Elastic wave device and filter

Abstract

The purpose of the present invention is to improve resonance characteristics and filter characteristics. This elastic wave device comprises: a support substrate; a first acoustic multilayer film provided on the upper side of the support substrate; a piezoelectric layer provided on the upper side of the first acoustic multilayer film; and a first IDT electrode provided between the first acoustic multilayer film and the piezoelectric layer. The first IDT electrode has a first bus bar, a second bus bar, a first electrode finger, and a second electrode finger that face each other. The first acoustic multilayer film includes a first plurality of layers. The first plurality of layers include a first layer in contact with the electrode fingers, and a second layer made of a material different from that of the first layer and laminated on the first layer. When d represents the thickness of the piezoelectric layer and p represents the distance between the centers of adjacent electrode fingers, d / p is 0.5 or less. When a region between adjacent electrode fingers, which is a region where the adjacent electrode fingers overlap each other in plan view from the arrangement direction of the electrode fingers, is defined as a first gap region, at least a part of the second layer is present in at least one first gap region.

Description

Elastic wave device and filter

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

[0002] Patent Document 1 describes an elastic wave device including 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.

[0003] Japanese Patent No. 5648695

[0004] In the elastic wave device shown in Patent Document 1, unnecessary waves may be generated, and the resonance characteristics and filter characteristics may deteriorate.

[0005] An object of the present invention is to provide an elastic wave device and a filter capable of improving resonance characteristics and filter characteristics.

[0006] An elastic wave device according to one aspect includes a support substrate, a first acoustic multilayer film provided on the upper side of the support substrate, a piezoelectric layer provided on the upper side of the first acoustic multilayer film, and a first IDT electrode provided between the first acoustic multilayer film and the piezoelectric layer. The first IDT electrode has a first bus bar and a second bus bar facing each other, at least one first electrode finger having a base end connected to the first bus bar, and at least one second electrode finger having a base end connected to the second bus bar. The first acoustic multilayer film includes a first plurality of layers laminated in the vertical direction. The first plurality of layers include a first layer contacting at least one of the first electrode finger and the second electrode finger, and a second layer made of a material different from the first layer and laminated on the first layer. When the film thickness of the piezoelectric layer is d and the center-to-center distance between adjacent first electrode fingers and second electrode fingers is p, d / p is 0.5 or less. When viewed in plan from the arrangement direction of the first electrode fingers and the second electrode fingers, in a region overlapping adjacent first electrode fingers and second electrode fingers and between the adjacent first electrode fingers and second electrode fingers, which is defined as a first gap region, at least a part of the second layer is present in at least one of the first gap regions.

[0007] A filter according to one embodiment is a filter comprising a resonator, wherein at least one of the resonators is the elastic wave device.

[0008] The elastic wave apparatus and filter of the present invention can improve resonance characteristics and filter characteristics.

[0009] 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' of Figure 1. Figure 3 is an enlarged cross-sectional view showing an enlarged view of Figure 2. Figure 4 is a cross-sectional view taken along line IV-IV' of Figure 1. Figure 5 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 6 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 7 is an explanatory diagram showing an example of the resonance characteristics of the elastic wave apparatus of the first embodiment. Figure 8 is an explanatory diagram showing the relationship between d / 2p and the specific bandwidth as a resonator, where p is the distance between the centers of adjacent electrodes or the average distance between the centers, and d is the average thickness of the piezoelectric layer, in the elastic wave apparatus of the first embodiment. Figure 9 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 10 is a reference diagram showing an example of the resonance characteristics of the elastic wave apparatus of the first embodiment. Figure 11 is an explanatory diagram showing the relationship between the relative bandwidth of the elastic wave apparatus of the first embodiment, when a large number of elastic wave resonators are configured, and the phase rotation amount of the spurious impedance normalized by 180 degrees as the spurious magnitude. Figure 12 is an explanatory diagram showing the relationship between d / 2p, the metallization ratio MR, and the relative bandwidth. Figure 13 shows LiNbO when d / p approaches 0. ３ Euler angle (0°, θ) ＬＮ ψ ＬＮThis is an explanatory diagram showing a map of the relative bandwidth for ). Figure 14 is an enlarged cross-sectional view showing an elastic wave apparatus according to Comparative Example 1. Figure 15 is an enlarged cross-sectional view showing an elastic wave apparatus according to Comparative Example 2. Figure 16 is an enlarged cross-sectional view showing elastic wave apparatuses according to Comparative Examples 3 and 4. Figure 17 is a diagram showing the resonance characteristics of the elastic wave apparatus according to Comparative Example 1 and Example 1. Figure 18 is a diagram showing the resonance characteristics of the elastic wave apparatus according to Examples 2 to 4. Figure 19 is a diagram showing the resonance characteristics of the elastic wave apparatus according to Comparative Example 2. Figure 20 is a diagram showing the resonance characteristics of the elastic wave apparatus according to Comparative Examples 3 and 4. Figure 21 is an enlarged cross-sectional view showing an elastic wave apparatus according to the second embodiment. Figure 22 is a cross-sectional view showing an elastic wave apparatus according to the third embodiment. Figure 23 is an enlarged cross-sectional view showing an elastic wave apparatus according to the fourth embodiment. Figure 24 is an enlarged cross-sectional view showing an elastic wave apparatus according to the fifth embodiment. Figure 25 is a diagram showing the resonance characteristics of the elastic wave apparatus according to Examples 5 and 6. Figure 26 is a cross-sectional view showing an elastic wave apparatus according to the sixth embodiment. Figure 27 is a cross-sectional view showing an elastic wave apparatus according to the seventh embodiment. Figure 28 is a circuit diagram showing a filter according to the eighth embodiment.

[0010] 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.

[0011] (First Embodiment) Figure 1 is a plan view showing an elastic wave apparatus of the first embodiment. Figure 2 is a cross-sectional view taken along line II-II' of Figure 1. Figure 3 is an enlarged cross-sectional view showing an enlarged version of Figure 2. Figure 4 is a cross-sectional view taken along line IV-IV' of Figure 1. Figure 3 is a diagram showing cross-sections of the piezoelectric layer 20, a pair of first electrode fingers 31 and second electrode fingers 32, the first layer 43a, and the second layer 43b.

[0012] As shown in Figures 1 and 2, the elastic wave apparatus 10 according to the first embodiment includes a support member, a piezoelectric layer 20, an IDT electrode 30, an acoustic multilayer film 43, a dielectric layer 41, and through electrodes 51 and 52.

[0013] (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.

[0014] In the following description, one orientation of the support substrate 11 in the thickness direction may be described as "up," and the other orientation of the support substrate 11 in the thickness direction may be described as "down." In addition, 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, and "provided on the lower side" includes being provided directly below in contact with it, and being provided indirectly or at a distance so as to be located below it.

[0015] (Support Substrate) In the first embodiment, the support substrate 11 is formed from at least one of the following materials: silicon (Si), quartz, silicon carbide, lithium niobate, lithium tantalate, sapphire, aluminum nitride, glass, and aluminum oxide. The support substrate 11 is preferably made of Si with high resistance of 4 kΩ or more.

[0016] (Intermediate layer) The intermediate layer 12 is formed of a dielectric material. The material of the intermediate layer 12 is silicon oxide (SiO ｘ It is preferable that the intermediate layer 12 contains at least one of ) and silicon nitride (SiN). Even when the intermediate layer 12 is provided, spurious emissions originating from the acoustic multilayer film 43 are more easily leaked to the support member, thereby improving the resonance characteristics. Note that the intermediate layer 12 is not an essential component and may not be provided.

[0017] (Acoustic Multilayer Film) The acoustic multilayer film 43 is a multilayer film containing multiple layers. The acoustic multilayer film 43 is provided on a support member. The acoustic multilayer film 43 is an example of the "first acoustic multilayer film" of this disclosure. In the example in Figure 2, the acoustic multilayer film 43 is laminated from the piezoelectric layer 20 side, with a first layer 43a, a second layer 43b, and the other layers 43c to 43g. Here, the first layer 43a, the second layer 43b, and the other layers 43c to 43g are examples of the "first multiple layers" of this disclosure. Note that the number of layers in the acoustic multilayer film 43 shown in Figure 2 is merely an example and is not particularly limited, and it is sufficient that it includes at least the first layer 43a and the second layer 43b. Details of the shapes of the first layer 43a and the second layer 43b will be described later.

[0018] In the acoustic multilayer film 43, layers with relatively low acoustic impedance and layers with relatively high acoustic impedance are alternately stacked. To explain in detail with a specific example, among the layers included in the acoustic multilayer film 43 (first layer 43a, second layer 43b, and other layers 43c to 43g), layer 43e, which is sandwiched between two layers 43d and 43f and has a lower acoustic impedance than one of the two layers 43d, has a lower acoustic impedance than the other layer 43f. On the other hand, layer 43f, which is sandwiched between two layers 43e and 43g and has a higher acoustic impedance than one of the two layers 43e, has a higher acoustic impedance than the other layer 43g. By arranging the acoustic impedance relationships between the layers included in the acoustic multilayer film 43 as described above, the bulk wave of the thickness-slip first mode can be confined within the piezoelectric layer 20.

