Acoustic wave device

Abstract

An acoustic wave device includes a cavity in a substrate, an overlap region in which portions of adjacent first and second interdigital electrodes face each other, a first gap region between the first bus bar and the overlap region and including the first interdigital electrode but not the second interdigital electrode, and a second gap region between the second bus bar and the overlap region and including the second interdigital electrode but not the first interdigital electrode. A ratio d / p is about 0.5 or less, where d is a thickness of a piezoelectric layer and p is a distance between centers of the adjacent first and second interdigital electrodes. A first wall of the cavity is located below the first bus bar or the first gap region, and a second wall of the cavity is located below the second bus bar or the second gap region.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 129,702, filed December 23, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to acoustic devices, each comprising a piezoelectric layer of lithium niobate or lithium tantalate. Background Technology

[0004] In known acoustic devices, thermal radiation characteristics are prone to degradation.

[0005] Heat tends to remain trapped in the cavity of an acoustic device, and in acoustic devices with such cavities, thermal radiation characteristics may be poor. Figure 12 It is a thermal image of the acoustic device 100 without cavity 109, and Figure 13 This is a thermal image of an acoustic device 100 with a cavity 109. (Example) Figure 13 As shown, heat can be retained in cavity 109. Figure 14 The relationship between the maximum temperature and the normalized input power is shown. In the acoustic device 100 without cavity 109, the maximum temperature is constant or substantially constant. However, in the acoustic device 100 with cavity 109, the maximum temperature increases with increasing temperature. Summary of the Invention

[0006] In a preferred embodiment of the invention, an acoustic device is provided in which the cavity walls are positioned to improve thermal radiation characteristics.

[0007] According to a preferred embodiment of the present invention, an acoustic wave device includes: a support; a piezoelectric layer on the support; and interdigital transducer electrodes on the piezoelectric layer and including a pair of bus bars opposite to each other and a plurality of electrode fingers. The ratio d / p is about 0.5 or less, where d is the thickness of the piezoelectric layer and p is the distance between the centers of adjacent electrode fingers among the plurality of electrode fingers. A cavity is provided in the support and opens toward the piezoelectric layer. The plurality of electrode fingers define an electrode finger extending direction, and the plurality of electrode fingers extend along the electrode finger extending direction. The periphery of the cavity includes a pair of walls opposite to each other in the electrode finger extending direction in a plan view. Each of the pair of bus bars includes an inner edge located inside in the electrode finger extending direction. The interdigital transducer electrodes have an overlapping region and a pair of gap regions, in which the plurality of electrode fingers overlap each other when observed in the direction opposite to the adjacent electrode fingers, and the pair of gap regions are respectively located between the overlapping region and a corresponding one of the pair of bus bars. In a plan view, the pair of walls of the cavity overlap with an outer side portion outside the overlapping region in the electrode finger extending direction. For each of the pair of walls, the equation 0 < L < Lb is satisfied, where Lc is the dimension of the overlapping region in the electrode finger extending direction, Lb is the dimension of each of the pair of bus bars in the electrode finger extending direction, and in a plan view, L is the position of each of the pair of walls of the cavity in the electrode finger extending direction, where the corresponding position of each inner edge of the pair of bus bars in the electrode finger extending direction is a zero reference, such that the outward direction of the interdigital transducer electrodes is the positive direction and the inward direction of the interdigital transducer electrodes is the negative direction.

[0008] For each of the pair of walls, the equation 0 < L < (8 / 25)×Lc is satisfied.

[0009] The support may include a support substrate and an electrically insulating layer provided between the support substrate and the piezoelectric layer, and the cavity may be provided in the electrically insulating layer. The support may include a support substrate, and the cavity may be in the support substrate. The ratio d / p is less than or equal to about 0.24. The equation MR ≤ 1.75(d / p) + 0.075 may be satisfied, where MR is the metallization ratio of the area of the plurality of electrode fingers in the overlapping region to the total area of the overlapping region.

[0010] According to a preferred embodiment of the present invention, an acoustic wave device includes: a support including a cavity having a first wall and a second wall opposite to each other; a piezoelectric layer on the support; interdigital transducer electrodes on the piezoelectric layer, and including: a first bus bar including a first inner edge; a first electrode extending from the first inner edge, each of the first electrodes including a first non-overlapping portion connected to the first inner edge and a first overlapping portion connected to the first non-overlapping portion; a second bus bar including a second inner edge facing the first inner edge; and a second electrode extending from the second inner edge, each of the second electrodes including: a second non-overlapping portion connected to the second inner edge; and a second overlapping portion connected to the non-overlapping portion and opposite to the corresponding first overlapping portion. The ratio d / p is about 0.5 or less, where d is the thickness of the piezoelectric layer and p is the distance between the centers of adjacent electrodes of the first electrode and the second electrode. The first wall of the cavity is located below each of the first non-overlapping portions of the first bus bar or the first electrodes. The second wall of the cavity is located below each of the second non-overlapping portions of the second bus bar or the second electrodes.

[0011] The equation 0 < L1 < (8 / 25)×Lc can be satisfied, where Lc is the length of the first overlapping portion of each of the first electrodes and the second overlapping portion of each of the second electrodes, and L1 is the distance from the first inner edge to the first wall. The equation 0 < L2 < (8 / 25)×Lc can be satisfied, where L2 is the distance from the second inner edge to the second wall.

[0012] The equation L1 > (1 / 25)×Lc can be satisfied, where Lc is the length of the first overlapping portion of each of the first electrodes and the second overlapping portion of each of the second electrodes, and L1 is the distance from the first inner edge to the first wall. The equation L2 > (1 / 25)×Lc can be satisfied, where L2 is the distance from the second inner edge to the second wall.

[0013] According to a preferred embodiment of the present invention, an acoustic wave device includes: a support; a cavity in the support and including a first wall and a second wall opposite to each other; a piezoelectric layer on the support; a first busbar including a first electrode extending from a first inner edge; a second busbar including a second electrode extending from a second inner edge and crossing the first electrode; an overlapping region where portions of adjacent first and second electrodes face each other; a first gap region adjacent to and between the first busbar and the overlapping region and including the first electrode but not the second electrode; and a second gap region adjacent to and between the second busbar and the overlapping region and including the second electrode but not the first electrode. The ratio d / p is about 0.5 or less, where d is the thickness of the piezoelectric layer and p is the distance between the centers of adjacent electrodes of the first and second electrodes. The first wall of the cavity is located below the first busbar or the first gap region. The second wall of the cavity is located below the second busbar or the second gap region.

[0014] The equation 0 < L1 < (8 / 25)×Lc can be satisfied, where Lc is the width of the overlapping region and L1 is the distance from the first inner edge to the first wall. The equation 0 < L2 < (8 / 25)×Lc can be satisfied, where L2 is the distance from the second inner edge to the second wall.

