Elastic wave device

Abstract

This elastic wave device has: a resonator that comprises a piezoelectric layer having a first main surface and a second main surface on the opposite side of the first main surface, an upper electrode provided on the first main surface of the piezoelectric layer, and a lower electrode provided on the second main surface of the piezoelectric layer; and a capacitive element that comprises an upper interdigital transducer (IDT) electrode provided on the first main surface of the piezoelectric layer, and a lower IDT electrode provided on the second main surface of the piezoelectric layer. The capacitive element is connected in parallel with the resonator, and the upper IDT electrode and the lower IDT electrode of the capacitive element are electrically connected to each other.

Description

Elastic Wave Device

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

[0002] Patent Document 1 describes an acoustic wave device including a bulk acoustic wave (BAW) element that utilizes bulk waves. The acoustic wave device of Patent Document 1 includes a Lamb wave loop circuit that generates an antiphase to a target signal at a specific frequency, and the Lamb wave loop circuit includes an IDT electrode.

[0003] US Patent Application Publication No. 2019 / 0273478

[0004] In such an acoustic wave device, it is required to achieve miniaturization and to adjust the passband characteristics favorably. In Patent Document 1, the IDT electrodes of the Lamb wave loop circuit are provided for exciting Lamb waves, and no consideration is given to forming a predetermined electrostatic capacitance with the IDT electrodes of the Lamb wave loop circuit.

[0005] An object of the present invention is to provide an acoustic wave device that can be miniaturized and has favorable adjustable pass characteristics.

[0006] An elastic wave device according to one embodiment includes a piezoelectric layer having a first main surface and a second main surface opposite the first main surface, a resonator including an upper electrode provided on the first main surface of the piezoelectric layer and a lower electrode provided on the second main surface of the piezoelectric layer, and a capacitive element including an upper IDT (Interdigital Transducer) electrode provided on the first main surface of the piezoelectric layer and a lower IDT electrode provided on the second main surface of the piezoelectric layer, wherein the capacitive element is connected in parallel with the resonator, and the upper IDT electrode and the lower IDT electrode of the capacitive element are electrically connected.

[0007] According to the acoustic wave device of the present invention, it is possible to achieve miniaturization and to favorably adjust the passband characteristics.

[0008] FIG. 1 is a perspective view of an elastic wave device according to a first preferred embodiment. FIG. 2 is a cross-sectional view taken along line II-II′ of FIG. 1 . FIG. 3 is a diagram illustrating capacitance formed in a capacitive element according to the first preferred embodiment. FIG. 4 is a cross-sectional view of an elastic wave device according to a second preferred embodiment. FIG. 5 is a diagram illustrating capacitance formed in a capacitive element according to the second preferred embodiment. FIG. 6 is a circuit diagram of an elastic wave device according to a third preferred embodiment. FIG. 7 is a graph illustrating the pass characteristics of elastic wave devices according to example 1 and comparative examples 1 and 2. FIG. 8 is a circuit diagram of an elastic wave device according to a fourth preferred embodiment. FIG. 9 is a graph illustrating the pass characteristics of elastic wave devices according to example 2 and comparative examples 1 and 3.

[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] First Embodiment FIG. 1 is a perspective view showing an elastic wave device according to a first embodiment. FIG. 2 is a cross-sectional view taken along line II-II' of FIG. 1. As shown in FIGS. 1 and 2, an elastic wave device 10 includes a support member 13, a piezoelectric layer 20, a resonator 30, and a capacitance element 40. The resonator 30 is a resonator that utilizes bulk waves, i.e., a BAW (Bulk Acoustic Wave) element. The capacitance element 40 is configured to include an IDT (Interdigital Transducer) electrode.

[0011] In the following description, the thickness direction of the piezoelectric layer 20 is referred to as the Z direction, the direction perpendicular to the Z direction is referred to as the X direction, and the direction perpendicular to the Z direction and the X direction is referred to as the Y direction. The X direction and the Y direction are each parallel to the surface (first main surface 20a) of the piezoelectric layer 20. In the following description, a plan view refers to the positional relationship when viewed from a direction perpendicular to the first main surface 20a of the piezoelectric layer 20 (Z direction).

[0012] The support member 13 is disposed opposite the second main surface 20b of the piezoelectric layer 20. The support member 13 includes a support substrate 11 and an insulating layer 12. The support substrate 11 is made of silicon (Si), quartz crystal, or the like. The insulating layer 12 is disposed between the support substrate 11 and the piezoelectric layer 20. The insulating layer 12 is formed of an insulating material such as silicon oxide. Note that the support member 13 may be configured without the insulating layer 12, with the piezoelectric layer 20 disposed on the support substrate 11. An adhesion layer of Ti, NiCr, or the like may be disposed between the lower electrode 32 and the insulating layer 12.

