Elastic wave devices, filters, and multiplexers

Abstract

To provide an elastic wave device that can suppress spurious emissions while suppressing degradation of characteristics. [Solution] The elastic wave device 100 comprises a piezoelectric layer 15, a pair of comb-shaped electrodes 21 provided on the piezoelectric layer 15, each having a plurality of electrode fingers 22, a plurality of dummy electrode fingers 23, and a busbar 24 to which the plurality of electrode fingers 22 and the plurality of dummy electrode fingers 23 are connected to a side surface 50, the side surface 50 is wave-shaped when viewed from the +Z direction, the gap regions 33 between the tips of the plurality of electrode fingers 22 and the tips of the plurality of dummy electrode fingers 23 are aligned along the X direction, the intersection regions 30 where the plurality of electrode fingers 22 intersect each other include an edge region 32 located at the edge in the Y direction and a central region 31 located inside the edge region 32, and the weight per unit length in the Y direction of the single-layer or multi-layer film including the metal film of the electrode fingers 22 provided on the piezoelectric layer 15 at the location where the electrode fingers 22 are located is greater in the edge region 32 than in the central region 31.

Description

Technical Field

[0001] The present invention relates to an elastic wave device, a filter, and a multiplexer.

Background Art

[0002] Elastic wave devices are used in high-frequency communication systems typified by mobile phones. As an elastic wave device, an elastic wave device including a pair of comb-shaped electrodes each having a plurality of electrode fingers, a plurality of dummy electrode fingers, and a bus bar to which the plurality of electrode fingers and the plurality of dummy electrode fingers are connected is known. By making the sound velocity of elastic waves in an edge region located at the longitudinal edge of the electrode fingers in the intersection region where the electrode fingers of each of the pair of comb-shaped electrodes intersect slower than the sound velocity of elastic waves in a central region located inside the edge region, it is known to realize a piston mode and suppress spurious signals (for example, Patent Document 1). Also, it is known to suppress spurious signals by using a comb-shaped electrode having an apodized structure in which the length of the intersection region in the longitudinal direction of the electrode fingers is changed in the arrangement direction of the electrode fingers (for example, Patent Document 2, Non-Patent Document 1, and Non-Patent Document 2). It is also known to suppress spurious signals by using a comb-shaped electrode having a double bus bar structure (for example, Non-Patent Document 3).

Prior Art Documents

Patent Documents

Patent Document 1

Patent Document 2

Non-Patent Documents

[0004] [[ID=3......], ​​​​Shogo Inoue and 4 others, “Optimized Apodization to Suppress Transverse Modes in Guided SAW Resonators”, IEEE International Ultrasonics Symposium, 2023 [Non-Patent Document 2] Yong Guo and 2 others, “Experimental Study of Transverse Mode Suppression on Wideband Hetero Acoustic Layer Surface Acoustic Wave Resonator”, IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, February 2024, VOL.71, NO.2, pp295-303 [Non-Patent Document 3] Yu-Po Wong and 5 others, “IHP SAW Transverse Edge Design for Energy Confinement with Suppressed Scattering Loss and Transverse Mode”, IEEE International Ultrasonics Symposium, 2021 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, there is still room for improvement in suppressing spurious emissions while suppressing the degradation of characteristics. The present invention has been made in view of the above problems, and aims to suppress spurious emissions while suppressing the degradation of characteristics. [Means for solving the problem]

[0006] The present invention is an elastic 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, a plurality of dummy electrode fingers, and a busbar to which the plurality of electrode fingers and the plurality of dummy electrode fingers are connected on the sides, wherein the sides of the busbar are wave-shaped when viewed from above the piezoelectric layer, the gap regions between the tips of the plurality of electrode fingers and the tips of the plurality of dummy electrode fingers are aligned along the direction of arrangement of the plurality of electrode fingers, and the intersection regions where the plurality of electrode fingers intersect each other include an edge region located at the longitudinal edge of the plurality of electrode fingers and a central region located inside the edge region, and the weight per unit length in the longitudinal direction of a single-layer or laminated film including the metal film of the plurality of electrode fingers provided on the piezoelectric layer at the location where each of the plurality of electrode fingers is located is greater in the edge region than in the central region.

[0007] The present invention is an elastic 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, a plurality of dummy electrode fingers, and a busbar to which the plurality of electrode fingers and the plurality of dummy electrode fingers are connected on the side, wherein the side of the busbar is wave-shaped when viewed from above the piezoelectric layer, the gap regions between the tips of the plurality of electrode fingers and the tips of the plurality of dummy electrode fingers are aligned along the arrangement direction of the plurality of electrode fingers, and the intersection regions where the plurality of electrode fingers intersect each other include an edge region located at the longitudinal edge of the plurality of electrode fingers and a central region located inside the edge region, and the speed of sound of elastic waves propagating in the edge region is slower than the speed of sound of elastic waves propagating in the central region.

[0008] In the above configuration, the side surfaces of the busbars of each of the pair of comb-shaped electrodes can be configured to change with the same period and the same amplitude.

[0009] In the above configuration, the side surfaces of the busbars of each of the pair of comb-shaped electrodes can be configured such that, when viewed from above the piezoelectric layer, the convex portions and concave portions face each other.

[0010] In the above configuration, the side surface of the bus bar can be configured to have a sinusoidal waveform when viewed from above the piezoelectric layer.

[0011] In the above configuration, the length of the intersection region in the longitudinal direction can be configured to be constant in the arrangement direction.

[0012] In the above configuration, the value obtained by dividing the number of pairs of the plurality of electrode fingers by the number of convex portions on the side surface of the bus bar can be 20 or more and 25 or less.

[0013] In the above configuration, a load film provided on the plurality of electrode fingers in the edge region and not provided in the central region can be provided.

[0014] In the above configuration, the plurality of electrode fingers can be configured to have a larger width in the edge region than in the central region.

[0015] The present invention is a filter including the elastic wave device described above.

[0016] The present invention is a multiplexer including the filter described above.

Advantages of the Invention

[0017] According to the present invention, spurious can be suppressed while suppressing deterioration of characteristics.

