Acoustic wave device, filter, and multiplexer

Abstract

The invention relates to an acoustic wave device, a filter, and a multiplexer. An acoustic wave device includes a piezoelectric layer and a pair of interdigital electrodes disposed on the piezoelectric layer, in which each of the interdigital electrodes includes an electrode finger, a dummy electrode finger, and a bus bar having a side surface to which the electrode finger and the dummy electrode finger are connected, the pair of interdigital electrodes includes a gap region and an intersection region, the gap region is arranged along the arrangement direction of the electrode fingers, and the intersection region comprises an edge region and a central region. And a weight per unit length in the longitudinal direction of a single-layer film or a multi-layer film including a metal film of the electrode fingers provided on the piezoelectric layer at a position where each of the electrode fingers is provided is greater in the edge region than in the central region.

Description

Technical Field

[0001] Specific aspects of this invention relate to acoustic devices, filters, and multiplexers. Background Technology

[0002] Acoustic wave devices are used in high-frequency communication systems, such as mobile phones. One known acoustic wave device includes a pair of interdigitated electrodes, each of which includes multiple electrode fingers, multiple dummy electrode fingers, and a busbar, with the multiple electrode fingers and dummy electrode fingers connected to the busbar. It is known that a piston mode is achieved to suppress spurious responses by making the sound velocity of the sound wave in the edge region located at the longitudinal edge of the electrode fingers in the intersection region of the pair of interdigitated electrodes slower than the sound velocity of the sound wave in the central region located within the edge region (e.g., Patent Document 1: Japanese Patent Application Publication No. 2016-136712). It is also known to suppress spurious emissions by using interdigitated electrodes, each with a toe-like structure, in which the length of the cross region of the electrode fingers in the longitudinal direction changes in the direction of the electrode fingers' arrangement (e.g., Patent Document 2: U.S. Patent Application Publication No. 2023 / 0133161; Non-Patent Document 1: Shogo Inoue et al., “Optimizing the toe-like structure to suppress transverse modes in guided SAW resonators,” IEEE International Symposium on Ultrasonics, 2023; and Non-Patent Document 2: Yong Guo et al., “Experimental study on transverse mode suppression in broadband heterosonic surface acoustic wave resonators,” IEEE Transactions on Ultrasonics, Ferroelectrics & Frequency Control, February 2024, Vol. 71, No. 2, pp. 295-303). It is also known to suppress spurious emissions by using interdigitated electrodes, each with a dual busbar structure (e.g., Non-Patent Document 3: Yu-Po Wong et al., “IHP SAW transverse edge design for energy confinement and suppression of scattering loss and transverse modes,” IEEE International Symposium on Ultrasonics, 2021). Summary of the Invention

[0003] According to a first aspect of this disclosure, an acoustic wave device is provided, comprising: a piezoelectric layer; and a pair of interdigitated electrodes disposed on the piezoelectric layer; wherein each of the interdigitated electrodes includes a plurality of electrode fingers, a plurality of dummy electrode fingers, and a busbar having a side surface to which the plurality of electrode fingers and the plurality of dummy electrode fingers are connected, wherein the side surface of the busbar has a wavy shape when viewed from above the piezoelectric layer, wherein the pair of interdigitated electrodes includes a plurality of gap regions between the tips of the plurality of electrode fingers and the tips of the plurality of dummy electrode fingers and an intersection region where the plurality of electrode fingers intersect each other, wherein the plurality of gap regions are arranged along the arrangement direction of the plurality of electrode fingers, wherein the intersection region includes an edge region located at the edge in the longitudinal direction of the plurality of electrode fingers and a central region located inside the edge region, and wherein the weight per unit length in the longitudinal direction of a single layer or multilayer film including a metal film comprising the plurality of electrode fingers disposed on the piezoelectric layer at the location of each of the plurality of electrode fingers is greater in the edge region than in the central region.

[0004] According to a second aspect of this disclosure, an acoustic wave device is provided, comprising: a piezoelectric layer; and a pair of interdigitated electrodes disposed on the piezoelectric layer; wherein each of the interdigitated electrodes includes a plurality of electrode fingers, a plurality of dummy electrode fingers, and a busbar having a side surface to which the plurality of electrode fingers and the plurality of dummy electrode fingers are connected, wherein, when viewed from above the piezoelectric layer, the side surface of the busbar has a wavy shape, wherein the pair of interdigitated electrodes includes a plurality of gap regions between the tips of the plurality of electrode fingers and the tips of the plurality of dummy electrode fingers and an intersection region where the plurality of electrode fingers intersect each other, wherein the plurality of gap regions are arranged along the arrangement direction of the plurality of electrode fingers, wherein the intersection region includes an edge region located at the edge in the longitudinal direction of the plurality of electrode fingers and a central region located inside the edge region, and wherein the sound speed of a sound wave propagating through the edge region is slower than the sound speed of a sound wave propagating through the central region.

[0005] In the first and second aspects of this disclosure, the side surfaces of the busbars of a pair of interdigital electrodes can vary with the same period and the same amplitude.

[0006] In the first and second aspects of this disclosure, when viewed from above the piezoelectric layer, the side surfaces of the busbars of a pair of interdigitated electrodes may have protrusions facing each other and concave portions facing each other.

[0007] In the first and second aspects of this disclosure, when viewed from above the piezoelectric layer, the side surface of the busbar may have a sinusoidal wave shape.

[0008] In the first and second aspects of this disclosure, the length of the intersection region in the longitudinal direction may be constant in the arrangement direction.

[0009] In the first and second aspects of this disclosure, the value obtained by dividing the number of multiple electrode finger pairs by the number of protrusions on the side surface of the busbar can be 20 or greater and 25 or less.

[0010] In the first and second aspects of this disclosure, the acoustic device may further include a load film disposed on a plurality of electrode fingers in an edge region and not disposed in a central region.

[0011] In the first and second aspects of this disclosure, the width of the plurality of electrode fingers in the edge region may be greater than the width in the central region.

[0012] According to a third aspect of this disclosure, a filter is provided that includes an acoustic wave device according to a first or second aspect of this disclosure.

[0013] According to a fourth aspect of this disclosure, a multiplexer including a filter according to a third aspect of this disclosure is provided. Attached Figure Description

[0014] Figure 1A This is a plan view of the acoustic device according to the first embodiment.

[0015] Figure 1B yes Figure 1A A magnified view of region R in the image.

[0016] Figure 2 It is along Figure 1B The cross-sectional view taken from line AA.

[0017] Figure 3 This is a diagram illustrating the sound speed of the sound wave in the first embodiment.

