Acoustic wave device and communication device

Abstract

To provide an acoustic wave device and a communication device having improved frequency characteristics.SOLUTION: An acoustic wave device 101 includes a piezoelectric body 1 having a surface on which grooves 19 are formed, an IDT electrode 2 located above the piezoelectric body 1 and including a portion located inside the groove 19, and having a first electrode finger 8, a second electrode finger 9 adjacent to the first electrode finger 8 in plan view, and a bus bar 10 electrically connected to the second electrode finger 9, and a dielectric layer 3 located above the surface on which the grooves 19 are formed. The piezoelectric body 1 has a thickness that is equal to or less than twice the pitch of the first electrode finger 8 and the second electrode finger 9, and the dielectric layer 3 includes a first region 12 overlapping with the tip portions of the first electrode finger 8 and the second region 14 overlapping with a gap between the tip portions of the first electrode finger 8 and the bus bar 10 in the plan view.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to acoustic wave devices and communication apparatus. [Background technology]

[0002] Patent Document 1 discloses a configuration in which a mass-adding film is provided on a first electrode finger and a second electrode finger of an IDT electrode. IDT is an abbreviation for interdigital transducer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-92095 A Summary of the Invention [Problem to be solved by the invention]

[0004] It is expected that the transverse mode spurious will be reduced and the frequency characteristics of acoustic wave devices will be improved. [Means for solving the problem]

[0005] An acoustic wave device according to one embodiment of the present disclosure comprises a piezoelectric body having a surface on which grooves are formed, an IDT electrode located above the piezoelectric body and including a portion located inside the groove, the IDT electrode having a first electrode finger, a second electrode finger adjacent to the first electrode finger in a planar view, and a bus bar electrically connected to the second electrode finger, and a dielectric layer located above the surface, wherein the thickness of the piezoelectric body is less than twice the pitch of the first electrode fingers and the second electrode fingers, and in the planar view, the dielectric layer includes a first region overlapping with the tip of the first electrode finger and a second region overlapping with a gap between the tip and the bus bar. Effect of the Invention

[0006] According to one aspect of the present disclosure, it is possible to improve the frequency characteristics of an acoustic wave device. [Brief description of the drawings]

[0007] [Figure 1] 1 is a plan view illustrating a schematic configuration of an acoustic wave device according to a first embodiment of the present disclosure. [Diagram 2] 1 is a cross-sectional view along the line AA illustrating a schematic configuration of an acoustic wave device according to a first embodiment of the present disclosure. [Diagram 3] FIG. 4 is a plan view illustrating a schematic configuration of another example of an acoustic wave device according to the first embodiment of the present disclosure. [Figure 4] FIG. 11 is a plan view illustrating a schematic configuration of yet another example of an acoustic wave device in accordance with the first embodiment of the present disclosure. [Diagram 5] 1 is a table showing initial simulation conditions for the LT model and the LN model. [Figure 6] 11 is a graph showing an example of frequency characteristics of a reference model. [Figure 7] 11 is a graph showing an example of frequency characteristics of a reference model. [Figure 8] 11 is a graph showing an example of frequency characteristics of a reference model. [Figure 9] 11 is a graph showing an example of frequency characteristics of a reference model. [Figure 10] 11 is a graph showing an example of frequency characteristics of a reference model. [Figure 11] 11 is a graph showing an example of frequency characteristics of a reference model. [Figure 12] 1 is a graph showing an example of frequency characteristics versus thickness of a dielectric layer in a quasi-101 model. [Figure 13] 1 is a graph showing an example of frequency characteristics versus thickness of a dielectric layer in a quasi-101 model. [Figure 14] FIG. 1 is a diagram illustrating FOM. [Figure 15] FIG. 1 is a diagram illustrating FOM. [Figure 16] FIG. 1 is a diagram illustrating FOM. [Figure 17] This is a table listing the conditions under which good frequency characteristics were obtained in the LT model. [Figure 18] This is a table listing the conditions under which good frequency characteristics were obtained in the LT model. [Figure 19] This is a table listing the conditions under which good frequency characteristics were obtained in the LT model. [Figure 20] This is a table listing the conditions under which good frequency characteristics were obtained in the LT model. [Figure 21] 1 is a graph showing an example of favorable frequency characteristics in the LT model. [Figure 22] 1 is a graph showing an example of favorable frequency characteristics in the LT model. [Diagram 23] 1 is a graph showing an example of favorable frequency characteristics in the LT model. [Figure 24] 1 is a graph showing an example of favorable frequency characteristics in the LT model. [Diagram 25] 1 is a graph showing an example of favorable frequency characteristics in the LT model. [Figure 26] 1 is a graph showing an example of favorable frequency characteristics in the LT model. [Figure 27] 1 is a graph showing an example of favorable frequency characteristics in the LT model. [Figure 28] 1 is a graph showing an example of favorable frequency characteristics in the LT model. [Figure 29] 1 is a graph showing an example of favorable frequency characteristics in the LT model. [Diagram 30] 1 is a graph showing an example of favorable frequency characteristics in the LT model. [Diagram 31] 1 is a graph showing an example of favorable frequency characteristics in the LT model. [Diagram 32] 1 is a graph showing an example of favorable frequency characteristics in the LT model. [Diagram 33] 1 is a graph showing an example of favorable frequency characteristics in the LT model. [Diagram 34] 1 is a graph showing an example of favorable frequency characteristics in the LT model. [Diagram 35] 1 is a graph showing an example of favorable frequency characteristics in the LT model. [Diagram 36] 1 is a graph showing an example of favorable frequency characteristics in the LT model. [Figure 37] 1 is a graph showing the relationship between FOM and the thickness of a dielectric layer in the LT model. [Figure 38] 1 is a graph showing the relationship between FOM and the thickness of a dielectric layer in the LT model. [Figure 39] 1 is a graph showing the relationship between FOM and the thickness of a dielectric layer in the LT model. [Diagram 40] 1 is a graph showing the relationship between FOM and the thickness of a dielectric layer in the LT model. [Diagram 41] 1 is a graph showing the relationship between FOM and the thickness of a dielectric layer in the LT model. [Diagram 42] 1 is a graph showing the relationship between FOM and the thickness of a dielectric layer in the LT model. [Diagram 43] 1 is a graph showing the relationship between FOM and the thickness of a dielectric layer in the LT model. [Diagram 44] 1 is a graph showing the relationship between FOM and the thickness of a dielectric layer in the LT model. [Diagram 45] 1 is a graph showing the relationship between FOM and the thickness of a dielectric layer in the LT model. [Figure 46] 13 is another graph showing the relationship of FOM to the thickness of the dielectric layer in the LT model. [Figure 47] 13 is another graph showing the relationship of FOM to the thickness of the dielectric layer in the LT model. [Figure 48] 1 is a table listing the conditions under which good frequency characteristics were obtained in the LN model. [Figure 49] 1 is a table listing the conditions under which good frequency characteristics were obtained in the LN model. [Figure 50] 1 is a table listing the conditions under which good frequency characteristics were obtained in the LN model. [Figure 51] 1 is a graph showing an example of favorable frequency characteristics in an LN model. [Figure 52] 1 is a graph showing an example of favorable frequency characteristics in an LN model. [Figure 53] 1 is a graph showing an example of favorable frequency characteristics in an LN model. [Figure 54] 1 is a graph showing an example of favorable frequency characteristics in an LN model. [Figure 55] 1 is a graph showing an example of favorable frequency characteristics in an LN model. [Figure 56] 1 is a graph showing an example of favorable frequency characteristics in an LN model. [Figure 57] 1 is a graph showing an example of favorable frequency characteristics in an LN model. [Figure 58] 1 is a graph showing an example of favorable frequency characteristics in an LN model. [Figure 59] 1 is a graph showing an example of favorable frequency characteristics in an LN model. [Figure 60] 1 is a graph showing an example of favorable frequency characteristics in an LN model. [Figure 61] 1 is a graph showing an example of favorable frequency characteristics in an LN model. [Figure 62] 1 is a graph showing an example of favorable frequency characteristics in an LN model. [Figure 63] 1 is a graph showing an example of favorable frequency characteristics in an LN model. [Figure 64] 1 is a graph showing an example of favorable frequency characteristics in an LN model. [Figure 65] 1 is a graph showing the relationship between FOM and the thickness of a dielectric layer in an LN model. [Figure 66] 1 is a graph showing the relationship between FOM and the thickness of a dielectric layer in an LN model. [Figure 67] 1 is a graph showing the relationship between FOM and the thickness of a dielectric layer in an LN model. [Figure 68]1 is a graph showing the relationship between FOM and the thickness of a dielectric layer in an LN model. [Figure 69] 1 is a graph showing the relationship between FOM and the thickness of a dielectric layer in an LN model. [Figure 70] 1 is a graph showing the relationship between FOM and the thickness of a dielectric layer in an LN model. [Figure 71] 1 is a graph showing the relationship between FOM and the thickness of a dielectric layer in an LN model. [Figure 72] 1 is a graph showing the relationship between FOM and the thickness of a dielectric layer in an LN model. [Figure 73] 1 is a graph showing the relationship between FOM and the thickness of a dielectric layer in an LN model. [Figure 74] 13 is another graph showing the relationship between FOM and the thickness of the dielectric layer in the LN model. [Figure 75] 13 is another graph showing the relationship between FOM and the thickness of the dielectric layer in the LN model. [Figure 76] 1 is a graph showing frequency characteristics versus gap width. [Figure 77] 1 is a graph showing frequency characteristics versus gap width. [Figure 78] 1 is a graph showing frequency characteristics versus gap width. [Figure 79] 1 is a graph showing frequency characteristics versus gap width. [Figure 80] 1 is a graph showing frequency characteristics versus gap width. [Figure 81] 1 is a graph showing frequency characteristics versus gap width. [Figure 82] 1 is a graph showing frequency characteristics versus gap width. [Figure 83] 1 is a graph showing frequency characteristics versus gap width. [Figure 84] 1 is a graph showing frequency characteristics versus gap width. [Figure 85] 1 is a graph showing frequency characteristics versus gap width. [Figure 86] 1 is a graph showing frequency characteristics versus gap width. [Figure 87] 1 is a graph showing frequency characteristics versus gap width. [Figure 88] 1 is a graph showing frequency characteristics versus gap width. [Figure 89] 1 is a graph showing frequency characteristics versus gap width. [Figure 90] 1 is a graph showing frequency characteristics versus gap width. [Figure 91] 1 is a graph showing frequency characteristics versus gap width. [Figure 92] 1 is a graph showing frequency characteristics versus gap width. [Figure 93] 1 is a graph showing frequency characteristics versus gap width. [Figure 94] 1 is a graph showing frequency characteristics versus gap width. [Figure 95] 1 is a graph showing frequency characteristics versus gap width. [Figure 96] 1 is a graph showing frequency characteristics versus gap width. [Figure 97] 1 is a graph showing frequency characteristics versus gap width. [Figure 98] FIG. 11 is a cross-sectional view illustrating a schematic configuration of an acoustic wave device according to a second embodiment of the present disclosure. [Figure 99] FIG. 11 is a schematic diagram of a communication device according to a third embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present disclosure. For convenience of explanation, the same reference numerals are given to components having the same functions as those described above, and the description thereof may not be repeated.