[0013] 2, a cavity 14 (hollow portion) is formed on the surface of the support member 13 (insulating layer 12) facing the second main surface 20b of the piezoelectric layer 20. The cavity 14 is provided so as to overlap, in plan view, with the excitation region of the resonator 30, which is configured by overlapping the piezoelectric layer 20, the upper electrode 31, and the lower electrode 32. This allows bulk waves to be reflected by the cavity 14.

[0014] 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 ) or lithium tantalate (LiTaO ３ The thickness of the piezoelectric layer 20 is not particularly limited, but is preferably 1 μm or less.

[0015] 1 and 2 , the resonator 30 includes a piezoelectric layer 20, an upper electrode 31 provided on a first main surface 20a of the piezoelectric layer 20, and a lower electrode 32 provided on a second main surface 20b of the piezoelectric layer 20. The resonator 30 is configured by laminating the lower electrode 32, the piezoelectric layer 20, and the upper electrode 31 in this order on a support member 13.

[0016] The resonator 30 has a so-called membrane structure in which a cavity 14 (hollow portion) is provided on the second main surface 20b side of the piezoelectric layer 20. As shown in Fig. 2, in the region overlapping with the cavity 14, the piezoelectric layer 20 is disposed between the upper electrode 31 and the lower electrode 32 in the Z direction. This allows bulk waves to propagate between the upper electrode 31 and the lower electrode 32.

[0017] The upper electrode 31 and the lower electrode 32 are formed of a metal such as aluminum (Al), platinum (Pt), copper (Cu), tungsten (W), or molybdenum (Mo), or an alloy containing at least one of these materials. The upper electrode 31 and the lower electrode 32 may be a laminated film.

[0018] 1, the upper electrode 31 and the lower electrode 32 are formed in a rectangular shape in a plan view, but are not limited to this, and the upper electrode 31 and the lower electrode 32 may be in other shapes such as a circular shape or a polygonal shape.

[0019] The capacitive element 40 includes an upper IDT electrode 41 provided on the first main surface 20a of the piezoelectric layer 20 and a lower IDT electrode 42 provided on the second main surface 20b of the piezoelectric layer 20. The upper IDT electrode 41 is provided in the same layer as the upper electrode 31 that constitutes the resonator 30. The lower IDT electrode 42 is provided in the same layer as the lower electrode 32 that constitutes the resonator 30.

[0020] The upper IDT electrode 41 and the lower IDT electrode 42 are electrically connected through a first via 35 and a second via 36 that penetrate the piezoelectric layer 20. The capacitance element 40 is connected in parallel with the resonator 30. That is, one end of the capacitance element 40 is connected to the upper electrode 31 through the connection wiring 33. The other end of the capacitance element 40 is connected to the lower electrode 32 through the connection wiring 34.

[0021] More specifically, the upper IDT electrode 41 has first electrode fingers 43A, second electrode fingers 44A, first busbar electrodes 45A, and second busbar electrodes 46A. The first electrode fingers 43A extend in the Y direction, and one end of each electrode finger 43A is connected to the first busbar electrode 45A. The second electrode fingers 44A extend in the Y direction, and the other end of each electrode finger 44A is connected to the second busbar electrode 46A. The first electrode fingers 43A and the second electrode fingers 44A are alternately arranged in the X direction with a gap therebetween. The first busbar electrodes 45A and the second busbar electrodes 46A each extend in the X direction and are spaced apart in the Y direction. The first electrode fingers 43A and the second electrode fingers 44A are arranged between the first busbar electrode 45A and the second busbar electrode 46A.

[0022] The lower IDT electrode 42 has third electrode fingers 43B, fourth electrode fingers 44B, third busbar electrodes 45B, and fourth busbar electrodes 46B. The third electrode fingers 43B extend in the Y direction, and one end of each of the third electrode fingers 43B is connected to the third busbar electrode 45B. The fourth electrode fingers 44B extend in the Y direction, and the other end of each of the fourth electrode fingers 44B is connected to the fourth busbar electrode 46B. The third electrode fingers 43B and the fourth electrode fingers 44B are alternately arranged in the X direction with a gap therebetween. The third busbar electrodes 45B and the fourth busbar electrodes 46B each extend in the X direction and are spaced apart in the Y direction. The third electrode fingers 43B and the fourth electrode fingers 44B are arranged between the third busbar electrode 45B and the fourth busbar electrode 46B.