[0018] Figure 4A and Figure 4B This is a cross-sectional view of the electrode fingers in the first embodiment.

[0019] Figure 5A It is a plan view of the acoustic device based on the first comparative example.

[0020] Figure 5B It is a plan view of the acoustic device based on the second comparative example.

[0021] Figure 6 It is a plan view of the acoustic device based on the third comparative example.

[0022] Figure 7A It is a plan view of the acoustic device based on the fourth comparative example.

[0023] Figure 7B yes Figure 7AA magnified view of region R in the image.

[0024] Figure 8 This is a graph illustrating the waveform curve represented by Equation 2.

[0025] Figure 9A and Figure 9B This is a graph illustrating the experimental results of the absolute value of admittance |Y| relative to frequency.

[0026] Figure 10A and Figure 10B This is a graph illustrating the experimental results of the real part of the admittance, Real(Y), relative to frequency.

[0027] Figure 11A and Figure 11B This is a graph illustrating the experimental results of the reflection coefficient relative to frequency.

[0028] Figure 12A and Figure 12B This is a graph illustrating the experimental results of Q value relative to frequency.

[0029] Figure 13A The figure illustrates the experimental results of ΔY in the second, third, and fourth comparative examples and the first embodiment.

[0030] Figure 13B The electromechanical coupling coefficient k in the second, third, and fourth comparative examples and the first embodiment is exemplified. 2 The experimental results are shown in the figure.

[0031] Figure 14A and Figure 14B This is a graph illustrating the experimental results of the throughput characteristics of the first and second multiplexers.

[0032] Figure 15A This is a diagram illustrating the experimental results of second-order harmonic distortion of the transmit filter in the first multiplexer and the transmit filter in the second multiplexer.

[0033] Figure 15B This is a graph illustrating the experimental results of third-order harmonic distortion of the transmit filter in the first multiplexer and the transmit filter in the second multiplexer.

[0034] Figure 16A This is a plan view of an acoustic wave device according to a first modified example of the first embodiment.

[0035] Figure 16B This is a plan view of the acoustic device according to the second modification of the first embodiment.

[0036] Figure 16C yes Figure 16B A magnified view of region R in the image.

[0037] Figure 17A This is a plan view of an acoustic device according to a third modification of the first embodiment.

[0038] Figure 17B This is a plan view of the acoustic device according to the fourth modified example of the first embodiment.

[0039] Figure 18A This is a circuit diagram of the filter according to the second embodiment.

[0040] Figure 18B This is a circuit diagram of a duplexer based on a modified example of the second embodiment. Detailed Implementation

[0041] However, there is still room for improvement in suppressing stray responses while suppressing the degradation of characteristics. This disclosure was made in view of the above-mentioned problems, and the purpose of this disclosure is to suppress stray responses while suppressing the degradation of characteristics.

[0042] In the following description, embodiments of the present invention will be described with reference to the accompanying drawings.

[0043] [First Implementation Method]

[0044] Figure 1A This is a plan view of the acoustic device 100 according to the first embodiment, and Figure 1B yes Figure 1A A magnified view of region R in the image. Figure 2 It is along Figure 1B The cross-sectional view is taken from line AA. The arrangement direction of electrode fingers 22 is defined as the X direction, the longitudinal direction of electrode fingers 22 is defined as the Y direction, and the stacking direction of substrate 10 and piezoelectric layer 15 is defined as the Z direction. The X, Y, and Z directions do not necessarily correspond to the X-axis direction of the crystal orientation of piezoelectric layer 15. When piezoelectric layer 15 is a rotationally Y-cutting X-propagating piezoelectric layer, the X direction is the X-axis direction of the crystal orientation.

[0045] like Figure 1A , Figure 1B and Figure 2 As shown, a piezoelectric layer 15 is disposed on a substrate 10. A first insulating layer 11 is disposed between the substrate 10 and the piezoelectric layer 15. A second insulating layer 12 is disposed between the first insulating layer 11 and the piezoelectric layer 15. A third insulating layer 13 is disposed between the second insulating layer 12 and the piezoelectric layer 15. A fourth insulating layer 14 is disposed between the third insulating layer 13 and the piezoelectric layer 15.

[0046] The substrate 10 is, for example, a sapphire substrate, alumina substrate, silicon substrate, spinel substrate, crystal substrate, quartz substrate, or silicon carbide substrate. The first insulating layer 11 is a porous insulating layer with numerous 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 alumina layer, silicon nitride layer, aluminum nitride layer, silicon carbide layer, or polycrystalline silicon layer. The first insulating layer 11 and the second insulating layer 12 can be formed from the same material. The sound speed of the bulk wave propagating through the first insulating layer 11 and the second insulating layer 12 is faster than the sound speed of the bulk wave propagating through the third insulating layer 13 and the piezoelectric layer 15. Therefore, the energy of the dominant response sound wave is confined within the piezoelectric layer 15 and the third insulating layer 13.

[0047] The third insulating layer 13 is a temperature-compensating film, and the sign of its temperature coefficient of elastic constant is opposite to that of the temperature coefficient of elastic constant of the piezoelectric layer 15. The third insulating layer 13 is, for example, an undoped or non-doped silicon oxide layer containing additional elements such as fluorine, phosphorus, or boron, and is, for example, polycrystalline or amorphous. This reduces the temperature coefficient of frequency. For the third insulating layer 13 to have temperature compensation functionality, the energy of the acoustic wave in the main response must be present to some extent in the third insulating layer 13. Although the range in which the energy of the surface acoustic wave is concentrated depends on the type of surface acoustic wave, it is typically within a range of about 2.0 λ from the upper surface of the piezoelectric layer 15, and particularly within a range of about 1.0 λ from the upper surface of the piezoelectric layer 15. Therefore, the distance from the lower surface of the third insulating layer 13 to the upper surface of the piezoelectric layer 15 is preferably equal to or less than 2.0 λ, more preferably equal to or less than 1.5 λ, and even more preferably equal to or less than 1.0 λ. The thickness of the piezoelectric layer 15 is preferably 0.1 λ or greater and 1.0 λ or less, and more preferably 0.2 λ or greater and 0.8 λ or less.

[0048] 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 can be, for example, a rotary Y-cut X-propagated lithium tantalate layer or a rotary Y-cut X-propagated lithium niobate layer, for example, a rotary Y-cut X-propagated lithium tantalate layer from 30° to 50°.

