Elastic wave apparatus

Abstract

Increase the relative bandwidth. [Solution] The elastic wave device comprises a support substrate, an acoustic multilayer film provided on the upper side of the support substrate, a piezoelectric layer provided on the upper side of the acoustic multilayer film, and an IDT electrode provided on the piezoelectric layer. The acoustic multilayer film includes a plurality of layers stacked in a first direction. The plurality of layers include a first layer and a second layer. At least one of the plurality of layers is made of a conductor. The IDT electrode has a first busbar, a second busbar, at least one first electrode finger, and at least one second electrode finger. When the thickness of the piezoelectric layer is d and the distance between the centers of adjacent electrode fingers is p, d / p is 0.5 or less. The acoustic multilayer film has a cavity that penetrates in a first direction through at least the layer closest to the piezoelectric layer among the plurality of layers. When viewed in a plan view in the first direction, at least a portion of the region between at least one pair of adjacent electrode fingers overlaps with the acoustic multilayer film. When viewed in a plan view in the first direction, the cavity overlaps with at least a portion of at least one of the electrode fingers.

Description

[Technical Field]

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

[0002] Patent Document 1 describes an elastic wave apparatus comprising an acoustic reflection layer having a low acoustic impedance layer and a high acoustic impedance layer having a higher acoustic impedance than the low acoustic impedance layer. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 5648695 [Overview of the project] [Problems that the invention aims to solve]

[0004] In the elastic wave apparatus shown in Patent Document 1, if a conductive layer is included in the acoustic reflection layer, parasitic capacitance may occur, potentially reducing the specific bandwidth.

[0005] The present invention aims to provide an elastic wave apparatus that can increase the relative bandwidth. [Means for solving the problem]

[0006] An elastic wave apparatus according to one embodiment comprises a support substrate, an acoustic multilayer film provided on the upper side of the support substrate, a piezoelectric layer provided on the upper side of the acoustic multilayer film, and an IDT electrode provided on at least one side of the upper or lower side of the piezoelectric layer, wherein the acoustic multilayer film includes a plurality of layers stacked in a first direction, the plurality of layers include a first layer and a second layer made of a different material from the first layer, at least one of the plurality of layers is made of a conductor, and the IDT electrode includes 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 a base on the second busbar The acoustic multilayer film has at least one second electrode finger whose ends are connected, and when the thickness of the piezoelectric layer is d and the distance between the centers of adjacent first and second electrode fingers is p, d / p is 0.5 or less, and the acoustic multilayer film has a cavity that penetrates in the first direction through at least the layer closest to the piezoelectric layer among the plurality of layers, and when viewed in plan in the first direction, at least a portion of the region between at least one pair of adjacent first and second electrode fingers overlaps with the acoustic multilayer film, and when viewed in plan in the first direction, the cavity overlaps with at least a portion of at least one of the first and second electrode fingers. [Effects of the Invention]

[0007] The elastic wave apparatus of the present invention allows for a large relative bandwidth. [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 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] 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]FIG. 5 is an explanatory diagram showing an example of resonance characteristics of the elastic wave device of the first embodiment. [Figure 6] FIG. 6 is an explanatory diagram showing the relationship between d / 2p and the ratio bandwidth as a resonator, where p is the center-to-center distance or the average center-to-center distance of adjacent electrodes and d is the average thickness of the piezoelectric layer, in the elastic wave device of the first embodiment. [Figure 7] FIG. 7 is a plan view showing an example in which a pair of electrodes are provided in the elastic wave device of the first embodiment. [Figure 8] FIG. 8 is a reference diagram showing an example of resonance characteristics of the elastic wave device of the first embodiment. [Figure 9] FIG. 9 is an explanatory diagram showing the relationship between the ratio bandwidth when a large number of elastic wave resonators are configured in the elastic wave device of the first embodiment and the phase rotation amount of the impedance of the spurious normalized by 180 degrees as the size of the spurious. [Figure 10] FIG. 10 is an explanatory diagram showing the relationship between d / 2p, the metallization ratio MR, and the ratio bandwidth. [Figure 11] FIG. 11 is an explanatory diagram showing a map of the ratio bandwidth with respect to the Euler angles (0°, θLN, ψLN) of LiNbO3 when d / p approaches 0 infinitely. [Figure 12] FIG. 12 is an enlarged cross-sectional view related to region A in FIG. 2. [Figure 13] FIG. 13 is a diagram showing a graph indicating resonance characteristics of the elastic wave device according to the first embodiment. [Figure 14] FIG. 14 is an enlarged cross-sectional view showing the elastic wave device according to the second embodiment. [Figure 15] FIG. 15 is an enlarged cross-sectional view showing the elastic wave device according to the third embodiment. [Figure 16] FIG. 16 is a diagram showing a graph indicating resonance characteristics of the elastic wave device according to the third embodiment. [Figure 17] FIG. 17 is an enlarged cross-sectional view showing the elastic wave device according to the fourth embodiment. [Figure 18] FIG. 18 is a diagram showing the magnitude of the ratio bandwidth of an elastic wave device in which the width in the X direction of the cavity is changed with respect to the width in the X direction of the electrode fingers. [Figure 19] FIG. 19 is an enlarged cross-sectional view showing an elastic wave device according to the first modification. [Figure 20] FIG. 20 is a plan view showing an elastic wave device according to the second modification. [Figure 21] FIG. 21 is a plan view showing an elastic wave device according to the third modification. [Figure 22] FIG. 22 is a plan view showing an elastic wave device according to the fourth modification.

