Elastic wave apparatus

Abstract

To provide an elastic wave device that can suppress propagation loss. [Solution] The elastic wave device comprises a piezoelectric layer having opposing first and second main surfaces, an IDT electrode including a plurality of electrode fingers arranged in a predetermined direction and provided on at least one of the first and second main surfaces of the piezoelectric layer, a dielectric layer provided on at least one 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 and having an acoustic reflector on the second main surface side of the piezoelectric layer, wherein a recess is provided in the region of the dielectric layer that overlaps with the electrode fingers in a plan view.

Description

Technical Field

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

Background Art

[0002] Patent Document 1 describes an elastic wave device having an IDT electrode.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the elastic wave device shown in Patent Document 1, elastic wave leakage occurs in the arrangement direction of the electrode fingers, which may cause propagation loss.

[0005] An object of the present invention is to provide an elastic wave device capable of suppressing propagation loss.

Means for Solving the Problems

[0006] An elastic wave device according to one aspect includes a piezoelectric layer having opposing first and second main surfaces, an IDT electrode provided on at least one of the first and second main surfaces of the piezoelectric layer and including a plurality of electrode fingers arranged in a predetermined direction, a dielectric layer provided on at least one 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 and having an acoustic reflection portion on the second main surface side of the piezoelectric layer, wherein a recess is provided in a region of the dielectric layer that overlaps the electrode fingers in plan view.

Effects of the Invention

[0007] According to the elastic wave device of the present invention, propagation loss can be suppressed. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a plan view showing an elastic wave apparatus according to the first embodiment. [Figure 2] Figure 2 is a cross-sectional view taken along line II-II' in Figure 1. [Figure 3] Figure 3 is a cross-sectional view showing an enlarged view of region A shown in Figure 2. [Figure 4] Figure 4 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 5] Figure 5 is a schematic cross-sectional view illustrating the amplitude direction of the bulk wave of the first-order mode of thickness sliding propagating through the piezoelectric layer of the first embodiment. [Figure 6] Figure 6 is an explanatory diagram showing an example of the resonance characteristics of the elastic wave apparatus of the first embodiment. [Figure 7] Figure 7 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. [Figure 8] Figure 8 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 9] Figure 9 is a reference diagram showing an example of the resonance characteristics of the elastic wave apparatus of the first embodiment. [Figure 10] Figure 10 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 magnitude of the spurious signal. [Figure 11] Figure 11 is an explanatory diagram showing the relationship between d / 2p, metallization ratio (MR), and specific bandwidth. [Figure 12] Figure 12 is an explanatory diagram showing the specific bandwidth map of LiNbO3 with respect to the Euler angle (0°, θ, ψ) when d / p approaches 0. [Figure 13]FIG. 13 is an explanatory diagram showing an example of the conductance characteristics of the elastic wave device according to the first embodiment and the comparative example. [Figure 14] FIG. 14 is a cross-sectional view showing the elastic wave device of the second embodiment. [Figure 15] FIG. 15 is an explanatory diagram showing an example of the conductance characteristics of the elastic wave device according to the second embodiment and the comparative example. [Figure 16] FIG. 16 is a cross-sectional view showing the elastic wave device of the third embodiment. [Figure 17] FIG. 17 is an explanatory diagram showing an example of the conductance characteristics of the elastic wave device according to the third embodiment and the comparative example. [Figure 18] FIG. 18 is a cross-sectional view showing the elastic wave device of the fourth embodiment. [Figure 19] FIG. 19 is an explanatory diagram showing an example of the conductance characteristics of the elastic wave device according to the fourth embodiment and the comparative example. [Figure 20] FIG. 20 is an explanatory diagram showing an example of the admittance characteristics of the elastic wave device according to the fourth embodiment and the comparative example. [Figure 21] FIG. 21 is a graph showing the relationship between the depth of the recess and the ratio bandwidth. [Figure 22] FIG. 22 is a cross-sectional view showing the elastic wave device of the fifth embodiment. [Figure 23] FIG. 30 is an explanatory diagram showing an example of the conductance characteristics of the elastic wave device according to the fifth embodiment and the comparative example. [Figure 24] FIG. 24 is a cross-sectional view showing the elastic wave device of the sixth embodiment. [Figure 25] FIG. 25 is an explanatory diagram showing an example of the conductance characteristics of the elastic wave device according to the sixth embodiment and the comparative example. [Figure 26] FIG. 26 is a graph showing the relationship between the amount of change in the resonance frequency and the ratio bandwidth when the depth of the recess is varied. [Figure 27] FIG. 27 is a cross-sectional view showing the elastic wave device of the seventh embodiment. [Figure 28] FIG. 28 is a circuit diagram showing the filter device according to the eighth embodiment. [Modes for carrying out the invention]

[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 the elastic wave apparatus of the first embodiment. Figure 2 is a cross-sectional view taken along line II-II' in Figure 1. Figure 3 is an enlarged cross-sectional view showing region A in Figure 2. In Figure 1, for the sake of clarity, the first dielectric layer 41 is shown with a dashed line, and the recesses 45 provided in the first dielectric layer 41 are shown with hatching.

[0011] As shown in Figures 1 and 2, the elastic wave apparatus 10 according to the first embodiment includes a piezoelectric layer 20, an IDT electrode 30, a support substrate 11 (support member), a first dielectric layer 41, and a second dielectric layer 42. As shown in Figure 2, the elastic wave apparatus 10 is laminated on the support substrate 11 in the following order: second dielectric layer 42, piezoelectric layer 20, IDT electrode 30, and first dielectric layer 41.

[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 formed of lithium niobate (LiNbO3). Alternatively, the piezoelectric layer 20 may be made of lithium tantalate (LiTaO3). In the first embodiment, the cut angle of LiNbO3 or LiTaO3 is a Z cut. The cut angle of LiNbO3 or LiTaO3 may be a rotational Y cut or an X cut. Preferably, the propagation direction is ±30° for Y propagation and X propagation. Preferably, the piezoelectric layer 20 contains lithium niobate (LiNbO3) or lithium tantalate (LiTaO3) and has a 120°±10° rotational Y cut or a 90°±10° rotational Y cut.