Brief Description of the Drawings

[0018] [Figure 1] FIG. 1(a) is a plan view of an elastic wave device according to Example 1, and FIG. 1(b) is an enlarged view of a region R in FIG. 1(a). [Figure 2] FIG. 2 is a cross-sectional view taken along line A-A of FIG. 1(b). [Figure 3] FIG. 3 is a diagram showing the sound velocity of elastic waves in Example 1. [Figure 4]Figures 4(a) and 4(b) are cross-sectional views of the electrode finger in Example 1. [Figure 5] Figure 5(a) is a plan view of the elastic wave device according to Comparative Example 1, and Figure 5(b) is a plan view of the elastic wave device according to Comparative Example 2. [Figure 6] Figure 6 is a plan view of the elastic wave device according to Comparative Example 3. [Figure 7] Figure 7(a) is a plan view of the elastic wave device according to Comparative Example 4, and Figure 7(b) is an enlarged view of region R in Figure 7(a). [Figure 8] Figure 8 shows the waveform curve represented by equation 2. [Figure 9] Figures 9(a) and 9(b) show the experimental results of the absolute value of admittance |Y| with respect to frequency. [Figure 10] Figures 10(a) and 10(b) show the experimental results of the real part of admittance, Real(Y), with respect to frequency. [Figure 11] Figures 11(a) and 11(b) show experimental results of the reflection coefficient with respect to frequency. [Figure 12] Figures 12(a) and 12(b) show the experimental results of the Q value as a function of frequency. [Figure 13] Figure 13(a) shows the experimental results for ΔY for Comparative Example 2, Comparative Example 3, Comparative Example 4, and Example 1, and Figure 13(b) shows the experimental results for the electromechanical coupling coefficient k2 for Comparative Example 2, Comparative Example 3, Comparative Example 4, and Example 1. [Figure 14] Figures 14(a) and 14(b) show the experimental results of the pass-through characteristics of the first and second multiplexers. [Figure 15] Figures 15(a) and 15(b) show the experimental results of the second and third harmonic distortions of the transmit filters of the first and second multiplexers, respectively. [Figure 16] Figure 16(a) is a plan view of the elastic wave device according to Modification 1 of Example 1, Figure 16(b) is a plan view of the elastic wave device according to Modification 2 of Example 1, and Figure 16(c) is an enlarged view of region R in Figure 16(b). [Figure 17] Figure 17(a) is a plan view of the elastic wave device according to Modification 3 of Example 1, and Figure 17(b) is a plan view of the elastic wave device according to Modification 4 of Example 1. [Figure 18] Figure 18(a) is a circuit diagram of the filter according to Example 2, and Figure 18(b) is a circuit diagram of a duplexer according to a modified example of Example 2. [Modes for carrying out the invention]

[0019] The embodiments of the present invention will be described below with reference to the drawings. [Examples]

[0020] Figure 1(a) is a plan view of the elastic wave device 100 according to Example 1, and Figure 1(b) is an enlarged view of region R in Figure 1(a). Figure 2 is a cross-sectional view of AA in Figure 1(b). The arrangement direction of the electrode fingers 22 is the X direction, the longitudinal 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, Y, and Z directions do not necessarily correspond to the X-axis direction of the crystal orientation of the piezoelectric layer 15. If the piezoelectric layer 15 is a piezoelectric layer with rotational Y-cut X propagation, the X direction is the X-axis direction of the crystal orientation.

[0021] As shown in Figures 1(a), 1(b), and 2, a piezoelectric layer 15 is provided on the 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.

[0022] The substrate 10 is, for example, a sapphire substrate, an alumina substrate, a silicon substrate, a spinel substrate, a quartz substrate, a silica substrate, or a silicon carbide substrate. The first insulating layer 11 is a porous insulating layer with many voids. The second insulating layer 12 is an insulating layer with fewer voids than the first insulating layer 11. The first insulating layer 11 and the second insulating layer 12 are, for example, polycrystalline or amorphous, and are aluminum oxide layers, silicon nitride layers, aluminum nitride layers, silicon carbide layers, or polysilicon layers. The first insulating layer 11 and the second insulating layer 12 may be formed from the same material. The speed of sound of bulk waves propagating through the first insulating layer 11 and the second insulating layer 12 is faster than the speed of sound of bulk waves propagating through the third insulating layer 13 and the piezoelectric layer 15. As a result, the energy of the elastic wave of the main response is confined within the piezoelectric layer 15 and the third insulating layer 13.

[0023] The third insulating layer 13 is a temperature compensation film and has a temperature coefficient of elasticity with the opposite sign to the sign of the temperature coefficient of elasticity of the piezoelectric layer 15. The third insulating layer 13 is, for example, an additive-free silicon oxide layer or a silicon oxide layer containing additive elements such as fluorine, phosphorus, or boron, and is, for example, polycrystalline or amorphous. This makes it possible to reduce the frequency temperature coefficient. For the third insulating layer 13 to have a temperature compensation function, it is required that some of the energy of the elastic wave of the main response be present within the third insulating layer 13. The range in which the energy of the surface acoustic wave is concentrated depends on the type of surface acoustic wave, but is typically in the range of 2.0λ from the upper surface of the piezoelectric layer 15, and particularly in the range of 1.0λ. Therefore, the distance from the lower surface of the third insulating layer 13 to the upper surface of the piezoelectric layer 15 is preferably 2.0λ or less, more preferably 1.5λ or less, and even more preferably 1.0λ or less. The thickness of the piezoelectric layer 15 is preferably 0.1λ or more and 1.0λ or less, and more preferably 0.2λ or more and 0.8λ or less.

[0024] The fourth insulating layer 14 is a bonding layer that joins the third insulating layer 13 and the piezoelectric layer 15, and is, for example, an aluminum oxynitride 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 layer. The piezoelectric layer 15 may also be, for example, a rotating Y-cut X-propagating lithium tantalate layer or a rotating Y-cut X-propagating lithium niobate layer, or for example, a 30° to 50° rotating Y-cut X-propagating lithium tantalate layer.

[0025] An IDT (Interdigital Transducer) 20 and a reflector 25 are provided on the piezoelectric layer 15. The IDT 20 comprises a pair of comb-shaped electrodes 21. Each comb-shaped electrode 21 has a plurality of electrode fingers 22, a plurality of dummy electrode fingers 23, and a busbar 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-shaped electrode 21 face the tips of the dummy electrode fingers 23 of the other comb-shaped 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, copper, molybdenum, iridium, platinum, rhenium, rhodium, ruthenium, tantalum, or tungsten. The IDT 20 and the reflector 25 may have an adhesive film such as a titanium film or a chromium film between the metal film 26 and the piezoelectric layer 15.