MODE FOR CARRYING OUT THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described in detail based on the drawings. Note that the present disclosure is not limited by this embodiment. Each embodiment described in the present disclosure is exemplary, and partial substitution or combination of configurations is possible between different embodiments. In the modifications and the second and subsequent embodiments, descriptions of matters common to the first embodiment will be omitted, and only different points will be described. In particular, the same operational effects due to the same configurations will not be sequentially mentioned for each embodiment.

[0010] (First Embodiment) FIG. 1 is a plan view showing an elastic wave device of the first embodiment. FIG. 2 is a cross-sectional view taken along the line II-II' of FIG. 1. FIG. 3 is an enlarged cross-sectional view showing the region A shown in FIG. 2.

[0011] As shown in FIGS. 1 and 2, the elastic wave device 10 according to the first embodiment includes a support member, a piezoelectric layer 20, and an IDT electrode 30.

[0012] (Support Member) In the first embodiment, the support member comprises a support substrate 11, an intermediate layer 12 provided on the upper side of the support substrate 11, and an acoustic multilayer film 43 provided on the upper side of the intermediate layer 12. That is, the intermediate layer 12 is provided between the support substrate 11 and the acoustic multilayer film 43. In the following description, one direction in the thickness direction of the support substrate 11 may be described as "up," and the other direction in the thickness direction of the support substrate 11 may be described as "down." In this disclosure, "provided on the upper side" includes being provided directly on top in contact with it, and being provided indirectly or at a distance so as to be located above it.

[0013] (Support base) In the first embodiment, the support substrate 11 is formed from at least one of the following materials: silicon (Si), silicon oxide, silicon carbide, lithium niobate, lithium tantalate, sapphire, aluminum nitride, glass, and aluminum oxide. Here, the glass may be, for example, glass made of silicon oxide. The support substrate 11 is preferably made of Si with a high resistivity of 4 kΩ or more.

[0014] (Middle class) The intermediate layer 12 is formed of a dielectric material. The material of the intermediate layer 12 is silicon dioxide (SiO₂). x ) and silicon nitride (SiN) are preferred. Note that the intermediate layer 12 is not an essential component and may not be provided.

[0015] The acoustic multilayer film 43 is a laminate having multiple layers 43a to 43g. The acoustic multilayer film 43 has a laminated structure consisting of first layers 43b, 43d, and 43f, and second layers 43a, 43c, 43e, and 43g. In the first embodiment, the first layers 43b, 43d, and 43f have a relatively higher acoustic impedance than the second layers 43a, 43c, 43e, and 43g. This allows bulk waves of the thickness-slip first mode to be confined within the piezoelectric layer 20. Note that the number of layers of the first layers 43b, 43d, and 43f and the second layers 43a, 43c, 43e, and 43g shown in Figure 2 is merely an example and is not particularly limited.

[0016] Of the multiple layers contained in the acoustic multilayer film 43, at least one layer is made of a conductor. In the first embodiment, at least one of the first layers 43b, 43d, 43f and the second layers 43a, 43c, 43e, 43g is made of a conductor. This makes it possible to increase the acoustic impedance difference between the first layer and the second layer, thereby improving the resonance characteristics.

[0017] The first layer 43b, 43d, and 43f are, for example, tungsten carbide (WC), tantalum carbide (TaC), rhenium oxide (ReO3), silicon chromium carbon (CrCSi), niobium carbide (NbC), zinc carbide (ZrC), zinc nitride (TiC), lanthanum boride (LaB6), vanadium carbide (VC), aluminum nitride (AlN), silicon carbide (SiC), yttrium oxide (Y2O3), and magnesium oxide (Mg It is preferable that the layers contain at least one of the following: O), silicon nitride (Si3N4), boron carbide (B4C), strontium fluoride (SrF2), barium fluoride (BaF2), tantalum oxide (Ta2O5), hafnium oxide (HfO2), tungsten oxide (WO3), hafnium nitride (HfN), tungsten nitride (WN), platinum (Pt), tungsten (W), copper (Cu), gold (Au), and silver (Ag). In particular, it is more preferable that the first layers 43b, 43d, and 43f contain at least one of the following: platinum (Pt), tungsten (W), copper (Cu), gold (Au), and silver (Ag). This makes it possible to make the acoustic impedance of the first layers 43b, 43d, and 43f greater than that of the second layers 43a, 43c, 43e, and 43g.

