Elastic wave device

Abstract

An elastic wave filter (1) has a longitudinal coupling type resonator (10) having a multilayer substrate (50) and a plurality of IDT electrodes (11-17), the multilayer substrate (50) includes a piezoelectric layer (51) having main surfaces (51a and 51b) facing each other and the plurality of IDT electrodes (11-17) disposed on the main surface (51a), and a metal layer (52) bonded to the main surface (51b) of the piezoelectric layer (51), and the plurality of IDT electrodes (11-17) each includes a plurality of electrode fingers disposed in parallel to each other, and in a case where the main surfaces (51a and 51b) are viewed in plan, the metal layer (52) is disposed so as to span adjacent electrode fingers included in one of the plurality of IDT electrodes (11-17).

Description

Technical Field

[0001] This invention relates to elastic wave devices. Background Technology

[0002] Patent Document 1 discloses a surface acoustic wave (SAW) filter comprising a longitudinally coupled resonator using a substrate with a stacked structure of a piezoelectric film, a low-velocity acoustic film, a high-velocity acoustic film, and a support substrate. By placing a metal film between the high-velocity acoustic film and the support substrate, the fractional bandwidth of the SAW filter can be reduced.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2015-109622 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] However, in the case of the surface acoustic wave filter disclosed in Patent Document 1, there is a problem that the attenuation characteristics deteriorate due to the useless electric field distribution generated in the piezoelectric film.

[0008] Therefore, the present invention was made to solve the above-mentioned problems, and its object is to provide an elastic wave device with a longitudinally coupled resonator that suppresses the degradation of attenuation characteristics.

[0009] Technical solutions for solving the problem

[0010] To achieve the above objectives, one aspect of the present invention relates to an elastic wave device comprising a longitudinally coupled resonator having a piezoelectric substrate and a plurality of IDT (Interdigital Transducer) electrodes. The piezoelectric substrate includes a piezoelectric layer having a first main surface and a second main surface opposite to each other and a plurality of IDT electrodes disposed on the first main surface, and a metal layer bonded to the second main surface of the piezoelectric layer. Each of the plurality of IDT electrodes includes a plurality of electrode fingers arranged parallel to each other. When viewed from above the first and second main surfaces, the metal layer is configured to span adjacent electrode fingers included in one of the plurality of IDT electrodes.

[0011] Invention Effects

[0012] According to the present invention, it is possible to provide an elastic wave device having a longitudinally coupled resonator that suppresses the degradation of attenuation characteristics. Attached Figure Description

[0013] Figure 1 This is a circuit diagram of the elastic wave filter involved in the implementation method.

[0014] Figure 2 This is a diagram of the electrode structure of the longitudinally coupled resonator according to the implementation method.

[0015] Figure 3 These are top and cross-sectional views of the elastic wave filter according to the implementation method.

[0016] Figure 4 This is a cross-sectional view of the elastic wave filter involved in the comparative example.

[0017] Figure 5 This is a coordinate graph showing the transmission characteristics of the elastic wave filter involved in the embodiments and comparative examples.

[0018] Figure 6A This is a cross-sectional view schematically showing the electric field distribution in the piezoelectric layer of the elastic wave filter involved in the comparative example.

[0019] Figure 6B This is a cross-sectional view schematically showing the electric field distribution in the piezoelectric layer of the elastic wave filter according to the embodiment.

[0020] Figure 7 These are top and cross-sectional views of an elastic wave filter according to a variation of embodiment 1.

[0021] Figure 8 This is a top view of the elastic wave filter involved in variation 2 of the implementation method. Detailed Implementation

[0022] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Furthermore, the embodiments described below are merely general or specific examples. The numerical values, shapes, materials, constituent elements, arrangements of constituent elements, and connection methods shown in the following embodiments are examples and are not intended to limit the invention. Constituent elements not described in the independent claims in the following embodiments will be described as arbitrary constituent elements. Moreover, the sizes or size ratios of the constituent elements shown in the drawings are not necessarily strict.

[0023] Furthermore, the figures are schematic diagrams that have been appropriately emphasized, omitted, or proportionally adjusted for the purpose of illustrating the invention, and are not necessarily strictly illustrative, sometimes differing from the actual shapes, positional relationships, and proportions. In the figures, substantially identical structures are labeled with the same reference numerals, and sometimes repeated descriptions are omitted or simplified.

[0024] In the component configurations disclosed herein, the term "component disposed on a substrate" includes cases where the component is disposed on the main surface of the substrate and cases where the component is disposed within the substrate. "Component disposed on the main surface of the substrate" includes not only cases where the component is disposed in contact with the main surface of the substrate, but also cases where the component is disposed above the main surface without contacting it (e.g., the component is stacked on top of other components disposed in contact with the main surface). Furthermore, "component disposed on the main surface of the substrate" may also include cases where the component is disposed in a recess formed on the main surface. "Component disposed within the substrate" includes not only cases where the component is encapsulated within a module substrate, but also cases where, although the entire component is disposed between the two main surfaces of the substrate, a portion of the component is not covered by the substrate, and cases where only a portion of the component is disposed within the substrate.

[0025] In the component configuration disclosed herein, the term "A layer and B layer are bonded" means that A layer and B layer do not come into contact via any other layer besides the adhesive layer.

[0026] In the circuit structure disclosed herein, the term "connection" includes not only direct connections using electrodes and / or wiring conductors, but also electrical connections via matching elements such as inductors and capacitors, and switching circuits. The term "connection between A and B" means a connection between A and B, and between both A and B.

[0027] Furthermore, terms such as "parallel" and "perpendicular" that indicate the relationship between elements, "rectangle" and other terms that indicate the shape of elements, and numerical ranges that do not only indicate strictness but also imply substantially equivalent ranges, such as including a few percent degree of error.

[0028] Furthermore, in the following implementation, the passband of the filter is defined as the frequency band between two frequencies whose minimum insertion loss is greater than 3dB within that passband.

[0029] (Implementation Method)

[0030] [1 Structure of Elastic Wave Filter 1]

[0031] First, the circuit structure of the elastic wave filter 1 involved in the implementation method will be described. Figure 1 This is a circuit diagram of the elastic wave filter 1 according to the embodiment. As shown in the figure, the elastic wave filter 1 is an example of an elastic wave device, which includes a longitudinally coupled resonator 10, series arm resonators 21, 22 and 23, and parallel arm resonators 31, 32 and 33.

[0032] The longitudinally coupled resonator 10, for example, has seven elastic wave resonators. Each of the seven elastic wave resonators has an IDT electrode formed on the multilayer substrate 50. Figure 2 as well as Figure 3The detailed construction of the longitudinally coupled resonator 10 is described below.