[0009] [Embodiment 1] Fig. 1 is a plan view showing a schematic configuration of an acoustic wave device 101 according to a first embodiment of the present disclosure, and Fig. 2 is a cross-sectional view taken along line AA showing a schematic configuration of the acoustic wave device 101 according to the first embodiment of the present disclosure.

[0010] The acoustic wave device 101 includes a piezoelectric body 1, an IDT electrode 2, a dielectric layer 3, multiple multilayer reflective films 4, and a support substrate 5. The support substrate 5, multiple multilayer reflective films 4, piezoelectric body 1, IDT electrode 2, and dielectric layer 3 are laminated in this order. Each of the multiple multilayer reflective films 4 includes, in order from the piezoelectric body 1 side, a low acoustic impedance layer 6 and a high acoustic impedance layer 7. As an example, the number of multilayer reflective films 4 in the acoustic wave device 101 is four.

[0011] The piezoelectric body 1 has a surface 18. A groove 19 is formed in the surface 18. The piezoelectric body 1 may include at least one of LiTaO3 and LiNbO3. LiTaO3 may be referred to as lithium tantalate and may be represented as LT. LiNbO3 may be referred to as lithium niobate and may be represented as LN. The thickness of the piezoelectric body 1 is T1.

[0012] The IDT electrode 2 is located in a layer above the piezoelectric body 1. The IDT electrode 2 includes a portion located inside the groove 19. In FIG. 2, the entire portion of the IDT electrode 2 shown in FIG. 2 is located inside the groove 19. The entire IDT electrode 2 may be located inside the groove 19, or a portion of the IDT electrode 2 may be located inside the groove 19. The IDT electrode 2 has a first electrode finger 8, a second electrode finger 9, and a bus bar 10. The second electrode finger 9 is adjacent to the first electrode finger 8 in a plan view of the acoustic wave device 101. Hereinafter, the plan view of the acoustic wave device may be simply referred to as a plan view. The bus bar 10 is electrically connected to the second electrode finger 9. Although not shown, the IDT electrode 2 further has a bus bar electrically connected to the first electrode finger 8.

[0013] 1 and 2 show directions D1, D2, and D3 that are perpendicular to each other. The D1 direction can be defined as the arrangement direction of the first electrode fingers 8 and the second electrode fingers 9. The D3 direction can be defined as the thickness direction of the piezoelectric body 1. The longitudinal direction of the first electrode fingers 8 and the longitudinal direction of the second electrode fingers 9 are approximately parallel to the D2 direction.

[0014] The dielectric layer 3 is located above the surface 18. The dielectric layer 3 may be located above the IDT electrode 2. In a plan view, the dielectric layer 3 includes a first region 12 overlapping with the tip 11 of the first electrode finger 8 and a second region 14 overlapping with the gap 13. The gap 13 is between the tip 11 and the bus bar 10. In a plan view, the first region 12 of the dielectric layer 3 and the tip 11 of the first electrode finger 8 overlap with each other. In a plan view, the second region 14 of the dielectric layer 3 and the gap 13 between the tip 11 and the bus bar 10 overlap with each other. The dielectric layer 3 has a thickness T3.

[0015] In a plan view, the dielectric layer 3 may include a third region 15 overlapping with the bus bar 10. In a plan view, the third region 15 of the dielectric layer 3 and the bus bar 10 may overlap with each other.

[0016] The dielectric layer 3 may include at least one of a high acoustic velocity dielectric material and Ta2O5. The high acoustic velocity dielectric material may be defined as a material in which the acoustic velocity in the high acoustic velocity dielectric material is higher than the acoustic velocity in the piezoelectric body 1. The high acoustic velocity dielectric material may be any of SiO2, AlN, SiN, Al2O3, and TiO2. By using a high acoustic velocity dielectric material, the reduction in acoustic velocity due to the dielectric layer 3 relative to the thickness of the dielectric layer 3 can be reduced.

