Acoustic wave device, filter, and multiplexer

Abstract

To provide an acoustic wave device capable of suppressing an increase in size.SOLUTION: An acoustic wave device 100 includes a piezoelectric layer 15 and a pair of comb-shaped electrodes 21 that is provided onto the piezoelectric layer 15 and has a plurality of electrode fingers 22 and a bus bar 24 to which the plurality of electrode fingers 22 are connected, an intersecting region 30 where the plurality of electrode fingers 22 intersect each other includes an edge region 33 located at an edge in a longitudinal direction of the plurality of electrode fingers 22, a central region 31 located inside the edge region, and an intermediate region 32 located between the edge region 33 and the central region 31. A second weight is larger than a first weight and a third weight is smaller than the first weight when the weight per unit length in a longitudinal direction of a single-layer or laminated film including a metal layer of the at least one electrode finger provided on the piezoelectric layer 15 at the location where the at least one electrode finger of the plurality of electrode fingers 22 is located is defined as a first weight in the central region 31, the second weight in the intermediate region 32, and the third weight in the edge region 33.SELECTED DRAWING: Figure 1

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. It is known that the acoustic velocity of an acoustic wave in an edge region, located at the edge in the longitudinal direction of the electrode fingers in an intersection region where the plurality of electrode fingers of each of the pair of interdigital transducers intersect, is made different from the acoustic velocity of an acoustic wave in a central region located inside the edge region (see, for example, Patent Document 1). It is known that a piston mode can be realized and spurious signals can be suppressed by making the acoustic velocity of an acoustic wave in the edge region slower than that in the central region (see, for example, Patent Documents 2 and 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2013-518455 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-136712 [Patent Document 3] Japanese Patent Application Publication No. 2019-125856 Summary of the Invention [Problem to be solved by the invention]

[0004] The difference between the acoustic velocity of the acoustic wave in the gap region between the electrode fingers and the busbar and the acoustic velocity in the center region may be large. In this case, the width of the edge region must be increased to realize the piston mode. However, increasing the width of the edge region increases the size of the device.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to prevent the device from becoming large in size. [Means for solving the problem]

[0006] The present invention provides an acoustic wave device comprising: a piezoelectric layer; and 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, wherein an intersection region where the plurality of electrode fingers intersect includes an edge region located at a longitudinal edge of the plurality of electrode fingers, a central region located inside the edge region, and an intermediate region located between the edge region and the central region; wherein, when a weight per unit length in the longitudinal direction of a single-layer or multilayer film including a metal layer of at least one electrode finger provided on the piezoelectric layer at a location where at least one of the plurality of electrode fingers is located is defined as a first weight in the central region, a second weight in the intermediate region, and a third weight in the edge region, the second weight is greater than the first weight and the third weight is less than the first weight.

[0007] In the above configuration, the second weight may be greater than 1.0 times and less than 2 times the first weight, and the third weight may be greater than 0.5 times and less than 1.0 times the first weight.

[0008] In the above configuration, the length of the edge region in the longitudinal direction may be three times or less the average pitch of the plurality of electrode fingers of the pair of comb-shaped electrodes.

[0009] In the above configuration, the at least one electrode finger may have a smaller width in the edge region than in the central region.

[0010] In the above configuration, the height of the at least one electrode finger in the edge region may be smaller than the height in the central region.

[0011] In the above configuration, the piezoelectric element may be configured to include a first additional film provided on at least one electrode finger in the central region, and a second additional film provided on at least one electrode finger in the edge region, the second additional film having a faster acoustic velocity than the first additional film.

[0012] The above-described configuration may further include an additional film provided on the at least one electrode finger in the intermediate region and not provided in the central region and the edge region.

[0013] In the above configuration, the at least one electrode finger may have a width greater in the intermediate region than in the central region.

[0014] The present invention is an acoustic wave device comprising: a piezoelectric layer; and 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, wherein an intersection region where the plurality of electrode fingers intersect includes an edge region located at the longitudinal edge of the plurality of electrode fingers, a central region located inside the edge region, and an intermediate region located between the edge region and the central region, wherein a second sound velocity of an acoustic wave propagating in the intermediate region is slower than a first sound velocity of an acoustic wave propagating in the central region, and a third sound velocity of an acoustic wave propagating in the edge region is faster than the first sound velocity.

[0015] In the above configuration, the third sound velocity may be 1.01 to 1.07 times the first sound velocity.

[0016] The above configuration may further include a floating conductor provided between the plurality of electrode fingers in the edge region.

[0017] In the above configuration, the plurality of electrode fingers may include a metal layer containing tungsten, molybdenum, ruthenium, platinum, iridium, rhenium, rhodium, or tantalum as a main component.

[0018] The present invention is a filter including the acoustic wave device described above.

[0019] The present invention is a multiplexer including the filter described above. [Effects of the Invention]

[0020] According to the present invention, it is possible to prevent the device from becoming large. [Brief explanation of the drawings]