[0026] The side surface 50 of the busbar 24 to which the electrode fingers 22 and dummy electrode fingers 23 are connected has a wave shape when viewed from above the piezoelectric layer 15 (viewed from the +Z direction). That is, when viewed from the +Z direction, the side surface 50 has convex portions 51 and concave portions 52 alternately arranged in the X direction. When viewed from the +Z direction, the side surface 50 has a wave shape, for example, that of a sinusoidal wave. In the Y direction, the convex portions 51 and concave portions 52 of the side surface 50 of the busbar 24 of one comb-shaped electrode 21 face each other. For example, the side surfaces 50 of the busbar 24 of each pair of comb-shaped electrodes 21 have wave shapes with the same period and the same amplitude, and in the Y direction, the vertices 53 of the convex portions 51 and the lowest points 54 of the concave portions 52 face each other.

[0027] The region where the electrode fingers 22 of each pair of comb-shaped 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-shaped electrodes 21 face each other such that the electrode fingers 22 are approximately staggered in the X direction in at least a portion of the intersection region 30. The main mode elastic wave (surface acoustic wave) excited by the electrode fingers 22 in the intersection region 30 propagates mainly in the X direction. The pitch of the electrode fingers 22 of one comb-shaped electrode 21 is approximately equal to 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 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. The reflector 25 reflects the surface acoustic wave excited by the electrode fingers 22. As a result, the surface acoustic wave is confined within the intersection region 30 of the IDT 20.

[0028] The crossing region 30 has an edge region 32, which is located at the edge in the Y direction, and a central region 31, which is located inside the edge region 32 in the Y direction. The edge region 32 can also be described as the region of the crossing region 30 where the tip of the electrode finger 22 is located. The gap region 33 is the region located between the tip of the electrode finger 22 of one comb-shaped electrode 21 and the tip of the dummy electrode finger 23 of the other comb-shaped electrode 21. The dummy region 34 is the region where the dummy electrode finger 23 is located. The busbar region 35 is the region where the busbar 24 is located.

[0029] The gap region 33 located between the tip of the electrode finger 22 of one comb-shaped electrode 21 and the tip of the dummy electrode finger 23 of the other comb-shaped electrode 21 is provided aligned along the X direction. In other words, the gap region 33 is provided on a straight line extending in the X direction. The length of the intersection region 30 in the Y direction (opening length) is approximately constant in the X direction. Since the side surface 50 of the busbar 24 is wave-shaped when viewed from the +Z direction, the length of the dummy electrode finger 23 in the Y direction is modulated in the X direction. That is, the dummy electrode finger 23 gradually shortens from the apex 53 of the convex portion 51 on the side surface 50 of the busbar 24 toward the lowest point 54 of the concave portion 52. Therefore, the lengths of the dummy region 34 and the busbar region 35 in the Y direction are also modulated in the X direction. At least one of the multiple electrode fingers 22 faces the convex portion 51 on the side surface 50 of the busbar 24 without the dummy electrode finger 23 in between.

[0030] A protective film 16 is provided on the piezoelectric layer 15, covering the IDT 20 and the reflector 25. Note that the protective film 16 is not shown in Figures 1(a) and 1(b). The protective film 16 is an insulating film, such as a silicon oxide film. A load film 40 is provided on the protective film 16 from the edge region 32 to a part of the gap region 33 so as to cover the tip of the electrode finger 22 in the edge region 32. The load film 40 is provided in a strip shape, for example, along the X direction. The load film 40 is not provided in the central region 31, the remaining part of the gap region 33, the dummy region 34, and the busbar region 35. The load film 40 may be provided only in the edge region 32 and not in the gap region 33. The load film 40 is an insulating film mainly composed of silicon oxide, tantalum oxide, or niobium oxide, or a metal film mainly composed of aluminum or titanium. The load film 40 may be a single-layer or multi-layer film mainly composed of other materials, as long as it is possible to adjust the sound velocity of the elastic waves propagating through the edge region 32.

[0031] Here, for a film to have a certain element as its main component, it is permissible for the film to contain intentional or unintentional impurities other than the main component. When a certain element is the main component in a film, the concentration of that element is, for example, 50 atomic percent or more, or for example, 80 atomic percent or more. When two or more elements are the main components, such as silicon oxide, the sum of the concentrations of the two or more elements is 50 atomic percent or more, 80 atomic percent or more, or 90 atomic percent or more. Each of the two or more elements is 10 atomic percent or more, or 20 atomic percent or more.

[0032] [Speed ​​of sound in elastic waves] Figure 3 shows the sound velocity of elastic waves in Example 1. As shown in Figure 3, since a load film 40 is provided in the edge region 32, the sound velocity of elastic waves propagating in the edge region 32 is slower than the sound velocity of elastic waves propagating in the central region 31. Since the gap region 33 has fewer electrode fingers 22 than the central region 31, the sound velocity of elastic waves propagating in the gap region 33 is faster than the sound velocity of elastic waves propagating in the central region 31. The sound velocity of elastic waves propagating in the dummy region 34 is approximately the same as the sound velocity of elastic waves propagating in the central region 31. The sound velocity of elastic waves propagating in the busbar region 35 is faster than the sound velocity of elastic waves propagating in the central region 31. By making the edge region 32 a low-sound-velocity region where the sound velocity of elastic waves is slower than in the central region 31, and the gap region 33 a high-sound-velocity region where the sound velocity of elastic waves is faster than in the central region 31, a piston mode can be realized.

[0033] The speed of sound in elastic waves can be determined, for example, by the formula in Equation 1. In Equation 1, V is the speed of sound, ρ is density, E is Young's modulus, and ν is Poisson's ratio.

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[0034] To achieve piston mode, it is preferable that the length of the central region 31 in the Y direction and the length of the edge region 32 in the Y direction satisfy a certain relationship. For example, it is preferable that the length of the central region 31 in the Y direction is longer than the sum of the lengths of the edge regions 32 in the Y direction. The length of each edge region 32 in the Y direction is preferably 1.0λ or less, and more preferably 0.5λ or less. The length of each edge region 32 in the Y direction is preferably 0.05λ or more, and more preferably 0.1λ or more. The edge region 32 may be provided only on one side of the central region 31. The length of each gap region 33 in the Y direction is preferably 1.5λ or less, and more preferably 1.0λ or less. The length of each gap region 33 in the Y direction is preferably 0.1λ or more, and more preferably 0.2λ or more.

