Elastic wave resonator and electronic device

Abstract

This elastic wave resonator includes: a piezoelectric layer having a first main surface and a second main surface opposite the first main surface; a first electrode provided on the first main surface of the piezoelectric layer; a second electrode provided on the second main surface of the piezoelectric layer and facing the first electrode with the piezoelectric layer interposed therebetween; an external terminal provided on the first main surface side of the piezoelectric layer and electrically connected to an external substrate; a plurality of connecting conductors joining the first and second electrodes to the external terminal; and a first acoustic reflection part formed from a laminate of a first low acoustic impedance layer having a relatively low acoustic impedance and a first high acoustic impedance layer having a relatively high acoustic impedance on the first main surface side of the piezoelectric layer. The first low acoustic impedance layer and the first high acoustic impedance layer of the first acoustic reflection part are both formed from an insulating material.

Description

Acoustic wave resonator and electronic device

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

[0002] Patent Document 1 describes an acoustic wave resonator (referred to as a bulk acoustic wave (BAW) device in Patent Document 1). The acoustic wave resonator shown in Patent Document 1 includes a piezoelectric layer, acoustic wave excitation electrodes (top and bottom electrodes in Patent Document 1) formed above and below the piezoelectric layer, an acoustic reflector (a Bragg mirror in Patent Document 1), and lead wiring (a connector in Patent Document 1) arranged to connect the acoustic wave excitation electrodes to an external circuit.

[0003] Special table 2018-514156 publication

[0004] In the acoustic wave resonator disclosed in Patent Document 1, interference occurs between the conductor of the acoustic reflecting portion and the connecting conductor, which may result in deterioration of the resonator characteristics.

[0005] An object of the present invention is to provide an acoustic wave resonator and an electronic device that can suppress deterioration of the resonator characteristics.

[0006] an elastic wave resonator according to one aspect of the present invention includes a piezoelectric layer having a first main surface and a second main surface opposite the first main surface; a first electrode provided on the first main surface of the piezoelectric layer; a second electrode provided on the second main surface of the piezoelectric layer and facing the first electrode across the piezoelectric layer; an external terminal provided on the first main surface side of the piezoelectric layer and electrically connecting to an external substrate; a plurality of connecting conductors connecting the first electrode and the second electrode to the external terminal; and a first acoustic reflecting portion on the first main surface side of the piezoelectric layer, the first acoustic reflecting portion comprising a laminate of a first low acoustic impedance layer having a relatively low acoustic impedance and a first high acoustic impedance layer having a relatively high acoustic impedance, wherein the first low acoustic impedance layer and the first high acoustic impedance layer of the first acoustic reflecting portion are both made of an insulating material.

[0007] An electronic device according to one embodiment includes the above-described acoustic wave resonator, a module substrate on which the acoustic wave resonator is mounted, and a sealing resin that covers the acoustic wave resonator and contacts at least each side surface of the piezoelectric layer and the first acoustic reflector.

[0008] According to the acoustic wave resonator and electronic device of the present invention, deterioration of the resonator characteristics can be suppressed.

[0009] FIG. 1 is a circuit diagram illustrating an acoustic wave filter according to a first preferred embodiment of the present invention. FIG. 2 is a plan view illustrating the acoustic wave filter according to the first preferred embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating a configuration of an acoustic wave resonator included in the acoustic wave filter according to the first preferred embodiment of the present invention. FIG. 4 is a cross-sectional view illustrating a configuration of an acoustic wave resonator according to a first modified example of the first preferred embodiment. FIG. 5 is a cross-sectional view illustrating a configuration of an acoustic wave resonator according to a second modified example of the first preferred embodiment. FIG. 6 is a cross-sectional view illustrating a portion of an electronic device including an acoustic wave resonator according to the second modified example of the first preferred embodiment. FIG. 7 is an explanatory diagram illustrating a method for manufacturing an acoustic wave resonator according to the second modified example of the first preferred embodiment. FIG. 8 is an explanatory diagram illustrating a method for manufacturing an acoustic wave resonator according to the second modified example of the first preferred embodiment. FIG. 9 is a cross-sectional view illustrating a configuration of an acoustic wave resonator according to a third modified example of the first preferred embodiment. FIG. 10 is a cross-sectional view illustrating a configuration of an acoustic wave resonator according to the second preferred embodiment of the present invention. FIG. 11 is an explanatory diagram illustrating a method for manufacturing an acoustic wave resonator according to the second preferred embodiment of the present invention. FIG. 12 is a cross-sectional view illustrating a configuration of an acoustic wave resonator according to a third preferred embodiment of the present invention. FIG. 13 is an explanatory diagram illustrating a method for manufacturing an acoustic wave resonator according to the third preferred embodiment of the present invention. Fig. 14 is a cross-sectional view illustrating a configuration of an acoustic wave resonator according to a fourth modification of the third embodiment. Fig. 15 is a cross-sectional view illustrating an electronic device according to the fourth embodiment.