[0049] An interdigital transducer (IDT) 20 and a reflector 25 are disposed on a piezoelectric layer 15. The IDT 20 includes a pair of interdigital electrodes 21. Each interdigital electrode 21 includes multiple electrode fingers 22, multiple dummy electrode fingers 23, and a busbar 24, with the electrode fingers 22 and dummy electrode fingers 23 connected to the busbar 24. The tip of the electrode finger 22 of one interdigital electrode 21 faces the tip of the dummy electrode finger 23 of the other interdigital electrode 21. The IDT 20 and the reflector 25 are formed from a metal film 26 on the piezoelectric layer 15. The metal film 26 is a film containing, for example, aluminum, copper, molybdenum, iridium, platinum, rhenium, rhodium, ruthenium, tantalum, or tungsten as a main component. An adhesive film, such as a titanium film or a chromium film, may be included between the metal film 26 and the piezoelectric layer 15 for the IDT 20 and the reflector 25.

[0050] When viewed from above the piezoelectric layer 15 (when viewed from the +Z direction), the side surfaces 50 of the busbars 24 to which the electrode fingers 22 and dummy electrode fingers 23 are connected have a wavy shape. That is, when viewed from the +Z direction, the side surfaces 50 are alternately provided with protrusions 51 and concave portions 52 in the X direction. When viewed from the +Z direction, the side surfaces 50 have, for example, a sinusoidal wave shape. The side surfaces 50 of the busbars 24 of one interdigital electrode 21 and the side surfaces 50 of the busbars 24 of the other interdigital electrode 21 are arranged such that the protrusions 51 face each other in the Y direction and the concave portions 52 face each other in the Y direction. For example, the side surfaces 50 of the busbars 24 of a pair of interdigital electrodes 21 have a wavy shape with the same period and the same amplitude, and the apexes 53 of the protrusions 51 face each other in the Y direction and the lowest points 54 of the concave portions 52 face each other in the Y direction.

[0051] The area where the electrode fingers 22 of a pair of interdigitated 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 interdigitated electrodes 21 face each other such that the electrode fingers 22 are substantially staggered in the X direction in at least a portion of the intersection region 30. The dominant mode acoustic wave (surface acoustic wave) excited by the electrode fingers 22 in the intersection region 30 propagates primarily in the X direction. The spacing of the electrode fingers 22 of the interdigitated electrodes 21 is substantially equal to the wavelength λ of the surface acoustic wave. The wavelength λ is substantially twice the average spacing D of the plurality of electrode fingers 22. The average spacing 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.

[0052] The cross region 30 includes an edge region 32 located at the edge in the Y direction, and a central region 31 located within the edge region 32 in the Y direction. The edge region 32 can also be described as the region where the tips of the electrode fingers 22 are located in the cross region 30. The region between the tip of the electrode finger 22 of one interdigitated electrode 21 and the tip of the dummy electrode finger 23 of another interdigitated electrode 21 is the gap region 33. The region where the dummy electrode finger 23 is located is the dummy region 34. The region where the busbar 24 is located is the busbar region 35.

[0053] A gap region 33 is arranged along the X direction, located between the tip of the electrode finger 22 of one of the interdigitated electrodes 21 and the tip of the dummy electrode finger 23 of the other interdigitated electrode 21. In other words, the gap region 33 is positioned on a straight line extending along the X direction. The length (aperture length) of the cross region 30 in the Y direction is substantially constant in the X direction. Since the side surface 50 of the busbar 24 has a wavy shape when viewed from the +Z direction, the length of the dummy electrode finger 23 in the Y direction is modulated along the X direction. That is, the dummy electrode finger 23 gradually shortens from the top 53 of the protrusion 51 of 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 along the X direction. When the dummy electrode finger 23 is not inserted between the electrode finger 22 and the protrusion 51 of the side surface 50 of the busbar 24, at least one of the plurality of electrode fingers 22 faces the protrusion 51 of the side surface 50 of the busbar 24.

[0054] A protective film 16 is disposed on the piezoelectric layer 15 to cover the IDT 20 and the reflector 25. Figure 1A and Figure 1B The protective film 16 is not shown in the diagram. The protective film 16 is an insulating film, such as a silicon oxide film. A load film 40 is disposed on the protective film 16 from a portion of the edge region 32 to the gap region 33, so as to cover the tip of the electrode finger 22 in the edge region 32. For example, the load film 40 is disposed in a strip shape along the X direction. The load film 40 is not disposed in the central region 31, the remainder of the gap region 33, the dummy region 34, and the busbar region 35. The load film 40 may be disposed only in the edge region 32, and not in the gap region 33. The load film 40 is, for example, an insulating film containing silicon oxide, tantalum oxide, or niobium oxide as the main component, or a metal film containing aluminum or titanium as the main component. The load film 40 may be a single-layer film or a multi-layer film containing another material as the main component, as long as the sound velocity of the sound waves propagating through the edge region 32 is adjustable.

[0055] Here, in order for a membrane to contain a certain element as its main component, the membrane may contain impurities, whether intentionally or unintentionally introduced in addition to the main component. When an element is the main component in a membrane, the density of that element is, for example, 50 atomic percent or more, and for example, 80 atomic percent or more. In the case where the main component is two or more elements (such as silicon oxide), the total density 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.

[0056] [Speed ​​of sound]

[0057] Figure 3 This is a diagram illustrating the speed of sound of the sound wave in the first embodiment. For example... Figure 3 As shown, since the load membrane 40 is disposed in the edge region 32, the sound speed of the sound wave propagating through the edge region 32 is slower than that of the sound wave propagating through the central region 31. Since the number of electrode fingers 22 in the gap region 33 is less than the number of electrode fingers 22 in the central region 31, the sound speed of the sound wave propagating through the gap region 33 is faster than that of the sound wave propagating through the central region 31. The sound speed of the sound wave propagating through the dummy region 34 is essentially the same as that of the sound wave propagating through the central region 31. The sound speed of the sound wave propagating through the busbar region 35 is faster than that of the sound wave propagating through the central region 31. The edge region 32 is a low-speed region where the sound wave speed is slower than that of the central region 31, and the gap region 33 is a high-speed region where the sound wave speed is faster than that of the central region 31, thus enabling a piston mode.

[0058] The speed of sound can be obtained, for example, by Equation 1. In Equation 1, V is the speed of sound, ρ is the density, E is Young's modulus, and v is Poisson's ratio.

[0059] [Formula 1]

[0060]

[0061] To achieve the piston mode, preferably, the lengths of the central region 31 and the edge regions 32 in the Y direction satisfy a specific relationship. For example, the length of the central region 31 in the Y direction is preferably longer than the total length of the edge regions 32 in the Y direction. The length of each of the edge regions 32 in the Y direction is preferably 1.0λ or less, and more preferably 0.5λ or less. The length of each of the edge regions 32 in the Y direction is preferably 0.05λ or more, and more preferably 0.1λ or more. The edge regions 32 may be located on only one side of the central region 31. The length of each of the gap regions 33 in the Y direction is preferably 1.5λ or less, and more preferably 1.0λ or less. The length of each of the gap regions 33 in the Y direction is preferably 0.1λ or more, and more preferably 0.2λ or more.

