Acoustic wave device

Abstract

To provide an elastic wave device capable of reducing loss.SOLUTION: In the acoustic wave device 1 including the acoustic reflective film 3 including the high-acoustic-impedance layers 5a and 5b having relatively high acoustic impedances and the low-acoustic-impedance layers 4a to 4c having relatively low acoustic impedances, the piezoelectric layer 7, and the IDT electrodes 8 including the plurality of electrodes (first and second electrodes 1819 and), a direction orthogonal or substantially orthogonal to a direction in which the plurality of electrodes extend is defined as an electrode-finger orthogonal direction. Among the plurality of electrode fingers, each of the electrode fingers located at both ends in the electrode finger orthogonal direction is an end electrode finger A, a region outside the acoustic reflection film 3 in the electrode finger orthogonal direction is an outer region O, a boundary between the outer region O and the acoustic reflection film 3 is an outer-reflection film boundary B, and a direction in which the acoustic reflection film 3 and the piezoelectric layer 7 are laminated is a lamination direction.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an acoustic wave device.

[0002] Acoustic wave devices have been widely used in filters for mobile phones and the like. Recently, an acoustic wave device using bulk waves in thickness shear mode has been proposed, as described in Patent Document 1 below. Patent Document 1 below discloses an example of an acoustic wave device. In this acoustic wave device, an acoustic reflection layer is provided on a support member. The acoustic reflection layer is formed by alternately laminating layers with high and low acoustic impedance. A piezoelectric layer is provided on the acoustic reflection layer. A functional electrode is provided on the piezoelectric layer.

[0003] The functional electrode has multiple pairs of electrode fingers. The pair of electrode fingers faces each other on the piezoelectric layer and is connected to different potentials. By applying an AC voltage between the electrode fingers, bulk waves in thickness shear mode are excited. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2023 / 204245 Summary of the Invention [Problem to be solved by the invention]

[0005] In the acoustic wave device described in Patent Document 1, the acoustic reflection layer is used as a layer for trapping energy. However, in recent years, there has been a demand for further reduction in loss.

[0006] An object of the present invention is to provide an acoustic wave device that can reduce loss. [Means for solving the problem]

[0007] An elastic wave device according to the present invention includes an acoustic reflection film including a high acoustic impedance layer having a relatively high acoustic impedance and a low acoustic impedance layer having a relatively low acoustic impedance; a piezoelectric layer provided on the acoustic reflection film and having a first main surface and a second main surface facing each other; and at least one IDT electrode provided on at least one of the first main surface and the second main surface of the piezoelectric layer and having a plurality of electrode fingers, wherein d / p is 0.5 or less, where d is the thickness of the piezoelectric layer and p is the center-to-center distance between adjacent electrode fingers, and When the direction perpendicular to the direction in which the plurality of electrode fingers extend is defined as the electrode finger perpendicular direction, the electrode fingers located at both ends in the electrode finger perpendicular direction among the plurality of electrode fingers are end electrode fingers, the region outside the acoustic reflection film in the electrode finger perpendicular direction is the outer region, the boundary between the outer region and the acoustic reflection film is the outer-reflection film boundary, and when the direction in which the acoustic reflection film and the piezoelectric layer are stacked is defined as the stacking direction, at least one of the end electrode fingers overlaps with the portion of the outer-reflection film boundary closest to the piezoelectric layer in the stacking direction. [Effects of the Invention]

[0008] According to an acoustic wave device according to a preferred embodiment of the present invention, loss can be reduced. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic front cross-sectional view of an elastic wave device according to a first preferred embodiment of the present invention. [Figure 2] FIG. 1 is a schematic plan view of an elastic wave device according to a first preferred embodiment of the present invention. [Figure 3] FIG. 3 is a schematic cross-sectional view taken along line II-II in FIG. 2. [Figure 4] FIG. 2 is a schematic front cross-sectional view illustrating a portion of an elastic wave device of a first comparative example. [Figure 5] FIG. 3 is a diagram showing admittance frequency characteristics in the first embodiment of the present invention and the first comparative example. [Figure 6]FIG. 10 is a diagram showing the relationship between the position of the IDT electrode in the direction orthogonal to the electrode fingers and the displacement near the resonance frequency in the first comparative example. [Figure 7] FIG. 3 is a diagram showing the relationship between the position of the IDT electrode in the direction orthogonal to the electrode fingers and the displacement near the resonance frequency in the first embodiment of the present invention. [Figure 8] FIG. 10 is a schematic front cross-sectional view illustrating a portion of an elastic wave device according to a second preferred embodiment of the present invention. [Figure 9] FIG. 10 is a diagram showing admittance frequency characteristics in the second embodiment of the present invention and the second comparative example. [Figure 10] FIG. 10 is a schematic front cross-sectional view illustrating a portion of an elastic wave device according to a third preferred embodiment of the present invention. [Figure 11] FIG. 10 is a schematic front cross-sectional view illustrating a portion of an elastic wave device according to a fourth preferred embodiment of the present invention. [Figure 12] FIG. 10 is a diagram showing admittance frequency characteristics in the fourth embodiment of the present invention and the third comparative example. [Figure 13] FIG. 10 is a schematic front cross-sectional view illustrating a portion of an elastic wave device according to a fifth preferred embodiment of the present invention. [Figure 14] FIG. 10 is a diagram showing admittance frequency characteristics in the fifth embodiment of the present invention and the fourth comparative example. [Figure 15] FIG. 10 is a schematic front cross-sectional view illustrating a portion of an elastic wave device according to a sixth preferred embodiment of the present invention. [Figure 16] FIG. 13 is a diagram showing admittance frequency characteristics in the sixth embodiment of the present invention and the first comparative example. [Figure 17] FIG. 13 is a schematic front cross-sectional view of an elastic wave device according to a seventh preferred embodiment of the present invention. [Figure 18] FIG. 13 is a diagram showing admittance frequency characteristics in the seventh embodiment of the present invention and the fifth comparative example. [Figure 19] FIG. 10 is a diagram illustrating the relationship between d / p and the fractional bandwidth of an elastic wave resonator. [Figure 20] FIG. 10 is a diagram illustrating the relationship between the bandwidth ratio and the magnitude of normalized spurious signals in an acoustic wave resonator. [Figure 21] FIG. 10 is a diagram showing the relationship between d / p, metallization ratio MR, and fractional bandwidth. [Figure 22] FIG. 10 is a diagram showing a map of the fractional bandwidth of LiNbO 3 versus the Euler angles (0°, θ, ψ) when d / p approaches 0 as close as possible. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be clarified below by describing specific embodiments of the present invention with reference to the drawings.