[0010] 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.

[0011] 1 is a circuit diagram illustrating an acoustic wave filter according to a first embodiment. As shown in FIG. 1 , an acoustic wave filter 51 according to the first embodiment includes a plurality of series arm resonators 61 a, 61 b, 61 c, 61 d, and 61 e, a plurality of parallel arm resonators 62 a, 62 b, 62 c, and 62 d, an input terminal 60A, an output terminal 60B, and ground terminals 63 and 64. At least one of the series arm resonators 61 a, 61 b, 61 c, 61 d, and 61 e and the parallel arm resonators 62 a, 62 b, 62 c, and 62 d is a bulk acoustic wave (BAW) element that utilizes bulk waves in a thickness extensional vibration mode or a thickness shear vibration mode.

[0012] The plurality of series arm resonators 61a, 61b, 61c, 61d, and 61e are connected in series to a signal path between the input terminal 60A and the output terminal 60B. The plurality of parallel arm resonators 62a, 62b, 62c, and 62d are connected in parallel between the signal path between the input terminal 60A and the output terminal 60B and ground terminals 63 and 64. The acoustic wave filter 51 according to the first embodiment is a so-called ladder filter.

[0013] One terminal of each of the series-connected series arm resonators 61a, 61b, 61c, 61d, and 61e 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 62a is electrically connected to a signal path connecting the series arm resonators 61a and 61b, and the other terminal is electrically connected to a ground terminal 63. One terminal of the parallel arm resonator 62b is electrically connected to a signal path connecting the series arm resonators 61b and 61c, and the other terminal is electrically connected to the ground terminal 63. One terminal of the parallel arm resonator 62c is electrically connected to a signal path connecting the series arm resonator 61c and 61d, and the other terminal is electrically connected to a ground terminal 64. One terminal of the parallel arm resonator 62 d is electrically connected to the signal path connecting the series arm resonators 61 d and 61 e , and the other terminal is electrically connected to the ground terminal 64 .

[0014] The configurations and numbers of the series arm resonators 61 a, 61 b, 61 c, 61 d, and 61 e and the parallel arm resonators 62 a, 62 b, 62 c, and 62 d in the acoustic wave filter 51 can be changed as needed depending on the desired filter characteristics. For example, the acoustic wave filter 51 may include at least one series arm resonator and at least one parallel arm resonator. The acoustic wave filter 51 may also include impedance elements such as inductors and capacitors.

[0015] 2 is a plan view showing an acoustic wave filter according to the first preferred embodiment. As shown in Fig. 2, an acoustic wave filter 51 includes a plurality of series arm resonators 61a, 61b, 61c, 61d, and 61e, a plurality of parallel arm resonators 62a, 62b, 62c, and 62d, and a plurality of terminals (an input terminal 60A, an output terminal 60B, and ground terminals 63, 64, 65, 66, and 67) disposed on a support member 11. The connections of the series arm resonators 61a, 61b, 61c, 61d, and 61e, the parallel arm resonators 62a, 62b, 62c, and 62d, and the plurality of terminals are the same as those in Fig. 1, and therefore, repeated description will be omitted.

[0016] The input terminal 60A and the output terminal 60B are located at diagonally opposite corners of the support member 11. The ground terminals 63, 64, 65, and 66 are located on the periphery of the support member 11. The ground terminal 67 is located in a region overlapping with the elastic wave excitation portion 28 (see FIG. 5) of the series arm resonator 61c. The location of the ground terminal 67 will be described later with reference to FIG. 5.

[0017] In the following description, when it is not necessary to distinguish between the multiple series arm resonators 61a, 61b, 61c, 61d, and 61e and the multiple parallel arm resonators 62a, 62b, 62c, and 62d, they will simply be referred to as elastic wave resonators 10.