[0019] In the example shown in Figure 2, the first layer 43a and layers 43c, 43e, and 43g have relatively lower acoustic impedances than the second layer 43b and layers 43d and 43f. However, the example is not limited to this, and the first layer 43a and layers 43c, 43e, and 43g may have relatively higher acoustic impedances than the second layer 43b and layers 43d and 43f.

[0020] The layers with relatively low acoustic impedance (in the example of Figure 2, the first layer 43a and layers 43c, 43e, and 43g) are, for example, silicon dioxide (SiO₂ ｘIt is preferable to contain at least one of them and aluminum (Al). Further, when both the layer and the intermediate layer 12 having relatively low acoustic impedance are made of silicon oxide (SiO ｘ ), the layer having relatively low acoustic impedance is preferably made of silicon oxide (SiO ｘ ) having a lower density than the intermediate layer 12. Thereby, the acoustic impedance of the layer having relatively low acoustic impedance can be sufficiently suppressed.

[0021] The layer having relatively high acoustic impedance (the second layer 43b and the layers 43d and 43f in the example of FIG. 2) is, for example, tungsten carbide (WC), tantalum carbide (TaC), rhenium oxide (ReO ３ ), carbon silicon chromium (CrCSi), niobium carbide (NbC), zirconium carbide (ZrC), titanium nitride (TiC), lanthanum boride (LaB ６ ), vanadium carbide (VC), aluminum nitride (AlN), silicon carbide (SiC), yttrium oxide (Y ２ O ３ ), magnesium oxide (MgO), silicon nitride (Si ３ N ４ ), boron carbide (B ４ C), strontium fluoride (SrF ２ ), barium fluoride (BaF ２ ), tantalum oxide (Ta ２ O ５ ), hafnium oxide (HfO ２ ), ytterbium oxide (Yb ２ O ３ ), tungsten oxide (WO ３ ), hafnium nitride (HfN), tungsten nitride (WN), platinum (Pt), tungsten (W), copper (Cu), gold (Au), and silver (Ag). Thereby, the acoustic impedance of the layer having relatively high acoustic impedance can be sufficiently improved.

[0022] The materials of the first layer 43a, the second layer 43b, and the other layers 43c to 43g are not limited to those shown above. For example, the materials of the first layer 43a and layers 43c, 43e, and 43g may be different from each other, and the materials of the second layer 43b and layers 43d and 43f may be different from each other. Also, the materials of the first layer 43a, the second layer 43b, and the other layers 43c to 43g are not limited to being made of one type of material, but may be layers of mixtures containing multiple materials.

[0023] 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. In the first embodiment, the piezoelectric layer 20 is lithium niobate (LiNbO ３ The piezoelectric layer 20 is formed of lithium tantalate (LiTaO), but is not limited to this. ３ ) may consist of LiNbO ３ ya LiTaO ３ The cut angle is, for example, a Z-cut. The piezoelectric layer 20 is LiNbO ３ ya LiTaO ３ The cut angle may be a rotational Y-cut or an X-cut, and a propagation direction of ±30° for Y propagation and X propagation is preferred. The piezoelectric layer 20 is lithium niobate (LiNbO ３ ) or lithium tantalate (LiTaO) ３ ) includes LiNbO ３ ya LiTaO ３ Preferably, the Y-cut is rotated 120°±10° or 90°±10°. Here, 120°±10° includes the range from 120°-10° to 120°+10°, and 90°±10° includes the range from 90°-10° to 90°+10°.

[0024] The thickness of the piezoelectric layer 20 is not particularly limited, but to effectively excite the thickness-sliding primary mode, a thickness of 50 nm to 1000 nm is preferred.

[0025] (IDT electrode) The IDT (Interdigital Transducer) electrode 30 is provided between the piezoelectric layer 20 and the acoustic multilayer film 43. Here, the IDT electrode 30 is an example of the "first IDT electrode" of this disclosure. The IDT electrode 30 may be provided directly on the second main surface 20b, or it may be provided indirectly on the second main surface 20b via a dielectric layer or the like. In the first embodiment, the IDT electrode 30 is provided directly on the second main surface 20b.

[0026] 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.

[0027] 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, and 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.

[0028] In the following description, the thickness direction of the support substrate 11 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. In the first embodiment, the X direction is perpendicular to the extension direction of the first electrode finger 31 and the second electrode finger 32.

[0029] The distance between the centers of the first electrode finger 31 and the second electrode finger 32 (electrode pitch) 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 of the first electrode finger 31 and the second electrode finger 32 (electrode width), 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.

[0030] 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).

[0031] 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 for all pairs. That is, the first electrode finger 31 and the second electrode finger 32 were arranged at equal pitches.

[0032] 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, is 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.

[0033] 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, 30 μm.

[0034] During operation, an AC voltage is applied between a plurality of first electrode fingers 31 and a plurality of 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.

[0035] 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.

[0036] 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.

[0037] The through electrodes 51 and 52 are wiring electrodes that provide an electrical connection to the IDT electrode 30. In the examples of Figures 2 and 4, the through electrode 51 is provided so as to be in contact with the first busbar 33 and the second busbar 34, and the through electrode 52 is provided so as to be in contact with the first busbar 33 and the second busbar 34.

[0038] (Dielectric layer) The dielectric layer is a dielectric layer provided on at least one main surface of the piezoelectric layer 20. In the first embodiment, the dielectric layer 41 is provided on the first main surface 20a. This makes it possible to suppress higher-order modes that occur in the thickness direction of the piezoelectric layer 20 and improve the resonance characteristics.

[0039] The material of the dielectric layer 41 is not particularly limited, and for example, silicon dioxide (SiO₂ ｘ ), silicon nitride (Si ３ N ４ ), aluminum nitride (AlN), aluminum oxide (Al ２O ３ ), tantalum oxide (Ta ２ O ５ ), niobium oxide (Nb ２ O ５ It may be at least one of the following. Also, the dielectric layer 41 may be made up of multiple layers stacked together.

[0040] Figure 5 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 6 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.

[0041] As shown in Figure 5, 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.

[0042] 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 6. Figure 6 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 into 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.

[0043] 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.

[0044] 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 to a ground potential, as described above, and no floating electrodes are provided.

[0045] Figure 7 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 7 are as follows.

[0046] Piezoelectric layer 20: LiNbO with Euler angles (0°, 0°, 90°) ３ Piezoelectric layer 20 thickness: 400 nm Support substrate 11: Si Length of cross region C: 40 μm Number of electrode pairs consisting of first electrode finger 31 and second electrode finger 32: 21 pairs Pitch between first electrode finger 31 and second electrode finger 32: 3 μm Width of first electrode finger 31 and second electrode finger 32: 500 nm d / p: 0.133

[0047] As is clear from Figure 7, despite the absence of a reflector, excellent resonance characteristics with a relative bandwidth of 12.5% ​​are obtained.

[0048] 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 8.

[0049] Figure 8 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 8, multiple elastic wave apparatuses were obtained in the same manner as the elastic wave apparatus that obtained the resonance characteristics shown in Figure 7, except that d / 2p was changed.

[0050] As shown in Figure 8, 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.

[0051] Figure 9 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 9, 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.

[0052] 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.

[0053] Figure 10 is a reference diagram showing an example of the resonance characteristics of the elastic wave apparatus of the first embodiment. As shown in Figure 10, the spurious signal indicated by arrow B appears between the resonant frequency and the anti-resonant frequency. Note that d / p = 0.08 and LiNbO ３ The Euler angles were set to (0°, 0°, 90°). Furthermore, the metallization ratio MR was set to 0.35.

[0054] 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.

[0055] 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 crossing region C should be defined as MR.

[0056] Figure 11 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 such as the thickness of the piezoelectric layer 20 and the dimensions of the first electrode fingers 31 and the second electrode fingers 32. Also, Figure 11 shows the Z-cut LiNbO ３ The results shown are for the case where a piezoelectric layer 20 consisting of the above is used, but a similar trend is observed when piezoelectric layers 20 with other cut angles are used.

[0057] In the region enclosed by the ellipse J in Figure 11, the spurious emission is large at 1.0. As is clear from Figure 11, when the relative bandwidth exceeds 0.17, that is, when it exceeds 17%, large spurious emissions with a spurious emission level of 1 or more appear within the passband, even if the parameters constituting the relative bandwidth are changed. In other words, as shown in the resonance characteristics in Figure 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 thickness of the piezoelectric layer 20 and the dimensions of the first electrode finger 31 and the second electrode finger 32.

[0058] Figure 12 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 12 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 12. In other words, if MR ≤ 1.75 (d / p) + 0.05, the relative bandwidth can be reliably reduced to 17% or less.

[0059] Figure 13 shows the LiNbO2 when d / p approaches 0. ３ Euler angle (0°, θ) ＬＮ ψ ＬＮ This is an explanatory diagram showing a map of the relative bandwidth for ). The hatched area in Figure 13 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).

[0060] (0°±10°, 0°~20°, any ψ) ＬＮ)...Equation (1) (0°±10°, 20°~80°, 0°~60°(1-(θ ＬＮ -50) ２ / 900) １／２ ) or (0°±10°, 20°~80°, [180°-60°(1-(θ) ＬＮ -50) ２ / 900) １／２ ]~180°) ...Formula (2) (0°±10°, [180°−30°(1−(ψ ＬＮ -90) ２ ( / 8100) １／２ ] ~180°, any ψ ＬＮ )...Formula (3)

[0061] Therefore, in the case of the Euler angle range of equation (1), equation (2), or equation (3) above, the relative bandwidth can be made sufficiently wide, which is preferable.

