Elastic wave device

Abstract

Provided is an elastic wave device capable of more reliably suppressing a transverse mode. The elastic wave device (1) of the present invention includes a high acoustic velocity film (14), a low acoustic velocity film (15), a piezoelectric layer (16) including lithium tantalate, and an IDT electrode (3) provided on the piezoelectric layer (16). The IDT electrode (3) has first and second bus bars (4, 5) and a plurality of first and second electrode fingers (6, 7). The first and second electrode fingers (6, 7) overlap in the elastic wave propagation direction at a crossover region (A). The crossover region (A) has a central region (B) and first and second edge regions (C1, C2). The IDT electrode (3) has first and second spacing regions (D1, D2) outside the first and second edge regions (C1, C2). The widths of the first and second electrode fingers (6, 7) in the first and second edge regions (C1, C2) are wider than the width in the central region (B). The duty ratio in the first and second edge regions (C1, C2) is 0.62 or more and 0.73 or less.

Description

Technical Field

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

[0002] In the past, elastic wave devices were widely used in filters for portable telephones, etc.

[0003] Patent Document 1 describes an elastic wave device comprising a high-velocity acoustic wave support substrate, a low-velocity acoustic wave film stacked on the high-velocity acoustic wave support substrate, a piezoelectric film including lithium tantalate stacked on the low-velocity acoustic wave film, and an IDT (Interdigital Transducer) electrode disposed on the piezoelectric film. The IDT electrode has a busbar and multiple electrode fingers connected to the busbar. Each electrode finger has a wide portion with a width dimension larger than the center of the electrode finger in the length direction at least on at least one side (base end side or front end side) closer to the central region. By providing the wide portion, the sound velocity at at least one side (base end side or front end side) of the electrode finger can be lower than the sound velocity at the center of the electrode finger. Thus, transverse mode ripple suppression is achieved by utilizing a piston mode. It is disclosed that the duty cycle of the wide portion is ideally set in the range of 0.6 to 0.9.

[0004] Prior art literature

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2018-174595 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] However, in the elastic wave device with a stacked structure as described in Patent Document 1, when the duty cycle of the disclosed wide section is applied, the sound velocity sometimes increases at the base or tip of the electrode fingers. Therefore, the use of the piston mode becomes difficult, and sometimes the transverse mode cannot be sufficiently suppressed.

[0009] The object of the present invention is to provide a device for more reliably suppressing transverse modes of elastic waves.

[0010] Methods for solving problems

[0011] The elastic wave device of the present invention comprises: a high-velocity acoustic material layer; a low-velocity acoustic film disposed on the high-velocity acoustic material layer; a piezoelectric layer disposed on the low-velocity acoustic film, including lithium tantalate; and an IDT electrode disposed on the piezoelectric layer. The sound velocity of a bulk wave propagating in the high-velocity acoustic material layer is higher than the sound velocity of an elastic wave propagating in the piezoelectric layer, and the sound velocity of a bulk wave propagating in the low-velocity acoustic film is lower than the sound velocity of a bulk wave propagating in the piezoelectric layer. The IDT electrode has a first busbar and a second busbar facing each other, a plurality of first electrode fingers connected at one end to the first busbar, and a plurality of second electrode fingers connected at one end to the second busbar and alternately inserted with the plurality of first electrode fingers. When the elastic wave propagation direction is set as a first direction and a direction orthogonal to the first direction is set as a second direction, the first electrode finger... The portion of the first electrode finger and the second electrode finger overlapping in the first direction is an intersection region. The intersection region has a central region located on the central side in the second direction, a first edge region disposed on the first busbar side of the central region, and a second edge region disposed on the second busbar side of the central region. The IDT electrode has a first gap region located between the first edge region and the first busbar, and a second gap region located between the second edge region and the second busbar. The width of the first electrode finger and the second electrode finger in at least one of the first edge region and the second edge region is wider than the width in the central region. The duty cycle of the first edge region and the second edge region is 0.62 or more and 0.73 or less.

[0012] Invention Effects

[0013] The elastic wave device according to the present invention can suppress transverse modes more reliably. Attached Figure Description

[0014] Figure 1 This is a schematic front cross-sectional view of the elastic wave device according to the first embodiment of the present invention.

[0015] Figure 2 This is a schematic top view of the elastic wave device according to the first embodiment of the present invention.

[0016] Figure 3 This is a graph showing the relationship between the duty cycle and the sound velocity ratio V2 / V1 in the edge region of the IDT electrode of the elastic wave device of the first comparative example.

[0017] Figure 4 This is a graph showing the relationship between the duty cycle in the edge region of the IDT electrode of the first embodiment and the second comparative example of the present invention and the sound velocity V2 in the edge region.

[0018] Figure 5This is a graph showing the relationship between the duty cycle in the edge region of the IDT electrode of the first embodiment and the second comparative example of the present invention and the intensity of the ripple in the transverse mode.

[0019] Figure 6 This is a graph showing the relationship between the length of the edge region and the intensity of the ripple in the horizontal mode when the duty cycle in the edge region is 0.65 in the first embodiment of the present invention.

[0020] Figure 7 This is a graph showing the relationship between the LT film thickness, the electrode film thickness, and the optimal duty cycle in the edge region of the IDT electrode.

[0021] Figure 8 This is a schematic front cross-sectional view of the elastic wave device of the fifth variation of the first embodiment of the present invention.

[0022] Figure 9 This is a schematic top view of the elastic wave device according to the second embodiment of the present invention.

[0023] Figure 10 This is a schematic top view of the elastic wave device of the first variation of the second embodiment of the present invention.

[0024] Figure 11 This is a schematic top view of an elastic wave device of a second variation of the second embodiment of the present invention.

[0025] Figure 12 This is a schematic top view of the elastic wave device of the third variation of the second embodiment of the present invention. Detailed Implementation

[0026] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings to make the present invention clear.

[0027] It should be noted that the embodiments described in this specification are illustrative, and it is indicated in advance that partial substitutions or combinations of structures can be made between different embodiments.

[0028] Figure 1 This is a schematic front sectional view of the elastic wave device according to the first embodiment of the present invention. It should be noted that... Figure 1 A cross-section of the central region of the IDT electrode, which will be described later, is shown.

[0029] The elastic wave device 1 includes a piezoelectric substrate 2. An IDT electrode 3 is disposed on the piezoelectric substrate 2. An elastic wave is excited by applying an alternating current voltage to the IDT electrode 3. Here, the propagation direction of the elastic wave is defined as a first direction x, and the direction orthogonal to the first direction x is defined as a second direction y. A pair of reflectors 8A and 8B are disposed on both sides of the elastic wave propagation direction of the IDT electrode 3 on the piezoelectric substrate 2. The elastic wave device 1 of this embodiment is an elastic wave resonator. However, the elastic wave device of the present invention is not limited to an elastic wave resonator, and may also be a filter device having multiple elastic wave resonators, a multiplexer including such a filter device, etc.