[0023] In this embodiment, the first electrode fingers 43A of the upper IDT electrode 41 are arranged to overlap the third electrode fingers 43B of the lower IDT electrode 42 and extend in the same direction as the third electrode fingers 43B. The second electrode fingers 44A of the upper IDT electrode 41 are arranged to overlap the fourth electrode fingers 44B of the lower IDT electrode 42 and extend in the same direction as the fourth electrode fingers 44B.

[0024] In the following description, when it is not necessary to distinguish between the first electrode fingers 43A, the second electrode fingers 44A, the third electrode fingers 43B, and the fourth electrode fingers 44B, they may be simply referred to as electrode fingers.Furthermore, when it is not necessary to distinguish between the first bus bar electrodes 45A, the second bus bar electrodes 46A, the third bus bar electrodes 45B, and the fourth bus bar electrodes 46B, they may be simply referred to as bus bar electrodes.

[0025] One end of the connection wiring 33 provided on the first main surface 20a of the piezoelectric layer 20 is connected to the upper electrode 31, and the other end of the connection wiring 33 is connected to the first bus bar electrode 45A. Furthermore, one end of the connection wiring 37 provided on the second main surface 20b of the piezoelectric layer 20 is connected to the connection wiring 33 through the first via 35. The other end of the connection wiring 37 is connected to the third bus bar electrode 45B.

[0026] As a result, the first electrode finger 43A of the upper IDT electrode 41 and the third electrode finger 43B of the lower IDT electrode 42 are electrically connected through the connection wiring 33, the first via 35, and the connection wiring 37. Furthermore, the multiple first electrode fingers 43A of the upper IDT electrode 41 and the multiple third electrode fingers 43B of the lower IDT electrode 42 are electrically connected to the upper electrode 31 of the resonator 30 through the connection wiring 33, the first via 35, and the connection wiring 37. As a result, the same potential is supplied to the first electrode finger 43A of the upper IDT electrode 41 and the third electrode finger 43B of the lower IDT electrode 42.

[0027] Similarly, one end of the connection wiring 34 provided on the second main surface 20b of the piezoelectric layer 20 is connected to the lower electrode 32, and the other end of the connection wiring 34 is connected to the fourth bus bar electrode 46B. Furthermore, one end of the connection wiring 38 provided on the first main surface 20a of the piezoelectric layer 20 is connected to the connection wiring 34 through the second via 36. The other end of the connection wiring 38 is connected to the second bus bar electrode 46A.

[0028] As a result, the second electrode finger 44A of the upper IDT electrode 41 and the fourth electrode finger 44B of the lower IDT electrode 42 are electrically connected through the connection wiring 34, the second via 36, ​​and the connection wiring 38. Furthermore, the second electrode fingers 44A of the upper IDT electrode 41 and the fourth electrode fingers 44B of the lower IDT electrode 42 are electrically connected to the lower electrode 32 of the resonator 30 through the connection wiring 34, the second via 36, ​​and the connection wiring 38. As a result, the same potential is supplied to the second electrode finger 44A of the upper IDT electrode 41 and the fourth electrode finger 44B of the lower IDT electrode 42. Furthermore, different potentials are supplied to the first electrode finger 43A of the upper IDT electrode 41 and the third electrode finger 43B of the lower IDT electrode 42, and the second electrode finger 44A of the upper IDT electrode 41 and the fourth electrode finger 44B of the lower IDT electrode 42.

[0029] The connection relationship between the upper IDT electrode 41 and the lower IDT electrode 42 of the capacitive element 40 and the upper electrode 31 and the lower electrode 32 of the resonator 30 is not limited to the above configuration. The multiple first electrode fingers 43A of the upper IDT electrode 41 and the multiple third electrode fingers 43B of the lower IDT electrode 42 may be electrically connected to the lower electrode 32 of the resonator 30, and the multiple second electrode fingers 44A of the upper IDT electrode 41 and the multiple fourth electrode fingers 44B of the lower IDT electrode 42 may be electrically connected to the upper electrode 31 of the resonator 30.

[0030] 2, the multiple first electrode fingers 43A of the upper IDT electrode 41 and the multiple third electrode fingers 43B of the lower IDT electrode 42 are electrically connected and arranged opposite to each other in the Z direction across the piezoelectric layer 20. As described above, the same potential is supplied to the multiple first electrode fingers 43A of the upper IDT electrode 41 and the multiple third electrode fingers 43B of the lower IDT electrode 42, which are arranged opposite to each other in the Z direction.