[0015] The equation L1 > (1 / 25)×Lc can be satisfied, where Lc is the width of the overlapping region and L1 is the distance from the first inner edge to the first wall. The equation L2 > (1 / 25)×Lc can be satisfied, where L2 is the distance from the second inner edge to the second wall.

[0016] The support may include a support substrate and an electrically insulating layer disposed between the support substrate and the piezoelectric layer, and the cavity may be disposed in the electrically insulating layer. The support may include a support substrate and the cavity may be disposed in the support substrate. The ratio d / p may be less than or equal to about 0.24. The equation MR ≤ 1.75(d / p) + 0.075 can be satisfied, where MR is the metallization ratio of the area of the first and second electrodes in the overlapping region to the total area of the overlapping region.

[0017] The above and other elements, features, steps, characteristics, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1A is a schematic perspective view showing an acoustic wave device according to a first preferred embodiment of the present invention.

[0019] Figure 1B is a plan view showing the electrode structure on the piezoelectric layer.

[0020] Figure 2 It is along Figure 1A The cross-sectional view taken from line AA in the diagram.

[0021] Figure 3A This is a schematic elevation cross-sectional view showing a Lamb wave propagating in a piezoelectric film of an acoustic device.

[0022] Figure 3B This is a cross-sectional view showing a bulk wave propagating in a piezoelectric film of an acoustic device.

[0023] Figure 4 The diagram schematically illustrates the body waves that occur when a voltage is applied across the electrodes of an acoustic device.

[0024] Figure 5 This is a graph showing the resonant characteristics of an acoustic wave device according to a first preferred embodiment of the present invention.

[0025] Figure 6 This is a graph showing the relationship between the ratio d / p and the fractional bandwidth of the acoustic device as a resonator.

[0026] Figure 7 This is a plan view of an acoustic device according to a second preferred embodiment of the present invention.

[0027] Figure 8 This is a reference graph illustrating an example of the resonant characteristics of an acoustic wave device according to a preferred embodiment of the present invention.

[0028] Figure 9 It is a graph showing the relationship between the fractional bandwidth and the amplitude of normalized spurious emissions of a large number of acoustic resonators.

[0029] Figure 10 The graph shows the relationship between the ratio d / 2p, the metallization ratio MR, and the fractional bandwidth.

[0030] Figure 11 This shows the Euler angles (0°, θ, ...) of LiNbO3 when the ratio d / p approaches zero. The fractional bandwidth plot of ).

[0031] Figure 12 It is a thermal image of an acoustic device without a cavity.

[0032] Figure 13 This is a thermal image of an acoustic device with a cavity.

[0033] Figure 14 It shows Figure 12 and Figure 13 A graph showing the relationship between the highest temperature of the acoustic device and the normalized input power.

[0034] Figure 15 and Figure 16 An acoustic device according to a first preferred embodiment is shown, wherein the cavity of the acoustic device overlaps with the busbar of the acoustic device.

[0035] Figure 17 An acoustic device according to a second preferred embodiment is shown, wherein the cavity of the acoustic device does not overlap with the busbar of the acoustic device.

[0036] Figures 18-20 It is a cross-sectional view of an acoustic device with different possible arrangements of an electrically insulating layer.

[0037] Figure 21 The offset between the outer periphery of the cavity and the inner edge of the busbar of the acoustic device is shown.

[0038] Figure 22 It shows Figure 21 A graph showing the relationship between the offset and the highest temperature of the acoustic device.

[0039] Figure 23 An acoustic device with a cavity having a non-linear outer perimeter is shown. Detailed Implementation

[0040] A preferred embodiment of the present invention includes a piezoelectric layer 2 made of lithium niobate or lithium tantalate, and a first electrode 3 and a second electrode 4 facing each other in a direction intersecting the thickness direction of the piezoelectric layer 2.

[0041] Bulk waves are used in the first thickness shear mode. Furthermore, the first electrode 3 and the second electrode 4 can be adjacent electrodes, and when the thickness of the piezoelectric layer 2 is d and the distance between the centers of the first electrode 3 and the second electrode 4 is p, the ratio d / p can, for example, be less than or equal to about 0.5. This configuration allows for a reduction in the size of the acoustic device and an increase in the Q value or quality factor.

[0042] The acoustic device 1 includes a piezoelectric layer 2 made of LiNbO3. The piezoelectric layer 2 can also be made of LiTaO3. The cutting angle of the LiNbO3 or LiTaO3 can be Z-cut, or it can be a rotary Y-cut or X-cut. For example, a propagation direction of approximately ±30° in Y or X propagation can be used. The thickness of the piezoelectric layer 2 is not limited and can be greater than or equal to approximately 50 nm and less than or equal to approximately 1000 nm, for example, to effectively excite a first thickness shear mode. The piezoelectric layer 2 has opposing first main surfaces 2a and second main surfaces 2b. Electrodes 3 and 4 are disposed on the first main surface 2a. Electrode 3 is an example of a "first electrode" and can be referred to as "a plurality of first electrode fingers," and electrode 4 is an example of a "second electrode" and can be referred to as "a plurality of second electrode fingers." Figure 1A and Figure 1B In this structure, multiple electrodes 3 are connected to a first busbar 5, and multiple electrodes 4 are connected to a second busbar 6. Electrodes 3 and 4 may intersect each other. Electrodes 3 and 4 may each have a rectangular shape and a length direction. In a direction perpendicular to the length direction, each electrode in electrode 3 is opposite to its adjacent electrode in electrode 4. The IDT (interdigital transducer) electrode can be defined by electrodes 3 and 4, the first busbar 5, and the second busbar 6. Both the length direction of electrodes 3 and 4 and the direction perpendicular to their length directions intersect the thickness direction of the piezoelectric layer 2. For this reason, it can be considered that each electrode in electrode 3 and its adjacent electrode in electrode 4 are opposite to each other in the direction intersecting the thickness direction of the piezoelectric layer 2. Alternatively, the length direction of electrodes 3 and 4 and the direction perpendicular to their length directions can be interchanged, such as... Figure 1A and Figure 1B As shown. In other words, electrodes 3 and 4 can... Figure 1A and Figure 1B The first busbar 5 and the second busbar 6 extend in the same direction. In this case, the first busbar 5 and the second busbar 6 are... Figure 1A and Figure 1B Electrodes 3 and 4 extend in the direction of extension. Adjacent electrode pairs, one connected to a potential and the other to a potential, are arranged in a direction perpendicular to the length direction of electrodes 3 and 4. The adjacent state of electrodes 3 and 4 does not mean that electrodes 3 and 4 are in direct contact, but rather that they are arranged with a gap between them. When electrodes 3 and 4 are adjacent, no electrodes connected to the hot electrode or ground electrode, including other electrodes 3 and 4, are arranged between electrodes 3 and 4.

