Elastic wave device

Abstract

An elastic wave device comprises at least two resonators. Each resonator is provided with: a piezoelectric layer having a first main surface and a second main surface that face each other; an electrode provided on at least one of the first main surface and the second main surface of the piezoelectric layer; a plurality of dielectric layers laminated on the first main surface or the second main surface of the piezoelectric layer, the plurality of dielectric layers including at least a first dielectric layer and a second dielectric layer; and a support member provided on the second-main-surface side of the piezoelectric layer, the support member having an acoustic reflection part on the second-main-surface side of the piezoelectric layer. Among the plurality of dielectric layers, at least the first dielectric layer and the second dielectric layer have mutually different acoustic impedances.

Description

Elastic Wave Device

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

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

[0003] U.S. Pat. No. 1,091,7070

[0004] In the acoustic wave device disclosed in Patent Document 1, the frequency characteristics may be adjusted by adjusting the film thickness of the dielectric layer that covers the electrodes.

[0005] An object of the present invention is to provide an acoustic wave device that can adjust frequency characteristics favorably.

[0006] An elastic wave device according to one embodiment is an elastic wave device having at least two resonators, each of which comprises a piezoelectric layer having opposing first and second main surfaces, an electrode provided on at least one of the first and second main surfaces of the piezoelectric layer, a plurality of dielectric layers stacked on the first or second main surface of the piezoelectric layer and including at least a first dielectric layer and a second dielectric layer, and a support member provided on the second main surface side of the piezoelectric layer and having an acoustic reflecting portion on the second main surface side of the piezoelectric layer, wherein the acoustic impedances of at least the first dielectric layer and the second dielectric layer among the plurality of dielectric layers are different from each other.

[0007] According to the acoustic wave device of the present invention, the frequency characteristics can be adjusted favorably.

[0008] FIG. 1 is a circuit diagram illustrating an elastic wave device according to a first embodiment. FIG. 2 is a plan view illustrating a resonator included in the elastic wave device according to the first embodiment. FIG. 3 is a cross-sectional view taken along III-III′ in FIG. 2 . FIG. 4 is a schematic cross-sectional view illustrating a bulk wave in a thickness-shear first-order mode propagating through a piezoelectric layer according to the first embodiment. FIG. 5 is a schematic cross-sectional view illustrating the amplitude direction of a bulk wave in a thickness-shear first-order mode propagating through a piezoelectric layer according to the first embodiment. FIG. 6 is an explanatory diagram illustrating an example of the resonance characteristics of a resonator according to the first embodiment. FIG. 7 is an explanatory diagram illustrating the relationship between d / 2p and the fractional bandwidth of the resonator according to the first embodiment, where p is the center-to-center distance or the average center-to-center distance between adjacent electrodes and d is the average thickness of the piezoelectric layer. FIG. 8 is a plan view illustrating an example of a resonator according to the first embodiment in which a pair of electrodes is provided. FIG. 9 is a reference diagram illustrating an example of the resonance characteristics of a resonator according to the first embodiment. Fig. 10 is an explanatory diagram showing the relationship between the fractional bandwidth when a large number of resonators are configured for the first embodiment and the amount of phase rotation of the spurious impedance normalized by 180 degrees as the magnitude of the spurious. Fig. 11 is an explanatory diagram showing the relationship between d / 2p, the metallization ratio MR, and the fractional bandwidth. Fig. 12 is an explanatory diagram showing the relationship between d / p and the metallization ratio MR of LiNbO when d / p approaches 0. ３FIG. 13 is a cross-sectional view of an elastic wave device according to a first preferred embodiment. FIG. 14 is a graph schematically illustrating the relationship between the thickness deviation of the piezoelectric layer and the thickness deviation of the dielectric layer in an elastic wave device according to a comparative example. FIG. 15 is a graph showing the pass characteristics of elastic wave devices according to a first preferred embodiment and a second preferred embodiment. FIG. 16 is a graph showing the relationship between the thickness of the piezoelectric layer and the thickness of the second dielectric layer at a constant resonant frequency in an elastic wave device according to a first preferred embodiment. FIG. 17 is a graph showing the relationship between the thickness of the piezoelectric layer and the thickness of the second dielectric layer at a constant resonant frequency in an elastic wave device according to a second preferred embodiment. FIG. 18 is a graph showing the relationship between the thickness deviation of the dielectric layer and the amount of change in resonant frequency in elastic wave devices according to a third preferred embodiment, a first comparative example, and a second comparative example. FIG. 19 is a cross-sectional view of an elastic wave device according to a second preferred embodiment. FIG. 20 is a cross-sectional view of a resonator included in an elastic wave device according to a third preferred embodiment. FIG. 21 is a cross-sectional view of a resonator included in an elastic wave device according to a fourth preferred embodiment.

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to these embodiments. Note that each embodiment described in the present disclosure is illustrative, and partial substitution or combination of configurations between different embodiments is possible. In modified examples and the second and subsequent embodiments, descriptions of matters common to the first embodiment will be omitted, and only differences will be described. In particular, similar effects resulting from similar configurations will not be mentioned in each embodiment.

[0010] 1 is a circuit diagram illustrating an elastic wave device according to a first embodiment. As shown in FIG. 1 , an elastic wave device 100 according to the first embodiment includes a plurality of series arm resonators 61, 62, and 63, a plurality of parallel arm resonators 64, 65, 66, and 67, an input terminal 60A, and an output terminal 60B.

[0011] The plurality of series arm resonators 61, 62, and 63 are connected in series to a signal path between an input terminal 60A and an output terminal 60B. The plurality of parallel arm resonators 64, 65, 66, and 67 are connected in parallel between the signal path between the input terminal 60A and the output terminal 60B and ground 68. The elastic wave device 100 according to the thirteenth preferred embodiment is a so-called ladder filter that includes the plurality of parallel arm resonators 64, 65, 66, and 67 (first resonators) and the plurality of series arm resonators 61, 62, and 63 (second resonators).

[0012] One terminal of each of the series-connected series arm resonators 61, 62, and 63 is electrically connected to the input terminal 60A, and the other terminal is electrically connected to the output terminal 60B. One terminal of the parallel arm resonator 64 is electrically connected to a signal path connecting the input terminal 60A and the series arm resonator 61, and the other terminal is electrically connected to ground 68. One terminal of the parallel arm resonator 65 is electrically connected to a signal path connecting the series arm resonators 61 and 62, and the other terminal is electrically connected to ground 68. One terminal of the parallel arm resonator 66 is electrically connected to a signal path connecting the series arm resonators 62 and 63, and the other terminal is electrically connected to ground 68. One terminal of the parallel arm resonator 67 is electrically connected to a signal path connecting the series arm resonator 63 and the output terminal 60B, and the other terminal is electrically connected to ground 68.

[0013] In the elastic wave device 100, the configurations and numbers of the plurality of series arm resonators 61, 62, and 63 and the plurality of parallel arm resonators 64, 65, 66, and 67 can be changed as appropriate depending on the required filter characteristics. For example, the elastic wave device 100 may have a configuration including at least one series arm resonator and at least one parallel arm resonator.

[0014] Next, the configuration of the resonator 10 will be described as an example of the plurality of series arm resonators 61, 62, and 63 and the plurality of parallel arm resonators 64, 65, 66, and 67 of the elastic wave device 100.

[0015] Fig. 2 is a plan view showing a resonator included in the elastic wave device of the first preferred embodiment. Fig. 3 is a cross-sectional view taken along line III-III' in Fig. 2. Note that in Fig. 2, the first dielectric layer 41 and the second dielectric layer 42 are indicated by dashed two-dot lines for ease of viewing.

