Elastic wave device

Abstract

Provided is an elastic wave device capable of effectively suppressing a transverse mode. An elastic wave device (1) of the present invention includes a piezoelectric substrate (2) and an IDT electrode (3A to 3C). The IDT electrode (3A to 3C) includes a first pitch portion (E) in which electrode fingers have a relatively wide pitch and a second pitch portion (F) in which electrode fingers have a relatively narrow pitch. A central region (B) is located on a central side in a direction in which the electrode fingers extend, and a first edge region (Ca) and a second edge region (Cb) are located on both sides of the central region (B). A plurality of mass addition films is provided in the first edge region (Ca) and the second edge region (Cb). The plurality of mass addition films includes a plurality of first mass addition films (9a) provided in the first pitch portion (E) and a plurality of second mass addition films (9b) provided in the second pitch portion (F). The length of the first mass addition films (9a) in an elastic wave propagation direction is longer than the length of the second mass addition films (9b) in the elastic wave propagation direction.

Description

TECHNICAL FIELD

[0001] The present application relates to an elastic wave device. BACKGROUND

[0002] Conventionally, elastic wave devices have been widely used for filters of portable telephones and the like.

[0003] In Patent Literature 1 described below, an example of a surface acoustic wave resonator is described. In the surface acoustic wave resonator, a plurality of IDT (Interdigital Transducer) electrodes are provided on a piezoelectric substrate. The plurality of IDT electrodes are arranged along an elastic wave propagation direction. A part of the electrode fingers of each IDT electrode has a different electrode finger pitch from the other part.

[0004] In the elastic wave device described in Patent Literature 2 described below, an IDT electrode has a central region and a pair of edge regions. The pair of edge regions are arranged to sandwich the central region in a direction in which the electrode fingers extend. In the edge regions, a mass addition film is provided on the IDT electrode. The mass addition film extends along the elastic wave propagation direction. Thus, suppression of a transverse mode using a piston mode is achieved.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: Japanese Patent Application Publication No. 2006-333171

[0008] Patent Literature 2: International Publication No. 2017 / 110586 SUMMARY

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] In a case where the IDT electrode has a part with a relatively narrow electrode finger pitch and a part with a relatively wide electrode finger pitch as in Patent Literature 1, even if a mass addition film is provided as in Patent Literature 2, the transverse mode cannot be sufficiently suppressed.

[0011] An object of the present application is to provide an elastic wave device capable of effectively suppressing a transverse mode.

[0012] MEANS FOR SOLVING THE PROBLEMS

[0013] In a certain broad aspect of the elastic wave device of the present application, there are provided: a piezoelectric substrate; a plurality of IDT electrodes provided on the piezoelectric substrate, arranged in an elastic wave propagation direction, and each having a pair of bus bars and a plurality of electrode fingers, at least one of the IDT electrodes including a first pitch portion in which electrode finger pitches are relatively wide and a second pitch portion in which electrode finger pitches are relatively narrow, a portion in which adjacent electrode fingers overlap in the elastic wave propagation direction being a crossover region, the crossover region including a central region located on a central side in a direction in which the plurality of electrode fingers extend and a pair of edge regions disposed on both sides of the central region in the direction in which the plurality of electrode fingers extend and each including a tip portion of the plurality of electrode fingers, a pair of gap regions being disposed between the crossover region and the pair of bus bars in each of the IDT electrodes, the elastic wave device further including a plurality of mass addition films provided so as to overlap, in plan view, portions of the plurality of electrode fingers located in the pair of edge regions, the plurality of mass addition films including a plurality of first mass addition films disposed in the first pitch portion and a plurality of second mass addition films disposed in the second pitch portion, each of the first mass addition films being provided so as to overlap, in plan view, at least one of the electrode fingers, each of the second mass addition films being provided so as to overlap, in plan view, one of the electrode fingers and not to overlap an electrode finger adjacent to the electrode finger, a length of the first mass addition film in the elastic wave propagation direction being longer than a length of the second mass addition film in the elastic wave propagation direction.

[0014] In another broad aspect of the elastic wave device of the present application, there is provided: a piezoelectric substrate; a plurality of IDT electrodes provided on the piezoelectric substrate, arranged in an elastic wave propagation direction, and each having a pair of bus bars and a plurality of electrode fingers, at least one of the IDT electrodes including a first pitch portion in which the electrode fingers have a relatively wide pitch and a second pitch portion in which the electrode fingers have a relatively narrow pitch, a portion in which adjacent ones of the electrode fingers overlap in the elastic wave propagation direction being a crossover region, the crossover region including a central region located on a central side in a direction in which the plurality of electrode fingers extend and a pair of edge regions disposed on both sides of the central region in the direction in which the plurality of electrode fingers extend and each including a leading end portion of the plurality of electrode fingers, a pair of gap regions being disposed between the crossover region and the pair of bus bars in each of the IDT electrodes, a width of the pair of edge regions of the plurality of electrode fingers in the first pitch portion being wider than a width in the central region, a width of the pair of edge regions of the plurality of electrode fingers in the second pitch portion being equal to or less than the width in the central region, and the elastic wave device further including a plurality of mass addition films provided so as to overlap, in plan view, the plurality of electrode fingers in the first pitch portion and the second pitch portion in the pair of edge regions, each of the mass addition films being provided so as to overlap, in plan view, the plurality of electrode fingers and a portion between the plurality of electrode fingers.

[0015] Effects of the Invention

[0016] According to the elastic wave device of the present application, a transverse mode can be effectively suppressed. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a plan view of an elastic wave device of a first embodiment of the present application.

[0018] Figure 2 is a front cross-sectional view showing a portion of the elastic wave device of the first embodiment of the present application.

[0019] Figure 3 is a plan view showing a portion of an elastic wave device of a first modified example of the first embodiment of the present application.

[0020] Figure 4 is a plan view showing a portion of an elastic wave device of a second modified example of the first embodiment of the present application.

[0021] Figure 5 is a plan view showing a portion of an elastic wave device of a third modified example of the first embodiment of the present application.

[0022] Figure 6 is a plan view of an elastic wave device of a fourth modified example of the first embodiment of the present application.

[0023] Figure 7 is a plan view showing a part of an elastic wave device of a second embodiment of the present application.

[0024] Figure 8 is a plan view of an elastic wave device of a third embodiment of the present application.

[0025] Figure 9 is a plan view showing a part of an elastic wave device of the third embodiment of the present application.

[0026] Figure 10 is a front sectional view showing a part of the elastic wave device of the third embodiment of the present application.