[0062] The shapes of the first layer 43a and the second layer 43b according to the first embodiment will be described in detail below. In the first embodiment, the first layer 43a is a layer included in the acoustic multilayer film 43 that is in contact with at least one of the first electrode finger 31 and the second electrode finger 32. The second layer 43b is a layer included in the acoustic multilayer film 43 that is laminated on the first layer 43a.

[0063] In the following description, the region that overlaps with adjacent first electrode fingers 31 and second electrode fingers 32 when viewed in plan in the X direction, and the region between adjacent first electrode fingers 31 and second electrode fingers 32, will be described as the first gap region G. In the example in Figure 3, since the shapes of the first electrode fingers 31 and second electrode fingers 32 when viewed from the Y direction are rectangular, the first gap region G is the region between the side surface 31b of the first electrode finger 31 and the side surface 32b of the second electrode finger 32.

[0064] Furthermore, the region that overlaps with the first electrode finger 31 or the second electrode finger 32 when viewed in a plan view in the Z direction is defined as the first electrode region E. That is, the first electrode region E is the region on both sides of the first gap region G in the X direction.

[0065] Furthermore, the region that overlaps with the first gap region G when viewed in a plan view in the Z direction will be described as the first inter-electrode region F. In other words, the first inter-electrode region F is the region that includes the first gap region G.

[0066] In the first embodiment, the first gap region G contains at least a portion of the second layer 43b. That is, as explained in the example in Figure 3, at least a portion of the second layer 43b is located between the side surfaces 31b and 32b of the adjacent first electrode finger 31 and second electrode finger 32. As a result, the displacement generated between the first electrode finger 31 and the second electrode finger 32 is suppressed by at least a portion of the second layer 43b present in the first gap region G, thereby suppressing unwanted waves and improving the resonance characteristics. Note that the second layer 43b does not need to be present in all of the first gap regions G; it is sufficient that at least a portion of the second layer 43b is present in at least one of the first gap regions G.

[0067] The presence or absence of the second layer 43b in the first gap region G can be determined by obtaining an image of the cross-section of the elastic wave apparatus parallel to the alignment direction (X direction) of the first electrode finger 31 and the second electrode finger 32 using an electron microscope such as a TEM (Transmission Electron Microscope).

[0068] As shown in Figure 3, in the first embodiment, the maximum distance between the upper surfaces 31a, 32a of the first electrode finger 31 or the second electrode finger 32 and the lower surface 431a of the first layer 43a in the first electrode region E is greater than the minimum thickness t1 of the first layer 43a in the first inter-electrode region F. This makes it possible to manufacture the elastic wave apparatus according to the first embodiment without grinding the first layer 43a, thereby improving manufacturability and suppressing unwanted waves to improve resonance characteristics. Note that the above thickness relationship does not necessarily have to hold in all first electrode regions E and first inter-electrode regions F. It is sufficient that the above thickness relationship holds for at least one first gap region in the first gap region G which contains at least a part of the second layer 43b, for the first electrode region E adjacent to that at least one first gap region, and for the first inter-electrode region F which includes that at least one first gap region. In this disclosure, a first electrode region being adjacent to a first gap region means that there are no other first electrode regions between the first gap region and the first electrode region.

[0069] The maximum distance between the upper surfaces 31a, 32a of the first electrode finger 31 or the second electrode finger 32 and the lower surface 431a of the first layer 43a in the first electrode region E can be measured by the following method. First, an observation image is obtained using an electron microscope such as a TEM of the cross-section of the elastic wave apparatus parallel to the alignment direction (X direction) of the first electrode finger 31 and the second electrode finger 32. Then, in this observation image, the length of a line segment extended in the Z direction from the upper surfaces 31a, 32a of the first electrode finger 31 or the second electrode finger 32 to the lower surface 431a of the first layer 43a is measured multiple times within one first electrode region E. Here, the maximum value of this length within one first electrode region E can be taken as the maximum distance between the upper surfaces 31a, 32a of the first electrode finger 31 or the second electrode finger 32 and the lower surface 431a of the first layer 43a in the first electrode region E. Furthermore, if there are multiple first gap regions G in the observed image above, each containing at least a portion of the second layer 43b, the maximum distance between the upper surfaces 31a, 32a of the first electrode finger 31 or the second electrode finger 32 and the lower surface 431a of the first layer 43a in the first electrode region E may be the largest of the maximum values ​​of such lengths in each of the multiple first electrode regions E adjacent to each of the multiple first gap regions G, or it may be the arithmetic mean of the maximum values ​​of such lengths.

[0070] The minimum thickness of the first layer 43a in the first inter-electrode region F can be measured by the following method. First, an observation image is obtained using an electron microscope such as a TEM of the cross-section of the elastic wave apparatus parallel to the alignment direction (X direction) of the first electrode finger 31 and the second electrode finger 32. Then, in this observation image, the length of a line segment extended in the Z direction from the upper surface 433a of the first layer 43a to the lower surface 432a of the first layer 43a is measured multiple times within one first inter-electrode region F. Here, the minimum value of this length within one first inter-electrode region F can be taken as the minimum thickness of the first layer 43a in the first inter-electrode region F. Furthermore, if the above observation image contains multiple first gap regions G in which at least a part of the second layer 43b is located, the minimum thickness of the first layer 43a in the first inter-electrode region F may be the smallest of the minimum lengths in each of the multiple first inter-electrode regions F, each containing one of the multiple first gap regions G, or it may be the arithmetic mean of the minimum lengths.

[0071] As shown in Figures 3 and 4, in the first embodiment, the thicknesses of the first electrode finger 31, the second electrode finger 32, and the first layer 43a are constant in the first electrode region E. Therefore, in the first embodiment, the maximum distance between the upper surfaces 31a, 32a of the first electrode finger 31 or the second electrode finger 32 and the lower surface 431a of the first layer 43a in the first electrode region E corresponds to the sum of the thickness te of the first electrode finger 31 or the second electrode finger 32 and the thickness t1e of the first layer 43a in the first electrode region E. That is, in the first embodiment, the relationship t1 < te + t1e holds.

[0072] In the first embodiment, the thickness t1e of the first layer 43a in the first electrode region E is equal to the minimum thickness t1 of the first layer 43a in the first inter-electrode region F. This eliminates the need to grind the first layer 43a to thin a portion of it during the manufacturing of the elastic wave apparatus according to the first embodiment, thereby improving manufacturability.

[0073] As shown in Figures 2 and 3, in the first embodiment, the upper surface of the second layer 43b is shaped to conform to the lower surface of the first layer 43a, and the lower surface 430b of the second layer 43b is flush with the surface.

[0074] As described above, the elastic wave apparatus 10 according to the first embodiment includes a support substrate 11, a first acoustic multilayer film (acoustic multilayer film 43) provided on the upper side of the support substrate 11, a piezoelectric layer 20 provided on the upper side of the first acoustic multilayer film, and a first IDT electrode provided between the first acoustic multilayer film and the piezoelectric layer 20. The first IDT electrode (IDT electrode 30) has a first busbar 33 facing each other, a second busbar 34, at least one first electrode finger 31 whose base end is connected to the first busbar 33, and at least one second electrode finger 32 whose base end is connected to the second busbar 34. The first acoustic multilayer film includes a first plurality of layers 43a to 43g stacked in the vertical direction. The first set of layers includes a first layer 43a in contact with at least one of the first electrode fingers 31 and the second electrode fingers 32, and a second layer 43b made of a different material from the first layer 43a and laminated on the first layer 43a. When the thickness of the piezoelectric layer 20 is d and the distance between the centers of adjacent first electrode fingers 31 and second electrode fingers 32 is p, d / p is 0.5 or less. When viewed from a plan view in the direction of arrangement (X direction) of the first electrode fingers 31 and second electrode fingers 32, if the region overlapping with adjacent first electrode fingers 31 and second electrode fingers 32, and the region between said adjacent first electrode fingers 31 and second electrode fingers 32 is defined as the first gap region G, then at least one of the first gap regions G contains at least a part of the second layer 43b. As a result, a portion of the second layer 43b present in the first gap region G suppresses the displacement occurring between the first electrode finger 31 and the second electrode finger 32, thereby suppressing unwanted waves and improving the resonance characteristics.

[0075] In a preferred embodiment, when viewed from above in a plan view, the region overlapping with the first electrode finger 31 or the second electrode finger 32 is defined as the first electrode region E, and when viewed from above in a plan view, the region overlapping with the first gap region G is defined as the first inter-electrode region F. In such a first electrode region E adjacent to at least one first gap region G (the first electrode region E adjacent to the first gap region G containing a portion of the second layer 43b), the maximum distance (e.g., thickness te + t1e) between the upper surfaces 31a, 32a of the first electrode finger 31 or the second electrode finger 32 and the lower surface 431a of the first layer 43a is greater than the minimum thickness t1 of the first layer 43a in the first inter-electrode region F including the at least one first gap region G (the first inter-electrode region F including the first gap region G containing a portion of the second layer 43b). This improves the manufacturability of the elastic wave apparatus according to the first embodiment and suppresses unwanted waves, thereby improving resonance characteristics.