[0016] 2 and 3, the resonator 10 according to the first embodiment includes a piezoelectric layer 20, an IDT electrode 30 (electrode), a support substrate 11 (support member), a first dielectric layer 41, and a second dielectric layer 42. As shown in Fig. 3, the resonator 10 has the piezoelectric layer 20, the IDT electrode 30, the first dielectric layer 41, and the second dielectric layer 42 stacked in this order on the support substrate 11.

[0017] The piezoelectric layer 20 is in the form of a flat plate having a first main surface 20a and a second main surface 20b opposite to the first main surface 20a. The piezoelectric layer 20 is made of lithium niobate (LiNbO ３ Alternatively, the piezoelectric layer 20 may be made of lithium tantalate (LiTaO ３ ) may be made of LiNbO ３ and LiTaO ３ In the first embodiment, the cut angle is a Z-cut. ３ and LiTaO ３ The cut angle may be a rotated Y cut or an X cut. Preferably, the propagation direction is Y propagation or X propagation ±30°. Preferably, the piezoelectric layer 20 is made of lithium niobate (LiNbO ３ ) or lithium tantalate (LiTaO ３ ) and is a 120°±10° rotated Y-cut or a 90°±10° rotated Y-cut.

[0018] The thickness of the piezoelectric layer 20 is not particularly limited, but is preferably 50 nm to 1000 nm inclusive in order to effectively excite the first-order thickness shear mode. The thickness of the piezoelectric layer 20 according to the first embodiment is, for example, about 400 nm (0.4 μm).

[0019] The support substrate 11 (support member) is disposed opposite the second principal surface 20b of the piezoelectric layer 20. The support substrate 11 has a recess 14 (acoustic reflecting portion) that opens toward the second principal surface 20b of the piezoelectric layer 20. More specifically, the support substrate 11 has a bottom 12 and a wall portion 13 provided in a frame shape on the upper surface of the bottom 12. The recess 14 is formed in the space surrounded by the bottom 12 and the wall portion 13. The recess 14 is also called a cavity portion or hollow portion. The piezoelectric layer 20 is laminated on the upper surface of the wall portion 13 of the support substrate 11. At least a portion of the piezoelectric layer 20 is disposed above the recess 14 (acoustic reflecting portion) in a plan view. In this way, the resonator 10 has a so-called membrane structure in which the recess 14 is provided on the second principal surface 20b of the piezoelectric layer 20.

[0020] The support member may include a support substrate 11 and an intermediate (insulating) layer. The piezoelectric layer 20 is bonded to the support substrate 11 directly or via the intermediate (insulating) layer. The recess 14 may be formed in the intermediate (insulating) layer. In this case, the support substrate 11 and the intermediate layer may have a frame-like shape, thereby forming the recess 14. Alternatively, the recess 14 may be formed in the intermediate layer.

[0021] The support substrate 11 is made of silicon (Si). The surface of the Si facing the piezoelectric layer 20 may have a (100), (110), or (111) plane orientation. Preferably, Si has a high resistivity of 4 kΩ or more. However, the support substrate 11 may also be made of an appropriate insulating material or semiconductor material. Examples of materials that can be used for the support substrate 11 include piezoelectric materials such as aluminum oxide, lithium tantalate, lithium niobate, and quartz; various ceramics such as alumina, magnesia, sapphire, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, steatite, and forsterite; dielectric materials such as diamond and glass; and semiconductors such as gallium nitride.

[0022] The IDT (Interdigital Transducer) electrode 30 is provided on the first main surface 20a of the piezoelectric layer 20. As shown in FIG. 2 , the IDT electrode 30 has first electrode fingers 31, second electrode fingers 32, first bus bar electrodes 33, and second bus bar electrodes 34. The first electrode fingers 31 extend in the Y direction, and one end of each electrode finger in the extension direction is connected to the first bus bar electrode 33. The second electrode fingers 32 extend in the Y direction, and the other end of each electrode finger in the extension direction is connected to the second bus bar electrode 34. The first electrode fingers 31 and the second electrode fingers 32 are alternately arranged in the X direction with a gap between them. The first bus bar electrodes 33 and the second bus bar electrodes 34 each extend in the X direction and are arranged opposite each other in the Y direction. A plurality of first electrode fingers 31 and a plurality of second electrode fingers 32 are arranged between the first bus bar electrode 33 and the second bus bar electrode 34 .

[0023] The IDT electrode 30 is not limited to a configuration having a plurality of first electrode fingers 31 and a plurality of second electrode fingers 32, but may also be configured to include at least one first electrode finger 31 whose base end is connected to a first busbar electrode 33 and at least one second electrode finger 32 whose base end is connected to a second busbar electrode 34.

[0024] In the following description, the thickness direction of the piezoelectric layer 20 may be referred to as the Z direction, the extension direction of the first electrode fingers 31 and the second electrode fingers 32 as the Y direction, and the arrangement direction of the first electrode fingers 31 and the second electrode fingers 32 as the X direction. In the following description, a planar view refers to the positional relationship when viewed from a direction perpendicular to the first main surface 20a of the piezoelectric layer 20. In the Z direction, the direction from the support substrate 11 toward the IDT electrode 30 on the outermost surface is referred to as up or upward, and the direction from the IDT electrode 30 toward the support substrate 11 is referred to as down or downward.

[0025] The center-to-center distance between the first electrode finger 31 and the second electrode finger 32 (hereinafter referred to as the inter-electrode pitch) is preferably in the range of 1 μm to 10 μm. The inter-electrode pitch is the distance between the center of the width of the first electrode finger 31 in a direction perpendicular to the extension direction of the first electrode finger 31 and the center of the width of the second electrode finger 32 in a direction perpendicular to the extension direction of the second electrode finger 32. The width of the first electrode finger 31 and the second electrode finger 32 (hereinafter referred to as the electrode width), i.e., the dimension in the direction perpendicular to the extension direction of the first electrode finger 31 and the second electrode finger 32, is preferably in the range of 150 nm to 1000 nm.

[0026] Furthermore, when there are multiple first electrode fingers 31 and multiple second electrode fingers 32 (when the first electrode fingers 31 and the second electrode fingers 32 are considered as a pair of electrode sets, there are 1.5 or more pairs of electrode sets), the inter-electrode pitch of the first electrode fingers 31 and the second electrode fingers 32 refers to the average value 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.

[0027] Furthermore, in the first embodiment, since a Z-cut piezoelectric layer is used, the direction perpendicular to the extension direction of the first electrode fingers 31 and the second electrode fingers 32 is perpendicular to the polarization direction of the piezoelectric layer 20. This does not apply when a piezoelectric material with a different cut angle is used as the piezoelectric layer 20. Here, "perpendicular" is not limited to strictly perpendicular, but may also be approximately perpendicular (the angle between the direction perpendicular to the extension direction of the first electrode fingers 31 and the second electrode fingers 32 and the polarization direction is, for example, 90°±10°).

[0028] The IDT electrode 30 (first electrode fingers 31, second electrode fingers 32, first bus bar electrodes 33, and second bus bar electrodes 34) is made of an appropriate metal or alloy such as Al or an AlCu alloy. In the first embodiment, the IDT electrode 30 has a structure in which an Al film is laminated on a titanium (Ti) film. Note that an adhesion layer other than the Ti film may also be used.