[0062] Figure 4A and Figure 4B This is a cross-sectional view of electrode finger 22 in the first embodiment. Figure 4A It is a cross-sectional view of electrode 22 in the central region 31 in the X direction, and Figure 4B This is a cross-sectional view of electrode finger 22 in the edge region 32 along the X direction. An example is given where electrode finger 22 is a stacked film containing metal films 28a and 28b, but electrode finger 22 can be a single-layer film. Figure 4A and Figure 4B As shown, the width and height of the electrode finger 22 in the central region 31 are basically the same as the width and height of the electrode finger 22 in the edge region 32, and the thickness of the protective film 16 in the central region 31 is also basically the same as the thickness of the protective film 16 in the edge region 32.

[0063] like Figure 4A As shown, the cross-sectional area of ​​the metal film 28a is denoted as S1, the cross-sectional area of ​​the metal film 28b is denoted as S2, and the cross-sectional area of ​​the protective film 16 on the electrode finger 22 is denoted as S3. The densities of the main components of the metal film 28a, metal film 28b, and protective film 16 are denoted as ρ1, ρ2, and ρ3, respectively. In this case, the weight per unit length in the Y direction obtained by multiplying the cross-sectional area of ​​the metal film 28a by its density is S1×ρ1, the weight per unit length in the Y direction obtained by multiplying the cross-sectional area of ​​the metal film 28b by its density is S2×ρ2, and the weight per unit length in the Y direction obtained by multiplying the cross-sectional area of ​​the protective film 16 by its density is S3×ρ3. Therefore, the weight per unit length in the Y direction of the metal film including the electrode finger 22 disposed on the piezoelectric layer 15 at the location where the electrode finger 22 is disposed (referred to as the first weight) is S1×ρ1 + S2×ρ2 + S3×ρ3.

[0064] like Figure 4BAs shown, in the edge region 32, in addition to the protective film 16, a load film 40 is also provided on the electrode finger 22. The cross-sectional area of ​​the load film 40 on the electrode finger 22 is denoted as S4. The density of the constituent material of the main component of the load film 40 is denoted as ρ4. In this case, the weight per unit length in the Y direction obtained by multiplying the cross-sectional area of ​​the load film 40 by the density is S4×ρ4. Therefore, the weight per unit length in the Y direction of the metal film including the electrode finger 22 provided on the piezoelectric layer 15 at the location where the electrode finger 22 is provided (referred to as the second weight) is S1×ρ1+S2×ρ2+S3×ρ3+S4×ρ4. Therefore, the second weight is greater than the first weight.

[0065] like Figure 3 As shown, since the second weight is greater than the first weight, the sound speed of the sound wave propagating through the edge region 32 is slower than the sound speed of the sound wave propagating through the central region 31. Therefore, a piston mode can be achieved. In this way, by observing the cross-section of the electrode finger 22 in the central region 31 and the edge region 32, the weight per unit length of the film disposed on the piezoelectric layer 15 at the location where the electrode finger 22 is disposed can be obtained from the cross-sectional area and density of the constituent material.

[0066] [Manufacturing Method]

[0067] A method for manufacturing 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 sequentially formed 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 using, for example, a sputtering method, a chemical vapor deposition (CVD) method, or a vacuum evaporation method. 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 have a desired thickness using, for example, a chemical mechanical polishing (CMP) method.

[0068] Next, after forming a metal film 26 on the piezoelectric layer 15, the metal film 26 is patterned into a desired shape. This forms an IDT 20 and a reflector 25 on the piezoelectric layer 15. The metal film 26 is formed by, for example, sputtering, CVD, or vacuum evaporation. The patterning of the metal film 26 is performed by, for example, photolithography and etching. Next, a protective film 16 is formed on the piezoelectric layer 15 to cover the IDT 20 and the reflector 25. The protective film 16 is formed by, for example, sputtering, CVD, or vacuum deposition.

[0069] Next, a load film 40 covering the tip of the electrode finger 22 is formed on the protective film 16 from a portion of the edge region 32 to the gap region 33. The load film 40 is formed by, for example, forming a mask layer with openings in the edge region 32 and the gap region 33 on the protective film 16, then using the mask layer as a mask, and then removing the mask layer. The mask layer is formed from, for example, photoresist. The load film 40 is formed by, for example, a sputtering method, a CVD method, or a vacuum deposition method. Thus, the acoustic wave device 100 according to the first embodiment is formed.

[0070] [Experiment 1]

[0071] The acoustic wave devices of the first comparative example, second comparative example, third comparative example, fourth comparative example, and first embodiment were manufactured and their characteristics were evaluated. The structures of the acoustic wave devices of the first comparative example, second comparative example, third comparative example, and fourth comparative example are illustrated below.

[0072] Figure 5A It is a plan view of the acoustic device 500 based on the first comparative example. Figure 5B It is a plan view of the acoustic device 600 according to the second comparative example. Figure 5A and Figure 5B Is with Figure 1B A floor plan of the corresponding section. For example... Figure 5A As shown, in the first comparative example, when viewed from the +Z direction, the side surface 50 of the busbar 24 has a linear shape. 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 busbar 24 and the tips of the electrode fingers 22 is the gap region 33. The lengths of the plurality of electrode fingers 22 in the Y direction are substantially the same as each other. No load film 40 is provided in the edge region 32. The other configurations are the same as those in the first embodiment, and therefore their description will be omitted. As described above, in the first comparative example, no load film 40 is provided in the edge region 32, therefore the piston mode is not implemented.

[0073] like Figure 5B As shown, in the second comparative example, similar to the first comparative example, when viewed from the +Z direction, the side surface 50 of the busbar 24 is linear, there are no dummy electrode fingers connected to the busbar 24, and the tips of the electrode fingers 22 face the busbar 24. The second comparative example differs from the first comparative example in that a load film 40 is provided from the edge region 32 to the gap region 33. Other configurations are the same as in the first embodiment, and therefore their description will be omitted. In the second comparative example, the load film 40 is provided in the edge region 32, thus enabling a piston-like configuration.