[0030] The piezoelectric substrate 2 is a laminated substrate in which a support substrate 13, a hypersonic film 14 as a hypersonic material layer, a low-velocity film 15, and a piezoelectric layer 16 are stacked in this order. The aforementioned IDT electrode 3, reflector 8A, and reflector 8B are disposed on the piezoelectric layer 16.

[0031] The piezoelectric layer 16 is a lithium tantalate layer. More specifically, the lithium tantalate used for the piezoelectric layer 16 is 50Y-cut X-propagated LiTaO3. It should be noted that the cutting angle and material of the piezoelectric layer 16 are not limited to the above; for example, lithium niobate, zinc oxide, aluminum nitride, quartz, or PZT (lead zirconate titanate) can also be used.

[0032] The low-velocity film 15 is a relatively low-velocity film. More specifically, the velocity of sound of bulk waves propagating in the low-velocity film 15 is lower than the velocity of sound of bulk waves propagating in the piezoelectric layer 16. The low-velocity film 15 is a silicon oxide film. Silicon oxide can be formed from SiO2. X In this embodiment, the low-velocity film 15 is a SiO2 film. It should be noted that the material of the low-velocity film 15 is not limited to the above; for example, materials containing glass, silicon oxynitride, tantalum oxide, or compounds obtained by adding fluorine, carbon, or boron to silicon oxide as the main component can also be used.

[0033] The hypersonic material layer is a relatively high-speed layer. More specifically, the speed of sound of bulk waves propagating in the hypersonic material layer is higher than the speed of sound of elastic waves propagating in the piezoelectric layer 16. The hypersonic film 14, which is the hypersonic material layer, is a silicon nitride film. It should be noted that the material of the hypersonic film 14 is not limited to the above, and for example, a medium mainly composed of the above materials such as silicon, alumina, silicon carbide, 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 can also be used.

[0034] In this embodiment, the support substrate 13 is a silicon substrate. It should be noted that the material of the support substrate 13 is not limited to the above-mentioned materials. For example, it can also be various ceramics such as alumina, lithium tantalate, lithium niobate, and crystal piezoelectric materials, bauxite, magnesium oxide, silicon nitride, aluminum nitride, silicon carbide, zirconium oxide, cordierite, mullite, block talc, and forsterite, as well as dielectrics such as sapphire, diamond, and glass, semiconductors such as gallium nitride, or resins.

[0035] By having a stacked structure in which a high-velocity acoustic film 14, a low-velocity acoustic film 15 and a piezoelectric layer 16 are stacked on the piezoelectric substrate 2, the Q value can be improved and the energy of elastic waves can be effectively contained on the side of the piezoelectric layer 16.

[0036] A protective film 9 is provided on the piezoelectric substrate 2 to cover the IDT electrode 3. In this embodiment, the protective film 9 is a silicon oxide film. It should be noted that the material of the protective film 9 is not limited to the above. It is also possible that the protective film 9 is not required. However, the elastic wave device 1 preferably has a protective film 9. As a result, the IDT electrode 3 is less likely to be damaged. Furthermore, when the protective film 9 is a silicon oxide film, the absolute value of the frequency temperature coefficient TCF can be reduced, and the frequency temperature characteristics can be improved.

[0037] Figure 2 This is a schematic top view of the elastic wave device according to the first embodiment. It should be noted that... Figure 2 The protective film 9 is omitted. (In the following...) Figure 2 In other schematic top views, the protective film 9 is sometimes omitted.

[0038] The IDT electrode 3 has a first busbar 4 and a second busbar 5 facing each other. The first busbar 4 has a plurality of first openings 4d along a first direction x. The second busbar 5 also has a plurality of second openings 5d along the first direction x. The IDT electrode 3 has a plurality of first electrode fingers 6, one end of which is connected to the first busbar 4. The other ends of the first electrode fingers 6 are spaced apart and facing the second busbar 5. The IDT electrode 3 has a plurality of second electrode fingers 7, one end of which is connected to the second busbar 5. The other ends of the second electrode fingers 7 are spaced apart and facing the first busbar 4. The plurality of first electrode fingers 6 and the plurality of second electrode fingers 7 are inserted alternately.

[0039] In the IDT electrode 3, the portion where the first electrode finger 6 and the second electrode finger 7 overlap in the first direction x is the intersection region A. The intersection region A has a central region B, a first edge region C1, and a second edge region C2. The central region B is located on the central side in the second direction y within the intersection region A. The first edge region C1 is disposed on the side of the first busbar 4 of the central region B. The second edge region C2 is disposed on the side of the second busbar 5 of the central region B. It should be noted that, hereinafter, the first edge region C1 and the second edge region C2 may sometimes be referred to simply as edge regions.

[0040] The IDT electrode 3 has a first spacing region D1 and a second spacing region D2. The first spacing region D1 is located between the first edge region C1 and the first busbar 4. The second spacing region D2 is located between the second edge region C2 and the second busbar 5.

[0041] The first busbar 4 has a first inner busbar region E1 and a first outer busbar region G1. The first inner busbar region E1 is located on the intersection region A side of the first busbar 4. The first outer busbar region G1 is located on the outer side of the first inner busbar region E1 in the second direction y. The portion of the first busbar 4 located in the first inner busbar region E1 is the first inner busbar portion 4a, and the portion located in the first outer busbar region G1 is the first outer busbar portion 4c.

[0042] The first busbar 4 has a first opening forming region F1. The first opening forming region F1 is located between the first inner busbar region E1 and the first outer busbar region G1 and has the aforementioned plurality of first openings 4d formed therein. It should be noted that the first busbar 4 has a plurality of first connecting electrodes 4b. The plurality of first connecting electrodes 4b connect the first inner busbar portion 4a and the first outer busbar portion 4c. The plurality of first openings 4d are openings surrounded by the first inner busbar portion 4a, the first outer busbar portion 4c and the plurality of first connecting electrodes 4b.

[0043] Multiple first connecting electrodes 4b extend along the extension lines of multiple first electrode fingers 6. Here, the width of the connecting electrodes and electrode fingers along the first direction x is defined as the width of the connecting electrodes and electrode fingers. The width of the first connecting electrodes 4b is the same as the width of the first electrode fingers 6 in the central region B. It should be noted that the configuration of the multiple first connecting electrodes 4b is not limited to the above, for example, they may also extend along the extension lines of multiple second electrode fingers 7. The width of the first connecting electrodes 4b may also be different from the width of the first electrode fingers 6 in the central region B.

[0044] Similarly, the second busbar 5 of the IDT electrode 3 has a second inner busbar region E2, a second outer busbar region G2, and a second opening forming region F2. The portion located in the second inner busbar region E2 is the second inner busbar portion 5a, and the portion located in the second outer busbar region G2 is the second outer busbar portion 5c. The aforementioned plurality of second openings 5d are formed in the second opening forming region F2.