[0027] Figure 11 is a sectional view showing a part of a cross section along the second direction of an elastic wave device of a fourth embodiment of the present application.

[0028] Figure 12 is a plan view showing a part of an elastic wave device of a fifth embodiment of the present application. DETAILED DESCRIPTION

[0029] Hereinafter, specific embodiments of the present application will be described with reference to the drawings, thereby making the present application clear.

[0030] Note that each of the embodiments described in this specification is an exemplary embodiment, and it is foreseen that partial substitution or combination of structures can be made between different embodiments.

[0031] Figure 1 is a plan view of an elastic wave device of a first embodiment of the present application.

[0032] The elastic wave device 1 of the present embodiment is a longitudinal-coupled resonator type elastic wave filter. The elastic wave device 1 has a piezoelectric substrate 2.

[0033] A plurality of IDT electrodes are provided on the piezoelectric substrate 2. More specifically, an IDT electrode 3A, an IDT electrode 3B, and an IDT electrode 3C are provided on the piezoelectric substrate 2. In this way, the elastic wave device 1 has three IDT electrodes. However, the number of IDT electrodes is not limited to the above.

[0034] IDT electrode 3A has a pair of busbars and multiple electrode fingers. More specifically, IDT electrode 3A has a first busbar 4, a second busbar 5, multiple first electrode fingers 6, and multiple second electrode fingers 7. The first busbar 4 and the second busbar 5 are opposite to each other. One end of each of the multiple first electrode fingers 6 is connected to the first busbar 4. One end of each of the multiple second electrode fingers 7 is connected to the second busbar 5. The multiple first electrode fingers 6 and the multiple second electrode fingers 7 are inserted alternately. It should be noted that in this specification, sometimes the first electrode finger 6 or the second electrode finger 7 is simply referred to as an electrode finger. IDT electrode 3B and IDT electrode 3C also each have a pair of busbars and multiple electrode fingers.

[0035] An elastic wave is excited by applying an alternating current voltage to IDT electrode 3A. The same applies to IDT electrodes 3B and 3C. Multiple IDT electrodes are arranged in the direction of elastic wave propagation. More specifically, IDT electrode 3B is positioned between IDT electrodes 3A and 3C.

[0036] Here, the direction of elastic wave propagation is defined as the first direction x, and the direction in which the multiple electrodes extend is defined as the second direction y. The first direction x and the second direction y are orthogonal. A pair of reflectors 8A and 8B are disposed on both sides of the multiple IDT electrodes on the piezoelectric substrate 2 along the first direction x. More specifically, reflectors 8A and 8B are configured to sandwich IDT electrodes 3A, 3B, and 3C. Reflector 8A is adjacent to IDT electrode 3A, and reflector 8B is adjacent to IDT electrode 3C. IDT electrodes 3A, 3B, and 3C, as well as reflectors 8A and 8B, may include a single-layer metal film or a stacked metal film.

[0037] like Figure 1 As shown, the IDT electrode 3B includes a first spacing portion E and a second spacing portion F. In the first spacing portion E, the electrode finger spacing is relatively wide. In the second spacing portion F, the electrode finger spacing is relatively narrow. The electrode finger spacing refers to the distance between the centers of adjacent electrode fingers. The IDT electrode 3B has one first spacing portion E and two second spacing portions F. More specifically, the first spacing portion E is located at the center in a first direction x of the IDT electrode 3B. A pair of second spacing portions F are located on either side of the first spacing portion E in the first direction x.

[0038] On the other hand, in the IDT electrode 3A, the second pitch portion F is located on the IDT electrode 3B side. The other portions in the IDT electrode 3A are configured as the first pitch portion E. Likewise, in the IDT electrode 3C, the second pitch portion F is located on the IDT electrode 3B side. The other portions in the IDT electrode 3C are configured as the first pitch portion E. By each IDT electrode having the first pitch portion E and the second pitch portion F, it is possible to improve the steepness in the filter characteristic. Note that, in the present specification, the steepness being high means that, near the end portion passing through the frequency band, the amount of change in frequency is small with respect to the amount of change in some fixed attenuation.

[0039] The configuration of the first pitch portion E and the second pitch portion F in each IDT electrode is not limited to the above. At least one of the plurality of IDT electrodes can have the first pitch portion E and the second pitch portion F.

[0040] In the present embodiment, the width of the electrode finger in the first pitch portion E and the width of the electrode finger in the second pitch portion F are the same. The width of the electrode finger refers to the dimension of the electrode finger in the first direction x. The width of each electrode finger is fixed in the second direction y. Note that, for example, the width of the electrode finger in the second pitch portion F can also be narrower than the width of the electrode finger in the first pitch portion E.

[0041] Here, in each IDT electrode, the portion where adjacent electrode fingers overlap in the first direction x is a cross region A. The cross region A includes a central region B and a pair of edge regions. The central region B is located on the central side in the second direction y. Specifically, the pair of edge regions is a first edge region Ca and a second edge region Cb. The first edge region Ca is located on the first bus bar 4 side. The second edge region Cb is located on the second bus bar 5 side. In the present embodiment, the central regions B of all the IDT electrodes overlap when viewed from the first direction x. The first edge regions Ca of all the IDT electrodes overlap when viewed from the first direction x. Further, the second edge regions Cb of all the IDT electrodes overlap when viewed from the first direction x.

[0042] The plurality of mass addition films are disposed so as to overlap, in plan view, the portions of the plurality of electrode fingers located in the first edge region Ca and the second edge region Cb. More specifically, the plurality of mass addition films are respectively provided on the IDT electrode 3A, on the IDT electrode 3B, and on the IDT electrode 3C. The plurality of mass addition films include a first mass addition film 9a provided on the first edge region Ca and the second edge region Cb, and a second mass addition film 9b provided on the first edge region Ca and the second edge region Cb. In other words, the plurality of mass addition films include a plurality of first mass addition films 9a and a plurality of second mass addition films 9b.

[0043] The first mass-added film 9a is strip-shaped and disposed on the first spacing portion E. Each first mass-added film 9a is disposed on the plurality of electrode fingers. More specifically, the first mass-added film 9a is not only disposed on the plurality of electrode fingers, but also disposed on the portion of the piezoelectric substrate 2 located between the plurality of electrode fingers.

[0044] On the other hand, a second mass-adding film 9b is disposed on the second spacing portion F. Each second mass-adding film 9b is disposed on one electrode finger. The second mass-adding films 9b are not disposed between the electrode fingers. Here, the dimension of the mass-adding film along the first direction x is defined as the length of the mass-adding film. The length of the first mass-adding film 9a is longer than the length of the second mass-adding film 9b. The first mass-adding film 9a and the second mass-adding film 9b can be metal films or dielectric films.