[0035] Figures 4(a) and 4(b) are cross-sectional views of the electrode finger 22 in Example 1. Figure 4(a) is a cross-sectional view of the electrode finger 22 in the X direction in the central region 31, and Figure 4(b) is a cross-sectional view of the electrode finger 22 in the X direction in the edge region 32. The electrode finger 22 is shown as a laminated film in which metal films 28a and 28b are stacked, but it may also be a single-layer film. As shown in Figures 4(a) and 4(b), the width and height of the electrode finger 22 are approximately the same in the central region 31 and the edge region 32, and the thickness of the protective film 16 is also approximately the same.

[0036] As shown in Figure 4(a), let S1 be the cross-sectional area of ​​the metal film 28a, S2 be the cross-sectional area of ​​the metal film 28b, and S3 be the cross-sectional area of ​​the protective film 16 on the electrode finger 22. Also, let ρ1 be the density of the main component metal material of the metal film 28a, ρ2 be the density of the main component metal material of the metal film 28b, and ρ3 be the density of the main component constituent material of the protective film 16. In this case, the weight per unit length in the Y direction obtained by multiplying the cross-sectional area and density of the metal film 28a is S1 × ρ1, the weight per unit length in the Y direction obtained by multiplying the cross-sectional area and density of the metal film 28b is S2 × ρ2, and the weight per unit length in the Y direction obtained by multiplying the cross-sectional area and density of the protective film 16 is S3 × ρ3. Therefore, the weight per unit length in the Y direction of the film including the metal film 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 first weight) is S1 × ρ1 + S2 × ρ2 + S3 × ρ3.

[0037] As shown in Figure 4(b), in the edge region 32, a load film 40 is provided on the electrode finger 22 in addition to the protective film 16. Let S4 be the cross-sectional area of ​​the load film 40 on the electrode finger 22. Let ρ4 be the density of the main component material of the load film 40. In this case, the weight per unit length in the Y direction, obtained by multiplying the cross-sectional area and density of the load film 40, is S4 × ρ4. Therefore, the weight per unit length in the Y direction of the film including the metal film of the electrode finger 22 provided on the piezoelectric layer 15 at the location of the electrode finger 22 (referred to as the second weight) is S1 × ρ1 + S2 × ρ2 + S3 × ρ3 + S4 × ρ4. Thus, the second weight is greater than the first weight.

[0038] Because the second mass is greater than the first mass, as shown in Figure 3, the speed of sound of the elastic wave propagating through the edge region 32 becomes slower than the speed of sound of the elastic wave propagating through the central region 31. Therefore, a piston mode can be realized. Thus, in the central region 31 and the edge region 32, the weight per unit length in the Y direction of the film provided on the piezoelectric layer 15 at the location where the electrode finger 22 is positioned can be determined from the cross-sectional area and the density of the constituent material by observing the cross-section of the electrode finger 22 in the central region 31 and the edge region 32.

[0039] [Manufacturing method] A method for manufacturing the elastic wave device 100 according to Example 1 will now 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 on a substrate 10 in this order. The first insulating layer 11, the second insulating layer 12, the third insulating layer 13, and the fourth insulating layer 14 are formed using, for example, sputtering, chemical vapor deposition (CVD), or vacuum deposition. Next, a piezoelectric layer 15 is bonded to the fourth insulating layer 14 using, for example, a surface activation method, and then the piezoelectric layer 15 is polished to a desired thickness using, for example, chemical mechanical polishing (CMP).

[0040] Next, a metal film 26 is formed on the piezoelectric layer 15, and then the metal film 26 is patterned into a desired shape. This forms the IDT 20 and reflector 25 on the piezoelectric layer 15. The metal film 26 is formed using, for example, sputtering, CVD, or vacuum deposition. The patterning of the metal film 26 is done using, for example, photolithography and etching. Next, a protective film 16 is formed on the piezoelectric layer 15 so as to cover the IDT 20 and reflector 25. The protective film 16 is formed using, for example, sputtering, CVD, or vacuum deposition.

[0041] Next, a load film 40 covering the tip of the electrode finger 22 is formed on the protective film 16 from the edge region 32 to a part of the gap region 33. The load film 40 is formed, for example, by forming a mask layer having openings in the edge region 32 and a part of the gap region 33 on the protective film 16, depositing the load film 40 on the mask layer, and then removing the mask layer. For example, a photoresist is used for the mask layer. For depositing the load film 40, for example, a sputtering method, a CVD method, or a vacuum deposition method is used. This forms the elastic wave device 100 according to Example 1.

[0042] [Experiment 1] Acoustic wave devices were fabricated and their characteristics evaluated for Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, and Example 1. The structures of the acoustic wave devices for Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 are shown below.

[0043] Figure 5(a) is a plan view of the elastic wave device 500 according to Comparative Example 1. Figure 5(b) is a plan view of the elastic wave device 600 according to Comparative Example 2. Figures 5(a) and 5(b) are plan views of the area corresponding to Figure 1(b). As shown in Figure 5(a), in Comparative Example 1, the side surface 50 of the busbar 24 is straight when viewed from the +Z direction. No dummy electrode fingers are connected to the busbar 24, and the tips of the electrode fingers 22 face the busbar 24. The area between the tips of the electrode fingers 22 and the busbar 24 is the gap area 33. The lengths of the multiple electrode fingers 22 in the Y direction are approximately the same as those of the other electrode fingers 22. No load film 40 is provided in the edge area 32. The other configurations are the same as in Example 1, so their description is omitted. Thus, in Comparative Example 1, since no load film 40 is provided in the edge area 32, the piston mode is not realized.

[0044] As shown in Figure 5(b), in Comparative Example 2, similar to Comparative Example 1, the side surface 50 of the busbar 24 is linear when viewed from the +Z direction, no dummy electrode fingers are connected to the busbar 24, and the tips of the electrode fingers 22 face the busbar 24. The difference from Comparative Example 1 is that a load film 40 is provided from the edge region 32 to a part of the gap region 33. The other configurations are the same as in Example 1, so their explanation is omitted. In Comparative Example 2, since a load film 40 is provided in the edge region 32, a piston mode can be realized.

