Elastic wave device

Abstract

This elastic wave device comprises: a piezoelectric layer having a first main surface and a second main surface on the opposite side from the first main surface; an IDT electrode provided on the main surface side of at least one of the first main surface and the second main surface of the piezoelectric layer; a dielectric layer provided on the main surface side of at leasat one of the first main surface and the second main surface of the piezoelectric layer; and a support member provided on the second main surface side of the piezoelectric layer. The IDT electrode has: a first bus bar and a second bus bar that face each other; at least one first electrode finger having a proximal end connected to the first bus bar, and at least one second electrode finger having a proximal end connected to the second bus bar. The support member has an acoustic reflection portion on the second main surface side. When the thickness of the piezoelectric layer is denoted by d, and the average of center-to-center distances between adjacent first electrode fingers and second electrode fingers is denoted by p, d / p is 0.5 or less. When a region outside the IDT electrode is defined as a specific region, a void is provided in at least a portion of the piezoelectric layer and the dielectric layer included in the specific region.

Description

Elastic wave apparatus

[0001] This invention relates to an elastic wave apparatus.

[0002] Patent Document 1 describes a membrane-type elastic wave apparatus.

[0003] Special Publication No. 2021-527344

[0004] The elastic wave apparatus shown in Patent Document 1 had the potential for elastic wave leakage in the direction of the electrode finger arrangement.

[0005] The present invention aims to provide an elastic wave device that can suppress the leakage of elastic waves.

[0006] An elastic wave apparatus according to one embodiment comprises a piezoelectric layer having a first main surface and a second main surface opposite to the first main surface, an IDT electrode provided on at least one of the main surfaces of the first and second main surfaces of the piezoelectric layer, a dielectric layer provided on at least one of the main surfaces of the first and second main surfaces of the piezoelectric layer, and a support member provided on the second main surface side of the piezoelectric layer, wherein the IDT electrode has a first busbar facing each other, a second busbar, at least one first electrode finger whose base end is connected to the first busbar, and at least one second electrode finger whose base end is connected to the second busbar, and the support member has The second main surface side has an acoustic reflection portion, and when the thickness of the piezoelectric layer is d and the average distance between the centers of adjacent first and second electrode fingers is p, d / p is 0.5 or less, and in a plan view from the thickness direction of the piezoelectric layer, the piezoelectric layer and the dielectric layer overlap in at least a part, overlap with the first electrode finger or the second electrode finger in the extending direction of the first and second busbars, and when the region outside the IDT electrode in the extending direction of the first and second busbars is defined as a specific region, a gap is provided in at least a part of the piezoelectric layer and the dielectric layer included in the specific region.

[0007] According to the elastic wave device of the present invention, leakage of elastic waves can be suppressed.

[0008] Figure 1 is a plan view showing an elastic wave apparatus according to the first embodiment. Figure 2 is a cross-sectional view taken along line II-II' of Figure 1. Figure 3 is a schematic cross-sectional view illustrating the bulk wave of the first-order thickness-slip mode propagating through the piezoelectric layer of the first embodiment. Figure 4 is a schematic cross-sectional view illustrating the amplitude direction of the bulk wave of the first-order thickness-slip mode propagating through the piezoelectric layer of the first embodiment. Figure 5 is an explanatory diagram showing an example of the resonance characteristics of the elastic wave apparatus of the first embodiment. Figure 6 is an explanatory diagram showing the relationship between d / 2p and the specific bandwidth as a resonator, where p is the distance between the centers of adjacent electrodes or the average distance between the centers, and d is the average thickness of the piezoelectric layer, in the elastic wave apparatus of the first embodiment. Figure 7 is a plan view showing an example in which a pair of electrodes are provided in the elastic wave apparatus of the first embodiment. Figure 8 is a reference diagram showing an example of the resonance characteristics of the elastic wave apparatus of the first embodiment. Figure 9 is an explanatory diagram showing the relationship between the relative bandwidth of the elastic wave apparatus of the first embodiment when a large number of elastic wave resonators are configured, and the phase rotation amount of the spurious impedance normalized by 180 degrees as the spurious magnitude. Figure 10 is an explanatory diagram showing the relationship between d / 2p, the metallization ratio MR, and the relative bandwidth. Figure 11 shows the LiNbO when d / p approaches 0. ３This is an explanatory diagram showing a map of the relative bandwidth with respect to the Euler angle (0°, θ, ψ). Figure 12 is an enlarged cross-sectional view of region A shown in Figure 2. Figure 13 is an explanatory diagram showing an example of the admittance characteristics of an elastic wave apparatus according to the first embodiment. Figure 14 is an explanatory diagram showing the distribution of vibration modes of an elastic wave apparatus according to the first embodiment. Figure 15 is an explanatory diagram showing the distribution of vibration modes of an elastic wave apparatus according to a comparative example. Figure 16 is a cross-sectional view showing an elastic wave apparatus according to the first modified example. Figure 17 is a cross-sectional view showing an elastic wave apparatus according to the second modified example. Figure 18 is a cross-sectional view showing an elastic wave apparatus according to the second embodiment. Figure 19 is an explanatory diagram showing an example of the admittance characteristics of an elastic wave apparatus according to the second embodiment. Figure 20 is a cross-sectional view showing an elastic wave apparatus according to the third embodiment. Figure 21 is an explanatory diagram showing an example of the admittance characteristics of an elastic wave apparatus according to the third embodiment. Figure 22 is an explanatory diagram showing the relationship between the ratio of the distance between the air gap and the electrode finger (SP) to the electrode pitch (p) (SP / p) and the actual admittance in an elastic wave apparatus according to the third embodiment. Figure 23 is a cross-sectional view showing an elastic wave apparatus according to the fourth embodiment. Figure 24 is an explanatory diagram showing an example of the admittance characteristics of an elastic wave apparatus according to the fourth embodiment. Figure 25 is a cross-sectional view showing an elastic wave apparatus according to the third modified example. Figure 26 is a cross-sectional view showing an elastic wave apparatus according to the fifth embodiment.

[0009] Embodiments of the present disclosure will be described in detail below with reference to the drawings. However, these embodiments do not limit the present disclosure. Each embodiment described in this disclosure is illustrative, and partial substitution or combination of configurations is possible between different embodiments. In modifications and subsequent embodiments, descriptions of matters common to the first embodiment will be omitted, and only the differences will be described. In particular, similar effects and benefits due to similar configurations will not be mentioned sequentially for each embodiment.

[0010] (First Embodiment) Figure 1 is a plan view showing an elastic wave apparatus according to the first embodiment. Figure 2 is a cross-sectional view taken along line II-II' in Figure 1. In Figure 1, the first dielectric layer 41 is shown by a dashed line for clarity.

[0011] As shown in FIG. 1 and FIG. 2, the acoustic wave device 10 according to the first embodiment includes a piezoelectric layer 20, an IDT electrode 30, a support substrate 11, a first dielectric layer 41, and a second dielectric layer 42. As shown in FIG. 2, the acoustic wave device 10 is formed by laminating the second dielectric layer 42, the piezoelectric layer 20, the IDT electrode 30, and the first dielectric layer 41 in this order on the support substrate 11.