[0045] This embodiment is characterized by the following structure: 1) At least one IDT electrode has a first spacing portion E and a second spacing portion F. 2) A strip-shaped first mass-adding film 9a is disposed in the first spacing portion E. 3) A second mass-adding film 9b is disposed in the second spacing portion F. 4) The length of the first mass-adding film 9a is longer than the length of the second mass-adding film 9b. 5) The first mass-adding film 9a and the second mass-adding film 9b overlap with portions of the electrode fingers located in the first edge region Ca and the second edge region Cb when viewed from above. Therefore, transverse mold can be effectively suppressed. The details are described below.

[0046] A first mass-added membrane 9a and a second mass-added membrane 9b are provided in the first edge region Ca. Therefore, the sound speed in the first edge region Ca is lower. Thus, the first edge region Ca constitutes a low-sound-speed region. A low-sound-speed region is a region where the sound speed is lower than that in the central region B. Similarly, the second edge region Cb also constitutes a low-sound-speed region. When the sound speed in the central region B is defined as V1 and the sound speed in the low-sound-speed region is defined as V2, V2 < V1.

[0047] like Figure 1 As shown, a first edge region Ca and a second edge region Cb are arranged on the outer side of the central region B in the second direction y. That is, a low-sound-velocity region is arranged on the outer side of the central region B in the second direction y. This can suppress transverse modes.

[0048] Here, the inventors discovered that the conditions for suppressing transverse dynamism differ in the first and second spacing portions. For example, the width of each electrode finger of the IDT electrode is fixed in the second direction, and the same mass-added film is provided in both the first and second spacing portions. In this case, it is difficult to sufficiently satisfy the conditions for suppressing transverse dynamism in both the first and second spacing portions. Therefore, it is difficult to sufficiently suppress transverse dynamism.

[0049] In contrast, in the present embodiment, the first mass-adding film 9a in a band shape is arranged in the first interval portion E, and the second mass-adding film 9b is arranged in the second interval portion F. Thus, in both the first interval portion E and the second interval portion F, the condition for suppressing the lateral mode can be satisfied exactly. Therefore, as a whole of the elastic wave device 1, the lateral mode can be suppressed effectively.

[0050] Further, the IDT electrode 3A, the IDT electrode 3B, and the IDT electrode 3C each have a pair of gap regions. The pair of gap regions is arranged between the crossover region A and the pair of bus bars in each IDT electrode. Specifically, the pair of gap regions is a first gap region Da and a second gap region Db. The first gap region Da is located between the first bus bar 4 and the plurality of second electrode fingers 7. In the first gap region Da, only the first electrode fingers 6 and the second electrode fingers 7 are arranged. Thus, a high sound velocity region is constituted in the first gap region Da. The high sound velocity region refers to a region in which the sound velocity is higher than that in the central region B.

[0051] On the other hand, the second gap region Db is located between the second bus bar 5 and the plurality of first electrode fingers 6. In the second gap region Db, only the first electrode fingers 6 and the second electrode fingers 7 are arranged. Thus, a high sound velocity region is constituted in the second gap region Db. When the sound velocity in the high sound velocity region is V3, V1 < V3. The relationship of the sound velocities in the low sound velocity region, the central region B, and the high sound velocity region becomes V2 < V1 < V3. Figure 1 The above-described relationship of each sound velocity is shown. Note that, in the portion in which the relationship of the sound velocities is shown in FIG. 6, as indicated by an arrow V, the more to the left the line indicating the height of each sound velocity is located, the higher the sound velocity is. Figure 1

[0052] In the IDT electrode 3A, the IDT electrode 3B, and the IDT electrode 3C, a low sound velocity region is arranged outside the central region B in the second direction y, and a high sound velocity region is arranged outside the low sound velocity region. Thus, the lateral mode can be suppressed effectively and more reliably.

[0053] Here, the dimension of the mass-adding film along the second direction y is referred to as the width of the mass-adding film. The dimension of the low sound velocity region along the second direction y is referred to as the width of the low sound velocity region. As shown in FIG. 6, the width of the first mass-adding film 9a is the same as the width of the second mass-adding film 9b. Thus, the width of the low sound velocity region does not have discontinuity. Therefore, the degradation of the insertion loss can be suppressed. Note that the width of the first mass-adding film 9a and the width of the second mass-adding film 9b can be different. Figure 1

[0054] ​​In the present embodiment, one first mass additional film 9a is provided in the first edge region Ca in accordance with each first pitch portion E. However, a plurality of first mass additional films 9a can be provided in the first edge region Ca in accordance with each first pitch portion E. Specifically, for example, each first mass additional film 9a can also be provided so as to reach two electrode fingers. In this case, different first mass additional films 9a are arranged on each two electrode fingers.

[0055] Likewise, in the present embodiment, one first mass additional film 9a is provided in the second edge region Cb in accordance with each first pitch portion E. However, a plurality of first mass additional films 9a can be provided in the second edge region Cb in accordance with each first pitch portion E.

[0056] Each second mass additional film 9b is not provided between the electrode fingers. However, the second mass additional film 9b can also reach a portion between the electrode fingers on the piezoelectric substrate 2. Each second mass additional film 9b is provided so as to overlap one electrode finger in plan view, and not overlap an electrode finger adjacent to the electrode finger.

[0057] Hereinafter, other structures of the present embodiment will be described in detail.

[0058] Figure 2 is a front cross-sectional view showing a portion of the elastic wave device of the first embodiment. Note that, Figure 2 shows a cross section in the central region B of the portion in which the IDT electrode 3B is provided.

[0059] The piezoelectric substrate 2 is a laminated substrate including a piezoelectric layer 16. More specifically, in the piezoelectric substrate 2, a support substrate 13, a high sound velocity film 14 as a high sound velocity material layer, a low sound velocity film 15, and the piezoelectric layer 16 are sequentially laminated. On the piezoelectric layer 16, the above-described IDT electrode 3A, IDT electrode 3B, IDT electrode 3C, reflector 8A, and reflector 8B are provided.

[0060] The piezoelectric layer 16 is a lithium tantalate layer. Note that the material of the piezoelectric layer 16 is not limited to the above, and for example, lithium niobate or the like can be used. Here, a wavelength defined by an average value of the electrode finger pitch of the IDT electrode is set to λ. In the present embodiment, the thickness of the piezoelectric layer 16 is 1λ or less. However, the thickness of the piezoelectric layer 16 is not limited to the above.