[0013] The thickness of the piezoelectric layer 20 is not particularly limited, but to effectively excite the thickness-sliding primary mode, it is preferably 50 nm to 1000 nm. The thickness of the piezoelectric layer 20 according to the first embodiment is, for example, about 180 nm (0.18 μm).

[0014] The support substrate 11 (support member) is positioned opposite the second main surface 20b of the piezoelectric layer 20. The support substrate 11 has a cavity portion 14 (acoustic reflection portion) that opens to the second main surface 20b side of the piezoelectric layer 20. More specifically, the support substrate 11 has 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 enclosed by the bottom portion 12 and the wall portion 13. The cavity portion 14 is also called a cavity. The piezoelectric layer 20 is laminated on the upper surface of the wall portion 13 of the support substrate 11. At least a part of the piezoelectric layer 20 is positioned on the cavity portion 14 (acoustic reflection portion) in a plan view. Thus, the elastic wave device 10 has a so-called membrane structure in which the cavity portion 14 is provided on the second main surface 20b side of the piezoelectric layer 20.

[0015] The support member may include a support substrate 11 and an intermediate (insulating) layer. Furthermore, the second dielectric layer 42 provided on the second main surface 20b of the piezoelectric layer 20 is optional. That is, the piezoelectric layer 20 is joined to the support substrate 11 directly or via the intermediate (insulating) layer. The cavity portion 14 may be formed in the intermediate (insulating) layer. In that case, the support substrate 11 and the intermediate layer may have a frame-like shape, thereby forming the cavity portion 14. Alternatively, the cavity portion 14 may be formed in the intermediate layer. Alternatively, the second dielectric layer 42 may be provided as an intermediate layer of the support member.

[0016] The support substrate 11 is made of silicon (Si). The plane orientation of the Si on the side facing the piezoelectric layer 20 may be (100) or (110), or it may be (111). Preferably, high-resistivity Si with a resistivity of 4 kΩ or more is desirable. However, the support substrate 11 can also be made of appropriate insulating or semiconductor materials. As materials for the support substrate 11, for example, piezoelectric materials 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 can be used.

[0017] 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 a first electrode finger 31, a second electrode finger 32, a first busbar electrode 33, and a second busbar electrode 34. The multiple first electrode fingers 31 extend in the Y direction, and one end in the extending direction is connected to the first busbar electrode 33. The multiple second electrode fingers 32 extend in the Y direction, and the other end in the extending direction is connected to the second busbar electrode 34. The multiple first electrode fingers 31 and the multiple second electrode fingers 32 are arranged alternately in the X direction with spacing between them. The first busbar electrode 33 and the second busbar electrode 34 each extend in the X direction and are arranged opposite each other in the Y direction. The multiple first electrode fingers 31 and the multiple second electrode fingers 32 are arranged between the first busbar electrode 33 and the second busbar electrode 34.

[0018] Furthermore, the IDT electrode 30 is not limited to a configuration having a plurality of first electrode fingers 31 and a plurality of second electrode fingers 32, but may also include a configuration with at least one first electrode finger 31 whose base end is connected to the first busbar electrode 33 and at least one second electrode finger 32 whose base end is connected to the second busbar electrode 34.

[0019] In the following description, the thickness direction of the piezoelectric layer 20 may be referred to as the Z direction, the extension direction of the first electrode finger 31 and the second electrode finger 32 as the Y direction, and the arrangement direction of the first electrode finger 31 and the second electrode finger 32 as the X direction. Also, in the following description, a plan view refers to the arrangement when viewed from a direction perpendicular to the first main surface 20a of the piezoelectric layer 20. In the Z direction, the direction from the support substrate 11 toward the outermost first dielectric layer 41 is referred to as up or upward, and the direction from the first dielectric layer 41 toward the support substrate 11 is referred to as down or downward.

[0020] The distance between the centers of the first electrode finger 31 and the second electrode finger 32 (hereinafter referred to as the electrode pitch) is preferably in the range of 1 μm or more and 10 μm or less. The electrode pitch is the distance between the center of the width dimension of the first electrode finger 31 in a direction perpendicular to the extending direction of the first electrode finger 31 and the center of the width dimension of the second electrode finger 32 in a direction perpendicular to the extending direction of the second electrode finger 32. The width of the first electrode finger 31 and the second electrode finger 32 (hereinafter referred to as the electrode width), that is, the dimension in the direction perpendicular to the extending direction of the first electrode finger 31 and the second electrode finger 32, is preferably in the range of 150 nm or more and 1000 nm or less.

[0021] Furthermore, if there are multiple instances of at least one of the first electrode finger 31 and the second electrode finger 32 (i.e., if the first electrode finger 31 and the second electrode finger 32 are considered as a pair of electrode sets, there are 1.5 or more pairs of electrode sets), the electrode pitch of the first electrode finger 31 and the second electrode finger 32 refers to the average value of the distance between the centers of adjacent first electrode finger 31 and second electrode finger 32 among the 1.5 or more pairs of first electrode finger 31 and second electrode finger 32.

[0022] Furthermore, in the first embodiment, since a Z-cut piezoelectric layer is used, the direction perpendicular to the extending direction of the first electrode finger 31 and the second electrode finger 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 the first electrode finger 31 and the second electrode finger 32 and the polarization direction is 90°±10°).

[0023] The IDT electrode 30 (first electrode finger 31, second electrode finger 32, first busbar electrode 33, and second busbar electrode 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.

[0024] 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. Specific examples of the configuration and dimensions of the IDT electrode 30 will be described later in Figure 13.

[0025] Here, the crossing region C (excitation region) shown in Figure 1 is the region where the first electrode finger 31 and the second electrode finger 32 overlap when viewed in the X direction. The length of the crossing region C is the dimension in the extending direction of the first electrode finger 31 and the second electrode finger 32 in the crossing region C. In this embodiment, the length of the crossing region C is, for example, 40 μm.

[0026] During operation, an AC voltage is applied between multiple first electrode fingers 31 and multiple second electrode fingers 32. More specifically, an AC voltage is applied between a first busbar electrode 33 and a second 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.