[0018] The second layer 43a, 43c, 43e, 43g is, for example, silicon dioxide (SiO₂). x It is preferable that the material contains at least one of the following: ) and aluminum (Al). In particular, it is preferable that the second layers 43a, 43c, 43e, and 43g contain, for example, aluminum (Al). This makes it possible to make the acoustic impedance of the second layers 43a, 43c, 43e, and 43g lower than that of the first layers 43b, 43d, and 43f.

[0019] The materials for the first layers 43b, 43d, and 43f and the second layers 43a, 43c, 43e, and 43g are not limited to those shown above. They can be made of any suitable material as long as the above acoustic impedance relationship is satisfied. For example, the materials for the first layers 43b, 43d, and 43f may be different from each other, and the materials for the second layers 43a, 43c, 43e, and 43g may be different from each other. Furthermore, the materials for the first layers 43b, 43d, and 43f and the second layers 43a, 43c, 43e, and 43g are not limited to being made of a single type of material, but may be layers of mixtures containing multiple materials.

[0020] The piezoelectric layer 20 is a flat plate-shaped layer provided on the upper side of the support member. The piezoelectric layer 20 has a first main surface 20a which is the upper surface and a second main surface 20b which is the lower surface. The piezoelectric layer 20 is formed of lithium niobate (LiNbO3). Alternatively, the piezoelectric layer 20 may be made of lithium tantalate (LiTaO3). The cut angle of LiNbO3 or LiTaO3 is, for example, a Z cut. The cut angle of LiNbO3 or LiTaO3 may also be a rotational Y cut or an X cut, and propagation directions of Y propagation and X propagation ±30° are preferred. Furthermore, the piezoelectric layer 20 contains lithium niobate (LiNbO3) or lithium tantalate (LiTaO3) and is preferably a 120°±10° rotational Y cut or a 90°±10° rotational Y cut. Here, 120°±10° includes the range from 120°-10° to 120°+10°, and 90°±10° includes the range from 90°-10° to 90°+10°.

[0021] 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.

[0022] (IDT electrode) The IDT (Interdigital Transducer) electrode 30 is provided on the upper side of the piezoelectric layer 20. That is, the IDT electrode 30 may be provided directly on the first main surface 20a, or it may be provided indirectly on the first main surface 20a via a dielectric layer or the like. In the first embodiment, the IDT electrode 30 is provided directly on the first main surface 20a.

[0023] As shown in Figure 1, the IDT electrode 30 has a first electrode finger 31, a second electrode finger 32, a first busbar 33, and a second busbar 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 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 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 33 and the second busbar 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 33 and the second busbar 34.

[0024] 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 a first busbar 33 and at least one second electrode finger 32 whose base end is connected to a second busbar 34.

[0025] 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 alignment direction of the first electrode finger 31 and the second electrode finger 32 as the X direction. In this disclosure, the Z direction is an example of the "first direction". In the first embodiment, the X direction is the direction perpendicular to the extension direction of the first electrode finger 31 and the second electrode finger 32. In this disclosure, the X direction is an example of the "width direction of the first electrode finger and the second electrode finger". Also, in the following description, "up" refers to the direction from the support substrate 11 toward the piezoelectric layer 20, and "down" refers to the direction from the piezoelectric layer 20 toward the support substrate 11.

[0026] The intercenter distance (electrode pitch) between the first electrode finger 31 and the second electrode finger 32 is not particularly limited, but is preferably in the range of 1 μm to 10 μm. Here, the electrode pitch refers to the distance between the center line of the dimensions of the first electrode finger 31 in the direction perpendicular to the extending direction (Y direction) of the first electrode finger 31 (X direction) and the center line of the dimensions of the second electrode finger 32 in the direction perpendicular to the extending direction (Y direction) of the second electrode finger 32 (X direction). In addition, the width (electrode width) of the first electrode finger 31 and the second electrode finger 32, that is, the dimensions in the direction perpendicular to the extending direction (Y direction) of the first electrode finger 31 and the second electrode finger 32 (X direction), is not particularly limited, but is preferably in the range of 150 nm to 1000 nm.