[0033] Series arm resonators 21 and 22 are configured on the series arm path connecting input / output terminal 110 and longitudinally coupled resonator 10. Series arm resonator 23 is configured on the series arm path connecting input / output terminal 120 and longitudinally coupled resonator 10. Parallel arm resonator 31 is connected between the connection point of series arm resonators 21 and 22 and ground. Parallel arm resonator 32 is connected between the connection point of series arm resonator 22 and longitudinally coupled resonator 10 and ground. Parallel arm resonator 33 is connected between the connection point of series arm resonator 23 and input / output terminal 120 and ground.

[0034] Through the above connection structure, the elastic wave filter 1 functions as a bandpass filter. The longitudinally coupled resonator 10 forms the basic passband and attenuation band of the elastic wave filter 1. The series arm resonators 21-23 and the parallel arm resonators 31-33 help to fine-tune the passband width, adjust the steepness of the passband end, and form the attenuation pole in the attenuation band.

[0035] Furthermore, the elastic wave filter 1 according to this embodiment only needs to include at least a longitudinally coupled resonator 10. Moreover, the number of elastic wave resonators constituting the longitudinally coupled resonator 10 is not limited to seven, as long as there are two or more. Furthermore, the number and connection structure of the series arm resonators and parallel arm resonators connected to the longitudinally coupled resonator 10 are arbitrary and determined by the required transmission characteristics of the elastic wave filter 1.

[0036] Figure 2 This is an electrode structure diagram of the longitudinally coupled resonator 10 according to the embodiment. The diagram shows the electrode structure of the IDT electrodes 11-17 and the reflecting electrodes 41 and 42 of the seven elastic wave resonators constituting the longitudinally coupled resonator 10. The longitudinally coupled resonator 10 includes IDT electrodes 11, 12, 13, 14, 15, 16, and 17, and reflecting electrodes 41 and 42. Furthermore, Figure 2 The IDT electrodes and reflecting electrodes shown are used to illustrate a typical structure of an elastic wave resonator constituting a longitudinally coupled resonator 10. The number and length of the electrode fingers constituting the IDT electrodes and reflecting electrodes are not limited to specific parameters. Figure 2 The contents recorded.

[0037] like Figure 2 As shown, the IDT electrode 11 has multiple electrode fingers 61 and busbar electrodes 71a and 71b.

[0038] Multiple electrode fingers 61 are arranged parallel to each other and extend in a direction perpendicular to the direction of elastic wave propagation (x-axis direction) (y-axis direction). The electrode fingers 61 connected to busbar electrode 71a and the electrode fingers 61 connected to busbar electrode 71b are arranged to interlock with each other.

[0039] Busbar electrode 71a is configured to connect one end of a portion of a plurality of electrode fingers 61 to each other. Busbar electrode 71b is configured to connect one end of the remaining portions of the plurality of electrode fingers 61 to each other. Busbar electrodes 71a and 71b extend in a direction intersecting the extending direction (y-axis direction) of the plurality of electrode fingers 61. Busbar electrodes 71a and 71b are arranged opposite each other, sandwiching the plurality of electrode fingers 61.

[0040] In addition, each of IDT electrodes 12-17, like IDT electrode 11, has a pair of busbar electrodes and multiple electrode fingers sandwiched between these busbar electrodes. IDT electrode 12 has multiple electrode fingers 62, IDT electrode 13 has multiple electrode fingers 63, IDT electrode 14 has multiple electrode fingers 64, IDT electrode 15 has multiple electrode fingers 65, IDT electrode 16 has multiple electrode fingers 66, and IDT electrode 17 has multiple electrode fingers 67.

[0041] Reflecting electrode 41 has multiple reflecting electrode fingers 81 and a pair of busbar electrodes. Reflecting electrode 42 has multiple reflecting electrode fingers 82 and a pair of busbar electrodes. The multiple reflecting electrode fingers 81 and 82 are each arranged parallel to each other and extend in a direction perpendicular to the elastic wave propagation direction (x-axis direction) (y-axis direction). Each of the multiple reflecting electrode fingers 81 is connected to both sides of a pair of busbar electrodes, which are arranged opposite each other, sandwiching the multiple reflecting electrode fingers. Each of the multiple reflecting electrode fingers 82 is connected to both sides of a pair of busbar electrodes, which are arranged opposite each other, sandwiching the multiple reflecting electrode fingers.

[0042] IDT electrodes 11-17 and reflective electrodes 41 and 42 are arranged along the elastic wave propagation direction (x-axis direction) in the order of reflective electrode 41, IDT electrodes 11, 12, 13, 14, 15, 16, 17, and reflective electrode 42. That is, the longitudinally coupled resonator 10 has a structure in which multiple IDT electrodes are arranged adjacent to each other along the elastic wave propagation direction.

[0043] In the above configuration of IDT electrodes 11-17, the busbar electrodes on the positive y-axis side of each of IDT electrodes 11, 13, 15, and 17 are connected to the input / output node n1, which serves as a signal (HOT) terminal. The busbar electrodes on the negative y-axis side of each of IDT electrodes 11, 13, 15, and 17 are connected to ground. The busbar electrodes on the negative y-axis side of each of IDT electrodes 12, 14, and 16 are connected to the input / output node n2, which serves as a signal terminal. The busbar electrodes on the positive y-axis side of each of IDT electrodes 12, 14, and 16 are connected to ground.

[0044] Here, the electrode parameters of the IDT electrodes constituting the longitudinally coupled resonator 10 are explained.

[0045] The electrode finger spacing of the IDT electrode 11 is defined as the repetition period of the plurality of electrode fingers 61. Furthermore, when the linewidth of the electrode finger 61 is set to W and the spacing between two adjacent electrode fingers 61 is set to S, the electrode finger spacing is defined by (W+S). Furthermore, the wavelength λ is defined as twice the electrode finger spacing. Furthermore, the duty cycle of the IDT electrode 11 is the linewidth occupancy rate of the plurality of electrode fingers 61, which is the ratio of the linewidth to the sum of the linewidth and spacing of the plurality of electrode fingers 61, defined by W / (W+S). Furthermore, the cross width of the IDT electrode 11 is the length of the repeating electrode fingers when viewed from the direction of elastic wave propagation (x-axis direction) when considering the electrode fingers 61 connected to busbar electrode 71a and the electrode fingers 61 connected to busbar electrode 71b.

[0046] Table 1 shows the electrode parameters of the IDT electrode and the reflective electrode that constitute the longitudinally coupled resonator 10.

[0047] [Table 1]

[0048]

[0049] As shown in Table 1, the IDT electrodes 11-17 involved in this embodiment each have multiple segmented regions with different electrode finger spacings. More specifically, each of the IDT electrodes 11-17 is divided into a main region having the main electrode finger spacing of each IDT electrode, and a narrow-spacing region having an electrode finger spacing smaller than that of the main region.