[0018] Next, the detailed configuration of the elastic wave resonator 10 (e.g., the series arm resonator 61a) included in the elastic wave filter 51 will be described. Fig. 3 is a cross-sectional view showing the configuration of an elastic wave resonator included in the elastic wave filter according to the first preferred embodiment. Note that the configuration of the elastic wave resonator 10 shown in Fig. 3 is not limited to the series arm resonator 61a, and can also be applied to the configurations of other resonators included in the elastic wave filter 51.

[0019] As shown in Fig. 3 , the acoustic wave resonator 10 includes a support member 11, a piezoelectric layer 20, a first electrode 21, a second electrode 22, an extension wiring 23, a via 24, a surface electrode 25, a first acoustic reflector 31, and a second acoustic reflector 32. As shown in Fig. 3 , the second acoustic reflector 32, the second electrode 22 and extension wiring 23b, the piezoelectric layer 20, the first electrode 21 and extension wiring 23a, the first acoustic reflector 31, and the surface electrode 25 are stacked on the support member 11 in this order. The extension wiring 23, 23a, 23b, the via 24, and the surface electrode 25 are collectively referred to as "connecting conductors" that connect the first electrode 21 and the second electrode 22 to external terminals (e.g., input terminal 60A and output terminal 60B). The external terminals and the connecting conductors are not limited to being separate components, but may be formed as an integrated component.

[0020] 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).

[0021] In addition, in the Z direction, the direction from the support member 11 toward the outermost surface electrode 25 may be referred to as "up" or "upper," and the direction from the surface electrode 25 toward the support member 11 may be referred to as "down" or "lower." However, the terms "up" and "down" are used simply for the purpose of defining the relative positional relationship of parts, and do not limit the spatial arrangement and position of the BAW resonator.

[0022] The support member 11 is provided to face the second main surface 20b of the piezoelectric layer 20. The support member 11 is a flat plate-shaped member made of silicon (Si), quartz crystal, or the like.

[0023] 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 ３The piezoelectric layer 20 is a substrate made of a single crystal of aluminum nitride (AlN). The material of the piezoelectric layer 20 is not limited to this, and aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), etc. may also be used. The thickness of the piezoelectric layer 20 is not particularly limited, but is preferably 1 μm or less. The piezoelectric layer 20 may have a structure in which a plurality of piezoelectric films having different polarization directions are stacked.

[0024] The first electrode 21 is provided on the top (first main surface 20a) of the piezoelectric layer 20. The second electrode 22 is provided on the bottom (second main surface 20b) of the piezoelectric layer 20. The first electrode 21 and the second electrode 22 face each other in the Z direction, sandwiching the piezoelectric layer 20 therebetween. In other words, the piezoelectric layer 20 is disposed between the first electrode 21 and the second electrode 22 in the Z direction. This allows bulk waves to propagate between the first electrode 21 and the second electrode 22. In the following description, the region where the first electrode 21 and the second electrode 22 overlap in a planar view may be described as the elastic wave exciting portion 28 of the resonator.

[0025] 2, the portions corresponding to the elastic wave exciting portion 28 of each resonator are indicated by hatching. As shown in Fig. 2, the first electrode 21 and the second electrode 22 constituting the elastic wave exciting portion 28 are each rectangular. However, this is not limiting, and the first electrode 21 and the second electrode 22 may be other shapes such as circular or polygonal.

[0026] The first electrode 21 and the second electrode 22 are formed of a conductive material such as aluminum (Al), platinum (Pt), gold (Au), copper (Cu), molybdenum (Mo), tungsten (W), titanium (Ti), chromium (Cr), ruthenium (Ru), tantalum (Ta), iridium (Ir), or an alloy containing at least one of these materials. The first electrode 21 and the second electrode 22 may also be a laminate film containing these materials.

[0027] The lead-out wiring 23a is provided on the first main surface 20a of the piezoelectric layer 20 in the same layer as the first electrode 21, and is connected to one side of the first electrode 21 in the X direction. The lead-out wiring 23b is provided on the second main surface 20b of the piezoelectric layer 20 in the same layer as the second electrode 22, and is connected to the other side of the second electrode 22 in the X direction. The lead-out wirings 23a and 23b are formed of the same material as the first electrode 21 and the second electrode 22, respectively. However, the lead-out wirings 23a and 23b may be made of a different material from the first electrode 21 and the second electrode 22.