[0045] The second busbar 5 has a plurality of second connecting electrodes 5b. The plurality of second connecting electrodes 5b connect the second inner busbar portion 5a and the second outer busbar portion 5c. The plurality of second openings 5d are openings surrounded by the second inner busbar portion 5a, the second outer busbar portion 5c and the plurality of second connecting electrodes 5b. It should be noted that the first busbar 4 and the second busbar 5 may also not have the first opening forming region F1 and the second opening forming region F2.

[0046] Reflector 8A also has multiple first openings 8a and multiple second openings 8c. Reflector 8B also has multiple first openings 8b and multiple second openings 8d. More specifically, the first openings 8a and 8b of reflectors 8A and 8B overlap with the first opening 4d of the first busbar 4 in the first direction x. The second openings 8c and 8d of reflectors 8A and 8B overlap with the second opening 5d of the second busbar 5 in the first direction x. It should be noted that reflectors 8A and 8B may also not have the first openings 8a and 8b, and the second openings 8c and 8d.

[0047] like Figure 2 As shown, the first electrode finger 6 of the IDT electrode 3 has a first width portion 6a in the portion located in the first edge region C1, which is wider than the portion located in the central region B. Similarly, the second electrode finger 7 has a first width portion 7a in the portion located in the first edge region C1. Furthermore, the first electrode finger 6 has a second width portion 6b in the portion located in the second edge region C2, which is wider than the portion located in the central region B. Similarly, the second electrode finger 7 has a second width portion 7b in the portion located in the second edge region C2.

[0048] In this embodiment, the duty cycle is 0.45 in the central region B of the IDT electrode 3. The duty cycle is 0.62 or higher and 0.73 or lower in the first edge region C1 and the second edge region C2. Therefore, the sound speed in the first edge region C1 and the second edge region C2 is lower than the sound speed in the central region B. A first low-sound-speed region L1 is formed in the first edge region C1. A second low-sound-speed region L2 is formed in the second edge region C2.

[0049] In this specification, the first low-sound speed region L1 and the second low-sound speed region L2 are sometimes simply referred to as low-sound speed regions. A low-sound speed region is a region where the sound speed is lower than that of the central region B. Here, the sound speed in the central region B is defined as V1, and the sound speed in the first edge region C1 and the second edge region C2 is defined as V2. In the case where the first low-sound speed region L1 and the second low-sound speed region L2 are respectively constructed in the first edge region C1 and the second edge region C2 as in this embodiment, V2 < V1.

[0050] However, the width of the first electrode finger 6 and the second electrode finger 7 in at least one of the first edge regions C1 and C2 is wider than their width in the central region B. Therefore, the duty cycle in the first edge region C1 and the second edge region C2 is 0.62 or higher and 0.73 or lower.

[0051] In the first interval region D1, only the first electrode finger 6 of the first electrode finger 6 and the second electrode finger 7 are provided. Therefore, the speed of sound in the first interval region D1 is higher than the speed of sound in the central region B. The first interval region D1 constitutes a first hypersonic region H1. Similarly, in the second interval region D2, only the second electrode finger 7 of the first electrode finger 6 and the second electrode finger 7 are provided. Therefore, the speed of sound in the second interval region D2 is higher than the speed of sound in the central region B. The second interval region D2 constitutes a second hypersonic region H2.

[0052] In this specification, the first hypersonic region H1 and the second hypersonic region H2 are sometimes simply referred to as hypersonic regions. A hypersonic region is a region where the speed of sound is higher than that of the central region B. Here, the speed of sound in the first interval region D1 and the second interval region D2 is set to V3. In the case where the first hypersonic region H1 and the second hypersonic region H2 are respectively constructed in the first interval region D1 and the second interval region D2 as in this embodiment, V1 < V3.

[0053] The relationship between the sound speeds in each region is V2 < V1 < V3. Figure 2 This illustrates the relationships between the various sound velocities as described above. It should be noted that, in... Figure 2 The section showing the relationship between sound speeds, as indicated by arrow V, shows that the line representing the altitude of each sound speed is further to the left, indicating a higher sound speed. Figure 2 The same applies to the other diagrams. It should be noted that high-speed regions are also formed in the first opening region F1 and the second opening region F2.

[0054] In this embodiment, the IDT electrode 3 comprises a stacked metal film consisting of a Ti layer, an AlCu layer, and another Ti layer stacked in that order, starting from the piezoelectric substrate 2 side. The Ti layer is a bonding layer, the AlCu layer is the main electrode layer, and the Ti layer is a bonding layer. It should be noted that the Cu content in the main electrode layer is 2% by weight or less. Here, in this specification, the main electrode layer refers to a layer that occupies 50% or more of the mass of the IDT electrode.

[0055] The materials of reflectors 8A and 8B are the same as those of IDT electrode 3. It should be noted that the materials of IDT electrode 3, reflector 8A, and reflector 8B are not limited to those described above. Alternatively, for example, IDT electrode 3 may consist only of the main electrode layer.

[0056] Wiring electrodes can also be disposed on the piezoelectric substrate 2. A portion of the wiring electrodes can also be stacked on the first busbar 4 and the second busbar 5 of the IDT electrode 3. In this case, the IDT electrode 3 is electrically connected to the outside via the wiring electrodes.

[0057] The feature of this embodiment is that the elastic wave device 1 has the following structure: 1) The first electrode finger 6 and the second electrode finger 7 of the IDT electrode 3 have a first width portion 6a, a first width portion 7a, a second width portion 6b, and a second width portion 7b in the first edge region C1 and the second edge region C2, respectively. 2) In the first edge region C1 and the second edge region C2, the duty cycle is 0.62 or more and 0.73 or less. Therefore, the sound velocity in the low-velocity region can be reduced more reliably. Therefore, the piston mode can be established more reliably, and the transverse mode can be suppressed more reliably. Hereinafter, details will be explained by comparing this embodiment, the first comparative example, and the second comparative example.

[0058] Several elastic wave devices of the first comparative examples were prepared. The first comparative examples differ from the first embodiment in that the piezoelectric substrate is a piezoelectric substrate comprising only a piezoelectric layer. It should be noted that the piezoelectric substrate in the first comparative examples is a lithium niobate substrate. The duty cycle in the edge region of the IDT electrode differs among the elastic wave devices of the various comparative examples. In the aforementioned elastic wave devices, the sound velocity ratio V2 / V1, which is the sound velocity V2 in the edge region and V1 in the central region, was investigated.

[0059] Figure 3 This is a graph showing the relationship between the duty cycle and the sound velocity ratio V2 / V1 in the edge region of the IDT electrode in the elastic wave device of the first comparative example. It should be noted that the duty cycle in the central region is 0.45.

[0060] like Figure 3 As shown, when the piezoelectric substrate only includes a piezoelectric layer, the larger the duty cycle in the edge region, the smaller the sound velocity ratio V2 / V1. Figure 3 In the case shown, the sound velocity V1 in the central region is constant. Therefore, the larger the duty cycle in the edge region, the lower the sound velocity V2 in the edge region. Thus, it can be seen that when the piezoelectric substrate only includes a piezoelectric layer, the aforementioned problem of the sound velocity V2 in the edge region increasing with the increase of the duty cycle will not occur.