[0045] Figure 6 is a plan view of the elastic wave device 700 according to Comparative Example 3. As shown in Figure 6, in Comparative Example 3, the busbar 24 is divided into a first busbar 42 and a second busbar 43. The first busbar 42 and the second busbar 43 are electrically connected by a metal film 44. Multiple electrode fingers 22 and multiple dummy electrode fingers 23 are connected to the side surface 45 of the first busbar 42. The side surface 45 of the first busbar 42 is linear when viewed from the +Z direction. The lengths of the multiple electrode fingers 22 in the Y direction are approximately the same as those of the multiple dummy electrode fingers 23 in the Y direction. The other configurations are the same as in Example 1, so their description is omitted. In Comparative Example 3 as well, a load film 40 is provided in the edge region 32, so a piston mode can be realized.

[0046] Figure 7(a) is a plan view of the elastic wave device 800 according to Comparative Example 4, and Figure 7(b) is an enlarged view of region R in Figure 7(a). As shown in Figures 7(a) and 7(b), in Comparative Example 4, the side surface 50 of the busbar 24 is linear when viewed from the +Z direction. The lengths of the multiple electrode fingers 22 in the Y direction and the lengths of the multiple dummy electrode fingers 23 in the Y direction are modulated in the X direction. Therefore, the pair of comb-shaped electrodes 21 have an apotized structure in which the length of the intersection region 30 in the Y direction is modulated in the X direction. The other configurations are the same as in Example 1, so their description is omitted. In Comparative Example 4 as well, a load film 40 is provided on the edge region 32, so the piston mode can be realized.

[0047] The fabrication conditions for the elastic wave devices of Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, and Example 1 are as follows. Common manufacturing conditions Substrate 10: Sapphire substrate First insulating layer 11: 1.8 μm thick aluminum oxide layer Second insulating layer 12: Aluminum oxide layer with a thickness of 6.17 μm. Third insulating layer 13: Silicon oxide layer with a thickness of 0.44 μm. Fourth insulating layer 14: 0.01 μm thick aluminum oxynitride layer Piezoelectric layer 15: 0.66 μm thick 48° rotated Y-cut X-propagating lithium tantalate layer Protective film 16: 15nm thick silicon oxide layer IDT20 and reflector 25: Laminated film of a 35nm thick titanium layer and a 129nm thick aluminum layer. Number of pairs of electrode fingers 22: 136 pairs IDT20 duty cycle: 55% Wavelength of surface acoustic wave λ: 2.2 μm

[0048] Fabrication conditions for the elastic wave device of Comparative Example 1 Aperture length: 12.5λ Length of edge region 32 in the Y direction: 0.4λ Length of gap region 33 in the Y direction: 0.3λ

[0049] Fabrication conditions for the elastic wave device in Comparative Example 2 Load film 40: 60 nm thick silicon oxide layer Aperture length: 12.5λ Length of edge region 32 in the Y direction: 0.4λ Length of gap region 33 in the Y direction: 0.3λ Length of the load film 40 extended into the gap region 33: 0.15λ

[0050] Fabrication conditions for the elastic wave device of Comparative Example 3 Load film 40: 60 nm thick silicon oxide layer Aperture length: 12.5λ Length of edge region 32 in the Y direction: 0.4λ Length of gap region 33 in the Y direction: 0.3λ Length of dummy region 34 in the Y direction: 0.5λ Length of the load film 40 extended into the gap region 33: 0.15λ Length of the first busbar 42 in the Y direction: 0.3λ Distance between the first busbar 42 and the second busbar 43: 0.9λ

[0051] Fabrication conditions for the elastic wave device of Comparative Example 4 Load film 40: 60 nm thick silicon oxide layer Maximum aperture length: 12.5λ Length of the longest dummy electrode finger 23 in the Y direction: 1.0λ Number of waves in the crossover region 30: 6 Length of edge region 32 in the Y direction: 0.4λ Length of gap region 33 in the Y direction: 0.3λ Length of the load film 40 extended into the gap region 33: 0.15λ

[0052] Fabrication conditions for the elastic wave device of Example 1 Load film 40: 60 nm thick silicon oxide layer Aperture length: 12.5λ Length of the longest dummy electrode finger 23 in the Y direction: 1.0λ Number of waves on side 50 of busbar 24: 6 Length of edge region 32 in the Y direction: 0.4λ Length of gap region 33 in the Y direction: 0.3λ Length of the load film 40 extended into the gap region 33: 0.15λ The waveform of the side surface 50 of the busbar 24 was approximately represented by the following equation 2. In equation 2, Wn is the number of waves on the side surface 50, which is 6 in Example 1. n is the nth electrode finger counted from one end in the X direction. Lp is the logarithm of the electrode fingers 22, which is 136 in Example 1. Ld is the length in the Y direction of the longest dummy electrode finger 23, which is 2.2 μm in Example 1. Figure 8 shows the waveform curve represented by equation 2. In Figure 8, the dashed area corresponds to the area of ​​the busbar 24.

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[0053] Figures 9(a) and 9(b) show the experimental results for the absolute value of admittance |Y| with respect to frequency. Figures 10(a) and 10(b) show the experimental results for the real part of admittance Real(Y) with respect to frequency. Figures 9(a) and 10(a) show the experimental results for Comparative Example 1 and Comparative Example 2, while Figures 9(b) and 10(b) show the experimental results for Comparative Example 3, Comparative Example 4, and Example 1. For the absolute value of admittance |Y|, peaks at the resonant frequency fr and anti-resonant frequency fa are observed. For the real part of admittance Real(Y), a larger spurious response is observed compared to the absolute value |Y|.

[0054] As shown in Figures 9(a) and 10(a), in Comparative Example 1, a large spurious signal occurs between the resonant frequency fr and the anti-resonant frequency fa, but in Comparative Example 2, which is equipped with a load film 40, the spurious signal is suppressed compared to Comparative Example 1. However, in Comparative Example 2, a small spurious signal occurs around 1776 MHz. As shown in Figures 9(b) and 10(b), in Comparative Examples 3, 4, and Example 1, the spurious signal is suppressed from the resonant frequency fr to the anti-resonant frequency fa. The spurious signal around 1776 MHz is also suppressed.

[0055] Figures 11(a) and 11(b) show the experimental results of the reflection coefficient with respect to frequency. Figure 11(a) shows the experimental results for Comparative Example 1 and Comparative Example 2, and Figure 11(b) shows the experimental results for Comparative Example 3, Comparative Example 4, and Example 1. As shown in Figure 11(a), in Comparative Example 1, large spurious emissions are generated in the vicinity of 1728MHz to 1776MHz, while in Comparative Example 2, spurious emissions are suppressed. As shown in Figure 11(b), spurious emissions are also suppressed in Comparative Example 3, Comparative Example 4, and Example 1, and in particular, spurious emissions around 1776MHz are suppressed compared to Comparative Example 2, resulting in an improved reflection coefficient. Therefore, as shown in Figures 10(a) and 10(b), it is considered that in Comparative Example 3, Comparative Example 4, and Example 1, spurious emissions around 1776MHz are suppressed compared to Comparative Example 2.