[0031] The second electrode fingers 44A of the upper IDT electrode 41 and the fourth electrode fingers 44B of the lower IDT electrode 42 are electrically connected and arranged opposite each other in the Z direction with the piezoelectric layer 20 sandwiched therebetween. As described above, the same potential is supplied to the second electrode fingers 44A of the upper IDT electrode 41 and the fourth electrode fingers 44B of the lower IDT electrode 42, which are arranged opposite each other in the Z direction. Different potentials are supplied to the first electrode fingers 43A and the second electrode fingers 44A of the upper IDT electrode 41, which are adjacent in the X direction. Different potentials are supplied to the third electrode fingers 43B and the fourth electrode fingers 44B of the lower IDT electrode 42.

[0032] 3 is an explanatory diagram illustrating capacitances formed in the capacitive element according to the first embodiment. As shown in FIG. 3 , in the capacitive element 40, a capacitance Cx1 is formed between the first electrode finger 43A and the second electrode finger 44A of the upper IDT electrode 41, which are adjacent in the X direction on the same layer. A capacitance Cx2 is also formed between the third electrode finger 43B and the fourth electrode finger 44B of the lower IDT electrode 42, which are adjacent in the X direction on the same layer. A capacitance Cz1 is also formed between the first electrode finger 43A of the upper IDT electrode 41 and the fourth electrode finger 44B of the lower IDT electrode 42, which are positioned diagonally across the piezoelectric layer 20. A capacitance Cz2 is also formed between the second electrode finger 44A of the upper IDT electrode 41 and the third electrode finger 43B of the lower IDT electrode 42, which are positioned diagonally across the piezoelectric layer 20.

[0033] As a result, the capacitance element 40 has the upper IDT electrode 41 and the lower IDT electrode 42 arranged on either side of the piezoelectric layer 20, so the capacitance of the entire capacitance element 40 can be increased compared to a configuration in which only one of the upper IDT electrode 41 and the lower IDT electrode 42 is provided. Alternatively, the size (planar area) of the capacitance element 40 for forming the same capacitance can be reduced compared to a configuration in which only one of the upper IDT electrode 41 and the lower IDT electrode 42 is provided.

[0034] Since the capacitive element 40 is connected to the resonator 30, the frequency of the attenuation pole of the resonator 30 can be appropriately adjusted. Therefore, the acoustic wave device 10 can be miniaturized and the pass characteristics can be appropriately adjusted. The pass characteristics of the resonator 30 will be described later in the third and fourth embodiments.

[0035] 1 to 3, for ease of viewing, the upper IDT electrode 41 is shown with two first electrode fingers 43A and two second electrode fingers 44A, and the lower IDT electrode 42 is shown with two third electrode fingers 43B and two fourth electrode fingers 44B. However, this is not limiting, and each electrode finger may have three or more. The width and arrangement pitch of each electrode finger are merely examples and can be changed as appropriate depending on the capacitance and size (planar area) required for the capacitive element 40.

[0036] Second Embodiment Fig. 4 is a cross-sectional view showing an elastic wave device according to a second embodiment. As shown in Fig. 4, an elastic wave device 10A according to the second embodiment differs from the first embodiment in the arrangement of the first electrode fingers 43A and second electrode fingers 44A of an upper IDT electrode 41 and the third electrode fingers 43B and fourth electrode fingers 44B of a lower IDT electrode 42. Note that the connection between the electrode fingers of the upper IDT electrode 41 and the electrode fingers of the lower IDT electrode 42 and the upper electrode 31 and lower electrode 32 of the resonator 30 is the same as in the first embodiment, and therefore a repeated description will be omitted.

[0037] Specifically, in the capacitive element 40A, the multiple first electrode fingers 43A of the upper IDT electrode 41 and the multiple fourth electrode fingers 44B of the lower IDT electrode 42 are arranged opposite each other in the Z direction with the piezoelectric layer 20 interposed therebetween. The multiple second electrode fingers 44A of the upper IDT electrode 41 and the multiple third electrode fingers 43B of the lower IDT electrode 42 are arranged opposite each other in the Z direction with the piezoelectric layer 20 interposed therebetween.

[0038] In this embodiment, the first electrode fingers 43A of the upper IDT electrode 41 are arranged to overlap the fourth electrode fingers 44B of the lower IDT electrode 42 and extend in the same direction as the fourth electrode fingers 44B. The second electrode fingers 44A of the upper IDT electrode 41 are arranged to overlap the third electrode fingers 43B of the lower IDT electrode 42 and extend in the same direction as the third electrode fingers 43B.