[0043] The number of electrode pairs 3 and 4 is not necessarily an integer and can be 1.5 pairs, 2.5 pairs, etc. For example, 1.5 electrode pairs means there are 3 electrodes 3 and 4, where two electrodes are in an electrode pair and one is not in a pair. For example, the distance between the centers of electrodes 3 and 4 (i.e., the spacing between electrodes 3 and 4) can fall within the range of greater than or equal to about 1 μm and less than or equal to about 10 μm. The distance between the centers of electrodes 3 and 4 can be the distance between the centers of the width dimensions of electrodes 3 and 4 in a direction perpendicular to the length direction of electrodes 3 and 4. In addition, when there is more than one electrode 3 and 4 (e.g., when the number of electrodes 3 and 4 is two such that electrodes 3 and 4 define an electrode pair, or when the number of electrodes 3 and 4 is three or more such that electrodes 3 and 4 define 1.5 or more electrode pairs), the distance between the centers of electrodes 3 and 4 represents the average of the distances between any adjacent electrodes 3 and 4 in 1.5 or more electrode pairs. For example, the width of each of electrodes 3 and 4 (i.e., the dimension of each of electrodes 3 and 4 in the direction perpendicular to the length direction) can fall within the range of approximately 150 nm greater than or equal to and approximately 1000 nm less than or equal to. The distance between the centers of electrodes 3 and 4 can be the distance between the center of the dimension (width dimension) of electrode 3 in the direction perpendicular to the length direction of electrode 3 and the center of the dimension (width dimension) of electrode 4 in the direction perpendicular to the length direction of electrode 4.

[0044] Since a Z-cut piezoelectric layer can be used, the direction perpendicular to the length direction of electrodes 3 and 4 is the same as the direction perpendicular to the polarization direction of piezoelectric layer 2. This does not apply when a piezoelectric material with a different cut angle is used as piezoelectric layer 2. The term "perpendicular" is not limited to the case of strict perpendicularity, but can be substantially perpendicular (the angle formed between the direction perpendicular to the length direction of electrodes 3 and 4 and the polarization direction can be, for example, about 90° ± 10°).

[0045] The support substrate 8 can be laminated to the second main surface 2b of the piezoelectric layer 2 via an electrically insulating layer or a dielectric film 7. For example... Figure 2 As shown, the electrically insulating layer 7 can be frame-shaped and may include an opening 7a, and the support substrate 8 can be frame-shaped and may include an opening 8a. With this configuration, a cavity 9 can be formed. The cavity 9 can be configured not to impede the vibration of the excitation region C of the piezoelectric layer 2. Therefore, the support substrate 8 can be laminated to the second main surface 2b via the electrically insulating layer 7 at a location that does not overlap with the portion where at least one electrode pair is disposed. The electrically insulating layer 7 is not required. Therefore, the support substrate 8 can be laminated directly or indirectly onto the second main surface 2b of the piezoelectric layer 2.

[0046] The electrically insulating layer 7 can be made of silicon oxide. In addition to silicon oxide, suitable electrically insulating materials such as silicon oxynitride or aluminum oxide can also be used. The support substrate 8 can be made of Si or other suitable materials. The planar orientation of the Si can be (100), (110), or (111). High-resistivity Si with a resistivity greater than or equal to about 4 kΩ can be used, for example. The support substrate 8 can also be made of suitable electrically insulating materials or suitable semiconductor materials. Examples of materials for the support substrate 8 include: piezoelectrics such as aluminum oxide, lithium tantalate, lithium niobate, and quartz crystals; various ceramics such as aluminum oxide, magnesium oxide, sapphire, silicon nitride, aluminum nitride, silicon carbide, zirconium oxide, cordierite, mullite, talc, and forsterite; dielectrics such as diamond and glass; and semiconductors such as gallium nitride.

[0047] The first electrode 3 and the second electrode 4, as well as the first busbar 5 and the second busbar 6, can be made of suitable metals or alloys (such as Al and AlCu alloys). The first electrode 3 and the second electrode 4, as well as the first busbar 5 and the second busbar 6, can include structures such as an Al film laminated onto a Ti film. Adhesive layers other than the Ti film can be used.

[0048] To drive the acoustic wave device 1, an alternating voltage is applied between the first electrode 3 and the second electrode 4. More specifically, an alternating voltage is applied between the first busbar 5 and the second busbar 6 to excite a bulk wave in a first thickness shear mode within the piezoelectric layer 2. In the acoustic wave device 1, when the thickness of the piezoelectric layer 2 is d and the distance between the centers of adjacent first electrodes 3 and second electrodes 4 in the electrode pair is p, the ratio d / p can, for example, be less than or equal to about 0.5. For this reason, a bulk wave in the first thickness shear mode can be effectively excited, resulting in good resonance characteristics. The ratio d / p can be less than or equal to about 0.24, and in this case, even better resonance characteristics can be obtained. When there is more than one electrode, the distance p between the centers of adjacent electrodes 3, 4 is the average distance between the centers of any two adjacent electrodes 3, 4.

[0049] With the above configuration, even if the number of electrode pairs is reduced to minimize size, the Q value or quality factor of the acoustic device 1 is unlikely to decrease. The Q value is unlikely to decrease with a reduced number of electrode pairs because the acoustic device 1 is a resonator that does not require reflectors on both sides, and therefore has low propagation loss. Since bulk waves in the first thickness shear mode are used, reflectors are not required.

[0050] Reference Figure 3A and Figure 3B Describe the differences between Lamb waves and volume waves in the first thickness shear mode used in known acoustic devices.

[0051] Figure 3AIt is a schematic elevation cross-sectional view used to illustrate a Lamb wave propagating in a piezoelectric film of an acoustic device described in Japanese Unexamined Patent Application Publication No. 2012-257019.

[0052] like Figure 3A As indicated by the arrow, the wave propagates in the piezoelectric film 201. In the piezoelectric film 201, the first main surface 201a and the second main surface 201b are opposite to each other, and the thickness direction connecting the first main surface 201a and the second main surface 201b is the Z-direction. The X-direction is the direction in which the electrode fingers of the interdigital transducer electrodes are arranged. Figure 3A As shown, the Lamb wave propagates along the X direction. The Lamb wave is a plate wave, therefore the piezoelectric film 201 vibrates as a whole. However, the wave propagates along the X direction. Therefore, resonant characteristics are obtained by arranging reflectors on both sides. For this reason, wave propagation loss occurs, and the Q value, or quality factor, decreases as the size decreases (i.e., when the number of electrode pairs is reduced).