[0017] The thickness T3 of the dielectric layer 3 may be 0.01 times or more and 0.2 times or less than the thickness T1 of the piezoelectric body 1. The thickness T3 of the dielectric layer 3 may be 0.005 μm or more and 0.07 μm or less. The thickness T3 of the dielectric layer 3 may satisfy at least one of the conditions of 0.01 times or more and 0.2 times or less than the thickness T1 of the piezoelectric body 1, and 0.005 μm or more and 0.07 μm or less. If the thickness T3 is less than 0.01 times and / or less than 0.005 μm of the thickness T1, the energy loss may be large in the second frequency band. If the thickness T3 is more than 0.2 times and / or more than 0.07 μm of the thickness T1, the energy loss may be large in the first frequency band.

[0018] The multilayer reflective film 4, i.e., the low acoustic impedance layer 6 and the high acoustic impedance layer 7, are located below the piezoelectric body 1. The acoustic impedance of the low acoustic impedance layer 6 is lower than the acoustic impedance of the high acoustic impedance layer 7. The low acoustic impedance layer 6 may contain SiO2. The high acoustic impedance layer 7 may contain at least one of HfO2, Ta2O5, and ZrO2.

[0019] The supporting substrate 5 supports the piezoelectric body 1, the IDT electrode 2, the dielectric layer 3, and the multiple multilayer reflective films 4. The supporting substrate 5 may be a Si substrate.

[0020] The acoustic wave device 101 may excite an antisymmetric A1 mode. The acoustic wave device 101 may excite a bulk wave. The vibration mode of the acoustic wave device 101 that excites a bulk wave may be a thickness shear mode. The acoustic wave device 101 may not include the multilayer reflective film 4.

[0021] Pitch p of first electrode finger 8 and second electrode finger 9 is defined as the distance between center 16 of first electrode finger 8 and center 17 of second electrode finger 9 in direction D1. The pitch means the center-to-center distance, and can also be said to mean the repetition interval. Thickness T1 of piezoelectric body 1 is equal to or less than twice pitch p of first electrode finger 8 and second electrode finger 9. This makes it possible to configure acoustic wave device 101 that matches the wavelength of acoustic waves propagating within piezoelectric body 1.

[0022] A length L11 of an overlapping portion between tip portion 11 and first region 12 in the longitudinal direction of first electrode finger 8 may be equal to or greater than thickness T1 of piezoelectric body 1 and equal to or less than five times thickness T1 of piezoelectric body 1. If length L11 is less than thickness T1, the area where dielectric layer 3 and first electrode finger 8 overlap in a plan view is too small, and the benefit of dielectric layer 3 is small. If length L11 exceeds five times thickness T1, the volume of dielectric layer 3 is too large, and energy loss may be large in the second frequency band.

[0023] The IDT electrode 2 may have a dummy electrode 20 located in the gap 13 and overlapping with the second region 14 in a plan view. A separation distance S8 between the first electrode fingers 8 and the dummy electrode 20 in the longitudinal direction of the first electrode fingers 8 may be twice or more the thickness T1 of the piezoelectric body 1. The dummy electrode 20 may have a function of more precisely controlling the frequency characteristics of the acoustic wave device 101. In FIG. 1, the dummy electrode 20 is a finger-like dummy electrode that extends in a finger-like manner from the bus bar 10 in the longitudinal direction of the second electrode fingers 9.

[0024] 3 is a plan view illustrating a schematic configuration of another example of the acoustic wave device 101 according to the first embodiment of the present disclosure. In FIG. 3, the dummy electrode 20 is a planar dummy electrode extending in a plane defined by the direction D1 from the bus bar 10 and the longitudinal direction of the second electrode fingers 9.

[0025] 4 is a plan view illustrating a schematic configuration of yet another example of the acoustic wave device 101 according to the first embodiment of the present disclosure. The IDT electrode 2 does not necessarily have to include the dummy electrode 20 that is located in the gap 13 and overlaps with the second region 14 in a plan view.

[0026] 1 to 4 are schematic diagrams of a cut-out portion of an acoustic wave element. In reality, a total of 50 to several hundreds of first electrode fingers 8 and second electrode fingers 9 of IDT electrode 2 are periodically arranged in the D1 direction. In the D2 direction, only the right half of the acoustic wave element is shown in Figs. 1 to 4, and the left half of the acoustic wave element is symmetrically shown thereto.

[0027] A simulation model of an acoustic wave device 101 in which the material of the piezoelectric body 1 is LT, and a simulation model of an acoustic wave device 101 in which the material of the piezoelectric body 1 is LN are used. The simulation model of the acoustic wave device 101 is also referred to as the 101 model. The 101 model in which the material of the piezoelectric body 1 is LT is also referred to as the LT model. The 101 model in which the material of the piezoelectric body 1 is LN is also referred to as the LN model.

[0028] These models are examples of parameters that efficiently excite an A1 mode SAW (Surface Acoustic Wave) resonator. However, the effects of the present disclosure are not limited to these parameters, and each parameter can be optimized as appropriate to have characteristics suited to the purpose.

[0029] Figure 5 is a table showing the initial simulation conditions for the LT model and the LN model. Unless otherwise specified, the LT model is assumed to have a configuration according to the initial simulation conditions for the LT model. Unless otherwise specified, the LN model is assumed to have a configuration according to the initial simulation conditions for the LN model.

[0030] For convenience of explanation, the explanation of the same definitions as those explained above may be omitted.

[0031] Cut angle: indicates the cut angle of the piezoelectric body 1 Pitch (um): Pitch p is expressed in units of μm. Duty: Duty is defined as the ratio of the sum of the width of the first electrode finger 8 and the width of the second electrode finger 9 to twice the pitch p. Overlap width (um): the overlap width of the first electrode finger 8 and the second electrode finger 9, expressed in units of μm Dummy length (um): The length of the dummy electrode 20 is shown in the unit μm. Gap (um): The length of the gap 13 between the first electrode finger 8 and the dummy electrode 20 in the longitudinal direction of the first electrode finger 8, expressed in μm. It may correspond to the separation distance S8. Electrode thickness (um): The thickness of the IDT electrode 2 is shown in μm. Al was used as the material for the IDT electrode 2. Piezoelectric thickness (um): The thickness T1 of the piezoelectric body 1 is shown in μm. SiO2 thickness (um): The thickness of the low acoustic impedance layer 6 made of SiO2, expressed in units of μm HfO2 thickness (um): The thickness of the high acoustic impedance layer 7 made of HfO2, expressed in units of μm The definitions in the table shown in Fig. 5 are as described above. In the simulation, the periodic boundary condition was used in the D1 direction (propagation direction of elastic waves).

[0032] Each of Figs. 6 to 11 is a graph showing an example of the frequency characteristic of the impedance of the reference model. The reference model is a simulation model of an acoustic wave device in which the dielectric layer 3 is omitted from the acoustic wave device 101. Figs. 6 to 8 show the characteristics when the material of the piezoelectric body 1 is LT. Figs. 9 to 11 show the characteristics when the material of the piezoelectric body 1 is LN. The frequency band around the resonance frequency is defined as the first frequency band, the frequency band around the anti-resonance frequency is defined as the third frequency band, and the frequency band between the first frequency band and the third frequency band is defined as the second frequency band.