[0011] It should be noted that the embodiments described in this specification are merely examples, and partial substitution or combination of configurations is possible between different embodiments.

[0012] FIG. 1 is a schematic front cross-sectional view of an elastic wave device according to a first preferred embodiment of the present invention.

[0013] The acoustic wave device 1 has a support substrate 2, an acoustic reflection film 3, and an IDT electrode 8. The acoustic reflection film 3 is provided on the support substrate 2. A piezoelectric layer 7 is provided on the acoustic reflection film 3. Hereinafter, the direction in which the acoustic reflection film 3 and the piezoelectric layer 7 are stacked is referred to as the stacking direction.

[0014] The acoustic reflecting film 3 is a laminate of multiple acoustic impedance layers. Specifically, the acoustic reflecting film 3 has multiple low acoustic impedance layers and multiple high acoustic impedance layers. The low acoustic impedance layers are layers with a relatively low acoustic impedance. More specifically, the low acoustic impedance layers are layers with a lower acoustic impedance than adjacent layers in the acoustic reflecting film 3. More specifically, the multiple low acoustic impedance layers in the acoustic reflecting film 3 are low acoustic impedance layer 4a, low acoustic impedance layer 4b, and low acoustic impedance layer 4c.

[0015] On the other hand, a high acoustic impedance layer is a layer with a relatively high acoustic impedance. More specifically, a high acoustic impedance layer is a layer with a higher acoustic impedance than an adjacent layer in the acoustic reflecting film 3. More specifically, the multiple high acoustic impedance layers in the acoustic reflecting film 3 are the high acoustic impedance layer 5a and the high acoustic impedance layer 5b. The low acoustic impedance layers and the high acoustic impedance layers are alternately stacked. The low acoustic impedance layer 4a is the acoustic impedance layer located closest to the piezoelectric layer 7 in the acoustic reflecting film 3.

[0016] The acoustic reflecting film 3 has three low acoustic impedance layers and two high acoustic impedance layers, although it is sufficient that the acoustic reflecting film 3 has at least one low acoustic impedance layer and one high acoustic impedance layer.

[0017] In this embodiment, silicon oxide is used as the material for the low acoustic impedance layer. The material for the low acoustic impedance layer is not limited to the above, and for example, an appropriate dielectric material other than silicon oxide, or a metal such as aluminum or titanium, can also be used. In this embodiment, hafnium oxide is used as the material for the high acoustic impedance layer. The material for the high acoustic impedance layer is not limited to the above, and for example, a dielectric material such as aluminum nitride, silicon nitride, or tungsten oxide, or a metal such as platinum or tungsten can also be used.

[0018] Support substrate 2 is made of silicon. However, the material of support substrate 2 is not limited to the above. Support substrate 2 may be made of semiconductors other than silicon, or ceramics such as aluminum oxide. In this specification, "a certain component is made of a certain material" includes the case where a small amount of impurities are contained to the extent that the electrical characteristics of the acoustic wave device are not significantly deteriorated.

[0019] In this embodiment, the piezoelectric layer 7 is made of 120° Y-cut LiNbO. The cut angle and material of the piezoelectric layer 7 are not limited to those described above. The piezoelectric layer 7 may be made of, for example, lithium niobate other than those described above, or lithium tantalate such as LiTaO.

[0020] The piezoelectric layer 7 has a first principal surface 7a and a second principal surface 7b. The first principal surface 7a and the second principal surface 7b face each other. Of the first principal surface 7a and the second principal surface 7b, the second principal surface 7b is located on the acoustic reflection film 3 side. An IDT electrode 8 is provided on the first principal surface 7a of the piezoelectric layer 7.

[0021] Fig. 2 is a schematic plan view of the elastic wave device according to the first preferred embodiment of the present invention. A dielectric film, which will be described later, is omitted from Fig. 2. Note that Fig. 1 is a schematic cross-sectional view taken along line II in Fig. 2.

[0022] As shown in FIG. 2 , the IDT electrode 8 has a pair of bus bars and a plurality of electrode fingers. The pair of bus bars is specifically a first bus bar 16 and a second bus bar 17. The first bus bar 16 and the second bus bar 17 face each other. The plurality of electrode fingers is specifically a plurality of first electrode fingers 18 and a plurality of second electrode fingers 19. One end of each of the plurality of first electrode fingers 18 is connected to the first bus bar 16. One end of each of the plurality of second electrode fingers 19 is connected to the second bus bar 17. The plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 are interdigitated with each other. The first electrode fingers 18 and the second electrode fingers 19 are connected to different potentials.

[0023] The IDT electrode 8 is made of a laminated metal film. Specifically, in the IDT electrode 8, a Ti layer and an Al layer are laminated in this order from the piezoelectric layer 7 side. The material of the IDT electrode 8 is not limited to the above. Alternatively, the IDT electrode 8 may be made of a single-layer metal film.

[0024] Hereinafter, the first electrode fingers 18 and the second electrode fingers 19 may be collectively referred to simply as electrode fingers. The direction in which the electrode fingers extend is referred to as the electrode finger extension direction, and the direction perpendicular to the electrode finger extension direction is referred to as the electrode finger perpendicular direction. In this specification, the electrode finger extension direction and the electrode finger perpendicular direction are also used for members other than the IDT electrode 8.

[0025] Of the multiple electrode fingers, the electrode fingers located at both ends in the direction perpendicular to the electrode fingers are end electrode fingers A. In this embodiment, one end electrode finger A is a first electrode finger 18, and the other end electrode finger A is a second electrode finger 19. Note that both end electrode fingers A may be first electrode fingers 18, or both end electrode fingers A may be second electrode fingers 19.

[0026] 1 , the outer region of the acoustic reflection film 3 in the direction perpendicular to the electrode fingers is an outer region O. In this embodiment, an outer wall member 6 is provided in the outer region O. A piezoelectric layer 7 is provided on the acoustic reflection film 3 and the outer wall member 6.

[0027] In this embodiment, silicon oxide is used as the material of the outer wall member 6. The material of the outer wall member 6 and the material of the low acoustic impedance layer are the same. The outer wall member 6 and the acoustic reflecting film 3 are in contact with each other. The low acoustic impedance layers of the outer wall member 6 and the acoustic reflecting film 3 are provided integrally. However, the material of the outer wall member 6 and the material of the low acoustic impedance layer may be different from each other. Alternatively, the material of the outer wall member 6 and the material of the high acoustic impedance layer may be the same.