[0039] Different potentials are supplied to the multiple first electrode fingers 43A of the upper IDT electrode 41 and the multiple fourth electrode fingers 44B of the lower IDT electrode 42, which are arranged opposite each other in the Z direction. Also, different potentials are supplied to the multiple second electrode fingers 44A of the upper IDT electrode 41 and the multiple third electrode fingers 43B of the lower IDT electrode 42, which are arranged opposite each other in the Z direction.

[0040] The first electrode fingers 43A of the upper IDT electrode 41 and the third electrode fingers 43B of the lower IDT electrode 42, which are electrically connected and supplied with the same potential, are arranged in non-overlapping positions. The second electrode fingers 44A of the upper IDT electrode 41 and the fourth electrode fingers 44B of the lower IDT electrode 42, which are electrically connected and supplied with the same potential, are arranged in non-overlapping positions.

[0041] 5 is an explanatory diagram illustrating capacitances formed in a capacitive element according to the second embodiment. As shown in Fig. 5, in capacitive element 40A, capacitance Cz3 is formed between first electrode finger 43A of upper IDT electrode 41 and fourth electrode finger 44B of lower IDT electrode 42, which face each other in the Z direction with piezoelectric layer 20 interposed therebetween. Similarly, capacitance Cz4 is formed between second electrode finger 44A of upper IDT electrode 41 and third electrode finger 43B of lower IDT electrode 42, which face each other in the Z direction with piezoelectric layer 20 interposed therebetween.

[0042] In the second embodiment, the distance between the first electrode finger 43A of the upper IDT electrode 41 and the fourth electrode finger 44B of the lower IDT electrode 42 is shorter than in the first embodiment. Also, the distance between the second electrode finger 44A of the upper IDT electrode 41 and the third electrode finger 43B of the lower IDT electrode 42 is shorter than in the first embodiment. As a result, the capacitances Cz3 and Cz4 of the capacitive element 40A are larger than the capacitances Cz1 and Cz2 of the capacitive element 40 shown in the first embodiment.

[0043] In the second embodiment, a capacitance Cx1 is also formed between the first electrode finger 43A and the second electrode finger 44A of the upper IDT electrode 41, which are adjacent in the X direction on the same layer. A capacitance Cx2 is also formed between the third electrode finger 43B and the fourth electrode finger 44B of the lower IDT electrode 42, which are adjacent in the X direction on the same layer. The capacitances Cx1 and Cx2 are the same as those in the first embodiment.

[0044] Therefore, the elastic wave device 10A according to the second preferred embodiment can increase the overall capacitance of the capacitive element 40A compared to the first preferred embodiment.

[0045] 6 is a circuit diagram illustrating an elastic wave device according to a third preferred embodiment of the present invention. As shown in FIG. 6, an elastic wave device 10B according to the third preferred embodiment of the present invention has a different configuration from the above-described preferred embodiments in that it has multiple resonators.

[0046] More specifically, the elastic wave device 10B includes a plurality of series arm resonators S1, S2, and S3, a plurality of parallel arm resonators P1 and P2, and a capacitive element 40. The plurality of series arm resonators S1, S2, and S3 are connected in series to a signal path between an input terminal 61 and an output terminal 62. The plurality of parallel arm resonators P1 and P2 are connected in parallel between a node on the signal path connecting the input terminal 61 and the output terminal 62 and a reference potential 63. The elastic wave device 10B according to the third preferred embodiment is a so-called ladder filter.

[0047] One terminal of each of the series-connected series arm resonators S1, S2, and S3 is electrically connected to an input terminal 61, and the other terminal is electrically connected to an output terminal 62. One terminal of the parallel arm resonator P1 is electrically connected to a node on the signal path connecting the series arm resonators S1 and S2, and the other terminal is electrically connected to a reference potential 63. One terminal of the parallel arm resonator P2 is electrically connected to a node on the signal path connecting the series arm resonators S2 and S3, and the other terminal is electrically connected to the reference potential 63.

[0048] In this embodiment, the reference potential 63 is, for example, a ground potential, but the reference potential 63 is not limited to the ground potential and may be another predetermined potential.

[0049] The capacitive element 40 is connected in parallel to the series arm resonator S1. That is, the capacitive element 40 is connected in parallel to the series arm resonator S1, and is also connected in series between the input terminal 61 and the output terminal 62. More specifically, one end of the capacitive element 40 is electrically connected to a node on the signal path connecting the input terminal 61 and the series arm resonator S1. The other end of the capacitive element 40 is electrically connected to a node on the signal path connecting the series arm resonator S1 and the series arm resonator S2.