[0029] More specifically, the IDT electrode 30 has a laminated structure of Ti / AlCu / Ti / AlCu from the piezoelectric layer 20 side, with respective film thicknesses of 12 nm / 70 nm / 18 nm / 12 nm. The IDT electrode 30 has a total of 51 first electrode fingers 31 and second electrode fingers 32. The interelectrode pitch of the first electrode fingers 31 and second electrode fingers 32 is 4.4 μm, and the electrode width is 0.6 μm. The structure (dimensions) of the IDT electrode 30 are merely an example and can be modified as appropriate.

[0030] 2 is a region where the first electrode fingers 31 and the second electrode fingers 32 overlap when viewed in the X direction. The length of the intersection region C is the dimension in the extension direction of the first electrode fingers 31 and the second electrode fingers 32 in the intersection region C. In this embodiment, the length of the intersection region C is, for example, 40 μm.

[0031] During operation, an AC voltage is applied between the plurality of first electrode fingers 31 and the plurality of second electrode fingers 32. More specifically, an AC voltage is applied between the first bus bar electrode 33 and the second bus bar electrode 34. This makes it possible to obtain resonance characteristics using bulk waves in the first thickness-shear mode excited in the piezoelectric layer 20.

[0032] In the resonator 10, when the thickness of the piezoelectric layer 20 is d and the inter-electrode pitch between the first and second electrode fingers 31 and 32 is p, the ratio d / p is set to 0.5 or less. This effectively excites the bulk wave in the thickness-shear first-order mode, resulting in good resonance characteristics. More preferably, d / p is set to 0.24 or less, resulting in even better resonance characteristics.

[0033] The resonator 10 of the first embodiment has the above-described configuration, and therefore has little propagation loss, and is unlikely to suffer from a decrease in the Q value even if the number of pairs of the first electrode fingers 31 and the second electrode fingers 32 is reduced in an attempt to reduce the size of the resonator 10. This is because the resonator 10 utilizes bulk waves in the thickness-shear primary mode.

[0034] 2 and 3 , the first dielectric layer 41 and the second dielectric layer 42 are laminated on the first main surface 20 a of the piezoelectric layer 20. The first dielectric layer 41 and the second dielectric layer 42 are provided to cover the IDT electrode 30. That is, in the Z direction, the IDT electrode 30 is provided between the first main surface 20 a of the piezoelectric layer 20 and the first dielectric layer 41. In this embodiment, no dielectric layer is provided on the second main surface 20 b of the piezoelectric layer 20, and the second main surface 20 b of the piezoelectric layer 20 and the support substrate 11 are in direct contact with each other at the peripheral portion where the recess 14 is not provided.

[0035] Table 1 shows examples of materials for the first dielectric layer 41 and the second dielectric layer 42. In Table 1, "LongV" indicates the phase velocity of a longitudinal bulk wave. "ShearV" indicates the phase velocity of a shear bulk wave. "LongZ" indicates the longitudinal wave acoustic impedance, which is the product of density and longitudinal wave sound velocity. "ShearZ" indicates the shear wave acoustic impedance, which is the product of density and shear wave sound velocity.

[0036]

[0037] As shown in Table 1, the first dielectric layer 41 and the second dielectric layer 42 are each made of silicon oxide (SiO ２ ), silicon nitride (SiN), aluminum nitride (AlN), tantalum oxide (Ta ２ O ５ ), hafnium oxide (HfO ２ Without being limited to the examples in Table 1, the first dielectric layer 41 and the second dielectric layer 42 may include, for example, niobium oxide (NbO).

[0038] In this embodiment, the first dielectric layer 41 and the second dielectric layer 42 have different acoustic impedances. That is, the first dielectric layer 41 and the second dielectric layer 42 are made of materials with different acoustic impedances. For example, the second dielectric layer 42 has a lower acoustic impedance than the first dielectric layer 41. In this case, for example, the second dielectric layer 42 includes silicon oxide, and the first dielectric layer 41 includes at least one of aluminum nitride, tantalum oxide, and niobium oxide.

[0039] Alternatively, the second dielectric layer 42 may have a higher acoustic impedance than the first dielectric layer 41. In this case, for example, the second dielectric layer 42 includes at least one of aluminum nitride, tantalum oxide, and niobium oxide, and the first dielectric layer 41 includes silicon oxide.

[0040] In the resonator 10 of this embodiment, the resonant frequency of the resonator 10 including the IDT electrode 30 and the piezoelectric layer 20 can be adjusted by changing the film thicknesses of the first dielectric layer 41 and the second dielectric layer 42. Furthermore, the resonant frequency can be appropriately adjusted by making the acoustic impedances of the first dielectric layer 41 and the second dielectric layer 42 different from each other. The characteristics of an elastic wave device 100 including a plurality of resonators 10 will be described later with reference to FIG. 13 and subsequent figures. Furthermore, methods for measuring the resonant frequency of an actual product include, for example, a method of contacting an RF probe with the wiring to which the resonator 10 is electrically connected, or a method of reproducing the frequency through simulations such as the finite element method using dimensional information obtained from cross-sectional analysis and material constants based on literature values.

[0041] 3 illustrates a configuration in which the resonator 10 has two dielectric layers (the first dielectric layer 41 and the second dielectric layer 42), but the present invention is not limited to this. The resonator 10 may have three or more dielectric layers. In this case, the first dielectric layer 41 of the multiple dielectric layers is provided close to the piezoelectric layer 20 and is provided in contact with the piezoelectric layer 20. The second dielectric layer 42 is provided farther from the piezoelectric layer 20 and is provided as the outermost layer of the multiple dielectric layers. Of the three or more multiple dielectric layers, the first dielectric layer 41 and the second dielectric layer 42 of at least two layers have different acoustic impedances.

[0042] 4 and 5 are schematic cross-sectional views illustrating a bulk wave in a first-order thickness-shear mode propagating through the piezoelectric layer of the first embodiment, respectively.

[0043] As shown in Figure 4, in the resonator 10 of the first embodiment, vibration displacement is in the thickness shear direction, so waves propagate and resonate almost entirely in the direction connecting the first principal surface 20a and the second principal surface 20b of the piezoelectric layer 20, i.e., the Z direction. That is, the X direction component of the wave is significantly smaller than the Z direction component. Furthermore, since resonance characteristics are obtained by this Z direction wave propagation, a reflector is not required. Therefore, no propagation loss occurs when the wave propagates to the reflector. Therefore, even if the number of electrode pairs consisting of the first electrode fingers 31 and the second electrode fingers 32 is reduced in an effort to reduce the size, the Q value is unlikely to decrease.

[0044] As shown in FIG. 5 , the amplitude direction of the bulk wave in the first thickness-shear mode is opposite between a first region 251 included in the intersection region C (see FIG. 2 ) of the piezoelectric layer 20 and a second region 252 included in the intersection region C. FIG. 5 schematically illustrates 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 has a higher potential than the first electrode finger 31. Here, the imaginary plane VP1 is a plane that is perpendicular to the thickness direction of the piezoelectric layer 20 and divides the piezoelectric layer 20 in half. The first region 251 is a region of the intersection region C between the imaginary plane VP1 and the first main surface 20a. The second region 252 is a region of the intersection region C between the imaginary plane VP1 and the second main surface 20b.

[0045] In the resonator 10, at least one pair of electrodes consisting of a first electrode finger 31 and a second electrode finger 32 is arranged, but since the resonator 10 does not propagate waves in the X direction, it is not necessary for the number of electrode pairs consisting of the first electrode finger 31 and the second electrode finger 32 to be multiple pairs. In other words, it is sufficient that at least one pair of electrodes is provided.

[0046] 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 the ground potential, and the second electrode finger 32 may be connected to the hot potential. In the first embodiment, at least one pair of electrodes is an electrode connected to a hot potential or an electrode connected to a ground potential, as described above, and no floating electrode is provided.