[0028] The boundary between the outer region O and the acoustic reflection film 3 is the outer-reflection film boundary B. In this embodiment, the outer-reflection film boundary B is the boundary between the outer wall member 6 and the acoustic reflection film 3. In FIG. 1, the outer-reflection film boundary B is indicated by a dashed dotted line. In the present invention, when the outer wall member 6 and the low acoustic impedance layer are integrated, the outer-reflection film boundary B is located on an extension of the boundary between the outer wall member 6 and the high acoustic impedance layer. On the other hand, when the outer wall member 6 and the high acoustic impedance layer are integrated, the outer-reflection film boundary B is located on an extension of the boundary between the outer wall member 6 and the low acoustic impedance layer.

[0029] For example, in this embodiment, the material of the low acoustic impedance layer 4a, which is the acoustic impedance layer closest to the piezoelectric layer 7, is the same as the material of the outer wall member 6. The boundary between the outer wall member 6 and the low acoustic impedance layer 4a is located on an extension of the boundary between the outer wall member 6 and the high acoustic impedance layer. In this embodiment, the boundary between the high acoustic impedance layer 5a, which is the acoustic impedance layer second closest to the piezoelectric layer 7, and the outer region O overlaps with the boundary between the low acoustic impedance layer 4a and the outer wall member 6 in the stacking direction.

[0030] The same may be true when the acoustic impedance layer closest to the piezoelectric layer 7 is a high acoustic impedance layer and the material of the high acoustic impedance layer is the same as the material of the outer wall member 6. Specifically, the boundary between the low acoustic impedance layer, which is the acoustic impedance layer second closest to the piezoelectric layer 7, and the outer region O may overlap with the boundary between the high acoustic impedance layer, which is the acoustic impedance layer closest to the piezoelectric layer 7, and the outer wall member 6 in the stacking direction.

[0031] The outer side of the acoustic reflection film 3 in the electrode finger extension direction is not the outer region O. The outer wall member 6 is not provided on the outer side of the acoustic reflection film 3 in the electrode finger extension direction. However, the outer wall member 6 may be provided on the outer side of the acoustic reflection film 3 in the electrode finger extension direction. The outer wall member 6 may be provided so as to surround the acoustic reflection film 3.

[0032] FIG. 3 is a schematic cross-sectional view taken along line II-II in FIG.

[0033] Each electrode finger of the IDT electrode 8 has a first surface 8a, a second surface 8b, and a side surface 8c. The first surface 8a and the second surface 8b face each other in the thickness direction. The side surface 8c connects the first surface 8a and the second surface 8b. In this embodiment, the side surface 8c extends at an inclination with respect to the normal direction of the second surface 8b. Specifically, when the angle formed by the second surface 8b and the side surface 8c is defined as the inclination angle, the inclination angle is 80°. Note that the side surface 8c may extend parallel to the normal direction of the second surface 8b. In other words, the inclination angle may be 90°.

[0034] A dielectric film 9 is provided on the first main surface 7a of the piezoelectric layer 7 so as to cover the IDT electrode 8. In this embodiment, the material of the dielectric film 9 is silicon oxide. However, the material of the dielectric film 9 is not limited to the above and may be, for example, silicon nitride or silicon oxynitride. However, the dielectric film 9 does not necessarily have to be provided.

[0035] The elastic wave device 1 of this preferred embodiment is an elastic wave resonator configured to utilize thickness-shear mode bulk waves as the main mode. More specifically, in the elastic wave device 1, where d is the thickness of the piezoelectric layer 7 and p is the center-to-center distance between adjacent electrode fingers, d / p is 0.5 or less. This allows thickness-shear mode bulk waves to be suitably excited. Note that the elastic wave device according to the present invention may also be a filter device or a multiplexer having multiple elastic wave resonators.

[0036] This embodiment is characterized in that it is configured to be able to use a thickness-shear bulk wave as the main mode, and that at least one of the end electrode fingers A overlaps with the portion of the boundary B between the outer layer and the reflective film closest to the piezoelectric layer 7 in the stacking direction. That is, in this embodiment, at least one of the end electrode fingers A overlaps with both the acoustic reflection film 3 and the outer region O in the stacking direction. This makes it possible to reduce loss. Details of this will be explained below by comparing this embodiment with a first comparative example.

[0037] As shown in FIG. 4 , the elastic wave device 101 of the first comparative example differs from the elastic wave device 1 of the first preferred embodiment in that the outer-reflecting film boundary B is located outside the IDT electrode 8 in a plan view. In this specification, a plan view refers to a view along the stacking direction from a direction corresponding to the top in FIGS. 3 and 4 . Note that in FIGS. 3 and 4 , for example, the piezoelectric layer 7 side is the top, out of the acoustic reflecting film 3 side and the piezoelectric layer 7 side. Furthermore, in this specification, a plan view is synonymous with a view from the principal surface opposing direction. The principal surface opposing direction is the direction in which the first principal surface 7 a and the second principal surface 7 b of the piezoelectric layer 7 face each other. More specifically, the principal surface opposing direction is, for example, the normal direction to the first principal surface 7 a.

[0038] In the first embodiment, the position of the portion of the end electrode finger A that overlaps with the boundary B between the outer layer and the reflective film in the stacking direction is the center in the direction perpendicular to the electrode fingers of the end electrode finger A. However, a portion of the end electrode finger A other than the center in the direction perpendicular to the electrode fingers may overlap with the boundary B between the outer layer and the reflective film in the stacking direction.

[0039] The admittance-frequency characteristics were compared between the first preferred embodiment and the first comparative example. The design parameters of the elastic wave device 1 of the first preferred embodiment for this comparison are as follows. Note that, among the design parameters, the width of the electrode fingers is the dimension of the electrode fingers in the direction perpendicular to the electrode fingers.

[0040] Piezoelectric layer: Material: 120° Y-cut LiNbO3, Thickness: 320 nm IDT electrode: Layer structure...Ti layer / Al layer from the piezoelectric layer side, thickness...12 nm / 80 nm from the piezoelectric layer side, center distance p: 2.48 μm, width...0.6 μm, tilt angle...80°, number of electrode fingers...53 Dielectric film: Material: SiO2, Thickness: 33 nm Acoustic reflection film: Layer structure...SiO2 layer / HfO2 layer / SiO2 layer / HfO2 layer / SiO2 layer from the piezoelectric layer side, thickness...132nm / 105nm / 132nm / 105nm / 132nm from the piezoelectric layer side Exterior wall material: SiO2 Support substrate: Material: Si, Thickness: Assuming semi-infinite length Position of the part of the edge electrode finger that overlaps with the boundary between the outer and reflective films in the lamination direction: Center of the edge electrode finger in the direction perpendicular to the electrode fingers

[0041] The design parameters of the first comparative example were the same as those of the first embodiment, except that the end electrode fingers A did not overlap the boundary B between the outer layer and the reflective film in the stacking direction.