[0021] [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] FIG. 2(a) is a plan view of an acoustic wave device according to a comparative example, and FIG. 2(b) is a cross-sectional view taken along line AA of FIG. 2(a). [Figure 3] FIG. 3(a) is a diagram showing the acoustic velocity of an elastic wave in the comparative example, and FIG. 3(b) is a diagram showing the acoustic velocity of an elastic wave in the first embodiment. [Figure 4] FIG. 4 is a diagram showing the length of the low sound velocity region in the Y direction relative to the sound velocity difference in the low sound velocity region in Simulation 1. [Figure 5] FIG. 5(a) is a plan view of the acoustic wave device used in Simulation 2, and FIG. 5(b) is a graph showing the difference in acoustic velocity of the acoustic wave versus the duty ratio in Simulation 2. [Figure 6] 6(a) to 6(c) are cross-sectional views of electrode fingers in the first embodiment. [Figure 7] FIG. 7A is a plan view of an acoustic wave device according to a first modification of the first embodiment, and FIG. 7B is a plan view of an acoustic wave device according to a second modification of the first embodiment. [Figure 8] FIG. 8(a) is a plan view of an acoustic wave device according to a third modification of the first embodiment, and FIG. 8(b) is a cross-sectional view taken along the line AA in FIG. 8(a). [Figure 9] FIG. 9(a) is a plan view of an acoustic wave device according to a fourth modification of the first embodiment, and FIG. 9(b) is a plan view of an acoustic wave device according to a fifth modification of the first embodiment. [Figure 10] FIG. 10(a) is a plan view of an acoustic wave device according to a sixth modification of the first embodiment, and FIG. 10(b) is a cross-sectional view taken along the line AA in FIG. 10(a). [Figure 11] 11(a) is a plan view of an acoustic wave device according to a seventh modification of the first embodiment, FIG. 11(b) is a cross-sectional view taken along line AA in FIG. 11(a), and FIG. 11(c) is a graph showing the acoustic velocity of an acoustic wave. [Figure 12] 12(a) is a plan view of the acoustic wave device in accordance with Example 2, FIG. 12(b) is a cross-sectional view taken along line AA in FIG. 12(a), and FIG. 12(c) is a graph showing the acoustic velocity of acoustic waves. [Figure 13] FIG. 13(a) is a circuit diagram of a filter according to the third embodiment, and FIG. 13(b) is a circuit diagram of a duplexer according to a modified example of the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [Example]

[0023] 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.

[0024] As shown in Figures 1(a) and 1(b), a piezoelectric layer 15 is provided on a substrate 10. A first insulating layer 11 is provided between the substrate 10 and the piezoelectric layer 15. A second insulating layer 12 is provided between the first insulating layer 11 and the piezoelectric layer 15. A third insulating layer 13 is provided between the second insulating layer 12 and the piezoelectric layer 15. A fourth insulating layer 14 is provided between the third insulating layer 13 and the piezoelectric layer 15. The substrate 10 is, for example, a sapphire substrate. The first insulating layer 11 is, for example, a porous aluminum oxide layer with many voids such as holes. The second insulating layer 12 is, for example, an aluminum oxide layer with fewer voids than the first insulating layer 11. The third insulating layer 13 is, for example, an aluminum nitride layer. The fourth insulating layer 14 is, for example, a silicon oxide layer. The piezoelectric layer 15 is, for example, a single-crystal lithium tantalate layer, a single-crystal lithium niobate layer, or a single-crystal quartz crystal 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, for example, a 30° to 50° rotated Y-cut X-propagation lithium tantalate layer.

[0025] 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 and a bus bar 24 to which the plurality of electrode fingers 22 are connected. The IDT 20 and the reflector 25 are formed by a metal film 26 on the piezoelectric layer 15. The metal film 26 includes at least a metal having a density greater than that of copper (Cu), and includes at least one metal layer whose main component is, for example, tungsten (W), molybdenum (Mo), ruthenium (Ru), platinum (Pt), iridium (Ir), rhenium (Re), rhodium (Rh), or tantalum (Ta). Examples of the density of the material are shown in Table 1. [Table 1]

[0026] Here, when a film is made to have a certain element as its main component, it is acceptable for the film to 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 atomic % or more, for example, 80 atomic % or more. When a film is made to have two or more elements as its main components, such as silicon oxide, the total concentration of the two or more elements is 50 atomic % or more, 80 atomic % or more, or 90 atomic % or more. Each of the two or more elements is 10 atomic % or more or 20 atomic %. For example, in the case of silicon oxide, the total concentration of silicon and oxygen is 50 atomic % or more, 80 atomic % or more, or 90 atomic % or more. The concentration of silicon and the concentration of oxygen are each, for example, 10 atomic % or more or 20 atomic % or more.

[0027] The region where the electrode fingers 22 of each of the pair of comb electrodes 21 intersect is the intersection region 30. The length of the intersection region 30 in the Y direction is the aperture length. 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 part 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 mainly in the X direction. The pitch of the electrode fingers 22 of one comb electrode 21 is approximately the wavelength λ of the surface acoustic wave. The wavelength λ is approximately twice the average pitch D of the multiple electrode fingers 22. The reflector 25 reflects the surface acoustic wave excited by the electrode fingers 22 of the IDT 20. As a result, the surface acoustic wave is confined within the intersection region 30 of the IDT 20.

[0028] The intersection region 30 has an edge region 33 located at the edge in the Y direction, a central region 31 located inside the edge region 33 in the Y direction, and an intermediate region 32 located between the central region 31 and the edge region 33. The edge region 33 is a region of the intersection region 30 where the tips 27 of the electrode fingers 22 are located. A gap region 34 is a region located between the tips of the electrode fingers 22 of one comb electrode 21 and the bus bar 24 of the other comb electrode 21. A bus bar region 35 is a region where the bus bar 24 is located.

[0029] An additional film 40 is provided on the piezoelectric layer 15 in the intermediate region 32. The additional film 40 is provided in a strip shape in the X direction and covers the electrode fingers 22 located in the intermediate region 32. The additional film 40 is not provided in the central region 31, the edge region 33, the gap region 34, or the busbar region 35. The additional film 40 is an insulating film mainly composed of, for example, silicon oxide (SiO2), tantalum oxide (Ta2O5), or niobium oxide (Nb2O5). The additional film 40 may be a single-layer or multilayer film mainly composed of other materials as long as it is capable of adjusting the sound velocity of elastic waves propagating in the intermediate region 32.

[0030] The tip portions 27 of the electrode fingers 22 have a smaller width, which is the length in the X direction, than the remaining portions of the electrode fingers 22. Therefore, the width W3 of the electrode fingers 22 in the edge regions 33 is smaller than the width W1 of the electrode fingers 22 in the central region 31 and the width W2 of the electrode fingers 22 in the intermediate region 32. The height of the electrode fingers 22 in the Z direction is constant from one end connected to the bus bar 24 to the other end, which is the opposite tip. Therefore, the height H3 of the electrode fingers 22 in the edge regions 33 is the same as the height H1 of the electrode fingers 22 in the central region 31 and the height H2 of the electrode fingers 22 in the intermediate region 32. The term "same height" allows for manufacturing errors.