[0047] 6 is an explanatory diagram showing an example of the resonance characteristics of the resonator of the first embodiment. The design parameters of the resonator 10 that obtained the resonance characteristics shown in FIG.

[0048] Piezoelectric layer 20: LiNbO with Euler angles (0°, 0°, 90°) ３ Thickness of the piezoelectric layer 20: 400 nm

[0049] Length of intersection region C: 40 μm Number of pairs of electrodes consisting of first electrode fingers 31 and second electrode fingers 32: 21 pairs Inter-electrode pitch between first electrode fingers 31 and second electrode fingers 32: 3 μm Width of first electrode fingers 31 and second electrode fingers 32: 500 nm d / p: 0.133

[0050] Support substrate 11: Si

[0051] In the first embodiment, the inter-electrode pitch of each electrode pair, which is made up of the first electrode fingers 31 and the second electrode fingers 32, is set to be equal for all pairs. That is, the first electrode fingers 31 and the second electrode fingers 32 are arranged at equal pitches.

[0052] As is clear from FIG. 6, good resonance characteristics with a relative bandwidth of 12.5% ​​are obtained despite the absence of a reflector.

[0053] In the first embodiment, when the thickness of the piezoelectric layer 20 is d and the interelectrode pitch between the first electrode fingers 31 and the second electrode fingers 32 is p, d / p is 0.5 or less, and more preferably 0.24 or less. This will be explained with reference to FIG. 7 .

[0054] 7 is a graph showing the relationship between d / 2p and the fractional bandwidth of the resonator, where p is the center-to-center distance or the average center-to-center distance between adjacent electrodes and d is the average thickness of the piezoelectric layer in the resonator of the first embodiment. In FIG. 7, multiple elastic wave devices were obtained by varying d / 2p, similar to the elastic wave device having the resonance characteristics shown in FIG.

[0055] As shown in Figure 7, when d / 2p exceeds 0.25, i.e., when d / p > 0.5, adjusting d / p results in a fractional bandwidth of less than 5%. In contrast, when d / 2p ≤ 0.25, i.e., when d / p ≤ 0.5, varying d / p within this range can increase the fractional bandwidth to 5% or more, thereby enabling the construction of a resonator with a high coupling coefficient. Furthermore, when d / 2p is 0.12 or less, i.e., when d / p is 0.24 or less, the fractional bandwidth can be increased to 7% or more. Furthermore, adjusting d / p within this range can result in a resonator with an even wider fractional bandwidth and a higher coupling coefficient. Therefore, by setting d / p to 0.5 or less, a resonator with a high coupling coefficient can be constructed using the bulk wave in the thickness-shear primary mode.

[0056] When the piezoelectric layer 20 has thickness variations, the thickness d of the piezoelectric layer 20 may be an average value of the thickness variations.

[0057] 8 is a plan view showing an example of the resonator of the first embodiment in which a pair of electrodes is provided. In the resonator 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. Note that K in FIG. 8 is the crossover width. As described above, the resonator 10 of the present disclosure may have only one pair of electrodes. Even in this case, if the above d / p is 0.5 or less, a bulk wave in the thickness-shear primary mode can be effectively excited.

[0058] In the resonator 10, it is preferable that the metallization ratio MR of the adjacent first electrode fingers 31 and second electrode fingers 32 with respect to the crossing region C satisfies MR≦1.75(d / p)+0.075. In this case, spurious components can be effectively reduced. This will be explained with reference to FIGS. 9 and 10.

[0059] 9 is a reference diagram showing an example of the resonance characteristics of the resonator of the first embodiment. As shown in FIG. 9, a spurious component indicated by an arrow B appears between the resonance frequency and the anti-resonance frequency. Note that, when d / p=0.08 and the resonator is made of LiNbO ３The Euler angles were (0°, 0°, 90°), and the metallization ratio was set to MR=0.35.

[0060] The metallization ratio MR will be described with reference to FIG. 2 . Focusing on a pair of first and second electrode fingers 31 and 32 in the electrode structure of FIG. 2 , assume that only this pair of first and second electrode fingers 31 and 32 is provided. In this case, the area surrounded by the dashed line is the intersection region C. When the first and second electrode fingers 31 and 32 are viewed in a direction perpendicular to the extension direction of the first and second electrode fingers 31 and 32, i.e., in the opposing direction, the intersection region C includes the region of the first electrode finger 31 overlapping with the second electrode finger 32, the region of the second electrode finger 32 overlapping with the first electrode finger 31, and the region between the first and second electrode fingers 31 and 32 where the first and second electrode fingers 31 and 32 overlap. The ratio of the area of ​​the first and second electrode fingers 31 and 32 within the intersection region C to the area of ​​the intersection region C is the metallization ratio MR. That is, the metallization ratio MR is the ratio of the area of ​​the metallization portion to the area of ​​the intersection region C.

[0061] When multiple pairs of first electrode fingers 31 and second electrode fingers 32 are provided, the ratio of the metallization portion included in all intersection regions C to the total area of ​​the intersection regions C may be defined as MR.

[0062] 10 is an explanatory diagram showing the relationship between the relative bandwidth when a large number of resonators are configured for the resonator of the first embodiment and the amount of phase rotation of the spurious impedance normalized by 180 degrees as the magnitude of the spurious. The relative bandwidth was adjusted by variously changing the film thickness of the piezoelectric layer 20 and the dimensions of the first electrode finger 31 and the second electrode finger 32. Also, FIG. 10 shows the relationship between the relative bandwidth and the spurious impedance normalized by 180 degrees as the magnitude of the spurious. ３ Although this is the result when a piezoelectric layer 20 having a cut angle of 100° is used, the same tendency is observed when a piezoelectric layer 20 having a different cut angle is used.

[0063] In the region surrounded by ellipse J in Fig. 10, the spurious is as large as 1.0. As is clear from Fig. 10, when the fractional bandwidth exceeds 0.17, i.e., 17%, large spurious signals with a spurious level of 1 or more appear within the passband, even if the parameters constituting the fractional bandwidth are changed. That is, as in the resonance characteristics shown in Fig. 9, large spurious signals indicated by arrow B appear within the passband. Therefore, it is preferable that the fractional bandwidth be 17% or less. In this case, the spurious signals can be reduced by adjusting the film thickness of piezoelectric layer 20 and the dimensions of first electrode fingers 31 and second electrode fingers 32, etc.

[0064] FIG. 11 is an explanatory diagram showing the relationship between d / 2p, metallization ratio MR, and fractional bandwidth. Various resonators 10 with different d / 2p and MR were constructed for the resonator 10 of the first embodiment, and the fractional bandwidth was measured. The hatched area to the right of dashed line D in FIG. 11 is the region where the fractional bandwidth is 17% or less. The boundary between this hatched area and the unhatched area 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 this case, it is easy to achieve a fractional bandwidth of 17% or less. More preferably, it is the region to the right of MR = 3.5(d / 2p) + 0.05, as indicated by dashed line D1 in FIG. 11. That is, if MR≦1.75(d / p)+0.05, the fractional bandwidth can be reliably kept to 17% or less.

[0065] FIG. 12 shows the results of LiNbO when d / p approaches 0. ３ 12 is an explanatory diagram showing a map of fractional bandwidths with respect to Euler angles (0°, θ, ψ). The hatched areas in FIG. 12 are regions where fractional bandwidths of at least 5% or more can be obtained. The range of the regions can be approximated as the ranges expressed by the following formulas (1), (2), and (3).