[0012] The piezoelectric layer 20 is a flat plate having a first main surface 20a and a second main surface 20b opposite to the first main surface 20a. The piezoelectric layer 20 is made of lithium niobate (LiNbO ３ ). Alternatively, the piezoelectric layer 20 may be made of lithium tantalate (LiTaO ３ ). In the first embodiment, the cut angle of LiNbO ３ and LiTaO ３ is Z-cut. The cut angle of LiNbO ３ and LiTaO ３ may also be rotated Y-cut or X-cut. Preferably, a propagation direction of Y-propagation or X-propagation ±30° is preferred. Preferably, the piezoelectric layer 20 includes lithium niobate (LiNbO ３ ) or lithium tantalate (LiTaO ３ ) and is 120°±10° rotated Y-cut or 90°±10° rotated Y-cut.

[0013] The thickness of the piezoelectric layer 20 is not particularly limited, but is preferably 50 nm or more and 1000 nm or less for effectively exciting the thickness shear primary mode. The film thickness t4 (see FIG. 12) of the piezoelectric layer 20 according to the first embodiment is, for example, approximately 180 nm.

[0014] The IDT (Interdigital Transducer) electrode 30 is provided on the first main surface 20a of the piezoelectric layer 20. As shown in Figure 1, the IDT electrode 30 has electrode fingers 31 and 32 and busbar electrodes 33 and 34. Multiple electrode fingers 31 (first electrode fingers) extend in the Y direction, and one end in the extending direction is connected to the busbar electrode 33 (first busbar). Multiple electrode fingers 32 (second electrode fingers) extend in the Y direction, and the other end in the extending direction is connected to the busbar electrode 34 (second busbar). The multiple electrode fingers 31 and multiple electrode fingers 32 are arranged alternately in the X direction with a gap between them. The busbar electrode 33 and busbar electrode 34 each extend in the X direction and are spaced apart in the Y direction. Multiple electrode fingers 31 and 32 are arranged between the busbar electrode 33 and the busbar electrode 34. Furthermore, the IDT electrode 30 includes embodiments in which it is provided on at least one of the main surfaces of the first main surface 20a and the second main surface 20b of the piezoelectric layer 20. Also, "provided on the main surface side" includes embodiments in which it is provided directly or indirectly on the first main surface 20a or the second main surface 20b of the piezoelectric layer 20.

[0015] In the following explanation, the arrangement direction of the electrode fingers 31 and 32 may be described as the X direction, the extension direction of the electrode fingers 31 and 32 as the Y direction, and the thickness direction of the piezoelectric layer 20 as the Z direction. Also, in the following explanation, a plan view refers to the arrangement when viewed from a direction perpendicular to the first main surface 20a of the piezoelectric layer 20 (the Z direction).

[0016] The distance between the centers of adjacent electrode fingers 31 and 32 (hereinafter referred to as the electrode pitch) is preferably in the range of 1 μm to 10 μm. The electrode pitch is the distance between the center of the width dimension of electrode finger 31 in a direction perpendicular to the extending direction of electrode finger 31 and the center of the width dimension of electrode finger 32 in a direction perpendicular to the extending direction of electrode finger 32. The width of electrode fingers 31 and 32 (hereinafter referred to as the electrode width), that is, the dimension in the direction perpendicular to the extending direction of electrode fingers 31 and 32, is preferably in the range of 150 nm to 1000 nm.

[0017] Furthermore, if at least one of the electrode fingers 31 and electrode fingers 32 is multiple (i.e., if electrode fingers 31 and electrode fingers 32 are considered as a pair of electrode sets, there are 1.5 or more pairs of electrode sets), the electrode pitch of electrode fingers 31 and electrode fingers 32 refers to the average value of the distance between the centers of adjacent electrode fingers 31 and electrode fingers 32 among the 1.5 or more pairs of electrode fingers 31 and electrode fingers 32.

[0018] Furthermore, in the first embodiment, since a Z-cut piezoelectric layer is used, the direction perpendicular to the extending direction of electrode fingers 31 and 32 is perpendicular to the polarization direction of the piezoelectric layer 20. This does not apply when a piezoelectric material with a different cut angle is used as the piezoelectric layer 20. Here, "perpendicular" is not limited to strictly perpendicular, but may also be approximately perpendicular (for example, the angle between the direction perpendicular to the extending direction of electrode fingers 31 and 32 and the polarization direction is 90° ± 10°).

[0019] The IDT electrode 30 (electrode fingers 31, 32 and busbar electrodes 33, 34) is made of a suitable metal or alloy such as Al or AlCu alloy. In the first embodiment, the IDT electrode 30 has a structure in which an Al film is laminated on a titanium (Ti) film. However, an adhesion layer other than a Ti film may also be used.

[0020] More specifically, the electrode configuration of the IDT electrode 30 is a multilayer film of Ti / AlCu / Ti / AlCu from the piezoelectric layer 20 side, with respective film thicknesses of 12 nm / 70 nm / 18 nm / 12 nm. The IDT electrode 30 has a total of 51 electrode fingers 31 and 32. The electrode pitch between electrode fingers 31 and 32 is 2.38 μm, and the electrode width of each is 0.6 μm.

[0021] Here, the crossing region C (excitation region) shown in Figure 1 is the region where electrode fingers 31 and 32 overlap when viewed in the X direction. The length of the crossing region C is the dimension of electrode fingers 31 and 32 in the extending direction within the crossing region C. In this embodiment, the length of the crossing region C is, for example, 40 μm.

[0022] During operation, an AC voltage is applied between multiple electrode fingers 31 and multiple electrode fingers 32. More specifically, an AC voltage is applied between busbar electrode 33 and busbar electrode 34. This makes it possible to obtain resonance characteristics using the bulk wave of the thickness-slip first mode excited in the piezoelectric layer 20.

[0023] Furthermore, in the elastic wave apparatus 10, when the thickness of the piezoelectric layer 20 is d and the pitch between the multiple pairs of electrode fingers 31 and electrode fingers 32 is p, d / p is set to 0.5 or less. As a result, the bulk wave of the thickness-slip first mode is effectively excited, and good resonance characteristics can be obtained. More preferably, d / p is 0.24 or less, in which case even better resonance characteristics can be obtained.

[0024] In the elastic wave device 10 of the first embodiment, because it has the above configuration, even if the logarithm of electrode fingers 31 and 32 is reduced in an attempt to miniaturize it, a decrease in the Q value is unlikely to occur. This is because it is a resonator that does not require reflectors on both sides, resulting in low propagation loss. Furthermore, the reason why the above reflectors are not required is because it utilizes a bulk wave of the first-order mode of thickness sliding.