[0027] When there are multiple first electrode fingers 31 and second electrode fingers 32, that is, when the first electrode fingers 31 and second electrode fingers 32 are considered as a pair of electrode sets, there are 1.5 or more pairs of electrode sets, the arithmetic mean of the center-to-center distances of adjacent first electrode fingers 31 and second electrode fingers 32 among the 1.5 or more pairs of first electrode fingers 31 and second electrode fingers 32 may be described as the average center-to-center distance between the first electrode fingers 31 and second electrode fingers 32 (average electrode pitch).

[0028] In the first embodiment, the electrode pitch 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.

[0029] In the first embodiment, the IDT electrode 30, i.e., the first electrode finger 31, the second electrode finger 32, the first busbar 33, and the second busbar 34, are made of a suitable metal or alloy such as Al or AlCu alloy. Alternatively, the IDT electrode 30 may be a laminate in which an Al film is laminated on an adhesion layer such as a titanium (Ti) film. Note that an adhesion layer other than a Ti film may also be used.

[0030] 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 of the first electrode finger 31 and the second electrode finger 32 in the extending direction within the crossing region C. In this embodiment, the length of the crossing region C is, for example, 30 μm.

[0031] 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 33 and a second busbar 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.

[0032] Furthermore, in the elastic wave apparatus 10, when the thickness of the piezoelectric layer 20 is d and the average electrode pitch is p, d / p is set to 0.5 or less. Therefore, the bulk wave of the thickness-slip first mode described above 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. Regarding the thickness d of the piezoelectric layer 20, if the piezoelectric layer 20 has thickness variations, the average value of its thickness is adopted.

[0033] In the elastic wave apparatus 10 of the first embodiment, because it has the above configuration, propagation loss is low, and even if the logarithm 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. This is because it utilizes a bulk wave of the first-order mode of thickness sliding.

[0034] 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.

[0035] 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 propagation direction 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.

[0036] In the first embodiment, the amplitude direction of the bulk wave in the thickness-slip primary mode is approximately opposite in the first region 251 and the second region 252, both included in the intersection region C (see Figure 1) of the piezoelectric layer 20, as shown in Figure 4. Figure 4 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.

[0037] 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.

[0038] 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 electrodes connected to a hot potential or electrodes connected to a ground potential, as described above, and no floating electrodes are provided.

[0039] 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.

[0040] Piezoelectric layer 20: LiNbO3 with Euler angles (0°, 0°, 90°) Thickness of piezoelectric layer 20: 400 nm Support substrate 11: Si 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

[0041] As is clear from Figure 5, good resonance characteristics with a relative bandwidth of 12.5% ​​are obtained despite the absence of a reflector.

[0042] By the way, if the thickness of the piezoelectric layer 20 is d and the average (average distance) of 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 6.

[0043] 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, except that d / 2p was changed.

[0044] 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 first-order thickness-slip mode described above.

[0045] 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 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 7, K is the crossover width. As mentioned above, in the elastic wave apparatus 10 of this disclosure, the number of electrode finger 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.

[0046] 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 7 and 8.

[0047] 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 the Euler angles of LiNbO3 were set to (0°, 0°, 90°). Also, the metallization ratio MR = 0.35 was set.

[0048] 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 the opposing direction, the area on the first electrode finger 31 that overlaps with the second 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.

[0049] Furthermore, if multiple pairs of first electrode fingers 31 and second electrode fingers 32 are provided, the ratio of the metallized portion to the total area of ​​the cross region C should be defined as MR.

[0050] 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 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 9 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.

[0051] 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, 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 7, 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 thickness of the piezoelectric layer 20 and the dimensions of the first electrode finger 31 and the second electrode finger 32.

[0052] 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. That is, if MR ≤ 1.75(d / p) + 0.05, the relative bandwidth can be reliably kept at 17% or less.

[0053] Figure 11 shows the Euler angle (0°, θ) of LiNbO3 when d / p approaches 0. LN ,ψ LN This is an explanatory diagram showing the relative bandwidth map for ). The hatched area in Figure 11 is the region where a relative bandwidth of at least 5% is obtained. Approximating the range of the region, it is the range expressed by the following equations (1), (2), and (3).

[0054] (0°±10°, 0°~20°, any ψ LN ) …Formula (1) (0° ± 10°, 20° to 80°, 0° to 60°(1 - (θ LN - 50) 2 / 900) 1 / 2 ) or (0° ± 10°, 20° to 80°, [180° - 60°(1 - (θ LN - 50) 2 / 900) 1 / 2 to 180°) … Equation (2) (0° ± 10°, [180° - 30°(1 - (ψ LN - 90) 2 / 8100) 1 / 2 to 180°, any ψ LN ) … Equation (3)

[0055] Therefore, in the case of the Euler angle range of the above Equation (1), Equation (2) or Equation (3), the ratio bandwidth can be made sufficiently wide, which is preferable.