[0066] (0°±10°, 0° to 20°, any ψ) ... Equation (1) (0°±10°, 20° to 80°, 0° to 60° (1-(θ-50) ２ / 900) １／２) or (0°±10°, 20° to 80°, [180°-60° (1-(θ-50) ２ / 900) １／２ ]~180°) ...Formula (2) (0°±10°, [180°-30°(1-(ψ-90) ２ / 8100) １／２ ] to 180°, any ψ) ...Equation (3)

[0067] Therefore, in the case of the Euler angle range of the above formula (1), formula (2), or formula (3), the relative bandwidth can be made sufficiently wide, which is preferable.

[0068] The resonator 10 of this embodiment has been described as being configured to utilize bulk waves in a thickness-shear first-order mode, but is not limited to this. The resonator 10 may also utilize plate waves. In this case, the resonator 10 has reflectors provided on both sides of the IDT electrode 30 in the acoustic wave propagation direction. In the resonator 10, Lamb waves as plate waves are excited by applying an AC electric field to the first electrode fingers 31 and the second electrode fingers 32 on the recess 14. At this time, since reflectors are provided on both sides, resonance characteristics due to the Lamb waves as plate waves can be obtained.

[0069] Fig. 13 is a cross-sectional view showing an elastic wave device according to a first preferred embodiment of the present invention. Fig. 13 shows the configurations of a series arm resonator 61 and a parallel arm resonator 64 among the multiple resonators 10 included in the elastic wave device 100. The series arm resonator 61 and the parallel arm resonator 64 each have the configurations of the resonators 10 shown in Figs. 2 to 12 . Note that Fig. 13 illustrates the series arm resonator 61 and the parallel arm resonator 64 among the multiple resonators 10 included in the elastic wave device 100. However, the series arm resonators 62 and 63 (see Fig. 1 ) included in the elastic wave device 100 have the same configuration as the series arm resonator 61, and the parallel arm resonators 65, 66, and 67 (see Fig. 1 ) included in the elastic wave device 100 have the same configuration as the parallel arm resonator 64.

[0070] 13 , the series arm resonator 61 and the parallel arm resonator 64 are configured to have a common piezoelectric layer 20. The IDT electrode 30 of the series arm resonator 61 and the IDT electrode 30 of the parallel arm resonator 64 are provided on the same first principal surface 20 a of the piezoelectric layer 20.

[0071] The first dielectric layer 41 is provided on the first main surface 20a of the piezoelectric layer 20, covering the IDT electrodes 30 of the series arm resonators 61 and the IDT electrodes 30 of the parallel arm resonators 64. The second dielectric layer 42 is provided on the first dielectric layer 41. In this embodiment, the second dielectric layer 42 has a lower acoustic impedance than the first dielectric layer 41.

[0072] The elastic wave device 100 of this preferred embodiment includes at least two resonators having different thickness resonance modes with different resonance frequencies. Specifically, in the elastic wave device 100, the series arm resonator 61 (second resonator) has a higher resonance frequency than the parallel arm resonator 64 (first resonator). The thickness resonance mode includes thickness-shear vibration and thickness-extension vibration modes.

[0073] The thickness ts11 of the first dielectric layer 41 of the series arm resonator 61 is different from the thickness ts12 of the first dielectric layer 41 of the parallel arm resonator 64. More specifically, the thickness ts12 of the first dielectric layer 41 of the parallel arm resonator 64 is thicker than the thickness ts11 of the first dielectric layer 41 of the series arm resonator 61.

[0074] The thickness ts21 of the second dielectric layer 42 of the series arm resonator 61 is equal to the thickness ts22 of the second dielectric layer 42 of the parallel arm resonator 64. The thicknesses tp of the piezoelectric layers 20 of the series arm resonators 61 and the parallel arm resonators 64 are equal to each other.

[0075] In this embodiment, the thicknesses ts11, ts12, ts21, and ts22 refer to the thicknesses of the first dielectric layer 41 and the second dielectric layer 42 at portions that do not overlap with the IDT electrode 30. That is, the thickness ts12 of the first dielectric layer 41 in the region between the first electrode finger 31 and the second electrode finger 32 of the parallel arm resonator 64 (first resonator) is different from the thickness ts11 of the first dielectric layer 41 in the region between the first electrode finger 31 and the second electrode finger 32 of the series arm resonator 61 (second resonator).

[0076] Furthermore, the thickness ts22 of the second dielectric layer 42 in the region between the first electrode finger 31 and the second electrode finger 32 of the parallel arm resonator 64 (first resonator) is equal to the thickness ts21 of the second dielectric layer 42 in the region between the first electrode finger 31 and the second electrode finger 32 of the series arm resonator 61 (second resonator).

[0077] 14 is a graph for schematically illustrating the relationship between the thickness deviation of the piezoelectric layer and the thickness deviation of the dielectric layer in an elastic wave device according to a comparative example. The elastic wave device according to the comparative example differs from elastic wave device 100 according to the first embodiment in that it has one dielectric layer. The elastic wave device according to the comparative example uses Z-cut LiNbO ３ The dielectric layer is SiO ２ It was a single layer.

[0078] 14, the vertical axis represents the thickness deviation Δtp of the piezoelectric layer 20 relative to the thickness tp at which a predetermined resonance frequency is obtained, and the horizontal axis represents the thickness deviation Δts of the dielectric layer thickness ts required to adjust the resonance frequency to the predetermined frequency when the thickness deviation Δtp of the piezoelectric layer 20 occurs.

[0079] 14 , in the elastic wave device according to the comparative example, the slope of the thickness difference Δtp of the piezoelectric layer 20 and the slope of the thickness difference Δts of the dielectric layer are different between the series arm resonator and the parallel arm resonator. In other words, if the thickness of the dielectric layer is constant, it becomes difficult to adjust the resonant frequency of at least one of the series arm resonator and the parallel arm resonator. Alternatively, in order to appropriately adjust the resonant frequencies of both the series arm resonator and the parallel arm resonator, it is necessary to adjust the thickness of the dielectric layer of each resonator, which may result in increased variation in the resonant frequencies.

[0080] In this embodiment, a first dielectric layer 41 and a second dielectric layer 42 having different acoustic impedances are provided. The second dielectric layer 42, which is the outermost layer, has a lower acoustic impedance than the first dielectric layer 41. The film thickness sensitivity of the second dielectric layer 42 in terms of the relationship between the thickness and the deviation in the resonant frequency is lower than that of the first dielectric layer 41. In other words, the amount of change in the resonant frequency due to the deviation in the thickness of the second dielectric layer 42 is smaller than the amount of change in the resonant frequency due to the deviation in the thickness of the first dielectric layer 41.

[0081] By making the thicknesses ts11, ts12 of the first dielectric layer 41, which has a relatively high acoustic impedance, different between the series arm resonator 61 and the parallel arm resonator 64, it is possible to create a difference in the resonant frequencies between the series arm resonator 61 and the parallel arm resonator 64. By making the thicknesses ts21, ts22 of the second dielectric layer 42, which has a relatively low acoustic impedance, constant and adjusting them to a common thickness, it is possible to appropriately adjust the resonant frequencies of the series arm resonator 61 and the parallel arm resonator 64.

[0082] Furthermore, the first dielectric layer 41, which has a relatively high acoustic impedance, is provided closer to the IDT electrode 30 than the second dielectric layer 42 and is provided to cover the IDT electrode 30, thereby improving the coupling coefficient of the IDT electrode 30.

[0083] Table 2 shows the materials and film thicknesses of the piezoelectric layer, first dielectric layer, and second dielectric layer of the acoustic wave devices according to the first and second examples.