[0031] [Manufacturing method] A manufacturing method of the acoustic wave device 100 according to the first embodiment will be described. First, a first insulating layer 11, a second insulating layer 12, a third insulating layer 13, and a fourth insulating layer 14 are formed in this order on a substrate 10. The first insulating layer 11, the second insulating layer 12, the third insulating layer 13, and the fourth insulating layer 14 are formed by, for example, sputtering, CVD (Chemical Vapor Deposition), or vacuum deposition. Next, a piezoelectric layer 15 is bonded to the fourth insulating layer 14 by, for example, surface activation, and then the piezoelectric layer 15 is polished to a desired thickness by, for example, CMP (Chemical Mechanical Polishing). Next, a metal film 26 is formed on the piezoelectric layer 15, and then the metal film 26 is patterned into a desired shape. As a result, an IDT 20 and a reflector 25 are formed on the piezoelectric layer 15. The metal film 26 is formed by, for example, sputtering, CVD, or vacuum deposition. The metal film 26 is patterned by, for example, photolithography and etching.

[0032] Next, an additional film 40 that covers the electrode fingers 22 is formed on the piezoelectric layer 15 in the intermediate region 32. The additional film 40 is formed, for example, by forming a mask layer having an opening in the intermediate region 32 on the piezoelectric layer 15, depositing the additional film 40 using the mask layer as a mask, and then removing the mask layer. The mask layer is made of, for example, photoresist. The additional film 40 is deposited by, for example, sputtering, CVD, or vacuum deposition. In this way, the acoustic wave device 100 in accordance with the first embodiment is formed.

[0033] [Comparative Example] FIG. 2(a) is a plan view of an acoustic wave device 500 according to a comparative example, and FIG. 2(b) is a cross-sectional view taken along line AA of FIG. 2(a). As shown in FIGS. 2(a) and 2(b), in the comparative example, the intersection region 30 has a central region 31 and an edge region 33. An additional film 40 is provided on the piezoelectric layer 15 in the edge region 33, covering the electrode fingers 22. The additional film 40 is not provided in the central region 31, the gap region 34, or the busbar region 35. The width and height of the electrode fingers 22 are constant from one end connected to the busbar 24 to the other end, which is the tip on the opposite side. The other configurations are the same as those of Example 1, and therefore will not be described again.

[0034] [Speed ​​of elastic waves] 3A is a diagram showing the acoustic velocity of an elastic wave in a comparative example. As shown in FIG. 3A, in the comparative example, because an additional film 40 is provided in the edge region 33, the acoustic velocity of the elastic wave propagating through the edge region 33 is slower than that of the elastic wave propagating through the central region 31. Because the gap region 34 has fewer electrode fingers 22 than the central region 31, the acoustic velocity of the elastic wave propagating through the gap region 34 is faster than that of the elastic wave propagating through the central region 31. By making the edge region 33 a low acoustic velocity region where the acoustic velocity of the elastic wave is slower than that of the central region 31 and making the gap region 34 a high acoustic velocity region where the acoustic velocity of the elastic wave is faster than that of the central region 31, a piston mode can be realized.

[0035] However, when the electrode fingers 22 include a metal layer mainly composed of a heavy metal such as W, Mo, Ru, Pt, Ir, Re, Rh, or Ta, the difference in acoustic velocity between the gap region 34 and the central region 31 becomes large. In this case, in order to establish the piston mode, the length of the edge region 33 in the Y direction must be increased, which results in an increase in the size of the device.

[0036] 3B is a diagram showing the acoustic velocity of an elastic wave in Example 1. As shown in FIG. 3B, in Example 1, because the additional film 40 is provided in the intermediate region 32, the acoustic velocity of the elastic wave propagating in the intermediate region 32 is slower than that of the elastic wave propagating in the central region 31. Because the width W3 of the electrode fingers 22 in the edge region 33 is smaller than the width W1 of the electrode fingers 22 in the central region 31, the acoustic velocity of the elastic wave propagating in the edge region 33 is faster than that of the elastic wave propagating in the central region 31. In this case, in the piston mode, the intermediate region 32 becomes a low acoustic velocity region where the acoustic velocity of the elastic wave is slower than that of the central region 31, and the edge region 33 becomes a high acoustic velocity region where the acoustic velocity of the elastic wave is faster than that of the central region 31. By appropriately making the width W3 of the electrode fingers 22 in the edge region 33 smaller than the width W1 of the electrode fingers 22 in the central region 31, the acoustic velocity of the elastic wave in the edge region 33 can be made appropriate relative to the acoustic velocity of the elastic wave in the central region 31. This prevents the edge region 33 from becoming too long in the Y direction, thereby preventing the device from becoming too large. Because the edge region 33 is a high acoustic velocity region, the gap region 34 only needs to have a length in the Y direction of about 300 nm. Therefore, the distance in the Y direction between the additional film 40 and the bus bar 24 is almost the same as in the comparative example, so the device is hardly increased in size in this respect. Because the gap region 34 is provided outside the edge region 33, the surface acoustic wave excited by the IDT 20 can be effectively confined to the intersection region 30.

[0037] [Simulation 1] For the acoustic wave devices according to Example 1 and the comparative example, a simulation was performed to determine the relationship between the difference in acoustic velocity of the acoustic wave between the central region 31 and the low acoustic velocity region (the middle region 32 in Example 1, and the edge region 33 in the comparative example) when the piston mode is established, and the length of the low acoustic velocity region in the Y direction. The difference in acoustic velocity of the acoustic wave between the central region 31 and the low acoustic velocity region was calculated by the equation: difference in acoustic velocity = (sonic velocity in the central region 31 - acoustic velocity in the low acoustic velocity region) / acoustic velocity in the central region 31.