[0076] In a desirable embodiment, the acoustic impedance of the first layer 43a is lower than that of the second layer 43b. This allows for good containment of the propagating waves of the piezoelectric layer 20.

[0077] In a desirable configuration, the acoustic impedance of the first layer 43a is higher than that of the second layer 43b. Even in this case, the propagating waves of the piezoelectric layer 20 can be effectively contained.

[0078] In a preferred embodiment, either the first layer 43a or the second layer 43b contains at least one of silicon oxide and aluminum. The other of the first layer 43a or the second layer 43b contains at least one of tungsten carbide, tantalum carbide, rhenium oxide, silicon chromium carbon, niobium carbide, zinc carbide, zinc nitride, lanthanum boride, vanadium carbide, aluminum nitride, silicon carbide, yttrium oxide, magnesium oxide, silicon nitride, boron carbide, strontium fluoride, barium fluoride, tantalum oxide, hafnium oxide, ytterbium oxide, tungsten oxide, hafnium nitride, tungsten nitride, platinum, tungsten, copper, gold, and silver. This reduces the acoustic impedance of the layer with relatively low acoustic impedance, thereby better confining the propagating waves of the piezoelectric layer 20.

[0079] In a more desirable embodiment, either the first layer 43a or the second layer 43b contains silicon oxide, and the other of the first layer 43a or the second layer 43b contains hafnium oxide. This reduces the acoustic impedance of the layer with relatively low acoustic impedance, thereby further confining the propagating waves of the piezoelectric layer 20.

[0080] In a preferred embodiment, an intermediate layer 12 is further provided between the support substrate 11 and the first acoustic multilayer film. In this case as well, the resonance characteristics can be improved.

[0081] In a preferred embodiment, the surface of the intermediate layer 12 facing the support substrate 11 is flush with the surface. In this case, the process of bonding the support substrate 11 to the acoustic multilayer film 43 via the intermediate layer 12 can be easily performed, improving the manufacturability of the elastic wave device 10.

[0082] In a preferred embodiment, the support substrate 11 has a different acoustic impedance from at least one of the first layer 43a and the second layer 43b. Even in this case, unwanted waves can be suppressed and resonance characteristics can be improved.

[0083] In a preferred embodiment, the support substrate 11 is made of at least one of silicon, quartz, silicon carbide, lithium niobate, lithium tantalate, sapphire, aluminum nitride, glass, and aluminum oxide. Even in this case, unwanted waves can be suppressed and resonance characteristics can be improved.

[0084] In a desirable configuration, the d / p ratio is 0.24 or less. This allows for even better resonance characteristics to be obtained.

[0085] In a desirable embodiment, when viewed from a direction perpendicular to the extending direction of the first electrode finger 31 and the second electrode finger 32, the region where adjacent first electrode finger 31 and second electrode finger 32 overlap, and the region between the centers of adjacent first electrode finger 31 and second electrode finger 32 in a direction perpendicular to the extending direction of the first electrode finger 31 and second electrode finger 32, is defined as the excitation region, and when the metallization ratio of the first electrode finger 31 and the second electrode finger 32 with respect to the excitation region is denoted as MR, the condition MR ≤ 1.75 (d / p) + 0.075 is satisfied. This effectively reduces spurious emissions and improves resonance characteristics.

[0086] In a preferred embodiment, the piezoelectric layer 20 contains lithium niobate. This allows for even better resonance characteristics to be obtained.

[0087] In a desirable embodiment, the Euler angle (φ) of the lithium niobate constituting the piezoelectric layer 20 is ＬＮ , θ ＬＮ ψ ＬＮ ) is within the range of equation (1), equation (2), or equation (3) below. This allows the relative bandwidth to be sufficiently wide. (0°±10°, 0°~20°, any ψ ＬＮ )...Equation (1) (0°±10°, 20°~80°, 0°~60°(1-(θ ＬＮ -50) ２ / 900) １／２ ) or (0°±10°, 20°~80°, [180°-60°(1-(θ) ＬＮ -50) ２ / 900) １／２ ]~180°) ...Formula (2) (0°±10°, [180°−30°(1−(ψ ＬＮ -90) ２ ( / 8100) １／２ ] ~180°, any ψ ＬＮ )...Formula (3)

[0088] The following describes an embodiment of the elastic wave apparatus according to the first embodiment.

[0089] (Example 1) The design parameters of the elastic wave apparatus according to Example 1 were as follows. In Example 1, t1 = 40 nm, te + t1e = 140 nm, a part of the second layer 43b is in the first gap region G, and te < t1 < te + t1e. Material of piezoelectric layer 20: 120° Y-cut LiNbO ３ Thickness of the piezoelectric layer 20: 320 nm Material of the first electrode finger 31 and the second electrode finger: Al Thickness of the first electrode finger 31 and the second electrode finger (te): 100 nm Line width of the first electrode finger 31 and the second electrode finger: 2 μm Distance between the first electrode finger 31 and the second electrode finger (electrode pitch): 5 μm Material of the dielectric layer 41: SiO ２ Thickness of dielectric layer 41: 20 nm Material of first layer 43a: SiO ２ Minimum thickness t1 of the first layer 43a in the first inter-electrode region F: 40 nm Thickness t1e of the first layer 43a in the first electrode region E: 40 nm Material of the second layer 43b: HfO ２ Thickness of the second layer 43b in the first electrode region E: 180 nm. Material of layers 43c, 43e, and 43g: SiO ２ Material for layers 43d and 43f: HfO ２ Thickness of layer 43c to 43g: 150 nm

[0090] (Comparative Example 1) Figure 14 is an enlarged cross-sectional view showing the elastic wave apparatus according to Comparative Example 1. The elastic wave apparatus according to Comparative Example 1 was designed in the same way as in Example 1, except that the design parameters of the elastic wave apparatus were as follows. That is, in Comparative Example 1, t1 = 140 nm, te + t1e = 140 nm, there is no part of the second layer 43b in the first gap region G, t1 = te + t1e, and as shown in Figure 14, the lower surface 430a of the first layer 43a is flush. Minimum thickness t1 of the first layer 43a in the first inter-electrode region F: 140 nm Thickness t1e of the first layer 43a in the first electrode region E: 40 nm

[0091] (Example 2) The elastic wave apparatus according to Example 2 was designed in the same way as Example 1, except that the thickness of the first layer 43a (t1 = t1e) was changed to 90 nm. That is, in Example 2, t1 = 90 nm, te + t1e = 190 nm, a part of the second layer 43b is in the first gap region G, and te < t1 < te + t1e.

[0092] (Example 3) The elastic wave apparatus according to Example 3 was designed in the same way as Example 1, except that the thickness of the first layer 43a (t1 = t1e) was changed to 80 nm. That is, in Example 3, t1 = 80 nm, te + t1e = 180 nm, a part of the second layer 43b is in the first gap region G, and te < t1 < te + t1e.

[0093] (Example 4) The elastic wave apparatus according to Example 4 was designed in the same way as Example 1, except that the thickness of the first layer 43a (t1 = t1e) was changed to 70 nm. That is, in Example 4, t1 = 70 nm, te + t1e = 170 nm, a part of the second layer 43b is in the first gap region G, and te < t1 < te + t1e.

[0094] (Comparative Example 2) Figure 15 is an enlarged cross-sectional view showing the elastic wave apparatus according to Comparative Example 2. The elastic wave apparatus according to Comparative Example 2 is designed in the same way as Example 1, except that the thickness of the first layer 43a (t1 = t1e) is changed to 100 nm, and the minimum value t1 of the thickness of the first layer 43a in the first inter-electrode region F is made the same as the thickness te of the electrode finger, as shown in Figure 15. That is, in Comparative Example 2, t1 = 100 nm, te + t1e = 200 nm, and there is no part of the second layer 43b in the first gap region G, so te = t1 < te + t1e.

[0095] (Comparative Example 3) Figure 16 is an enlarged cross-sectional view showing the elastic wave apparatus according to Comparative Example 3 and Comparative Example 4. The elastic wave apparatus according to Comparative Example 3 is designed in the same way as Example 1, except that the thickness of the first layer 43a (t1 = t1e) is changed to 110 nm, and the minimum value t1 of the thickness of the first layer 43a in the first inter-electrode region F is made greater than the thickness te of the electrode finger, as shown in Figure 16. That is, in Comparative Example 3, t1 = 110 nm, te + t1e = 210 nm, and te < t1 < te + t1e.

[0096] (Comparative Example 4) The elastic wave apparatus according to Comparative Example 4 was designed in the same way as in Example 1, except that the thickness of the first layer 43a (t1 = t1e) was changed to 120 nm, and the minimum value t1 of the thickness of the first layer 43a in the first inter-electrode region F was made greater than the thickness te of the electrode finger, as shown in Figure 16. That is, in Comparative Example 4, t1 = 120 nm, te + t1e = 220 nm, and te < t1 < te + t1e.