[0027] Furthermore, in the elastic wave device 10, when the thickness of the piezoelectric layer 20 is d and the inter-electrode pitch of the multiple pairs of first electrode fingers 31 and second electrode fingers 32 is p, d / p is set to 0.5 or less. Therefore, the bulk wave of the first-order mode of thickness sliding 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.

[0028] In the elastic wave apparatus 10 of the first embodiment, because it has the above configuration, even if the logarithm of the first electrode finger 31 and the second electrode finger 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-mentioned reflectors are not required is because it utilizes a bulk wave of the first-order mode of thickness sliding.

[0029] As shown in Figures 1 and 2, the first dielectric layer 41 is provided on the first main surface 20a of the piezoelectric layer 20. The first dielectric layer 41 is also provided covering the IDT electrode 30. That is, in the Z direction, the IDT electrode 30 is provided between the first main surface 20a of the piezoelectric layer 20 and the first dielectric layer 41. The second dielectric layer 42 is provided on the second main surface 20b of the piezoelectric layer 20. The second dielectric layer 42 is in contact with the support substrate 11.

[0030] The first dielectric layer 41 and the second dielectric layer 42 are formed of silicon oxide (SiO2). The first dielectric layer 41 and the second dielectric layer 42 can be formed of any suitable insulating material other than silicon oxide, such as silicon nitride or alumina. The first dielectric layer 41 and the second dielectric layer 42 are made of the same material and have the same thickness. The thickness of the first dielectric layer 41 and the second dielectric layer 42 refers to the thickness in the region where the electrode fingers (first electrode finger 31 and second electrode finger 32) and recess 45 are not provided, i.e., the thickness in the region between the first electrode finger 31 and the second electrode finger 32. Note that the materials of the first dielectric layer 41 and the second dielectric layer 42 may be different, and they may have different thicknesses. Furthermore, at least one of the first dielectric layer 41 and the second dielectric layer 42 may be 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.

[0031] As shown in Figures 1 to 3, recesses 45 are provided in the region of the first dielectric layer 41 that overlaps with the first electrode finger 31 and the second electrode finger 32 of the IDT electrode 30. Each of the multiple recesses 45 is formed in the shape of a groove extending in the Y direction and is arranged spaced apart in the X direction. That is, in a plan view from the Z direction, each of the multiple recesses 45 overlaps with each electrode finger (first electrode finger 31 and second electrode finger 32) and extends in the same direction (Y direction) as the extension direction of each electrode finger.

[0032] As shown in Figure 3, the width Wa of the recess 45 in the X direction is smaller than the width Wb of the first electrode finger 31 in the X direction. In other words, the recess 45 is not provided in the region between the first electrode finger 31 and the second electrode finger 32. Furthermore, the pair of sides forming the recess 45 are provided in a position that overlaps with the first electrode finger 31.

[0033] The depth Ha of the recess 45 is less than the thickness between the upper surface of the first dielectric layer 41 and the upper surface of the first electrode finger 31 in the region where the recess 45 is not formed. The recess 45 does not reach the first electrode finger 31 in the Z direction, and the first dielectric layer 41 is provided between the bottom of the recess 45 and the upper surface of the first electrode finger 31. In addition, in the region between the first electrode finger 31 and the second electrode finger 32, the thickness of the first dielectric layer 41 is set to be constant, and the upper surface of the first dielectric layer 41 (excluding the portion where the recess 45 is provided) is formed flat.

[0034] No recesses are provided in the second dielectric layer 42. That is, the thickness of the second dielectric layer 42 is kept constant, and the lower surface of the second dielectric layer 42 (the surface opposite to the piezoelectric layer 20) is formed flat.

[0035] Although Figure 3 shows a recess 45 that overlaps with the first electrode finger 31, the recess 45 that overlaps with the second electrode finger 32 has a similar configuration.

[0036] Since the recess 45 is provided overlapping with the first electrode finger 31 and the second electrode finger 32, the acoustic impedance in the region where the recess 45 is provided overlaps with multiple electrode fingers is different from the acoustic impedance in the region between the first electrode finger 31 and the second electrode finger 32 where the recess 45 is not provided. As a result, an acoustic reflection surface is formed at the boundary between the portion with the recess 45 and the portion without the recess 45 (the portion overlapping with the side surface of the recess 45).

[0037] As a result, the elastic waves excited in the piezoelectric layer 20 are reflected by the acoustic reflection surface, so the elastic wave device 10 can suppress elastic wave leakage in the direction of the arrangement of the multiple electrode fingers (first electrode finger 31 and second electrode finger 32). In addition, the amplitude of the standing wave in the direction of the arrangement of the multiple electrode fingers is larger between the first electrode finger 31 and the second electrode finger 32, and the energy of the main mode is concentrated between the electrode fingers. Therefore, since the recess 45 is provided overlapping each of the multiple electrode fingers, fluctuations in the characteristics of the main mode can be suppressed.

[0038] In this embodiment, the recess 45 is shown overlapping each of the first electrode fingers 31 and the second electrode fingers 32, but the embodiment is not limited to this, and the recess 45 only needs to be provided in a region that overlaps with at least one first electrode finger 31 or the second electrode finger 32. Also, the length of the recess 45 in the extending direction (Y direction) can be changed as appropriate. For example, the end of the recess 45 in the extending direction may extend to a position that overlaps with the first busbar electrode 33 and the second busbar electrode 34.

[0039] Figure 4 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 5 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.

[0040] As shown in Figure 4, 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 logarithms of electrode pairs consisting of the first electrode finger 31 and the second electrode finger 32 is reduced in an attempt to miniaturize the device, a decrease in the Q value is unlikely to occur.

[0041] Furthermore, as shown in Figure 5, 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 5 schematically shows the bulk wave when a voltage is applied between the first electrode finger 31 and the second electrode finger 32 such that the second electrode finger 32 is at a higher potential than the first 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.

[0042] In the elastic wave device 10, at least one pair of electrodes consisting of a first electrode finger 31 and a second 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 electrodes consisting of the first electrode finger 31 and the second electrode finger 32. In other words, it is sufficient that at least one pair of electrodes is provided.