[0038] The simulation conditions are as follows: Common conditions between Example 1 and Comparative Example Wavelength of surface acoustic wave λ: 4.1 μm Substrate 10: sapphire substrate with a thickness of 38.4 μm First insulating layer 11: None Second insulating layer 12: None Third insulating layer 13: None Fourth insulating layer 14: 0.83 μm thick silicon oxide layer Piezoelectric layer 15: 1.25 μm thick 42° rotated Y-cut X-propagating lithium tantalate layer IDT20, reflector 25: A film consisting of a 10 nm thick titanium layer, a 220 nm thick tungsten layer, and a 230 nm thick aluminum layer stacked in this order. Additional film 40: 150 nm thick silicon oxide film Opening length: 80.2μm Number of pairs of electrode fingers 22: 60 pairs Duty ratio in the central region 31 of the IDT 20: 50% Length of busbar region 35 in the Y direction: 12.3 μm Conditions of Example 1 Length of gap region 34 in the Y direction: 4.1 μm Length of edge region 33 in the Y direction: 4.1 μm Length of the intermediate region 32 in the Y direction: 3.69 μm Duty ratio in the edge region 33 of the IDT 20: 40% The difference in acoustic wave velocity A1 between the central region 31 and the edge region 33 is 3%. Sound velocity difference A1 = (sound velocity in edge region 33 - sound velocity in central region 31) / sound velocity in central region 31 Conditions for the comparative example Length of gap region 34 in the Y direction: 8.2 μm Length of edge region 33 in the Y direction: 5.33 μm The difference A2 in acoustic wave velocity between the central region 31 and the gap region 34: 20% Sound velocity difference A2 = (sound velocity in gap region 34 - sound velocity in central region 31) / sound velocity in central region 31

[0039] FIG. 4 is a diagram showing the length of the low sound velocity region in the Y direction relative to the sound velocity difference in the low sound velocity region in Simulation 1. The horizontal axis of FIG. 4 is the difference in sound velocity of elastic waves between the central region 31 and the low sound velocity region (the middle region 32 in Example 1 and the edge region 33 in the Comparative Example). The vertical axis is the length of the low sound velocity region in the Y direction. In FIG. 4, the simulation results of Example 1 are shown by black circles, the simulation results of the Comparative Example are shown by black triangles, and the respective approximate curves are shown by solid and dotted lines. Furthermore, when the conditions for establishing the piston mode when the sound velocity difference A1 in Example 1 and the sound velocity difference A2 in the Comparative Example are calculated using the scalar potential method, the calculation results for Example 1 are shown by white circles, the calculation results for the Comparative Example are shown by white triangles, and the respective approximate curves are shown by dashed and dashed lines.

[0040] As shown in Figure 4, the results of calculation using the scalar potential method and the simulation results were similar. In both cases, when the sound velocity difference in the low sound velocity region was the same, the length of the low sound velocity region in the Y direction required for establishing the piston mode was shorter in Example 1 than in the comparative example. This shows that Example 1 can achieve the piston mode while suppressing an increase in device size compared to the comparative example. Note that increasing the sound velocity difference in the low sound velocity region reduces the length of the low sound velocity region in the Y direction. However, increasing the sound velocity difference in the low sound velocity region means increasing the thickness of the additional film 40, which raises concerns about the occurrence of burrs during manufacturing and insufficient film thickness of the mask layer, as well as resulting in an increase in device size due to an increase in height.

[0041] [Simulation 2] A simulation was performed to examine the relationship between the duty ratio of the IDT 20 and the acoustic velocity. FIG. 5(a) is a plan view of the acoustic wave device used in Simulation 2. As shown in FIG. 5(a), in Simulation 2, the electrode fingers 22 provided on the piezoelectric layer 15 have a constant width and height from one end connected to the bus bar 24 to the other end, which is the opposite tip. No additional film 40 is provided on the piezoelectric layer 15. For an acoustic wave device with this structure, a simulation was performed to examine the acoustic velocity of acoustic waves propagating through the intersection region 30 by changing the duty ratio of the IDT 20. The duty ratio of the IDT 20 is (thickness of the electrode fingers 22) / (pitch of the electrode fingers 22).

[0042] Fig. 5(b) is a diagram showing the difference in acoustic velocity of the elastic wave versus the duty ratio in Simulation 2. The horizontal axis of Fig. 5(b) is the duty ratio, and the vertical axis is the difference in acoustic velocity relative to the acoustic velocity when the duty ratio is 50%. As shown in Fig. 5(b), compared to when the duty ratio of the IDT 20 is 50%, the acoustic velocity of the elastic wave is about 3% faster when the duty ratio of the IDT 20 is 40%, and about 7% faster when the duty ratio is 30%.

[0043] The results of Simulation 2 show that in Example 1, by appropriately reducing the width W3 of the electrode fingers 22 in the edge regions 33, the acoustic velocity of the elastic waves in the edge regions 33 can be made appropriate relative to the acoustic velocity of the elastic waves in the central region 31. Since the acoustic velocity of the elastic waves in the high acoustic velocity region is preferably about 2% to 7% faster than the acoustic velocity of the elastic waves in the central region, it is preferable to set the width W3 of the electrode fingers 22 in the edge regions 33 to about 60% to 80% of the width W1 of the electrode fingers 22 in the central region 31.

[0044] In Example 1, the length L (see FIG. 1(b)) of each edge region 33 in the Y direction is 0.1λ or more and 1.5λ or less. This is because, if the length L is large, the excitation of acoustic waves in the edge region 33 becomes large, leading to the generation of unwanted spurious. On the other hand, if the length L is small, the gap region 34 functions as a high sound velocity region in the piston mode.

[0045] Furthermore, to achieve the piston mode, it is preferable that the Y-direction length of the central region 31 and the Y-direction length of the intermediate 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 intermediate regions 32. The Y-direction length of each of the intermediate regions 32 is preferably 1.0λ or less, and more preferably 0.5λ or less. The Y-direction length of each of the intermediate regions 32 is preferably 0.05λ or more, and more preferably 0.1λ or more. The intermediate region 32 and the edge region 33 may be provided on only one side of the central region 31.

[0046] 6(a) to 6(c) are cross-sectional views of the electrode fingers 22 in Example 1. FIG. 6(a) is a cross-sectional view of the electrode fingers 22 in the X direction in the central region 31, FIG. 6(b) is a cross-sectional view of the electrode fingers 22 in the X direction in the intermediate region 32, and FIG. 6(c) is a cross-sectional view of the electrode fingers 22 in the X direction in the edge region 33. In FIGS. 6(a) to 6(c), the electrode fingers 22 are assumed to be films in which a first metal layer 51 and a second metal layer 52 are laminated. Note that the electrode fingers 22 are not limited to being laminated films, and may be single-layer films.