[0028] The first acoustic reflector 31 is provided on the first main surface 20a side of the piezoelectric layer 20, covering the first electrode 21 and the lead-out wiring 23a. In other words, the first acoustic reflector 31 is provided between the piezoelectric layer 20 and the plurality of surface electrodes 25 in the Z direction.

[0029] The first acoustic reflecting portion 31 is made of a laminate of first low acoustic impedance layers 31 a, 31 c having a relatively low acoustic impedance and first high acoustic impedance layers 31 b, 31 d having a relatively high acoustic impedance. The first low acoustic impedance layer 31 a, the first high acoustic impedance layer 31 b, the first low acoustic impedance layer 31 c, and the first high acoustic impedance layer 31 d are laminated in this order on the first main surface 20 a of the piezoelectric layer 20.

[0030] The first low acoustic impedance layers 31a and 31c and the first high acoustic impedance layers 31b and 31d are all made of an insulating material. The first low acoustic impedance layers 31a and 31c are made of, for example, silicon oxide (SiO ２ The first high acoustic impedance layers 31b and 31d 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 ) or the like. Note that the insulating material used here is a dielectric layer having an electrical resistivity of 1.0×10 －６ This refers to materials with a resistance of Ω·m or more.

[0031] Note that there is no particular limitation on the number of layers of the first low acoustic impedance layers 31 a, 31 c and the first high acoustic impedance layers 31 b, 31 d in the first acoustic reflecting portion 31. The first acoustic reflecting portion 31 may have three or fewer layers, or five or more layers. It is sufficient that at least one of the first high acoustic impedance layers 31 b, 31 d is disposed farther from the piezoelectric layer 20 than the first low acoustic impedance layers 31 a, 31 c.

[0032] The second acoustic reflector 32 is provided on the second main surface 20b side of the piezoelectric layer 20, covering the second electrode 22 and the lead-out wiring 23b. In other words, the second acoustic reflector 32 is located on the opposite side of the piezoelectric layer 20 from the plurality of surface electrodes 25 in the Z direction, and is provided between the piezoelectric layer 20 and the support member 11.

[0033] The second acoustic reflecting portion 32 is made of a laminate of second low acoustic impedance layers 32 a, 32 c, and 32 e, each having a relatively low acoustic impedance, and second high acoustic impedance layers 32 b and 32 d, each having a relatively high acoustic impedance. The second low acoustic impedance layer 32 a, the second high acoustic impedance layer 32 b, the second low acoustic impedance layer 32 c, the second high acoustic impedance layer 32 d, and the second low acoustic impedance layer 32 e are laminated in this order on the second main surface 20 b of the piezoelectric layer 20.

[0034] The second low acoustic impedance layers 32a, 32c, and 32e are made of an insulating material. The second high acoustic impedance layers 32b and 32d are made of a conductive material. The second low acoustic impedance layers 32a, 32c, and 32e are made of, for example, silicon oxide (SiO ２ ) The second high acoustic impedance layers 32b and 32d are made of a metal material such as tungsten (W), molybdenum (Mo), ruthenium (Ru), or platinum (Pt). However, the second high acoustic impedance layers 32b and 32d are not limited to these, and may be an alloy containing at least one of the above metal materials. Note that the conductive material here refers to a material having an electrical resistivity of 1.0×10 －６ An insulating material is a material with an electrical resistivity of less than 1.0 x 10 －６ This refers to materials with a resistance of Ω·m or more.

[0035] Note that there is no particular limitation on the number of layers of the second low acoustic impedance layers 32a, 32c, and 32e and the second high acoustic impedance layers 32b and 32d in the second acoustic reflecting portion 32. The second acoustic reflecting portion 32 may have four or fewer layers, or six or more layers. It is sufficient that at least one of the second high acoustic impedance layers 32b and 32d is disposed farther from the piezoelectric layer 20 than the second low acoustic impedance layers 32a, 32c, and 32e.