[0061] The low sound velocity film 15 is a film in which the sound velocity is relatively low. More specifically, the sound velocity of a bulk wave propagating in the low sound velocity film 15 is lower than the sound velocity of a bulk wave propagating in the piezoelectric layer 16. The low sound velocity film 15 is a silicon oxide film. Silicon oxide can be formed by SiO xIn the present embodiment, the low-sonic-velocity film 15 is a SiO2 film. Note that the material of the low-sonic-velocity film 15 is not limited to the above, and for example, a material in which glass, silicon oxynitride, tantalum oxide, or a compound obtained by adding fluorine, carbon, or boron to silicon oxide is a main component can be used.

[0062] The high-sonic-velocity material layer is a layer in which the sonic velocity of a bulk wave propagating through the layer is relatively high. More specifically, the sonic velocity of a bulk wave propagating through the high-sonic-velocity material layer is higher than the sonic velocity of an elastic wave propagating through the piezoelectric layer 16. The high-sonic-velocity film 14, which is a high-sonic-velocity material layer, is a silicon nitride film. Note that the material of the high-sonic-velocity film 14 is not limited to the above, and for example, silicon, aluminum oxide, silicon carbide, silicon oxynitride, sapphire, lithium tantalate, lithium niobate, quartz, alumina, zirconia, cordierite, mullite, bulk talc, forsterite, magnesium oxide, a DLC (diamond-like carbon) film, or diamond, or a dielectric in which the above materials are main components can be used.

[0063] In the present embodiment, the support substrate 13 is a silicon substrate. Note that the material of the support substrate 13 is not limited to the above, and for example, a piezoelectric body such as aluminum oxide, lithium tantalate, lithium niobate, or quartz, various ceramics such as alumina, magnesium oxide, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, bulk talc, or forsterite, a dielectric such as sapphire or diamond, a semiconductor such as gallium nitride, or a resin can be used.

[0064] In the piezoelectric substrate 2, the high-sonic-velocity film 14, the low-sonic-velocity film 15, and the piezoelectric layer 16 are sequentially stacked. By the piezoelectric substrate 2 having such a stacked structure, the Q value can be increased, and the energy of an elastic wave can be effectively confined to the piezoelectric layer 16 side.

[0065] However, the stacked structure of the piezoelectric substrate 2 is not limited to the above. For example, the piezoelectric substrate 2 can not have the low-sonic-velocity film 15. In this case, the piezoelectric substrate 2 can be a three-layer stacked substrate. Specifically, in the piezoelectric substrate 2, the support substrate 13, the high-sonic-velocity film 14, and the piezoelectric layer 16 can be sequentially stacked.

[0066] The high-sonic-velocity material layer can also be a high-sonic-velocity support substrate. In this case, the piezoelectric substrate 2 can be a three-layer stacked substrate. Specifically, in the piezoelectric substrate 2, a high-sonic-velocity support substrate, the low-sonic-velocity film 15, and the piezoelectric layer 16 can be sequentially stacked. Alternatively, the piezoelectric substrate 2 can be a two-layer stacked substrate. Specifically, in the piezoelectric substrate 2, a high-sonic-velocity support substrate and the piezoelectric layer 16 can be sequentially stacked. In these cases, the Q value can be increased. Note that the piezoelectric substrate 2 can be a piezoelectric substrate including only the piezoelectric layer 16.

[0067] Materials used as high-velocity support substrates include, for example, silicon, alumina, silicon carbide, silicon nitride, silicon oxynitride, sapphire, lithium tantalate, lithium niobate, quartz, bauxite, zirconium oxide, cordierite, mullite, block talc, forsterite, magnesium oxide, DLC (diamond-like carbon) film, or diamond, etc., and media with the above materials as the main components.

[0068] like Figure 1 As shown, a mass-addition film 9c is provided on reflector 8A and reflector 8B respectively. The mass-addition film 9c is also strip-shaped, just like the first mass-addition film 9a. However, the mass-addition film 9c may not be provided on reflector 8A and reflector 8B.

[0069] In this embodiment, the elastic wave device 1 is a longitudinally coupled resonator type elastic wave filter. However, it is not limited to this; the elastic wave device 1 may also be a transverse type filter device, etc. In this case, reflectors 8A and 8B may not be provided.

[0070] The following describes a first and a second modification of the first embodiment. In the first and second modifications, the shapes of the electrode fingers in the first spacing portion E or the second spacing portion F of the IDT electrodes 3A, 3B, and 3C differ from those in the first embodiment. In the first and second modifications, the transverse mold can be effectively suppressed in the same way as in the first embodiment.

[0071] exist Figure 3 In the first variation shown, the shape of the electrode fingers in the second spacing portion F differs from that in the first embodiment. The width of the first edge region Ca and the second edge region Cb of the plurality of electrode fingers in the second spacing portion F is less than or equal to the width of the central region B. More specifically, the width of the portion of the second spacing portion F including the front ends of the plurality of electrode fingers is less than or equal to the width of the central region B. Here, the front end of the second electrode finger 27 is contained in the first edge region Ca. In the first edge region Ca, the width of the second electrode finger 27 narrows from the central region B side toward the front end side. Therefore, the width of the front end of the second electrode finger 27 is narrower than the width of the second electrode finger 27 in the central region B. Thus, the width of the second electrode finger 27 in the first edge region Ca is less than or equal to the width of the second electrode finger 27 in the central region B. It should be noted that the width of the first electrode finger 26 in the first edge region Ca is the same as the width of the first electrode finger 26 in the central region B. It should be noted that, as described above, the width of the electrode finger refers to the dimension of the electrode finger along the first direction x.

[0072] On the other hand, the front end portion of the first electrode finger 26 is included in the second edge region Cb. In the second edge region Cb, the width of the first electrode finger 26 narrows from the central region B side toward the front end side. Thus, the width of the front end of the first electrode finger 26 is narrower than the width of the first electrode finger 26 in the central region B. In this way, the width of the first electrode finger 26 in the second edge region Cb is below the width of the electrode finger in the central region B. Note that the width of the second electrode finger 27 in the second edge region Cb is the same as the width of the second electrode finger 27 in the central region B.