[0053] On the contrary, such as Figure 3B As shown, in the acoustic wave device 1, vibrational displacement is induced in the thickness shear direction, so the wave propagates and resonates essentially along the direction connecting the first main surface 2a and the second main surface 2b of the piezoelectric layer 2 (i.e., the Z direction). In other words, the X-direction component of the wave is significantly smaller than the Z-direction component. Since the resonance characteristic is obtained from the propagation of the wave along the Z-direction, a reflector is not required. Therefore, no propagation loss is caused when the wave propagates to the reflector. Thus, even if the number of electrode pairs is reduced to decrease the size, the Q value or quality factor is unlikely to decrease.

[0054] like Figure 4 As shown, the amplitude direction of the bulk wave in the first thickness shear mode is opposite in the first region 451 and the second region 452 included in the excitation region C of the piezoelectric layer 2, wherein the excitation region C is as follows: Figure 1B As shown. Figure 4 The diagram schematically illustrates the bulk wave when a higher voltage is applied to electrode 4 than to electrode 3. The first region 451 is the region in excitation region C between the first main surface 2a and a virtual plane VP1 perpendicular to the thickness direction of the piezoelectric layer 2 and dividing the piezoelectric layer 2 in two. The second region 452 is the region in excitation region C between the virtual plane VP1 and the second main surface 2b.

[0055] As described above, the acoustic device 1 includes at least one electrode pair. However, since waves do not propagate in the X direction, the number of electrode pairs 4 does not necessarily need to be two or more. In other words, only one electrode pair may be provided.

[0056] For example, the first electrode 3 is an electrode connected to a thermal potential, and the second electrode 4 is an electrode connected to a ground potential. Of course, the first electrode 3 can be connected to a ground potential, and the second electrode 4 can be connected to a thermal potential. As described above, each of the first electrode 3 or the second electrode 4 is connected to a thermal potential or to a ground potential, and no floating electrode is provided.

[0057] Figure 5 The graph shows the resonant characteristics of the acoustic wave device 1. The design parameters of the acoustic wave device 1 with resonant characteristics are shown below. For example, the piezoelectric layer 2 is made of LiNbO3 with Euler angles of (0°, 0°, 90°) and has a thickness of approximately 400 nm. However, as mentioned above, the piezoelectric layer 2 can be LiTaO3, and other suitable Euler angles and thicknesses can be used.

[0058] For example, when viewed in a direction perpendicular to the length direction of the first electrode 3 and the second electrode 4, the length of the overlapping region of the first electrode 3 and the second electrode 4 (i.e., the excitation region C) can be about 40 μm, the number of electrode pairs of electrodes 3 and 4 can be 21, the distance between the centers of the first electrode 3 and the second electrode 4 can be about 3 μm, the width of each electrode in the first electrode 3 and the second electrode 4 can be about 500 nm, and the ratio d / p can be about 0.133.

[0059] For example, the electrical insulating layer 7 can be made of a silicon oxide film with a thickness of about 1 μm.

[0060] The support substrate 8 can be made of Si.

[0061] The length of the excitation region C can be along the length direction of the first electrode 3 and the second electrode 4.

[0062] Within the manufacturing and measurement tolerances of all electrode pairs, the distance between any adjacent electrodes in an electrode pair can be equal or substantially equal. In other words, the first electrode 3 and the second electrode 4 can be set with a constant spacing.

[0063] from Figure 5 It is evident that, despite the absence of a reflector, a good resonant characteristic with a fractional bandwidth of approximately 12.5% ​​can be obtained.

[0064] When the thickness of the piezoelectric layer 2 is d and the distance between the centers of the electrode pairs is p, the ratio d / p can, for example, be less than or equal to about 0.5, or less than or equal to about 0.24. See below for reference. Figure 6 Further discussion on the ratio d / p.

[0065] With Figure 5 Similar to the case of acoustic devices with resonant characteristics shown, acoustic devices can be set with different ratios d / p. Figure 6It is a graph showing the relationship between the ratio d / p and the fractional bandwidth when the acoustic device 1 is used as a resonator.

[0066] from Figure 6 The non-limiting example shown readily demonstrates that when the ratio d / p > 0.5, even with adjustments to the ratio d / p, the fractional bandwidth remains below approximately 5%. Conversely, for example, when the ratio d / p ≤ 0.5, the ratio d / p varies within this range, and the fractional bandwidth can be set to approximately 5% or higher; that is, a resonator with a high coupling coefficient can be configured. For example, when the ratio d / p is less than or equal to approximately 0.24, the fractional bandwidth can be increased to approximately 7% or higher. Furthermore, when the ratio d / p is adjusted within this range, a resonator with a wider fractional bandwidth can be obtained, thus enabling the realization of a resonator with a higher coupling coefficient. Therefore, it has been found and confirmed that when the ratio d / p is set to approximately 0.5 or less, for example, a resonator with a high coupling coefficient using a bulk wave in a first thickness shear mode can be configured.

[0067] As described above, at least one electrode pair can be a pair, and in the case of one electrode pair, p is defined as the distance between the centers of adjacent first electrode 3 and second electrode 4. In the case of 1.5 or more electrode pairs, the average distance between the centers of any adjacent electrodes 3, 4 can be defined as p.

[0068] For the thickness d of the piezoelectric layer 2, when the piezoelectric layer 2 has a thickness variation, the average thickness can be used.

[0069] Figure 7 This is a plan view of an acoustic wave device 31 according to a second preferred embodiment of the present invention. In the acoustic wave device 31, an electrode pair including a first electrode 3 and a second electrode 4 is disposed on the first main surface 2a of the piezoelectric layer 2. Figure 7 In this context, K represents the overlap width. As mentioned above, in the acoustic device 31, the number of electrode pairs can be one. Similarly, in this case, when the ratio d / p is less than or equal to about 0.5, for example, a bulk wave in the first thickness shear mode can be effectively excited.

[0070] In the acoustic device 31, the metallization ratio MR of any adjacent first electrode 3 and second electrode 4 within the excitation region C (i.e., the region where any adjacent electrodes 3 and 4 overlap when viewed from opposite directions) to the total area of ​​the excitation region C can satisfy MR ≤ 1.75(d / p) + 0.075, thereby effectively reducing the occurrence of stray particles. (Refer to...) Figure 8 and Figure 9 Describe this reduction. Figure 8This is a reference graph illustrating an example of the resonant characteristics of the acoustic device 31. The stray phenomenon indicated by arrow B occurs between the resonant frequency and the anti-resonant frequency. For example, the ratio d / p can be set to approximately 0.08, and the Euler angles of LiNbO3 can be set to (0°, 0°, 90°). For example, the metallization ratio MR can be set to approximately 0.35.