[0074] Figure 6This is a plan view of the acoustic device 700 based on the third comparative example. For example... Figure 6 As shown, in the third comparative example, 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 to each other via a metal film 44. A plurality of electrode fingers 22 and a plurality of dummy electrode fingers 23 are connected to the side surface 45 of the first busbar 42. When viewed from the +Z direction, the side surface 45 of the first busbar 42 has a linear shape. The lengths of the plurality of electrode fingers 22 in the Y direction are substantially the same as each other, and the lengths of the plurality of dummy electrode fingers 23 in the Y direction are also substantially the same as each other. Other configurations are the same as those in the first embodiment, and therefore their description will be omitted. Also in the third comparative example, a load film 40 is provided in the edge region 32, thus enabling a piston mode.

[0075] Figure 7A It is based on the plan view of the acoustic device 800 in the fourth comparative example, and Figure 7B yes Figure 7A A magnified view of region R in the image. (See image below.) Figure 7A and Figure 7B As shown, in the fourth comparative example, when viewed from the +Z direction, the side surface 50 of the busbar 24 has a linear shape. The lengths of the plurality of electrode fingers 22 in the Y direction and the lengths of the plurality of dummy electrode fingers 23 in the Y direction are modulated along the X direction. Therefore, a pair of interdigitated electrodes 21 have a toe-like structure in which the length of the intersecting region 30 in the Y direction is modulated along the X direction. Other configurations are the same as those in the first embodiment, and therefore their description will be omitted. Also in the fourth comparative example, a load film 40 is provided in the edge region 32, thus enabling a piston mode.

[0076] The acoustic wave devices of the first comparative example, the second comparative example, the third comparative example, the fourth comparative example, and the first embodiment are manufactured under the following manufacturing conditions.

[0077] General manufacturing conditions

[0078] Substrate 10: Sapphire substrate

[0079] First insulating layer 11: an aluminum oxide layer with a thickness of 1.8 μm

[0080] Second insulating layer 12: an aluminum oxide layer with a thickness of 6.17 μm.

[0081] Third insulating layer 13: a silicon oxide layer with a thickness of 0.44 μm.

[0082] Fourth insulating layer 14: A layer of aluminum oxynitride with a thickness of 0.01 μm

[0083] Piezoelectric layer 15: A 0.66 μm thick lithium tantalate layer with 48° rotational Y-cutting and X-propagation.

[0084] Protective film 16: Silicon oxide layer with a thickness of 15 nm

[0085] IDT 20 and Reflector 25: A laminate of a 35 nm thick titanium layer and a 129 nm thick aluminum layer.

[0086] Number of electrode pairs: 136

[0087] IDT 20 duty cycle: 55%

[0088] The wavelength λ of surface acoustic waves is 2.2 μm.

[0089] Manufacturing conditions of the acoustic device in the first comparative example

[0090] Aperture length: 12.5 λ

[0091] The length of edge region 32 in the Y direction: 0.4λ

[0092] The length of gap region 33 in the Y direction: 0.3 λ

[0093] Manufacturing conditions of the acoustic device in the second comparative example

[0094] Supported film 40: A silicon oxide layer with a thickness of 60 nm

[0095] Aperture length: 12.5 λ

[0096] The length of edge region 32 in the Y direction: 0.4λ

[0097] The length of gap region 33 in the Y direction: 0.3 λ

[0098] The length of the loaded membrane 40 extending into the gap region 33: 0.15 λ

[0099] Manufacturing conditions of the acoustic device in the third comparative example

[0100] Supported film 40: A silicon oxide layer with a thickness of 60 nm

[0101] Aperture length: 12.5 λ

[0102] The length of edge region 32 in the Y direction: 0.4λ

[0103] The length of gap region 33 in the Y direction: 0.3 λ

[0104] The length of the dummy region 34 in the Y direction is 0.5λ.

[0105] The length of the loaded membrane 40 extending into the gap region 33: 0.15 λ

[0106] The length of the first busbar 42 in the Y direction is 0.3 λ.

[0107] The spacing between the first bus bar 42 and the second bus bar 43: 0.9 λ

[0108] Manufacturing conditions of the acoustic device in the fourth comparative example

[0109] Supported film 40: A silicon oxide layer with a thickness of 60 nm

[0110] Maximum aperture length: 12.5 λ

[0111] The longest dummy electrode refers to the length of 23 in the Y direction: 1.0 λ

[0112] Number of waves in cross region 30: 6

[0113] The length of edge region 32 in the Y direction: 0.4λ

[0114] The length of gap region 33 in the Y direction: 0.3 λ

[0115] The length of the loaded membrane 40 extending into the gap region 33: 0.15 λ

[0116] Manufacturing conditions of the acoustic wave device in the first embodiment

[0117] Supported film 40: A silicon oxide layer with a thickness of 60 nm

[0118] Aperture length: 12.5 λ

[0119] The longest dummy electrode refers to the length of 23 in the Y direction: 1.0 λ

[0120] Number of waves on the side surface 50 of the busbar 24: 6

[0121] The length of edge region 32 in the Y direction: 0.4λ

[0122] The length of gap region 33 in the Y direction: 0.3 λ

[0123] The length of the loaded membrane 40 extending into the gap region 33: 0.15 λ

[0124] The side surface 50 of the busbar 24 is formed in a wave shape, approximately as represented by Equation 2 below. In Equation 2, Wn is the number of waves on the side surface 50, and in the first embodiment, it is six. The symbol "n" indicates the nth electrode finger from one end in the X direction. Lp is the number of pairs of electrode fingers 22, and in the first embodiment, it is 136 pairs. Ld is the length of the longest dummy electrode finger 23 in the Y direction, and in the first embodiment, it is 2.2 μm. Figure 8 This is a graph illustrating the waveform curve represented by Equation 2. In Figure 8 In the middle, the shaded area corresponds to the area of ​​busbar 24.

[0125] [Equation 2]

[0126]

[0127] Figure 9A and Figure 9B This is a graph illustrating the experimental results of the absolute value of admittance |Y| relative to frequency. Figure 10A and Figure 10B This is a graph illustrating the experimental results of the real part of the admittance, Real(Y), relative to frequency. Figure 9A and Figure 10A The experimental results of the first and second comparative examples are illustrated, and Figure 9B and Figure 10B Experimental results for the third comparative example, the fourth comparative example, and the first embodiment are illustrated. Peak values ​​of the resonant frequency fr and the anti-resonant frequency fa are observed in the absolute value of the admittance |Y|. In the real part of the admittance, Real(Y), a stray response greater than that in the absolute value |Y| is observed.