[0036] The plurality of surface electrodes 25 are provided on the first main surface 20a side of the piezoelectric layer 20. Specifically, the plurality of surface electrodes 25 are provided on the first high acoustic impedance layer 31d, which is the outermost layer of the first acoustic reflector 31. One surface electrode 25 is electrically connected to the lead-out wiring 23a through a via 24 that penetrates the first acoustic reflector 31 in the Z direction. The other surface electrode 25 is electrically connected to the lead-out wiring 23b through a via 24 that penetrates the first acoustic reflector 31 and the piezoelectric layer 20 in the Z direction.

[0037] Each of the surface electrodes 25 is provided with an external terminal (e.g., an input terminal 60A, an output terminal 60B, etc.). The external terminals, such as the input terminal 60A and the output terminal 60B, are, for example, solder bumps or Au bumps. The protective layer 41 is provided to cover the surface electrodes 25 and the first acoustic reflector 31 and has openings in areas where the external terminals are provided. The protective layer 41 is formed of an insulating resin material and is also called a solder resist. With this configuration, the surface electrodes 25 electrically connect the first electrode 21 and the second electrode 22 constituting the acoustic wave excitation unit 28 to the module substrate 101 (see FIG. 15 ), which is an external substrate. Note that the acoustic wave resonator 10 does not necessarily have to have the external terminals and the protective layer 41.

[0038] With the above-described configuration, in the elastic wave resonator 10 of this embodiment, the first acoustic reflecting portion 31 and the second acoustic reflecting portion 32 are provided on both sides of the piezoelectric layer 20, so that bulk waves in the thickness-extensional vibration mode or the thickness-shear vibration mode can be confined within the piezoelectric layer 20.

[0039] The first acoustic reflector 31, which is provided on the same side as the plurality of surface electrodes 25, is made of an insulating material. That is, because the first acoustic reflector 31 does not contain a conductive material, interference due to electromagnetic coupling between the first acoustic reflector 31 and the surface electrodes 25, the vias 24, the external terminals (e.g., input terminal 60A, output terminal 60B, etc.), etc. can be suppressed compared to when the first acoustic reflector 31 is configured to contain a conductive material. Therefore, the elastic wave resonator 10 of this embodiment can suppress deterioration of the resonator characteristics due to interference from the first acoustic reflector 31.

[0040] If the first acoustic reflecting portion 31 were configured to include a conductive material, in the high frequency band (e.g., approximately 600 MHz or higher and 20 GHz or lower) in which the elastic wave resonator 10 is used, it would be necessary to provide a sufficient distance between the conductive material of the first acoustic reflecting portion 31 and the surface electrode 25, via 24, etc., in order to suppress interference. In this embodiment, because the first acoustic reflecting portion 31 does not include a conductive material, the degree of freedom in the arrangement of the surface electrode 25, via 24, etc. can be increased, and the elastic wave resonator 10 can be made smaller.

[0041] In the first acoustic reflecting section 31, the first high acoustic impedance layers 31b, 31d are provided over the entire surface, including both the region overlapping with the elastic wave excitation section 28 and the region not overlapping with the elastic wave excitation section 28. Therefore, the process of patterning the first high acoustic impedance layers 31b, 31d can be omitted when forming the first acoustic reflecting section 31. Furthermore, in the first acoustic reflecting section 31, the first low acoustic impedance layers 31a, 31c and the first high acoustic impedance layers 31b, 31d are formed flat without any steps, which can suppress the occurrence of cracks.

[0042] Furthermore, in the elastic wave resonator 10 of this embodiment, the first acoustic reflecting portion 31 and the second acoustic reflecting portion 32 are provided on either side of the piezoelectric layer 20, which increases the strength of the piezoelectric layer 20 compared to a configuration in which a cavity 12 (see FIG. 10 ) is provided in the support member 11 instead of the first acoustic reflecting portion 31 and the second acoustic reflecting portion 32. Furthermore, the first acoustic reflecting portion 31 and the second acoustic reflecting portion 32 are in contact with the first electrode 21 and the second electrode 22 of the elastic wave exciting portion 28, respectively, which improves the heat dissipation of the piezoelectric layer 20.

[0043] In the second acoustic reflecting portion 32 provided on the second main surface 20b side of the piezoelectric layer 20 (i.e., the side opposite the surface electrode 25), the second high acoustic impedance layers 32b and 32d made of a conductive material have a higher acoustic impedance than an insulating material. This improves the acoustic wave confinement and reflection effects in the second acoustic reflecting portion 32. This allows the acoustic wave resonator 10 to achieve good resonator characteristics.