[0033] frequency(MHz):Frequency is expressed in units of MHz No dummy: indicates that the dummy electrode 20 is not provided Dummy: Indicates that a finger-shaped dummy electrode is included Dummy solid: Indicates that a planar dummy electrode is provided 6 to 11 are defined as above. Looking at the arrows 22 to 29 in Fig. 6 to 11, it can be seen that in an acoustic wave device in which the dielectric layer 3 is omitted from the acoustic wave device 101, a large number of ripples occur in the impedance frequency characteristics, and the frequency characteristics are poor, regardless of the presence or absence of the dummy electrode 20.

[0034] 12 and 13 are graphs showing an example of frequency characteristics of impedance phase values ​​with respect to the thickness T3 of the dielectric layer 3 in the quasi-101 model. The quasi-101 model is a simulation model of an acoustic wave device in which the first region 12 or the second region 14 is omitted from the acoustic wave device 101. In the following, for convenience of explanation, the quasi-101 model is treated as a type of 101 model.

[0035] IDT ends only: showing that the dielectric layer 3 includes a first region 12 overlapping the tip 11 and does not include a second region 14 overlapping the gap 13. Additional film thickness=Lt: indicates that the thickness T3 of the dielectric layer 3 is L times the thickness T1 of the piezoelectric body 1. The definitions of Figures 12 and 13 are as described above. The characteristics of the LT model are shown in Figures 12 and 13. The material of the dielectric layer 3 corresponding to Figures 12 and 13 is AlN.

[0036] When paying attention to the arrows 30 and 31 in FIG. 12 and FIG. 13, the following can be seen. As the thickness T3 increases, the frequency characteristics tend to improve in the second frequency band, while the frequency characteristics tend to deteriorate in the first frequency band. As the thickness T3 decreases, the frequency characteristics tend to improve in the first frequency band, while the frequency characteristics tend to deteriorate in the second frequency band. It is said that the smaller the impedance phase disturbance with respect to frequency, the better the frequency characteristics are, and the larger the disturbance, the worse the frequency characteristics are. There may be an appropriate range for the thickness T3 of the dielectric layer 3 that allows relatively good frequency characteristics to be exhibited. This range may vary slightly depending on the configuration of the acoustic wave device 101, including the material selection of the dielectric layer 3. According to the present disclosure, it is possible to obtain generally good characteristics.

[0037] In the following, a characteristic called figure of merit, or FOM for short, is used as an index of the improvement effect of the frequency characteristic in the 101 model. Each of Figs. 14 to 16 is a diagram for explaining FOM.

[0038] Phase (deg): Impedance phase in degrees The definitions in Figures 14 to 16 are as described above. The material of the piezoelectric body 1 of the reference model corresponding to Figures 14 to 16 is LT. In Figures 14 to 16, the LT model α and the LT model β are each illustrated as a 101 model.

[0039] The ratio of the average BodeQ of the 101 model to the average BodeQ of the reference model in the first frequency band 32 is defined as FOM1. The ratio of the average BodeQ of the 101 model to the average BodeQ of the reference model in the second frequency band 33 is defined as FOM2. The ratio of the average BodeQ of the 101 model to the average BodeQ of the reference model in the third frequency band 34 is defined as FOM3. BodeQ is one of the indices that indicate the loss characteristics of an acoustic wave device. It can be said that the larger the BodeQ, the better the loss characteristics of the acoustic wave device.

[0040] FOM1×FOM2×FOM3 is defined as FOM. As can be seen from Fig. 16, the FOM is 1.00 for the reference model, and is a value according to the BodeQ of the 101 model. It can be said that the larger the FOM, the better the loss characteristics of the acoustic wave device.

[0041] The specific frequency ranges of the first frequency band 32, the second frequency band 33, and the third frequency band 34 are not particularly limited as long as they are consistent among all FOMs.

[0042] Each of Figs. 17 to 20 is a table listing conditions under which good frequency characteristics were obtained in the LT model.

[0043] Dummy: Shows either no dummy, with dummy, or solid dummy Additional film location: "Dummy section + IDT end" indicates that the dielectric layer 3 includes both the first region 12 and the second region 14. "IDT end only" indicates that the dielectric layer 3 includes the first region 12 but does not include the second region 14. "Dummy section only" indicates that the dielectric layer 3 does not include the first region 12 but includes the second region 14. Additional film thickness xt: Shows the ratio of thickness T3 to thickness T1 Characteristics Resonant side: Shows the evaluation of the frequency characteristics of the first frequency band Characteristics Δf: Shows the evaluation of the frequency characteristics of the second frequency band Anti-resonance side: Shows the evaluation of the frequency characteristics of the third frequency band Additional film material: indicates the material of the dielectric layer 3 The definitions in the tables shown in Figures 17 to 20 are as described above. The material of the dielectric layer 3 corresponding to Figure 17 is SiO2. The material of the dielectric layer 3 corresponding to Figure 18 is AlN. The material of the dielectric layer 3 corresponding to Figure 19 is Ta2O5. Figure 20 shows the characteristics when there is no dummy and the dielectric layer 3 includes both the first region 12 and the second region 14.

[0044] For the resonance side, within Δf, and anti-resonance side, the evaluation is made on a two-level scale: "○", indicating that the improvement in frequency characteristics is significant, and "△", indicating that the improvement in frequency characteristics is not significant but is somewhat significant.

[0045] When the dielectric layer 3 includes both the first region 12 and the second region 14, the following can be said. According to Figs. 17 to 19, it can be seen that there is an improvement effect in the frequency characteristics in all of the first, second, and third frequency bands under the following conditions (1) to (3). According to Fig. 20, it can be seen that there is an improvement effect in the frequency characteristics in all of the first, second, and third frequency bands under the following conditions (4) to (8). Regarding the ratio of the thickness T3 of the dielectric layer 3 to the thickness T1 of the piezoelectric body 1, a numerical range is defined that takes into consideration an error of -15% or more and 15% or less that may occur based on the current technical level with respect to the numerical values ​​shown in Figs. 17 to 20.

[0046] (1) The material of the piezoelectric body 1 is LiTaO3. The material of the dielectric layer 3 is SiO2. The IDT electrode 2 has a planar dummy electrode that is located in the gap 13 and overlaps with the second region 14 in a planar view. The thickness T3 of the dielectric layer 3 is 0.012×0.85 times or more the thickness T1 of the piezoelectric body 1 and is 0.024×1.15 times or less the thickness T1 of the piezoelectric body 1.

[0047] (2) The material of the piezoelectric body 1 is LiTaO3. The material of the dielectric layer 3 is Ta2O5. The IDT electrode 2 has a planar dummy electrode that is located in the gap 13 and overlaps with the second region 14 in a planar view. The thickness T3 of the dielectric layer 3 is 0.012×0.85 times or more the thickness T1 of the piezoelectric body 1 and is 0.012×1.15 times or less the thickness T1 of the piezoelectric body 1.

[0048] The following conditions (3) to (8) are based on the premise that the IDT electrode 2 does not have a dummy electrode 20 that is located in the gap 13 and overlaps with the second region 14 in a plan view.

[0049] (3) The material of the piezoelectric body 1 is LiTaO3. The material of the dielectric layer 3 is Ta2O5. The thickness T3 of the dielectric layer 3 is 0.024×0.85 times the thickness T1 of the piezoelectric body 1 or more and 0.024×1.15 times the thickness T1 of the piezoelectric body 1 or less.

[0050] (4) The material of the piezoelectric body 1 is LiTaO3. The material of the dielectric layer 3 is Al2O3. The thickness T3 of the dielectric layer 3 is 0.049×0.85 times the thickness T1 of the piezoelectric body 1 or more and 0.049×1.15 times the thickness T1 of the piezoelectric body 1 or less.