[0042] Fig. 5 is a diagram showing admittance frequency characteristics in the first embodiment and the first comparative example. The admittance frequency characteristics shown in Fig. 5 were derived by FEM (Finite Element Method) simulation. The same applies to figures showing admittance frequency characteristics other than Fig. 5.

[0043] In Fig. 5, in the vicinity of the frequency indicated by the dashed line, the admittance in the first embodiment is smaller than the admittance in the first comparative example. That is, the first embodiment can reduce loss more than the first comparative example. The reason for this will be explained below together with the details of the configuration of the first embodiment.

[0044] As shown in FIG. 2 , when viewed from the direction perpendicular to the electrode fingers, the excitation region C is a region where adjacent first electrode fingers 18 and second electrode fingers 19 overlap and between the centers of the adjacent first electrode fingers 18 and second electrode fingers 19. The excitation region C is a region of the piezoelectric layer 7 that is defined based on the configuration of the IDT electrode 8. The acoustic wave device 1 has multiple excitation regions C. Note that FIG. 1 shows only one of the multiple excitation regions C. By applying an AC voltage to the IDT electrode 8, thickness-shear mode bulk waves are excited in each excitation region C. This is ideally the same in the first comparative example.

[0045] Fig. 6 is a diagram showing the relationship between the position of the IDT electrode in the direction perpendicular to the electrode fingers and the displacement near the resonance frequency in the first comparative example. Fig. 7 is a diagram showing the relationship between the position of the IDT electrode in the direction perpendicular to the electrode fingers and the displacement near the resonance frequency in the first embodiment. The scales on the horizontal axis in Figs. 6 and 7 indicate the center positions between the electrode fingers.

[0046] As shown in Fig. 6, in the first comparative example, the displacement is large in some areas where the electrode fingers are located, rather than in the areas between the electrode fingers. The change in displacement in the direction perpendicular to the electrode fingers is not a regular wave-like change, but rather is disturbed. Thus, in the first comparative example, the state in which thickness-shear mode bulk waves are excited is different from the ideal state.

[0047] In contrast, as shown in FIG. 7, in the first embodiment, the displacement is large in the region between the electrode fingers. The change in displacement in the direction perpendicular to the electrode fingers is a regular wave-like change. In this way, in the first embodiment, the state in which thickness-shear mode bulk waves are excited can be made closer to the ideal state. This can reduce loss.

[0048] More specifically, in the first embodiment, as shown in FIG. 3 , the end electrode finger A overlaps with the portion of the boundary B between the outer and the reflective film closest to the piezoelectric layer 7 in the stacking direction. This allows the portion of the end electrode finger A that overlaps with the boundary B between the outer and the reflective film in the stacking direction to serve as a reflective surface, thereby reflecting waves. This allows the waves to be confined to the portion where the IDT electrode 8 is provided. As a result, the breakdown of regularity when thickness-shear mode bulk waves are excited can be suppressed in the entire portion where the IDT electrode 8 is provided. This reduces loss.

[0049] In the first embodiment, the IDT electrode 8 overlaps with the acoustic reflection film 3 in a planar view. More specifically, a plurality of excitation regions C overlap with the acoustic reflection film 3 in a planar view. This allows the thickness-shear mode bulk waves to be reflected by the acoustic reflection film 3 toward the piezoelectric layer 7. This allows the energy of the thickness-shear mode bulk waves to be effectively trapped on the piezoelectric layer 7 side.

[0050] 1, it is preferable that both end electrode fingers A overlap with the portion of the boundary B between the external and the reflective film closest to the piezoelectric layer 7 in the stacking direction. In this case, more specifically, one end electrode finger A overlaps with the portion of the boundary B between the external and the reflective film closest to the piezoelectric layer 7 in the stacking direction. At the same time, the other end electrode finger A overlaps with the portion of the boundary B between the external and the reflective film closest to the piezoelectric layer 7 in the stacking direction. This makes it possible to more reliably reduce loss.

[0051] As in the first preferred embodiment, the material of the outer wall member 6 is preferably the same as the material of the low acoustic impedance layer in the acoustic reflecting film 3. This facilitates the manufacture of the acoustic wave device 1, thereby increasing productivity.

[0052] In the acoustic wave device 1, the boundary B between the outer and reflective films extends in the stacking direction. However, the boundary B between the outer and reflective films may extend in a direction intersecting the stacking direction. In this case, it is also sufficient that at least one end electrode finger A overlaps with the portion of the boundary B between the outer and reflective films closest to the piezoelectric layer 7 in the stacking direction.

[0053] FIG. 8 is a schematic front cross-sectional view illustrating a portion of an elastic wave device according to a second preferred embodiment of the present invention.

[0054] This embodiment differs from the first embodiment in that an IDT electrode 8 is provided on the second main surface 7b of the piezoelectric layer 7. The IDT electrode 8 is embedded in the acoustic reflection film 3. Except for the above, the elastic wave device 21 of this embodiment has the same configuration as the elastic wave device 1 of the first embodiment.

[0055] No IDT electrode 8 is provided on first principal surface 7a of piezoelectric layer 7 of acoustic wave device 21. A dielectric film 9 is provided on first principal surface 7a. However, dielectric film 9 is not necessarily provided.

[0056] The end electrode fingers A of the IDT electrode 8 are embedded in the low acoustic impedance layer 4a of the acoustic reflection film 3 and the outer wall member 6. Therefore, the end electrode fingers A are in contact with the boundary B between the outer and the reflection film. Therefore, in the stacking direction, the end electrode fingers A overlap with the part of the boundary B between the outer and the reflection film that is closest to the piezoelectric layer 7. This can reduce loss. Details of this effect will be explained below by comparing the second embodiment with a second comparative example.

[0057] The second comparative example differs from the first preferred embodiment in that boundary B between the outer layer and the reflective film is located outside IDT electrode 8 in plan view. The admittance-frequency characteristics of the second preferred embodiment and the second comparative example were compared. The design parameters of acoustic wave device 21 of the second preferred embodiment for this comparison are as follows:

[0058] Piezoelectric layer: Material: 120° Y-cut LiNbO3, Thickness: 300 nm IDT electrode: Material...Al, thickness...100nm, center distance p:3.9μm, width...0.9μm, tilt angle...90°, number of electrode fingers...53 Dielectric film: Material: SiO2, Thickness: 20 nm Acoustic reflection film: Layer structure...SiO2 layer / HfO2 layer / SiO2 layer / HfO2 layer / SiO2 layer from the piezoelectric layer side, thickness...175nm / 100nm / 150nm / 150nm / 100nm from the piezoelectric layer side Exterior wall material: SiO2 Support substrate: Material: Si, Thickness: Assuming semi-infinite length Position of the part of the edge electrode finger that overlaps with the boundary between the outer and reflective films in the lamination direction: Center of the edge electrode finger in the direction perpendicular to the electrode fingers

[0059] The design parameters of the second comparative example were the same as those of the second embodiment, except that the end electrode fingers A did not overlap the boundary B between the outer layer and the reflective film in the stacking direction.