[0071] Reference Figure 1B Describe the metallization ratio MR. In Figure 1B In the electrode structure, when focusing on an electrode pair, it is assumed that only one electrode pair is provided. In this case, the portion surrounded by alternating long and short dashed lines C is the excitation region. When the first electrode 3 and the second electrode 4 are observed in a direction perpendicular to the length direction of the first electrode 3 and the second electrode 4 (i.e., in the opposite direction), the excitation region C includes: a first region where the first electrode 3 and the second electrode 4 overlap, a second region where the second electrode 4 and the first electrode 3 overlap, and a third region where the first electrode 3 and the second electrode 4 overlap in the region between the first and second electrodes. Then, the ratio of the area of ​​the first electrode 3 and the second electrode 4 in the excitation region C to the area of ​​the excitation region C is the metallization ratio MR. In other words, the metallization ratio MR is the ratio of the area of ​​the metallized portion to the area of ​​the excitation region C.

[0072] When multiple electrode pairs are provided, the ratio of the metallized portion to the total area of ​​the excitation region is the metallization ratio MR. That is, the metallization ratio MR can be the ratio of the area of ​​the first electrode 3 and the second electrode 4 in the overlapping region (i.e., the region where the first electrode 3 and the second electrode 4 overlap) to the total area of ​​the overlapping region.

[0073] Figure 9 This is a graph showing the relationship between the fractional bandwidth and the normalized spurious amplitude of a large number of acoustic resonators, in which the phase rotation of the spurious impedance is normalized by 180° as the spurious amplitude. The phase rotation of the impedance is an indicator of the spurious amplitude, which is related to the impedance ratio. The impedance ratio is related to the difference between the minimum and maximum impedance values, while the phase rotation of the impedance is related to the peak impedance. For the fractional bandwidth, the film thickness of the piezoelectric layer 2 and the dimensions of the first electrode 3 and the second electrode 4 can be varied and adjusted. Figure 8 The graph shows the resonance characteristics when the material of piezoelectric layer 2 is Z-cut LiNbO3, and similar resonance characteristics can be obtained when the material of piezoelectric layer 2 is cut at another angle.

[0074] In the Figure 9 Within the region surrounded by the ellipse J, the stray energy is approximately 1.0, and is relatively large. From... Figure 9It is evident that when the fractional bandwidth exceeds approximately 0.17 (i.e., approximately 17%), even changing the fractional bandwidth parameters will result in larger spurious levels with a spurious level greater than or equal to 1 in the passband. In other words, as in Figure 8 In the case of the resonant characteristics shown, the larger spurious signal indicated by arrow B appears in the passband. Therefore, for example, the fractional bandwidth is preferably less than or equal to about 17%. In this case, the spurious signal can be reduced by adjusting the film thickness of the piezoelectric layer 2, the dimensions of the first electrode 3 and the second electrode 4, etc.

[0075] Figure 10 This is a graph showing the relationship between the ratio d / 2p, the metallization ratio MR, and the fractional bandwidth. The fractional bandwidth of various acoustic devices with different d / 2p ratios and different metallization ratios MR was measured. For example, Figure 10 The shaded area to the right of the dashed line D in the diagram represents the region where the fractional bandwidth is less than or equal to approximately 17%. The dashed line D between the shaded and unshaded regions is represented as MR = 3.5(d / 2p) + 0.075 = 1.75(d / p) + 0.075. For example, when the metallization ratio MR satisfies MR ≤ 1.75(d / p) + 0.075, the fractional bandwidth can be set to approximately 17% or lower. Furthermore, Figure 10 The long and short dashed lines D1 are shown, represented by MR = 3.5(d / 2p) + 0.05. For example, when the metallization ratio MR satisfies MR ≤ 1.75(d / p) + 0.05, the fractional bandwidth can be reliably set to about 17% or lower.

[0076] Figure 11 This shows the Euler angles (0°, θ, ...) of LiNbO3 when the ratio d / p approaches zero. The fractional bandwidth plot of ). Figure 11 The shaded region is a region with a fractional bandwidth of at least about 5% or higher, and the boundary of the shaded region is approximated by the following expressions (1), (2) and (3): (0°±10°, 0° to 20°, any) ...(1) (0°±10°, 20° to 80°, 0° to 60°(1-(θ-50)) 2 / 900) 1 / 2 )or (0°±10°, 20° to 80°, [180°-60°(1-(θ-50))) 2 / 900) 1 / 2 (180°) ... (2) (0°±10°,[180°-30°(1-( -90) 2 / 8100)1 / 2 Up to 180°, any ...(3)

[0077] Therefore, when the Euler angles of the material of the piezoelectric layer 2 used in the acoustic resonator satisfy the above expressions (1), (2) and (3), the fractional bandwidth of the acoustic resonator can be sufficiently widened.

[0078] Figures 15-17 An acoustic device 1 comprising a piezoelectric layer 2 and an IDT electrode 50 on the piezoelectric layer 2 is shown. Although Figures 15-17 Not shown, but the acoustic device 1 may include a support substrate 8 (such as...) Figures 18-20 (as shown) and optional electrical insulation layer 7 (as shown) Figure 18 and Figure 19 The support member is defined as shown. The IDT electrode 50 may at least partially overlap with the cavity in the support member and may include: a first busbar 5; a first electrode 3 connected to and extending from the first busbar 5; a second busbar 6; and a second electrode 4 connected to the first busbar 5 and extending from the second busbar 6. The first electrode 3 and the second electrode 4 may be interdigitated electrodes. Figures 15-17 The outline of cavity 9 is shown in dashed lines. A first generatrix 5 may include a first inner edge 5a, and a second generatrix 6 may include a second inner edge 5b. A first electrode 3 may extend from the first inner edge 5a, and a second electrode 4 may extend from the second inner edge 6a.

[0079] The overlapping region 20 is the region where adjacent first electrodes 3 and second electrodes 4 partially overlap. The first gap region 31 is the region that includes only the portion of the first electrode 3 between the first busbar 5 and the overlapping region 20, and the second gap region 32 is the region that includes only the portion of the second electrode 4 between the second busbar 6 and the overlapping region 20. Each first electrode 3 may include a non-overlapping portion in the first gap region 31 connected to the first busbar 5, and may also include an overlapping portion in the overlapping region 20 connected to the non-overlapping portion. Similarly, each second electrode 4 may include a non-overlapping portion in the second gap region 31 connected to the second busbar 6, and may also include an overlapping portion in the overlapping region 20 connected to the non-overlapping portion. The first electrodes 3 and second electrodes 4 may intersect, such that adjacent overlapping portions of the first electrodes 3 and second electrodes 4 are opposite each other.