[0051] (5) The material of the piezoelectric body 1 is LiTaO3. The material of the dielectric layer 3 is SiN. The thickness T3 of the dielectric layer 3 is 0.049×0.85 times or more the thickness T1 of the piezoelectric body 1 and is 0.073×1.15 times or less the thickness T1 of the piezoelectric body 1.

[0052] (6) The material of the piezoelectric body 1 is LiTaO3. The material of the dielectric layer 3 is AlN. The thickness T3 of the dielectric layer 3 is 0.049×0.85 times or more the thickness T1 of the piezoelectric body 1 and is 0.073×1.15 times or less the thickness T1 of the piezoelectric body 1.

[0053] (7) The material of the piezoelectric body 1 is LiTaO3. The material of the dielectric layer 3 is SiO2. The thickness T3 of the dielectric layer 3 is 0.024×0.85 times the thickness T1 of the piezoelectric body 1 or more and 0.049×1.15 times the thickness T1 of the piezoelectric body 1 or less.

[0054] (8) The material of the piezoelectric body 1 is LiTaO3. The material of the dielectric layer 3 is TiO2. The thickness T3 of the dielectric layer 3 is 0.024×0.85 times or more the thickness T1 of the piezoelectric body 1 and is 0.049×1.15 times or less the thickness T1 of the piezoelectric body 1.

[0055] Each of Figs. 21 to 36 is a graph showing an example of good frequency characteristics in the LT model. Each of Figs. 37 to 45 is a graph showing the relationship of FOM to thickness T3 of dielectric layer 3 in the LT model. Each of Figs. 46 and 47 is another graph showing the relationship of FOM to thickness T3 of dielectric layer 3 in the LT model. Figs. 21 to 47 provide data proving that the above conditions (1) to (8) are effective.

[0056] Figures 21 and 22: SiO2 Figures 23 and 24: AlN Figures 25 and 26: Ta2O5 Figures 27 and 28: Al2O3 Figures 29 and 30: SiN x (SiN) Figures 31 and 32: AlN Figures 33 and 34: SiO2 Figures 35 and 36: TiO2 The material of the dielectric layer 3 corresponding to FIGS. 21 to 36 is as described above.

[0057] Reference: Characteristics of the reference model in which the material of piezoelectric body 1 is LT The definitions in Figs. 21 to 36 are as above. The following rules are established for the notation of simulation conditions in Figs. 21 to 36. In Figs. 21 to 36, simulation conditions are notated using X1 to X5 along with the corresponding line type notation. For examples of X1 to X5, please refer to Fig. 21 for Figs. 21 to 26 and Fig. 27 for Figs. 27 to 36.

[0058] X1: Material of dielectric layer 3. For ease of illustration, the subscripts are converted to standard font. X2: Indicates either no dummy, with dummy, or with dummy solid. For convenience of notation, the notation for no dummy is "without dummy" X3: "Dummy section + IDT end" indicates that the dielectric layer 3 includes both the first region 12 and the second region 14. "IDT end only" indicates that the dielectric layer 3 includes the first region 12 but does not include the second region 14. "Dummy section only" indicates that the dielectric layer 3 does not include the first region 12 but includes the second region 14. X4: "Additional film thickness Mt" indicates that the thickness T3 of the dielectric layer 3 is M times the thickness T1 of the piezoelectric body 1. X5: "penetration depth Nt" indicates that the length L11 of the overlapping portion between tip portion 11 and first region 12 in the longitudinal direction of first electrode finger 8 is N times the thickness T1 of piezoelectric body 1. 27 to 36 show characteristics when there is no dummy and when the dielectric layer 3 includes both the first region 12 and the second region 14. In FIG.

[0059] LT Device: Indicates that it is an LT model Additional film: (Material name): The material of the dielectric layer 3 is (Material name). For convenience of illustration, the subscripts are converted to a standard font. Additional film thickness (xt): Shown as a ratio of thickness T3 to thickness T1 The definitions in Figures 37 to 45 are as described above.

[0060] 46 and 47, the type of lines in the graphs is indicated together with the material of the dielectric layer 3. For convenience of illustration, subscripts are converted to a standard font.

[0061] Each of Figs. 48 to 50 is a table listing conditions under which good frequency characteristics were obtained in the LN model.

[0062] The material of the dielectric layer 3 corresponding to Fig. 48 is SiO2. The material of the dielectric layer 3 corresponding to Fig. 49 is AlN. Fig. 50 shows characteristics when there is no dummy and the dielectric layer 3 includes both the first region 12 and the second region 14. As in Figs. 17 to 20, the evaluation is performed on a two-level scale of "○" and "△" for the resonance side, within Δf, and the anti-resonance side.

[0063] When the dielectric layer 3 includes both the first region 12 and the second region 14, the following can be said. According to Figs. 48 to 50, it can be seen that under the following conditions (A) to (E), there is an improvement effect on the frequency characteristics in all of the first, second, and third frequency bands. Regarding the ratio of the thickness T3 of the dielectric layer 3 to the thickness T1 of the piezoelectric body 1, a numerical range is set that takes into consideration an error of -15% or more and 15% or less that may occur based on the current technical level with respect to the numerical values ​​shown in Figs. 48 to 50. The following conditions (A) to (E) are based on the premise that the IDT electrode 2 does not have a dummy electrode 20 that is located in the gap 13 and overlaps with the second region 14 in a plan view.

[0064] (A) The material of the piezoelectric body 1 is LiNbO3. The material of the dielectric layer 3 is Al2O3. The thickness T3 of the dielectric layer 3 is 0.081×0.85 times the thickness T1 of the piezoelectric body 1 or more and 0.108×1.15 times the thickness T1 of the piezoelectric body 1 or less.

[0065] (B) The material of the piezoelectric body 1 is LiNbO3. The material of the dielectric layer 3 is SiN. The thickness T3 of the dielectric layer 3 is 0.081×0.85 times or more the thickness T1 of the piezoelectric body 1 and is 0.081×1.15 times or less the thickness T1 of the piezoelectric body 1.

[0066] (C) The material of the piezoelectric body 1 is LiNbO3. The material of the dielectric layer 3 is AlN. The thickness T3 of the dielectric layer 3 is 0.081×0.85 times or more the thickness T1 of the piezoelectric body 1 and is 0.135×1.15 times or less the thickness T1 of the piezoelectric body 1.

[0067] (D) The material of the piezoelectric body 1 is LiNbO3. The material of the dielectric layer 3 is SiO2. The thickness T3 of the dielectric layer 3 is 0.081×0.85 times the thickness T1 of the piezoelectric body 1 or more and 0.081×1.15 times the thickness T1 of the piezoelectric body 1 or less.

[0068] (E) The material of the piezoelectric body 1 is LiNbO3. The material of the dielectric layer 3 is TiO2. The thickness T3 of the dielectric layer 3 is 0.081×0.85 times or more the thickness T1 of the piezoelectric body 1 and is 0.081×1.15 times or less the thickness T1 of the piezoelectric body 1.

[0069] Each of Figs. 51 to 64 is a graph showing an example of good frequency characteristics in the LN model. Each of Figs. 65 to 73 is a graph showing the relationship of FOM to thickness T3 of dielectric layer 3 in the LN model. Each of Figs. 74 and 75 is another graph showing the relationship of FOM to thickness T3 of dielectric layer 3 in the LN model. Figs. 51 to 75 provide data proving that the above conditions (A) to (E) are effective.