[0061] On the other hand, multiple elastic wave devices having the same structure as the first embodiment and multiple elastic wave devices of the second comparative examples were prepared. The elastic wave devices of the second comparative examples differ from those of the first embodiment in that their duty cycle in the edge region is less than 0.62 or greater than 0.73. Among the multiple elastic wave devices having the same structure as the first embodiment, the duty cycle and the wavelength of the IDT electrode are different. Similarly, among the multiple elastic wave devices of the second comparative examples, the duty cycle and the wavelength of the IDT electrode are also different. The sound velocity V2 in the edge region of each of the above elastic wave devices was investigated.

[0062] The design parameters for the aforementioned elastic wave devices are summarized below. It should be noted that the wavelength defined by the electrode finger spacing of the IDT electrodes is denoted as λ. The electrode finger spacing refers to the distance between the centers of adjacent first and second electrode fingers.

[0063] Support substrate: Material…Si

[0064] High sonic membrane: Material...SiN, film thickness...900nm

[0065] Low-velocity membrane: Material…SiO2, film thickness…600nm

[0066] Piezoelectric layer: Material…50Y cut X-propagation LiTaO3, film thickness…600nm

[0067] IDT Electrode: Material… Ti / AlCu / Ti from the piezoelectric substrate side, film thickness of each layer… 12nm / 100nm / 4nm from the piezoelectric substrate side.

[0068] Duty cycle: Central region…0.45, peripheral region…varies within the range of 0.45 to 0.9.

[0069] The wavelength λ of the IDT electrode is 1.5μm, 2μm, or 2.5μm.

[0070] Protective film: Material...SiO2, film thickness...35nm

[0071] Figure 4 This is a graph showing the relationship between the duty cycle in the edge region of the IDT electrode of the first embodiment and the sound velocity V2 in the edge region.

[0072] like Figure 4 As shown, when the wavelength λ is 2.5 μm, the sound velocity V2 is lowest when the duty cycle in the edge region is approximately 0.65. When the duty cycle is less than approximately 0.65, the higher the duty cycle, the lower the sound velocity V2. On the other hand, when the duty cycle is greater than approximately 0.65, the higher the duty cycle, the higher the sound velocity. The same trend is observed when the wavelength λ is 1.5 μm or 2 μm. Thus, in piezoelectric substrates with... Figure 1 In the case of the layered structure shown, the sound speed increases when the duty cycle is too large. In the first embodiment, the duty cycle in the edge region is 0.62 or more and 0.73 or less. It can be seen that the sound speed in the edge region is particularly low within this range.

[0073] Here, the intensity of the ripple in the transverse mode was investigated in each of the aforementioned elastic wave devices. It should be noted that the wavelength λ was set to 2 μm, and the number of electrode finger pairs of the IDT electrodes was set to 100 pairs. When the dimension of the cross region along the second direction is defined as the cross width, the cross width is set to 10λ. Other design parameters are the same as described above.

[0074] Figure 5 This is a graph showing the relationship between the duty cycle in the edge region of the IDT electrode of the first embodiment and the intensity of the ripple in the transverse mode.

[0075] like Figure 5 As shown, in the first embodiment, ripple can be suppressed compared to the second comparative example. As described above, in the first embodiment, the sound velocity in the edge region can be reduced more reliably and effectively. Therefore, the piston mode can be established more reliably. Therefore, in the first embodiment, the transverse mode can be suppressed more reliably and effectively.

[0076] Furthermore, in the elastic wave device having the structure of the first embodiment, the relationship between the length of the edge region of the IDT electrode and the intensity of the ripple in the transverse mode was investigated. It should be noted that the length of the edge region refers to the dimension of the edge region along the second direction y. The duty cycle in the edge region is 0.65.

[0077] Figure 6 This is a graph showing the relationship between the length of the edge region and the intensity of the ripple in the horizontal mode when the duty cycle in the edge region is 0.65 in the first embodiment.

[0078] like Figure 6As shown, when the length of the edge region is approximately 0.7λ, the absolute value of the ripple intensity in the transverse mode becomes minimal. The length of the edge region is preferably 0.49λ or more and 0.93λ or less. In this case, the absolute value of the ripple intensity in the transverse mode can be set to 1dB or less, further suppressing the transverse mode. The length of the edge region is more preferably 0.6λ or more and 0.9λ or less. In this case, the transverse mode can be suppressed even more effectively.

[0079] As described above, in the first embodiment, the piezoelectric layer 16 is a lithium tantalate layer, and the main electrode layer of the IDT electrode 3 is an AlCu layer. Here, the thickness of the Ti layer on the piezoelectric layer 16 side is 12 nm, and the thickness of the Ti layer on the main electrode layer is 4 nm, thus varying the thickness of the main electrode layer. It should be noted that the Cu content in the main electrode layer is 2% by weight or less. Here, the thickness of the piezoelectric layer 16 is defined as the LT thickness, and the thickness of the first electrode finger 6 and the second electrode finger 7 is defined as the electrode thickness. It should be noted that the LT thickness and the electrode thickness are wavelength-normalized thicknesses normalized to wavelength λ. Furthermore, the duty cycle in the first edge region C1 and the second edge region C2 where the sound velocity is lowest is the optimal duty cycle. In this case, the LT thickness and the electrode thickness are preferably in the range of 0.62 or more and 0.73 or less in the optimal duty cycle of Equation 1 below. This allows for more reliable suppression of transverse modes. This will be explained below.

[0080] [Formula 1]

[0081] Equation 1: Optimal duty cycle = 0.66831566544375 + 0.821829726029454 × ((″electrode film thickness [λ]″) - 0.0625000000000001) + 0.0377723825227273 × ((″LT film thickness [λ]″) - 0.275) + 5.41169053151292 × (((″electrode film thickness [λ]″) - 0.0625000000000001) × ((″electrode film thickness [λ]″) - 0.0625000000000001)-0.00053125)+(-0.325118002174692)×(((″Electrode film thickness[λ]″)-0..0625000000000001)×((″LT film thickness[λ]″)-0.275))+(-0.0722908233901528)×(((″LT film thickness[λ]″)-0.275)×((″LT film thickness[λ]″)-0.275)-0.020625) …Equation 1

[0082] In finding Figure 4When discussing the relationship between the duty cycle and the sound velocity V2 in the edge region, as described above, the thickness of the main electrode layer of the IDT electrode 3 is set to 100 nm, and the thickness of the piezoelectric layer 16 is set to 600 nm. With a wavelength λ of 2.5 μm, the LT film thickness is 0.24λ, and the electrode film thickness is 0.04λ (in Equation 1, substituting "LT film thickness [λ]" = 0.24 and "electrode film thickness [λ]" = 0.04). At this point, as described above, the sound velocity V2 is lowest when the duty cycle in the edge region is approximately 0.65. In this case, transverse modes can be effectively suppressed. Therefore, with an LT film thickness of 0.24λ and an electrode film thickness of 0.04λ, the optimal duty cycle in the edge region is approximately 0.65. The relationship between this optimal duty cycle and the LT film thickness and electrode film thickness was determined.