[0073] Here, in the first embodiment, the width of the first electrode finger 6 in the first edge region Ca in the first pitch portion E is below the width of the first electrode finger 6 in the central region B. In this way, the width of the first electrode finger 6 in the first edge region Ca in the first pitch portion E is narrower than the width of the first electrode finger 6 in the central region B. In the first embodiment, the width of the second electrode finger 7 in the second edge region Cb in the first pitch portion E is below the width of the second electrode finger 7 in the central region B. In this way, the width of the second electrode finger 7 in the second edge region Cb in the first pitch portion E is narrower than the width of the second electrode finger 7 in the central region B. Figure 3 In the first embodiment, the width of the first electrode finger 6 in the first edge region Ca in the first pitch portion E is below the width of the first electrode finger 6 in the central region B. In this way, the width of the first electrode finger 6 in the first edge region Ca in the first pitch portion E is narrower than the width of the first electrode finger 6 in the central region B. In the first embodiment, the width of the second electrode finger 7 in the second edge region Cb in the first pitch portion E is below the width of the second electrode finger 7 in the central region B. In this way, the width of the second electrode finger 7 in the second edge region Cb in the first pitch portion E is narrower than the width of the second electrode finger 7 in the central region B.

[0074] Further, in the present modification example, the shape of the second mass additional film 29b is different from that of the first embodiment. More specifically, in the first embodiment, the shape of the second mass additional film 9b is a rectangular shape. On the other hand, in the present modification example, the shape of the second mass additional film 29b is a substantially elliptical shape. In the second pitch portion F, in a case where the width of the second electrode finger 27 in the first edge region Ca is below the width of the second electrode finger 27 in the central region B, the second mass additional film 29b provided to the second electrode finger 27 also sometimes becomes a shape with a roundness as in the present modification example.

[0075] In the second modification example shown in FIG. 8, the first electrode finger 36 in the first pitch portion E has a wide portion 36a and a wide portion 36b. The wide portions 36a and 36b are portions where the width of the electrode finger is wider than other portions. The wide portion 36a is located in the first edge region Ca. The wide portion 36b is located in the second edge region Cb. Likewise, the second electrode finger 37 in the first pitch portion E has a wide portion 37a and a wide portion 37b. The wide portion 37a is located in the first edge region Ca. The wide portion 37b is located in the second edge region Cb. Figure 4 In the second modification example shown in FIG. 8, the first electrode finger 36 in the first pitch portion E has a wide portion 36a and a wide portion 36b. The wide portions 36a and 36b are portions where the width of the electrode finger is wider than other portions. The wide portion 36a is located in the first edge region Ca. The wide portion 36b is located in the second edge region Cb. Likewise, the second electrode finger 37 in the first pitch portion E has a wide portion 37a and a wide portion 37b. The wide portion 37a is located in the first edge region Ca. The wide portion 37b is located in the second edge region Cb.

[0076] In this modified example, all the first electrode fingers 36 in the first spacing portion E have wide portions 36a and 36b. All the second electrode fingers 37 in the first spacing portion E have wide portions 37a and 37b. It should be noted that the first spacing portion E may also include first electrode fingers 26 that do not have wide portions 36a or 36b. The first spacing portion E may also include second electrode fingers 27 that do not have wide portions 37a or 37b.

[0077] Here, in the second spacing portion F, the electrode finger spacing is narrow. Therefore, if the multiple electrode fingers in the second spacing portion F have wide portions, the surge resistance may deteriorate. In contrast, in this modified example, the multiple electrode fingers in the second spacing portion F do not have wide portions. Therefore, the surge resistance is less likely to deteriorate.

[0078] In the first spacing portion E of this modified example, the sound velocity in the first edge region Ca and the second edge region Cb decreases through both the width portions and the first mass-added films 9a. Here, in this modified example, the thickness of the first mass-added film 9a is preferably thicker than the thickness of the second mass-added film 9b. In this case, it is easier to further adjust the first spacing portion E and the second spacing portion F to the optimal conditions for suppressing transverse cavitation. Therefore, transverse cavitation can be suppressed more reliably.

[0079] like Figure 1 As shown, a first mass-added film 9a and a second mass-added film 9b are disposed on IDT electrode 3A, IDT electrode 3B, and IDT electrode 3C. More specifically, the first mass-added film 9a and the second mass-added film 9b are disposed on the side of the plurality of electrode fingers opposite to the piezoelectric substrate 2 side. However, each second mass-added film 9b can overlap with one electrode finger when viewed from above. In this case, the edge of each second mass-added film 9b can also be as shown... Figure 4 As shown in the second modified example, it is positioned inside the tip edge of the electrode finger when viewed from above. Alternatively, the tips of each second mass-added film 9b can also be positioned as follows: Figure 5 As shown in the third modified example, it is configured to reach the edge of the electrode fingers when viewed from above. Each of the first mass-added films 9a overlaps with the plurality of electrode fingers when viewed from above. Figure 6 In the fourth variation of the first embodiment shown, a first mass-added film 9a and a second mass-added film 9b are disposed between each IDT electrode and the piezoelectric substrate 2. More specifically, the first mass-added film 9a and the second mass-added film 9b are disposed between the plurality of electrode fingers and the piezoelectric substrate 2. A strip-shaped mass-added film is also disposed between reflectors 8A and 8B and the piezoelectric substrate 2. It should be noted that in Figure 6 In the diagram, each mass of the additional membrane is shown by a dashed line.

[0080] In the first embodiment and its variants, the first mass-adding film 9a is in a strip shape. However, the first mass-adding film 9a can be longer than the second mass-adding film 9b, and the first mass-adding film 9a can not be in a strip shape.

[0081] Figure 7 is a plan view showing a part of the elastic wave device of the second embodiment.

[0082] The present embodiment differs from the first embodiment in that the first mass-adding film 49a is in a single sheet shape. Each first mass-adding film 49a is disposed to overlap with one electrode finger in plan view. The first mass-adding film 49a is not disposed between the electrode fingers. In the above-mentioned aspects other than this, the elastic wave device of the second embodiment has the same structure as the elastic wave device 1 of the first embodiment.

[0083] In the present embodiment, the appropriate condition for suppressing the lateral mode can be provided in both the first spacing portion E and the second spacing portion F. Thus, the lateral mode can be effectively suppressed.

[0084] Note that the first mass-adding film 49a can reach the portion between the electrode fingers on the piezoelectric substrate 2. In this case, for example, two first mass-adding films 49a can reach the same portion between the electrode fingers on the piezoelectric substrate 2.

[0085] In the first embodiment and its variants and the second embodiment, an example in which the first mass-adding film is disposed in the first spacing portion and the second mass-adding film is disposed in the second spacing portion is shown. Hereinafter, an example in which the same mass-adding film is disposed in the first spacing portion and the second spacing portion is shown.