[0047] As shown in Figures 6(a) and 6(b), when comparing the central region 31 and the intermediate region 32, the width and height of the electrode fingers 22 are the same, but in the intermediate region 32, an additional film 40 is provided on the electrode fingers 22.

[0048] 6(a) and 6(c), comparing the central region 31 with the edge region 33, at least some of the electrode fingers 22 among the plurality of electrode fingers 22 have a smaller width in the edge region 33 than in the central region 31. The height of the electrode fingers 22 is the same in the central region 31 and the edge region 33.

[0049] 6(a), the cross-sectional area of ​​the first metal layer 51 is S1, and the cross-sectional area of ​​the second metal layer 52 is S2. The density of the metal material that is the main component of the first metal layer 51 is ρ1, and the density of the metal material that is the main component of the second metal layer 52 is ρ2. In this case, the weight per unit length in the Y direction obtained by multiplying the cross-sectional area and density of the first metal layer 51 is S1×ρ1, and the weight per unit length in the Y direction obtained by multiplying the cross-sectional area and density of the second metal layer 52 is S2×ρ2. Therefore, the weight per unit length in the Y direction of the film including the metal layer of the electrode fingers 22 provided on the piezoelectric layer 15 at the locations where the electrode fingers 22 are located (referred to as the first weight) is S1×ρ1+S2×ρ2.

[0050] As shown in FIG. 6(b), in the intermediate region 32, an additional film 40 is provided on the electrode fingers 22. The cross-sectional area of ​​the additional film 40 on the electrode fingers 22 is S3. The density of the main constituent material of the additional film 40 is ρ3. In this case, the weight per unit length in the Y direction obtained by multiplying the cross-sectional area and density of the additional film 40 is S3×ρ3. Therefore, the weight per unit length in the Y direction of the film including the metal layer of the electrode fingers 22 provided on the piezoelectric layer 15 at the location where the electrode fingers 22 are located (referred to as the second weight) is S1×ρ1+S2×ρ2+S3×ρ3. Therefore, the second weight is greater than the first weight.

[0051] As shown in FIG. 6( c), the width of at least one of the electrode fingers 22 in the edge region 33 is smaller than the width in the central region 31. For example, it is 70% of the width in the central region 31. In this case, the cross-sectional area of ​​the first metal layer 51 is 0.7S1, and the cross-sectional area of ​​the second metal layer 52 is 0.7S2. Therefore, the weight per unit length in the Y direction of the film including the metal layer of the electrode finger 22 provided on the piezoelectric layer 15 at the location where the electrode finger 22 is located (referred to as the third weight) is 0.7S1×ρ1+0.7S2×ρ2. Therefore, the third weight is smaller than the first weight.

[0052] 3(b), the acoustic velocity of the elastic wave in the intermediate region 32 is slower than the acoustic velocity of the elastic wave in the central region 31, and the acoustic velocity of the elastic wave in the edge region 33 is faster than the acoustic velocity of the elastic wave in the central region 31. Therefore, the intermediate region 32 becomes a low acoustic velocity region in the piston mode, and the edge region 33 becomes a high acoustic velocity region.

[0053] In this way, the weight per unit length in the Y direction of the film provided on the piezoelectric layer 15 at the locations where the electrode fingers 22 are located in the central region 31, the intermediate region 32, and the edge region 33 can be obtained from the cross-sectional area and constituent materials by observing the cross-sections of the electrode fingers 22 in the central region 31, the intermediate region 32, and the edge region 33. When the sum of the first weights, the sum of the second weights, and the sum of the third weights for a plurality of electrode fingers 22, such as two or four, that are continuous in the X direction are compared, the sum of the second weights is greater than the sum of the first weights, and the sum of the third weights is less than the sum of the first weights.

[0054] [Variation] FIG. 7(a) is a plan view of an acoustic wave device 110 according to a first modification of the first embodiment. As shown in FIG. 7(a), in the first modification of the first embodiment, the tip end 27 of the electrode finger 22 has a wide portion 28 that is wide near the intermediate region 32. The wide portion 28 narrows with increasing distance from the intermediate region 32. The other configurations are the same as those of the first embodiment, and therefore description thereof will be omitted. The presence of the wide portion 28 in the tip end 27 of the electrode finger 22 near the intermediate region 32 can improve power durability. From the viewpoint of realizing a piston mode, the length of the wide portion 28 in the Y direction is preferably 1 / 5 or less of the length of the edge region 33 in the Y direction, more preferably 1 / 10 or less, and even more preferably 1 / 20 or less.

[0055] 7B is a plan view of an acoustic wave device 120 according to a second modification of the first embodiment. As shown in FIG. 7B, in the second modification of the first embodiment, the electrode fingers 22 have a small width at their tip portions 27 located in the edge regions 33, and also have a small width at the portion opposite the tip portions 27 located in the edge regions 33. The other configurations are the same as those of the first embodiment, and therefore a description thereof will be omitted. Alternatively, the width of the tip portions 27 of the electrode fingers 22 may not be small, and only the portion opposite the tip portions 27 located in the edge regions 33 may be small.

[0056] 8(a) is a plan view of an acoustic wave device 130 according to a third modification of the first embodiment, and FIG. 8(b) is a cross-sectional view taken along line AA in FIG. 8(a). As shown in FIGS. 8(a) and 8(b), in the third modification of the first embodiment, the width of the electrode fingers 22 is constant from one end connected to the bus bar 24 to the other end, which is the tip on the opposite side. A height H3 of the tip portions 27 of the electrode fingers 22 in the edge region 33 is smaller than a height H1 of the electrode fingers 22 in the central region 31 and a height H2 of the electrode fingers 22 in the intermediate region 32. The other configurations are the same as those of the first embodiment, and therefore will not be described again.