[0025] The first dielectric layer 41 is provided on the first main surface 20a of the piezoelectric layer 20, covering the IDT electrode 30. The second dielectric layer 42 is provided on the second main surface 20b of the piezoelectric layer 20. The first dielectric layer 41 and the second dielectric layer 42 are made of silicon oxide (SiO ｘ The first dielectric layer 41 and the second dielectric layer 42 are formed from silicon oxide, silicon nitride, alumina, or other suitable insulating materials. The thickness of the first dielectric layer 41 and the second dielectric layer 42 is greater than the thickness of the IDT electrode 30. The thickness of the first dielectric layer 41 and the second dielectric layer 42 is 142 nm each. Note that it is sufficient if at least one of the first dielectric layer 41 and the second dielectric layer 42 is provided. For example, a configuration in which the first dielectric layer 41 is provided and the second dielectric layer 42 is not provided is also possible.

[0026] Here, in the X direction (the extending direction of the bus bar electrode 33 and the bus bar electrode 34), a region that overlaps the electrode finger 31 or the electrode finger 32 and is located outside the IDT electrode 30 in the X direction (the extending direction of the bus bar electrode 33 and the bus bar electrode 34) is defined as the specific region E. Voids 51 and 52 are provided in the first dielectric layer 41 included in the specific region E.

[0027] The void 51 is provided outside the outermost electrode finger 31 (hereinafter referred to as the outermost electrode finger 31a) in the arrangement direction of the plurality of electrode fingers 31 and 32 among the plurality of electrode fingers 31 and 32. The void 51 is located between the outer edge on the left side of the first dielectric layer 41 and the outermost electrode finger 31a. Further, the void 52 is provided on the opposite side to the outermost electrode finger 31a, outside the outermost electrode finger 32 (hereinafter referred to as the outermost electrode finger 32a). The void 52 is located between the outer edge on the right side of the first dielectric layer 41 and the outermost electrode finger 32a.

[0028] As shown in FIG. 2, the voids 51 and 52 are each formed in a concave shape on the lower surface of the first dielectric layer 41 (the surface in contact with the first main surface 20a of the piezoelectric layer 20). Each of the voids 51 and 52 is a space surrounded by the first main surface 20a of the piezoelectric layer 20 and the first dielectric layer 41. Further, in a plan view, the void 51 extends in the Y direction along the electrode finger 31 (the outermost electrode finger 31a). The void 52 extends in the Y direction along the electrode finger 32 (the outermost electrode finger 32a). The detailed configuration of the voids 51 and 52 will be described later with reference to FIGS. 12 and 13.

[0029] The supporting substrate 11 (supporting member) is disposed to face the second main surface 20b of the piezoelectric layer 20. The supporting substrate 11 has a cavity portion 14 (space portion) on the surface facing the second main surface 20b of the piezoelectric layer 20. More specifically, the supporting substrate 11 includes a bottom portion 12 and a wall portion 13 provided in a frame shape on the upper surface of the bottom portion 12. The cavity portion 14 is formed in the space surrounded by the bottom portion 12 and the wall portion 13. The piezoelectric layer 20 is laminated on the upper surface of the wall portion 13 of the supporting substrate 11 via the second dielectric layer 42. As described above, the elastic wave device 10 has a so-called membrane structure in which the cavity portion 14 (hollow portion) is provided on the second main surface 20b side of the piezoelectric layer 20.

[0030] Note that the support member may include a support substrate 11 and an intermediate (insulating) layer. That is, the support substrate 11 may be indirectly laminated on the second main surface 20b of the piezoelectric layer 20. In this case, the support substrate 11 and the intermediate layer may have a frame shape, and the cavity portion 14 may be formed thereby. Alternatively, a recess may be provided in the intermediate layer, and the cavity portion 14 may be formed thereby.

[0031] The cavity portion 14 is provided so as not to hinder the vibration of the intersecting region C of the piezoelectric layer 20. Note that the second dielectric layer 42 is provided to cover the opening of the cavity portion 14. However, as described above, the second dielectric layer 42 may not be provided. In this case, the support substrate 11 can be directly laminated on the second main surface 20b of the piezoelectric layer 20. Alternatively, the second dielectric layer 42 may be provided in the region between the upper surface of the wall portion 13 and the second main surface 20b of the piezoelectric layer 20, and may not be provided in the region overlapping the cavity portion 14.

[0032] The support substrate 11 is formed of silicon (Si). The plane orientation of the surface of Si on the piezoelectric layer 20 side may be (100), (110), or (111). High-resistance Si with a resistivity of 4 kΩ or more is preferable. However, the support substrate 11 can also be configured using an appropriate insulating material or semiconductor material. Examples of materials for the support substrate 11 include piezoelectrics such as aluminum oxide, lithium tantalate, lithium niobate, and quartz; various ceramics such as alumina, magnesia, sapphire, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, steatite, and forsterite; dielectrics such as diamond and glass; and semiconductors such as gallium nitride, any of which can be used.

[0033] FIG. 3 is a schematic cross-sectional view for explaining bulk waves in the first-order thickness-shear mode propagating through the piezoelectric layer of the first embodiment. FIG. 4 is a schematic cross-sectional view for explaining the amplitude direction of bulk waves in the first-order thickness-shear mode propagating through the piezoelectric layer of the first embodiment.

[0034] As shown in Figure 3, in the elastic wave device 10 of the first embodiment, since the vibration displacement is in the thickness sliding direction, the wave propagates almost entirely in the direction connecting the first main surface 20a and the second main surface 20b of the piezoelectric layer 20, i.e., in the Z direction, and resonates. That is, the X-direction component of the wave is significantly smaller than the Z-direction component. And since the resonance characteristics are obtained by the propagation of this Z-direction wave, a reflector is not required. Therefore, no propagation loss occurs when the wave propagates to the reflector. Accordingly, even if the number of electrode pairs consisting of electrode fingers 31 and electrode fingers 32 is reduced in an attempt to miniaturize the device, a decrease in the Q value is unlikely to occur.

[0035] Furthermore, as shown in Figure 4, the amplitude direction of the bulk wave in the first-order thickness-slip mode is reversed between the first region 251, which is included in the intersection region C (see Figure 1) of the piezoelectric layer 20, and the second region 252, which is also included in the intersection region C. Figure 4 schematically shows the bulk wave when a voltage is applied between electrode finger 31 and electrode finger 32 such that electrode finger 32 is at a higher potential than electrode finger 31. Here, the virtual plane VP1 is a plane that is perpendicular to the thickness direction of the piezoelectric layer 20 and divides the piezoelectric layer 20 in two. The first region 251 is the region between the virtual plane VP1 and the first main surface 20a within the intersection region C. The second region 252 is the region between the virtual plane VP1 and the second main surface 20b within the intersection region C.

[0036] In the elastic wave device 10, at least one pair of electrodes, consisting of electrode finger 31 and electrode finger 32, are arranged. However, since waves are not propagated in the X direction, it is not necessarily required that there be multiple pairs of these electrode fingers 31 and 32. In other words, it is sufficient that at least one pair of electrodes is provided.