[0086] Figure 8 is a plan view of the elastic wave device of the third embodiment. Figure 9 is a plan view showing a part of the elastic wave device of the third embodiment.

[0087] As Figure 8As shown in the drawing, in the present embodiment, one mass addition film 59 is provided so as to overlap, in plan view, the portions of the plurality of electrode fingers located in the first edge region Ca. The mass addition film 59 is in a band shape. More specifically, the mass addition film 59 is provided to both the plurality of electrode fingers and the portions located between the plurality of electrode fingers. The mass addition film 59 is provided between the IDT electrodes 3A, 3B, and 3C and the piezoelectric substrate 52. In this way, one mass addition film 59 overlaps, in plan view, all of the IDT electrodes in the elastic wave device 51. Therefore, the mass addition film 59 overlaps, in plan view, both the electrode fingers in the first gap portion E and the electrode fingers in the second gap portion F. Likewise, one mass addition film 59 is provided so as to overlap, in plan view, the portions of the plurality of electrode fingers located in the second edge region Cb.

[0088] As shown in the drawing, in the present embodiment, the plurality of electrode fingers in the first gap portion E have the same structure as the first embodiment shown in the drawing. Figure 9 As shown in the drawing, in the present embodiment, the plurality of electrode fingers in the first gap portion E have the same structure as the first embodiment shown in the drawing. Figure 4 As shown in the drawing, in the present embodiment, the plurality of electrode fingers in the first gap portion E have the same structure as the first embodiment shown in the drawing. More specifically, all of the first electrode fingers 36 in the first gap portion E have the wide portion 36a and the wide portion 36b. All of the second electrode fingers 37 in the first gap portion E have the wide portion 37a and the wide portion 37b. Note that, in the first gap portion E, the first electrode finger 26 not having the wide portion 36a or the wide portion 36b can be included. In the first gap portion E, the second electrode finger 27 not having the wide portion 37a or the wide portion 37b can be included.

[0089] In the present embodiment, the mass addition film 59 is provided between the IDT electrodes 3A, 3B, and 3C and the piezoelectric substrate 52. However, the mass addition film 59 can be provided on the IDT electrode 3A, on the IDT electrode 3B, and on the IDT electrode 3C.

[0090] Figure 10 is a front sectional view showing a part of the elastic wave device of the third embodiment.

[0091] The piezoelectric substrate 52 of the elastic wave device 51 is a piezoelectric substrate including only a piezoelectric layer. More specifically, the piezoelectric substrate 52 is a lithium niobate substrate. However, the material and the layer structure of the piezoelectric substrate 52 are not limited to the above. For example, it can be the two-layer or three-layer layer structure described above, or the same layer structure as the first embodiment. Alternatively, the piezoelectric substrate 52 can be a lithium tantalate substrate or the like.

[0092] The characteristic of the present embodiment has the following structure. 1) At least one IDT electrode has a first pitch portion E and a second pitch portion F. 2) The width in the first edge region Ca and the second edge region Cb of the plurality of electrode fingers in the first pitch portion E is wider than the width in the central region B. 3) A strip-shaped mass addition film 59 is disposed in the first pitch portion E and the second pitch portion F. 4) The mass addition film 59 overlaps, in plan view, the portions of the plurality of electrode fingers located in the first edge region Ca and the second edge region Cb.

[0093] In the elastic wave device 51, in the first pitch portion E and the second pitch portion F, the shapes of the electrode fingers in the first edge region Ca and the second edge region Cb are different. More specifically, the plurality of electrode fingers in the second pitch portion F do not have a wide portion, and the plurality of electrode fingers in the first pitch portion E have a wide portion. On the other hand, in the first pitch portion E and the second pitch portion F, the same mass addition film 59 is disposed. Thereby, in both the first pitch portion E and the second pitch portion F, it is possible to set appropriate conditions for suppressing the lateral mode. Therefore, as a whole of the elastic wave device 51, it is possible to effectively suppress the lateral mode.

[0094] Further, the width of the mass addition film 59 is fixed, and the width of the low sound velocity region is also fixed. Therefore, it is possible to suppress the deterioration of the insertion loss.

[0095] Note that, in the present embodiment, the mass addition film 59 extends from between the reflector 8A and the piezoelectric substrate 52 to between the reflector 8B and the piezoelectric substrate 52. However, the mass addition film 59 can not overlap, in plan view, the reflector 8A and the reflector 8B.

[0096] In the present embodiment, one mass addition film 59 is provided in each of the first edge region Ca and the second edge region Cb. Each mass addition film 59 overlaps, in plan view, all of the IDT electrodes. Note that, the mass addition film 59 can not be provided between the IDT electrodes. In this case, a plurality of mass addition films 59 overlap, in plan view, the portions of the plurality of IDT electrodes located in the first edge region Ca. For example, the mass addition film 59 that overlaps, in plan view, the portion of the IDT electrode 3A located in the first edge region Ca and the mass addition film 59 that overlaps, in plan view, the portion of the IDT electrode 3B located in the first edge region Ca are not integral. However, it is preferable that, as in the present embodiment, one mass addition film 59 overlaps, in plan view, the plurality of IDT electrodes. In this case, it is possible to easily form the mass addition film 59, and it is possible to improve productivity.

[0097] The electrode fingers in the second pitch portion F can also be configured similarly to the first modification of the first embodiment. More specifically, the width of the portion of the electrode fingers in the first edge region Ca or the second edge region Cb that contains the leading end portion in the edge region can also be equal to or less than the width in the central region B.

[0098] Figure 11 is a cross-sectional view showing a portion of a cross section of the elastic wave device along the second direction according to the fourth embodiment. More specifically, Figure 11 A portion near the boundary of the central region B and the second edge region Cb of the first electrode finger 6 and the like is shown.

[0099] The present embodiment differs from the first embodiment in that the protective film 64 is provided on the piezoelectric substrate 2. The elastic wave device of the present embodiment has the same structure as the elastic wave device 1 of the first embodiment except for the above aspect.

[0100] The protective film 64 covers the IDT electrode 3B and the plurality of first mass additional films 9a. In addition, the protective film 64 also covers the IDT electrode 3A, the IDT electrode 3C, and the plurality of second mass additional films 9b. Figure 1 The IDT electrode 3A, the IDT electrode 3C, and the plurality of second mass additional films 9b are shown. Each IDT electrode has a portion directly covered by the protective film 64 and a portion indirectly covered by the protective film 64 via each mass additional film. By providing the protective film 64, each IDT electrode is less likely to be damaged.