[0043] For example, the first electrode finger 31 is an electrode connected to a hot potential, and the second electrode finger 32 is an electrode connected to a ground potential. However, the first electrode finger 31 may be connected to a ground potential and the second electrode finger 32 may be connected to a hot potential. In the first embodiment, at least one pair of electrodes are either connected to a hot potential or connected to a ground potential, as described above, and no floating electrodes are provided.

[0044] Figure 6 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 6 are as follows.

[0045] Piezoelectric layer 20: LiNbO3 with Euler angles (0°, 0°, 90°) Thickness of piezoelectric layer 20: 400 nm

[0046] Length of crossover region C: 40 μm Number of electrode pairs consisting of the first electrode finger 31 and the second electrode finger 32: 21 pairs Electrode pitch between the first electrode finger 31 and the second electrode finger 32: 3 μm Width of first electrode finger 31 and second electrode finger 32: 500 nm d / p:0.133

[0047] Support substrate 11: Si

[0048] In the first embodiment, the electrode spacing between electrode pairs consisting of a first electrode finger 31 and a second electrode finger 32 was made equal in all pairs. That is, the first electrode finger 31 and the second electrode finger 32 were arranged at equal pitches.

[0049] As is clear from Figure 6, good resonance characteristics with a relative bandwidth of 12.5% ​​are obtained despite the absence of a reflector.

[0050] By the way, if the thickness of the piezoelectric layer 20 is d and the electrode pitch between the first electrode finger 31 and the second electrode finger 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 7.

[0051] Figure 7 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 7, multiple elastic wave apparatuses were obtained in the same manner as the elastic wave apparatus that obtained the resonance characteristics shown in Figure 6, but by changing d / 2p.

[0052] As shown in Figure 7, 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 first-order thickness-slip mode described above.

[0053] 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.

[0054] Figure 8 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 a first electrode finger 31 and a second electrode finger 32 is provided on the first main surface 20a of the piezoelectric layer 20. In Figure 8, K is the crossover width. As mentioned 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.

[0055] In the elastic wave apparatus 10, it is preferable that the metallization ratio MR of the adjacent first electrode finger 31 and second electrode finger 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 9 and 10.

[0056] Figure 9 is a reference diagram showing an example of the resonance characteristics of the elastic wave apparatus of the first embodiment. As shown in Figure 9, the spurious signal indicated by arrow B appears between the resonant frequency and the anti-resonant frequency. Note that d / p = 0.08 and the Euler angles of LiNbO3 were set to (0°, 0°, 90°). Also, the metallization ratio MR = 0.35 was set.

[0057] 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 first electrode fingers 31 and second electrode fingers 32, we assume that only this pair of first electrode fingers 31 and second electrode fingers 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 the first electrode finger 31 that overlaps with the second electrode finger 32 when viewed in a direction perpendicular to the extending direction of the first electrode finger 31 and the second electrode finger 32, i.e., in an opposing direction, the area on the first electrode finger 31 that overlaps with the first electrode finger 32, the area on the second electrode finger 32 that overlaps with the first electrode finger 31, and the area between the first electrode finger 31 and the second electrode finger 32 that overlaps. The area of ​​the first electrode finger 31 and the second electrode finger 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 cross region C.

[0058] Furthermore, if multiple pairs of first electrode fingers 31 and second electrode fingers 32 are provided, the ratio of the metallized portion included in all crossing regions C to the total area of ​​the crossing regions C should be defined as MR.

[0059] Figure 10 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 to 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 first electrode fingers 31 and the second electrode fingers 32. Figure 10 shows the results when a piezoelectric layer 20 made of Z-cut LiNbO3 is used, but a similar trend is observed when piezoelectric layers 20 with other cut angles are used.

[0060] In the region enclosed by the ellipse J in Figure 10, the spurious emission is large at 1.0. As is clear from Figure 10, when the relative bandwidth exceeds 0.17, i.e., 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. That is, as shown in the resonance characteristics in Figure 9, 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, the spurious emissions can be reduced by adjusting the film thickness of the piezoelectric layer 20 and the dimensions of the first electrode finger 31 and the second electrode finger 32.

[0061] Figure 11 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 11 is the region where the relative bandwidth is 17% or less. The boundary between this hatched region and the unhashed 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 11. That is, if MR ≤ 1.75(d / p) + 0.05, the relative bandwidth can be reliably kept at 17% or less.

[0062] Figure 12 is an explanatory diagram showing the relative bandwidth map of LiNbO3 with respect to the Euler angle (0°, θ, ψ) when d / p approaches 0. The hatched area in Figure 12 is the region where a relative bandwidth of at least 5% is obtained. Approximating the range of this region, it is represented by the following equations (1), (2), and (3).

[0063] (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°) …Equation (2) (0°±10°, [180°-30°(1-(ψ-90) 2 ( / 8100) 1 / 2 ]~180°, any ψ) …Equation (3)

[0064] Therefore, in the case of the Euler angle range of equation (1), equation (2), or equation (3) above, the specific bandwidth can be made sufficiently wide, which is preferable.

[0065] The elastic wave apparatus 10 of this embodiment has been described in a configuration that makes it possible to use a bulk wave of the first-order thickness-slip mode, but it is not limited to this. The elastic wave apparatus 10 may also use a plate wave. In this case, the elastic wave apparatus 10 has reflectors provided on both sides of the IDT electrode 30 in the direction of elastic wave propagation. In the elastic wave apparatus 10, a Lamb wave as a plate wave is excited by applying an AC electric field to the first electrode finger 31 and the second electrode finger 32 on the cavity portion 14. At this time, since reflectors are provided on both sides, resonance characteristics due to the Lamb wave as a plate wave can be obtained.

[0066] Figure 13 is an explanatory diagram showing an example of the conductance characteristics of the elastic wave apparatus according to the first embodiment and the comparative example. The elastic wave apparatus 10 according to the first embodiment has a configuration in which a recess 45 is provided in the region of the first dielectric layer 41 that overlaps with the first electrode finger 31 and the second electrode finger 32. The elastic wave apparatus according to the comparative example has a configuration in which the recess 45 is not provided.