[0060] FIG. 9 is a diagram showing admittance frequency characteristics in the second embodiment and the second comparative example.

[0061] 9, in the vicinity of the frequency indicated by the dashed line, the admittance in the second embodiment is smaller than the admittance in the second comparative example. In this way, the second embodiment can reduce loss.

[0062] Incidentally, when an acoustic wave is excited, heat is generated in the portion where the IDT electrode 8 is provided. In the second embodiment, as shown in FIG. 8, the IDT electrode 8 is embedded in the acoustic reflection film 3. Therefore, the position of the IDT electrode 8 is closer to the support substrate 2 than in the first embodiment shown in FIG. 3. The support substrate 2 is used as a heat dissipation path. Therefore, in the second embodiment, heat dissipation can be improved.

[0063] For example, an appropriate through electrode may be provided that penetrates the piezoelectric layer 7. The IDT electrode 8 may be electrically connected to the outside via the through electrode and appropriate wiring.

[0064] FIG. 10 is a schematic front cross-sectional view illustrating a portion of an elastic wave device according to a third preferred embodiment of the present invention.

[0065] This embodiment differs from the first embodiment in that IDT electrodes are provided on both main surfaces of the piezoelectric layer 7. Except for the above, the elastic wave device 31 of this embodiment has the same configuration as the elastic wave device 1 of the first embodiment.

[0066] An IDT electrode 8A is provided on a first main surface 7a of the piezoelectric layer 7. An IDT electrode 8B is provided on a second main surface 7b of the piezoelectric layer 7. The IDT electrodes 8A and 8B face each other with the piezoelectric layer 7 interposed therebetween.

[0067] The excitation regions defined by the configuration of IDT electrode 8A and the excitation regions defined by the configuration of IDT electrode 8B overlap in a planar view. More specifically, the centers of the electrode fingers of IDT electrode 8A in the orthogonal direction overlap with the centers of the electrode fingers of IDT electrode 8B in the orthogonal direction. Note that the positions of the centers of the electrode fingers of IDT electrode 8A and the centers of the electrode fingers of IDT electrode 8B may be misaligned in a planar view to the extent that the electrical characteristics of acoustic wave device 31 are not significantly degraded.

[0068] In this embodiment, similarly to the first embodiment, the end electrode fingers A overlap with the portion of the boundary B between the outer layer and the reflective film closest to the piezoelectric layer 7 in the stacking direction, thereby reducing loss.

[0069] FIG. 11 is a schematic front cross-sectional view illustrating a portion of an elastic wave device according to a fourth preferred embodiment of the present invention.

[0070] This embodiment differs from the first embodiment in that the material of the outer wall member 6 is metal. Except for the above, the elastic wave device 41 of this embodiment has the same configuration as the elastic wave device 1 of the first embodiment.

[0071] In this embodiment, the loss can be reduced in the same way as in the first embodiment, which will be shown below by comparing the admittance frequency characteristics in this embodiment and the third comparative example.

[0072] The third comparative example differs from the fourth embodiment in that the boundary B between the outer layer and the reflective film is located outside the IDT electrode 8 in plan view. The design parameters of the fourth embodiment and the third comparative example are the same as those of the first comparative embodiment shown in Fig. 5 except for the material of the outer wall member. The materials of the outer wall member in the fourth embodiment and the third comparative example are as follows:

[0073] Exterior wall material: Aluminum

[0074] FIG. 12 is a diagram showing admittance frequency characteristics in the fourth embodiment and the third comparative example.

[0075] 12, in the vicinity of the frequency indicated by the dashed line, the admittance in the fourth embodiment is smaller than the admittance in the third comparative example. In this way, the fourth embodiment can reduce loss.

[0076] In addition, an outer wall member 6 made of metal is provided on the support substrate 2. Therefore, the outer wall member 6 can be used as a heat dissipation path together with the support substrate 2. Therefore, in the fourth embodiment, heat dissipation can be effectively improved.

[0077] At least one of the low acoustic impedance layers and the high acoustic impedance layers in the acoustic reflecting film 3 may be made of a metal. For example, the outer wall member 6 and the low acoustic impedance layer may be made of the same metal, or the outer wall member 6 and the high acoustic impedance layer may be made of the same metal.

[0078] FIG. 13 is a schematic front cross-sectional view illustrating a portion of an elastic wave device according to a fifth preferred embodiment of the present invention.

[0079] This embodiment differs from the second embodiment in that outer wall member 56 is made of metal and that outer wall member 56 penetrates piezoelectric layer 7. Except for the above differences, elastic wave device 51 of this embodiment has a similar configuration to elastic wave device 21 of the second embodiment.

[0080] The end electrode fingers A of the IDT electrode 8 are embedded in the low acoustic impedance layer 4a of the acoustic reflection film 3 and in the outer wall member 56. Therefore, the end electrode fingers A are electrically connected to the outer wall member 56. However, this configuration does not significantly affect the electrical characteristics of the acoustic wave device 51. This is because the configuration of an acoustic wave device utilizing thickness-shear mode bulk waves is approximately equivalent to a configuration in which multiple resonators, each having an excitation region, are connected in parallel.

[0081] The outer wall member 56 is a through electrode that is electrically connected to the IDT electrode 8 and penetrates the piezoelectric layer 7. Therefore, the IDT electrode 8 can be electrically connected to the outside via the outer wall member 56 and appropriate wiring. Therefore, a separate through electrode for connecting the IDT electrode 8 to the outside is not required. This allows the acoustic wave device 51 to be made compact.

[0082] As in the second embodiment, the end electrode fingers A are in contact with the boundary B between the outer and reflective films. Therefore, in the stacking direction, the end electrode fingers A overlap with the portion of the boundary B between the outer and reflective films closest to the piezoelectric layer 7. This reduces loss. Details of this effect will be shown below by comparing the admittance-frequency characteristics of the fifth embodiment and the fourth comparative example.

[0083] The fourth comparative example differs from the fifth embodiment in that the boundary B between the outer layer and the reflective film is located outside the IDT electrode 8 in plan view. The design parameters of the fifth embodiment and the fourth comparative example are the same as those of the second comparative embodiment shown in FIG. 9 except for the material of the outer wall member. The materials of the outer wall members in the fifth embodiment and the fourth comparative example are as follows:

[0084] Exterior wall material: Aluminum

[0085] FIG. 14 is a diagram showing admittance frequency characteristics in the fifth embodiment and the fourth comparative example.