[0080] The cavity 9 may include a first wall or outer peripheral portion 9a and a second wall or outer peripheral portion 9b. For example... Figure 15 and Figure 16 As shown, the first wall 9a may be below the first busbar 5, and / or the second wall 9b may be below the second busbar 6, and as... Figure 17As shown, the first wall 9a may be below the first gap region 31, and / or the second wall 9b may be below the second gap region 32.

[0081] Lc can be the overlapping region 20 along the direction of electrode extension (i.e., Figure 15 and Figure 16 The dimension in the y-direction of the cavity 9; Lg can be the dimension of each of the first gap region 31 and the second gap region 32 in the electrode finger extension direction; Lb can be the dimension of the first generatrix 5 and the second generatrix 6 in the electrode finger extension direction; and in the plan view, the offset distance L can be the dimension of each of the first wall 9a and the second wall 9b of the cavity 9 in the electrode finger extension direction (e.g., in the y-direction); Lg can be the dimension of each of the first wall 9a and the second wall 9b of the cavity 9 in the electrode finger extension direction (e.g., in the y-direction of the cavity 9); Lg can be the dimension of each of the first gap region 31 and the second gap region 32 in the electrode finger extension direction; Lb can be the dimension of the first generatrix 5 and the second generatrix 6 in the electrode finger extension direction; and in the plan view, the offset distance Figure 16 Instead Figure 15 The position of the IDT electrode 50 on the electrode finger extension direction (as shown), wherein the position of each of the first inner edge 5a and the second inner edge 5b in the electrode finger extension direction can be considered as a zero reference, such that the outward direction of the IDT electrode 50 is the positive direction (i.e., in the direction shown). Figures 15-17 In the positive y-direction), and make the inward direction of the IDT electrode 50 negative (i.e., in Figures 15-17 (in the negative y direction). Figures 15-17 The zero reference on the right is shown, with the positive and negative directions marked by arrows.

[0082] For example, Lc can be the length of the overlapping portion of the first electrode 3 and the second electrode 4, or the width of the overlapping region 20; Lg can be the length of the non-overlapping portion of the first electrode 3 and the second electrode 4, or the width of the non-overlapping regions 31 and 32; the offset distance L can be the distance from the first inner edge 5a or the second inner edge 6a to the corresponding wall in the first wall 9a or the second wall 9b, wherein the distance extending in the first generatrix 5 and the second generatrix 6 is positive, and wherein the distance extending in the opposite direction (i.e., along the first electrode 3 or the second electrode 4) is negative.

[0083] like Figure 15 and Figure 16 As shown, for each of the first wall 9a and the second wall 9b, the equation 0 < L < Lb can be satisfied.

[0084] In the plan view, the first wall 9a and the second wall 9b of cavity 9 overlap with the outer portion of the overlapping region 20 in the direction of electrode extension. The overlapping region 20 is the area where portions of the first electrode 3 and the second electrode 4 overlap each other when viewed in opposite directions of adjacent electrodes 3 and 4. That is, as shown... Figure 15 and Figure 16 As shown, the first wall 9a can be below the first busbar 5, and the second wall 9b can be below the second busbar 6.

[0085] exist Figure 16In the middle, the acoustic device 1 includes: a support member, including a support substrate 8 ( Figure 16 (not shown in the image) and optional electrical insulation layer 7 ( Figure 16 (not shown in the image); piezoelectric layer 2, via cavity 9 on support substrate 8; and IDT electrode 50, disposed on piezoelectric layer 2.

[0086] The IDT electrode 50 may include: a first busbar 5 and a second busbar 6 opposite to each other; a plurality of first electrodes 3, the proximal ends of which are connected to the first busbar 5 and the distal ends of which extend toward the second busbar 6; and a plurality of second electrodes 4, the proximal ends of which are connected to the second busbar 6 and the distal ends of which extend toward the first busbar 5. The plurality of first electrodes 3 and the plurality of second electrodes 4 intersect each other. At least a portion of the IDT electrode 50 overlaps with the cavity 9 in a plan view along the thickness direction of the supporting substrate 8.

[0087] In a plane along the thickness direction of the supporting substrate 8, the first wall 9a and the second wall 9b of the cavity 9 are located outside the first inner edge 5a of the first generatrix 5 and the second inner edge 6a of the second generatrix 6. In the direction of electrode finger extension of the cavity 9 (i.e., Figure 16 In the outer or outer edge of the cavity 9 (in the y-direction), either the outer edge of the first busbar side (first wall 9a) or the outer edge of the second busbar side (second wall or second wall 9b) can be located beyond the electrode finger side outer edges (first inner edge 5a and second inner edge 6a) of the first busbar 5 and the second busbar 6. That is, the first wall 9a of the cavity 9 can be located below the first busbar 5, and the second wall 9b of the cavity 9 can be located below the second busbar 6.

[0088] In the IDT electrode 50, the first gap region 31 may be located between the overlapping region 20 and the first busbar 5, and the second gap region 32 may be located between the overlapping region 20 and the second busbar 6.

[0089] Lc can be the overlapping region 20 along the direction of electrode extension (i.e., Figure 16 The dimension of the IDT electrode 50 in the y-direction; Lg can be the dimension of each gap region in the first gap region 31 and the second gap region 32 in the electrode finger extension direction; Lb can be the dimension of each of the first busbars 5 and the second busbars 6 in the electrode finger extension direction; and in the plan view, the offset distance L can be the position of each of the first wall 9a and the second wall 9b of the cavity 9 in the electrode finger extension direction, wherein the position of each of the inner edges of the first inner edge 5a and the second inner edge 5b is a zero reference, such that the outward direction of the IDT electrode 50 is a positive direction (i.e., in the positive y-direction) and the inward direction of the IDT electrode 50 is a negative direction (i.e., in the negative y-direction).

[0090] exist Figure 16In this case, the equation 0 < L < Lb is satisfied. That is, the first wall 9a of the cavity 9 is below the first generatrix 5, and the second wall 9b of the cavity 9 is below the second generatrix 6. Alternatively, it is not necessary for both the first wall 9a and the second wall 9b to be below one of the first generatrix 5 and the second generatrix 6. That is, the first wall 9a of the cavity 9 is below the first generatrix 5, or the second wall 9b of the cavity 9 is below the second generatrix 6.