[0037] For example, electrode finger 31 is an electrode connected to a hot potential, and electrode finger 32 is an electrode connected to a ground potential. However, electrode finger 31 may be connected to a ground potential and electrode finger 32 may be connected to a hot potential. In the first embodiment, at least one pair of electrodes are, as described above, electrodes connected to a hot potential or electrodes connected to a ground potential, and no floating electrodes are provided.

[0038] Figure 5 is an explanatory diagram showing an example of the resonance characteristics of the elastic wave apparatus of the first embodiment. The design parameters of the elastic wave apparatus 10 that obtained the resonance characteristics shown in Figure 5 are as follows.

[0039] Piezoelectric layer 20: LiNbO with Euler angles (0°, 0°, 90°) ３ Thickness of piezoelectric layer 20: 400 nm

[0040] Length of crossover region C: 40 μm Number of electrode pairs consisting of electrode fingers 31 and 32: 21 Pitch between electrode fingers 31 and 32: 3 μm Width of electrode fingers 31 and 32: 500 nm d / p: 0.133

[0041] First dielectric layer 41, second dielectric layer 42: silicon oxide film with a thickness of 1 μm

[0042] Support substrate 11: Si

[0043] In the first embodiment, the electrode spacing between electrode pairs, consisting of electrode fingers 31 and 32, was made equal in all pairs. That is, electrode fingers 31 and 32 were arranged at equal pitches.

[0044] As is clear from Figure 5, good resonance characteristics with a relative bandwidth of 12.5% ​​are obtained despite the absence of a reflector.

[0045] By the way, if the thickness of the piezoelectric layer 20 is d and the pitch between electrode fingers 31 and 32 is p, then in the first embodiment, d / p is 0.5 or less, more preferably 0.24 or less. This will be explained with reference to Figure 6.

[0046] Figure 6 is an explanatory diagram showing the relationship between d / 2p and the specific bandwidth of the resonator in the elastic wave apparatus of the first embodiment, where p is the distance between the centers of adjacent electrodes or the average distance between the centers, and d is the average thickness of the piezoelectric layer. In Figure 6, multiple elastic wave apparatuses were obtained in the same manner as the elastic wave apparatus that obtained the resonance characteristics shown in Figure 5, but by changing d / 2p.

[0047] As shown in Figure 6, when d / 2p exceeds 0.25, i.e., d / p > 0.5, the relative bandwidth is less than 5% even when d / p is adjusted. In contrast, when d / 2p ≤ 0.25, i.e., d / p ≤ 0.5, the relative bandwidth can be increased to 5% or more by changing d / p within that range, i.e., a resonator with a high coupling coefficient can be constructed. Furthermore, when d / 2p is 0.12 or less, i.e., when d / p is 0.24 or less, the relative bandwidth can be increased to 7% or more. In addition, by adjusting d / p within this range, a resonator with an even wider relative bandwidth can be obtained, and a resonator with an even higher coupling coefficient can be realized. Therefore, it can be seen that by setting d / p to 0.5 or less, a resonator with a high coupling coefficient can be constructed using the bulk wave of the thickness-slip first mode described above.

[0048] Regarding the thickness d of the piezoelectric layer 20, if the piezoelectric layer 20 has variations in thickness, the average value of its thickness should be used.

[0049] Figure 7 is a plan view showing an example in which a pair of electrodes is provided in the elastic wave apparatus of the first embodiment. In the elastic wave apparatus 10, a pair of electrodes having electrode fingers 31 and electrode fingers 32 are provided on the first main surface 20a of the piezoelectric layer 20. In Figure 7, K is the crossover width. As described above, in the elastic wave apparatus 10 of this disclosure, the number of electrode pairs may be one. Even in this case, if the above d / p is 0.5 or less, the bulk wave of the thickness-slip first mode can be effectively excited.

[0050] In the elastic wave apparatus 10, it is preferable that the metallization ratio MR of the adjacent electrode fingers 31 and 32 with respect to the crossing region C satisfies MR ≤ 1.75 (d / p) + 0.075. In this case, spurious emissions can be effectively reduced. This will be explained with reference to Figures 8 and 9.

[0051] Figure 8 is a reference diagram showing an example of the resonance characteristics of the elastic wave apparatus of the first embodiment. As shown in Figure 8, the spurious signal indicated by arrow B appears between the resonant frequency and the anti-resonant frequency. Note that d / p = 0.08 and LiNbO ３The Euler angles were set to 0°, 0°, and 90°. Furthermore, the metallization ratio MR was set to 0.35.

[0052] The metallization ratio MR will be explained with reference to Figure 1. In the electrode structure of Figure 1, if we focus on a pair of electrode fingers 31 and 32, we assume that only this pair of electrode fingers 31 and 32 are provided. In this case, the area enclosed by the dashed line becomes the intersection region C. This intersection region C is the area on electrode finger 31 that overlaps with electrode finger 32 when viewed in a direction perpendicular to the extending direction of electrode fingers 31 and 32, i.e., in the opposing direction, the area on electrode finger 31 that overlaps with electrode finger 32, the area on electrode finger 32 that overlaps with electrode finger 31, and the area between electrode finger 31 and electrode finger 32 that overlaps. The area of ​​electrode fingers 31 and 32 within the intersection region C relative to the area of ​​the intersection 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 intersection region C.

[0053] Furthermore, if multiple pairs of electrode fingers 31 and electrode fingers 32 are provided, the ratio of the metallized portion included in all intersection regions C to the total area of ​​the intersection regions C should be defined as MR.

[0054] Figure 9 is an explanatory diagram showing the relationship between the relative bandwidth of the elastic wave device of the first embodiment, when a large number of elastic wave resonators are configured, and the phase rotation amount of the spurious impedance normalized by 180 degrees as the spurious magnitude. The relative bandwidth was adjusted by changing various aspects of the thickness of the piezoelectric layer 20 and the dimensions of the electrode fingers 31 and 32. Also, Figure 9 shows the Z-cut LiNbO ３ The results shown are for the case where a piezoelectric layer 20 consisting of the above is used, but a similar trend is observed when piezoelectric layers 20 with other cut angles are used.

[0055] In the region enclosed by the ellipse J in Figure 9, the spurious emission is large at 1.0. As is clear from Figure 9, when the relative bandwidth exceeds 0.17, that is, when it exceeds 17%, large spurious emissions with a spurious emission level of 1 or more appear within the passband, even if the parameters constituting the relative bandwidth are changed. In other words, as shown in the resonance characteristics in Figure 8, large spurious emissions indicated by arrow B appear within the bandwidth. Therefore, it is preferable that the relative bandwidth be 17% or less. In this case, spurious emissions can be reduced by adjusting the film thickness of the piezoelectric layer 20 and the dimensions of the electrode fingers 31 and 32.