[0086] 14, in the vicinity of the frequency indicated by the dashed line, the admittance in the fifth embodiment is smaller than the admittance in the fourth comparative example. In this way, the fifth embodiment can reduce loss.

[0087] In addition, an outer wall member 56 made of metal is provided on the support substrate 2. Therefore, the outer wall member 56 can be used as a heat dissipation path together with the support substrate 2. Furthermore, the outer wall member 56 penetrates the piezoelectric layer 7. Therefore, the outer wall member 56 is exposed from the piezoelectric layer 7. The outer wall member 56 is directly connected to the end electrode fingers A of the IDT electrode 8. Therefore, in the fifth embodiment, heat dissipation can be improved even more effectively.

[0088] FIG. 15 is a schematic front cross-sectional view illustrating a portion of an elastic wave device according to a sixth preferred embodiment of the present invention.

[0089] This embodiment differs from the first embodiment in that no outer wall member is provided in the outer region O. In this embodiment, the boundary B between the outer region and the reflective film is the boundary between the acoustic reflection film 3 and the air. This embodiment also differs from the first embodiment in that a support member 62 is provided in a portion of the support substrate 2 located in the outer region O so as not to come into contact with the acoustic reflection film 3. Except for the above points, the elastic wave device 61 of this embodiment has the same configuration as the elastic wave device 1 of the first embodiment.

[0090] The piezoelectric layer 7 is provided on the acoustic reflection film 3 and on a support member 62. The support member 62 is provided on the support substrate 2, separated from the acoustic reflection film 3 by a space. The support member 62 can be made of an appropriate dielectric material or an appropriate metal. Note that the support member 62 does not necessarily have to be provided.

[0091] To obtain the acoustic wave device 61, for example, a piezoelectric substrate is prepared and a sacrificial layer is provided on the piezoelectric substrate. Next, an acoustic reflection film 3 and a support member 62 are provided on the piezoelectric substrate. Next, the acoustic reflection film 3 and the support substrate 2 are bonded. Next, the thickness of the piezoelectric substrate is adjusted, for example, by polishing the main surface of the piezoelectric substrate on which the acoustic reflection film 3 is not provided. This results in a piezoelectric layer 7. Next, an IDT electrode 8 is provided on the first main surface 7a of the piezoelectric layer 7. Next, a through hole is formed in the piezoelectric layer 7. The sacrificial layer is then removed by etching using the through hole. However, the above method is merely an example, and the method for manufacturing the acoustic wave device 61 is not limited to the above.

[0092] In this embodiment, the loss can be reduced in the same way as in the first embodiment, which will be shown below by comparing the admittance frequency characteristics of this embodiment and the first comparative example shown in FIG.

[0093] The design parameters of the sixth comparative embodiment were the same as those of the first comparative embodiment shown in Fig. 5, except that the sixth comparative embodiment did not have an outer wall member. The design parameters of the first comparative example were the same as those of the first comparative example shown in Fig. 5.

[0094] FIG. 16 is a diagram showing admittance frequency characteristics in the sixth embodiment and the first comparative example.

[0095] 16, in the vicinity of the frequency indicated by the dashed line, the admittance in the sixth embodiment is smaller than the admittance in the first comparative example. In this way, in the sixth embodiment, it is possible to reduce loss.

[0096] FIG. 17 is a schematic front cross-sectional view of an elastic wave device according to a seventh preferred embodiment of the present invention.

[0097] This embodiment differs from the first embodiment in that the high acoustic impedance layers 5a and 5b in the acoustic reflecting film 3 are made of metal. Except for this difference, the elastic wave device 71 of this embodiment has the same configuration as the elastic wave device 1 of the first embodiment.

[0098] Specifically, the material of the high acoustic impedance layers 5a and 5b in the acoustic reflecting film 3 is tungsten. However, the material of each high acoustic impedance layer may be a metal other than tungsten.

[0099] The acoustic impedance of metals is often higher than the acoustic impedance of dielectrics. Therefore, by using a metal as the material for the high acoustic impedance layer, the impedance of the high acoustic impedance layer can be easily increased. This makes it easy to increase the difference in acoustic impedance between the low acoustic impedance layer and the high acoustic impedance layer. This allows the Q value of the acoustic wave device 71 to be increased even when the number of acoustic impedance layers in the acoustic reflecting film 3 is reduced. This, in turn, improves productivity.

[0100] In this embodiment, the loss can be reduced in the same way as in the first embodiment, which will be shown below by comparing the admittance frequency characteristics in this embodiment and the fifth comparative example.

[0101] The fifth comparative example differs from the seventh embodiment in that the boundary B between the outer layer and the reflective film is located outside the IDT electrode 8 in plan view. The design parameters of the seventh comparative embodiment and the fifth comparative example are the same as those of the first comparative embodiment shown in FIG. 5 except for the materials of the high acoustic impedance layers. The parameters of the acoustic reflective film in the seventh embodiment and the fifth comparative example are as follows:

[0102] Acoustic reflection film: Layer structure...SiO2 layer / W layer / SiO2 layer / W layer / SiO2 layer from the piezoelectric layer side, thickness...132nm / 105nm / 132nm / 105nm / 132nm from the piezoelectric layer side

[0103] FIG. 18 is a diagram showing admittance frequency characteristics in the seventh embodiment and the fifth comparative example.

[0104] 18, in the vicinity of the frequency indicated by the dashed line, the admittance in the seventh embodiment is smaller than the admittance in the fifth comparative example. In this way, the seventh embodiment can reduce loss.

[0105] A preferred configuration of the present invention will be described below with reference to Fig. 2. However, the following preferred configuration can also be applied to configurations of the present invention other than the first embodiment.

[0106] In the first embodiment, where d is the thickness of the piezoelectric layer 7 and p is the center-to-center distance between adjacent electrode fingers, d / p is 0.5 or less. It is preferable that d / p is 0.24 or less. This allows thickness-shear mode bulk waves to be more effectively excited and enables the value of the bandwidth fraction of the elastic wave resonator to be sufficiently large. The bandwidth fraction is expressed as (|fa-fr| / fr)×100[%], where fr is the resonant frequency and fa is the antiresonant frequency.

[0107] FIG. 19 is a graph showing the relationship between d / p and the fractional bandwidth of an acoustic wave resonator.