[0091] In Figure 17 this case, in a plan view along the thickness direction of the support substrate 8 (the support substrate 8 is not shown in Figure 17 this case), the first wall 9a and the second wall 9b of the cavity 9 are disposed at positions inside the first inner edge 5a of the first generatrix 5 and the second inner edge 6a of the second generatrix 6 and outside the envelope line (i.e., the overlapping region 20) connecting the distal ends of the plurality of first electrodes 3 and the plurality of second electrodes 4. In the plan view, among the first wall 9a and the second wall 9b of the cavity 9, only either the first wall 9a or the second wall 9b may be disposed at a position inside the first inner edge 5a of the first generatrix 5 and the second inner edge 6a of the second generatrix 6 and outside the envelope line connecting the distal ends of the plurality of first electrodes 3 and the plurality of second electrodes 4. In other words, at least one of the first wall 9a and the second wall 9b may overlap with one of the first gap region 31 or the second gap region 32.

[0092] In Figure 17 this case, the first wall 9a and / or the second wall 9b of the cavity 9 satisfies the equation -Lg < L < 0. That is, the first wall 9a of the cavity 9 may be located below the first gap region 31, and / or the second wall 9b of the cavity 9 may be located below the second gap region 32. Alternatively, the first wall 9a of the cavity 9 may be located below the non-overlapping portion of each first electrode in the first electrodes 3, and / or the second wall 9b of the cavity 9 may be located below the non-overlapping portion of each second electrode in the second electrodes 4.

[0093] Figures 18-20 Different possible arrangements of the support, the electrical insulating layer 7, and the cavity 9 are shown. Figure 18 and Figure 19 include an optional electrical insulating layer 7, but Figure 20 do not include an optional electrical insulating layer 7. In Figure 18 this case, the cavity 9 extends through the electrical insulating layer 7 into the support substrate 8. In Figure 19 this case, the cavity 9 is only provided in the electrical insulating layer 7. As Figure 20 shown, the support may only include the support substrate 8 and not include the electrical insulating layer 7. In Figure 20 this case, the cavity 9 is in the support substrate 8. Figures 18-20 The arrangements shown can be used with different preferred embodiments of the present invention (including the arrangement shown in Figures 15-17 this case).

[0094] like Figure 21 As shown, the distance in the plan view between each of the first wall 9a and the second wall 9b of the cavity 9 and the corresponding inner edge of the first inner edge 5a of the first generatrix 5 and the second inner edge 6a of the second generatrix 6 is the offset distance of the cavity 9 in the y-direction (electrode refers to the extension direction). Figure 21 The offset distance L is marked as L), and when the offset distance L is positive (i.e., when each of the first walls 9a and the second walls 9b of the cavity 9 is located outside the corresponding inner edge in the first inner edge 5a of the first generatrix 5 and the second inner edge 6a of the second generatrix 6 in the plan view), the surface temperature of the piezoelectric layer 2 can be easily reduced compared to when the offset distance is zero (i.e., each of the first walls 9a and the second walls 9b of the cavity 9 is the same as or flush with the corresponding inner edge in the first inner edge 5a of the first generatrix 5 and the second inner edge 6a of the second generatrix 6 in the plan view). Therefore, as Figure 22 As shown, this can improve thermal radiation characteristics.

[0095] Figure 22 A graph showing the relationship between the highest temperature and the offset distance L of a device with the following parameters is presented: LN: ZYLN 500nmt IDT: AL 500nmt Two-layer cabling: AL 3µmt Electrical insulation layer: SiO2 600nmt Support substrate: Si 250µmt

[0096] IDT spacing 4.55µm, 80 IDT line width 1.1µm 50µm overlap width 200mW pin equivalent

[0097] When the first wall 9a and the second wall 9b of the cavity 9 are below the first busbar 5 and the second busbar 6, the offset distance L is negative (i.e., offset distance L < 0), and when the first wall 9a and the second wall 9b of the cavity 9 are below the first gap region 31 and the second gap region 32, the offset distance is positive (i.e., offset distance L > 0).

[0098] like Figure 22As shown, when the offset distance L is, for example, a value less than or equal to -1 / 25 of the overlap width Lc, the heat radiation characteristics can be further significantly improved. And when the offset distance L is, for example, a value less than or equal to +8 / 25 of the overlap width Lc, the heat radiation characteristics can be improved compared to when the offset distance L is zero. Therefore, when -Lg < L < -(1 / 25)×Lc or 0 < L < (8 / 25)×Lc, the heat radiation characteristics can be effectively enhanced. Alternatively, the offset distances of the first wall 9a and the second wall 9b can be different. That is, if the offset distance L1 is the offset distance of the first wall 9a and if the offset distance L2 is the offset distance of the second wall 9a, then: -Lg < L1 < -(1 / 25)×Lc or 0 < L1 < (8 / 25)×Lc; and -Lg < L2 < -(1 / 25)×Lc or 0 < L2 < (8 / 25)×Lc.

[0099] Figure 23 An acoustic wave device 1 including an IDT 50 and a cavity 9 is shown. As Figure 23 shown, the cavity 9 does not have to include a straight line. Although not shown in Figure 23 , the IDT electrodes 50 can be apodized to a diamond shape.

[0100] The wall 9c of the cavity 9 or the outer edges 5b of the first bus bar 5 and the outer edges 6b of the second bus bar 6 do not have to have a straight shape. Figure 23 A cavity 9 having a curved wall 9c is shown. Figure 23 An average imaginary straight line 60 (the horizontal dotted line passing through the first bus bar 5) within the range of the wall in the x direction (i.e., the direction in which the plurality of first electrodes 3 and the plurality of second electrodes 4 of the IDT electrode 50 are arranged) is shown in. The driving region of the IDT 50 is the region sandwiched between the outermost electrodes of the IDT electrode 50 in the X direction (i.e., the overlapping region 20).

[0101] If the average offset distance Lo is the average value of the offset distances of the overlapping portion of the wall 9c of the cavity 9 and the overlapping region 20 in the electrode finger extension direction (i.e., the Figure 23 y direction in), then the equation Lo ≠ 0 and -Lg < Lo < Lb can be satisfied. That is, if the average offset distance Lo is the distance between the average imaginary straight line 60 and the first inner edge 5a of the first bus bar 5, the upper part of the cavity 9 can satisfy the equation Lo ≠ 0 and -Lg < Lo < Lb. Although not shown in Figure 23 , a corresponding average imaginary straight line can also be drawn through the second bus bar 6, which can be the corresponding average offset distance Lo from the second inner edge 6a of the second bus bar 6, such that the lower part of the cavity 9 can satisfy the equation Lo ≠ 0 and -Lg < Lo < Lb.

[0102] It should be noted that each preferred embodiment described herein is exemplary, and partial substitutions or combinations of configurations are possible between different preferred embodiments. While preferred embodiments of the invention have been described above, it should be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Therefore, the scope of the invention is defined only by the appended claims.