[0083] Figure 7 This is a graph showing the relationship between the LT film thickness, the electrode film thickness, and the optimal duty cycle in the edge region of the IDT electrode.

[0084] exist Figure 7 For example, the curve representing 0.62 shows the relationship between the LT film thickness and the electrode film thickness when the optimal duty cycle in the edge region of IDT electrode 3 is 0.62. Similarly, in Figure 7 The diagram shows the relationship between the LT film thickness and the electrode film thickness for various optimal duty cycles increasing from 0.62 to 0.73 in increments of 0.005. Equation 1 above satisfies all these relationships. Therefore, by using LT film thickness and electrode film thickness within the range of 0.62 to 0.73 for the optimal duty cycle in Equation 1, transverse modes can be suppressed more reliably.

[0085] The main electrode layer of the IDT electrode 3 can also be an Al layer. In this case, the Cu content in the main electrode layer is 0% by weight. Even when the main electrode layer is an Al layer, when the LT film thickness and electrode film thickness are used in Equation 1 with an optimal duty cycle in the range of 0.62 or higher and 0.73 or lower, transverse modes can be suppressed more reliably. It should be noted that, as in the first embodiment, the IDT electrode 3 can also have a bonding layer or the like without compromising the above-mentioned effects.

[0086] As described above, the IDT electrode 3 is not limited to cases including stacked metal films containing Ti layers, AlCu layers, and Ti layers. Hereinafter, first to fourth modifications of the material structure for the IDT electrode are shown, which differ from the first embodiment. In the first to fourth modifications, similar to the first embodiment, the Q value can be improved, and transverse modes can be suppressed more reliably.

[0087] In the first variation, the IDT electrode has a Cu layer. In this variation, the Cu layer is the main electrode layer of the IDT electrode. The film thickness of the Cu layer is defined as the Cu film thickness. Here, similar to the first embodiment, the relationship between the optimal duty cycle, the LT film thickness, and the Cu film thickness is determined. The LT film thickness and the Cu film thickness are preferably within the range of 0.62 or more and 0.73 or less for the optimal duty cycle in Equation 2 below. This allows for more reliable suppression of transverse modes. It should be noted that the IDT electrode may also have a bonding layer, etc., without compromising the above-mentioned effects.

[0088] [Formula 2]

[0089] Equation 2: Optimal duty cycle = 0.722361035255556 + 0.0561123231333331 × ((″LT film thickness [λ]″) - 0.3) + 0.450142117104374 × ((″Cu film thickness [λ]″) - 0.055) + (-0.189939099134199) × (((″LT film thickness [λ]″) - 0.3) × ((″LT film thickness [λ]″) - 0.3 )-0.0166666666666667)+0.0947647208080766×((″LT film thickness [λ]″)-0.3)×((“Cu film thickness [λ]″)-0.055)+ 5.94554881734021×(((″Cu film thickness [λ]″)-0.055)×((“Cu film thickness [λ]″)-0.055)-0.000824999999999999) ...Formula 2

[0090] In the second variation, the IDT electrode has a Pt layer and an Al layer. The Pt layer is directly stacked on the piezoelectric layer. The Al layer is directly stacked on the Pt layer. In this variation, the Pt layer is the main electrode layer of the IDT electrode. The Al layer is a conductive auxiliary layer. In this specification, a conductive auxiliary layer refers to a layer with a lower resistance than the main electrode layer. The film thickness of the Pt layer is defined as the Pt film thickness, and the film thickness of the Al layer is defined as the Al film thickness. Here, similar to the first embodiment, the relationship between the optimal duty cycle, the LT film thickness, the Pt film thickness, and the Al film thickness is determined. The LT film thickness, the Pt film thickness, and the Al film thickness are preferably within the range of 0.62 or more and 0.73 or less for the optimal duty cycle in Equation 3 below. This allows for more reliable suppression of transverse modes.

[0091] [Formula 3]

[0092] Equation 3: Optimal duty cycle = 0.706311420324445 + 0.0515443705199995 × (("LT film thickness [λ]") - 0.3) + 0.340692430577689 × (("Al film thickness [λ]") - 0.0750000000000001) + 1.92242704222223 × (("Pt film thickness [λ]") - 0.0 125)+(-0.1623038581645)×(((″LT film thickness[λ]″)-0.3)×((″LT film thickness[λ]″)-0.3)-0.016666666666667)+0.0686507973333415×((″LT film thickness[λ]″)-0.3)×((″Al film thickness[λ]″)-0.0750000000000001) +5.08720585142787×(((″Al film thickness[λ]″)-0.0750000000000001)×((″Al film thickness[λ]″)-0.0750000000000001)-0.0003125)+0.292474862666682×((″LT film thickness[λ]″)-0.3)×((″Pt film thickness[λ]″)-0.01 25)+(-22.1884852444445)×((″Al film thickness[λ]″)-0.0750000000000001)×((″Pt film thickness[λ]″)-0.0125)+-63.3669675555578×(((″Pt film thickness[λ]″)-0.0125)×((″Pt film thickness[λ]″)-0.0125)-0.00005)…Equation 3

[0093] It should be noted that the IDT electrode may also have a bonding layer, etc., without compromising the above-mentioned effects. For example, a Pt layer may be indirectly stacked on the piezoelectric layer via a bonding layer. An Al layer may also be indirectly stacked on the Pt layer via a diffusion-preventing layer.

[0094] In the third variation, the IDT electrode has a W layer and an Al layer. The W layer is directly stacked on the piezoelectric layer. The Al layer is directly stacked on the W layer. In this variation, the W layer is the main electrode layer of the IDT electrode. The Al layer is a conductive auxiliary layer. The film thickness of the W layer is defined as the W film thickness, and the film thickness of the Al layer is defined as the Al film thickness. Here, similar to the first embodiment, the relationship between the optimal duty cycle, LT film thickness, W film thickness, and Al film thickness is determined. The LT film thickness, W film thickness, and Al film thickness are preferably within the range of 0.62 or more and 0.73 or less in Equation 4 below. This allows for more reliable suppression of transverse modes. It should be noted that the IDT electrode may also have a bonding layer, a diffusion prevention layer, etc., similar to the second variation, without compromising the above-mentioned effects.