[0108] As is clear from FIG. 19, when d / p>0.5, the fractional bandwidth is less than 5%. In contrast, when d / p≦0.5, the fractional bandwidth can be increased to 5% or more. This increases the electromechanical coupling coefficient of the thickness-shear mode bulk wave. When d / p≦0.24, the fractional bandwidth can be increased to 7% or more. This effectively increases the electromechanical coupling coefficient of the thickness-shear mode bulk wave.

[0109] When the metallization ratio of the electrode fingers to the excitation region C is MR, it is preferable to satisfy MR≦1.75(d / p)+0.075. In this case, the value of the fractional bandwidth of the acoustic wave resonator does not become too large, and spurious emissions between the resonant frequency and the antiresonant frequency can be suppressed. Details of this are described below.

[0110] In this specification, the metallization ratio MR of the electrode fingers to the excitation region C is the proportion of the portion of the piezoelectric layer 7 that is covered with the metal constituting the electrode fingers in the excitation region C in a planar view. Specifically, the metallization ratio MR is the ratio of the area of ​​the first electrode fingers 18 and the second electrode fingers 19 in the excitation region C to the area of ​​the excitation region C in a planar view. If the width of the electrode fingers located in the excitation region C is constant, the metallization ratio MR can also be calculated by dividing the sum of the widths of the electrode fingers located in the excitation region C by the dimension of the excitation region C in the direction perpendicular to the electrode fingers. The width of the electrode fingers is the dimension of the electrode fingers in the direction perpendicular to the electrode fingers.

[0111] FIG. 20 shows the relationship between the bandwidth ratio and the normalized magnitude of spurious signals in an acoustic wave resonator. FIG. 20 shows the results of measuring the phase rotation of spurious signals each time the bandwidth ratio is changed by varying the thickness of the piezoelectric layer and the dimensions of the electrode fingers. The normalized spurious signals in FIG. 20 are values ​​obtained by normalizing the phase rotation of the spurious impedance by 180°. The results shown in FIG. 20 are for a piezoelectric layer made of Z-cut LiNbO3, but similar trends are observed when piezoelectric layers with other cut angles are used.

[0112] In the region surrounded by ellipse D in Figure 20, the normalized magnitude of the spurious response between the resonant frequency and the anti-resonant frequency is 1.0. If the bandwidth fraction of the elastic wave resonator exceeds 17%, the normalized magnitude of the spurious response may be 1.0 or more. For this reason, it is preferable that the bandwidth fraction be 17% or less. This makes it possible to suppress the spurious response between the resonant frequency and the anti-resonant frequency.

[0113] Fig. 21 is a diagram showing the relationship between d / p, metallization ratio MR, and bandwidth ratio, which shows the results of calculating bandwidth ratios for different d / p and metallization ratios MR.

[0114] In Figure 21, the hatched area is the area where the fractional bandwidth is 17% or less. The boundary between this hatched area and the non-hatched area is roughly represented by dashed line E. Dashed line E is represented by MR = 1.75(d / p) + 0.075. It is preferable that MR ≤ 1.75(d / p) + 0.075. In this case, it is easy to keep the fractional bandwidth at 17% or less.

[0115] On the other hand, the dashed-dotted line E1 in Figure 21 indicates the boundary where the slope of the change in metallization ratio MR with respect to changes in d / p is the same as that of the dashed line E, and where the fractional bandwidth is 17% or less over the entire range. The dashed-dotted line E1 is represented by MR = 1.75(d / p) + 0.05. It is more preferable that MR ≤ 1.75(d / p) + 0.05. In this case, the fractional bandwidth can be more reliably kept below 17%.

[0116] Figure 22 is a diagram showing a map of the fractional bandwidth versus the Euler angles (0°, θ, ψ) of LiNbO3 when d / p approaches 0. The hatched area in Figure 22 is the region where a fractional bandwidth of at least 5% or more is obtained, and the range of this region can be approximated as the range expressed by the following equations (1), (2), and (3).

[0117] (0°±10°, 0°~20°, any ψ) ...Equation (1) (0°±10°,20°~80°,0°~60°(1-(θ-50) 2 / 900) 1 / 2 ) or (0°±10°, 20°~80°, [180°-60°(θ-50) 2 / 900) 1 / 2 ]~180°) …Equation (2) (0°±10°,[180°-30°(1-(ψ-90) 2 / 8100) 1 / 2 ]~180°, any ψ) ...Equation (3)

[0118] It is preferable that the Euler angles (φ, θ, ψ) of the lithium niobate constituting the piezoelectric layer 7 are within the range of the above formula (1), formula (2), or formula (3). This allows the relative bandwidth of the elastic wave resonator to be sufficiently wide. The same applies when the piezoelectric layer 7 is made of lithium tantalate.

[0119] Examples of embodiments of the acoustic wave device according to the present invention will be described below.

[0120] <1> An acoustic reflection film including a high acoustic impedance layer having a relatively high acoustic impedance and a low acoustic impedance layer having a relatively low acoustic impedance; a piezoelectric layer provided on the acoustic reflection film and having a first main surface and a second main surface facing each other; and at least one IDT electrode provided on at least one of the first main surface and the second main surface of the piezoelectric layer and having a plurality of electrode fingers, wherein, when the thickness of the piezoelectric layer is d and the center-to-center distance between adjacent electrode fingers is p, d / p is 0.5 or less, and the plurality of electrode fingers extend when a direction perpendicular to the direction in which the acoustic reflection film and the piezoelectric layer are stacked is defined as a stacking direction, at least one of the end electrode fingers overlaps with a portion of the outer-reflection film boundary closest to the piezoelectric layer in the stacking direction.

[0121] <2> In the stacking direction, both of the end electrode fingers overlap with a portion of the boundary between the outer layer and the reflective film that is closest to the piezoelectric layer. <1> The acoustic wave device according to claim 1.

[0122] <3> an outer wall member is provided in the outer region, the outer-reflection film boundary is a boundary between the outer wall member and the acoustic reflection film, and the material of the outer wall member is the same as the material of the low acoustic impedance layer; <1> or <2> The acoustic wave device according to claim 1.