[0057] 9(a) is a plan view of an acoustic wave device 140 according to a fourth modification of the first embodiment. As shown in FIG. 9(a), in the fourth modification of the first embodiment, the additional film 40 is not provided in the intermediate region 32. Instead, the width W2 of the electrode fingers 22 in the intermediate region 32 is larger than the width W1 of the electrode fingers 22 in the central region 31. The other configurations are the same as those in the first embodiment, and therefore will not be described again.

[0058] 9(b) is a plan view of an acoustic wave device 150 according to a fifth modification of the first embodiment. As shown in FIG. 9(b), in the fifth modification of the first embodiment, the additional film 40 provided in the intermediate region 32 is provided only on the electrode fingers 22, and is not provided between the electrode fingers 22. That is, while the additional film 40 is provided in a strip shape in the first embodiment, the additional film 40 is provided in a dot shape in the fifth modification of the first embodiment. The other configurations are the same as those in the first embodiment, and therefore description thereof will be omitted.

[0059] FIG. 10(a) is a plan view of an acoustic wave device 160 according to a sixth variation of the first embodiment, and FIG. 10(b) is a cross-sectional view taken along line AA of FIG. 10(a). For clarity, the protective film 42 is omitted from FIG. 10(a). As shown in FIGS. 10(a) and 10(b), in the sixth variation of the first embodiment, the protective film 42 is provided on the piezoelectric layer 15 in the central region 31, the intermediate region 32, the gap region 34, and the busbar region 35. The protective film 42 covers the electrode fingers 22 and the busbar 24. The protective film 44 is provided on the piezoelectric layer 15 in the edge region 33. The protective film 44 covers the electrode fingers 22 and is primarily composed of a material with a faster acoustic velocity than the protective film 42. Since the acoustic velocity can be calculated by the square root of Young's modulus divided by density, for example, the protective film 42 is primarily composed of silicon oxide, and the protective film 44 is primarily composed of aluminum oxide or silicon nitride. The protective films 42 and 44 have the same thickness. The other configurations are the same as those in the first embodiment, so the description will be omitted.

[0060] FIG. 11(a) is a plan view of an acoustic wave device 170 according to a seventh modification of the first embodiment, and FIG. 11(b) is a cross-sectional view taken along line AA of FIG. 11(a). As shown in FIGS. 11(a) and 11(b), in the seventh modification of the first embodiment, the interdigital transducer 21 has a plurality of electrode fingers 22, a plurality of dummy electrode fingers 23, and a bus bar 24. The dummy electrode fingers 23 have the same width and height as the electrode fingers 22 in the central region 31. The region where the dummy electrode fingers 23 are located is a dummy region 36. The other configurations are the same as those of the first embodiment, and therefore will not be described again.

[0061] Fig. 11(c) is a diagram showing the acoustic velocity of an elastic wave in Modification 7 of Example 1. As shown in Fig. 11(c), in Modification 7 of Example 1, the dummy electrode fingers 23 provided in the dummy region 36 have the same width and height as the electrode fingers 22 in the central region 31, and therefore the acoustic velocity of an elastic wave propagating through the dummy region 36 is the same as the acoustic velocity of an elastic wave propagating through the central region 31. The rest is the same as Fig. 3(b), and therefore description thereof will be omitted.

[0062] In the first to seventh modifications of the first embodiment, the weight per unit length in the Y direction of the single-layer or multilayer film including the metal layer of the electrode fingers 22 provided on the piezoelectric layer 15 at the locations where the electrode fingers 22 are located is such that the second weight in the intermediate region 32 is greater than the first weight in the central region 31, and the third weight in the edge region 33 is less than the first weight in the central region 31. Therefore, similar to FIG. 3(b), the acoustic velocity of the elastic wave propagating in the intermediate region 32 is slower than the acoustic velocity of the elastic wave propagating in the central region 31, and the acoustic velocity of the elastic wave propagating in the edge region 33 is faster than the acoustic velocity of the elastic wave propagating in the central region 31.

[0063] As described above, according to Example 1 and its modifications, when the weight per unit length in the Y direction of a single-layer or multilayer film including a metal layer of electrode finger 22 provided on piezoelectric layer 15 at a location where at least one of multiple electrode fingers 22 is located is defined as a first weight in central region 31, a second weight in intermediate region 32, and a third weight in edge region 33, the second weight is greater than the first weight and the third weight is less than the first weight. That is, the acoustic velocity of the elastic wave propagating through intermediate region 32 (second acoustic velocity) is slower than the acoustic velocity of the elastic wave propagating through central region 31 (first acoustic velocity), and the acoustic velocity of the elastic wave propagating through edge region 33 (third acoustic velocity) is faster than the acoustic velocity of the elastic wave propagating through central region 31 (first acoustic velocity). As a result, the intermediate region 32 becomes a low acoustic velocity region where the acoustic velocity of the elastic wave is slower than that of the central region 31, and the edge region 33 becomes a high acoustic velocity region where the acoustic velocity of the elastic wave is faster than that of the central region 31, thereby realizing a piston mode. Furthermore, the acoustic velocity of the elastic wave in the edge region 33 can be adjusted by the width and / or height of the electrode fingers 22 located in the edge region 33, so that the acoustic velocity of the elastic wave in the edge region 33 can be made appropriate relative to the acoustic velocity of the elastic wave in the central region 31. This prevents the length of the intermediate region 32 in the Y direction from becoming too large, thereby preventing the device from becoming too large.

[0064] From the viewpoint of realizing the piston mode, the second weight is preferably greater than 1.0 and less than 2.0 times the first weight, more preferably 1.05 to 1.6 times, and even more preferably 1.1 to 1.4 times. The third weight is preferably greater than 0.5 and less than 1.0 times the first weight, more preferably 0.55 to 0.9 times, and even more preferably 0.6 to 0.8 times. The number of electrode fingers 22 whose second weight is greater than the first weight and whose third weight is smaller than the first weight is preferably 50% or more of the plurality of electrode fingers 22, more preferably 80% or more, even more preferably 90% or more, and most preferably all. Furthermore, from the viewpoint of preventing the length of the intermediate region 32 in the Y direction from increasing, the acoustic velocity (third acoustic velocity) of the elastic wave propagating through the edge region 33 is preferably 1.01 to 1.07 times the acoustic velocity (first acoustic velocity) of the elastic wave propagating through the central region 31, more preferably 1.02 to 1.06 times, and even more preferably 1.03 to 1.05 times.