Claims

1. An acoustic wave device, comprising: A support; A piezoelectric layer on the support; And Interdigital transducer electrodes on the piezoelectric layer and including a pair of bus bars opposite to each other and a plurality of electrode fingers, wherein The ratio d / p is 0.5 or less, where d is the thickness of the piezoelectric layer and p is the distance between the centers of adjacent electrode fingers among the plurality of electrode fingers, and A cavity is provided in the support and opens towards the piezoelectric layer, The plurality of electrode fingers define an electrode finger extension direction, and the plurality of electrode fingers extend along the electrode finger extension direction, The periphery of the cavity includes a pair of walls opposite to each other in the electrode finger extension direction in a plan view, Each of the pair of bus bars includes an inner edge located inside in the electrode finger extension direction, The interdigital transducer electrodes have an overlapping region and a pair of gap regions. In the overlapping region, when observed in the direction opposite to the adjacent electrode fingers, the plurality of electrode fingers overlap each other. The pair of gap regions are respectively located between the overlapping region and a corresponding one of the pair of bus bars, In a plan view, the pair of walls of the cavity overlap with an outer side portion outside the overlapping region in the electrode finger extension direction, and For each of the pair of walls, the equation 0 < L < Lb is satisfied, where Lc is the dimension of the overlapping region in the electrode finger extension direction, Lb is the dimension of each of the pair of bus bars in the electrode finger extension direction, and in a plan view, L is the position of each of the pair of walls of the cavity in the electrode finger extension direction. The corresponding position of each inner edge of the pair of bus bars in the electrode finger extension direction is the zero reference, such that the outward direction of the interdigital transducer electrodes is the positive direction and the inward direction of the interdigital transducer electrodes is the negative direction.

2. The acoustic device according to claim 1, wherein, In each of the pair of walls, the equation 0 < L < (8 / 25)×Lc is satisfied.

3. The acoustic wave device according to claim 1, wherein The support comprises: A support substrate; and An electrically insulating layer provided between the support substrate and the piezoelectric layer, and The cavity is provided in the electrically insulating layer.

4. The acoustic wave device according to claim 1, wherein The support comprises a support substrate, and The cavity is in the support substrate.

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

24.

6. The acoustic device according to claim 1, wherein, The equation MR ≤ 1.75(d / p)+0.075 is satisfied, where MR is the metallization ratio of the area of the plurality of electrode fingers in the overlapping region to the total area of the overlapping region.

7. An acoustic wave device, comprising: A support including a cavity, the cavity including a first wall and a second wall opposite to each other; A piezoelectric layer on the support; Interdigital transducer electrodes on the piezoelectric layer and including: A first bus bar including a first inner edge; First electrodes extending from the first inner edge, each of the first electrodes including: A first non-overlapping portion connected to the first inner edge; and A first overlapping portion connected to the first non-overlapping portion; A second bus bar, including a second inner edge facing the first inner edge; and A second electrode extending from the second inner edge, each second electrode in the second electrode including: A second non-overlapping portion connected to the second inner edge; and A second overlapping portion connected to the non-overlapping portion and opposite to a corresponding first overlapping portion in an overlapping region; wherein, The ratio d / p is 0.5 or less, where d is the thickness of the piezoelectric layer and p is the distance between the centers of adjacent electrodes of the first electrode and the second electrode; The first wall of the cavity is located below the first non-overlapping portion of each first electrode of the first bus bar or the first electrode; and The second wall of the cavity is located below the second non-overlapping portion of each second electrode of the second bus bar or the second electrode.

8. The acoustic wave device according to claim 7, wherein, The equation 0 < L1 < (8 / 25)×Lc is satisfied, where Lc is the length of the first overlapping portion of each first electrode of the first electrode and the second overlapping portion of each second electrode of the second electrode, and L1 is the distance from the first inner edge to the first wall.

9. The acoustic wave device according to claim 8, wherein, Satisfy the equation 0 < L2 < (8 / 25) × Lc, where L2 is the distance from the second inner edge to the second wall.

10. The acoustic wave device according to claim 7, wherein, The equation L1 > (1 / 25)×Lc is satisfied, where Lc is the length of the first overlapping portion of each first electrode of the first electrode and the second overlapping portion of each second electrode of the second electrode, and L1 is the distance from the first inner edge to the first wall.

11. The acoustic wave device according to claim 10, wherein, The equation L2>(1 / 25)×Lc is satisfied, where, L2 is the distance from the second inner edge to the second wall.

12. An acoustic wave device, including: A support; A cavity in the support and including a first wall and a second wall opposite to each other; A piezoelectric layer on the support; A first bus bar including a first electrode extending from a first inner edge; A second bus bar including a second electrode, the second electrode extending from a second inner edge and intersecting with the first electrode; An overlapping region where portions of adjacent first electrodes and second electrodes face each other; A first gap region adjacent to the first bus bar and the overlapping region and between the first bus bar and the overlapping region, and including the first electrode but not including the second electrode; and A second gap region adjacent to the second bus bar and the overlapping region and between the second bus bar and the overlapping region, and including the second electrode but not including the first electrode; wherein, The ratio d / p is 0.5 or less, where d is the thickness of the piezoelectric layer and p is the distance between the centers of adjacent electrodes of the first electrode and the second electrode; The first wall of the cavity is located below the first bus bar or the first gap region; and The second wall of the cavity is located below the second bus bar or the second gap region.

13. The acoustic wave device according to claim 12, wherein, Satisfy the equation 0 < L1 < (8 / 25)×Lc, where Lc is the width of the overlapping region, and L1 is the distance from the first inner edge to the first wall.

14. The acoustic wave device according to claim 13, wherein, Satisfy the equation 0 < L2 < (8 / 25)×Lc, where L2 is the distance from the second inner edge to the second wall.

15. The acoustic wave device according to claim 12, wherein, Satisfy the equation L1 > (1 / 25)×Lc, where Lc is the width of the overlapping region, and L1 is the distance from the first inner edge to the first wall.

16. The acoustic wave device according to claim 15, wherein, Satisfy the equation L2 > (1 / 25)×Lc, where L2 is the distance from the second inner edge to the second wall.

17. The acoustic wave device according to claim 12, wherein, The support member includes: A support substrate; and An electrically insulating layer disposed between the support substrate and the piezoelectric layer, and The cavity is disposed in the electrically insulating layer.

18. The acoustic wave device according to claim 12, wherein, The support member includes a support substrate, and The cavity is disposed in the support substrate.

19. The acoustic device according to claim 12, wherein, The ratio d / p is less than or equal to 0.

24.

20. The acoustic wave device according to claim 12, wherein, Satisfy the equation MR ≤ 1.75(d / p) + 0.075, where MR is the metallization ratio of the area of the first electrode and the second electrode in the overlapping region to the total area of the overlapping region.

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