[0056] Figure 12 is an enlarged cross-sectional view of the region A in Figure 2. As shown in Figures 1 and 12, in the first embodiment, the acoustic multilayer film 43 has a cavity portion 14. In the first embodiment, the cavity portion 14 penetrates the acoustic multilayer film 43 in the Z direction. Thereby, the parasitic capacitance generated between the IDT electrode 30 and the layer made of a conductor among the plurality of layers included in the acoustic multilayer film 43 can be suppressed, so that the ratio bandwidth can be increased.

[0057] In the first embodiment, the cavity portion 14 overlaps at least a part of the first electrode finger 31 and the second electrode finger 32 in the excitation region C when viewed in plan in the Z direction. In the example of Figure 1, the cavity portion 14 overlaps with the portions that overlap with the intersection region C among the first electrode finger 31 and the second electrode finger 32 when viewed in plan in the Z direction.

[0058] Here, when viewed in a plane in the Z direction, at least a portion of the region between at least one pair of adjacent first electrode fingers 31 and second electrode fingers 32 is superimposed with the acoustic multilayer film 43. Preferably, when viewed in a plane in the Z direction, at least a portion of the region between at least one pair of adjacent first electrode fingers 31 and second electrode fingers 32 is superimposed with all of the multiple layers (layers 43a to 43g) included in the acoustic multilayer film 43. Also preferably, when viewed in a plane in the Z direction, at least a portion of the region between all adjacent first electrode fingers 31 and second electrode fingers 32 is superimposed with the acoustic multilayer film 43. This allows the acoustic multilayer film 43 to reflect propagating waves well.

[0059] In the first embodiment, the center of the width of the cavity 14 (center in the X direction) coincides with the center of the width of the first electrode finger 31 and the second electrode finger 32 when viewed in plan in the Z direction, but this is merely one example. As long as the cavity 14 overlaps with at least a portion of the first electrode finger 31 and the second electrode finger 32 when viewed in plan in the Z direction, the center of the width of the cavity 14 (center in the X direction) does not have to coincide with the center of the width of the first electrode finger 31 and the second electrode finger 32 when viewed in plan in the Z direction, due to manufacturing variations, etc.

[0060] The following describes embodiments according to the first embodiment. However, the embodiments are not limited to those described in this example.

[0061] The elastic wave apparatus according to Example 1-1 was designed as follows. Here, the acoustic multilayer film 43 is a laminate containing a 3-layer first layer and a 4-layer second layer, and the first layer and the second layer are stacked alternately. The elastic wave apparatus according to Example 1-1 is an elastic wave apparatus according to the first embodiment. Piezoelectric layer 20: Single-crystal LiNbO3 layer (thickness 340 nm, Euler angles (0°, 30°, 0°)) IDT electrode 30: Laminate of Ti layer (thickness 12nm) and AlCu layer (thickness 80nm) Electrode pitch: 3.5 μm Electrode width: 0.6μm Acoustic multilayer film, first layer: Tungsten (W) layer (thickness 131.2 nm) Acoustic multilayer film, second layer: SiO2 layer (thickness 176.3 nm) Width of the cavity: 1800 nm Intermediate layer 12: SiO2 layer (thickness 500nm) Support substrate 11: Single crystal silicon layer (thickness 4.0 μm)

[0062] The elastic wave apparatus according to Comparative Example 1-1 was designed in the same way as Example 1-1, except that the acoustic multilayer film 43 did not have a cavity 14.

[0063] The characteristics of admittance Y were investigated by simulation for the elastic wave apparatus according to Example 1-1 and Comparative Example 1-1 described above. Figure 13 is a graph showing the resonance characteristics of the elastic wave apparatus according to the first embodiment.

[0064] As shown in Figure 13, in Example 1-1, where the acoustic multilayer film 43 has cavities 14, the relative bandwidth was larger compared to Comparative Example 1-1, where the acoustic multilayer film 43 does not have cavities 14. This shows that the presence of cavities 14 in the acoustic multilayer film 43 can improve the resonance characteristics.

[0065] (Second Embodiment) Figure 14 is an enlarged cross-sectional view showing the elastic wave apparatus according to the second embodiment. Here, Figure 14 shows the same region as the enlarged cross-sectional view in Figure 12. As shown in Figure 14, the elastic wave apparatus 10A according to the second embodiment differs from the first embodiment in that the cavity 14A penetrates only a portion of the acoustic multilayer film 43.