[0097] The resonance characteristics of the elastic wave apparatuses according to Examples 1 to 4 and Comparative Examples 1 to 4 described above were investigated by simulation. The results are shown in Figures 17 to 20. Figure 17 shows the resonance characteristics of the elastic wave apparatus according to Comparative Example 1 and Example 1. Figure 18 shows the resonance characteristics of the elastic wave apparatuses according to Examples 2 to 4. Figure 19 shows the resonance characteristics of the elastic wave apparatus according to Comparative Example 2. Figure 20 shows the resonance characteristics of the elastic wave apparatus according to Comparative Example 3 and Comparative Example 4. Figures 17 to 20 show the dependence of admittance Y on frequency for each example and comparative example.

[0098] As shown in Figures 17 to 20, in Examples 1 to 4, where the second layer 43b is present in the first gap region G, the unwanted wave S1 observed in Comparative Example 1, where the second layer 43b is absent in the first gap region G, is suppressed, as is the unwanted wave S2 observed in Comparative Examples 2 to 4, where the second layer 43b is absent in the first gap region G. Therefore, it can be seen that the resonance characteristics can be improved by suppressing unwanted waves when t1 < te + t1e.

[0099] As shown in Figures 17 to 20, in Examples 1 to 4 where t1 < te + t1e, the unwanted wave S1 observed in Comparative Example 1 where t1 = te + t1e is suppressed, and the unwanted wave S2 observed in Comparative Examples 2 to 4 where te ≤ t1 is also suppressed. Therefore, it can be seen that by setting t1 < te + t1e, unwanted waves can be suppressed and resonance characteristics can be improved.

[0100] (Second Embodiment) Figure 21 is an enlarged cross-sectional view showing an elastic wave apparatus according to the second embodiment. Figure 21 is an enlarged cross-sectional view showing the piezoelectric layer 20, a pair of first electrode fingers 31 and second electrode fingers 32, a first layer 43a, a second layer 43b, and a layer 43c laminated below the second layer 43b. As shown in Figure 21, the elastic wave apparatus according to the second embodiment differs from the first embodiment in that the lower surface 430b of the second layer 43b is not flush.

[0101] As shown in Figure 21, in the second embodiment, the maximum distance between the upper surfaces 31a, 32a of the first electrode finger 31 or the second electrode finger 32 and the lower surface 431b of the second layer 43b in the first electrode region E is greater than the minimum distance between the upper surface of the first layer 43a and the lower surface 431b of the second layer 43b in the first inter-electrode region F. Note that the above thickness relationship does not have to hold for all first electrode regions E and first inter-electrode regions F. It is sufficient that the above thickness relationship holds for at least one first gap region in the first gap region G which contains at least a part of the second layer 43b, for the first electrode region E adjacent to that at least one first gap region, and for the first inter-electrode region F which includes that at least one first gap region.

[0102] The maximum distance between the upper surfaces 31a, 32a of the first electrode finger 31 or the second electrode finger 32 and the lower surface 431b of the second layer 43b in the first electrode region E can be measured by the following method. First, an observation image of the cross-section of the elastic wave apparatus parallel to the alignment direction (X direction) of the first electrode finger 31 and the second electrode finger 32 is obtained using an electron microscope such as a TEM. Then, in this observation image, the length of a line segment extended in the Z direction from the upper surfaces 31a, 32a of the first electrode finger 31 or the second electrode finger 32 to the lower surface 431b of the second layer 43b is measured multiple times within one first electrode region E. Here, the maximum value of this length within one first electrode region E can be taken as the maximum distance between the upper surfaces 31a, 32a of the first electrode finger 31 or the second electrode finger 32 and the lower surface 431b of the second layer 43b in the first electrode region E. Furthermore, if there are multiple first gap regions G in the observed image above, each containing at least a portion of the second layer 43b, the maximum distance between the upper surfaces 31a, 32a of the first electrode finger 31 or the second electrode finger 32 and the lower surface 431b of the second layer 43b in the first electrode region E may be the largest of the maximum values ​​of such lengths in each of the multiple first electrode regions E adjacent to each of the multiple first gap regions G, or it may be the arithmetic mean of the maximum values ​​of such lengths.

[0103] The minimum distance between the upper surface 433a of the first layer 43a and the lower surface 431b of the second layer 43b in the first inter-electrode region F can be measured by the following method. First, an observation image of the cross-section of the elastic wave apparatus parallel to the alignment direction (X direction) of the first electrode finger 31 and the second electrode finger 32 is obtained using an electron microscope such as a TEM. Then, in this observation image, the length of a line segment extended in the Z direction from the upper surface 433a of the first layer 43a to the lower surface 432b of the second layer 43b is measured multiple times within one first inter-electrode region F. Here, the minimum value of this length within one first inter-electrode region F can be taken as the minimum distance between the upper surface 433a of the first layer 43a and the lower surface 432b of the second layer 43b in the first inter-electrode region F. Furthermore, if the above observation image contains multiple first gap regions G in which at least a part of the second layer 43b is located, the minimum value of the distance between the upper surface 433a of the first layer 43a and the lower surface 431b of the second layer 43b in the first inter-electrode region F may be the smallest of the minimum values ​​of the length in each of the multiple first inter-electrode regions F that each contain one of the multiple first gap regions G, or it may be the arithmetic mean of the minimum values ​​of the lengths.

[0104] As shown in Figure 21, in the second embodiment, the thicknesses of the first electrode finger 31, the second electrode finger 32, and the second layer 43b in the first electrode region E are constant. Therefore, in the second embodiment, the maximum distance between the upper surfaces 31a, 32a of the first electrode finger 31 or the second electrode finger 32 and the lower surface 431b of the second layer 43b corresponds to the sum of the thickness te of the first electrode finger 31 or the second electrode finger 32, the thickness t1e of the first layer 43a in the first electrode region E, and the thickness t2e of the second layer 43b in the first electrode region E, te + t1e + t2e. Also, in the first inter-electrode region F, the minimum distance between the upper surface of the first layer 43a and the lower surface 432b of the second layer 43b corresponds to the sum of the minimum thickness t1 of the first layer 43a and the minimum thickness t2 of the second layer 43b, t1 + t2. In other words, in the second embodiment, the relationship t1 + t2 < te + t1e + t2e holds true.

[0105] As shown in Figure 21, in the second embodiment, the minimum thickness t2 of the second layer 43b in the first electrode region E is equal to the thickness t2e of the second layer 43b in the first inter-electrode region F. This eliminates the need to grind the lower surface 431b of the second layer 43b for flattening or other purposes during the manufacturing of the elastic wave apparatus, thus simplifying the manufacturing process.

[0106] As described above, in the elastic wave apparatus 10A according to the second embodiment, the maximum distance (e.g., te + t1e + t2e) between the upper surfaces 31a, 32a of the first electrode finger 31 or the second electrode finger 32 and the lower surface 431b of the second layer 43b in the first electrode region E adjacent to at least one first gap region G (the first electrode region E adjacent to the first gap region G where a part of the second layer 43b is located) is greater than the minimum distance (e.g., t1 + t2) between the upper surface 433a of the first layer 43a and the lower surface 432b of the second layer 43b in the first inter-electrode region F including the at least one first gap region G (the first inter-electrode region F including the first gap region G where a part of the second layer 43b is located). Even in this case, unwanted waves can be reduced and resonance characteristics can be improved. Furthermore, if the second layer 43b is made of a harder material than layer 43c, the lower surface of layer 43c, which is easier to process, can be made flat, allowing the layers 43d to 43g below layer 43c to be laminated in a flat plate shape, thereby improving manufacturability.

[0107] (Third Embodiment) Figure 22 is a cross-sectional view showing an elastic wave apparatus according to the third embodiment. Here, Figure 22 is a cross-section of the elastic wave apparatus corresponding to Figure 2 described above. The elastic wave apparatus 10A according to the third embodiment differs from the first embodiment in that it is equipped with an acoustic multilayer film 43A instead of a dielectric layer 41.

[0108] The acoustic multilayer film 43A is a multilayer film similar to the acoustic multilayer film 43 described in the first embodiment. Here, the acoustic multilayer film 43A is an example of the "second acoustic multilayer film" of this disclosure. In the example in Figure 2, the acoustic multilayer film 43A has a third layer 43h, a fourth layer 43i, and other layers 43j to 43n stacked from the piezoelectric layer 20 side. Here, the third layer 43h, the fourth layer 43i, and the other layers 43j to 43n are examples of the "second plurality of layers" of this disclosure. In the third embodiment, the third layer 43h is a layer included in the acoustic multilayer film 43A that is in contact with the piezoelectric layer 20. The fourth layer 43i is a layer included in the acoustic multilayer film 43A that is stacked on the third layer 43h. Note that the number of layers in the acoustic multilayer film 43A shown in Figure 22 is merely an example and is not particularly limited.

[0109] In the acoustic multilayer film 43A, similar to the acoustic multilayer film 43, layers with relatively low acoustic impedance and layers with relatively high acoustic impedance are alternately stacked. By arranging the acoustic impedance relationships between the layers in the acoustic multilayer film 43A as described above, the bulk wave of the thickness-slip first mode can be further confined within the piezoelectric layer 20, thereby improving reliability and heat dissipation.