[0101] As shown in Figure 11 the first mass additional film 9a has a first main face 19d, a second main face 19e, and a side face 19f. The first main face 19d is in contact with the IDT electrode 3B. The second main face 19e is opposite the first main face 19d. The side face 19f connects the first main face 19d and the second main face 19e. The side face 19f is inclined with respect to the thickness direction of the first mass additional film 9a. Note that the thickness direction of the first mass additional film 9a refers to the direction in which the first main face 19d and the second main face 19e are opposite each other. Figure 1 The second mass additional film 9b also has a first main face, a second main face, and a side face similarly to the first mass additional film 9a. The side face of the second mass additional film 9b is also inclined with respect to the thickness direction of the second mass additional film 9b. However, the side face of each mass additional film can not necessarily be inclined.

[0102] In the protective film 64 in this embodiment, the thickness of the portion covering the side surface 19f of each first mass additional film 9a is thinner than the thickness of the portion covering the second main surface 19e of each first mass additional film 9a and the thickness of the portion directly covering each IDT electrode. Further, in the protective film 64, the thickness of the portion covering the side surface of each second mass additional film 9b is thinner than the thickness of the portion covering the second main surface of each second mass additional film 9b and the thickness of the portion directly covering each IDT electrode. Thus, even in the case where the side surface of each first mass additional film 9a and each second mass additional film 9b is inclined, the change in the speed of sound in the vicinity of the boundary between the central region B and the second edge region Cb can be made sharp. More specifically, in the vicinity of the above boundary, the inclination of the change in the speed of sound with respect to the distance in the second direction y can be increased. Likewise, the change in the speed of sound in the vicinity of the boundary between the central region B and the first edge region Ca can also be made sharp. Thus, the lateral mode can be effectively suppressed.

[0103] Figure 12 Fig. 16 is a plan view showing a portion of an elastic wave device of a fifth embodiment.

[0104] The present embodiment is different from the first embodiment in that the first bus bar 74 and the second bus bar 75 of each IDT electrode are each provided with a plurality of opening portions along the first direction x. The elastic wave device of the present embodiment has the same structure as the first embodiment except for the above aspect.

[0105] The first bus bar 74 has a first opening portion formation region Ga. A plurality of opening portions 74d are formed in the first opening portion formation region Ga. Further, the first bus bar 74 has an inner bus bar portion 74a and an outer bus bar portion 74c, and a plurality of connection electrodes 74b. The first opening portion formation region Ga is located between the inner bus bar portion 74a and the outer bus bar portion 74c in the second direction y. Note that the inner bus bar portion 74a among the inner bus bar portion 74a and the outer bus bar portion 74c is located on the side of the intersection region A. The inner bus bar portion 74a and the outer bus bar portion 74c are connected by the plurality of connection electrodes 74b. The plurality of opening portions 74d are opening portions surrounded by the inner bus bar portion 74a, the outer bus bar portion 74c, and the plurality of connection electrodes 74b.

[0106] Likewise, the second bus bar 75 has a second opening portion formation region Gb. A plurality of opening portions 75d are provided in the second opening portion formation region Gb. Further, the second bus bar 75 has an inner bus bar portion 75a and an outer bus bar portion 75c, and a plurality of connection electrodes 75b. The plurality of opening portions 75d are opening portions surrounded by the inner bus bar portion 75a, the outer bus bar portion 75c, and the plurality of connection electrodes 75b. In the present embodiment, a high-speed region is constituted in the first opening portion formation region Ga and the second opening portion formation region Gb.

[0107] In the present embodiment as well as in the first embodiment, the first mass-adding film 9a is arranged in the first interval portion E, and the second mass-adding film 9b is arranged in the second interval portion F. Thus, the transverse mode can be effectively suppressed.

[0108] Explanation of Reference Numerals

[0109] 1 … Elastic wave device;

[0110] 2 … Piezoelectric substrate;

[0111] 3A, 3B, 3C … IDT electrode;

[0112] 4 … First bus bar;

[0113] 5 … Second bus bar;

[0114] 6, 7 … First electrode finger, second electrode finger;

[0115] 8A, 8B … Reflector;

[0116] 9a, 9b … First mass-adding film, second mass-adding film;

[0117] 9c … Mass-adding film;

[0118] 13 … Support substrate;

[0119] 14 … High acoustic velocity film;

[0120] 15 … Low acoustic velocity film;

[0121] 16 … Piezoelectric layer;

[0122] 19d, 19e … First main surface, second main surface;

[0123] 19f … Side surface;

[0124] 26, 27 … First electrode finger, second electrode finger;

[0125] 29b … Second mass-adding film;

[0126] 36, 37 … First electrode finger, second electrode finger;

[0127] 36a, 36b, 37a, 37b … Wide portion;

[0128] 49a … First mass-adding film;

[0129] 51 … Elastic wave device;

[0130] 52 … Piezoelectric substrate;

[0131] 59 … Mass-adding film;

[0132] 64 … protective film

[0133] 74, 75 … first bus bar, second bus bar

[0134] 74a, 75a … inner bus bar portion

[0135] 74b, 75b … connection electrode

[0136] 74c, 75c … outer bus bar portion

[0137] 74d, 75d … opening portion

[0138] A … intersection region

[0139] B … central region

[0140] Ca, Cb … first edge region, second edge region

[0141] Da, Db … first gap region, second gap region

[0142] E, F … first spacing portion, second spacing portion

[0143] Ga, Gb … first opening portion formation region, second opening portion formation region

Claims

1. An elastic wave device comprising: a piezoelectric substrate; and a plurality of IDT electrodes provided on the piezoelectric substrate, arranged in an elastic wave propagation direction, and each having a pair of bus bars and a plurality of electrode fingers, at least one of the IDT electrodes including a first pitch portion in which a pitch of the electrode fingers is relatively wide and a second pitch portion in which a pitch of the electrode fingers is relatively narrow, a portion in which adjacent electrode fingers overlap in the elastic wave propagation direction being a crossover region, the crossover region including a central region located on a central side in a direction in which the plurality of electrode fingers extend and a pair of edge regions disposed on both sides of the central region in the direction in which the plurality of electrode fingers extend and each including a tip end portion of the plurality of electrode fingers, a pair of gap regions being disposed between the crossover region and the pair of bus bars in each of the IDT electrodes, the elastic wave device further comprising a plurality of mass addition films provided so as to overlap, in plan view, portions of the plurality of electrode fingers located in the pair of edge regions, the plurality of mass addition films including a plurality of first mass addition films disposed in the first pitch portion and a plurality of second mass addition films disposed in the second pitch portion, the first mass addition films being provided so as to overlap, in plan view, at least one of the electrode fingers, each of the second mass addition films being provided so as to overlap, in plan view, one of the electrode fingers and not to overlap an electrode finger adjacent to the electrode finger, and a length of the first mass addition films in the elastic wave propagation direction being longer than a length of the second mass addition films in the elastic wave propagation direction.