[0066] As shown in Figure 14, in the second embodiment, the cavity 14A penetrates in the Z direction from layer 43a to layer 43d, which is the layer closest to the piezoelectric layer 20 among the multiple layers included in the acoustic multilayer film 43, but does not penetrate from layer 43e to layer 43g. That is, in the second embodiment, the first electrode finger 31 and the second electrode finger 32, when viewed in plan in the Z direction, overlap the cavity 14A and some of the layers included in the acoustic multilayer film 43 (layers 43e to 43g in the example of Figure 14). Even in this case, the relative bandwidth can be increased. In the example of Figure 14, four layers from layer 43a to layer 43d among the multiple layers included in the acoustic multilayer film 43 are penetrated in the Z direction, but this is not limited to this. The cavity 14A only needs to penetrate at least layer 43a, which is the layer closest to the piezoelectric layer 20 among the multiple layers included in the acoustic multilayer film 43.

[0067] The following describes an embodiment according to the second embodiment. However, this embodiment does not limit the possible embodiments.

[0068] In Example 2-1, the design was the same as in Example 1-1, except that the cavity 14A was designed to penetrate only one layer (i.e., only layer 43a) from the piezoelectric layer side of the acoustic multilayer film 43. The elastic wave apparatus according to Example 2-1 is an elastic wave apparatus according to the second embodiment.

[0069] In Examples 2-2 to 2-7, the design was the same as in Example 1-1, except that the cavity 14A was designed to penetrate 2 to 7 layers of the acoustic multilayer film 43 from the piezoelectric layer. The elastic wave apparatus in Examples 2-2 to 2-7 is an elastic wave apparatus according to the second embodiment. The elastic wave apparatus in Example 2-7 is an elastic wave apparatus similar to that in Example 1-1.

[0070] Comparative Example 2-1 is a comparative example similar to Comparative Example 1-1. That is, Comparative Example 2-1 does not have a cavity 14A in the acoustic multilayer film 43.

[0071] The relative bandwidth was investigated by simulation for Examples 2-1 to 2-7 and Comparative Example 2-1. The results are shown in Table 1. Table 1 shows the simulation results for Examples 2-1 to 2-7 and Comparative Example 2-1.

[0072] [Table 1]

[0073] As shown in Table 1, in Examples 2-1 to 2-7, where the acoustic multilayer film 43 has cavities 14A, the relative bandwidth was larger compared to Comparative Example 2-1, where the acoustic multilayer film 43 does not have cavities 14A. This indicates that the presence of cavities 14A in at least one layer of the acoustic multilayer film 43 can improve the resonance characteristics.

[0074] (Third embodiment) Figure 15 is an enlarged cross-sectional view showing the elastic wave apparatus according to the third embodiment. Here, Figure 15 shows the same region as the enlarged cross-sectional view in Figure 12. As shown in Figure 15, the elastic wave apparatus 10B according to the third embodiment differs from the first embodiment in that the IDT electrode is provided on the second main surface 20b of the piezoelectric layer 20. The elastic wave apparatus 10B in the third embodiment can also have a large specific bandwidth.

[0075] The following describes an embodiment according to the third embodiment. However, this embodiment does not limit the possible embodiments.

[0076] The elastic wave apparatus according to Example 3-1 has the same design as Example 1-1, except that the IDT electrode is provided on the second main surface 20b. The elastic wave apparatus according to Example 3-1 is an elastic wave apparatus according to the third embodiment.

[0077] The elastic wave apparatus in Comparative Example 3-1 was designed in the same way as in Comparative Example 2-1. Specifically, in Comparative Example 3-1, the IDT electrode is provided on the first main surface 20a, and there is no cavity 14 in the acoustic multilayer film 43.

[0078] The characteristics of admittance Y were investigated by simulation for the elastic wave apparatus according to Example 3-1 and Comparative Example 3-1 described above. Figure 16 is a graph showing the resonance characteristics of the elastic wave apparatus according to the third embodiment.

[0079] As shown in Figure 16, in Example 3-1, where the acoustic multilayer film 43 has a cavity 14, the relative bandwidth was larger compared to Comparative Example 3-1, where the acoustic multilayer film 43 does not have a cavity 14. This shows that even with a design where the IDT electrode 30 is located below the piezoelectric layer 20, the presence of a cavity 14 in the acoustic multilayer film 43 can improve the resonance characteristics.