[0084]

[0085] As shown in Table 2, the piezoelectric layer 20 of the elastic wave device 100 according to the first and second examples is made of Z-cut LiNbO ３ The thickness tp of the piezoelectric layer 20 in the first embodiment is 347 nm, and the thickness tp of the piezoelectric layer 20 in the second embodiment is 372 nm.

[0086] In the elastic wave device 100 according to the first preferred embodiment, the first dielectric layer 41 is made of silicon nitride (Si ３ N ４ ), and the second dielectric layer 42 is silicon oxide (SiO ２ ) In other words, in the first embodiment, the acoustic impedance of the second dielectric layer 42 is lower than the acoustic impedance of the first dielectric layer 41.

[0087] In the first example, the thickness ts12 of the first dielectric layer 41 of the parallel arm resonator 64 is 119 nm, and the thickness ts11 of the first dielectric layer 41 of the series arm resonator 61 is 39 nm. That is, in the first example, the thickness ts12 of the first dielectric layer 41 of the parallel arm resonator 64 is thicker than the thickness ts11 of the first dielectric layer 41 of the series arm resonator 61. The thicknesses ts21 and ts22 of the second dielectric layer 42 are both 47 nm. That is, the thicknesses ts21 and ts22 of the second dielectric layer 42 are constant in the series arm resonator 61 and the parallel arm resonator 64.

[0088] In the acoustic wave device according to the second preferred embodiment, the first dielectric layer 41 is made of silicon oxide (SiO ２ ), and the second dielectric layer 42 is silicon nitride (Si ３ N ４ ) In other words, in the second embodiment, the acoustic impedance of the first dielectric layer 41 is lower than the acoustic impedance of the second dielectric layer 42.

[0089] In the second example, the thickness ts12 of the first dielectric layer 41 of the parallel arm resonator 64 is 137 nm, and the thickness ts11 of the first dielectric layer 41 of the series arm resonator 61 is 12 nm. That is, in the first example, the thickness ts12 of the first dielectric layer 41 of the parallel arm resonator 64 is thicker than the thickness ts11 of the first dielectric layer 41 of the series arm resonator 61. The thicknesses ts21 and ts22 of the second dielectric layer 42 are both 30 nm. That is, the thicknesses ts21 and ts22 of the second dielectric layer 42 are constant in the series arm resonator 61 and the parallel arm resonator 64.

[0090] Fig. 15 is a graph showing the pass characteristics of the elastic wave devices according to Examples 1 and 2. Fig. 16 is a graph showing the relationship between the thickness of the piezoelectric layer and the thickness of the second dielectric layer when a constant resonant frequency is maintained for the elastic wave device according to Example 1. Fig. 17 is a graph showing the relationship between the thickness of the piezoelectric layer and the thickness of the second dielectric layer when a constant resonant frequency is maintained for the elastic wave device according to Example 2.

[0091] As shown in FIG. 15, the elastic wave devices 100 according to the first and second preferred embodiments have equivalent pass characteristics (S12).

[0092] As shown in FIG. 16, in the first embodiment, the first dielectric layer 41 is made of silicon nitride (Si ３ N ４ ) is used as the second dielectric layer 42, and silicon oxide (SiO ２ ) is used. In the first example, the film thickness sensitivity (the amount of change in resonant frequency with respect to the amount of change in film thickness) of the second dielectric layer 42 is smaller than that of the first dielectric layer 41. Therefore, even if the thickness tp of the piezoelectric layer 20 deviates from the center value (tp = 347 nm) indicated by the arrow C1, it is sufficient to adjust the thicknesses ts21 and ts22 of the second dielectric layers 42 of the series arm resonator 61 and the parallel arm resonator 64 to the same thickness. In other words, it was shown that as long as the thicknesses ts11 and ts12 of the first dielectric layers 41 of the series arm resonator 61 and the parallel arm resonator 64 are formed to appropriate thicknesses, it is not necessary to adjust the thicknesses ts21 and ts22 of the second dielectric layers 42 individually, and they can be adjusted to a constant thickness.

[0093] As shown in FIG. 17, in the second embodiment, the first dielectric layer 41 is made of silicon oxide (SiO ２ ) is used as the second dielectric layer 42, and silicon nitride (Si ３ N ４ ) is used. In the second embodiment, the film thickness sensitivity (the amount of change in resonant frequency with respect to the amount of change in film thickness) of the second dielectric layer 42 is greater than that of the first dielectric layer 41. Therefore, even if the thickness tp of the piezoelectric layer 20 deviates from the center value (tp = 372 nm) indicated by the arrow C2, the adjustment amount of the thicknesses ts21 and ts22 of the second dielectric layer 42 can be made smaller than in the first embodiment. In other words, the adjustment amount of the resonant frequency can be made larger than in the first embodiment. Furthermore, by individually adjusting the thicknesses ts21 and ts22 of the second dielectric layer 42 in the series arm resonator 61 and the parallel arm resonator 64, the respective resonant frequencies can be appropriately adjusted.

[0094] Table 3 shows the materials and film thicknesses of the piezoelectric layer, first dielectric layer, and second dielectric layer of the elastic wave devices according to the third preferred embodiment, the first comparative example, and the second comparative example.

[0095]

[0096] As shown in Table 3, the elastic wave device 100 according to the third example differs from the first and second examples in that the thickness ts11 of the first dielectric layer 41 of the series arm resonator 61 is equal to the thickness ts12 of the first dielectric layer 41 of the parallel arm resonator 64. The thickness ts21 of the second dielectric layer 42 of the series arm resonator 61 is equal to the thickness ts22 of the second dielectric layer 42 of the parallel arm resonator 64. Unlike the third example, the elastic wave devices according to the first and second comparative examples do not include a second dielectric layer and have a single first dielectric layer 41.

[0097] The piezoelectric layers of the third embodiment, the first comparative example, and the second comparative example are all Z-cut LiNbO ３ The thickness tp of the piezoelectric layer 20 in the third example is 368 nm, and the thicknesses tp of the piezoelectric layer 20 in the first and second comparative examples are 367 nm and 367.5 nm, respectively.

[0098] In the elastic wave device 100 according to the third preferred embodiment, the first dielectric layer 41 is made of silicon oxide (SiO ２ ), and the second dielectric layer 42 is silicon nitride (Si ３ N ４ ) In other words, in the third embodiment, the acoustic impedance of the first dielectric layer 41 is lower than the acoustic impedance of the second dielectric layer 42, as in the second embodiment described above.

[0099] In the third preferred embodiment, the thickness ts11 of the first dielectric layer 41 of the series arm resonator 61 and the thickness ts12 of the first dielectric layer 41 of the parallel arm resonator 64 are both 20 nm.

[0100] In the first comparative example, the single-layer first dielectric layer 41 is made of silicon nitride (Si ３ N ４ The first dielectric layer 41 (Si ３ N ４ In the second comparative example, the first dielectric layer 41 is a single layer made of silicon oxide (SiO ２ The first dielectric layer 41 (SiO ２ ) has a film thickness of 58 nm.

[0101] FIG. 18 is a graph showing the relationship between the deviation in film thickness of the dielectric layer and the amount of change in resonant frequency for the elastic wave devices according to the third preferred embodiment, the first comparative example, and the second comparative example.

[0102] In the graph shown in Fig. 18, the horizontal axis represents the deviation in the dielectric layer thickness, i.e., the deviation from the dielectric layer thickness at which a predetermined resonant frequency is obtained. In the third example, the deviation in the thickness of the outermost second dielectric layer 42 is shown, while in the first and second comparative examples, the deviation in the thickness of the single first dielectric layer is shown. The vertical axis of the graph shown in Fig. 18 represents the amount of change in the resonant frequency.