[0056] Figures 12(a) and 12(b) show the experimental results of the Q value against frequency. Figure 12(a) shows the experimental results for Comparative Example 1 and Comparative Example 2, while Figure 12(b) shows the experimental results for Comparative Example 3, Comparative Example 4, and Example 1. As shown in Figures 12(a) and 12(b), in the range of 1728MHz to 1776MHz, Comparative Example 2, Comparative Example 3, and Example 1 obtained similar Q values, while Comparative Example 4 showed a deterioration in Q value.

[0057] From the above experimental results, it can be seen that by providing a load film 40 on the edge region 32 to realize a piston mode, as in Comparative Examples 2, 3, 4, and 1, spurious emissions can be suppressed from the resonant frequency fr to the anti-resonant frequency fa. By using the configurations of Comparative Examples 3, 4, and 1, spurious emissions can be further suppressed compared to Comparative Example 2. In Example 1, the length of the dummy electrode finger 23 in the Y direction is modulated in the X direction, and since it has the same configuration as the dummy electrode finger 23 of Comparative Example 4 which has an apodized structure, it is thought that spurious emissions were suppressed in the same way as in Comparative Example 4.

[0058] However, while Comparative Example 4 is able to suppress spurious emissions, its Q-factor is worse than that of Example 1. The reason for the deterioration of the Q-factor in Comparative Example 4 is thought to be that, due to its apodized structure, the length of the crossover region 30 in the Y-direction is modulated in the X-direction, which adversely affects the propagation of the main mode elastic wave.

[0059] Figure 13(a) shows the experimental results of ΔY for Comparative Example 2, Comparative Example 3, Comparative Example 4, and Example 1. Figure 13(b) shows the electromechanical coupling coefficient k for Comparative Example 2, Comparative Example 3, Comparative Example 4, and Example 1. 2 This figure shows the experimental results. Three elastic wave devices were fabricated for each of Comparative Example 2, Comparative Example 3, Comparative Example 4, and Example 1, and the ΔY and electromechanical coupling coefficient k were measured. 2 The following was evaluated: ΔY is the difference between the absolute value of admittance |Y| at the resonant frequency fr and the absolute value of admittance |Y| at the anti-resonant frequency fa. The electromechanical coupling coefficient k 2The following equation (Equation 3) was used to calculate it. In Equation 3, fr is the resonant frequency and fa is the anti-resonant frequency.

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[0060] As shown in Figure 13(a), Example 1 had a larger ΔY than Comparative Examples 3 and 4, and a ΔY of a similar magnitude to that of Comparative Example 2. As shown in Figure 13(b), Example 1 had a greater electromechanical coupling coefficient k than Comparative Example 4. 2 The electromechanical coupling coefficient k is large and is of a similar magnitude to that of Comparative Examples 2 and 3. 2 That was the case.

[0061] From the experimental results above, Example 1 has a Q value, ΔY, and electromechanical coupling coefficient k. 2 It can be seen that spurious emissions can be suppressed while suppressing the degradation of the characteristics. The experimental results of Example 1 shown above are for the case where the value of Lp / Wn in equation 2 is 22.7. From the viewpoint of suppressing spurious emissions while suppressing the degradation of characteristics, the value of Lp / Wn is preferably 20 or more and 25 or less, more preferably 21 or more and 24 or less, and even more preferably 22 or more and 23 or less.

[0062] [Experiment 2] A first multiplexer was fabricated using the elastic wave devices of Example 1 for the series and parallel resonators of the transmitting filter, and the elastic wave devices of Comparative Example 2 for the series and parallel resonators of the receiving filter. A second multiplexer was also fabricated using the elastic wave devices of Comparative Example 2 for the series and parallel resonators of both the transmitting and receiving filters. The transmission characteristics of the first and second multiplexers were then evaluated.

[0063] Figures 14(a) and 14(b) show the experimental results of the passband characteristics (Band 3) of the first and second multiplexers. Figure 14(b) is an enlarged view of the vicinity of the transmission bandwidth (1710MHz~1785MHz) in Figure 14(a). The reception bandwidth is 1805MHz~1880MHz. As shown in Figures 14(a) and 14(b), the first multiplexer suppresses spurious emissions more effectively than the second multiplexer on the high-frequency side of the transmission bandwidth (around 1760MHz~1780MHz).

[0064] The first multiplexer exhibits suppressed spurious emissions compared to the second multiplexer for the following reasons. The second multiplexer uses the elastic wave device of Comparative Example 2 as its transmit filter, while the first multiplexer uses the elastic wave device of Example 1 as its transmit filter. As shown in Figures 10(a) and 10(b), the elastic wave device of Example 1 suppresses spurious emissions around 1776 MHz compared to the elastic wave device of Comparative Example 2. Therefore, the first multiplexer is considered to have suppressed spurious emissions on the high-frequency side of the transmit bandwidth (around 1770 MHz to 1780 MHz) compared to the second multiplexer.

[0065] Figures 15(a) and 15(b) show the experimental results of the second and third harmonic distortion of the transmit filters of the first and second multiplexers, respectively. As shown in Figure 15(a), the transmit filter of the first multiplexer shows an improvement of approximately 4.7 dB in the second harmonic around 3555 MHz compared to the transmit filter of the second multiplexer. As shown in Figure 15(b), the transmit filter of the first multiplexer shows an improvement of approximately 5.7 dB in the third harmonic around 5350 MHz compared to the transmit filter of the second multiplexer.

[0066] The improvement in the second and third harmonics of the first multiplexer's transmit filter compared to the second multiplexer's transmit filter is thought to be due to the same reasons explained in Figures 14(a) and 14(b). Specifically, the elastic wave device of Example 1 used in the first multiplexer's transmit filter suppresses spurious emissions around 1776 MHz compared to the elastic wave device of Comparative Example 2 used in the second multiplexer's transmit filter. For this reason, the improvement in the second harmonic around 3555 MHz and the third harmonic around 5350 MHz of the first multiplexer's transmit filter is thought to be due to the same reasons explained in Figures 14(a) and 14(b).