[0095] [Formula 4]

[0096] Equation 4: Optimal duty cycle = 0.670366655408889 + 0.0569799749733328 × (("LT film thickness [λ]") - 0.3) + 0.601791697955469 × (("Al film thickness [λ]") - 0.0750000000000001) + 0.0898163408888796 × (("W film thickness [λ]") - 0 .0125)+(-0.186654102147184)×(((″LT film thickness[λ]″)-0.3)×((″LT film thickness[λ]″)-0.3)-0.0166666666666667)+0.00960756266667166×((″LT film thickness[λ]″)-0.3)×((″Al film thickness[λ]″)-0.0750000000 000001)+4.24356009650733×(((″Al film thickness[λ]″)-0.0750000000000001)×((″Al film thickness[λ]″)-0.0750000000000001)-0.0003125)+0.54235624266667×((″LT film thickness[λ]″)-0.3)×((″W film thickness[λ]″) )-0.0125)+(-19.6658167822222)×((″Al film thickness [λ]″)-0.0750000000000001)×((″W film thickness [λ]″) -0.0125)+154875977777752×(((″W Film Thickness[λ]″)-0.0125)×((″W Film Thickness[λ]″)-0.0125)-0.00005) ...Formula 4

[0097] In the fourth variation, the IDT electrode has a Mo layer and an Al layer. The Mo layer is directly stacked on the piezoelectric layer. The Al layer is directly stacked on the Mo layer. In this variation, the Mo layer is the main electrode layer of the IDT electrode. The Al layer is a conductive auxiliary layer. The film thickness of the Mo layer is defined as the Mo film thickness, and the film thickness of the Al layer is defined as the Al film thickness. Here, similar to the first embodiment, the relationship between the optimal duty cycle, LT film thickness, Mo film thickness, and Al film thickness is determined. The LT film thickness, Mo film thickness, and Al film thickness are preferably within the range of 0.62 or more and 0.73 or less in Equation 5 below. This allows for more reliable suppression of transverse modes. It should be noted that, similar to the second variation, the IDT electrode may also have a bonding layer, a diffusion prevention layer, etc., without compromising the above-mentioned effects. However, more specifically, the Cu film thickness, Pt film thickness, Al film thickness, W film thickness, and Mo film thickness in Equations 2 to 5 are the film thicknesses in the first electrode reference 6 and the second electrode reference 7.

[0098] [Formula 5]

[0099] Equation 5: Optimal duty cycle = 0.650578355337778 + 0.0565759044933328 × ((″LT film thickness [λ]″) 0.3) + 0.896476823999908 × ((″Al film thickness [λ]″) - 0.0750000000000001) + (-0.835424887999999) × ((″Mo film thickness [λ]″) - 0. 0125)+(-0.182142102839825)×(((″LT film thickness[λ]″)-0.3)×((″LT film thickness[λ]″)-0.3)-0.0166666666666667)+(-0.0337296554666596)×((″LT film thickness[λ]″)-0.3)×((″Al film thickness[λ]″)-0.07500000000 00001)+3.10610546793597×(((″Al film thickness[λ]″)-0.0750000000000001)×((″AI film thickness[λ]″)-0.0750000000000001)-0.0003125)+0.286014725333341×((″LT film thickness[λ]″)-0.3)×((″Mo film thickness[λ]″) -0.0125)+(-8.1523516622225)×((″Al film thickness [λ]″)-0.0750000000000001)×((″Mo film thickness [λ]″)-0 .0125)+63.3934203174576×(((″Mo film thickness [λ]″)-0.0125)×((“Mo film thickness [λ]″)-0.0125)-0.00005) …Formula 5

[0100] Figure 8 This is a schematic front cross-sectional view of the elastic wave device of the fifth variation of the first embodiment.

[0101] In this modified example, the high-velocity material layer is the high-velocity support substrate 24. The piezoelectric substrate 22 is a laminated substrate in which the high-velocity support substrate 24, the low-velocity film 15, and the piezoelectric layer 16 are stacked in this order. In this case, similar to the first embodiment, the Q value can be improved, and transverse modes can be suppressed more reliably.

[0102] As the material for the hypersonic support substrate 24, a medium in which the above-mentioned materials, such as 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 film, or diamond are used as the main components can be used.

[0103] Figure 9 This is a schematic top view of the elastic wave device according to the second embodiment.

[0104] This embodiment differs from the first embodiment in that the first busbar 34 and the second busbar 35 of the IDT electrode 33 do not have opening forming regions, and that reflectors 38A and 38B do not have a first opening and a second opening, respectively. Apart from the above aspects, the elastic wave device 31 of this embodiment has the same structure as the first embodiment.

[0105] In this embodiment, the first electrode finger 6 and the second electrode finger 7 of the IDT electrode 33 also have a first width portion 6a, a first width portion 7a, a second width portion 6b, and a second width portion 7b in the first edge region C1 and the second edge region C2, respectively. In the first edge region C1 and the second edge region C2, the duty cycle is 0.62 or higher and 0.73 or lower. This allows for more reliable reduction of the sound velocity in the low-velocity region. Consequently, the piston mode can be established more reliably, and the transverse mode can be suppressed more reliably.

[0106] In the first embodiment, its variations, and the second embodiment described above, the first electrode finger and the second electrode finger each have a first width portion and a second width portion, respectively. This constitutes a low-velocity region. It should be noted that, in addition to this, a low-velocity region can also be constituted by providing a mass-added membrane. This example is illustrated by the following first to third variations of the second embodiment. In the first to third variations, the transverse mode can be suppressed more reliably, similar to the second embodiment.

[0107] exist Figure 10 In the first modified example shown, multiple mass-added films 39A are provided on multiple first electrode fingers 6 and multiple second electrode fingers 7 in the first edge region C1. More specifically, a mass-added film 39A is provided on each first electrode finger 6 and each second electrode finger 7 respectively. Similarly, multiple mass-added films 39A are provided on multiple first electrode fingers 6 and multiple second electrode fingers 7 in the second edge region C2. The mass-added films 39A can be metal films or dielectric films. In the case of metal films, Pt, W, Au, etc. can be used, and in the case of dielectric films, Ta2O5, HfO2, WO3, etc. can be used. It should be noted that in the first edge region C1 and the second edge region C2, strip-shaped mass-added films can also be provided on multiple first electrode fingers 6 and multiple second electrode fingers 7 respectively. In this case, a dielectric film is used as a strip-shaped mass-added film.

[0108] exist Figure 11In the second modified example shown, a mass-added film 39B is provided between the IDT electrode 33 and the piezoelectric substrate 2. More specifically, in the first edge region C1, a strip-shaped mass-added film 39B is provided between the first electrode finger 6 and the second electrode finger 7 and the piezoelectric layer 16. Similarly, in the second edge region C2, a strip-shaped mass-added film 39B is provided between the first electrode finger 6 and the second electrode finger 7 and the piezoelectric layer 16. Each mass-added film 39B also extends to the portions in the first edge region C1 and the second edge region C2 where the first electrode finger 6 and the second electrode finger 7 are not provided. As the strip-shaped mass-added film 39B, a dielectric film is used in the same way as described above. It should be noted that a dielectric film can also be used instead of a dielectric film. Figure 10 Multiple mass-added films 39A shown are disposed between the first electrode finger 6 and the second electrode finger 7 and the piezoelectric layer 16.