[0103] 18 , in the elastic wave device according to the third example, the slope of the relationship between the deviation in the thickness of the dielectric layer and the change in the resonant frequency is greater than in the first and second comparative examples. That is, in the third example, the change in the resonant frequency when the thickness of the outermost second dielectric layer 42 is changed is greater than in the first and second comparative examples. Therefore, even when the deviation from the predetermined resonant frequency is large (for example, when the thickness of the piezoelectric layer 20 is large), the resonant frequency can be appropriately adjusted by adjusting the thickness of the second dielectric layer 42.

[0104] The materials, film thicknesses, etc. of the first dielectric layer 41 and the second dielectric layer 42 shown in the first to third embodiments are merely examples and can be changed as appropriate.

[0105] 19 is a cross-sectional view of an elastic wave device according to a second embodiment. As shown in FIG. 19 , an elastic wave device 100A according to the second embodiment differs from the first embodiment in that the IDT electrode 30 is provided on the second main surface 20 b of the piezoelectric layer 20.

[0106] The first dielectric layer 41 and the second dielectric layer 42 are laminated on the side opposite the IDT electrode 30 with the piezoelectric layer 20 interposed therebetween, that is, on the first main surface 20 a of the piezoelectric layer 20 .

[0107] In the example shown in FIG. 19, similarly to the first embodiment described above, the first dielectric layer 41 is made of, for example, silicon nitride (Si ３ N ４ ), and the second dielectric layer 42 is silicon oxide (SiO ２) The thickness ts12 of the first dielectric layer 41 of the parallel arm resonator 64 is greater than the thickness ts11 of the first dielectric layer 41 of the series arm resonator 61. The thicknesses ts21 and ts22 of the second dielectric layer 42 are constant in the series arm resonator 61 and the parallel arm resonator 64.

[0108] However, the present invention is not limited to this, and the configuration of the second or third example described above may be applied to the second embodiment. Furthermore, if necessary, a dielectric layer may be provided on the second main surface 20b of the piezoelectric layer 20 to cover the IDT electrode 30.

[0109] 20 is a cross-sectional view showing a resonator included in an elastic wave device according to a third embodiment. In the above-described embodiments, a so-called membrane structure has been described in which the support substrate 11 has the recess 14 and the recess 14 is provided on the second main surface 20b of the piezoelectric layer 20. However, the present invention is not limited to this.

[0110] 20, in the resonator 10A according to the third embodiment, an acoustic multilayer film 43 is laminated on the second main surface 20b of the piezoelectric layer 20. The acoustic multilayer film 43 has a laminate structure of low acoustic impedance layers 43a, 43c, and 43e having a relatively low acoustic impedance and high acoustic impedance layers 43b and 43d having a relatively high acoustic impedance. The low acoustic impedance layers 43a, 43c, and 43e are made of, for example, silicon oxide (SiO ２ ), and the high acoustic impedance layers 43b and 43d are made of, for example, silicon nitride (SiN) or aluminum oxide (Al ２ O ３ ), tantalum oxide (Ta ２ O ５ ), hafnium oxide (HfO ２ When the acoustic multilayer film 43 is used, bulk waves in the first thickness-shear mode can be confined within the piezoelectric layer 20 without using the recesses 14.

[0111] Furthermore, the materials of the low acoustic impedance layers 43a, 43c, and 43e and the high acoustic impedance layers 43b and 43d have a lower dielectric constant than the piezoelectric layer 20. That is, the low acoustic impedance layers 43a, 43c, and 43e and the high acoustic impedance layers 43b and 43d are formed of a material different from that of the first dielectric layer 41.

[0112] There is no particular limitation on the number of stacked low acoustic impedance layers 43a, 43c, 43e and high acoustic impedance layers 43b, 43d in the acoustic multilayer film 43. It is sufficient that at least one of the high acoustic impedance layers 43b, 43d is disposed farther from the piezoelectric layer 20 than the low acoustic impedance layers 43a, 43c, 43e.

[0113] The low acoustic impedance layers 43 a, 43 c, and 43 e and the high acoustic impedance layers 43 b and 43 d can be made of any suitable material as long as the above acoustic impedance relationship is satisfied. For example, the high acoustic impedance layers 43 b and 43 d can be made of aluminum nitride (AlN) or metals such as tungsten (W) and platinum (Pt).

[0114] The first dielectric layer 41 and the second dielectric layer 42 are laminated on the first main surface 20a of the piezoelectric layer 20, covering the IDT electrode 30. The first dielectric layer 41 and the second dielectric layer 42 are provided on the side of the piezoelectric layer 20 opposite the acoustic multilayer film 43.

[0115] The configuration of the resonator 10A according to the third embodiment can be applied to at least one of the above-described series arm resonators 61, 62, and 63 and the parallel arm resonators 64, 65, 66, and 67. In addition, in the third embodiment, the relationships between the materials, acoustic impedances, thicknesses, etc. of the first dielectric layer 41 and the second dielectric layer 42 can be applied to the configurations of the above-described first to third embodiments.

[0116] 21 is a cross-sectional view showing a resonator included in an elastic wave device according to a fourth embodiment. As shown in FIG. 21 , a resonator 10B according to the fourth embodiment has a different configuration from the above-described embodiments in that an electrode 30A includes an upper electrode 38 and a lower electrode 39.

[0117] The upper electrode 38 and lower electrode 39 of the electrode 30A are each a flat electrode. The upper electrode 38 is provided on the first main surface 20a of the piezoelectric layer 20. The lower electrode 39 is provided on the second main surface 20b of the piezoelectric layer 20. The upper electrode 38 and the lower electrode 39 overlap in a region overlapping with the recess 14. In other words, in the region overlapping with the recess 14, the piezoelectric layer 20 is disposed between the upper electrode 38 and the lower electrode 39 in the Z direction. This allows bulk waves to propagate between the upper electrode 38 and the lower electrode 39.

[0118] The upper electrode 38 and the lower electrode 39 are formed of a metal such as aluminum (Al), platinum (Pt), copper (Cu), tungsten (W), molybdenum (Mo), or ruthenium (Ru), or an alloy containing at least one of these materials.

[0119] The first dielectric layer 41 and the second dielectric layer 42 are provided on the first major surface 20 a of the piezoelectric layer 20 to cover the upper electrode 38 .

[0120] The configuration of the resonator 10B according to the fourth embodiment can be applied to at least one of the above-described series arm resonators 61, 62, and 63 and the parallel arm resonators 64, 65, 66, and 67. In addition, in the fourth embodiment, the relationships between the materials, acoustic impedances, thicknesses, etc. of the first dielectric layer 41 and the second dielectric layer 42 can be applied to the configurations of the above-described first to third embodiments.

[0121] The above-described embodiment is intended to facilitate understanding of the present invention, and is not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit and scope of the present invention, and equivalents thereof are also included in the present invention.

[0122] The present disclosure may also have the following configurations.