[0050] Fig. 7 is a graph showing the pass characteristics of elastic wave devices according to Example 1 and Comparative Examples 1 and 2. The elastic wave device according to Example 1 shown in Fig. 7 is a so-called ladder-type filter shown in Fig. 6 and is configured with a capacitive element 40 connected to series arm resonator S1. The elastic wave device according to Comparative Example 1 is a ladder-type filter similar to Example 1, but differs from Example 1 in that it does not include capacitive element 40. The elastic wave device according to Comparative Example 2 has a capacitive element connected to series arm resonator S1 like Example 1, but differs from Example 1 in that the capacitive element only includes one of upper IDT electrode 41 and lower IDT electrode 42.

[0051] The vertical axis of the graph shown in Fig. 7 represents the level (dB) of the S parameter S21, and the horizontal axis of the graph shown in Fig. 7 represents the frequency (GHz).

[0052] 7 , the pass characteristics of the elastic wave devices according to Example 1 and Comparative Examples 1 and 2 each have two attenuation poles. In the elastic wave device according to Example 1, the capacitive element 40 is connected to the series arm resonator S1. Therefore, compared to Comparative Example 1, which does not include the capacitive element 40, the attenuation pole on the high-frequency side, indicated by the arrow f1, of the two attenuation poles can be shifted to the low-frequency side.

[0053] Furthermore, in the elastic wave device according to Example 1, capacitive element 40 has upper IDT electrode 41 and lower IDT electrode 42, and therefore has a larger capacitance than comparative example 2, which has only one of upper IDT electrode 41 and lower IDT electrode 42. As a result, the elastic wave device according to Example 1 can shift the attenuation pole on the high-frequency side, indicated by arrow f1, to the low-frequency side compared to comparative example 2.

[0054] This indicates that the elastic wave device in accordance with Example 1 can adjust the pass characteristics better than the elastic wave devices in accordance with Comparative Examples 1 and 2.

[0055] 6 is merely an example and can be modified as appropriate. For example, the capacitive element 40A of the second embodiment can be used instead of the capacitive element 40. The number and connection configuration of the multiple series arm resonators S1, S2, and S3 and the multiple parallel arm resonators P1 and P2 can be modified as appropriate depending on the pass characteristics required of the elastic wave device 10B.

[0056] 8 is a circuit diagram illustrating an elastic wave device according to a fourth preferred embodiment of the present invention. As shown in FIG. 8 , an elastic wave device 10C according to the fourth preferred embodiment of the present invention has a different configuration from that of the third preferred embodiment of the present invention in that a capacitive element 40 is connected to a parallel arm resonator P1.

[0057] The capacitive element 40 is connected in parallel to the parallel arm resonator P1. One terminal of the capacitive element 40 is connected to a signal path between the input terminal 61 and the output terminal 62. More specifically, one terminal of the capacitive element 40 is electrically connected to a node on the signal path connecting the series arm resonators S1 and S2. The other terminal of the capacitive element 40 is electrically connected to a reference potential 63.

[0058] The configurations of the plurality of series arm resonators S1, S2, and S3 and the plurality of parallel arm resonators P1 and P2 are the same as those in the third embodiment, and therefore repeated description will be omitted.

[0059] Fig. 9 is a graph showing the pass characteristics of elastic wave devices according to Example 2 and Comparative Examples 1 and 3. The elastic wave device according to Example 2 shown in Fig. 9 is the so-called ladder filter shown in Fig. 8 , and is configured by connecting a capacitive element 40 to a parallel arm resonator P1. The elastic wave device according to Comparative Example 3, like Example 2, has a capacitive element connected to a parallel arm resonator P1. However, the elastic wave device according to Comparative Example 3 differs from Example 2 in that the capacitive element has only one of the upper IDT electrode 41 and the lower IDT electrode 42.

[0060] As shown in FIG. 9 , in the elastic wave device according to Example 2, the capacitive element 40 is connected to the parallel arm resonator P1. Therefore, compared to Comparative Example 1, which does not include the capacitive element 40, the attenuation pole on the low frequency side, indicated by the arrow f2, of the two attenuation poles can be shifted to the high frequency side.