[0128] like Figure 9A and Figure 10A As shown, in the first comparative example, a large spurious response occurs between the resonant frequency fr and the anti-resonant frequency fa. However, compared to the first comparative example, in the second comparative example with the load film 40 applied, the spurious response is suppressed. Nevertheless, a slight spurious response occurs near 1776 MHz in the second comparative example. Figure 9B and Figure 10B As shown, in the third comparative example, the fourth comparative example, and the first embodiment, spurious responses were suppressed in the range from the resonant frequency fr to the anti-resonant frequency fa. Spurious responses near 1776 MHz were also suppressed.

[0129] Figure 11A and Figure 11B This is a graph illustrating the experimental results of the reflection coefficient relative to frequency. Figure 11A The experimental results of the first and second comparative examples are illustrated, and Figure 11B Experimental results from the third comparative example, the fourth comparative example, and the first embodiment are illustrated. Figure 11A As shown, in the first comparative example, a large spurious response was generated in the vicinity of 1728 MHz to 1776 MHz, while in the second comparative example, the spurious response was suppressed. Figure 11BAs shown, in the third comparative example, the fourth comparative example, and the first embodiment, spurious response is suppressed, and in particular, compared with the second comparative example, spurious response near 1776 MHz is suppressed and reflection coefficient is improved. Therefore, as Figure 10A and Figure 10B As shown, it is believed that, compared with the second comparative example, the spurious response near 1776MHz is suppressed in the third comparative example, the fourth comparative example, and the first embodiment.

[0130] Figure 12A and Figure 12B This is a graph illustrating the experimental results of Q value relative to frequency. Figure 12A The experimental results of the first and second comparative examples are illustrated, and Figure 12B Experimental results from the third comparative example, the fourth comparative example, and the first embodiment are illustrated. Figure 12A and Figure 12B As shown, in the range of 1728 MHz to 1776 MHz, the Q values ​​of the second comparative example, the third comparative example, and the first embodiment are almost identical to each other, while the Q value of the fourth comparative example deteriorates.

[0131] Based on the experimental results described above, as shown in the second, third, fourth, and first comparative examples, by providing a load film 40 in the edge region 32 to achieve a piston mode, spurious responses in the range from the resonant frequency fr to the anti-resonant frequency fa can be suppressed. Compared to the second comparative example, the configurations in the third, fourth, and first comparative examples can further reduce spurious responses. In the first embodiment, since the length of the dummy electrode finger 23 in the Y direction is modulated along the X direction, the configuration of the dummy electrode finger 23 is similar to the configuration of the dummy electrode finger 23 with a toe-like structure in the fourth comparative example, and therefore, it is considered that the spurious response is suppressed similarly to that in the fourth comparative example.

[0132] However, although the stray response was suppressed in the fourth comparative example, the Q value deteriorated compared to the first embodiment. The reason for the Q value deterioration in the fourth comparative example is believed to be the provision of the apodized structure and the modulation of the length of the cross region 30 in the Y direction along the X direction, thus adversely affecting the propagation of the main mode acoustic wave.

[0133] Figure 13A The figure illustrates the experimental results of ΔY in the second, third, and fourth comparative examples and the first embodiment. Figure 13B The electromechanical coupling coefficient k in the second, third, and fourth comparative examples and the first embodiment is exemplified. 2The experimental results are shown in the figure. Three acoustic devices were fabricated for each of the second, third, fourth, and first embodiments, and the ΔY and electromechanical coupling coefficient k were evaluated. 2 ΔY is the difference between the absolute value of the admittance |Y| at the resonant frequency fr and the absolute value of the admittance |Y| at the anti-resonant frequency fa. The electrical coupling coefficient k is calculated using the following equation (3). 2 In Equation 3, fr is the resonant frequency, and fa is the anti-resonant frequency.

[0134] [Formula 3]

[0135]

[0136] like Figure 13A As shown, ΔY in the first embodiment is greater than ΔY in the third and fourth comparison examples, and is substantially the same as ΔY in the second comparison example. Figure 13B As shown, the electromechanical coupling coefficient k in the first embodiment 2 The electromechanical coupling coefficient k is greater than that of the fourth comparison example. 2 Furthermore, the electromechanical coupling coefficient k of the first embodiment 2 Electromechanical coupling coefficient k compared with the second and third comparative examples 2 They are basically the same.

[0137] The experimental results above show that the first embodiment can suppress the Q value, ΔY, and electromechanical coupling coefficient k. 2 This suppresses stray responses while mitigating the degradation of the properties. Since the experimental results of the first embodiment described above were obtained when the value of Lp / Wn in Formula 2 was 22.7, from the perspective of suppressing the degradation of properties while suppressing stray responses, the value of Lp / Wn is preferably 20 or greater and 25 or less, more preferably 21 or greater and 24 or less, and even more preferably 22 or greater and 23 or less.

[0138] [Experiment 2]

[0139] A first multiplexer was fabricated using the acoustic wave device of the first embodiment as the series resonator and parallel resonator of the transmitting filter, and the acoustic wave device of the second comparative example as the series resonator and parallel resonator of the receiving filter. A second multiplexer was fabricated using the acoustic wave device of the second comparative example as the series resonator and parallel resonator of the transmitting and receiving filters. The throughput characteristics of the first and second multiplexers were evaluated.

[0140] Figure 14A and Figure 14B This is a graph illustrating the experimental results of the pass-through characteristics (Band3) of the first and second multiplexers. Figure 14B yes Figure 14AA magnified view of the transmit band (1710 MHz to 1785 MHz). The receive band is 1805 MHz to 1880 MHz. Figure 14A and Figure 14B As shown, compared to the second multiplexer on the high-frequency side of the transmission band (around 1760 MHz to 1780 MHz), the first multiplexer reduces or prevents spurious responses.

[0141] The reason why spurious responses are suppressed in the first multiplexer compared to the second multiplexer is considered below. The acoustic device of the second comparative example is used as the transmit filter in the second multiplexer, while the acoustic device of the first embodiment is used as the transmit filter in the first multiplexer. Figure 10A and Figure 10B As shown, compared to the acoustic device of the second comparative example, the spurious response near 1776 MHz is suppressed in the acoustic device of the first embodiment. Therefore, compared to the second multiplexer, it is considered that the spurious response on the high-frequency side of the transmission band (around 1770 MHz to 1780 MHz) is suppressed in the first multiplexer.

[0142] Figure 15A This is a diagram illustrating the experimental results of second-order harmonic distortion of the transmit filter in the first multiplexer and the transmit filter in the second multiplexer. Figure 15B This is a graph illustrating the experimental results of third-order harmonic distortion of the transmit filter in the first multiplexer and the transmit filter in the second multiplexer. (See figure.) Figure 15A As shown, compared to the transmit filter of the second multiplexer, the transmit filter of the first multiplexer exhibits an improvement of approximately 4.7 dB in the second harmonic near 3555 MHz. Figure 15B As shown, the transmit filter of the first multiplexer has an improvement of about 5.7 dB in the third harmonic near 5350 MHz compared to the transmit filter of the second multiplexer.