[0110] In the example shown in Figure 22, the third layer 43h and layers 43j, 43l, and 43n are made of the same material as the first layer 43a, and the fourth layer 43i and layers 43k and 43m are made of the same material as the second layer 43b. As a result, the third layer 43h and layers 43j, 43l, and 43n have relatively lower acoustic impedances than the fourth layer 43i and layers 43k and 43m, but this is not limited to this, and the first layer 43a and layers 43c, 43e, and 43g may have relatively higher acoustic impedances than the second layer 43b and layers 43d and 43f.

[0111] As described above, the elastic wave device 10B according to the third embodiment further comprises a second acoustic multilayer film (acoustic multilayer film 43A) provided on the upper side of the piezoelectric layer 20. The second acoustic multilayer film includes a second plurality of layers 43h to 43n stacked in the vertical direction. The second plurality of layers include a third layer 43h in contact with the piezoelectric layer 20 and a fourth layer 43i made of a different material from the third layer 43h and stacked on the third layer 43h. This improves reliability and heat dissipation.

[0112] (Fourth Embodiment) Figure 23 is an enlarged cross-sectional view showing an elastic wave apparatus according to the fourth embodiment. Figure 23 is an enlarged cross-sectional view showing the cross-section of a support substrate 11, an intermediate layer 12, a piezoelectric layer 20, a pair of first electrode fingers 31 and second electrode fingers 32, a first layer 43a, a second layer 43b, layers 43c to 43e laminated below the second layer 43b, and a dielectric layer 41. As shown in Figure 23, the elastic wave apparatus according to the fourth embodiment differs from the second embodiment in that the lower surfaces of layers 43c to 43e are not flush.

[0113] As shown in Figure 23, in the fourth embodiment, the maximum distance between the upper surfaces 31a, 32a of the first electrode finger 31 or the second electrode finger 32 and the lower surfaces of layers 43c to 43e in the first electrode region E is greater than the minimum distance between the upper surface 433a of the first layer 43a and the lower surfaces of layers 43c to 43e in the first inter-electrode region F. Note that the above thickness relationship does not have to hold for all first electrode regions E and first inter-electrode regions F. It is sufficient that the above thickness relationship holds for at least one first gap region in the first gap region G which contains at least a part of the second layer 43b, for the first electrode region E adjacent to that at least one first gap region, and for the first inter-electrode region F which includes that at least one first gap region.

[0114] The maximum distance between the upper surfaces 31a, 32a of the first electrode finger 31 or the second electrode finger 32 and the lower surfaces of layers 43c to 43e in the first electrode region E can be measured by the following method. First, an observation image of the cross-section of the elastic wave apparatus parallel to the alignment direction (X direction) of the first electrode finger 31 and the second electrode finger 32 is obtained using an electron microscope such as a TEM. Then, in the observation image, the length of line segments extended in the Z direction from the upper surfaces 31a, 32a of the first electrode finger 31 or the second electrode finger 32 to the lower surfaces of layers 43c to 43e is measured multiple times within one first electrode region E. Here, the maximum value of this length within one first electrode region E can be taken as the maximum distance between the upper surfaces 31a, 32a of the first electrode finger 31 or the second electrode finger 32 and the lower surfaces of layers 43c to 43e in the first electrode region E. Furthermore, if there are multiple first gap regions G in the observed image above, each containing at least a portion of the second layer 43b, the maximum distance between the upper surfaces 31a, 32a of the first electrode finger 31 or the second electrode finger 32 and the lower surfaces of layers 43c to 43e in the first electrode region E may be the largest of the maximum values ​​of such lengths in each of the multiple first electrode regions E adjacent to each of the multiple first gap regions G, or it may be the arithmetic mean of the maximum values ​​of such lengths.

[0115] The minimum distance between the upper surface of the first layer 43a and the lower surfaces of layers 43c to 43e in the first inter-electrode region F can be measured by the following method. First, an observation image of the cross-section of the elastic wave apparatus parallel to the alignment direction (X direction) of the first electrode finger 31 and the second electrode finger 32 is obtained using an electron microscope such as a TEM. Then, in this observation image, the length of a line segment extended in the Z direction from a point on the upper surface 433a of the first layer 43a to the lower surfaces of layers 43c to 43e is measured multiple times within one first inter-electrode region F. Here, the minimum value of this length within one first inter-electrode region F can be taken as the minimum distance between the upper surface 433a of the first layer 43a and the lower surfaces of layers 43c to 43e in the first inter-electrode region F. Furthermore, if the above observation image contains multiple first gap regions G in which at least a part of the second layer 43b is located, the minimum distance between the upper surface of the first layer 43a and the lower surfaces of layers 43c to 43e in the first inter-electrode region F may be the smallest of the minimum lengths in each of the multiple first inter-electrode regions F, each containing one of the multiple first gap regions G, or it may be the arithmetic mean of the minimum lengths.

[0116] As shown in Figure 23, in the fourth embodiment, the thickness of the first electrode finger 31, the second electrode finger 32 in the first electrode region E and the multiple layers 43a to 43e included in the acoustic multilayer film 43 are constant. Therefore, in the fourth embodiment, if tke is the thickness of the k-th layer from the piezoelectric layer 20 side in the first electrode region E among the multiple layers included in the acoustic multilayer film 43, and tk is the minimum thickness of the k-th layer in the first inter-electrode region F, then the relationship in equation (4) holds for all k. t1 + t2 + ... + tk < te + t1e + t2e + ... + tke ... (4) Here, the right-hand side of equation (4) corresponds to the maximum distance between the upper surfaces 31a, 32a of the first electrode finger 31 or the second electrode finger 32 and the lower surface of the k-th layer in the first electrode region E. Furthermore, the left side of equation (4) corresponds to the minimum distance between the upper surface 433a of the first layer 43a and the lower surface of the k-th layer in the first inter-electrode region F. Specifically, using the example in Figure 23, similar to the second layer 43b in the second embodiment, if the thicknesses of layers 43a to 43e in the first electrode region E are set to t1e to t5e, and the minimum thicknesses of layers 43a to 43e in the first inter-electrode region F are set to t1 to t5, then in the example in Figure 23, all of the following relationships (5) to (9) hold true. t1<te+t1e...(5) t1+t2<te+t1e+t2e...(6) t1+t2+t3<te+t1e+t2e+t3e...(7) t1+t2+t3+t4<te+t1e+t2e+t3e+t4e...(8) t1+t2+t3+t4+t5<te+t1e+t2e+t3e+t4e+t5e...(9)

[0117] In the fourth embodiment, the thicknesses of the multiple layers included in the acoustic multilayer film 43 in the first electrode region E are each equal to the minimum thickness of the corresponding layer in the first inter-electrode region F. Specifically, as explained in the example in Figure 23, t1 = t1e, t2 = t2e, t3 = t3e, t4 = t4e, and t5 = t5e. As a result, in the manufacture of the elastic wave device, it is not necessary to grind the lower surfaces of the multiple layers 43a to 43e included in the acoustic multilayer film 43 for flattening or the like, thus simplifying the manufacturing process.

[0118] As described above, in the elastic wave apparatus 10A according to the fourth embodiment, the first plurality of layers further include at least one layer 43c to 43e laminated on the second layer 43b. In the first electrode region E adjacent to at least one first gap region G (the first electrode region E adjacent to the first gap region G where a part of the second layer 43b is located), the maximum distance between the upper surface of the first electrode finger 31 or the second electrode finger 32 and the lower surface of at least one layer is greater than the minimum distance between the upper surface of the first layer 43a and the lower surface of at least one layer in the first inter-electrode region F including the at least one first gap region G (the first inter-electrode region F including the first gap region G where a part of the second layer 43b is located). Even in this case, unwanted waves can be reduced and resonance characteristics can be improved.

[0119] Furthermore, the elastic wave apparatus according to the fourth embodiment preferably further comprises an intermediate layer 12 provided on the lower side of the acoustic multilayer film 43. This improves manufacturability because the bonding surface with the support substrate 11 can be flattened by grinding the intermediate layer 12, which is easier to process.

[0120] (Fifth Embodiment) Figure 24 is an enlarged cross-sectional view showing an elastic wave apparatus according to the fifth embodiment. Figure 24 is a diagram showing cross-sections of the piezoelectric layer 20, a pair of first electrode fingers 31 and second electrode fingers 32, a first layer 43a, and a second layer 43b. As shown in Figure 24, the elastic wave apparatus according to the fifth embodiment differs from the elastic wave apparatus according to the first embodiment in that the thickness t1e of the first layer 43a in the first electrode region E is smaller than the minimum thickness t1 in the first gap region G. That is, in the fifth embodiment, t1 > t1e. This makes it possible to further suppress unwanted waves and further improve the resonance characteristics.

[0121] As described above, in the elastic wave apparatus according to the fifth embodiment, the maximum thickness of the first layer 43a in the first electrode region E adjacent to at least one first gap region G (the first electrode region E adjacent to the first gap region G where a part of the second layer 43b is located) is smaller than the minimum thickness of the first layer 43a in the first inter-electrode region F including the at least one first gap region G (the first inter-electrode region F including the first gap region G where a part of the second layer 43b is located). This further suppresses unwanted waves and improves resonance characteristics.

[0122] Here, an embodiment of the elastic wave apparatus according to the fifth embodiment will be described.