[0061] Furthermore, in the elastic wave device according to Example 2, capacitive element 40 has upper IDT electrode 41 and lower IDT electrode 42, and therefore has a larger capacitance than comparative example 3, which has only one of upper IDT electrode 41 and lower IDT electrode 42. As a result, the elastic wave device according to Example 2 can shift the attenuation pole on the low-frequency side, indicated by arrow f2, to the high-frequency side.

[0062] This indicates that the elastic wave device in accordance with Example 2 can adjust the pass characteristics better than the elastic wave devices in accordance with Comparative Examples 1 and 3.

[0063] Note that the configuration of the elastic wave device 10C is not limited to that shown in FIG. 8 . For example, the capacitive element 40A of the second embodiment may be applied instead of the capacitive element 40. The configuration of the fourth embodiment can be combined with the configuration of the third embodiment. That is, the elastic wave device 10C may include multiple capacitive elements 40, and the capacitive element 40 may be connected to the series arm resonator S1 and the parallel arm resonator P1.

[0064] 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.

[0065] The present disclosure may also have the following configurations.

[0066] (1) An elastic wave device comprising: a resonator including a piezoelectric layer having a first main surface and a second main surface opposite to the first main surface, an upper electrode provided on the first main surface of the piezoelectric layer, and a lower electrode provided on the second main surface of the piezoelectric layer; and a capacitive element including an upper IDT (Interdigital Transducer) electrode provided on the first main surface of the piezoelectric layer and a lower IDT electrode provided on the second main surface of the piezoelectric layer, wherein the capacitive element is connected in parallel with the resonator, and the upper IDT electrode and the lower IDT electrode of the capacitive element are electrically connected. (2) The elastic wave device according to (1), wherein the upper IDT electrode and the lower IDT electrode each include a plurality of electrode fingers arranged in a predetermined direction, the plurality of electrode fingers of the upper IDT electrode are arranged opposite the plurality of electrode fingers of the lower IDT electrode across the piezoelectric layer, and the same potential is supplied to the electrode fingers of the upper IDT electrode and the electrode fingers of the lower IDT electrode arranged opposite to each other across the piezoelectric layer. (3) The elastic wave device according to (1), wherein the upper IDT electrode and the lower IDT electrode each include a plurality of electrode fingers arranged in a predetermined direction, the plurality of electrode fingers of the upper IDT electrode are arranged opposite to the plurality of electrode fingers of the lower IDT electrode across the piezoelectric layer, and different potentials are supplied to the electrode fingers of the upper IDT electrode and the electrode fingers of the lower IDT electrode arranged opposite to each other across the piezoelectric layer. (4) The elastic wave device according to any one of (1) to (3), wherein the upper IDT electrode includes a plurality of first electrode fingers and a plurality of second electrode fingers alternately arranged in a predetermined direction, the lower IDT electrode includes a plurality of third electrode fingers and a plurality of fourth electrode fingers alternately arranged in a predetermined direction, the plurality of first electrode fingers of the upper IDT electrode and the plurality of third electrode fingers of the lower IDT electrode are electrically connected through first vias that penetrate the piezoelectric layer, and the plurality of second electrode fingers of the upper IDT electrode and the plurality of fourth electrode fingers of the lower IDT electrode are electrically connected through second vias that penetrate the piezoelectric layer.(5) The elastic wave device according to (4), wherein the plurality of first electrode fingers of the upper IDT electrode and the plurality of third electrode fingers of the lower IDT electrode are electrically connected to one of the upper electrode and the lower electrode of the resonator, and the plurality of second electrode fingers of the upper IDT electrode and the plurality of fourth electrode fingers of the lower IDT electrode are electrically connected to the other of the upper electrode and the lower electrode of the resonator. (6) The elastic wave device according to any one of (1) to (5), comprising a plurality of the resonators, the plurality of resonators including series arm resonators and parallel arm resonators, the series arm resonators being connected in series between an input terminal and an output terminal, the parallel arm resonators being connected in parallel between a signal path between the input terminal and the output terminal and a reference potential, and the capacitive element being connected in parallel to the series arm resonators and in series between the input terminal and the output terminal. (7) The elastic wave device according to any one of (1) to (5), including a plurality of the resonators, the plurality of resonators including series arm resonators and parallel arm resonators, the series arm resonators being connected in series between an input terminal and an output terminal, the parallel arm resonators being connected in parallel between a signal path between the input terminal and the output terminal and a reference potential, the capacitive element being connected in parallel to the parallel arm resonators, one terminal of the capacitive element being connected to the signal path between the input terminal and the output terminal and the other terminal of the capacitive element being connected to the reference potential. (8) The elastic wave device according to any one of (1) to (7), wherein the piezoelectric layer includes single crystal lithium niobate or lithium tantalate.