[0050] Furthermore, in the segmented region of the IDT electrode, when the spacing between adjacent electrode fingers is not fixed, the electrode finger spacing in the aforementioned segmented region is defined by the average electrode finger spacing of the segmented region. Regarding the average electrode finger spacing of the segmented region, if the total number of electrode fingers contained in the segmented region is set as Ni, and the distance between the centers of the electrode fingers at one end of the segmented region in the direction of elastic wave propagation and the electrode fingers at the other end is set as Di, then it is defined as Di / (Ni-1).

[0051] Alternatively, each of the multiple IDT electrodes 11 to 17 constituting the longitudinally coupled resonator 10 can also be composed of only one region with the same electrode finger spacing.

[0052] Next, the construction of the elastic wave filter 1 according to the embodiment will be described. Figure 3 These are top and cross-sectional views of the elastic wave filter 1 according to the embodiment. In figure (a), a view is shown of the main surface 51a (first main surface) of the piezoelectric layer 51 constituting the elastic wave filter 1, viewed from the positive z-axis direction. Furthermore, in Figure 3 In (a), as a result of viewing the piezoelectric layer 51, a metal layer 52 bonded to the main surface 51b (second main surface) of the piezoelectric layer 51 is also shown. Figure 3 (b) is to Figure 3 The diagram in (a) shows the section where lines IIIb-IIIb are cut off. Additionally, in... Figure 3 In (b), for convenience, two electrode fingers (a pair of electrode fingers) are shown for a single IDT electrode, but actual IDT electrodes 11-17 each have three or more electrode fingers. Furthermore, in Figure 3 In (b), for convenience, two reflective electrode fingers (a pair of reflective electrode fingers) are shown for a single reflective electrode, but the actual reflective electrodes 41 and 42 may each have more than three reflective electrode fingers.

[0053] like Figure 3 As shown in (a), the longitudinally coupled resonator 10 has a multilayer substrate 50, multiple IDT electrodes 11-17, and reflective electrodes 41 and 42. Alternatively, the longitudinally coupled resonator 10 may also omit the reflective electrodes 41 and 42. Furthermore, in Figure 3 In (a), regarding IDT electrodes 11-17 and reflective electrodes 41 and 42, there is no [example of something]. Figure 2 The electrode fingers and reflective electrode fingers were described in such detail, but were illustrated using simplified notation.

[0054] like Figure 3 As shown in (a), the busbar electrodes on the positive y-axis side of IDT electrodes 11, 13, 15, and 17 are commonly connected to connection wiring 70a (corresponding to input / output node n1), which serves as a signal terminal. Furthermore, the busbar electrodes on the negative y-axis side of IDT electrodes 12, 14, and 16 are commonly connected to connection wiring 70b (corresponding to input / output node n2), which serves as a signal terminal. Additionally, in Figure 3 In (a), the busbar electrodes and grounding connection structure of IDT electrodes 11-17 are omitted.

[0055] like Figure 3 As shown in (b), the multilayer substrate 50 is an example of a piezoelectric substrate, comprising a piezoelectric layer 51, a metal layer 52, a low-velocity layer 53, a high-velocity layer 54, and a support substrate 55. The multilayer substrate 50 is a substrate that includes the piezoelectric layer 51 and is piezoelectric.

[0056] The piezoelectric layer 51 has a main surface 51a (first main surface) and a main surface 51b (second main surface) that are opposite each other. IDT electrodes 11-17 and reflective electrodes 41 and 42 are disposed on the main surface 51a. The piezoelectric layer 51 can be, for example, lithium tantalate (LiTaO3). The film thickness of the piezoelectric layer 51 is, for example, 900 nm.

[0057] The metal layer 52 is bonded to the main surface 51b of the piezoelectric layer 51. For example... Figure 3 As shown in (a), when viewed from above, the main surfaces 51a and 51b of the piezoelectric layer 51 overlap the entire area of ​​the plurality of IDT electrodes 11 to 17.

[0058] The metal layer 52 can be, for example, titanium (Ti). The film thickness of the metal layer 52 is, for example, 50 nm. Alternatively, the metal layer 52 can be an alloy comprising multiple metal materials, or it can be a stack of multiple layers composed of different metal materials. Furthermore, an adhesive layer can exist between the metal layer 52 and the piezoelectric layer 51 to ensure their bonding strength.

[0059] In addition, the so-called adhesive layer is a dielectric layer with a thickness of less than 1 / 10 of the thickness of the piezoelectric layer 51, such as epoxy resin.

[0060] The support substrate 55 is disposed in the multilayer substrate 50 at the position furthest from the IDT electrodes 11-17. The support substrate 55, the metal layer 52, and the piezoelectric layer 51 are stacked sequentially. The support substrate 55 can be made of silicon (Si), for example. The thickness of the support substrate 55 is, for example, 125 μm.

[0061] A low-velocity acoustic layer 53 is disposed between the metal layer 52 and the support substrate 55. The velocity of sound of the bulk wave propagating in the low-velocity acoustic layer 53 is lower than that of the bulk wave propagating in the piezoelectric layer 51. Based on this structure and the property that elastic waves inherently concentrate energy in a low-velocity medium, leakage of surface acoustic wave energy to the outside of the piezoelectric layer 51 can be suppressed. The low-velocity acoustic layer 53 can be, for example, a dielectric material such as silicon oxide (SiO2), glass, silicon oxynitride, lithium oxide, tantalum oxide, or a compound of silicon oxide with added fluorine, carbon, or boron, or a material with the above materials as the main component. The film thickness of the low-velocity acoustic layer 53 is, for example, 300 nm.

[0062] A high-velocity acoustic layer 54 is disposed between the low-velocity acoustic layer 53 and the support substrate 55. The sound velocity of the bulk wave propagating in the high-velocity acoustic layer 54 is higher than that of the elastic wave propagating in the piezoelectric layer 51. The high-velocity acoustic layer 54 can be made of, for example, piezoelectric materials such as silicon nitride (SiN), aluminum nitride, lithium tantalate, lithium niobate, and quartz; ceramics such as alumina, sapphire, magnesium oxide, silicon carbide, zirconium oxide, cordierite, mullite, block talc, and forsterite; dielectrics such as diamond and glass; semiconductors such as silicon and gallium nitride; or resins; or materials using the above materials as main components. The film thickness of the high-velocity acoustic layer 54 is, for example, 300 nm.

[0063] Based on the above-described stacked structure of the multilayer substrate 50, compared to the conventional structure using a single-layer substrate containing only piezoelectric material, i.e., a piezoelectric body, the resonant frequency and Q value at the anti-resonant frequency of the elastic wave resonator can be significantly improved. That is, an elastic wave resonator with a high Q value can be constructed, and therefore, this elastic wave resonator can be used to construct an elastic wave filter with low insertion loss.