[0056] Figure 10 is an explanatory diagram showing the relationship between d / 2p, the metallization ratio MR, and the relative bandwidth. In the elastic wave apparatus 10 of the first embodiment, various elastic wave apparatuses 10 with different d / 2p and MR were configured, and the relative bandwidth was measured. The hatched area to the right of the dashed line D in Figure 10 is the region where the relative bandwidth is 17% or less. The boundary between this hatched region and the unhatched region is represented by MR = 3.5(d / 2p) + 0.075. That is, MR = 1.75(d / p) + 0.075. Therefore, preferably, MR ≤ 1.75(d / p) + 0.075. In that case, it is easy to keep the relative bandwidth at 17% or less. More preferably, it is the region to the right of MR = 3.5(d / 2p) + 0.05, shown by the dashed line D1 in Figure 10. In other words, if MR ≤ 1.75 (d / p) + 0.05, the relative bandwidth can be reliably reduced to 17% or less.

[0057] Figure 11 shows LiNbO when d / p approaches 0. ３ This is an explanatory diagram showing the relative bandwidth map for Euler angles (0°, θ, ψ). The hatched area in Figure 11 is the region where a relative bandwidth of at least 5% is obtained. Approximating the range of this region, it is the range expressed by the following equations (1), (2), and (3).

[0058] (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°(1-(θ-50) ２ / 900) １／２ ]~180°) ...Formula (2) (0°±10°, [180°-30°(1-(ψ-90) ２ ( / 8100) １／２ ] ~180°, any ψ) ...Equation (3)

[0059] Therefore, in the case of the Euler angle range of equation (1), equation (2), or equation (3) above, the relative bandwidth can be made sufficiently wide, which is preferable.

[0060] Next, the detailed configuration of the gap 51 will be described. Figure 12 is an enlarged cross-sectional view of region A shown in Figure 2. In Figure 12, the gap 51 adjacent to the outermost electrode finger 31a, which is located in the direction of the arrangement of the multiple electrode fingers 31 and 32, will be described. However, the gap 52 (see Figures 1 and 2) adjacent to the outermost electrode finger 32a, which is located on the opposite side from the outermost electrode finger 31a, also has a symmetrical arrangement with respect to the gap 51. The description of the gap 51 can also be applied to the gap 52.

[0061] As shown in Figure 12, the void 51 is a recess provided on the lower surface of the first dielectric layer 41 and is in contact with the side surface of the electrode finger 31 (outermost electrode finger 31a). More specifically, the void 51 is a space enclosed by the first dielectric layer 41, the first main surface 20a of the flatly formed piezoelectric layer 20, and the side surface of the electrode finger 31 (outermost electrode finger 31a). One side surface of the void 51 is formed by the first dielectric layer 41, and the other side surface of the void 51 is formed by the electrode finger 31 (outermost electrode finger 31a). A stepped portion of the first dielectric layer 41 is formed on one side surface of the void 51 (the left side surface in Figure 12).

[0062] The width W1 of the gap 51 in the X direction is smaller than the width of the electrode finger 31 (outermost electrode finger 31a) in the X direction. The width W1 of the gap 51 in the X direction is, for example, 0.3 μm. As described above, the width of the electrode finger 31 (outermost electrode finger 31a) in the X direction is, for example, 0.6 μm. The height of the gap 51 (i.e., the distance between the first dielectric layer 41 and the piezoelectric layer 20 in the Z direction) is, for example, 0.06 μm.

[0063] Furthermore, the film thickness t1 of the first dielectric layer 41 and the film thickness t2 of the second dielectric layer 42 are 142 nm, and the film thickness t4 of the piezoelectric layer 20 is 180 nm. Also, the film thickness t3 of the IDT electrode 30 is 112 nm. The film thickness t1 of the first dielectric layer 41 is thicker than the height of the void 51 and is thicker than the film thickness t3 of the IDT electrode 30.

[0064] The void 51 can be formed, for example, by the following method. A sacrificial layer is formed on the piezoelectric layer 20 using, for example, zinc oxide (ZnO), and patterned so as to be in contact with the electrode finger 31 (outermost electrode finger 31a). After that, the first dielectric layer 41 is formed over the sacrificial layer, and then the sacrificial layer is removed. As a result, the void 51 is formed in the region of the first dielectric layer 41 where the sacrificial layer has been removed.

[0065] As described above, since the air gap 51 is provided in contact with the electrode finger 31 (outermost electrode finger 31a), in a specific region E (see Figure 1) outside the IDT electrode 30 in the arrangement direction (X direction) of the multiple electrode fingers 31 and 32, the region where the air gap 51 is provided in the first dielectric layer 41 has a different acoustic impedance than the region where the air gap 51 is not provided and the first dielectric layer 41 and the piezoelectric layer 20 are stacked in contact. As a result, an acoustic reflection surface is formed on the side surface of the air gap 51 (the left side surface in Figure 12).

[0066] As a result, the elastic waves excited by the piezoelectric layer 20 are reflected by the acoustic reflection surface, so the elastic wave device 10 can suppress the leakage of elastic waves in the direction of the arrangement of the multiple electrode fingers 31 and 32.

[0067] Figure 13 is an explanatory diagram showing an example of the admittance characteristics of the elastic wave apparatus according to the first embodiment. More specifically, Figure 13 is an explanatory diagram showing the actual admittance, i.e., the conductance component, of the elastic wave apparatus according to the first embodiment. The admittance characteristics shown in Figure 13 represent the simulation results of the admittance characteristics of the elastic wave apparatus 10 according to the first embodiment. Figure 13 also shows the simulation results of the admittance characteristics of an elastic wave apparatus according to a comparative example. The comparative example is an elastic wave apparatus that does not have the air gap 51 compared to the first embodiment.

[0068] As shown in Figure 13, in the comparative example elastic wave apparatus, ripple occurs in a frequency range different from the resonant frequency. In particular, large ripples are generated in the comparative example, as shown by the dotted lines F1 and F2. In contrast, in the elastic wave apparatus 10 according to the first embodiment, it was shown that the ripples shown by the dotted lines F1 and F2 are suppressed compared to the comparative example by providing the air gap 51.

[0069] Figure 14 is an explanatory diagram showing the distribution of vibration modes of the elastic wave apparatus according to the first embodiment. Figure 15 is an explanatory diagram showing the distribution of vibration modes of the elastic wave apparatus according to a comparative example. In Figures 14 and 15, for the first embodiment and the comparative example, the distribution of the magnitude of displacement of the piezoelectric layer 20 is shown with the horizontal axis in the X direction (arrangement direction of electrode fingers 31 and 32) and the vertical axis in the frequency. The upper figures of Figures 14 and 15 schematically show cross-sectional views of the elastic wave apparatus corresponding to the X direction, and the left figures of Figures 14 and 15 show the impedance characteristics of the elastic wave apparatus.

[0070] As shown in Figure 15, in the elastic wave apparatus of the comparative example, the X-direction dependence of the displacement (the X-direction positions of the antinodes and nodes of the displacement) has a large frequency dependence. For example, the X-direction position showing the displacement peak shifts with frequency, indicating that the electrodes are not stably excited. Furthermore, focusing on a predetermined X-position (near X = 5.0 μm), the phase is inverted at the resonant frequency of 5030 MHz and at the ripple frequencies of 4900 MHz and 5120 MHz. Thus, in the elastic wave apparatus of the comparative example, an ideal excitation mode may not be obtained.