[0067] REFERENCE SIGNS LIST 10, 10A, 10B, 10C Acoustic wave device 11 Support substrate 12 Insulating layer 13 Support member 14 Cavity portion 20 Piezoelectric layer 20a First principal surface 20b Second principal surface 30 Resonator 31 Upper electrode 32 Lower electrode 33, 34, 37, 38 Connection wiring 40, 40A Capacitor element 41 Upper IDT electrode 42 Lower IDT electrode 43A First electrode finger 43B Third electrode finger 44A Second electrode finger 44B Fourth electrode finger P1, P2 Parallel arm resonator S1, S2, S3 Series arm resonator 61 Input terminal 62 Output terminal 63 Reference potential

Claims

1. An elastic wave device comprising: a piezoelectric layer having a first main surface and a second main surface opposite the first main surface; a resonator including an upper electrode provided on the first main surface of the piezoelectric layer and a lower electrode provided on the second main surface of the piezoelectric layer; and a capacitive element including an upper IDT (Interdigital Transducer) electrode provided on the first main surface of the piezoelectric layer and a lower IDT electrode provided on the second main surface of the piezoelectric layer, wherein the capacitive element is connected in parallel with the resonator, and the upper IDT electrode and the lower IDT electrode of the capacitive element are electrically connected.

2. The elastic wave device of claim 1, wherein the upper IDT electrode and the lower IDT electrode each include a plurality of electrode fingers arranged in a predetermined direction, the plurality of electrode fingers of the upper IDT electrode are arranged opposite the plurality of electrode fingers of the lower IDT electrode across the piezoelectric layer, and the same potential is supplied to the electrode fingers of the upper IDT electrode and the electrode fingers of the lower IDT electrode that are arranged opposite each other across the piezoelectric layer.

3. The elastic wave device of claim 1, wherein the upper IDT electrode and the lower IDT electrode each include a plurality of electrode fingers arranged in a predetermined direction, the plurality of electrode fingers of the upper IDT electrode are arranged opposite the plurality of electrode fingers of the lower IDT electrode across the piezoelectric layer, and different potentials are supplied to the electrode fingers of the upper IDT electrode and the electrode fingers of the lower IDT electrode that are arranged opposite each other across the piezoelectric layer.

4. An elastic wave device as described in any one of claims 1 to 3, wherein the upper IDT electrode includes a plurality of first electrode fingers and a plurality of second electrode fingers arranged alternately in a predetermined direction, the lower IDT electrode includes a plurality of third electrode fingers and a plurality of fourth electrode fingers arranged alternately in the predetermined direction, the plurality of first electrode fingers of the upper IDT electrode and the plurality of third electrode fingers of the lower IDT electrode are electrically connected through a first via that penetrates the piezoelectric layer, and the plurality of second electrode fingers of the upper IDT electrode and the plurality of fourth electrode fingers of the lower IDT electrode are electrically connected through a second via that penetrates the piezoelectric layer.

5. The elastic wave device of claim 4, wherein the multiple first electrode fingers of the upper IDT electrode and the multiple third electrode fingers of the lower IDT electrode are electrically connected to one of the upper electrode and the lower electrode of the resonator, and the multiple second electrode fingers of the upper IDT electrode and the multiple fourth electrode fingers of the lower IDT electrode are electrically connected to the other of the upper electrode and the lower electrode of the resonator.

6. An elastic wave device as claimed in any one of claims 1 to 5, comprising a plurality of the resonators, the plurality of resonators including series arm resonators and parallel arm resonators, the series arm resonators being connected in series between an input terminal and an output terminal, the parallel arm resonators being connected in parallel between a signal path between the input terminal and the output terminal and a reference potential, and the capacitive element being connected in parallel with the series arm resonators and in series between the input terminal and the output terminal.

7. The elastic wave device according to any one of claims 1 to 5, comprising a plurality of the resonators, the plurality of resonators including series arm resonators and parallel arm resonators, the series arm resonators being connected in series between an input terminal and an output terminal, the parallel arm resonators being connected in parallel between a signal path between the input terminal and the output terminal and a reference potential, and the capacitive element being connected in parallel with the parallel arm resonators, one terminal of the capacitive element being connected to the signal path between the input terminal and the output terminal, and the other terminal of the capacitive element being connected to the reference potential.

8. The acoustic wave device according to any one of claims 1 to 7, wherein the piezoelectric layer contains single crystal lithium niobate or lithium tantalate.

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