[0064] Alternatively, the high-velocity acoustic layer 54 and the support substrate 55 can be combined into a single high-velocity acoustic support substrate. The high-velocity acoustic support substrate supports the IDT electrodes 11-17, the piezoelectric layer 51, the metal layer 52, and the low-velocity acoustic layer 53. The high-velocity acoustic support substrate is a substrate where the velocity of the bulk waves propagating in the high-velocity acoustic support substrate is significantly higher than that of elastic waves such as surface waves and boundary waves propagating in the piezoelectric layer 51. This function confines the surface acoustic waves within the portion where the piezoelectric layer 51 and the low-velocity acoustic layer 53 are stacked, preventing leakage to areas further below the high-velocity acoustic support substrate. Materials used as high-velocity support substrates include, for example, piezoelectric materials such as aluminum nitride, lithium tantalate, lithium niobate, and quartz; bauxite; sapphire; magnesium oxide; silicon nitride; silicon carbide; zirconium oxide; cordierite; mullite; block talc; forsterite; spinel; silicon oxynitride; alumina; silicon oxynitride; DLC (diamond-like carbon); diamond; semiconductors such as silicon; or materials using the above materials as main components. Furthermore, the spinels mentioned above contain aluminum compounds containing one or more elements selected from Mg, Fe, Zn, and Mn, and oxygen. Examples of the aforementioned spinels include MgAl₂O₄, FeAl₂O₄, ZnAl₂O₄, and MnAl₂O₄.

[0065] Furthermore, in this specification, the term "main component of the material" refers to a component that accounts for more than 50% by weight in the material. This main component may exist in any of the following states: single crystal, polycrystalline, and amorphous, or a mixture thereof.

[0066] Furthermore, the piezoelectric substrate according to this embodiment can also replace the multilayer substrate 50 and have a structure in which a support substrate 55, an energy sealing layer, a metal layer 52, and a piezoelectric layer 51 are stacked in sequence. In this case, IDT electrodes 11-17 and reflective electrodes 41 and 42 are disposed on the piezoelectric layer 51.

[0067] The energy-sealing layer comprises one or more layers, wherein the speed of bulk acoustic waves propagating in at least one layer is greater than the speed of elastic waves propagating near the piezoelectric layer 51. For example, the energy-sealing layer can also be a stacked structure of low-velocity and high-velocity layers. The low-velocity layer is a film in which the speed of bulk waves is low compared to the speed of elastic waves propagating in the piezoelectric layer 51. The high-velocity layer is a film in which the speed of bulk waves is high compared to the speed of elastic waves propagating in the piezoelectric layer 51. Alternatively, the support substrate 55 can also be configured as a high-velocity layer.

[0068] In addition, the energy sealing layer can also be an acoustic impedance layer, that is, a structure in which low acoustic impedance layers with relatively low acoustic impedance and high acoustic impedance layers with relatively high acoustic impedance are stacked alternately.

[0069] Furthermore, the piezoelectric substrate involved in this embodiment can also replace the multilayer substrate 50 and have the following structure, that is, the support substrate 55, the metal layer 52 and the piezoelectric layer 51 are stacked in sequence, and the low-velocity layer 53 and the high-velocity layer 54 are not provided.

[0070] Next, the structure of the electrode fingers constituting IDT electrodes 11 to 17 and the reflective electrode fingers constituting reflective electrodes 41 and 42 will be described.

[0071] The electrode fingers constituting IDT electrodes 11 to 17 and the reflective electrode fingers constituting reflective electrodes 41 and 42 are, for example, a stacked structure of a close-fitting layer and a main electrode layer.

[0072] The main electrode layer, for example, uses aluminum (Al) as the main component, and has a film thickness of, for example, 100 nm. A bonding layer is disposed between the main electrode layer and the piezoelectric layer 51, configured to increase the adhesion of the main electrode layer to the multilayer substrate 50. The bonding layer, for example, contains titanium (Ti), and has a film thickness of, for example, 10 nm. In addition, the IDT electrodes 11-17 and the reflective electrodes 41 and 42 are not limited to the above-described stacked structure. For example, they may be made of metals or alloys such as Ti, Al, Cu, Pt, Au, Ag, and Pd. Furthermore, they may be constructed by multiple stacks made of the aforementioned metals or alloys.

[0073] Next, the construction of the elastic wave filter 200 involved in the comparative example will be described. Figure 4 This is a cross-sectional view of the elastic wave filter 200 involved in the comparative example. As shown in the figure, the elastic wave filter 200 has a multilayer substrate 250 and a plurality of IDT electrodes 11-17 (in... Figure 4 The diagram shows electrodes 61-67 and reflective electrodes 41 and 42 (in...). Figure 4 The diagram shows reflective electrodes 81 and 82. Compared to the elastic wave filter 1 of the embodiment, the elastic wave filter 200 in the comparative example differs in the layering structure of the multilayer substrate 250. Hereinafter, the elastic wave filter 200 in the comparative example will be described focusing on the structure of the multilayer substrate 250, which differs from that of the elastic wave filter 1 of the embodiment.

[0074] like Figure 4 As shown, the multilayer substrate 250 includes a piezoelectric layer 51, a low-velocity layer 53, a high-velocity layer 54, a metal layer 52, and a support substrate 55. The piezoelectric layer 51, the low-velocity layer 53, the high-velocity layer 54, the metal layer 52, and the support substrate 55 are stacked sequentially from the positive z-axis direction. That is, the metal layer 52 is not bonded to the piezoelectric layer 51, but is disposed between the support substrate 55 and the high-velocity layer 54.

[0075] [2 Transmission characteristics of elastic wave filter 1]

[0076] Next, the transmission characteristics of the elastic wave filter 1 according to the embodiment will be explained. Figure 5 This is a graph showing the transmission characteristics of the elastic wave filters according to the embodiments and comparative examples. As shown in the graph, when comparing the transmission characteristics of the elastic wave filter 1 according to the embodiment and the elastic wave filter 200 according to the comparative example, no difference was observed in the transmission characteristics near the passband. In contrast, in the attenuation band (700-760MHz) lower than the passband, the elastic wave filter 1 according to the embodiment has a greater attenuation (a larger minimum insertion loss) compared to the elastic wave filter 200 according to the comparative example. In other words, the elastic wave filter 1 according to the embodiment suppresses the degradation of attenuation characteristics better than the elastic wave filter 200 according to the comparative example.

[0077] The following explains the main reasons why the elastic wave filter 1 according to the embodiment can better suppress the deterioration of attenuation characteristics compared with the elastic wave filter 200 according to the comparative example.

[0078] Figure 6A This is a cross-sectional view schematically showing the electric field distribution in the piezoelectric layer 51 of the elastic wave filter 200 involved in the comparative example. In a piezoelectric substrate having a piezoelectric layer, a low-velocity layer, a high-velocity layer, and a supporting substrate, the electric field density is high in the piezoelectric layer, which has the highest dielectric constant. Therefore, as... Figure 6AAs shown, unwanted electric field coupling occurs between two adjacent IDT electrodes, between adjacent IDT electrodes, and between the reflecting electrode. Consequently, unwanted inter-resonator coupling occurs between the multiple elastic wave resonators constituting the longitudinally coupled resonator, which degrades the attenuation characteristics of the elastic wave filter 200.