[0143] The reason why the second and third harmonics in the transmit filter of the first multiplexer are improved compared to the transmit filter of the second multiplexer is related to the reference. Figure 14A and Figure 14B The reasons described are the same. That is, compared with the acoustic device of the second comparative example used in the transmit filter of the second multiplexer, the acoustic device of the first embodiment used in the transmit filter of the first multiplexer suppresses spurious responses around 1776 MHz. Therefore, it is considered that the second harmonic around 3555 MHz and the third harmonic around 5350 MHz in the transmit filter of the first multiplexer are improved compared with the transmit filter of the second multiplexer.

[0144] [Modified Example]

[0145] Figure 16A This is a plan view of the acoustic device 110 according to a first modification of the first embodiment. In the first embodiment, as... Figure 1A As shown, when viewed from the +Z direction, the side surface 50 to which the electrode fingers 22 and dummy electrode fingers 23 of the busbar 24 are connected has a wavy shape, while when viewed from the +Z direction, the side surface of the busbar 24 opposite to the side surface 50 has a linear shape. In the first modification of the first embodiment, as... Figure 16A As shown, when viewed from the +Z direction, both the side surface 50 and the side surface 55 opposite to the side surface 50 in the busbar 24 have a wavy shape. As described above, when viewed from the +Z direction, the boundary between the busbar 24 and the wiring 27 is not limited to a linear shape and can have a wavy shape. When the side surfaces 50 and 55 have a wavy shape, they can have a wavy shape containing the same period and the same amplitude. Other configurations of the first modification are the same as those of the first embodiment, and therefore their description will be omitted.

[0146] Figure 16B This is a plan view of the acoustic device 120 according to the second modification of the first embodiment, and Figure 16C yes Figure 16B A magnified view of region R in the image. Figure 16B Is with Figure 1B A plan view of the corresponding parts. In the first embodiment, as... Figure 1B As shown, when viewed from the +Z direction, the side surface 50 of the busbar 24 between electrode finger 22 and dummy electrode finger 23 has a curved shape. In the second modification of the first embodiment, as... Figure 16B and Figure 16C As shown, when viewed from the +Z direction, the side surface 50 of the busbar 24 between the electrode finger 22 and the dummy electrode finger 23 can have a linear shape extending in the X direction. The other configurations of the second modification are the same as those of the first embodiment, and therefore their description will be omitted. Even when the side surface 50 of the busbar 24 between the electrode finger 22 and the dummy electrode finger 23 is linear as in the second modification, the side surface 50 as a whole can be described as having a sinusoidal wave shape.

[0147] Figure 17A This is a plan view of the acoustic device 130 according to the third modification of the first embodiment. Figure 17A Is with Figure 1B A floor plan of the corresponding section. For example... Figure 17AAs shown, in the third modification of the first embodiment, the load film 40 is located only on the electrode fingers 22 and not between the electrode fingers 22. That is, in the first embodiment, the load film 40 is arranged in a strip shape, while in the third modification of the first embodiment, the load film 40 is arranged in a dot shape. The other configurations of the third modification are the same as those of the first embodiment, so their description will be omitted.

[0148] Figure 17B This is a plan view of the acoustic device 140 according to the fourth modified example of the first embodiment. Figure 17B Is with Figure 1B A floor plan of the corresponding section. For example... Figure 17B As shown, in the fourth modification of the first embodiment, the load film 40 is not provided in the edge region 32. Instead, the width W2 of the electrode finger 22 in the edge region 32 is greater than the width W1 of the electrode finger 22 in the central region 31. The other configurations of the fourth modification are the same as those of the first embodiment, and therefore their description will be omitted.

[0149] In the third and fourth modifications of the first embodiment, at the location of the electrode finger 22, the weight per unit length of the single-layer or multi-layer film including the metal layer of the electrode finger 22 disposed on the piezoelectric layer 15 in the Y direction is configured such that the second weight in the edge region 32 is greater than the first weight in the central region 31. Therefore, the sound speed of the sound wave propagating through the edge region 32 is slower than the sound speed of the sound wave propagating through the central region 31.

[0150] In the first embodiment and its modifications, such as Figure 4A and Figure 4B As shown, at the location of electrode finger 22, the weight per unit length of the single-layer or multi-layer metal film including electrode finger 22 disposed on the piezoelectric layer 15 is greater in the edge region 32 than in the central region 31. That is, as Figure 3 As shown, the sound wave propagating through the edge region 32 travels at a slower speed than the sound wave propagating through the central region 31. This allows for a piston mode to be achieved. In this case, as... Figure 1A and Figure 1B As shown, when viewed from the +Z direction, the side surface 50 of the busbar 24 to which the electrode finger 22 and the dummy electrode finger 23 are connected is formed in a wavy shape, and the gap region 33 is arranged side by side along the X direction. Therefore, the configuration of the busbar 24 is similar to a toe-shaped structure in which the length of the dummy electrode finger 23 in the Y direction is modulated along the X direction, thus allowing it to be... Figure 10B This suppresses stray response. Furthermore, the gap regions 33 are arranged side-by-side along the X direction, thus suppressing the change in the length (aperture length) of the cross region 30 in the Y direction along the X direction. Therefore, as shown... Figure 12B , Figure 13A and Figure 13B As shown, factors such as Q-value, ΔY, and electromechanical coupling coefficient k can be suppressed. 2 The characteristics deteriorate. Therefore, the first embodiment and its modifications can suppress stray responses while suppressing the deterioration of characteristics.

[0151] According to the first embodiment and its modifications, such as Figure 1A As shown, the side surfaces 50 of the busbar 24 of the pair of interdigital electrodes 21 change with the same period and the same amplitude. Thus, as... Figure 10B , Figure 12B , Figure 13A and Figure 13B As shown, stray responses can be suppressed while suppressing the degradation of the suppressive properties.

[0152] Furthermore, according to the first embodiment and its modifications, such as Figure 1A As shown, the side surfaces 50 of the busbar 24 of the pair of interdigitated electrodes 21 are arranged such that, when viewed from the +Z direction, the protrusions 51 face each other and the concave portions 52 face each other. Thus, as... Figure 10B , Figure 12B , Figure 13A and Figure 13B As shown, stray responses can be suppressed while suppressing the degradation of the suppressive properties.