[0070] Figure 51 and Figure 52: SiO2 Figures 53 and 54: AlN Figure 55 and Figure 56: Al2O3 Figures 57 and 58: SiN x (SiN) Figures 59 and 60: AlN Figure 61 and Figure 62: SiO2 Figure 63 and Figure 64: TiO2 The material of the dielectric layer 3 corresponding to FIGS. 51 to 64 is as described above.

[0071] Reference: Characteristics of the reference model in which the material of piezoelectric body 1 is LN The definitions in Figures 51 to 64 are as described above. The notation of simulation conditions in Figures 51 to 64 follows the same rules as in Figures 21 to 36. For examples of X1 to X5, see Figure 51 for Figures 51 to 54, and see Figure 55 for Figures 55 to 64.

[0072] 55 to 64 show characteristics when there is no dummy and when the dielectric layer 3 includes both the first region 12 and the second region 14. In FIG.

[0073] LN device: Indicates that it is an LN model. The definitions in Figures 65 to 73 are as described above.

[0074] 74 and 75, the type of lines in the graphs is indicated together with the material of the dielectric layer 3. For convenience of illustration, subscripts are converted to a standard font.

[0075] 76 to 97 are graphs showing frequency characteristics versus gap width D. Gap width D is the sum of gap S8 and the length of the portion where dummy electrodes 20 are arranged in the longitudinal direction of first electrode fingers 8 in a configuration without a dummy. In other words, it is the distance between the tip of first electrode finger 8 and bus bar 10 in FIG.

[0076] Figures 76 to 85 show characteristics in the LT model, and Figures 86 to 97 show characteristics in the LN model.

[0077] Figure 76 and Figure 77: Al2O3 Figures 78 and 79: AlN Figures 80 and 81: SiN x (SiN) Figure 82 and Figure 83: SiO2 Figure 84 and Figure 85: TiO2 Figure 86 and Figure 87: Al2O3 Figures 88 and 89: AlN Figure 90 and Figure 91: HfO2 Figure 92 and Figure 93: SiN x (SiN) Figure 94 and Figure 95: SiO2 Figure 96 and Figure 97: TiO2 The material of the dielectric layer 3 corresponding to FIGS. 76 to 97 is as described above.

[0078] D=Jt: This indicates that the gap width is J times the thickness T1 of the piezoelectric body 1. In the same graph, the largest J corresponds to a gap width of 3 μm, a gap width of 2 μm, and a gap width of 1 μm. The definitions in Figures 76 to 97 are as described above.

[0079] 76 to 97, it can be seen that even if the gap width D is reduced to about three times the thickness T1 of the piezoelectric body 1, the frequency characteristics of the 101 model do not deteriorate significantly.

[0080] [Embodiment 2] Fig. 98 is a cross-sectional view showing a schematic configuration of an acoustic wave device 101 according to embodiment 2 of the present disclosure. As shown in Fig. 98, the acoustic wave device 101 may have a membrane structure. The acoustic wave device 101 having a membrane structure shown in Fig. 98 does not need to have a multilayer reflective film 4, and an opening 21 is formed on the piezoelectric body 1 side of the support substrate 5, and the piezoelectric body 1 is provided so as to cover the opening 21.

[0081] [Embodiment 3] 99 is a schematic diagram of a communication device 201 according to a third embodiment of the present disclosure. The communication device 201 is an application example of the acoustic wave device 101, and performs wireless communication using radio waves. The communication device 201 may include a transmit filter 111 and a receive filter 112. Each of the transmit filter 111 and the receive filter 112 may include the acoustic wave device 101.

[0082] In the communication device 201, a transmission information signal TIS including information to be transmitted may be modulated and frequency-raised (converted into a high-frequency signal having a carrier frequency) by an RF-IC (Radio Frequency-Integrated Circuit) 113, and converted into a transmission signal TS. A band-pass filter 114 may remove unnecessary components from the transmission signal TS that are not in the transmission passband. Next, the transmission signal TS after removing the unnecessary components may be amplified by an amplifier 115 and input to the transmission filter 111.

[0083] The transmission filter 111 may remove unnecessary components outside the transmission passband from the input transmission signal TS. The transmission filter 111 may output the transmission signal TS after removing the unnecessary components to the antenna 116 via the antenna terminal. The antenna 116 may convert the transmission signal TS, which is an electrical signal input thereto, into radio waves as a wireless signal and transmit the radio waves to the outside of the communication device 201.

[0084] Furthermore, the antenna 116 may convert the received radio wave from the outside into a received signal RS, which is an electric signal, and input the received signal RS to the receiving filter 112 via the antenna terminal. The receiving filter 112 may remove unnecessary components outside the receiving passband from the input received signal RS. The receiving filter 112 may output the received signal RS after the unnecessary components have been removed to the amplifier 117. The output received signal RS may be amplified by the amplifier 117. The bandpass filter 118 may remove unnecessary components outside the receiving passband from the amplified received signal RS. The received signal RS after the unnecessary components have been removed may be frequency-downgraded and demodulated by the RF-IC 113, and converted into a received information signal RIS.

[0085] The transmission information signal TIS and the reception information signal RIS may be low-frequency signals (baseband signals) containing appropriate information. For example, the transmission information signal TIS and the reception information signal RIS may be analog voice signals or digitalized voice signals. The passband of the wireless signal may be set appropriately and may conform to various known standards.

[0086] 〔summary〕 An acoustic wave device according to a first aspect of the present disclosure comprises a piezoelectric body having a surface on which grooves are formed, an IDT electrode located above the piezoelectric body and including a portion located inside the groove, the IDT electrode having a first electrode finger, a second electrode finger adjacent to the first electrode finger in a planar view, and a bus bar electrically connected to the second electrode finger, and a dielectric layer located above the surface, wherein the thickness of the piezoelectric body is less than twice the pitch of the first electrode fingers and the second electrode fingers, and in the planar view, the dielectric layer includes a first region overlapping with the tip of the first electrode finger and a second region overlapping with a gap between the tip and the bus bar.

[0087] A second aspect of the present disclosure relates to an acoustic wave device according to the first aspect, wherein the dielectric layer includes at least one of a high acoustic velocity dielectric material and Ta2O5.

[0088] A third aspect of the present disclosure relates to an acoustic wave device according to the second aspect, wherein the high acoustic velocity dielectric material is any one of SiO2, AlN, SiN, Al2O3, and TiO2.

[0089] According to a fourth aspect of the present disclosure, in the acoustic wave device of any one of the first to third aspects, the thickness of the dielectric layer is not less than 0.01 times and not more than 0.2 times the thickness of the piezoelectric body.

[0090] A fifth aspect of the present disclosure relates to an acoustic wave device in accordance with any one of the first to fourth aspects, wherein the dielectric layer has a thickness of 0.005 μm or more and 0.07 μm or less.

[0091] An acoustic wave device according to aspect 6 of the present disclosure, in any one of aspects 1 to 5, has a length of the overlapping portion between the tip portion and the first region in the longitudinal direction of the first electrode finger that is greater than or equal to the thickness of the piezoelectric body and less than or equal to 5 times the thickness of the piezoelectric body.

[0092] According to a seventh aspect of the present disclosure, in the acoustic wave device of any one of the first to sixth aspects, the dielectric layer includes a third region overlapping with the bus bar in the plan view.

[0093] An acoustic wave device according to an eighth aspect of the present disclosure is any one of the first to seventh aspects, wherein the IDT electrode does not include a dummy electrode that is located in the gap and overlaps with the second region in the plan view.

[0094] An acoustic wave device according to a ninth aspect of the present disclosure is any one of the first to seventh aspects, wherein the IDT electrode has a dummy electrode located in the gap and overlapping with the second region in the planar view, and the distance between the first electrode finger and the dummy electrode in the longitudinal direction of the first electrode finger is more than twice the thickness of the piezoelectric body.