[0079] Figure 6B This is a cross-sectional view schematically showing the electric field distribution in the piezoelectric layer 51 of the elastic wave filter 1 according to the embodiment. As shown in the figure, the metal layer 52, which is bonded to the main surface 51b of the piezoelectric layer 51, is capacitively coupled to the electrode fingers constituting the IDT electrodes, and this capacitive coupling forms a charge path from each electrode to the metal layer 52. In other words, the aforementioned charge path is formed by the metal layer 52 bonded to the main surface 51b of the piezoelectric layer 51, thereby suppressing unwanted electric field coupling generated in adjacent IDT electrodes, adjacent IDT electrodes, and the reflecting electrode. Thus, in the elastic wave filter 1 according to the embodiment, the effect of shielding the electric field coupling between the IDT electrodes constituting the longitudinally coupled resonator 10 and between the IDT electrode and the reflecting electrode due to the metal layer 52 can be utilized, and the deterioration of the attenuation characteristics can be suppressed.

[0080] In addition, in the elastic wave filter 1 of this embodiment, the metal layer 52 may also be connected to ground.

[0081] Therefore, the unwanted electric field generated in the piezoelectric layer 51 can be released to the ground through the metal layer 52, thus suppressing the deterioration of the attenuation characteristics.

[0082] Furthermore, in the elastic wave filter 1 of this embodiment, when viewed from above the main surfaces 51a and 51b of the piezoelectric layer 51, the metal layer 52 may not overlap with the entire area of ​​the plurality of IDT electrodes 11 to 17, or it may be configured to span two adjacent electrode fingers across any one of the IDT electrodes 11 to 17.

[0083] Therefore, the metal layer 52 is configured to face the two adjacent electrode fingers in the above top view, thus forming charge paths from each of the two electrode fingers to the metal layer 52, which can suppress unwanted electric field coupling generated between the two electrode fingers. Consequently, the degradation of the attenuation characteristics of the elastic wave filter can be suppressed.

[0084] [3 Structure of the elastic wave filter 1A involved in Modification Example 1]

[0085] Next, the structure of the elastic wave filter 1A according to Modification Example 1 will be described. The elastic wave filter 1A according to this modification example is an example of an elastic wave device, comprising a longitudinally coupled resonator 10A, series arm resonators 21, 22, and 23, and parallel arm resonators 31, 32, and 33. Compared with the elastic wave filter 1 according to the embodiment, the elastic wave filter 1A according to this modification example differs only in the structure of the longitudinally coupled resonator 10A. Hereinafter, regarding the elastic wave filter 1A according to this modification example, descriptions of structures identical to those of the elastic wave filter 1 according to the embodiment will be omitted, and the description will focus on the different structures.

[0086] The longitudinally coupled resonator 10A has seven elastic wave resonators. Each of the seven elastic wave resonators has an IDT electrode formed on the multilayer substrate 50A. In addition, the structure of the IDT electrode and the reflecting electrode constituting the seven elastic wave resonators is the same as that of the IDT electrode and the reflecting electrode of the longitudinally coupled resonator 10, and the electrode parameters are the same as those shown in Table 1.

[0087] Figure 7 These are top and cross-sectional views of the elastic wave filter 1A according to a variation of embodiment 1. In figure (a), a view is shown of the main surface 51a (first main surface) of the piezoelectric layer 51A constituting the elastic wave filter 1A, viewed from the positive z-axis direction. Furthermore, in Figure 7 In (a), as a result of the perspective view of the piezoelectric layer 51A, a metal layer 52A bonded to the main surface 51b (second main surface) of the piezoelectric layer 51A is also shown. Figure 7 (b) is to Figure 7 The diagram in (a) shows lines VIIb-VIIb that have been cut off. Additionally, in... Figure 7 In (b), for convenience, two electrode fingers (a pair of electrode fingers) are shown for a single IDT electrode, but actual IDT electrodes 11-17 each have three or more electrode fingers. Furthermore, in Figure 7 In (b), for convenience, two reflective electrode fingers (a pair of reflective electrode fingers) are shown for a single reflective electrode, but the actual reflective electrodes 41 and 42 may each have more than three reflective electrode fingers.

[0088] like Figure 7 As shown in (a), the longitudinally coupled resonator 10A has a multilayer substrate 50A, multiple IDT electrodes 11-17, and reflective electrodes 41 and 42. Alternatively, the longitudinally coupled resonator 10A may not include reflective electrodes 41 and 42. Furthermore, in... Figure 7 In (a), regarding IDT electrodes 11-17 and reflective electrodes 41 and 42, there is no [example of something]. Figure 2The electrode fingers and reflective electrode fingers were described in such detail, but were illustrated using simplified notation.

[0089] like Figure 7 As shown in (a), the busbar electrodes on the positive y-axis side of IDT electrodes 11, 13, 15, and 17 are commonly connected to connection wiring 70a (corresponding to input / output node n1), which serves as a signal terminal. Furthermore, the busbar electrodes on the negative y-axis side of IDT electrodes 12, 14, and 16 are commonly connected to connection wiring 70b (corresponding to input / output node n2), which serves as a signal terminal. Additionally, in Figure 7 In (a), the grounding connection structure of IDT electrodes 11-17 is omitted.

[0090] like Figure 7 As shown in (b), the multilayer substrate 50A is an example of a piezoelectric substrate having piezoelectric properties, comprising a piezoelectric layer 51A, a metal layer 52A, a low-velocity layer 53, a high-velocity layer 54, and a support substrate 55.

[0091] The piezoelectric layer 51A has opposing main surfaces 51a (first main surface) and 51b (second main surface). IDT electrodes 11-17 and reflective electrodes 41 and 42 are disposed on the main surface 51a. The piezoelectric layer 51A can be, for example, lithium tantalate (LiTaO3). The film thickness of the piezoelectric layer 51A is, for example, 900 nm.

[0092] The metal layer 52A is bonded to the main surface 51b of the piezoelectric layer 51A. For example... Figure 7 As shown in (a), when viewed from above on the main surfaces 51a and 51b of the piezoelectric layer 51A, the metal layer 52A is divided into multiple metal layers 520. In this view, each of the multiple metal layers 520 overlaps with any one of the IDT electrodes 11-17 and the reflective electrodes 41 and 42. For example, the first metal layer, which is one of the multiple metal layers 520, overlaps with the IDT electrode 11 in this view, and the second metal layer, which is another of the multiple metal layers 520, overlaps with the IDT electrode 12 in this view. The first and second metal layers are separated. Furthermore, in this view, the metal layer 52A does not overlap with the inter-electrode region of the IDT electrodes that is sandwiched between the IDT electrodes 11 (the first IDT electrode) and 12 (the second IDT electrode) and does not have electrode fingers disposed therein. In other words, the metal layer 52A does not overlap with the inter-electrode region of the IDT, which is sandwiched by the electrode finger among the plurality of electrode fingers included in the first IDT electrode that is closest to the second IDT electrode, and the electrode finger among the plurality of electrode fingers included in the second IDT electrode that is closest to the first IDT electrode.