[0067] The parameters of the elastic wave apparatus 10 according to the first embodiment are as follows:

[0068] Piezoelectric layer 20: LiNbO3 with Euler angles (0°, 30°, 0°) Piezoelectric layer 20 thickness: 180 nm

[0069] Number of first electrode fingers 31 and second electrode fingers 32: 51 IDT electrode 30 (first electrode finger 31 and second electrode finger 32): Ti / AlCu / Ti / AlCu multilayer film Film thickness of IDT electrode 30 (first electrode finger 31 and second electrode finger 32): 12nm / 70nm / 18nm / 12nm Electrode pitch p: 2.38 μm Width Wb: 0.6μm

[0070] Material of the first dielectric layer 41 and the second dielectric layer 42: SiO2 Film thickness of the first dielectric layer 41 and the second dielectric layer 42: 142 nm

[0071] Width of recess 45 Wa: 520nm The distance Wc, Wd between the side surface of the recess 45 and the side surface of the first electrode finger 31 is 40 nm. Depth of recess 45 Ha: 20nm

[0072] In the elastic wave apparatus 10 according to the first embodiment, the multiple recesses 45 are provided corresponding to each of the first electrode fingers 31 and the second electrode fingers 32. The elastic wave apparatus according to the comparative example differs from the first embodiment in that it does not have recesses 45, but the other configurations are the same as the various parameters described above.

[0073] In the graph shown in Figure 13, the vertical axis represents the real part of the admittance, i.e., the conductance component, of the elastic wave apparatus according to the first embodiment and comparative example. The horizontal axis of the graph represents frequency.

[0074] 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 E1 and E2. In contrast, in the elastic wave apparatus 10 according to the first embodiment, by providing a recess 45 in the first dielectric layer 41, the ripples shown by the dotted lines E1 and E2 are suppressed compared to the comparative example, and propagation loss is suppressed.

[0075] (Second Embodiment) Figure 14 is a cross-sectional view showing an elastic wave apparatus of the second embodiment. As shown in Figure 14, the elastic wave apparatus 10A according to the second embodiment differs from the first embodiment described above in that a recess 46 is provided in the region of the second dielectric layer 42 that overlaps with the first electrode finger 31 and the second electrode finger 32 of the IDT electrode 30.

[0076] In the elastic wave apparatus 10A according to the second embodiment, the recess 46 is provided on the lower surface of the second dielectric layer 42 (the surface opposite to the piezoelectric layer 20). The configuration of the recess 46 in plan view is the same as in the first embodiment described above (see Figure 1), so a repeated explanation will be omitted. Furthermore, the first dielectric layer 41 does not have a recess 45, and the upper surface of the first dielectric layer 41 is formed flat.

[0077] In this embodiment as well, an acoustic reflection surface is formed at the boundary between the portion with the recess 46 and the portion without the recess 46 (the portion that overlaps with the side surface of the recess 46). Since the elastic waves excited in the piezoelectric layer 20 are reflected by the acoustic reflection surface, the elastic wave device 10A can suppress the leakage of elastic waves in the direction of the arrangement of the multiple electrode fingers (first electrode finger 31 and second electrode finger 32).

[0078] Figure 15 is an explanatory diagram showing an example of the conductance characteristics of an elastic wave apparatus according to the second embodiment and comparative example. In the elastic wave apparatus 10A according to the second embodiment, the parameters of the recess 46 provided in the second dielectric layer 42 are as follows. All other parameters are the same as in the first embodiment.

[0079] Width of recess 46: We: 520nm Distance Wf, Wg between the side surface of the recess 46 and the side surface of the first electrode finger 31: 40 nm Depth of recess 46 Hb: 20nm

[0080] As shown in Figure 15, in the second embodiment as well, the recess 46 is provided in the second dielectric layer 42, so the ripple shown by the dotted lines E1 and E2 is suppressed compared to the comparative example, and propagation loss is suppressed.

[0081] (Third embodiment) Figure 16 is a cross-sectional view showing an elastic wave apparatus of the third embodiment. As shown in Figure 16, the elastic wave apparatus 10B according to the third embodiment differs from the embodiments described above in that recesses 45 and 46 are provided in the first dielectric layer 41 and the second dielectric layer 42, respectively.

[0082] Specifically, a recess 45 is provided in the region of the first dielectric layer 41 that overlaps with the first electrode finger 31 and the second electrode finger 32 of the IDT electrode 30, and a recess 46 is provided in the region of the second dielectric layer 42 that overlaps with the first electrode finger 31 and the second electrode finger 32 of the IDT electrode 30.

[0083] The recesses 45 and 46 are not provided in the region between the first electrode finger 31 and the second electrode finger 32. In the region between the first electrode finger 31 and the second electrode finger 32, the thickness of the first dielectric layer 41 is constant, and the upper surface of the first dielectric layer 41 is formed flat. Also, in the region between the first electrode finger 31 and the second electrode finger 32, the thickness of the second dielectric layer 42 is constant, and the lower surface of the second dielectric layer 42 is formed flat.

[0084] With this configuration, the elastic wave apparatus 10B according to the third embodiment can more effectively suppress elastic wave leakage in the direction of the arrangement of the multiple electrode fingers (first electrode finger 31 and second electrode finger 32).

[0085] Figure 17 is an explanatory diagram showing an example of the conductance characteristics of an elastic wave apparatus according to the third embodiment and comparative example. In the elastic wave apparatus 10B according to the third embodiment, the parameters of the recess 45 provided in the first dielectric layer 41 are the same as those of the first embodiment described above. Also, the parameters of the recess 46 provided in the second dielectric layer 42 are the same as those of the second embodiment described above. Other various parameters are the same as those of the first embodiment.

[0086] As shown in Figure 17, in the third embodiment, a recess 45 is provided in the first dielectric layer 41 and a recess 46 is provided in the second dielectric layer 42. This configuration effectively suppresses the ripple shown by the dotted lines E1 and E2 compared to the comparative example, and demonstrates that propagation loss is suppressed.