[0109] exist Figure 12 In the third variation shown, a mass-added film 39C is provided between the portion of the IDT electrode 33 other than the portion located in the central region B and the piezoelectric substrate 2. More specifically, in the first edge region C1 and the first spacing region D1, a mass-added film 39C is provided between the plurality of first electrode fingers 6 and the plurality of second electrode fingers 7 and the piezoelectric layer 16. Furthermore, the mass-added film 39C extends between the first busbar 34 and the piezoelectric layer 16. Similarly, in the second edge region C2 and the second spacing region D2, a mass-added film 39C is provided between the plurality of first electrode fingers 6 and the plurality of second electrode fingers 7 and the piezoelectric layer 16. Furthermore, the mass-added film 39C extends between the second busbar 35 and the piezoelectric layer 16. Each mass-added film 39C is sheet-like and also extends to the portions of the first edge region C1 and the first spacing region D1, as well as the second edge region C2 and the second spacing region D2, where the first electrode fingers 6 and the second electrode fingers 7 are not provided.

[0110] Explanation of reference numerals in the attached figures

[0111] 1…elastic wave device;

[0112] 2…piezoelectric substrate;

[0113] 3…IDT electrode;

[0114] 4…First busbar;

[0115] 4a…First inner busbar section;

[0116] 4b…First connecting electrode;

[0117] 4c…First outer busbar section;

[0118] 4d…first opening;

[0119] 5…Second busbar;

[0120] 5a…Second inner busbar section;

[0121] 5b…Second connecting electrode;

[0122] 5c…Second outer busbar section;

[0123] 5d…Second opening;

[0124] 6, 7… First electrode finger, second electrode finger;

[0125] 6a, 7a… First width section;

[0126] 6b, 7b… the second width section;

[0127] 8A, 8B... reflectors;

[0128] 8a, 8b... First opening;

[0129] 8c, 8d… second opening;

[0130] 9…protective film;

[0131] 13...support base plate;

[0132] 14…high-speed sound membrane;

[0133] 15…low-velocity membrane;

[0134] 16…piezoelectric layer;

[0135] 22…Piezoelectric substrate;

[0136] 24…High-speed acoustic support substrate;

[0137] 31…elastic wave device;

[0138] 33…IDT electrode;

[0139] 34, 35… First busbar, Second busbar;

[0140] 38A, 38B… reflectors;

[0141] 39A~39C… quality-added film;

[0142] A…intersection area;

[0143] B…Central Area;

[0144] C1, C2... First edge region, second edge region;

[0145] D1, D2... First interval region, second interval region;

[0146] E1, E2... First inner busbar region, second inner busbar region;

[0147] F1, F2… First opening forming region, second opening forming region;

[0148] G1, G2… First outer busbar region, second outer busbar region;

[0149] H1, H2... First hypersonic region, second hypersonic region;

[0150] L1, L2... First low-sound speed region, second low-sound speed region.

Claims

1. An elastic wave device, comprising: High-speed sound material layer; A low-velocity membrane is disposed on the high-velocity material layer; A piezoelectric layer disposed on the low-velocity film, comprising lithium tantalate; and An IDT electrode is disposed on the piezoelectric layer. The sound speed of the bulk wave propagating in the high-velocity material layer is higher than the sound speed of the elastic wave propagating in the piezoelectric layer. The sound speed of the bulk wave propagating in the low-velocity membrane is lower than that of the bulk wave propagating in the piezoelectric layer. The IDT electrode has a first bus bar and a second bus bar opposite to each other, a plurality of first electrode fingers with one end connected to the first bus bar, and a plurality of second electrode fingers with one end connected to the second bus bar and inserted alternately with the plurality of first electrode fingers. When the elastic wave propagation direction is defined as a first direction and a direction orthogonal to the first direction is defined as a second direction, the portion where the first electrode finger and the second electrode finger overlap in the first direction is an intersection region. This intersection region has a central region located on the central side in the second direction, a first edge region disposed on the side of the first busbar in the central region, and a second edge region disposed on the side of the second busbar in the central region. The IDT electrode has a first gap region located between the first edge region and the first busbar, and a second gap region located between the second edge region and the second busbar. The width of the first electrode finger and the second electrode finger in at least one of the first edge regions and the second edge regions is wider than their width in the central region. The duty cycle in the first edge region and the second edge region is greater than 0.62 and less than 0.

73. The IDT electrode has a main electrode layer. The main electrode layer is an Al layer or an AlCu layer. The Cu content in the main electrode layer is less than 2% by weight. When the duty cycle in the first and second edge regions where the sound velocity is lowest is set as the optimal duty cycle, the film thickness of the piezoelectric layer is set as the LT film thickness, and the film thickness of the main electrode layer in the first and second electrode fingers of the IDT electrode is set as the electrode film thickness, the LT film thickness and the electrode film thickness are within the range of 0.62 or more and 0.73 or less for the optimal duty cycle described in Equation 1 below. 。 2. An elastic wave device, comprising: High-speed sound material layer; A low-velocity membrane is disposed on the high-velocity material layer; A piezoelectric layer disposed on the low-velocity film, comprising lithium tantalate; and An IDT electrode is disposed on the piezoelectric layer. The sound speed of the bulk wave propagating in the high-velocity material layer is higher than the sound speed of the elastic wave propagating in the piezoelectric layer. The sound speed of the bulk wave propagating in the low-velocity membrane is lower than that of the bulk wave propagating in the piezoelectric layer. The IDT electrode has a first bus bar and a second bus bar opposite to each other, a plurality of first electrode fingers with one end connected to the first bus bar, and a plurality of second electrode fingers with one end connected to the second bus bar and inserted alternately with the plurality of first electrode fingers. When the elastic wave propagation direction is defined as a first direction and a direction orthogonal to the first direction is defined as a second direction, the portion where the first electrode finger and the second electrode finger overlap in the first direction is an intersection region. This intersection region has a central region located on the central side in the second direction, a first edge region disposed on the side of the first busbar in the central region, and a second edge region disposed on the side of the second busbar in the central region. The IDT electrode has a first gap region located between the first edge region and the first busbar, and a second gap region located between the second edge region and the second busbar. The width of the first electrode finger and the second electrode finger in at least one of the first edge regions and the second edge regions is wider than their width in the central region. The duty cycle in the first edge region and the second edge region is greater than 0.62 and less than 0.