[0153] In the first embodiment and its modifications, such as Figure 1A As shown, when viewed from the +Z direction, the side surface 50 of the busbar 24 has a sinusoidal wave shape. Therefore, as... Figure 10B , Figure 12B , Figure 13A and Figure 13B As shown, stray responses can be suppressed while suppressing the degradation of the suppressive properties.

[0154] In the first embodiment and its modifications, such as Figure 1B As shown, the length (aperture length) of the intersection region 30 in the Y direction is constant along the X direction. Therefore, as... Figure 12B , Figure 13A and Figure 13B As shown, this can suppress the degradation of characteristics. The constant length of the cross region 30 means that length differences due to manufacturing errors are permissible.

[0155] In the first embodiment, such as Figure 1B As shown, a load film 40 is disposed on the electrode finger 22 in the edge region 32, but no load film 40 is disposed in the central region 31. The load film 40 is disposed such that the second weight in the edge region 32 is greater than the first weight in the central region 31. Therefore, the sound speed of the sound wave in the edge region 32 is slower than the sound speed of the sound wave in the central region 31, thereby enabling a piston mode. The load film 40 can be as follows... Figure 1B As shown, it is arranged in a strip shape in the X direction in the edge region 32, or it can be as follows: Figure 17A As shown, the electrode fingers 22 are arranged in a dot shape in the edge region 32.

[0156] In the fourth modification of the first embodiment, such as Figure 17B As shown, the width W2 of the plurality of electrode fingers 22 in the edge region 32 is greater than the width W1 of the plurality of electrode fingers 22 in the central region 31. Therefore, the second weight in the edge region 32 is greater than the first weight in the central region 31. Therefore, the sound speed of the sound wave in the edge region 32 is slower than the sound speed of the sound wave in the central region 31, thereby enabling the piston mode.

[0157] By providing a load film 40 on the electrode finger 22 in the edge region 32 and increasing the width of the electrode finger 22 in the edge region 32, the sound speed of the sound wave in the edge region 32 can be made slower than the sound speed of the sound wave in the central region 31.

[0158] [Second Implementation]

[0159] Figure 18A This is a circuit diagram of the filter 200 according to the second embodiment. (e.g.) Figure 18A As shown, one or more series resonators S1 to S4 are connected in series between terminals Tin and Tout. One or more parallel resonators P1 to P3 are connected in parallel between terminals Tin and Tout. The acoustic wave device of the first embodiment and its modifications can be used for at least one of the series resonators S1 to S4 and the parallel resonators P1 to P3. The number of series resonators and parallel resonators can be suitably set. Although a trapezoidal filter is illustrated as an example of a filter, the filter can be a multimode filter.

[0160] Figure 18B This is a circuit diagram of a duplexer 210 according to a modified example of the second embodiment. For example... Figure 18B As shown, a transmit filter 60 is connected between a common terminal Ant and a transmit terminal Tx. A receive filter 61 is connected between a common terminal Ant and a receive terminal Rx. The transmit filter 60 transmits a signal from the transmit band of the high-frequency signal input from the transmit terminal Tx to the common terminal Ant as a transmit signal, and suppresses signals with frequencies outside the transmit band. The receive filter 61 transmits a signal from the receive band of the high-frequency signal input from the common terminal Ant to the receive terminal Rx as a receive signal, and suppresses signals with frequencies outside the receive band. At least one of the transmit filter 60 and the receive filter 61 can be a filter of the second embodiment. Although the duplexer is illustrated as an example of a multiplexer, a tripplexer or a quadplexer can be used.

[0161] Although embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the specific embodiments, and various changes, substitutions and modifications can be made thereto without departing from the spirit and scope of the present disclosure.

Claims

1. An acoustic wave device, the acoustic wave device comprising: piezoelectric layer; as well as A pair of interdigitated electrodes disposed on the piezoelectric layer; Each of the interdigitated electrodes includes a plurality of electrode fingers, a plurality of dummy electrode fingers, and a busbar, wherein the busbar has a side surface to which the plurality of electrode fingers and the plurality of dummy electrode fingers are connected. When viewed from above the piezoelectric layer, the side surface of the busbar has a wavy shape. The pair of interdigitated electrodes includes multiple gap regions between the tips of the plurality of electrode fingers and the tips of the plurality of dummy electrode fingers, as well as intersection regions where the plurality of electrode fingers intersect each other. The plurality of gap regions are arranged along the arrangement direction of the plurality of electrode fingers. The intersection region includes an edge region located at the edge of the plurality of electrode fingers in the longitudinal direction and a central region located within the edge region. In the longitudinal direction, the weight per unit length of the single-layer or multi-layer film, including the metal film of the multiple electrode fingers, disposed on the piezoelectric layer at each of the multiple electrode fingers is greater in the edge region than in the central region.

2. An acoustic wave device, the acoustic wave device comprising: piezoelectric layer; as well as A pair of interdigitated electrodes disposed on the piezoelectric layer; Each of the interdigitated electrodes includes a plurality of electrode fingers, a plurality of dummy electrode fingers, and a busbar, wherein the busbar has a side surface to which the plurality of electrode fingers and the plurality of dummy electrode fingers are connected. When viewed from above the piezoelectric layer, the side surface of the busbar has a wavy shape. The pair of interdigitated electrodes includes multiple gap regions between the tips of the plurality of electrode fingers and the tips of the plurality of dummy electrode fingers, as well as intersection regions where the plurality of electrode fingers intersect each other. The plurality of gap regions are arranged along the arrangement direction of the plurality of electrode fingers. The intersection region includes an edge region located at the edge of the plurality of electrode fingers in the longitudinal direction and a central region located within the edge region. The sound waves propagating through the edge region travel at a slower speed than the sound waves propagating through the central region.

3. The acoustic device according to claim 1 or 2, in, The side surfaces of the busbars of the pair of interdigitated electrodes change with the same period and the same amplitude.

4. The acoustic device according to claim 1 or 2, in, When viewed from above the piezoelectric layer, the side surfaces of the busbars of the pair of interdigitated electrodes have protrusions facing each other and concave portions facing each other.

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

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

7. The acoustic device according to claim 1 or 2, in, The value obtained by dividing the number of pairs of electrodes by the number of protrusions on the side surface of the busbar is 20 or greater and 25 or less.

8. The acoustic wave device according to claim 1 or 2, further comprising a load film disposed on the plurality of electrode fingers in the edge region and not disposed in the central region.

9. The acoustic device according to claim 1 or 2, in, The plurality of electrodes are defined as having a width in the edge region that is greater than its width in the central region.

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

11. A multiplexer comprising the filter of claim 10.

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