[0123] (Example 5) The design parameters of the elastic wave apparatus according to Example 5 were as follows. That is, in Example 5, t1 > t1e. The elastic wave apparatus according to Example 5 is an elastic wave apparatus according to the fifth embodiment. Material of piezoelectric layer 20: 120° Y-cut LiNbO ３ Thickness of the piezoelectric layer 20: 320 nm Material of the first electrode finger 31 and the second electrode finger: Al Thickness of the first electrode finger 31 and the second electrode finger (te): 80 nm Line width of the first electrode finger 31 and the second electrode finger: 0.9 μm Distance between the first electrode finger 31 and the second electrode finger (electrode pitch): 3.9 μm Material of the dielectric layer 41: SiO ２ Thickness of dielectric layer 41: 20 nm Material of first layer 43a: SiO ２ Minimum thickness t1 of the first layer 43a in the first inter-electrode region F: 60 nm Thickness t1e of the first layer 43a in the first electrode region E: 40 nm Material of the second layer 43b: HfO ２ Maximum thickness of the second layer 43b in the first inter-electrode region F: 125 nm Thickness of the second layer 43b in the first electrode region E: 65 nm Material of layers 43c, 43e, and 43g: SiO ２ Thickness of layers 43c, 43e, and 43g: 121 nm. Material of layers 43d and 43f: HfO ２ Thickness of layers 43d and 43f: 125 nm

[0124] (Example 6) The elastic wave apparatus according to Example 6 has the same design as Example 5, except that t1e is changed to 60 nm and the thickness of the second layer 43b in the first electrode region E is changed to 45 nm. That is, in Example 6, t1 = t1e. The elastic wave apparatus according to Example 6 is the elastic wave apparatus according to the first embodiment.

[0125] The resonance characteristics of the elastic wave apparatuses according to Examples 5 and 6 described above were investigated by simulation. The results are shown in Figure 25. Figure 25 shows the resonance characteristics of the elastic wave apparatuses according to Examples 5 and 6. Figure 25 shows the dependence of admittance Y on frequency for Examples 5 and 6.

[0126] As shown in Figure 25, in Example 5, where t1 > t1e, the unwanted wave S3 observed in Example 6, where t1 = t1e, is suppressed. Therefore, it can be seen that by setting t1 > t1e, unwanted waves can be further suppressed and the resonance characteristics can be further improved.

[0127] (Sixth Embodiment) Figure 26 is a cross-sectional view showing the elastic wave apparatus according to the sixth embodiment. Figure 26 corresponds to Figure 2, which shows the cross-sectional view taken along line II-II' in Figure 1. As shown in Figure 26, the elastic wave apparatus 10B according to the sixth embodiment differs from the elastic wave apparatus according to the first embodiment in that it further comprises an IDT electrode 30A provided on the upper side of the piezoelectric layer 20.

[0128] The IDT electrode 30A has a third electrode finger 31A, a fourth electrode finger 32A, a third busbar, and a fourth busbar. The multiple third electrode fingers 31A extend in the Y direction, and one end in the extending direction is connected to the third busbar. The multiple fourth electrode fingers 32A extend in the Y direction, and the other end in the extending direction is connected to the fourth busbar. The multiple third electrode fingers 31A and the multiple fourth electrode fingers 32A are arranged alternately in the X direction with a gap between them. The third busbar and the fourth busbar (not shown) each extend in the X direction and are arranged opposite each other in the Y direction. The multiple third electrode fingers 31A and the multiple fourth electrode fingers 32A are arranged between the third busbar and the fourth busbar.

[0129] Furthermore, the IDT electrode 30 is not limited to a configuration having a plurality of third electrode fingers 31A and a plurality of fourth electrode fingers 32A, but may also include a configuration with at least one third electrode finger 31A whose base end is connected to a third busbar and at least one fourth electrode finger 32A whose base end is connected to a fourth busbar.

[0130] In the example shown in Figure 26, the dielectric layer 41 is provided so as to cover the IDT electrode 30A provided on the first main surface 20a. That is, the IDT electrode 30A is provided between the dielectric layer 41 and the first main surface 20a of the piezoelectric layer 20 in the Z direction.

[0131] As described above, the elastic wave apparatus 10B according to the sixth embodiment further comprises a second IDT electrode (IDT electrode 30A) provided on the upper side of the piezoelectric layer 20. The second IDT electrode has a third busbar facing each other, a fourth busbar, at least one third electrode finger 31A whose base end is connected to the third busbar, and at least one fourth electrode finger 32A whose base end is connected to the fourth busbar. Even in this case, unwanted waves can be suppressed and resonance characteristics can be improved.

[0132] (Seventh Embodiment) Figure 27 is a cross-sectional view showing the elastic wave apparatus according to the seventh embodiment. Figure 27 corresponds to Figure 2, which shows the cross-sectional view taken along line II-II' in Figure 1. As shown in Figure 27, the elastic wave apparatus 10C according to the seventh embodiment differs from the sixth embodiment in that it includes an acoustic multilayer film 43A instead of a dielectric layer 41. That is, the elastic wave apparatus 10C according to the seventh embodiment differs from the elastic wave apparatus 10A according to the third embodiment in that it includes an IDT electrode 30A between the acoustic multilayer film 43A and the piezoelectric layer 20.

[0133] In the seventh embodiment, the shapes of the third layer 43h and the fourth layer 43i are preferably the same as those of the first layer 43a and the second layer 43b in the first embodiment, respectively. In other words, when viewed in a plan view in the X direction, the region overlapping with adjacent third electrode fingers 31A and fourth electrode fingers 32A, and the region between adjacent third electrode fingers 31A and fourth electrode fingers 32A is defined as the second gap region, it is preferable that at least a part of the fourth layer 43i is present in that region. As a result, the displacement generated between the third electrode finger 31A and the fourth electrode finger 32A is suppressed by the part of the fourth layer 43i present in the second gap region, thereby suppressing unwanted waves and improving the resonance characteristics. Note that the fourth layer 43i is not required to be present in all second gap regions; it is sufficient that at least a part of the fourth layer 43i is present in at least one second gap region.

[0134] The presence or absence of the fourth layer 43i in the second gap region can be determined by obtaining an observation image of the cross-section of the elastic wave apparatus parallel to the alignment direction (X direction) of the third electrode finger 31A and the fourth electrode finger 32A using an electron microscope such as a TEM.

[0135] As shown in Figure 27, in the seventh embodiment, the lower surface of the fourth layer 43i is shaped to conform to the upper surface of the third layer 43h, and the upper surface of the fourth layer 43i is flush with the surface.

[0136] As described above, the elastic wave apparatus 10C according to the seventh embodiment further comprises a second acoustic multilayer film (acoustic multilayer film 43A) provided on the upper side of the piezoelectric layer 20. The second acoustic multilayer film includes a second plurality of layers 43h to 43n stacked in the vertical direction. The second plurality of layers include a third layer 43h that is in contact with at least one of the third electrode finger 31A and the fourth electrode finger 32A, and a fourth layer 43i made of a different material from the third layer 43h and stacked on the third layer 43h. When viewed in plan from the direction of arrangement of the third electrode finger 31A and the fourth electrode finger 32A, if the region that overlaps with adjacent third electrode finger 31A and fourth electrode finger 32A, and the region between adjacent third electrode finger 31A and fourth electrode finger 32A is defined as a second gap region, then at least one of the second gap regions contains at least a part of the fourth layer 43i. As a result, unwanted waves can be suppressed and resonance characteristics can be improved even when excitation is performed by the second IDT electrode (IDT electrode 30A).

[0137] The configuration of the acoustic multilayer film 43A according to the seventh embodiment is not limited to that described above, and may be the same as that of the acoustic multilayer film 43 according to the embodiment described above.

[0138] (Eighth Embodiment) Figure 28 is a circuit diagram showing a filter according to the eighth embodiment. As shown in Figure 28, the filter 1 according to the eighth embodiment is a so-called ladder type filter.

[0139] In the eighth embodiment, filter 1 is a so-called bandpass filter that allows waves of a specific frequency band to pass through. Filter 1 includes a plurality of series arm resonators SR1, SR2, SR3, SR4 and a plurality of parallel arm resonators PR1, PR2, PR3. The plurality of series arm resonators SR1, SR2, SR3, SR4 are connected in series to the signal path (series arm) between the input terminal IN and the output terminal OUT. The plurality of parallel arm resonators PR1, PR2, PR3 are connected in parallel to the signal path (parallel arm) connecting the nodes on the series arm to ground GND.

[0140] One terminal of each of the series-connected series arm resonators SR1, SR2, SR3, and SR4 is electrically connected to the input terminal IN, and the other terminal is electrically connected to the output terminal OUT. One terminal of the parallel arm resonator PR1 is electrically connected to a node between the series arm resonators SR1 and SR2, and the other terminal is electrically connected to ground GND. One terminal of the parallel arm resonator PR2 is electrically connected to a node between the series arm resonators SR2 and SR3, and the other terminal is electrically connected to ground GND. One terminal of the parallel arm resonator PR3 is electrically connected to a node between the series arm resonators SR3 and SR4, and the other terminal is electrically connected to ground GND. One terminal of the parallel arm resonator PR4 is electrically connected to a node between the series arm resonator SR4 and the output terminal OUT, and the other terminal is electrically connected to ground GND.