[0123] (1) An elastic wave device having at least two resonators, the resonators comprising: a piezoelectric layer having a first main surface and a second main surface facing each other; an electrode provided on at least one of the first main surface and the second main surface of the piezoelectric layer; a plurality of dielectric layers stacked on the first main surface or the second main surface of the piezoelectric layer, the dielectric layers including at least a first dielectric layer and a second dielectric layer; and a support member provided on the second main surface side of the piezoelectric layer, the support member having an acoustic reflector on the second main surface side of the piezoelectric layer, wherein at least the first dielectric layer and the second dielectric layer among the plurality of dielectric layers have mutually different acoustic impedances. (2) The elastic wave device according to (1), wherein, among the plurality of dielectric layers, the first dielectric layer is provided in a layer close to the piezoelectric layer and the second dielectric layer is provided in a layer distant from the piezoelectric layer, and the second dielectric layer has a lower acoustic impedance than the first dielectric layer. (3) The elastic wave device according to (1) or (2), wherein the at least two resonators have mutually different resonance frequencies in thickness resonance modes. (4) The elastic wave device according to (1) or (2), wherein the at least two resonators include a first resonator and a second resonator having a higher resonant frequency than the first resonator, wherein the first dielectric layer of the first resonator and the second resonator have different thicknesses, wherein the second dielectric layer of the first resonator and the second resonator have the same thickness, and wherein the piezoelectric layer of the first resonator and the second resonator have the same thickness. (5) The elastic wave device according to (1), wherein the first dielectric layer of the plurality of dielectric layers is provided in a layer close to the piezoelectric layer and the second dielectric layer is provided in a layer distant from the piezoelectric layer, and wherein the second dielectric layer has a higher acoustic impedance than the first dielectric layer. (6) The elastic wave device according to any one of (1) to (5), including an input terminal and an output terminal, wherein the at least two resonators include a first resonator and a second resonator having a higher resonant frequency than the first resonator, wherein at least one of the first resonators is connected in parallel to a signal path connecting the input terminal and the output terminal, and at least one of the second resonators is connected in series to a signal path connecting the input terminal and the output terminal.(7) The elastic wave device according to (6), which is a ladder-type filter including a plurality of the first resonators that are parallel arm resonators and a plurality of the second resonators that are series arm resonators. (8) The elastic wave device according to (4), in which the electrodes are IDT electrodes including a first bus bar and a second bus bar that face 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, and in which the thickness of the first dielectric layer in a region between the first electrode finger and the second electrode finger of the first resonator is different from the thickness of the first dielectric layer in a region between the first electrode finger and the second electrode finger of the second resonator. (9) The elastic wave device according to (1), in which the electrodes are flat electrodes. (10) The elastic wave device according to any one of (1) to (9), in which the first dielectric layer includes at least one of silicon nitride, aluminum nitride, tantalum oxide, and niobium oxide. (11) The elastic wave device according to any one of (1) to (10), wherein the second dielectric layer contains silicon oxide. (12) The elastic wave device according to any one of (1) to (10), wherein the outermost dielectric layer of the plurality of dielectric layers contains at least one of silicon oxide, silicon nitride, aluminum nitride, tantalum oxide, and niobium oxide. (13) The elastic wave device according to any one of (1) to (12), wherein the acoustic reflecting portion is a recess that opens toward the piezoelectric layer of the support member. (14) The elastic wave device according to any one of (1) to (12), wherein the acoustic reflecting portion is an acoustic reflecting film including a high acoustic impedance layer having a relatively high acoustic impedance and a low acoustic impedance layer having a relatively low acoustic impedance, and wherein the support member and the piezoelectric layer are arranged to face each other with the acoustic reflecting film sandwiched therebetween.

[0124] REFERENCE SIGNS LIST 10, 10A, 10B Resonator 11 Support substrate 14 Recess 20 Piezoelectric layer 20a First principal surface 20b Second principal surface 30 IDT electrode 30A Electrode 31 First electrode finger 32 Second electrode finger 33 First bus bar electrode 34 Second bus bar electrode 38 Upper electrode 39 Lower electrode 41 First dielectric layer 42 Second dielectric layer 43 Acoustic multilayer film 43a, 43c, 43e Low acoustic impedance layer 43b, 43d High acoustic impedance layer 61, 62, 63 Series arm resonator 64, 65, 66, 67 Parallel arm resonator 100, 100A Acoustic wave device

Claims

1. An elastic wave device having at least two resonators, wherein the resonators comprise: a piezoelectric layer having opposing first and second main surfaces; an electrode provided on at least one of the first and second main surfaces of the piezoelectric layer; a plurality of dielectric layers including at least a first dielectric layer and a second dielectric layer stacked on the first or second main surface of the piezoelectric layer; and a support member provided on the second main surface side of the piezoelectric layer, the support member having an acoustic reflector on the second main surface side of the piezoelectric layer; and wherein the acoustic impedances of at least the first dielectric layer and the second dielectric layer among the plurality of dielectric layers are different from each other.

2. The elastic wave device according to claim 1, wherein, of the plurality of dielectric layers, the first dielectric layer is provided in a layer close to the piezoelectric layer, and the second dielectric layer is provided in a layer distant from the piezoelectric layer, and the second dielectric layer has a lower acoustic impedance than the first dielectric layer.

3. The elastic wave device according to claim 1 or 2, wherein the at least two resonators have different resonance frequencies in thickness resonance mode.

4. The elastic wave device according to claim 1 or 2, wherein the at least two resonators include a first resonator and a second resonator having a higher resonant frequency than the first resonator, the first dielectric layers of the first resonator and the second resonator have different thicknesses, the second dielectric layers of the first resonator and the second resonator have the same thickness, and the piezoelectric layers of the first resonator and the second resonator have the same thickness.

5. The elastic wave device according to claim 1, wherein, of the plurality of dielectric layers, the first dielectric layer is provided in a layer close to the piezoelectric layer, and the second dielectric layer is provided in a layer distant from the piezoelectric layer, and the second dielectric layer has a higher acoustic impedance than the first dielectric layer.

6. The elastic wave device according to any one of claims 1 to 5, comprising an input terminal and an output terminal, wherein the at least two resonators comprise a first resonator and a second resonator having a higher resonant frequency than the first resonator, wherein at least one of the first resonators is connected in parallel to a signal path connecting the input terminal and the output terminal, and at least one of the second resonators is connected in series to a signal path connecting the input terminal and the output terminal.

7. The acoustic wave device according to claim 6, which is a ladder-type filter including a plurality of the first resonators which are parallel arm resonators and a plurality of the second resonators which are series arm resonators.

8. The elastic wave device according to claim 4, wherein the electrodes are IDT electrodes including 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, and the thickness of the first dielectric layer in the region between the first electrode finger and the second electrode finger of the first resonator is different from the thickness of the first dielectric layer in the region between the first electrode finger and the second electrode finger of the second resonator.

9. The acoustic wave device according to claim 1, wherein the electrode is a flat electrode.

10. The acoustic wave device according to any one of claims 1 to 9, wherein the first dielectric layer contains at least one of silicon nitride, aluminum nitride, tantalum oxide, and niobium oxide.

11. The acoustic wave device according to any one of claims 1 to 10, wherein the second dielectric layer contains silicon oxide.

12. The elastic wave device according to any one of claims 1 to 10, wherein the outermost dielectric layer of the plurality of dielectric layers contains at least one of silicon oxide, silicon nitride, aluminum nitride, tantalum oxide, and niobium oxide.

13. The elastic wave device according to any one of claims 1 to 12, wherein the acoustic reflection portion is a recess that opens to the piezoelectric layer side of the support member.

14. An elastic wave device according to any one of claims 1 to 12, wherein the acoustic reflection portion is an acoustic reflection film including a high acoustic impedance layer having a relatively high acoustic impedance and a low acoustic impedance layer having a relatively low acoustic impedance, and the support member and the piezoelectric layer are arranged to face each other with the acoustic reflection film in between.

15. The elastic wave device according to any one of claims 1 to 14, wherein the dielectric layer is provided on a principal surface of the piezoelectric layer that is different from a principal surface on which the electrode is provided.

16. The elastic wave device according to any one of claims 1 to 15, wherein the dielectric layer is provided on the same principal surface of the piezoelectric layer as the electrode.

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