[0067] [Differentiation] Figure 16(a) is a plan view of the elastic wave device 110 according to Modification 1 of Example 1. In Example 1, as shown in Figure 1(a), the side surface 50 of the busbar 24 to which the electrode fingers 22 and dummy electrode fingers 23 are connected is wave-shaped when viewed from the +Z direction, while the side surface of the busbar 24 opposite to side surface 50 is linear when viewed from the +Z direction. In Modification 1 of Example 1, as shown in Figure 16(a), both side surface 50 and side surface 55 opposite to side surface 50 of the busbar 24 are wave-shaped when viewed from the +Z direction. Thus, the boundary between the busbar 24 and the wiring 27 is not limited to being linear when viewed from the +Z direction, but may also be wave-shaped. When side surfaces 50 and 55 are wave-shaped, side surfaces 50 and 55 may have waveforms with the same period and the same amplitude. The other configurations are the same as in Example 1, so their explanation is omitted.

[0068] Figure 16(b) is a plan view of the elastic wave device 120 according to Modification 2 of Example 1, and Figure 16(c) is an enlarged view of region R in Figure 16(b). Figure 16(b) is a plan view of the area corresponding to Figure 1(b). In Example 1, as shown in Figure 1(b), the side surface 50 of the busbar 24 between the electrode finger 22 and the dummy electrode finger 23 is curved when viewed from the +Z direction. In Modification 2 of Example 1, as shown in Figures 16(b) and 16(c), the side surface 50 of the busbar 24 between the electrode finger 22 and the dummy electrode finger 23 may be a straight line extending in the X direction when viewed from the +Z direction. The other configurations are the same as in Example 1, so their explanation is omitted. Even if the side surface 50 of the busbar 24 between the electrode finger 22 and the dummy electrode finger 23 is straight, as in Modification 2, the side surface 50 as a whole can be said to have a sinusoidal wave shape.

[0069] Figure 17(a) is a plan view of the elastic wave device 130 according to Modification 3 of Example 1. Figure 17(a) is a plan view of the area corresponding to Figure 1(b). As shown in Figure 17(a), in Modification 3 of Example 1, the load film 40 is provided only on the electrode fingers 22 and not between the electrode fingers 22. That is, in Example 1, the load film 40 was provided in a strip shape, whereas in Modification 3 of Example 1, the load film 40 is provided in a dot shape. The other configurations are the same as in Example 1, so their explanation is omitted.

[0070] Figure 17(b) is a plan view of the elastic wave device 140 according to Modification 4 of Example 1. Figure 17(b) is a plan view of the area corresponding to Figure 1(b). As shown in Figure 17(b), in Modification 4 of Example 1, the load film 40 is not provided in the edge region 32. Instead, the width W2 of the electrode fingers 22 in the edge region 32 is greater than the width W1 of the electrode fingers 22 in the central region 31. The other configurations are the same as in Example 1, so their explanation is omitted.

[0071] In modified examples 3 and 4 of Example 1, the weight per unit length in the Y direction of the single-layer or laminated 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, is such that the second weight in the edge region 32 is greater than the first weight in the central region 31. Therefore, the speed of sound of the elastic wave propagating through the edge region 32 is slower than the speed of sound of the elastic wave propagating through the central region 31.

[0072] According to Example 1 and its modified form, as shown in Figures 4(a) and 4(b), the weight per unit length in the Y direction of the single-layer or multi-layer film including the metal film of the electrode finger 22 provided on the piezoelectric layer 15 at the location where each of the multiple electrode fingers 22 is located is greater in the edge region 32 than in the central region 31. That is, as shown in Figure 3, the speed of sound of elastic waves propagating in the edge region 32 is slower than the speed of sound of elastic waves propagating in the central region 31. This makes it possible to realize a piston mode. In such a case, as shown in Figures 1(a) and 1(b), the side surface 50 of the busbar 24 to which the electrode finger 22 and the dummy electrode finger 23 are connected is made wavy when viewed from the +Z direction, and the gap region 33 is arranged along the X direction. This results in a configuration similar to an apodized structure in which the length of the dummy electrode finger 23 in the Y direction is modulated in the X direction, and spurious emissions can be suppressed as shown in Figure 10(b). Furthermore, by arranging the gap regions 33 along the X direction, the change in the length (opening length) of the intersection region 30 in the Y direction in the X direction is suppressed. Therefore, as shown in Figures 12(b), 13(a), and 13(b), the Q value, ΔY, and electromechanical coupling coefficient k are suppressed. 2 This makes it possible to suppress the deterioration of such characteristics. Therefore, according to Example 1 and its modified form, spurious emissions can be suppressed while suppressing the deterioration of characteristics.

[0073] Furthermore, according to Example 1 and its modified form, as shown in Figure 1(a), the side surfaces 50 of the busbars 24 of each pair of comb-shaped electrodes 21 change with the same period and amplitude. As a result, spurious emissions can be suppressed while suppressing degradation of characteristics, as shown in Figures 10(b), 12(b), 13(a), and 13(b).

[0074] Furthermore, according to Example 1 and its modified form, as shown in Figure 1(a), the side surfaces 50 of the busbars 24 of each pair of comb-shaped electrodes 21 have their convex portions 51 and concave portions 52 facing each other when viewed from the +Z direction. As a result, as shown in Figures 10(b), 12(b), 13(a), and 13(b), spurious emissions can be suppressed while suppressing degradation of characteristics.

[0075] Furthermore, according to Example 1 and its modified form, as shown in Figure 1(a), the side surface 50 of the busbar 24 has a sinusoidal wave shape when viewed from the +Z direction. As a result, spurious emissions can be suppressed while suppressing degradation of characteristics, as shown in Figures 10(b), 12(b), 13(a), and 13(b).

[0076] Furthermore, in Example 1 and its modified form, as shown in Figure 1(b), the length (opening length) of the intersection region 30 in the Y direction is constant in the X direction. This makes it possible to suppress the deterioration of characteristics, as shown in Figures 12(b), 13(a), and 13(b). Note that "constant length" means that variations in length to the extent of manufacturing tolerances are permitted.