[0141] In the eighth embodiment, at least one of the resonators included in the filter 1 (series arm resonators SR1, SR2, SR3, SR4 and parallel arm resonators PR1, PR2, PR3) is an elastic wave device 10 according to any of the first to seventh embodiments. Since the filter 1 according to the eighth embodiment has an elastic wave device 10 according to any of the first to seventh embodiments, unwanted waves can be suppressed, and thus the filter characteristics can be improved.

[0142] In the eighth embodiment, it is preferable that at least one of the series arm resonators SR1, SR2, SR3, and SR4 is an elastic wave device 10 according to any of the first to seventh embodiments, and it is more preferable that all of the series arm resonators SR1, SR2, SR3, and SR4 are elastic wave devices 10 according to any of the first to seventh embodiments. Since the series arm resonators are resonators that affect the filter characteristics near the resonant frequency of the filter 1, using the elastic wave device 10 of this disclosure as series arm resonators suppresses unwanted waves and improves the filter characteristics.

[0143] As described above, the filter 1 according to the eighth embodiment is a filter equipped with resonators (series arm resonators SR1, SR2, SR3, SR4 and parallel arm resonators PR1, PR2, PR3). At least one of the resonators is an elastic wave device according to any one of the first to seventh embodiments. This allows for the suppression of unwanted waves, thereby improving the filter characteristics.

[0144] As described above, the filter 1 according to the eighth embodiment comprises a plurality of resonators (series arm resonators SR1, SR2, SR3, SR4 and parallel arm resonators PR1, PR2, PR3), and has an input terminal IN, an output terminal OUT, a series arm connecting the input terminal IN and the output terminal OUT, and a parallel arm connecting the node of the series arm to ground GND. The plurality of resonators include the series arm resonators SR1, SR2, SR3, SR4 provided on the series arm and the parallel arm resonators PR1, PR2, PR3 provided on the parallel arm. At least one of the series arm resonators SR1, SR2, SR3, SR4 is an elastic wave device according to any one of the first to seventh embodiments. This suppresses unwanted waves and further improves the filter characteristics.

[0145] 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.

[0146] 1 Filter 10, 10A, 10B, 10C Elastic wave device 11 Support substrate 12 Intermediate layer 20 Piezoelectric layer 20a First main surface 20b Second main surface 30, 30A IDT electrode 31 First electrode finger 32 Second electrode finger 31a, 32a Top surface 31b, 32b Side surface 31A Third electrode finger 32A Fourth electrode finger 33 First busbar 34 Second busbar 41 Dielectric layer 43, 43A Acoustic multilayer film 43a First layer 43b Second layer 43h Third layer 43i Fourth layer 430a, 430b, 431a, 431b, 432a, 432b Bottom surface 433a Top surface 51, 52 Through electrode E First electrode region F First inter-electrode region G First gap region: SR1-SR4 series arm resonators, PR1-PR4 parallel arm resonators

Claims

1. The device comprises a support substrate, a first acoustic multilayer film provided on the upper side of the support substrate, a piezoelectric layer provided on the upper side of the first acoustic multilayer film, and a first IDT electrode provided between the first acoustic multilayer film and the piezoelectric layer, wherein the first IDT electrode has a first busbar facing each other, a second busbar, at least one first electrode finger whose base end is connected to the first busbar, and at least one second electrode finger whose base end is connected to the second busbar, the first acoustic multilayer film includes a first plurality of layers stacked in the vertical direction, the first plurality of layers include a first layer in contact with at least one of the first electrode finger and the second electrode finger, and a second layer made of a different material from the first layer and stacked on the first layer, and when the thickness of the piezoelectric layer is d and the distance between the centers of adjacent first electrode fingers and second electrode fingers is p, d / p is 0.5 or less, An elastic wave apparatus wherein, when viewed in plan from the direction of arrangement of the first electrode fingers and the second electrode fingers, the region overlapping with adjacent first electrode fingers and second electrode fingers, and the region between adjacent first electrode fingers and second electrode fingers, is defined as a first gap region, and at least one of the first gap regions contains at least a portion of the second layer.

2. When viewed from above in plan, the region overlapping with the first electrode finger or the second electrode finger is defined as the first electrode region, and when viewed from above in plan, the region overlapping with the first gap region is defined as the first inter-electrode region, the maximum distance between the upper surface of the first electrode finger or the second electrode finger and the lower surface of the first layer in the first electrode region adjacent to at least one of the first gap regions is greater than the minimum thickness of the first layer in the inter-electrode region including the at least one of the first gap regions, according to claim 1.

3. The elastic wave apparatus according to claim 2, wherein the maximum distance between the upper surface of the first electrode finger or the second electrode finger and the lower surface of the second layer in the first electrode region adjacent to the at least one gap region is greater than the minimum distance between the upper surface of the first layer and the lower surface of the second layer in the first inter-electrode region including the at least one first gap region.

4. The elastic wave apparatus according to claim 3, wherein the first plurality of layers further include at least one layer laminated on the second layer, and the maximum distance between the upper surface of the first electrode finger or the second electrode finger and the lower surface of the at least one layer in the first electrode region adjacent to the at least one first gap region is greater than the minimum distance between the upper surface of the first layer and the lower surface of the at least one layer in the first inter-electrode region including the at least one first gap region.

5. The elastic wave apparatus according to any one of claims 2 to 4, wherein the maximum thickness of the first layer in the first electrode region adjacent to the at least one first gap region is less than the minimum thickness of the first layer in the first inter-electrode region including the at least one first gap region.

6. The elastic wave apparatus according to any one of claims 1 to 5, further comprising a second acoustic multilayer film provided on the upper side of the piezoelectric layer, wherein the second acoustic multilayer film includes a plurality of second layers stacked in the vertical direction, and the plurality of second layers include a third layer in contact with the piezoelectric layer and a fourth layer made of a different material from the third layer and stacked on the third layer.

7. The elastic wave apparatus according to any one of claims 1 to 6, further comprising a second IDT electrode provided on the upper side of the piezoelectric layer, wherein the second IDT electrode has a third busbar facing each other, a fourth busbar, at least one third electrode finger whose base end is connected to the third busbar, and at least one fourth electrode finger whose base end is connected to the fourth busbar.

8. The elastic wave apparatus according to claim 7, further comprising a second acoustic multilayer film provided on the upper side of the piezoelectric layer, the second acoustic multilayer film comprising a second plurality of layers stacked in the vertical direction, the second plurality of layers comprising a third layer in contact with at least one of the third electrode finger and the fourth electrode finger, and a fourth layer made of a different material from the third layer and stacked on the third layer, and when viewed in plan from the direction of arrangement of the third electrode finger and the fourth electrode finger, the region overlapping with adjacent third electrode finger and the fourth electrode finger, and the region between adjacent third electrode finger and the fourth electrode finger is defined as a second gap region, at least one of the second gap regions comprises at least a part of the fourth layer.

9. The elastic wave apparatus according to any one of claims 1 to 8, wherein the acoustic impedance of the first layer is lower than the acoustic impedance of the second layer.

10. The elastic wave apparatus according to any one of claims 1 to 8, wherein the acoustic impedance of the first layer is higher than the acoustic impedance of the second layer.

11. The elastic wave apparatus according to any one of claims 1 to 8, wherein one of the first layer and the second layer comprises at least one of silicon oxide and aluminum, and the other of the first layer and the second 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, ytterbium oxide, tungsten oxide, hafnium nitride, tungsten nitride, platinum, tungsten, copper, gold, and silver.

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

13. The elastic wave apparatus according to claim 12, wherein the surface of the intermediate layer on the support substrate side is flush with the surface.

14. The elastic wave apparatus according to any one of claims 1 to 13, wherein the support substrate has an acoustic impedance different from at least one of the first layer and the second layer.

15. The elastic wave apparatus according to any one of claims 1 to 14, wherein the support substrate is made of at least one of silicon, quartz, silicon carbide, lithium niobate, lithium tantalate, sapphire, aluminum nitride, glass, and aluminum oxide.

16. The elastic wave apparatus according to any one of claims 1 to 15, wherein the d / p is 0.24 or less.

17. The elastic wave apparatus according to any one of claims 1 to 16, 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 satisfied.

18. The elastic wave apparatus according to any one of claims 1 to 17, wherein the piezoelectric layer comprises lithium niobate.

19. The Euler angles (φ ＬＮ , θ ＬＮ , ψ ＬＮ ) of the lithium niobate constituting the piezoelectric layer are within the range of the following formula (1), formula (2), or formula (3). The elastic wave device according to claim 18. (0° ± 10°, 0° to 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°) … Formula (2) (0° ± 10°, [180° - 30°(1 - (ψ ＬＮ - 90) ２ / 8100) １／２ to 180°, any ψ ＬＮ ) … Formula (3) 20. A filter comprising a resonator, wherein at least one of the resonators is an elastic wave apparatus according to any one of claims 1 to 19.

21. A filter comprising a plurality of resonators, having an input terminal, an output terminal, a series arm connecting the input terminal and the output terminal, and a parallel arm connecting the node of the series arm to ground, wherein the plurality of resonators include a series arm resonator provided on the series arm and a parallel arm resonator provided on the parallel arm, and at least one of the series arm resonators is an elastic wave device according to any one of claims 1 to 19.

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