[0095] According to a tenth aspect of the present disclosure, in the acoustic wave device of any one of the first to ninth aspects, the acoustic wave device further includes a low acoustic impedance layer and a high acoustic impedance layer located below the piezoelectric body.

[0096] An acoustic wave device according to an eleventh aspect of the present disclosure is any one of the first to tenth aspects, wherein the piezoelectric body includes at least one of LiTaO3 and LiNbO3.

[0097] An acoustic wave device according to aspect 12 of the present disclosure is the same as aspect 1, except that the material of the piezoelectric body is LiTaO3, the material of the dielectric layer is SiO2, the IDT electrode has a planar dummy electrode located in the gap and overlapping the second region in the planar view, and the thickness of the dielectric layer is greater than or equal to 0.012 x 0.85 times the thickness of the piezoelectric body and less than or equal to 0.024 x 1.15 times the thickness of the piezoelectric body.

[0098] An acoustic wave device according to aspect 13 of the present disclosure is the same as aspect 1, except that the material of the piezoelectric body is LiTaO3, the material of the dielectric layer is Ta2O5, the IDT electrode has a planar dummy electrode located in the gap and overlapping the second region in the planar view, and the thickness of the dielectric layer is at least 0.012 x 0.85 times the thickness of the piezoelectric body and is not more than 0.012 x 1.15 times the thickness of the piezoelectric body.

[0099] The acoustic wave device of aspect 14 of the present disclosure is the same as aspect 8, except that the material of the piezoelectric body is LiTaO3, the material of the dielectric layer is Ta2O5, and the thickness of the dielectric layer is 0.024 x 0.85 times or more the thickness of the piezoelectric body and 0.024 x 1.15 times or less the thickness of the piezoelectric body.

[0100] An acoustic wave device according to aspect 15 of the present disclosure is the same as aspect 8, except that the material of the piezoelectric body is LiTaO3, the material of the dielectric layer is Al2O3, and the thickness of the dielectric layer is greater than or equal to 0.049 x 0.85 times the thickness of the piezoelectric body and is less than or equal to 0.049 x 1.15 times the thickness of the piezoelectric body.

[0101] The acoustic wave device of aspect 16 of the present disclosure is the same as aspect 8, except that the material of the piezoelectric body is LiTaO3, the material of the dielectric layer is SiN, and the thickness of the dielectric layer is greater than or equal to 0.049 x 0.85 times the thickness of the piezoelectric body and is less than or equal to 0.073 x 1.15 times the thickness of the piezoelectric body.

[0102] An acoustic wave device according to aspect 17 of the present disclosure is the same as aspect 8, except that the material of the piezoelectric body is LiTaO3, the material of the dielectric layer is AlN, and the thickness of the dielectric layer is greater than or equal to 0.049 x 0.85 times the thickness of the piezoelectric body and is less than or equal to 0.073 x 1.15 times the thickness of the piezoelectric body.

[0103] An acoustic wave device according to aspect 18 of the present disclosure is the same as aspect 8, except that the material of the piezoelectric body is LiTaO3, the material of the dielectric layer is SiO2, and the thickness of the dielectric layer is greater than or equal to 0.024 x 0.85 times the thickness of the piezoelectric body and is less than or equal to 0.049 x 1.15 times the thickness of the piezoelectric body.

[0104] The acoustic wave device of aspect 19 of the present disclosure is the same as aspect 8, except that the material of the piezoelectric body is LiTaO3, the material of the dielectric layer is TiO2, and the thickness of the dielectric layer is greater than or equal to 0.024 x 0.85 times the thickness of the piezoelectric body and is less than or equal to 0.049 x 1.15 times the thickness of the piezoelectric body.

[0105] An acoustic wave device according to aspect 20 of the present disclosure is the same as aspect 8, except that the material of the piezoelectric body is LiNbO3, the material of the dielectric layer is Al2O3, and the thickness of the dielectric layer is greater than or equal to 0.081 x 0.85 times the thickness of the piezoelectric body and is less than or equal to 0.108 x 1.15 times the thickness of the piezoelectric body.

[0106] An acoustic wave device according to aspect 21 of the present disclosure is the same as aspect 8, except that the material of the piezoelectric body is LiNbO3, the material of the dielectric layer is SiN, and the thickness of the dielectric layer is greater than or equal to 0.081 x 0.85 times the thickness of the piezoelectric body and is less than or equal to 0.081 x 1.15 times the thickness of the piezoelectric body.

[0107] An acoustic wave device according to aspect 22 of the present disclosure is the same as aspect 8, except that the material of the piezoelectric body is LiNbO3, the material of the dielectric layer is AlN, and the thickness of the dielectric layer is greater than or equal to 0.081 x 0.85 times the thickness of the piezoelectric body and is less than or equal to 0.135 x 1.15 times the thickness of the piezoelectric body.

[0108] An acoustic wave device according to aspect 23 of the present disclosure is the same as aspect 8, except that the material of the piezoelectric body is LiNbO3, the material of the dielectric layer is SiO2, and the thickness of the dielectric layer is greater than or equal to 0.081 x 0.85 times the thickness of the piezoelectric body and is less than or equal to 0.081 x 1.15 times the thickness of the piezoelectric body.

[0109] An acoustic wave device according to aspect 24 of the present disclosure is the same as aspect 8, except that the material of the piezoelectric body is LiNbO3, the material of the dielectric layer is TiO2, and the thickness of the dielectric layer is greater than or equal to 0.081 x 0.85 times the thickness of the piezoelectric body and is less than or equal to 0.081 x 1.15 times the thickness of the piezoelectric body.

[0110] An acoustic wave device according to a twenty-fifth aspect of the present disclosure, in any one of the first to twenty-fourth aspects, excites the A1 mode, which is an antisymmetric mode.

[0111] An acoustic wave device according to a twenty-sixth aspect of the present disclosure is in any one of the first to twenty-fourth aspects, in which a bulk wave is excited.

[0112] The acoustic wave device according to a twenty-seventh aspect of the present disclosure is in any one of the first to twenty-sixth aspects, which has a membrane structure.

[0113] A communication device according to a twenty-eighth aspect of the present disclosure includes the acoustic wave device according to any one of the first to twenty-seventh aspects.

[0114] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure.

[0115] For example, the characteristic degradation corresponding to the arrow 30 in the first frequency band 32 described in Fig. 12 is believed to occur because the resonance frequency of the first region 12 is reduced by the dielectric layer 3 in the first region 12. This frequency reduction can be reduced by reducing the duty of the IDT electrode 2 in the first region 12 or by reducing the thickness T1 of the piezoelectric body 1, thereby mitigating the characteristic degradation.

[0116] For example, acoustic wave device 101 may have additional structures that can be employed in typical acoustic wave devices.