[0123] <4> an outer wall member is provided in the outer region, the outer-reflection film boundary is a boundary between the outer wall member and the acoustic reflection film, and the material of the outer wall member is metal; <1> ~ <3> 10. The acoustic wave device according to claim 9, wherein:

[0124] <5> a material of at least one of the low acoustic impedance layer and the high acoustic impedance layer in the acoustic reflection film is a metal; <1> ~ <4> 10. The acoustic wave device according to claim 9, wherein:

[0125] <6> of the first principal surface and the second principal surface of the piezoelectric layer, the second principal surface is the principal surface on the acoustic reflection film side, and the IDT electrode is provided on the first principal surface; <1> ~ <5> 10. The acoustic wave device according to claim 9, wherein:

[0126] <7> of the first principal surface and the second principal surface of the piezoelectric layer, the second principal surface is a principal surface on the acoustic reflection film side, and the IDT electrode is provided on the second principal surface; <1> ~ <5> 10. The acoustic wave device according to claim 9, wherein:

[0127] <8> Of the first principal surface and the second principal surface of the piezoelectric layer, the second principal surface is a principal surface on the acoustic reflection film side, and the IDT electrode is provided on the first principal surface, and the IDT electrode is provided on the second principal surface. <1> ~ <5> 10. The acoustic wave device according to claim 9, wherein:

[0128] <9> The acoustic reflecting film further includes a support substrate on which the acoustic reflecting film is provided. <1> ~ <8> 10. The acoustic wave device according to claim 9, wherein:

[0129] <10> d / p is 0.24 or less, <1> ~ <9> 10. The acoustic wave device according to claim 9, wherein:

[0130] <11> an excitation region is a region where adjacent electrode fingers overlap each other in a direction perpendicular to the electrode fingers and a region between the centers of adjacent electrode fingers, and when a metallization ratio of the electrode fingers to the excitation region is MR, the ratio satisfies MR≦1.75(d / p)+0.075; <1> ~ <10> 10. The acoustic wave device according to claim 9, wherein:

[0131] <12> the piezoelectric layer is made of lithium niobate or lithium tantalate, and the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of the following formula (1), formula (2), or formula (3), <1> ~ <11> 10. The acoustic wave device according to claim 9, wherein: (0°±10°, 0°~20°, any ψ) ...Equation (1) (0°±10°,20°~80°,0°~60°(1-(θ-50) 2 / 900) 1 / 2 ) or (0°±10°, 20°~80°, [180°-60°(θ-50) 2 / 900) 1 / 2 ]~180°) …Equation (2) (0°±10°,[180°-30°(1-(ψ-90) 2 / 8100) 1 / 2 ]~180°, any ψ) ...Equation (3) [Explanation of symbols]

[0132] 1...Elastic wave device 2...Support substrate 3…Acoustic reflective film 4a to 4c: Low acoustic impedance layers 5a, 5b...High acoustic impedance layers 6...Exterior wall components 7...Piezoelectric layer 7a, 7b...first and second principal surfaces 8,8A,8B…IDT electrode 8a, 8b...first and second faces 8c...side 9...Dielectric film 16, 17...1st and 2nd bus bars 18, 19...First and second electrode fingers 21, 31, 41, 51... Elastic wave device 56...Exterior wall components 61...Elastic wave device 62...Support member 71,101...Elastic wave device A...End electrode finger B...Boundary between outer and reflective film C…Excitation region O…outer area

Claims

1. an acoustic reflection film including a high acoustic impedance layer having a relatively high acoustic impedance and a low acoustic impedance layer having a relatively low acoustic impedance; a piezoelectric layer provided on the acoustic reflection film and having a first main surface and a second main surface facing each other; at least one IDT electrode having a plurality of electrode fingers, the IDT electrode being provided on at least one of the first principal surface and the second principal surface of the piezoelectric layer; Equipped with where d is the thickness of the piezoelectric layer and p is the center-to-center distance between adjacent electrode fingers, d / p is 0.5 or less, when a direction orthogonal to a direction in which the plurality of electrode fingers extend is defined as an electrode finger orthogonal direction, the electrode fingers located at both ends in the electrode finger orthogonal direction among the plurality of electrode fingers are end electrode fingers, an outer region is an outer region of the acoustic reflection film in a direction perpendicular to the electrode fingers, and a boundary between the outer region and the acoustic reflection film is an outer-reflection film boundary; When the direction in which the acoustic reflection film and the piezoelectric layer are stacked is defined as the stacking direction, at least one of the end electrode fingers overlaps with the portion of the boundary between the outer film and the reflection film that is closest to the piezoelectric layer in the stacking direction.

2. 2. The acoustic wave device according to claim 1, wherein both of the end electrode fingers overlap with a portion of the boundary between the outer layer and the reflective film that is closest to the piezoelectric layer in the stacking direction.

3. an outer wall member is provided in the outer region, and the outer-to-reflection film boundary is a boundary between the outer wall member and the acoustic reflection film; The acoustic wave device according to claim 1 , wherein the outer wall member and the low acoustic impedance layer are made of the same material.

4. an outer wall member is provided in the outer region, and the outer-to-reflection film boundary is a boundary between the outer wall member and the acoustic reflection film; The acoustic wave device according to claim 1 , wherein the outer wall member is made of a metal.

5. The acoustic wave device according to claim 1 , wherein at least one of the low acoustic impedance layer and the high acoustic impedance layer in the acoustic reflection film is made of a metal.

6. of the first principal surface and the second principal surface of the piezoelectric layer, the second principal surface is the principal surface on the acoustic reflection film side, The acoustic wave device according to claim 1 , wherein the IDT electrode is provided on the first principal surface.

7. of the first principal surface and the second principal surface of the piezoelectric layer, the second principal surface is the principal surface on the acoustic reflection film side, The acoustic wave device according to claim 1 , wherein the IDT electrode is provided on the second principal surface.

8. of the first principal surface and the second principal surface of the piezoelectric layer, the second principal surface is the principal surface on the acoustic reflection film side, the IDT electrode provided on the first principal surface; the IDT electrode provided on the second principal surface; The acoustic wave device according to claim 1 , comprising:

9. Further comprising a support substrate; The acoustic wave device according to claim 1 , wherein the acoustic reflection film is provided on the support substrate.

10. The acoustic wave device according to claim 1 , wherein d / p is equal to or less than 0.

24.

11. an excitation region is a region where adjacent electrode fingers overlap each other in the direction perpendicular to the electrode fingers and between the centers of the adjacent electrode fingers; The acoustic wave device according to claim 1 , wherein MR satisfies MR≦1.75(d / p)+0.075, where MR is a metallization ratio of the electrode fingers to the excitation region.

12. the piezoelectric layer is made of lithium niobate or lithium tantalate, 2. The elastic wave device according to claim 1, wherein the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of the following formula (1), formula (2), or formula (3): (0°±10°, 0° to 20°, any ψ) ...Equation (1) (0°±10°, 20°~80°, 0°~60° (1-(θ-50) ２ / 900) １／２ ) or (0°±10°, 20° to 80°, [180°-60° (1-(θ-50) ２ / 900) １／２ ] ~ 180°) …Formula (2) (0°±10°, [180°-30°(1-(ψ-90) ２ / 8100) １／２ ] to 180°, any ψ) ...Equation (3)

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