[0071] In contrast, as shown in Figure 14, the elastic wave apparatus 10 according to the first embodiment does not exhibit frequency dependence of the displacement in the X direction (the X-direction positions of the antinodes and nodes of the displacement). That is, the X-direction position showing the displacement peak is constant regardless of frequency, indicating that the electrodes are stably excited. Furthermore, the magnitude (amplitude) of the displacement is also constant for each region between the electrodes, and no phase inversion occurs at the resonant frequency or the frequency array where ripple occurs. Thus, the elastic wave apparatus 10 according to the first embodiment demonstrates that a better excitation mode can be obtained compared to the comparative example by providing an air gap 51 in the first dielectric layer 41 in a specific region E (see Figure 1) outside the IDT electrode 30 in the X direction.

[0072] The shapes, widths, and film thicknesses of the void 51, the first dielectric layer 41, and the IDT electrode 30 described above are merely examples and can be modified as appropriate. For example, the IDT electrode 30 is not limited to being provided on the first main surface 20a of the piezoelectric layer 20, but may also be provided on the second main surface 20b of the piezoelectric layer 20. The IDT electrode 30 is not limited to being provided in direct contact with the first main surface 20a or the second main surface 20b of the piezoelectric layer 20, but may also be provided indirectly via another layer.

[0073] Furthermore, the void 51 is not limited to being provided in the first dielectric layer 41, but may be provided in at least a part of the piezoelectric layer 20 and dielectric layers (first dielectric layer 41 and second dielectric layer 42) included in the specific region E. The left side of the void 51 in Figure 12 may be tapered. The void 51 and void 52 shown in Figure 1 may have the same width and height. Alternatively, the void 51 and void 52 may have different widths and different film thicknesses, for example, due to variations in the manufacturing process.

[0074] (First Modified Example) Figure 16 is a cross-sectional view showing an elastic wave apparatus according to the first modified example. As shown in Figure 16, the elastic wave apparatus 10A according to the first modified example differs from the first embodiment described above in that a gap 51 is provided in the piezoelectric layer 20 and the first dielectric layer 41.

[0075] More specifically, the void 51 is a space enclosed by a recess provided on the lower surface of the first dielectric layer 41 and a recess 20c provided on the first main surface 20a of the piezoelectric layer 20. In this modified example as well, the void 51 is in contact with the side surface of the electrode finger 31 (outermost electrode finger 31a). One side surface of the void 51 is formed by the first dielectric layer 41 and the piezoelectric layer 20, and the other side surface of the void 51 is formed by the electrode finger 31 (outermost electrode finger 31a) and the piezoelectric layer 20. Steps are formed on the side surface of the void 51 (for example, the left side surface in Figure 16) in both the piezoelectric layer 20 and the first dielectric layer 41.

[0076] In a specific region E (see Figure 1) outside the IDT electrode 30 in the X direction, the region where a gap 51 is provided between the piezoelectric layer 20 and the first dielectric layer 41 has a different acoustic impedance than the region where the gap 51 is not provided and the first dielectric layer 41 and the piezoelectric layer 20 are stacked in contact. As a result, an acoustic reflection surface is formed on the side surface of the gap 51 (the left side surface in Figure 16).

[0077] (Second Modification) Figure 17 is a cross-sectional view showing an elastic wave apparatus according to the second modification. As shown in Figure 17, the elastic wave apparatus 10B according to the second modification differs from the first embodiment and the first modification described above in that the first dielectric layer 41 does not have a void 51, while the piezoelectric layer 20 has a void 51.

[0078] More specifically, the void 51 is a space enclosed by the flat lower surface of the first dielectric layer 41 and the recess 20c provided in the piezoelectric layer 20. In this modified example, the upper end of the side surface of the void 51 (the right side surface in Figure 17) is in contact with the lower end of the side surface of the electrode finger 31 (the outermost electrode finger 31a). In the second modified example, both the side surface of the void 51 and the other side surface are formed of the piezoelectric layer 20.

[0079] In a specific region E (see Figure 1) outside the IDT electrode 30 in the X direction, the region where a gap 51 is provided in the piezoelectric layer 20 has a different acoustic impedance than the region where the gap 51 is not provided and the first dielectric layer 41 and the piezoelectric layer 20 are stacked in contact. As a result, acoustic reflection surfaces are formed on one side and the other side of the gap 51.

[0080] (Second Embodiment) Figure 18 is a cross-sectional view showing an elastic wave apparatus according to the second embodiment. As shown in Figure 18, unlike the first embodiment and its various modifications described above, the elastic wave apparatus 10C according to the second embodiment has a gap 51 positioned between a part of the outermost electrode finger 31 (outermost electrode finger 31a) among the plurality of electrode fingers 31 and plurality of electrode fingers 32 in the Z direction and the piezoelectric layer 20. In addition, in the second embodiment, a protrusion is formed in a part of the first dielectric layer 41 (the region overlapping with the gap 51).

[0081] More specifically, the void 51 extends from the region between a part of the electrode finger 31 (outermost electrode finger 31a) and the piezoelectric layer 20 to the region of the first dielectric layer 41 that is outside the side surface of the electrode finger 31 (outermost electrode finger 31a) (specific region E (see Figure 1)). In other words, the void 51 is provided across the portion where the first dielectric layer 41 and the electrode finger 31 (outermost electrode finger 31a) overlap, and the portion where the first dielectric layer 41 overlaps but the electrode finger 31 (outermost electrode finger 31a) does not overlap.

[0082] In the second embodiment, the void 51 is a space surrounded by a recess formed on the lower surface of the first dielectric layer 41 and the electrode finger 31 (outermost electrode finger 31a), and the first main surface 20a of the flatly formed piezoelectric layer 20. One side of the void 51 is formed by the first dielectric layer 41, and the other side of the void 51 is formed by the electrode finger 31 (outermost electrode finger 31a).

[0083] The width W1 in the X direction of the portion of the gap 51 that does not overlap with the electrode finger 31 (outermost electrode finger 31a) is, for example, 0.3 μm. The width W2 in the X direction of the portion of the gap 51 that overlaps with the electrode finger 31 (outermost electrode finger 31a) is, for example, 0.3 μm. The width of the electrode finger 31 (outermost electrode finger 31a) in the X direction is, for example, 0.6 μm.

[0084] Figure 19 is an explanatory diagram showing an example of the admittance characteristics of the elastic wave apparatus according to the second embodiment. As shown in Figure 19, in the elastic wave apparatus 10C according to the second embodiment, even when the air gap 51 is arranged between a part of the electrode finger 31 (outermost electrode finger 31a) and the piezoelectric layer 20 in the Z direction, it is shown that the ripple shown by the dotted lines F1 and F2 is suppressed compared to the comparative example.

[0085] (Third Embodiment) Figure 20 is a cross-sectional view showing an elastic wave apparatus according to the third embodiment. As shown in Figure 20, unlike the first embodiment, the second embodiment and each of the modifications described above, the elastic wave apparatus 10D according to the third embodiment has the gap 51 positioned at a distance from the outermost electrode finger 31 (outermost electrode finger 31a) among the plurality of electrode fingers 31 and plurality of electrode fingers 32.