[0087] (Fourth Embodiment) Figure 18 is a cross-sectional view showing the elastic wave apparatus of the fourth embodiment. As shown in Figure 18, the elastic wave apparatus 10C according to the fourth embodiment differs from the embodiments described above in that the recess 46A penetrates the second dielectric layer 42 in the Z direction and is provided across the piezoelectric layer 20.

[0088] In other words, the depth Hb of the recess 46A is greater than the thickness of the second dielectric layer 42, but less than the combined thickness of the second dielectric layer 42 and the piezoelectric layer 20. The bottom surface of the recess 46A is composed of the piezoelectric layer 20.

[0089] Figure 19 is an explanatory diagram showing an example of the conductance characteristics of the elastic wave apparatus according to the fourth embodiment and comparative example. Figure 20 is an explanatory diagram showing an example of the admittance characteristics of the elastic wave apparatus according to the fourth embodiment and comparative example. Figure 21 is a graph showing the relationship between the depth of the recess and the specific bandwidth. In the elastic wave apparatus 10C according to the fourth embodiment, the parameters of the recess 46A provided in the second dielectric layer 42 and the piezoelectric layer 20 are as follows. Other various parameters are the same as in the first embodiment.

[0090] Width of recess 46: We: 520nm Distance Wf, Wg between the side surface of the recess 46 and the side surface of the first electrode finger 31: 40 nm Depth of recess 46 Hb: 160nm

[0091] As shown in Figure 19, in the fourth embodiment, the configuration in which the recess 46A is provided across the second dielectric layer 42 and the piezoelectric layer 20 suppresses the ripple shown by the dotted lines E3 and E4 compared to the comparative example, and thus suppresses propagation loss.

[0092] As shown in Figure 20, the relative bandwidth in the fourth embodiment is smaller than that of the comparative example. The relative bandwidth of the elastic wave apparatus 10C according to the fourth embodiment is 10.3%, while the relative bandwidth of the elastic wave apparatus according to the comparative example is 11.4%. The relative bandwidth was calculated as (Fa-Fr) / Fr × 100 (%), where Fr is the resonant frequency and Fa is the anti-resonant frequency.

[0093] The graph in Figure 21 shows the relationship between the depth H of the recess and the specific bandwidth for elastic wave apparatuses in which the depth H of the recess is varied within the range of 20 nm to 200 nm. Elastic wave apparatuses in which the depth H of the recess 46 is in the range of 142 nm or less correspond to the second embodiment (second example) described above, and elastic wave apparatuses in which the depth H of the recess 46A is in the range of 142 nm or more correspond to the fourth embodiment (fourth example) described above. In Figure 21, various parameters other than the depth H of the recesses 46 and 46A are the same as in the first embodiment described above.

[0094] As shown in Figure 21, increasing the depth H of the recess reduces the relative bandwidth. As shown in the fourth embodiment (fourth example), by providing the recess 46A across the second dielectric layer 42 and the piezoelectric layer 20, the range over which the relative bandwidth can be adjusted can be increased compared to the comparative example and the second embodiment.

[0095] (Fifth embodiment) Figure 22 is a cross-sectional view showing the elastic wave apparatus of the fifth embodiment. As shown in Figure 22, the elastic wave apparatus 10D according to the fifth embodiment differs from the embodiments described above in that the first dielectric layer 41 and the second dielectric layer 42 are formed thinner. In the fifth embodiment, the upper surface of the first dielectric layer 41 has a convex shape along the IDT electrode 30 (first electrode finger 31 and second electrode finger 32).

[0096] Furthermore, in the elastic wave apparatus 10D according to the fifth embodiment, similar to the second embodiment described above, the recess 46 is provided in the region of the second dielectric layer 42 that overlaps with the first electrode finger 31 and the second electrode finger 32 of the IDT electrode 30.

[0097] Figure 23 is an explanatory diagram showing an example of the conductance characteristics of the elastic wave apparatus according to the fifth embodiment and comparative example. The various parameters of the elastic wave apparatus 10D according to the fifth embodiment are as follows.

[0098] Piezoelectric layer 20: LiNbO3 with 120° rotation Y-cut Piezoelectric layer 20 thickness: 360 nm

[0099] Number of first electrode fingers 31 and second electrode fingers 32: 102 IDT electrode 30 (first electrode finger 31 and second electrode finger 32): Ti / AlCu / Ti / AlCu multilayer film Film thickness of IDT electrode 30 (first electrode finger 31 and second electrode finger 32): 12nm / 27nm / 18nm / 12nm Electrode pitch p: 1.96 μm Width Wb: 0.6μm

[0100] Material of the first dielectric layer 41 and the second dielectric layer 42: SiO2 Film thickness of the first dielectric layer 41 and the second dielectric layer 42: 30 nm

[0101] The parameters of the recess 46 are the same as those of the second embodiment described above.

[0102] As shown in Figure 23, in the fifth embodiment, even though the first dielectric layer 41 and the second dielectric layer 42 are formed with thin films, the second dielectric layer 42 is provided with a recess 46, which suppresses the ripple shown by the dotted line E5 compared to the comparative example, and thus suppresses propagation loss.

[0103] (Sixth Embodiment) Figure 24 is a cross-sectional view showing the elastic wave apparatus of the sixth embodiment. As shown in Figure 24, the elastic wave apparatus 10E according to the sixth embodiment differs from the embodiments described above in that it has a first recess 46B in the second dielectric layer 42 that overlaps with the IDT electrode 30 (first electrode finger 31 and second electrode finger 32), and a second recess 47 in the piezoelectric layer 20 that overlaps with the first recess 46B.

[0104] The width We and depth Hb of the first recess 46B are equivalent to the width Wh and depth Hc of the second recess 47. The second dielectric layer 42 is provided to fill the second recess 47 of the piezoelectric layer 20. That is, the thickness of the second dielectric layer 42 is constant across the region where the first recess 46B and the second recess 47 are provided and the region where the first recess 46B and the second recess 47 are not provided.