[0093] Therefore, electric field coupling between the electrode fingers of IDT electrode 11 and IDT electrode 12 via metal layer 52A can be suppressed. Consequently, the degradation of the attenuation characteristics of elastic wave filter 1A can be suppressed.

[0094] Furthermore, the metal layer 52A can be, for example, titanium (Ti). The film thickness of the metal layer 52A is, for example, 50 nm. Additionally, the metal layer 52A can be an alloy containing multiple metal materials, or it can be a laminate of multiple layers composed of different metal materials. Furthermore, an adhesive layer can exist between the metal layer 52A and the piezoelectric layer 51A to ensure their bonding strength.

[0095] In addition, each of the plurality of metal layers 520 may not overlap with the entire area of ​​any one of the IDT electrodes 11-17 and the reflective electrodes 41 and 42 in the above top view, or may overlap with at least a portion of any one of them.

[0096] Furthermore, the metal layer 52A may not be composed of multiple separated metal layers 520, and may also have a slit portion where no metal film is formed. In this case, the slit portion overlaps with the inter-electrode region of the IDT in the above top view.

[0097] Therefore, electric field coupling between two adjacent IDT electrodes via metal layer 52A can be suppressed. Consequently, the degradation of the attenuation characteristics of elastic wave filter 1A can be suppressed.

[0098] Furthermore, the spaces between the multiple metal layers constituting metal layer 52A are filled with the same material as that constituting piezoelectric layer 51A. Alternatively, the spaces between the multiple metal layers constituting metal layer 52A may be filled with the same material as that constituting low-velocity layer 53.

[0099] The low-velocity layer 53, high-velocity layer 54, and support substrate 55 involved in this variation have the same structure as the low-velocity layer 53, high-velocity layer 54, and support substrate 55 involved in the embodiment, so the description is omitted.

[0100] [4. Structure of elastic wave filter 1B involved in Modification Example 2]

[0101] Next, the structure of the elastic wave filter 1B according to Modification Example 2 will be described. The elastic wave filter 1B according to this modification example is an example of an elastic wave device, comprising a longitudinally coupled resonator 10B, series arm resonators 21, 22, and 23, and parallel arm resonators 31, 32, and 33. Compared to the elastic wave filter 1 according to the embodiment, the elastic wave filter 1B according to this modification example differs only in the construction of the multilayer substrate 50B. Hereinafter, regarding the elastic wave filter 1B according to this modification example, descriptions of structures identical to those of the elastic wave filter 1 according to the embodiment will be omitted, and the description will focus on the different structures.

[0102] The longitudinally coupled resonator 10B has seven elastic wave resonators. Each of the seven elastic wave resonators has an IDT electrode formed on the multilayer substrate 50B. In addition, the structure of the IDT electrode and the reflecting electrode constituting the seven elastic wave resonators is the same as that of the IDT electrode and the reflecting electrode of the longitudinally coupled resonator 10, and the electrode parameters are the same as those shown in Table 1.

[0103] Figure 8 This is a top view of the elastic wave filter 1B according to a variation of embodiment 2. In this figure, a view of the main surface 51a (first main surface) of the piezoelectric layer 51 constituting the elastic wave filter 1B, viewed from the positive z-axis direction, is shown. Additionally, as a result of viewing the piezoelectric layer 51 from a perspective view, a metal layer 52B bonded to the main surface 51b (second main surface) of the piezoelectric layer 51 is also shown in this figure.

[0104] like Figure 8 As shown, the longitudinally coupled resonator 10B has a multilayer substrate 50B, multiple IDT electrodes 11-17, and reflective electrodes 41 and 42. Alternatively, the longitudinally coupled resonator 10B may not include reflective electrodes 41 and 42. Furthermore, in... Figure 8 In the text, regarding IDT electrodes 11-17 and reflective electrodes 41 and 42, there is no mention of... Figure 2 The electrode fingers and reflective electrode fingers were described in such detail, but were illustrated using simplified notation.

[0105] In addition, such as Figure 8 As shown, the series arm resonator 23 has an IDT electrode 18 (the third IDT electrode) disposed on the multilayer substrate 50B.

[0106] like Figure 8As shown, the busbar electrodes on the positive y-axis side of IDT electrodes 11, 13, 15, and 17 are commonly connected to connection wiring 70a (corresponding to input / output node n1), which serves as a signal terminal. Furthermore, the busbar electrodes on the negative y-axis side of IDT electrodes 12, 14, and 16 are commonly connected to connection wiring 70b (corresponding to input / output node n2), which serves as a signal terminal. Additionally, in Figure 8 The grounding connection structure of IDT electrodes 11-17 is omitted here. Furthermore, IDT electrode 18 is connected to connection wiring 70b (equivalent to input / output node n2).

[0107] The multilayer substrate 50B is an example of a piezoelectric substrate with piezoelectric properties, comprising a piezoelectric layer 51, a metal layer 52B, a low-velocity layer 53, a high-velocity layer 54, and a support substrate 55.

[0108] The piezoelectric layer 51 has a main surface 51a (first main surface) and a main surface 51b (second main surface) that are opposite to each other. IDT electrodes 11 to 18 and reflective electrodes 41 and 42 are disposed on the main surface 51a.

[0109] The metal layer 52B is bonded to the main surface 51b of the piezoelectric layer 51. For example... Figure 8 As shown, when viewed from above, the main surfaces 51a and 51b of the piezoelectric layer 51 overlap with the plurality of IDT electrodes 11 to 17 and at least a portion of the IDT electrodes 18 of the series arm resonator 23.

[0110] Therefore, the metal layer 52B is configured to overlap with both the longitudinally coupled resonator 10B and the series arm resonator 23 constituting the elastic wave filter 1B, thereby improving the thermal uniformity of the elastic wave filter 1B. As a result, the frequency temperature offset of the longitudinally coupled resonator 10B and the series arm resonator 23 is homogenized, thus enabling high-precision adjustment of the frequency temperature characteristics of the elastic wave filter 1B.

[0111] Furthermore, the metal layer 52B can be, for example, titanium (Ti). The film thickness of the metal layer 52B is, for example, 50 nm. Additionally, the metal layer 52B can be an alloy containing multiple metal materials, or it can be a laminate of multiple layers composed of different metal materials. Furthermore, an adhesive layer can exist between the metal layer 52B and the piezoelectric layer 51 to ensure their bonding strength.