[0086] The void 51 is a space enclosed by a recess formed on the lower surface of the first dielectric layer 41 and the first main surface 20a of the flat piezoelectric layer 20. One side and the other side of the void 51 are formed by the first dielectric layer 41.

[0087] The distance SP is defined as the distance between the gap 51 and the electrode finger 31 adjacent to the gap 51 (the outermost electrode finger 31a). Distance SP is the shortest distance between the outermost electrode finger 31a and the gap 51. Distance SP is less than or equal to the electrode pitch p between adjacent electrode fingers 31 and electrode fingers 32. As described above, the electrode pitch p is the distance between the centers of adjacent electrode fingers 31 and electrode fingers 32, or the average of the distances between their centers. For example, the electrode pitch p is 2.38 μm. In this case, the distance SP between the gap 51 and the electrode finger 31 (the outermost electrode finger 31a) is 2.38 μm or less.

[0088] Figure 21 is an explanatory diagram showing an example of the admittance characteristics of the elastic wave apparatus according to the third embodiment. As shown in Figure 21, even in the elastic wave apparatus 10D according to the third embodiment, even when the air gap 51 is arranged at a distance from the electrode finger 31 (outermost electrode finger 31a), it is shown that the ripple, at least as shown by the dotted line F2, is suppressed compared to the comparative example.

[0089] Figure 22 is an explanatory diagram showing the relationship between the distance between the air gap and the electrode fingers (SP), the ratio of the electrode pitch (p) (SP / p), and the real part of admittance in an elastic wave apparatus according to the third embodiment. The vertical axis of the graph in Figure 22 represents the real part of admittance at the ripple frequency shown by the dotted line F2 in Figure 21. The horizontal axis of the graph in Figure 22 represents the ratio (SP / p).

[0090] As shown in Figure 22, the admittance portion decreases as the ratio (SP / p) decreases. More specifically, for example, if the electrode pitch p is kept constant, the admittance portion can be reduced by reducing the distance SP between the air gap 51 and the electrode finger 31 (outermost electrode finger 31a). As shown by arrow G in Figure 22, the admittance portion can be effectively suppressed by setting the ratio (SP / p) to 1.0 or less. That is, it has been shown that the ripple shown by the dotted line F2 in Figure 21 can be suppressed by setting the ratio (SP / p) to 1.0 or less. More preferably, the admittance portion can be effectively suppressed by setting the ratio (SP / p) to 0.4 or less.

[0091] Furthermore, the third embodiment can be combined with the first or second modified example described above. That is, in the third embodiment, the void 51 is not limited to being provided in the first dielectric layer 41, but may be provided in at least a part of the piezoelectric layer 20 and dielectric layers (first dielectric layer 41 and second dielectric layer 42) included in the specific region E.

[0092] (Fourth Embodiment) Figure 23 is a cross-sectional view showing an elastic wave apparatus according to the fourth embodiment. As shown in Figure 23, the elastic wave apparatus 10E according to the fourth embodiment differs from the first to third embodiments and their respective modifications described above in that the void 51 includes a first portion 51a and a second portion 51b.

[0093] The first portion 51a is a recess formed on the lower surface of the first dielectric layer 41 included in a specific region E (see Figure 1), and extends along the surface (first main surface 20a) of the piezoelectric layer 20. The second portion 51b is continuous with the first portion 51a and extends in the thickness direction of the first dielectric layer 41. The upper end of the second portion 51b opens onto the upper surface of the first dielectric layer 41, and the lower end of the second portion 51b is connected to the left end of the first portion 51a. Note that the upper end of the second portion 51b does not necessarily have to be open.

[0094] In other words, the first dielectric layer 41 in the portion overlapping with the void 51 has a cantilever structure.

[0095] In the fourth embodiment, the gap 51 (first portion 51a) is positioned at a distance from the electrode finger 31 (outermost electrode finger 31a). However, it is not limited to this. The gap 51 (first portion 51a) may be in contact with the electrode finger 31 (outermost electrode finger 31a).

[0096] Figure 24 is an explanatory diagram showing an example of the admittance characteristics of the elastic wave apparatus according to the fourth embodiment. As shown in Figure 24, even in the elastic wave apparatus 10E according to the fourth embodiment, where the air gap 51 has a configuration having a first portion 51a and a second portion 51b, it is shown that the ripple shown by the dotted lines F1 and F2 is suppressed compared to the comparative example.

[0097] (Third Modification) Figure 25 is a cross-sectional view showing an elastic wave apparatus according to the third modification. As shown in Figure 25, the elastic wave apparatus 10F according to the third modification differs from the fourth embodiment described above in that the first portion 51a of the gap 51 is positioned between a part of the electrode finger 31 (outermost electrode finger 31a) and the piezoelectric layer 20 in the Z direction.

[0098] Similar to the fourth embodiment described above, the void 51 includes a first portion 51a and a second portion 51b provided in the first dielectric layer 41 included in a specific region E (see Figure 1). In the third modified example, the first portion 51a is formed to extend to the portion overlapping with the electrode finger 31 (outermost electrode finger 31a). In other words, the elastic wave device 10F according to the third modified example is a configuration that combines the fourth embodiment and the second embodiment described above.

[0099] However, the fourth embodiment may be appropriately combined with each of the embodiments and modifications described above. For example, in the fourth embodiment (Figure 23), the first portion 51a of the gap 51 may be in contact with the electrode finger 31 (outermost electrode finger 31a), similar to the first embodiment. The first portion 51a of the gap 51 is not limited to being provided in the first dielectric layer 41, but may be provided in at least a part of the piezoelectric layer 20 and dielectric layers (first dielectric layer 41 and second dielectric layer 42) included in the specific region E.

[0100] (Fifth Embodiment) Figure 26 is a cross-sectional view showing an elastic wave apparatus according to the fifth embodiment. As shown in Figure 26, the elastic wave apparatus 10G according to the fifth embodiment differs from the first embodiment described above in that, instead of a cavity portion 14 provided on the support substrate 11, an acoustic multilayer film 43 is laminated on the second main surface 20b of the piezoelectric layer 20.

[0101] The acoustic multilayer film 43 has a laminated structure consisting of low acoustic impedance layers 43a, 43c, and 43e (second layer) with relatively low acoustic impedance, and high acoustic impedance layers 43b and 43d (first layer) with relatively high acoustic impedance. The acoustic impedance of the high acoustic impedance layers 43b and 43d is higher than the acoustic impedance of the low acoustic impedance layers 43a, 43c, and 43e.

[0102] The materials of the high acoustic impedance layers 43b and 43d are different from the materials of the low acoustic impedance layers 43a, 43c, and 43e.