[0105] Figure 25 is an explanatory diagram showing an example of the conductance characteristics of an elastic wave apparatus according to the sixth embodiment and comparative example. In the elastic wave apparatus 10E according to the sixth embodiment, the parameters of the first recess 46B and the second recess 47 are as follows. The other parameters are the same as in the first embodiment.

[0106] Width of the first recess 46B We: 520nm Distance Wf, Wg between the side surface of the first recess 46B and the side surface of the first electrode finger 31: 40 nm Depth Hb of the first recess 46B: 60 nm

[0107] Width Wh of the second recess 47: 520nm The distance Wf, Wg between the side surface of the second recess 47 and the side surface of the first electrode finger 31 is 40 nm. Depth Hc of the second recess 47: 60 nm

[0108] As shown in Figure 25, in the sixth embodiment, the second dielectric layer 42 is provided with a first recess 46B and the piezoelectric layer 20 is provided with a second recess 47. Compared to the comparative example, the ripple shown by the dotted lines E6 and E7 is suppressed, and propagation loss is suppressed. Furthermore, in the sixth embodiment, fluctuations in the resonant frequency can be suppressed compared to the fourth embodiment described above (see Figure 19).

[0109] Figure 26 is a graph showing the relationship between the variation in resonant frequency and the relative bandwidth when the depth of the recess is varied. In Figure 26, the relationship between the variation in resonant frequency and the relative bandwidth when the depth of the recess is varied is shown for each of the elastic wave apparatuses of the fourth and sixth embodiments. In the graph shown in Figure 26, the vertical axis is the relative bandwidth, and the horizontal axis is the variation in the resonant frequency of the fourth and sixth embodiments relative to the resonant frequency of the elastic wave apparatus of the comparative example which does not have a recess.

[0110] As shown in Figure 26, in both the fourth and sixth embodiments, increasing the depth of the recess reduces the relative bandwidth and increases the variation in the resonant frequency, i.e., the resonant frequency decreases. In the sixth embodiment, compared to the fourth embodiment, the configuration in which the first recess 46B is provided in the second dielectric layer 42 and the second recess 47 is provided in the piezoelectric layer 20 allows for adjustment of the relative bandwidth while suppressing a decrease in the resonant frequency.

[0111] It should be noted that the configurations of each embodiment described above, and the numerical values ​​shown for the parameters of each embodiment, are merely examples and can be changed as appropriate. For example, in the first embodiment, the distances Wc and Wd between the side surface of the recess 45 and the side surface of the first electrode finger 31 are provided to be equal and symmetrical, but this is not limited to this, and the distances Wc and Wd may be different. Furthermore, the embodiments described above may be combined as appropriate. For example, the fourth embodiment and the first embodiment may be combined. Alternatively, the fifth embodiment and the first embodiment may be combined, or the fifth embodiment and the fourth embodiment may be combined. Also, the sixth embodiment and the first embodiment may be combined.

[0112] (Seventh Embodiment) Figure 27 is a cross-sectional view showing the elastic wave apparatus of the seventh embodiment. In the embodiments described above, a so-called membrane structure was described in which the support substrate 11 has a cavity portion 14 and the cavity portion 14 is provided on the second main surface 20b side of the piezoelectric layer 20, but the invention is not limited thereto.

[0113] As shown in Figure 27, in the elastic wave apparatus 10F according to the seventh embodiment, an acoustic multilayer film 43 is laminated on the second main surface 20b of the piezoelectric layer 20. The acoustic multilayer film 43 has a laminated structure of low acoustic impedance layers 43a, 43c, and 43e with relatively low acoustic impedance and high acoustic impedance layers 43b and 43d with relatively high acoustic impedance. The low acoustic impedance layers 43a, 43c, and 43e are, for example, layers of silicon oxide (SiO2), and the high acoustic impedance layers 43b and 43d are dielectric layers such as silicon nitride (SiN), aluminum oxide (Al2O3), tantalum oxide (Ta2O5), and hafnium oxide (HfO2). When the acoustic multilayer film 43 is used, bulk waves of the thickness-slip first mode can be confined within the piezoelectric layer 20 without using the cavity portion 14.

[0114] In addition, the number of layers of low acoustic impedance layers 43a, 43c, 43e and high acoustic impedance layers 43b, 43d in the acoustic multilayer film 43 is not particularly limited. It is sufficient that at least one high acoustic impedance layer 43b or 43d is located further away from the piezoelectric layer 20 than the low acoustic impedance layers 43a, 43c, 43e.

[0115] The low acoustic impedance layers 43a, 43c, 43e and the high acoustic impedance layers 43b, 43d can be made of any suitable material as long as the above acoustic impedance relationship is satisfied. For example, the materials for the high acoustic impedance layers 43b, 43d may be aluminum nitride (AlN), or metals such as tungsten (W) or platinum (Pt). The low acoustic impedance layers 43a, 43c, 43e and the high acoustic impedance layers 43b, 43d may be made of different materials from the first dielectric layer 41 and the second dielectric layer 42, or they may be made of the same material.

[0116] Although the second dielectric layer 42 is not shown in Figure 27, the second dielectric layer 42 may be provided between the second main surface 20b of the piezoelectric layer 20 and the acoustic multilayer film 43.

[0117] (Eighth embodiment) Figure 28 is a circuit diagram showing a filter device according to the eighth embodiment. As shown in Figure 28, the filter device 100 according to the eighth embodiment includes a plurality of series arm resonators 61, 62, 63, a plurality of parallel arm resonators 64, 65, 66, 67, an input terminal 60A, and an output terminal 60B. The plurality of series arm resonators 61, 62, 63 and the plurality of parallel arm resonators 64, 65, 66, 67 are each one of the elastic wave devices from the first embodiment to the seventh embodiment 10F described above.

[0118] Multiple series arm resonators 61, 62, and 63 are connected in series to the signal path between the input terminal 60A and the output terminal 60B. Multiple parallel arm resonators 64, 65, 66, and 67 are connected in parallel between the signal path between the input terminal 60A and the output terminal 60B and the ground 68. The filter device 100 according to the eighth embodiment is a so-called ladder-type filter that includes multiple series arm resonators 61, 62, and 63 and multiple parallel arm resonators 64, 65, 66, and 67.