73. The IDT electrode has a Cu layer. When the duty cycle in the first and second edge regions where the sound velocity is lowest is set as the optimal duty cycle, the film thickness of the piezoelectric layer is set as the LT film thickness, and the film thickness of the Cu layer in the first and second electrode fingers of the IDT electrode is set as the Cu film thickness, the LT film thickness and the Cu film thickness are within the range of 0.62 or more and 0.73 or less for the optimal duty cycle described in Equation 2 below. 。 3. An elastic wave device, comprising: High-speed sound material layer; A low-velocity membrane is disposed on the high-velocity material layer; A piezoelectric layer disposed on the low-velocity film, comprising lithium tantalate; and An IDT electrode is disposed on the piezoelectric layer. The sound speed of the bulk wave propagating in the high-velocity material layer is higher than the sound speed of the elastic wave propagating in the piezoelectric layer. The sound speed of the bulk wave propagating in the low-velocity membrane is lower than that of the bulk wave propagating in the piezoelectric layer. The IDT electrode has a first bus bar and a second bus bar opposite to each other, a plurality of first electrode fingers with one end connected to the first bus bar, and a plurality of second electrode fingers with one end connected to the second bus bar and inserted alternately with the plurality of first electrode fingers. When the elastic wave propagation direction is defined as a first direction and a direction orthogonal to the first direction is defined as a second direction, the portion where the first electrode finger and the second electrode finger overlap in the first direction is an intersection region. This intersection region has a central region located on the central side in the second direction, a first edge region disposed on the side of the first busbar in the central region, and a second edge region disposed on the side of the second busbar in the central region. The IDT electrode has a first gap region located between the first edge region and the first busbar, and a second gap region located between the second edge region and the second busbar. The width of the first electrode finger and the second electrode finger in at least one of the first edge regions and the second edge regions is wider than their width in the central region. The duty cycle in the first edge region and the second edge region is greater than 0.62 and less than 0.

73. The IDT electrode has a Pt layer stacked on the piezoelectric layer and an Al layer stacked on the Pt layer. When the duty cycle in the first and second edge regions, where the sound velocity in the first and second edge regions is minimized, is set as the optimal duty cycle, and the film thickness of the piezoelectric layer is set as LT film thickness, and the film thicknesses of the Pt layer and the Al layer in the first and second electrode fingers of the IDT electrode are respectively set as Pt film thickness and Al film thickness, the LT film thickness, the Pt film thickness, and the Al film thickness are within the range of 0.62 or more and 0.73 or less for the optimal duty cycle described in Equation 3 below. 。 4. An elastic wave device, comprising: High-speed sound material layer; A low-velocity membrane is disposed on the high-velocity material layer; A piezoelectric layer disposed on the low-velocity film, comprising lithium tantalate; and An IDT electrode is disposed on the piezoelectric layer. The sound speed of the bulk wave propagating in the high-velocity material layer is higher than the sound speed of the elastic wave propagating in the piezoelectric layer. The sound speed of the bulk wave propagating in the low-velocity membrane is lower than that of the bulk wave propagating in the piezoelectric layer. The IDT electrode has a first bus bar and a second bus bar opposite to each other, a plurality of first electrode fingers with one end connected to the first bus bar, and a plurality of second electrode fingers with one end connected to the second bus bar and inserted alternately with the plurality of first electrode fingers. When the elastic wave propagation direction is defined as a first direction and a direction orthogonal to the first direction is defined as a second direction, the portion where the first electrode finger and the second electrode finger overlap in the first direction is an intersection region. This intersection region has a central region located on the central side in the second direction, a first edge region disposed on the side of the first busbar in the central region, and a second edge region disposed on the side of the second busbar in the central region. The IDT electrode has a first gap region located between the first edge region and the first busbar, and a second gap region located between the second edge region and the second busbar. The width of the first electrode finger and the second electrode finger in at least one of the first edge regions and the second edge regions is wider than their width in the central region. The duty cycle in the first edge region and the second edge region is greater than 0.62 and less than 0.

73. The IDT electrode has a W layer stacked on the piezoelectric layer and an Al layer stacked on the W layer. When the duty cycle in the first and second edge regions, where the sound velocity in the first and second edge regions is minimized, is set as the optimal duty cycle, and the film thickness of the piezoelectric layer is set as LT film thickness, and the film thicknesses of the W layer and the Al layer in the first and second electrode fingers of the IDT electrode are respectively set as W film thickness and Al film thickness, the LT film thickness, the W film thickness, and the Al film thickness are within the range of 0.62 or more and 0.73 or less for the optimal duty cycle described in Equation 4 below. 。 5. An elastic wave device, comprising: High-speed sound material layer; A low-velocity membrane is disposed on the high-velocity material layer; A piezoelectric layer disposed on the low-velocity film, comprising lithium tantalate; and An IDT electrode is disposed on the piezoelectric layer. The sound speed of the bulk wave propagating in the high-velocity material layer is higher than the sound speed of the elastic wave propagating in the piezoelectric layer. The sound speed of the bulk wave propagating in the low-velocity membrane is lower than that of the bulk wave propagating in the piezoelectric layer. The IDT electrode has a first bus bar and a second bus bar opposite to each other, a plurality of first electrode fingers with one end connected to the first bus bar, and a plurality of second electrode fingers with one end connected to the second bus bar and inserted alternately with the plurality of first electrode fingers. When the elastic wave propagation direction is defined as a first direction and a direction orthogonal to the first direction is defined as a second direction, the portion where the first electrode finger and the second electrode finger overlap in the first direction is an intersection region. This intersection region has a central region located on the central side in the second direction, a first edge region disposed on the side of the first busbar in the central region, and a second edge region disposed on the side of the second busbar in the central region. The IDT electrode has a first gap region located between the first edge region and the first busbar, and a second gap region located between the second edge region and the second busbar. The width of the first electrode finger and the second electrode finger in at least one of the first edge regions and the second edge regions is wider than their width in the central region. The duty cycle in the first edge region and the second edge region is greater than 0.62 and less than 0.

73. The IDT electrode has a Mo layer stacked on the piezoelectric layer and an Al layer stacked on the Mo layer. When the duty cycle in the first and second edge regions, where the sound velocity in the first and second edge regions is minimized, is set as the optimal duty cycle, the film thickness of the piezoelectric layer is set as LT film thickness, and the film thicknesses of the Mo and Al layers in the first and second electrode fingers of the IDT electrode are respectively set as Mo film thickness and Al film thickness, the LT film thickness, the Mo film thickness, and the Al film thickness are within the range of 0.62 or more and 0.73 or less for the optimal duty cycle described in Equation 5 below. 。 6. The elastic wave device according to any one of claims 1 to 5, wherein, The first edge region and the second edge region each constitute a low-sound-speed region where the sound speed is lower than that of the central region. The outer side of the first edge region in the second direction and the outer side of the second edge region in the second direction respectively constitute high-sound-speed regions where the sound speed is higher than that of the central region.

7. The elastic wave device according to any one of claims 1 to 5, wherein, The first and second interval regions respectively constitute high-speed sound regions.

8. The elastic wave device according to any one of claims 1 to 5, wherein, The hypersonic material layer is a hypersonic support substrate.

9. The elastic wave device according to any one of claims 1 to 5, wherein, The elastic wave device also includes a support substrate. The hypersonic material layer is a hypersonic film disposed on the support substrate.

Images