[0103] Specifically, the high acoustic impedance layers 43b and 43d are made of tungsten carbide (WC), tantalum carbide (TaC), and rhenium oxide (ReO). ３ ), carbon silicon chromium (CrCSI), niobium carbide (NbC), zinc carbide (ZrC), zinc nitride (TiC), lanthanum boride (LaB ６ ), vanadium carbide (VC), aluminum nitride (AlN), silicon carbide (SiC), yttrium oxide (Y ２ O ３ ), magnesium oxide (MgO), silicon nitride (Si ３ N ４ ), boron carbide (B ４ C), Strontium fluoride (SrF ２ ), barium fluoride (BaF ２ ), tantalum oxide (Ta ２ O ５ ), hafnium oxide (HfO ２ ), tungsten oxide (WO ３ ), hafnium nitride (HfN), tungsten nitride (WN), ytterbium oxide (Yb ２ O ３It contains at least one of the following: platinum (Pt), tungsten (W), copper (Cu), gold (Au), and silver (Ag).

[0104] The low acoustic impedance layers 43a, 43c, and 43e are made of silicon dioxide (SiO₂). ｘ ) and at least one of aluminum (Al).

[0105] When the acoustic multilayer film 43 is used, the bulk wave of the first-order thickness-slip mode can be confined within the piezoelectric layer 20 without using the cavity portion 14. Furthermore, in the elastic wave device 10G, by setting the d / p to 0.5 or less, resonance characteristics based on the bulk wave of the first-order thickness-slip mode can be obtained.

[0106] The acoustic multilayer film 43 shown in the fifth embodiment can be combined with the embodiments and modifications described above.

[0107] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. The present invention may be modified or improved without departing from its spirit, and equivalents thereof are also included.

[0108] 10, 10A, 10B, 10C, 10D, 10E, 10F, 10G Elastic wave device 11 Support substrate 12 Bottom 13 Wall 14 Cavity 20 Piezoelectric layer 20a First main surface 20b Second main surface 30 IDT electrodes 31, 32 Electrode fingers 31a, 32a Outermost electrode fingers 33, 34 Busbar electrodes 41 First dielectric layer 42 Second dielectric layer 43 Acoustic multilayer film 43a, 43c, 43e Low acoustic impedance layer 43b, 43d High acoustic impedance layer 51, 52 Gap

Claims

1. A piezoelectric layer having a first main surface and a second main surface opposite to the first main surface; an IDT electrode provided on at least one of the main surfaces of the first and second main surfaces of the piezoelectric layer; a dielectric layer provided on at least one of the main surfaces of the first and second main surfaces of the piezoelectric layer; and a support member provided on the second main surface side of the piezoelectric layer, wherein the IDT electrode has a first busbar facing each other, a second busbar, at least one first electrode finger whose base end is connected to the first busbar, and at least one second electrode finger whose base end is connected to the second busbar; the support member has an acoustic reflecting portion on the second main surface side; when the thickness of the piezoelectric layer is d and the average distance between the centers of adjacent first and second electrode fingers is p, d / p is 0.5 or less; and in a plan view from the thickness direction of the piezoelectric layer, the piezoelectric layer and the dielectric layer overlap in at least a portion. An elastic wave apparatus wherein, in the extending direction of the first busbar and the second busbar, the first electrode finger or the second electrode finger overlaps with the first electrode finger, and when the region outside the IDT electrode in the extending direction of the first busbar and the second busbar is designated as a specific region, a gap is provided in at least a portion of the piezoelectric layer and the dielectric layer included in the specific region.

2. The elastic wave apparatus according to claim 1, wherein the gap is in contact with the first electrode finger or the second electrode finger, which is the outermost of the first and second electrode fingers in the direction of extension of the first and second busbars.

3. The elastic wave apparatus according to claim 1, wherein the gap is not in contact with the first electrode finger or the second electrode finger that is located furthest outward in the extending direction of the first busbar and the second busbar.

4. The elastic wave apparatus according to claim 1, wherein, among the first electrode finger and the second electrode finger, the first electrode finger or the second electrode finger located furthest out in the extending direction of the first busbar and the second busbar is designated as the outermost electrode finger, and the gap is arranged between a part of the outermost electrode finger and the piezoelectric layer in the thickness direction of the piezoelectric layer.

5. The elastic wave apparatus according to claim 1, wherein the gap is provided in the piezoelectric layer.

6. The elastic wave apparatus according to claim 1, wherein the void is provided in the dielectric layer included in the specific region and includes a first portion extending along the surface of the piezoelectric layer and a second portion continuous with the first portion and extending in the thickness direction of the dielectric layer.

7. The elastic wave apparatus according to claim 3, wherein the distance between the gap and the first electrode finger or second electrode finger adjacent to the gap is less than or equal to the average distance between the centers of adjacent first electrode fingers and second electrode fingers.

8. The acoustic wave apparatus according to any one of claims 1 to 7, wherein the acoustic reflection portion is a cavity provided in the support member.

9. The acoustic wave apparatus according to any one of claims 1 to 7, wherein the acoustic reflection portion is an acoustic multilayer film comprising a first layer and a second layer, and the material of the first layer is different from the material of the second layer.

10. The elastic wave apparatus according to claim 9, wherein the acoustic impedance of the first layer is higher than the acoustic impedance of the second layer.

11. The elastic wave apparatus according to claim 9, wherein the first layer comprises at least one of tungsten carbide, tantalum carbide, rhenium oxide, silicon chromium carbon, niobium carbide, zinc carbide, zinc nitride, lanthanum boride, vanadium carbide, aluminum nitride, silicon carbide, yttrium oxide, magnesium oxide, silicon nitride, boron carbide, strontium fluoride, barium fluoride, tantalum oxide, hafnium oxide, tungsten oxide, hafnium nitride, tungsten nitride, ytterbium oxide, platinum, tungsten, copper, gold, and silver, and the second layer comprises at least one of silicon oxide and aluminum.

12. The elastic wave apparatus according to any one of claims 1 to 11, wherein the d / p is 0.24 or less.

13. An elastic wave apparatus according to any one of claims 1 to 12, wherein, when viewed from the extending direction of the first busbar and the second busbar, the region in which adjacent first electrode fingers and second electrode fingers overlap, and the region between the centers of adjacent first electrode fingers and second electrode fingers in the extending direction of the first busbar and the second busbar is the excitation region, and when the metallization ratio of the first electrode finger and the second electrode finger with respect to the excitation region is MR, MR ≤ 1.75 (d / p) + 0.

075.

14. The elastic wave apparatus according to any one of claims 1 to 13, wherein the piezoelectric layer is made of lithium tantalate or lithium niobate.

15. An elastic wave apparatus according to any one of claims 1 to 14, 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 equations (1), (2), or (3): (0°±10°, 0° to 20°, any ψ) ...Equation (1) (0°±10°, 20° to 80°, 0° to 60° (1 - (θ - 50)) ２ / 900) １／２ ) or (0°±10°, 20°~80°, [180°-60°(1-(θ-50) ２ / 900) １／２ ]~180°) ...Formula (2) (0°±10°, [180°-30°(1-(ψ-90) ２ ( / 8100) １／２ ] ~180°, any ψ) ...Equation (3)

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