[0077] Furthermore, in Example 1, as shown in Figure 1(b), a load film 40 is provided on the electrode finger 22 in the edge region 32, but not in the central region 31. By providing the load film 40, the second weight in the edge region 32 becomes greater than the first weight in the central region 31. Therefore, the sound velocity of the elastic wave in the edge region 32 becomes slower than the sound velocity of the elastic wave in the central region 31, and the piston mode can be realized. The load film 40 may be provided in a strip shape in the X direction in the edge region 32, as shown in Figure 1(b), or it may be provided as a point on the electrode finger 22 in the edge region 32, as shown in Figure 17(a).

[0078] Furthermore, in the modified example 4 of Embodiment 1, as shown in Figure 17(b), the width W2 of the multiple electrode fingers 22 in the edge region 32 is greater than the width W1 in the central region 31. As a result, the second weight in the edge region 32 is greater than the first weight in the central region 31. Therefore, the sound velocity of the elastic wave in the edge region 32 becomes slower than the sound velocity of the elastic wave in the central region 31, and the piston mode can be realized.

[0079] Furthermore, by providing a load film 40 on the electrode finger 22 in the edge region 32 and widening the width of the electrode finger 22 in the edge region 32, the speed of sound of the elastic wave in the edge region 32 may be made slower than the speed of sound of the elastic wave in the central region 31. [Examples]

[0080] Figure 18(a) is a circuit diagram of the filter 200 according to Embodiment 2. As shown in Figure 18(a), one or more series resonators S1 to S4 are connected in series between the input terminal Tin and the 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. At least one of the series resonators S1 to S4 and the parallel resonators P1 to P3 can be an elastic wave device from Embodiment 1 or a modified version thereof. The number of series and parallel resonators can be set as appropriate. A ladder filter is shown as an example of the filter, but a multimode filter may also be used.

[0081] Figure 18(b) is a circuit diagram of a duplexer 210 according to a modified example of Embodiment 2. As shown in Figure 18(b), a transmit filter 60 is connected between the common terminal Ant and the transmit terminal Tx. A receive filter 61 is connected between the common terminal Ant and the receive terminal Rx. The transmit filter 60 allows the transmit band signal from the high-frequency signal input from the transmit terminal Tx to pass to the common terminal Ant as the transmit signal, and suppresses signals of other frequencies. The receive filter 61 allows the receive band signal from the high-frequency signal input from the common terminal Ant to pass to the receive terminal Rx as the receive signal, and suppresses signals of other frequencies. At least one of the transmit filter 60 and the receive filter 61 can be the filter of Embodiment 2. A duplexer is shown as an example of a multiplexer, but a triplexer or quadplexer may also be used.

[0082] Although embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Explanation of Symbols]

[0083] 10...Substrate, 11...First insulating layer, 12...Second insulating layer, 13...Third insulating layer, 14...Fourth insulating layer, 15...Piezoelectric layer, 16...Protective film, 20...IDT, 21...Comb-type electrode, 22...Electrode finger, 23...Dummy electrode finger, 24...Busbar, 25...Reflector, 26...Metal film, 27...Wiring, 28a, 28b...Metal film, 30...Crossing region, 31...Central region, 32...Edge region, 33...Gap region, 34...Dummy region 35...Busbar region, 40...Load film, 42...First busbar, 43...Second busbar, 44...Metal film, 45...Side, 50...Side, 51...Convex part, 52...Concave, 53...Vertex, 54...Lowest point, 55...Side, 60...Transmitting filter, 61...Receiving filter, 100, 110, 120, 130, 140, 500, 600, 700, 800...Elastic wave device, 200...Filter, 210...Duplexer

Claims

1. Piezoelectric layer and An elastic wave device comprising: a pair of comb-shaped electrodes provided on the piezoelectric layer, each having a plurality of electrode fingers, a plurality of dummy electrode fingers, and a busbar to which the plurality of electrode fingers and the plurality of dummy electrode fingers are connected on the side, wherein the side of the busbar is wave-shaped when viewed from above the piezoelectric layer, the gap regions between the tips of the plurality of electrode fingers and the tips of the plurality of dummy electrode fingers are aligned along the arrangement direction of the plurality of electrode fingers, and the intersection regions where the plurality of electrode fingers intersect each other include an edge region located at the longitudinal edge of the plurality of electrode fingers and a central region located inside the edge region, and the weight per unit length in the longitudinal direction of the single-layer or laminated film including the metal film of the plurality of electrode fingers provided on the piezoelectric layer at the location where each of the plurality of electrode fingers is located is greater in the edge region than in the central region.

2. Piezoelectric layer and An elastic wave device comprising a pair of comb-shaped electrodes provided on the piezoelectric layer, each having a plurality of electrode fingers, a plurality of dummy electrode fingers, and a bus bar to which the plurality of electrode fingers and the plurality of dummy electrode fingers are connected on the side, wherein the side of the bus bar is wave-shaped when viewed from above the piezoelectric layer, the gap regions between the tips of the plurality of electrode fingers and the tips of the plurality of dummy electrode fingers are aligned along the direction of arrangement of the plurality of electrode fingers, and the intersection regions where the plurality of electrode fingers intersect each other include an edge region located at the longitudinal edge of the plurality of electrode fingers and a central region located inside the edge region, and the speed of sound of elastic waves propagating in the edge region is slower than the speed of sound of elastic waves propagating in the central region.

3. The elastic wave device according to claim 1 or 2, wherein the sides of the busbars of each of the pair of comb-shaped electrodes change with the same period and the same amplitude.

4. The elastic wave device according to claim 1 or 2, wherein the sides of the busbars of each of the pair of comb-shaped electrodes face each other when viewed from above the piezoelectric layer, with their convex portions facing each other and their concave portions facing each other.

5. The elastic wave device according to claim 1 or 2, wherein the side surface of the busbar has a sinusoidal wave shape when viewed from above the piezoelectric layer.

6. The elastic wave device according to claim 1 or 2, wherein the length of the intersection region in the longitudinal direction is constant in the arrangement direction.

7. The elastic wave device according to claim 1 or 2, wherein the value obtained by dividing the number of pairs of the plurality of electrode fingers by the number of protrusions on the side surface of the busbar is 20 or more and 25 or less.

8. The elastic wave device according to claim 1 or 2, further comprising a loading membrane provided on the plurality of electrode fingers in the edge region and not in the central region.

9. The elastic wave device according to claim 1 or 2, wherein the width of the plurality of electrode fingers is greater in the edge region than in the central region.

10. A filter comprising the elastic wave device according to claim 1 or 2.

11. A multiplexer comprising the filter described in claim 10.

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