[0080] (Fourth Embodiment) Figure 17 is an enlarged cross-sectional view showing the elastic wave apparatus according to the fourth embodiment. Here, Figure 17 shows the same region as the enlarged cross-sectional view in Figure 12. As shown in Figure 17, in the elastic wave apparatus 10C according to the fourth embodiment, the width w2 of the cavity 14C in the X direction is different from that of the first embodiment in relation to the width w1 of the first electrode finger 31 and the second electrode finger 32 in the X direction. In the example of Figure 17, the width w1 of the first electrode finger 31 and the second electrode finger 32 in the X direction is greater than the width w2 of the cavity 14C in the X direction.

[0081] The following describes an embodiment according to the fourth embodiment. However, this embodiment does not limit the available embodiments.

[0082] Figure 18 shows the relative bandwidth of an elastic wave apparatus when the width of the cavity in the X direction is changed relative to the width of the electrode finger in the X direction. In the elastic wave apparatus shown in Figure 18, the design is the same as in Example 1-1, except that the width w2 of the cavity in the X direction is changed relative to the width w1 of the electrode finger (first electrode finger 31 and second electrode finger 32) in the X direction by changing the width w2 of the cavity 14C in the X direction.

[0083] As shown in Figure 18, when w2 / w1 is greater than 0, the relative bandwidth is larger compared to when w2 / w1 is 0, i.e., when there is no cavity 14C in the acoustic multilayer film 43. This shows that even if the width w2 in the X direction of the cavity 14 is different from the width w1 in the X direction of the first electrode finger 31 and the second electrode finger 32, the presence of the cavity 14C in the acoustic multilayer film 43 can improve the resonance characteristics.

[0084] Furthermore, as shown in Figure 18, when w2 / w1 is 1 or greater, that is, when the width w2 of the cavity 14 in the X direction is greater than the width w1 of the first electrode finger 31 and the second electrode finger 32 in the X direction, the relative bandwidth is larger compared to when w2 / w1 is greater than 0 and less than 1, that is, when the width w2 of the cavity 14C in the X direction is smaller than the width w1 of the first electrode finger 31 and the second electrode finger 32 in the X direction. This shows that the resonance characteristics can be further improved by making the width w2 of the cavity 14C in the X direction greater than or equal to the width w1 of the first electrode finger 31 and the second electrode finger 32 in the X direction.

[0085] The elastic wave apparatus described herein is not limited to the embodiments described above. Modifications are shown below with reference to the drawings. These modifications can be appropriately combined with other embodiments and other modifications.

[0086] Figure 19 is an enlarged cross-sectional view showing the elastic wave apparatus according to the first modified example. Here, Figure 19 shows the same region as the enlarged cross-sectional view in Figure 12. As shown in Figure 19, the elastic wave apparatus 10D according to the first modified example differs from the elastic wave apparatus according to the first embodiment in that IDT electrodes are provided on both the first main surface 20a and the second main surface 20b of the piezoelectric layer 20.

[0087] Figure 20 is a plan view showing an elastic wave apparatus according to a second modified example. As shown in Figure 20, the elastic wave apparatus 10E according to the second modified example differs from the first embodiment in that, when viewed in plan in the Z direction, the cavity 14E is provided from the base end of the first electrode finger 31 to the inner end of the second busbar 34 in the Y direction, or from the base end of the second electrode finger 32 to the inner end of the first busbar 33 in the Y direction.

[0088] Figure 21 is a plan view showing an elastic wave apparatus according to a third modified example. As shown in Figure 21, the elastic wave apparatus 10F according to the third modified example differs from the first embodiment in that the cavity portions 14F are provided separately so as to be aligned in the Y direction.

[0089] Figure 22 is a plan view showing an elastic wave apparatus according to the fourth modified example. As shown in Figure 21, the elastic wave apparatus 10G according to the fourth modified example differs from the first embodiment in that, when viewed in plan in the Z direction, the cavity 14G is provided so as to overlap only with the first electrode finger 31.

[0090] 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.

[0091] For example, a dielectric layer may be further provided on at least one main surface of the piezoelectric layer 20. This can suppress higher-order modes that occur in the thickness direction of the piezoelectric layer 20 and improve the resonance characteristics. The dielectric layer may be provided so as to cover the IDT electrode, or it may be provided between the IDT electrode and the piezoelectric layer. The material of the dielectric layer is not particularly limited, and for example, silicon dioxide (SiO₂) x The dielectric layer may be at least one of the following: silicon nitride (Si3N4), aluminum nitride (AlN), aluminum oxide (Al2O3), tantalum oxide (Ta2O5), or niobium oxide (Nb2O5). In this case, the dielectric layer may consist of multiple layers stacked together. [Explanation of Symbols]

[0092] 10. Elastic wave apparatus 11 Support substrate 12 Middle Class 20 piezoelectric layers 20a First main surface 20b 2nd principal surface 30 IDT electrodes 31 1st electrode finger 32 2nd electrode finger 33 First Bus Bar 34 Second Bus Bar 43 Acoustic multilayer film