[0119] One terminal of each of the series-connected series arm resonators 61, 62, and 63 is electrically connected to the input terminal 60A, and the other terminal is electrically connected to the output terminal 60B. One terminal of the parallel arm resonator 64 is electrically connected to the signal path between the input terminal 60A and the series arm resonator 61, and the other terminal is electrically connected to ground 68. One terminal of the parallel arm resonator 65 is electrically connected to the signal path between the series arm resonator 61 and the series arm resonator 62, and the other terminal is electrically connected to ground 68. One terminal of the parallel arm resonator 66 is electrically connected to the signal path between the series arm resonator 62 and the series arm resonator 63, and the other terminal is electrically connected to ground 68. One terminal of the parallel arm resonator 67 is electrically connected to the signal path between the series arm resonator 63 and the output terminal 60B, and the other terminal is electrically connected to ground 68.

[0120] In the filter device 100, the configuration and number of the multiple series arm resonators 61, 62, 63 and the multiple parallel arm resonators 64, 65, 66, 67 can be appropriately changed according to the required filter characteristics. For example, the filter device 100 may be configured to include at least one series arm resonator and at least one parallel arm resonator.

[0121] 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.

[0122] Furthermore, this disclosure may also take the following form.

[0123] (1) A piezoelectric layer having opposing first main surface and second main surface, An IDT electrode is provided on at least one of the first main surface and the second main surface of the piezoelectric layer and includes a plurality of electrode fingers arranged in a predetermined direction, A dielectric layer provided on at least one of the first main surface and the second main surface of the piezoelectric layer, The system comprises a support member provided on the second main surface side of the piezoelectric layer and having an acoustic reflecting portion on the second main surface side of the piezoelectric layer, A recess is provided in the dielectric layer in a region that overlaps with the electrode finger in a plan view. Elastic wave device. (2) The dielectric layer includes a first dielectric layer provided on the first main surface and a second dielectric layer provided on the second main surface. (1) The elastic wave apparatus described above. (3) The IDT electrode is provided on the first main surface, The recess is provided in the second dielectric layer (2) The elastic wave apparatus described above. (4) The recess is provided in a direction perpendicular to the first main surface, penetrating the second dielectric layer and extending across the piezoelectric layer. (2) The elastic wave apparatus described above. (5) The first dielectric layer and the second dielectric layer are made of the same material and have the same thickness. An elastic wave apparatus as described in any one of (2) to (4). (6) The dielectric layer material is silicon oxide An elastic wave apparatus as described in any one of (1) to (5). (7) A first recess provided in the region of the second dielectric layer that overlaps with the electrode finger, The piezoelectric layer has a second recess provided in a region overlapping with the first recess. (2) The elastic wave apparatus described above. (8) The IDT electrode is provided on the first main surface, The first dielectric layer is provided covering the IDT electrode, The recess is provided in the first dielectric layer (2) The elastic wave apparatus described above. (9) The sound-reflecting portion is a cavity portion that opens to the piezoelectric layer side of the support member. An elastic wave apparatus as described in any one of (1) to (8). (10) The acoustic reflection portion is an acoustic reflection film that includes a high acoustic impedance layer with a relatively high acoustic impedance and a low acoustic impedance layer with a relatively low acoustic impedance. The support member and the piezoelectric layer are arranged to face each other with the acoustic reflective film in between. An elastic wave apparatus as described in any one of (1) to (8). [Explanation of symbols]

[0124] 10, 10A, 10B, 10C, 10D, 10E, 10F Elastic wave apparatus 11 Support substrate 14 Cavity section 20 piezoelectric layers 20a First main surface 20b 2nd principal surface 30 IDT electrodes 31 1st electrode finger 32 2nd electrode finger 33 First busbar electrode 34. Second busbar electrode 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 45, 46, 46A recess 46B First recess 47. Second recess 61, 62, 63 Series arm resonators 64, 65, 66, 67 Parallel Arm Resonators 100 Filter device

Claims

1. A piezoelectric layer having opposing first main surface and second main surface, An IDT electrode is provided on at least one of the first main surface and the second main surface of the piezoelectric layer and includes a plurality of electrode fingers arranged in a predetermined direction, A dielectric layer provided on at least one of the first main surface and the second main surface of the piezoelectric layer, The system comprises a support member provided on the second main surface side of the piezoelectric layer and having an acoustic reflecting portion on the second main surface side of the piezoelectric layer, A recess is provided in the dielectric layer in a region that overlaps with the electrode finger in a plan view. Elastic wave device.

2. The dielectric layer includes a first dielectric layer provided on the first main surface and a second dielectric layer provided on the second main surface. The elastic wave apparatus according to claim 1.

3. The IDT electrode is provided on the first main surface, The recess is provided in the second dielectric layer The elastic wave apparatus according to claim 2.

4. The recess is provided in a direction perpendicular to the first main surface, penetrating the second dielectric layer and extending across the piezoelectric layer. The elastic wave apparatus according to claim 2.

5. The first dielectric layer and the second dielectric layer are made of the same material and have equal thickness. The elastic wave apparatus according to claim 2.

6. The material of the dielectric layer is silicon oxide. The elastic wave apparatus according to claim 1.

7. A first recess is provided in the region of the second dielectric layer that overlaps with the electrode finger, The piezoelectric layer has a second recess provided in a region overlapping with the first recess. The elastic wave apparatus according to claim 2.

8. The IDT electrode is provided on the first main surface, The first dielectric layer is provided covering the IDT electrode, The recess is provided in the first dielectric layer The elastic wave apparatus according to claim 1.

9. The aforementioned acoustic reflection portion is a cavity portion that opens on the piezoelectric layer side of the support member. The elastic wave apparatus according to claim 1.

10. The aforementioned acoustic reflection portion is an acoustic reflection film that includes a high acoustic impedance layer with relatively high acoustic impedance and a low acoustic impedance layer with relatively low acoustic impedance. The support member and the piezoelectric layer are arranged to face each other with the acoustic reflective film in between. The elastic wave apparatus according to claim 1.

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