[0112] Furthermore, the metal layer 52B can overlap not only with the longitudinally coupled resonator 10B and the series arm resonator 23 in the above-mentioned top view, but also with the IDT electrodes of other elastic wave resonators in the above-mentioned top view.

[0113] [5. Effects, etc.]

[0114] As described above, the elastic wave filter 1 according to the embodiment includes a longitudinally coupled resonator 10 having a multilayer substrate 50 and a plurality of IDT electrodes 11 to 17. The multilayer substrate 50 includes a piezoelectric layer 51 having opposing main surfaces 51a and 51b and a plurality of IDT electrodes 11 to 17 disposed on the main surface 51a, and a metal layer 52 bonded to the main surface 51b of the piezoelectric layer 51. Each of the plurality of IDT electrodes 11 to 17 includes a plurality of electrode fingers arranged parallel to each other. When viewed from above the main surfaces 51a and 51b, the metal layer 52 is configured to span the adjacent electrode fingers included in one of the plurality of IDT electrodes 11 to 17.

[0115] Thus, the metal layer 52, bonded to the main surface 51b of the piezoelectric layer 51, is capacitively coupled to each of the plurality of electrode fingers constituting the IDT electrodes, forming a charge path from each electrode to the metal layer 52. Because of this charge path, unwanted electric field coupling generated in adjacent IDT electrodes can be suppressed. Therefore, an elastic wave filter 1 with suppressed attenuation characteristics can be provided.

[0116] For example, in the elastic wave filter 1A according to Modification 1, a plurality of IDT electrodes 11 to 17 include IDT electrodes 11 and 12 arranged adjacently in a direction perpendicular to the extension direction of the plurality of electrode fingers. When viewed from above the main surfaces 51a and 51b, the metal layer 52A does not overlap with the inter-IDT electrode region, which is sandwiched by the electrode finger of the plurality of electrode fingers included in the IDT electrode 11 that is closest to the IDT electrode 12, and the electrode finger of the plurality of electrode fingers included in the IDT electrode 12 that is closest to the IDT electrode 11.

[0117] Therefore, electric field coupling between the electrode fingers of IDT electrode 11 and IDT electrode 12 via metal layer 52A can be suppressed. Consequently, the degradation of the attenuation characteristics of elastic wave filter 1A can be suppressed.

[0118] For example, in the elastic wave filter 1A, a slit portion without a metal film is formed in the metal layer 52A. When viewed from above the main surfaces 51a and 51b, the slit portion overlaps with the region between the IDT electrodes.

[0119] Therefore, electric field coupling between two adjacent IDT electrodes via metal layer 52A can be suppressed. Consequently, the degradation of the attenuation characteristics of elastic wave filter 1A can be suppressed.

[0120] For example, in the elastic wave filter 1A, the metal layer 52A includes a plurality of metal layers 520 that are separated from each other. When viewed from above the main surfaces 51a and 51b, one of the plurality of metal layers 520 overlaps with the IDT electrode 11, and another of the plurality of metal layers 520 overlaps with the IDT electrode 12.

[0121] Therefore, electric field coupling between two adjacent IDT electrodes via metal layer 52A can be suppressed. Consequently, the degradation of the attenuation characteristics of elastic wave filter 1A can be suppressed.

[0122] For example, in the elastic wave filter 1, when viewed from above the main surfaces 51a and 51b, the metal layer 52 overlaps with the entire area of ​​the plurality of IDT electrodes 11 to 17.

[0123] This creates charge paths from each electrode constituting the IDT electrode to the metal layer 52, suppressing unwanted electric field coupling generated between adjacent IDT electrodes. Consequently, an elastic wave filter 1 with suppressed attenuation characteristics can be provided.

[0124] For example, the elastic wave filter 1B involved in Modification Example 2 also includes a series arm resonator 23 connected to a longitudinally coupled resonator 10B. The series arm resonator 23 has an IDT electrode 18 disposed on the piezoelectric layer 51. When viewed from above the main surfaces 51a and 51b, the metal layer 52B overlaps with at least a portion of the IDT electrode 18.

[0125] Therefore, the metal layer 52B is configured to overlap with both the longitudinally coupled resonator 10B and the series arm resonator 23, thus improving the thermal uniformity of the elastic wave filter 1B. Consequently, the frequency temperature offset of the longitudinally coupled resonator 10B and the series arm resonator 23 is homogenized, thereby enabling high-precision adjustment of the frequency temperature characteristics of the elastic wave filter 1B.

[0126] For example, in the elastic wave filter 1, the metal layer 52 is connected to ground.

[0127] Therefore, the unwanted electric field generated in the piezoelectric layer 51 can be released to the ground through the metal layer 52, thus suppressing the deterioration of the attenuation characteristics.

[0128] For example, in the elastic wave filter 1, the multilayer substrate 50 also includes a support substrate 55, and the support substrate 55, the metal layer 52 and the piezoelectric layer 51 are stacked in sequence.

[0129] For example, in the elastic wave filter 1, the multilayer substrate 50 further includes: a low-velocity sound layer 53 disposed between the metal layer 52 and the support substrate 55, wherein the velocity of the bulk wave is lower than that of the bulk wave propagating in the piezoelectric layer 51; and a high-velocity sound layer 54 disposed between the low-velocity sound layer 53 and the support substrate 55, wherein the velocity of the propagated bulk wave is higher than that of the elastic wave propagating in the piezoelectric layer 51.

[0130] This suppresses the leakage of surface acoustic wave energy to the piezoelectric layer 51. It significantly increases the resonant frequency and Q-value at the anti-resonant frequency of the elastic wave resonator constituting the elastic wave filter, thus providing an elastic wave filter with low insertion loss.

[0131] (Other implementation methods)

[0132] The elastic wave device of the present invention has been described above with examples of embodiments and modifications, but the present invention is not limited to the above embodiments and modifications. Other embodiments implemented by combining any of the constituent elements in the above embodiments and modifications, as well as modifications that can be conceived by those skilled in the art by implementing the above embodiments and modifications without departing from the spirit of the present invention, are also included in the present invention.

[0133] The features of the elastic wave device described below, based on the above embodiments and variations, are shown below.

[0134] <1>

[0135] An elastic wave device includes a longitudinally coupled resonator, which has a piezoelectric substrate and multiple IDT electrodes.

[0136] The piezoelectric substrate comprises:

[0137] A piezoelectric layer having a first main surface and a second main surface opposite to each other, wherein the plurality of IDT electrodes are disposed on the first main surface; and

[0138] The metal layer is bonded to the second main surface of the piezoelectric layer.

[0139] Each of the plurality of IDT electrodes comprises a plurality of electrode fingers arranged in parallel with each other.

[0140] Viewed from above the first and second main surfaces, the metal layer is configured to span adjacent electrode fingers included in one of the plurality of IDT electrodes.