Claims

1. Support substrate and An acoustic multilayer film provided on the upper side of the support substrate, A piezoelectric layer provided on the upper side of the acoustic multilayer film, An IDT electrode provided on at least one side of the upper or lower side of the piezoelectric layer, Equipped with, The acoustic multilayer film includes a plurality of layers stacked in a first direction, The plurality of layers include a first layer and a second layer made of a different material from the first layer. At least one of the aforementioned plurality of layers is made of a conductor, The IDT electrode comprises a first busbar facing each other, a second busbar, at least one first electrode finger whose proximal end is connected to the first busbar, and at least one second electrode finger whose proximal end is connected to the second busbar. When the thickness of the piezoelectric layer is d and the distance between the centers of adjacent first and second electrode fingers is p, d / p is 0.5 or less. The acoustic multilayer film has a cavity that penetrates in the first direction, at least the layer closest to the piezoelectric layer among the plurality of layers. Viewed in the first direction from a plan, at least a portion of the region between at least one pair of adjacent first electrode fingers and second electrode fingers is superimposed on the acoustic multilayer film. The aforementioned cavity, when viewed in plan in the first direction, overlaps with at least a portion of at least one of the first electrode finger and the second electrode finger, in an elastic wave device.

2. The elastic wave apparatus according to claim 1, wherein, when viewed from a direction perpendicular to the extending direction of the first electrode finger and the second electrode finger, 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 a direction perpendicular to the extending direction of the first electrode finger and second electrode finger is defined as the excitation region, the cavity overlaps with at least a portion of the first electrode finger and second electrode finger in the excitation region when viewed in plan in the first direction.

3. The elastic wave apparatus according to claim 1, wherein the length of the cavity portion in the width direction of the first electrode finger and the second electrode finger is equal to or greater than the width of at least one of the first electrode finger and the second electrode finger.

4. The elastic wave apparatus according to any one of claims 1 to 3, wherein the cavity, when viewed in plan in the first direction, overlaps with at least a portion of the center in the width direction of at least one of the first electrode finger and the second electrode finger.

5. The acoustic wave apparatus according to any one of claims 1 to 4, wherein the cavity penetrates the acoustic multilayer film in a first direction.

6. The elastic wave apparatus according to any one of claims 1 to 5, wherein the IDT electrodes are provided on the upper and lower sides of the piezoelectric layer.

7. The elastic wave apparatus according to any one of claims 1 to 6, wherein the acoustic impedance of the first layer is higher than the acoustic impedance of the second layer.

8. The elastic wave apparatus according to any one of claims 1 to 7, wherein the first layer comprises at least one of tungsten carbide, tantalum carbide, rhenium oxide, silicon chromium, 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, platinum, tungsten, copper, gold, and silver.

9. The elastic wave apparatus according to claim 8, wherein the first layer comprises at least one of platinum, tungsten, copper, gold, and silver.

10. The elastic wave apparatus according to any one of claims 1 to 9, wherein the second layer comprises at least one of silicon oxide and aluminum.

11. The acoustic wave apparatus according to any one of claims 1 to 10, further comprising an intermediate layer provided between the support substrate and the acoustic multilayer film.

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

13. The elastic wave apparatus according to any one of claims 1 to 12, wherein, when viewed from a direction perpendicular to the extending direction of the first electrode finger and the second electrode finger, the region in which adjacent first electrode finger and second electrode finger overlap, and the region between the centers of adjacent first electrode finger and second electrode finger in a direction perpendicular to the extending direction of the first electrode finger and second electrode finger, is defined as the excitation region, and when the metallization ratio of the first electrode finger and second electrode finger with respect to the excitation region is denoted as MR, the condition MR ≤ 1.75 (d / p) + 0.075 is met.

14. The Euler angle (φ) of the lithium niobate constituting the piezoelectric layer ＬＮ , θ ＬＮ ,ψ ＬＮ The elastic wave apparatus according to any one of claims 1 to 13, wherein ) is within the range of formula (1), formula (2), or formula (3) below. (0°±10°, 0°~20°, any ψ) ＬＮ ) ...Formula (1) (0° ± 10°, 20° to 80°, 0° to 60°(1 - (θ ＬＮ - 50)) ２ / 900)) １／２ ) or (0° ± 10°, 20° to 80°, [180° - 60°(1 - (θ ＬＮ - 50)) ２ / 900)) １／２ ] to 180°)... Equation (2) (0°±10°, [180°-30°(1-(ψ ＬＮ -90) ２ ( / 8100) １／２ ] ~180°, any ψ ＬＮ )...Formula (3)

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