2. The elastic wave device according to claim 1, wherein a width in the pair of edge regions of the plurality of electrode fingers in the second pitch portion is smaller than a width in the central region.

3. The elastic wave device according to claim 1 or 2, wherein each of the first mass addition films is provided so as to overlap, in plan view, the plurality of electrode fingers in the first pitch portion and portions located between the plurality of electrode fingers.

4. The elastic wave device according to claim 1 or 2, wherein each of the first mass addition films is provided so as to overlap, in plan view, one of the electrode fingers and not to overlap an electrode finger adjacent to the electrode finger.

5. The elastic wave device according to claim 1 or 2, wherein a length of the first mass addition films in a direction in which the plurality of electrode fingers extend is the same as a length of the second mass addition films in the direction in which the plurality of electrode fingers extend.

6. The elastic wave device according to claim 1 or 2, wherein the plurality of mass addition films are provided on a side opposite to the piezoelectric substrate side of the plurality of electrode fingers.

7. The elastic wave device according to claim 6, wherein the plurality of mass addition films each have a first main surface in contact with the IDT electrode, a second main surface opposite to the first main surface, and a side surface connecting the first main surface and the second main surface, the side surface being inclined with respect to a thickness direction of the mass addition film. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The elastic wave device further includes a protective film provided on the piezoelectric substrate so as to cover the IDT electrode and the plurality of mass additional films, In the protective film, a thickness of a portion covering the side surface of the mass additional film is thinner than a thickness of a portion covering the second main surface of the mass additional film and a thickness of a portion directly covering the IDT electrode.

8. The elastic wave device according to claim 1 or 2, wherein The plurality of mass additional films are provided between the plurality of electrode fingers and the piezoelectric substrate.

9. The elastic wave device according to claim 1 or 2, wherein The pair of bus bars of the IDT electrode are each provided with a plurality of opening portions along an elastic wave propagation direction.

10. The elastic wave device according to claim 1 or 2, wherein The piezoelectric substrate is a layered substrate in which a support substrate, a high acoustic velocity film, a low acoustic velocity film, and a piezoelectric layer are sequentially stacked, An acoustic velocity of a bulk wave propagating in the low acoustic velocity film is lower than an acoustic velocity of a bulk wave propagating in the piezoelectric layer, An acoustic velocity of a bulk wave propagating in the high acoustic velocity film is higher than an acoustic velocity of an elastic wave propagating in the piezoelectric layer.

11. The elastic wave device according to claim 1 or 2, wherein The elastic wave device is an elastic wave filter of a longitudinal coupling resonator type further including reflectors provided on both sides of the plurality of IDT electrodes in an elastic wave propagation direction of the piezoelectric substrate.

12. An elastic wave device comprising: a piezoelectric substrate; and a plurality of IDT electrodes provided on the piezoelectric substrate, arranged in an elastic wave propagation direction, and each including a pair of bus bars and a plurality of electrode fingers, at least one of the IDT electrodes includes a first pitch portion in which a pitch of the electrode fingers is relatively wide and a second pitch portion in which a pitch of the electrode fingers is relatively narrow, a portion in which adjacent electrode fingers overlap in the elastic wave propagation direction is a cross region, the cross region includes a central region located on a central side in a direction in which the plurality of electrode fingers extend and a pair of edge regions disposed on both sides of the central region in the direction in which the plurality of electrode fingers extend and each including a tip end portion of the plurality of electrode fingers, in each of the IDT electrodes, a pair of gap regions is disposed between the cross region and the pair of bus bars, a width in the pair of edge regions of the plurality of electrode fingers in the first pitch portion is wider than a width in the central region, a width in the pair of edge regions of the plurality of electrode fingers in the second pitch portion is equal to or less than a width in the central region, the elastic wave device further includes a plurality of mass additional films provided so as to overlap, in plan view, portions of the plurality of electrode fingers in the pair of edge regions in the first pitch portion and the second pitch portion, each of the mass additional films is provided so as to overlap, in plan view, the plurality of electrode fingers and portions between the plurality of electrode fingers.

13. The elastic wave device according to claim 12, wherein each of the mass additional films overlaps, in plan view, all of the IDT electrodes.

14. The elastic wave device according to claim 12 or 13, wherein the plurality of mass-attached films are provided on a side opposite to the piezoelectric substrate side of the plurality of electrode fingers.

15. The elastic wave device according to claim 14, wherein the plurality of mass-attached films each have a first main surface in contact with the IDT electrode, a second main surface opposite to the first main surface, and a side surface connecting the first main surface and the second main surface, the side surface being inclined with respect to a thickness direction of the mass-attached film, the elastic wave device further comprises a protective film provided on the piezoelectric substrate so as to cover the IDT electrode and the plurality of mass-attached films, in the protective film, a thickness of a portion covering the side surface of the mass-attached film is thinner than a thickness of a portion covering the second main surface of the mass-attached film and a thickness of a portion directly covering the IDT electrode.

16. The elastic wave device according to claim 12 or 13, wherein the plurality of mass-attached films are provided between the plurality of electrode fingers and the piezoelectric substrate.

17. The elastic wave device according to claim 12 or 13, wherein the pair of bus bars of the IDT electrode each has a plurality of opening portions provided along an elastic wave propagation direction.

18. The elastic wave device according to claim 12 or 13, wherein the piezoelectric substrate is a layered substrate in which a support substrate, a high acoustic velocity film, a low acoustic velocity film, and a piezoelectric layer are sequentially stacked, an acoustic velocity of a bulk wave propagating in the low acoustic velocity film is lower than an acoustic velocity of a bulk wave propagating in the piezoelectric layer, an acoustic velocity of a bulk wave propagating in the high acoustic velocity film is higher than an acoustic velocity of an elastic wave propagating in the piezoelectric layer.

19. The elastic wave device according to claim 12 or 13, wherein the elastic wave device is a longitudinal-coupled resonator type elastic wave filter further comprising reflectors provided on both sides of the plurality of IDT electrodes in an elastic wave propagation direction of the piezoelectric substrate.

Images