 3T4ρ a / 2ρ b +2T3≦T1≦11T4ρ a / 2ρ b +6T3, where T4 is the thickness of the electrode finger 22, T3 is the thickness of the additional film 40 in the fourth region 54, and ρ a is the density of the electrode fingers 22, ρ b is the density of the additional film 40. As a result, as in Simulation 4, the reflection coefficient increases, and spurious signals can be suppressed. From the viewpoint of suppressing spurious signals, the thickness T1 is set to 5T4ρ a / 2ρ b +3T3≦T1≦11T4ρ a / 2ρ b It is also possible to satisfy +6T3, and 7T4ρ a / 2ρ b +4T3≦T1≦9T4ρ a / 2ρ b It is also acceptable to satisfy +5T3, and 3T4ρ a / 2ρ b +2T3≦T1≦7T4ρ a / 2ρ b It is also acceptable if +3T3 is met. [Example]

[0078] 18 is a plan view of an acoustic wave device 300 in accordance with Example 3. As shown in FIG. 18, in Example 3, the comb-shaped electrodes 21 do not include dummy electrode fingers. In this case, the tips of the electrode fingers 22 of one comb-shaped electrode 21 face the bus bars 24 of the other comb-shaped electrode 21, and a gap region 33 is formed therebetween. The other configurations are the same as those of Example 1, and therefore description thereof will be omitted.

[0079] As in Example 1 and its modifications and Example 2, comb electrode 21 may include dummy electrode fingers 23, and gap region 33 may be located between electrode fingers 22 and dummy electrode fingers 23. As in Example 3, comb electrode 21 may not include dummy electrode fingers, and electrode fingers 22 and bus bar 24 may face each other across gap region 33.

[0080] In Example 1 and its modifications, Example 2, and Example 3, in order to realize the piston mode, it is preferable that the Y-direction length of the central region 31 and the Y-direction length of the edge region 32 satisfy a certain relationship. For example, it is preferable that the Y-direction length of the central region 31 is longer than the total Y-direction length of the edge regions 32. The Y-direction length of each edge region 32 is preferably 1.0λ or less, more preferably 0.5λ or less. The Y-direction length of each edge region 32 is preferably 0.05λ or more, more preferably 0.1λ or more. The edge region 32 may be provided on only one side of the central region 31. [Example]

[0081] FIG. 19(a) is a circuit diagram of a filter 400 according to a fourth embodiment. As shown in FIG. 19(a), 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 device according to the first embodiment, its modifications, the second embodiment, or the third embodiment can be used for at least one of the series resonators S1 to S4 and the parallel resonators P1 to P3. The numbers of the series resonators and the parallel resonators can be set as appropriate. Although a ladder-type filter is shown as an example of the filter, the filter may also be a multi-mode filter.

[0082] FIG. 19(b) is a circuit diagram of a duplexer 410 according to a modified example of the fourth embodiment. As shown in FIG. 19(b), 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 passes, to the common terminal Ant, signals in the transmit band among the high-frequency signals input from the transmit terminal Tx as transmit signals, and suppresses signals of other frequencies. The receive filter 72 passes, to the receive terminal Rx, signals in the receive band among the high-frequency signals input from the common terminal Ant as receive signals, and suppresses signals of other frequencies. At least one of the transmit filter 70 and the receive filter 72 can be the filter of the third embodiment. Although a duplexer has been shown as an example of a multiplexer, a triplexer or a quadplexer may also be used.

[0083] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims. [Explanation of symbols]

[0084] 10...substrate, 12...insulating film, 15...piezoelectric layer, 20...IDT, 21...comb-shaped electrode, 22...electrode finger, 23...dummy electrode finger, 24...busbar, 25...reflector, 26...metal film, 27...insulating film, 30...intersection region, 31...center region, 32...edge region, 33...gap region, 34...dummy region, 35...busbar region, 40...additional film, 41...first film, 42...second film, 51...first region, 52...second region, 53...third region, 54...fourth region, 55...fifth region, 56...sixth region, 70...transmitting filter, 72...receiving filter, 100, 200, 300...acoustic wave device, 400...filter, 410...duplexer

Claims

1. a piezoelectric layer; a pair of comb-shaped electrodes provided on the piezoelectric layer, each having a plurality of electrode fingers and a bus bar connecting the plurality of electrode fingers, and having an intersection region where the plurality of electrode fingers intersect with each other and a gap region located between the intersection region and the bus bar and adjacent to the intersection region, the intersection region including edge regions located at edges of the plurality of electrode fingers in the longitudinal direction and a central region located inside the edge regions; an additional film provided on the piezoelectric layer in the edge region and a first region of the gap region that is located on the edge region side, and not provided in the central region or a second region of the gap region that is outside the first region, and having a first thickness in the first region that is greater than a second thickness in a third region of the edge region that is located on the gap region side.

2. 2. The acoustic wave device of claim 1, wherein the first thickness of the additional film is greater than a third thickness in a fourth region of the edge region that is located between the third region and the central region, and the third thickness is greater than the second thickness.

3. The first thickness is T １ , the second thickness is T ２ , the third thickness is T ３ , the thickness of the plurality of electrode fingers is T ４ , the density of the plurality of electrode fingers is ρ ａ , the density of the additional film is ρ ｂ In this case, 1.6T ２ ≦T ３ ≦3.2T ２ and T １ =T ４ ρ ａ / 2ρ ｂ +T ３ The acoustic wave device according to claim 2 , wherein

4. The acoustic wave device according to claim 3 , wherein a second length of the third region in the longitudinal direction is greater than a first length of the first region in the longitudinal direction and a third length of the fourth region in the longitudinal direction.

5. 2. The acoustic wave device of claim 1, wherein the second thickness of the additional film is equal to a third thickness in a fourth region of the edge region that is located between the third region and the central region, and the first thickness is greater than the second thickness and the third thickness.

6. The first thickness is T １ , the third thickness is T ３ , the thickness of the plurality of electrode fingers is T ４ , the density of the plurality of electrode fingers is ρ ａ , the density of the additional film is ρ ｂ In this case, 3T ４ ρ ａ / 2ρ ｂ +2T ３ ≦T １ ≦11T ４ ρ ａ / 2ρ ｂ +6T ３ The acoustic wave device according to claim 5 , wherein

7. The acoustic wave device according to claim 1 , wherein the additional film has the first thickness over the entire length in the first region.

8. 6. The acoustic wave device according to claim 1, wherein the additional film is mainly composed of niobium oxide, silicon oxide, tantalum oxide, aluminum, titanium, or tungsten.

9. A filter comprising the acoustic wave device according to claim 1, 2 or 5.

10. A multiplexer including the filter of claim 9.

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