[0141] <2>

[0142] according to <1> The elastic wave device, wherein,

[0143] The plurality of IDT electrodes includes a first IDT electrode and a second IDT electrode arranged adjacent to each other in a direction perpendicular to the extension direction of the plurality of electrode fingers.

[0144] When viewed from above the first and second main surfaces, the metal layer does not overlap with the inter-electrode region of the IDT, which is sandwiched by the electrode finger of the plurality of electrode fingers included in the first IDT electrode that is closest to the second IDT electrode, and the electrode finger of the plurality of electrode fingers included in the second IDT electrode that is closest to the first IDT electrode.

[0145] <3>

[0146] according to <2> The elastic wave device, wherein,

[0147] A slit portion where no metal film is formed is formed in the metal layer.

[0148] When viewed from above, the first main surface and the second main surface overlap with the region between the IDT electrodes.

[0149] <4>

[0150] according to <2> The elastic wave device, wherein,

[0151] The metal layer comprises a first metal layer and a second metal layer that are separated from each other.

[0152] When viewed from above, the first main surface and the second main surface overlap with the first IDT electrode, and the second metal layer overlaps with the second IDT electrode.

[0153] <5>

[0154] according to <1> The elastic wave device, wherein,

[0155] When viewed from above the first and second main surfaces, the metal layer overlaps with the entire area of ​​the plurality of IDT electrodes.

[0156] <6>

[0157] according to <1> ~ <5> The elastic wave device described in any one of the following, wherein,

[0158] The elastic wave device also includes an elastic wave resonator connected to the longitudinally coupled resonator.

[0159] The elastic wave resonator has a third IDT electrode disposed on the piezoelectric layer.

[0160] When viewed from above the first and second main surfaces, the metal layer overlaps with at least a portion of the third IDT electrode.

[0161] <7>

[0162] according to <1> ~ <6> The elastic wave device described in any one of the following, wherein,

[0163] The metal layer is connected to the ground.

[0164] <8>

[0165] according to <1> ~ <7> The elastic wave device described in any one of the following, wherein,

[0166] The piezoelectric substrate further includes a support substrate.

[0167] The supporting substrate, the metal layer, and the piezoelectric layer are stacked in sequence.

[0168] <9>

[0169] according to <8> The elastic wave device, wherein,

[0170] The piezoelectric substrate further comprises:

[0171] A low-velocity sound layer, disposed between the metal layer and the supporting substrate, wherein the sound velocity of the bulk waves is lower than that of the bulk waves propagating in the piezoelectric layer; and

[0172] A high-velocity sound layer is disposed between the low-velocity sound layer and the support substrate, wherein the volume wave sound velocity propagating therein is higher than the elastic wave sound velocity propagating in the piezoelectric layer.

[0173] Industrial availability

[0174] This invention, as an elastic wave device configured at the front end, can be widely used in communication devices such as portable telephones.

[0175] Explanation of reference numerals in the attached figures

[0176] 1, 1A, 1B, 200: Elastic wave filters;

[0177] 10, 10A, 10B: Longitudinal coupled resonators;

[0178] 11, 12, 13, 14, 15, 16, 17, 18: IDT electrodes;

[0179] 21, 22, 23: Series arm harmonic oscillators;

[0180] 31, 32, 33: Parallel arm harmonic oscillators;

[0181] 41, 42: Reflective electrodes;

[0182] 50, 50A, 50B, 250: Multilayer substrates;

[0183] 51, 51A: Piezoelectric layer;

[0184] 51a, 51b: Main face;

[0185] 52, 52A, 52B, 520: Metal layers;

[0186] 53: Low-sound-velocity layer;

[0187] 54: Hypersonic layer;

[0188] 55: Support base plate;

[0189] 61, 62, 63, 64, 65, 66, 67: Electrode fingers;

[0190] 70a, 70b: Connection wiring;

[0191] 71a, 71b: Busbar electrodes;

[0192] 81, 82: Reflective electrode refers to...

[0193] 110, 120: Input / output terminals.

Claims

1. An elastic wave device comprising a longitudinally coupled resonator, the longitudinally coupled resonator having a piezoelectric substrate and a plurality of IDT electrodes, i.e., interdigital transducer electrodes. The piezoelectric substrate comprises: A piezoelectric layer having a first main surface and a second main surface opposite to each other, wherein the plurality of IDT electrodes are disposed on the first main surface; and The metal layer is bonded to the second main surface of the piezoelectric layer. Each of the plurality of IDT electrodes comprises a plurality of electrode fingers arranged in parallel with each other. Viewed from above the first and second main surfaces, the metal layer is configured to span adjacent electrode fingers included in one of the plurality of IDT electrodes.

2. The elastic wave device according to claim 1, wherein, The plurality of IDT electrodes includes a first IDT electrode and a second IDT electrode arranged adjacent to each other in a direction perpendicular to the extension direction of the plurality of electrode fingers. When viewed from above the first and second main surfaces, the metal layer does not overlap with the inter-electrode region of the IDT, which is sandwiched by the electrode finger of the plurality of electrode fingers included in the first IDT electrode that is closest to the second IDT electrode, and the electrode finger of the plurality of electrode fingers included in the second IDT electrode that is closest to the first IDT electrode.

3. The elastic wave device according to claim 2, wherein, A slit portion where no metal film is formed is formed in the metal layer. When viewed from above, the first main surface and the second main surface overlap with the region between the IDT electrodes.

4. The elastic wave device according to claim 2, wherein, The metal layer comprises a first metal layer and a second metal layer that are separated from each other. When viewed from above, the first main surface and the second main surface overlap with the first IDT electrode, and the second metal layer overlaps with the second IDT electrode.

5. The elastic wave device according to claim 1, wherein, When viewed from above the first and second main surfaces, the metal layer overlaps with the entire area of ​​the plurality of IDT electrodes.

6. The elastic wave device according to any one of claims 1 to 5, wherein, The elastic wave device also includes an elastic wave resonator connected to the longitudinally coupled resonator. The elastic wave resonator has a third IDT electrode disposed on the piezoelectric layer. When viewed from above the first and second main surfaces, the metal layer overlaps with at least a portion of the third IDT electrode.

7. The elastic wave device according to any one of claims 1 to 6, wherein, The metal layer is connected to the ground.

8. The elastic wave device according to any one of claims 1 to 7, wherein, The piezoelectric substrate further includes a support substrate. The supporting substrate, the metal layer, and the piezoelectric layer are stacked in sequence.

9. The elastic wave device according to claim 8, wherein, The piezoelectric substrate further comprises: A low-velocity sound layer is disposed between the metal layer and the support substrate, wherein the sound velocity of the bulk wave is lower than that of the bulk wave propagating in the piezoelectric layer. and A high-velocity layer is disposed between the low-velocity layer and the support substrate, wherein the velocity of the propagating bulk wave is higher than the velocity of the elastic wave propagating in the piezoelectric layer.

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