[0065] 1(a) and 1(b), in Example 1, the length L of the edge region 33 in the Y direction is three times or less (1.5λ or less) the average pitch D of the plurality of electrode fingers 22. This suppresses the excitation of acoustic waves in the edge region 33, thereby suppressing the occurrence of spurious signals. From the viewpoint of suppressing the occurrence of spurious signals, the length L is preferably 2.5 times or less, more preferably 2 times or less, and even more preferably 1.5 times or less, the average pitch D. In Example 1, the length L is 0.2 times or more (0.1λ or more) the average pitch D. This enables the edge region 33 to function as a high acoustic velocity region. From the viewpoint of making the edge region 33 a high acoustic velocity region, the length L is preferably 0.4 times or more, more preferably 0.6 times or more, and even more preferably 1.0 times or more, the average pitch D. The average pitch D of the plurality of electrode fingers 22 can be calculated by dividing the width of the IDT 20 in the X direction by the number of electrode fingers 22.

[0066] 1(a), the plurality of electrode fingers 22 include an electrode finger 22 whose width W3 in the edge region 33 is smaller than its width W1 in the central region 31. In such an electrode finger 22, the third weight in the edge region 33 is smaller than the first weight in the central region 31. Therefore, the acoustic velocity of the elastic wave in the edge region 33 is faster than that in the central region 31, realizing a piston mode. Furthermore, by adjusting the rate of decrease in the width W3 in the edge region 33 relative to the width W1 in the central region 31 of the electrode finger 22, the acoustic velocity of the elastic wave in the edge region 33 can be made appropriate relative to the acoustic velocity of the elastic wave in the central region 31. Therefore, the length of the intermediate region 32 in the Y direction can be prevented from increasing.

[0067] The width of the electrode fingers 22 in the edge region 33 is not limited to being reduced only at the tip portions 27 of the electrode fingers 22 as shown in Fig. 1(a), but may be reduced at both the tip portions 27 and the portion opposite to the tip portions 27 as shown in Fig. 7(b). However, from the viewpoint of ensuring power durability, it is preferable to reduce the width only at the tip portions 27.

[0068] 8(a) and 8(b), the plurality of electrode fingers 22 includes an electrode finger 22 whose height H3 in the edge region 33 is smaller than its height H1 in the central region 31. In such an electrode finger 22, the third weight in the edge region 33 is smaller than the first weight in the central region 31. Therefore, the acoustic velocity of the elastic wave in the edge region 33 is faster than that in the central region 31, realizing a piston mode. Furthermore, by adjusting the rate of decrease in the height H3 in the edge region 33 relative to the height H1 in the central region 31 of the electrode finger 22, the acoustic velocity of the elastic wave in the edge region 33 can be made appropriate relative to the acoustic velocity of the elastic wave in the central region 31. Therefore, the length of the intermediate region 32 in the Y direction can be prevented from increasing.

[0069] It is also possible to adjust both the width and height of the electrode fingers 22 in the edge regions 33 so that the acoustic velocity of the elastic waves in the edge regions 33 is appropriate relative to the acoustic velocity of the elastic waves in the central region 31 .

[0070] 10(a) and 10(b), in the sixth modification of the first embodiment, a protective film 42 (first additional film) is provided on the electrode fingers 22 in the central region 31. A protective film 44 (second additional film) having a faster acoustic velocity than the protective film 42 is provided on the electrode fingers 22 in the edge region 33. This also makes it possible to make the third weight in the edge region 33 smaller than the first weight in the central region 31.

[0071] 1(a), the first embodiment includes an additional film 40 that is provided on the electrode fingers 22 in the intermediate region 32 but not in the central region 31 or the edge region 33. By providing the additional film 40, the second weight in the intermediate region 32 becomes greater than the first weight in the central region 31. Therefore, the acoustic velocity of the acoustic wave in the intermediate region 32 becomes slower than the acoustic velocity of the acoustic wave in the central region 31, thereby realizing a piston mode. The additional film 40 may be provided in a strip shape in the X direction in the intermediate region 32 as shown in FIG. 1(a), or may be provided in a dot shape on the electrode fingers 22 in the intermediate region 32 as shown in FIG. 9(b).

[0072] 9(a), the plurality of electrode fingers 22 includes an electrode finger 22 whose width W2 in the intermediate region 32 is larger than the width W1 in the central region 31. In such an electrode finger 22, the second weight in the intermediate region 32 is larger than the first weight in the central region 31. Therefore, the acoustic velocity of the elastic wave in the intermediate region 32 is slower than the acoustic velocity of the elastic wave in the central region 31, and a piston mode can be realized.

[0073] In addition, the acoustic velocity of the elastic wave in the intermediate region 32 may be made slower than the acoustic velocity of the elastic wave in the central region 31 by both providing an additional film 40 on the electrode finger 22 in the intermediate region 32 and widening the width of the electrode finger 22 in the intermediate region 32. [Example]

[0074] FIG. 12(a) is a plan view of an acoustic wave device 200 according to a second embodiment. FIG. 12(b) is a cross-sectional view taken along the line AA in FIG. 12(a). As shown in FIGS. 12(a) and 12(b), in the second embodiment, the width and height of the electrode fingers 22 are constant from one end connected to the bus bar 24 to the other end, which is the opposite tip. In the edge region 33, a floating conductor 46 is provided on the piezoelectric layer 15 alongside the electrode fingers 22. The floating conductor 46 is made of, for example, the same material as the electrode fingers 22 and has the same width and height as the electrode fingers 22. The other configurations are the same as those of the first embodiment, and therefore will not be described again.