[0117] For example, there may be a protective film that protects the acoustic wave device 101 from moisture and the like. For example, the protective film entirely covers the IDT electrode 2, the piezoelectric body 1, and the dielectric layer 3. The protective film may cover the IDT electrode 2 and the piezoelectric body 1, and the dielectric layer 3 may be provided above the protective film. [Explanation of symbols]

[0118] 1 Piezoelectric 2 IDT electrode 3 Dielectric Layer 4 Multilayer reflective film 5 Support substrate 6. Low acoustic impedance layer 7 High acoustic impedance layer 8 1st electrode finger 9 Second electrode finger 10 Busbar 11 Tip of first electrode finger 12 First area 13 Gap between first electrode finger and bus bar 14 Second area 15 Third area 16 Center of the first electrode finger in the D1 direction 17 Center of the second electrode finger in the D1 direction 18 Piezoelectric surface 19 Groove 20 Dummy electrode 21 Opening 101 Acoustic Wave Devices 201 Communication equipment p Pitch of the first and second electrode fingers L11: Length of the overlapping portion of the tip and the first region in the longitudinal direction of the first electrode finger S8: Distance between the first electrode finger and the dummy electrode in the longitudinal direction of the first electrode finger T1 Thickness of the piezoelectric element T3 Dielectric layer thickness

Claims

1. a piezoelectric body having a surface with grooves formed therein; an IDT electrode located in a layer above the piezoelectric body and including a portion located inside the groove, the IDT electrode having first electrode fingers, second electrode fingers adjacent to the first electrode fingers in a plan view, and a bus bar electrically connected to the second electrode fingers; a dielectric layer located above the surface, a thickness of the piezoelectric body is equal to or smaller than twice the pitch of the first electrode fingers and the second electrode fingers; In the planar view, the dielectric layer includes a first region overlapping with a tip of the first electrode finger and a second region overlapping with a gap between the tip and the bus bar.

2. The dielectric layer is made of a high acoustic velocity dielectric material and Ta. ２ O ５ The acoustic wave device of claim 1 , comprising at least one of:

3. The high acoustic velocity dielectric material is SiO ２ , AlN, SiN, Al ２ O ３ , and TiO ２ 3. The acoustic wave device according to claim 2, wherein

4. The acoustic wave device according to claim 1 , wherein the thickness of the dielectric layer is not less than 0.01 times and not more than 0.2 times the thickness of the piezoelectric body.

5. The acoustic wave device according to claim 1 , wherein the dielectric layer has a thickness of not less than 0.005 μm and not more than 0.07 μm.

6. 2. The acoustic wave device according to claim 1, wherein a length of an overlapping portion between the tip portion and the first region in the longitudinal direction of the first electrode finger is greater than or equal to a thickness of the piezoelectric body and is less than five times the thickness of the piezoelectric body.

7. The acoustic wave device according to claim 1 , wherein in the plan view, the dielectric layer includes a third region that overlaps with the bus bar.

8. The acoustic wave device according to claim 1 , wherein the IDT electrode does not have a dummy electrode that is located in the gap and overlaps with the second region in the plan view.

9. the IDT electrode has a dummy electrode located in the gap and overlapping with the second region in the plan view, The acoustic wave device according to claim 1 , wherein a distance between the first electrode finger and the dummy electrode in a longitudinal direction of the first electrode finger is at least twice as large as a thickness of the piezoelectric body.

10. The acoustic wave device according to claim 1 , further comprising a low acoustic impedance layer and a high acoustic impedance layer located below the piezoelectric body.

11. The piezoelectric body is LiTaO ３ and LiNbO ３ The acoustic wave device of claim 1 , comprising at least one of:

12. The material of the piezoelectric body is LiTaO ３ and The material of the dielectric layer is SiO ２ and the IDT electrode has a planar dummy electrode located in the gap and overlapping with the second region in the planar view, The acoustic wave device according to claim 1 , wherein the thickness of the dielectric layer is not less than 0.012×0.85 times the thickness of the piezoelectric body and not more than 0.024×1.15 times the thickness of the piezoelectric body.

13. The material of the piezoelectric body is LiTaO ３ and The material of the dielectric layer is Ta. ２ O ５ and the IDT electrode has a planar dummy electrode located in the gap and overlapping with the second region in the planar view, The acoustic wave device according to claim 1 , wherein the thickness of the dielectric layer is not less than 0.012×0.85 times the thickness of the piezoelectric body and not more than 0.012×1.15 times the thickness of the piezoelectric body.

14. The material of the piezoelectric body is LiTaO ３ and The material of the dielectric layer is Ta. ２ O ５ and The acoustic wave device according to claim 8 , wherein the thickness of the dielectric layer is not less than 0.024×0.85 times the thickness of the piezoelectric body and not more than 0.024×1.15 times the thickness of the piezoelectric body.

15. The material of the piezoelectric body is LiTaO ３ and The material of the dielectric layer is Al ２ O ３ and The acoustic wave device according to claim 8 , wherein the thickness of the dielectric layer is not less than 0.049×0.85 times the thickness of the piezoelectric body and not more than 0.049×1.15 times the thickness of the piezoelectric body.

16. The material of the piezoelectric body is LiTaO ３ and the material of the dielectric layer is SiN; The acoustic wave device according to claim 8 , wherein the thickness of the dielectric layer is not less than 0.049×0.85 times the thickness of the piezoelectric body and not more than 0.073×1.15 times the thickness of the piezoelectric body.

17. The material of the piezoelectric body is LiTaO ３ and the material of the dielectric layer is AlN; The acoustic wave device according to claim 8 , wherein the thickness of the dielectric layer is not less than 0.049×0.85 times the thickness of the piezoelectric body and not more than 0.073×1.15 times the thickness of the piezoelectric body.

18. The material of the piezoelectric body is LiTaO ３ and The material of the dielectric layer is SiO ２ and The acoustic wave device according to claim 8 , wherein the thickness of the dielectric layer is not less than 0.024×0.85 times the thickness of the piezoelectric body and not more than 0.049×1.15 times the thickness of the piezoelectric body.

19. The material of the piezoelectric body is LiTaO ３ and The material of the dielectric layer is TiO ２ and The acoustic wave device according to claim 8 , wherein the thickness of the dielectric layer is not less than 0.024×0.85 times the thickness of the piezoelectric body and not more than 0.049×1.15 times the thickness of the piezoelectric body.

20. The material of the piezoelectric body is LiNbO ３ and The material of the dielectric layer is Al ２ O ３ and The acoustic wave device according to claim 8 , wherein the thickness of the dielectric layer is not less than 0.081×0.85 times the thickness of the piezoelectric body and not more than 0.108×1.15 times the thickness of the piezoelectric body.

21. The material of the piezoelectric body is LiNbO ３ and the material of the dielectric layer is SiN; The acoustic wave device according to claim 8 , wherein the thickness of the dielectric layer is not less than 0.081×0.85 times the thickness of the piezoelectric body and not more than 0.081×1.15 times the thickness of the piezoelectric body.

22. The material of the piezoelectric body is LiNbO ３ and the material of the dielectric layer is AlN; The acoustic wave device according to claim 8 , wherein the thickness of the dielectric layer is not less than 0.081×0.85 times the thickness of the piezoelectric body and not more than 0.135×1.15 times the thickness of the piezoelectric body.

23. The material of the piezoelectric body is LiNbO ３ and The material of the dielectric layer is SiO ２ and The acoustic wave device according to claim 8 , wherein the thickness of the dielectric layer is not less than 0.081×0.85 times the thickness of the piezoelectric body and not more than 0.081×1.15 times the thickness of the piezoelectric body.

24. The material of the piezoelectric body is LiNbO ３ and The material of the dielectric layer is TiO ２ and The acoustic wave device according to claim 8 , wherein the thickness of the dielectric layer is not less than 0.081×0.85 times the thickness of the piezoelectric body and not more than 0.081×1.15 times the thickness of the piezoelectric body.

25. Antisymmetric mode A １ The acoustic wave device of claim 1 , wherein the acoustic wave device excites a mode.

26. The acoustic wave device of claim 1 , which excites bulk waves.

27. The acoustic wave device of claim 1 , which is a membrane structure.

28. A communication device comprising an acoustic wave device according to any one of claims 1 to 27.

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