[0075] Fig. 12(c) is a diagram showing the acoustic velocity of the elastic wave in Example 2. As shown in Fig. 12(c), by providing the floating conductor 46 in the edge region 33, the acoustic velocity of the elastic wave propagating in the edge region 33 is faster than the acoustic velocity of the elastic wave propagating in the central region 31, as in Fig. 3(b) of Example 1. The rest is the same as Fig. 3(b), so a description thereof will be omitted. The acoustic velocity of the elastic wave is increased by providing the floating conductor 46 because the reflectivity of the elastic wave at the electrode is reduced.

[0076] In the second embodiment, the acoustic velocity of the elastic waves propagating through the intermediate region 32 (second acoustic velocity) is slower than the acoustic velocity of the elastic waves propagating through the central region 31 (first acoustic velocity), and the acoustic velocity of the elastic waves propagating through the edge region 33 (third acoustic velocity) is faster than the acoustic velocity of the elastic waves propagating through the central region 31 (first acoustic velocity). This allows the intermediate region 32 to function as a low acoustic velocity region where the acoustic velocity of the elastic waves is slower than that of the central region 31, while the edge region 33 to function as a high acoustic velocity region where the acoustic velocity of the elastic waves is faster than that of the central region 31, thereby realizing a piston mode. Furthermore, the acoustic velocity of the elastic waves in the edge region 33 can be adjusted by adjusting the width and height of the floating conductor 46, so that the acoustic velocity of the elastic waves in the edge region 33 can be set to an appropriate value relative to the acoustic velocity of the elastic waves in the central region 31. This prevents the length of the intermediate region 32 in the Y direction from increasing, thereby preventing the device from becoming larger in size.

[0077] In addition to providing the floating conductor 46 in the edge region 33, the acoustic velocity of the elastic wave in the edge region 33 may be adjusted by adjusting the width and / or height of the electrode fingers 22 in the edge region 33.

[0078] In Example 1, its modifications, and Example 2, the electrode fingers 22 include a metal layer mainly composed of W, Mo, Ru, Pt, Ir, Re, Rh, or Ta. In this case, the configuration of the comparative example shown in Figures 2(a) and 2(b) tends to increase the difference in acoustic velocity between the central region 31 and the high acoustic velocity region (edge ​​region 33 in the comparative example). Therefore, in this case, the configurations of Example 1, its modifications, and Example 2 are preferable. [Example]

[0079] FIG. 13(a) is a circuit diagram of a filter 300 according to a third embodiment. As shown in FIG. 13(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 modification, and the second 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 multimode filter.

[0080] FIG. 13(b) is a circuit diagram of a duplexer 310 according to a modified example of the third embodiment. As shown in FIG. 13(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.

[0081] 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]

[0082] 10...substrate, 11...first insulating layer, 12...second insulating layer, 13...third insulating layer, 14...fourth insulating layer, 15...piezoelectric layer, 20...IDT, 21...comb-shaped electrode, 22...electrode finger, 23...dummy electrode finger, 24...bus bar, 25...reflector, 26...metal film, 27...tip portion, 28...wide portion, 30...intersection region, 31...central region, 32...intermediate region, 33...edge region, 34 ...gap region, 35...busbar region, 40...additional film, 42...protective film, 44...protective film, 46...floating conductor, 51...first metal layer, 52...second metal layer, 70...transmitting filter, 72...receiving filter, 100, 110, 120, 130, 140, 150, 160, 170, 200, 500...acoustic wave device, 300...filter, 310...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 an intersection region where the plurality of electrode fingers intersect each other including edge regions located at edges in the longitudinal direction of the plurality of electrode fingers, a central region located inside the edge regions, and an intermediate region located between the edge regions and the central region; An acoustic wave device, wherein when the weight per unit length in the longitudinal direction of a single-layer or multilayer film including a metal layer of at least one electrode finger provided on the piezoelectric layer at a location where at least one of the plurality of electrode fingers is located is defined as a first weight in the central region, a second weight in the intermediate region, and a third weight in the edge region, the second weight is greater than the first weight and the third weight is less than the first weight.

2. the second weight is greater than 1.0 times and less than 2 times the first weight; The acoustic wave device according to claim 1 , wherein the third weight is equal to or greater than 0.5 times and less than 1.0 times the first weight.

3. The acoustic wave device according to claim 1 , wherein the length of the edge region in the longitudinal direction is equal to or less than three times the average pitch of the plurality of electrode fingers of the pair of comb-shaped electrodes.

4. The acoustic wave device according to claim 1 , wherein the at least one electrode finger has a width in the edge region that is smaller than a width in the central region.

5. The acoustic wave device according to claim 1 , wherein the height of the at least one electrode finger in the edge region is smaller than the height in the central region.

6. a first additional film provided on the at least one electrode finger in the central region; 3. The acoustic wave device according to claim 1, further comprising: a second additional film provided on the at least one electrode finger in the edge region, the second additional film having a faster acoustic velocity than the first additional film.

7. The acoustic wave device according to claim 1 , further comprising an additional film provided on the at least one electrode finger in the intermediate region, but not provided in the central region or the edge region.

8. The acoustic wave device according to claim 1 , wherein the at least one electrode finger has a width in the intermediate region that is larger than a width in the central region.

9. a piezoelectric layer; an elastic wave device comprising: 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, wherein an intersection region where the plurality of electrode fingers intersect includes an edge region located at a longitudinal edge of the plurality of electrode fingers, a central region located inside the edge region, and an intermediate region located between the edge region and the central region, wherein a second sound velocity of an elastic wave propagating in the intermediate region is slower than a first sound velocity of an elastic wave propagating in the central region, and a third sound velocity of an elastic wave propagating in the edge region is faster than the first sound velocity.

10. The acoustic wave device according to claim 9 , wherein the third sound velocity is 1.01 to 1.07 times the first sound velocity.

11. The acoustic wave device according to claim 9 , further comprising a floating conductor provided between the plurality of electrode fingers in the edge region.

12. The acoustic wave device according to claim 1 , wherein the plurality of electrode fingers include a metal layer containing tungsten, molybdenum, ruthenium, platinum, iridium, rhenium, rhodium, or tantalum as a main component.

13. A filter comprising the acoustic wave device according to claim 1 or 9.

14. A multiplexer including the filter of claim 13.

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