[0044] In the second acoustic reflecting section 32, the second high acoustic impedance layers 32b and 32d are provided in an area overlapping with the elastic wave excitation section 28, but are not provided in an area not overlapping with the elastic wave excitation section 28. In other words, in the area overlapping with the elastic wave excitation section 28, the second low acoustic impedance layer 32a, the second high acoustic impedance layer 32b, the second low acoustic impedance layer 32c, the second high acoustic impedance layer 32d, and the second low acoustic impedance layer 32e are stacked in this order. In the area not overlapping with the elastic wave excitation section 28, the second low acoustic impedance layers 32a, 32c, and 32e are stacked in this order. This makes it possible to suppress unintended interference in areas not overlapping with the elastic wave excitation section 28, while enhancing the effects of confining and reflecting elastic waves.

[0045] 4 is a cross-sectional view showing the configuration of an elastic wave resonator according to a first modification of the first embodiment. As shown in FIG. 4, an elastic wave resonator 10A according to the first modification of the first embodiment has a different configuration from the first embodiment described above in that it has a high-viscoelastic layer 42.

[0046] The high-viscoelastic layer 42 is provided between the first acoustic reflector 31 and the plurality of surface electrodes 25. The high-viscoelastic layer 42 is formed of a material having higher viscoelasticity than the first low acoustic impedance layers 31a, 31c and the first high acoustic impedance layers 31b, 31d of the first acoustic reflector 31. When the elastic wave resonator 10A is mounted on the module substrate 101 (see FIG. 6 ), a sealing resin 105 is provided to cover the elastic wave resonator 10A. The high-viscoelastic layer 42 is formed of a material having higher viscoelasticity than the sealing resin 105.

[0047] The high-viscoelastic layer 42 is made of a material having a relatively high viscoelasticity, such as a polyimide resin, polybenzoxazole, a urethane resin, a silicone resin, an acrylic resin, or a cycloolefin resin, while the sealing resin 105 is made of a material having a relatively low viscoelasticity, such as an epoxy resin (containing a filler).

[0048] In the first modified example, the high-viscoelastic layer 42 is provided closer to the surface electrode 25 than the elastic wave excitation section 28 and the first acoustic reflection section 31, so that fluctuations in the resonator characteristics due to the influence of the module substrate 101 and the sealing resin 105 (see Figure 6) can be suppressed.

[0049] (Second Modification of First Embodiment) Fig. 5 is a cross-sectional view showing the configuration of an elastic wave resonator according to a second modification of the first embodiment. Fig. 6 is a cross-sectional view showing a portion of an electronic device including an elastic wave resonator according to the second modification of the first embodiment. An elastic wave resonator 10B shown in Figs. 5 and 6 corresponds to, for example, the series arm resonator 61c in Fig. 2.

[0050] As shown in Figure 5, the elastic wave resonator 10B according to the second variant of the first embodiment differs from the first embodiment and the first variant described above in that at least one of the multiple surface electrodes 25 is arranged in a region that overlaps with the elastic wave excitation section 28 in a planar view.

[0051] A ground terminal 67 made of a conductive material is provided on the surface electrode 25 at a position overlapping the elastic wave excitation unit 28. As shown in Fig. 2, the surface electrode 25 at the position overlapping the elastic wave excitation unit 28 is led out to a corner of the support member 11 through the connection wiring 26 and connected to the ground terminal 66. The ground terminals 66, 67 are, for example, solder bumps.

[0052] 2 , the surface electrode 25 at the position overlapping with the elastic wave excitation unit 28 may be connected in any manner. Alternatively, the surface electrode 25 at the position overlapping with the elastic wave excitation unit 28 may be provided with only the ground terminal 67 and may not be connected to other wiring or terminals such as the connection wiring 26.

[0053] 6 , the elastic wave resonator 10B is mounted on the module substrate 101 via the input terminal 60A, the output terminal 60B, and the ground terminal 67. The sealing resin 105 is provided to cover the elastic wave resonator 10B. The sealing resin 105 is provided to fill the space between the module substrate 101 and the protective layer 41 of the elastic wave resonator 10B. The sealing resin 105 is also provided to cover the first acoustic reflector 31, the piezoelectric layer 20, the second acoustic reflector 32, the side surface of the support member 11, and the surface of the support member 11 opposite the module substrate 101.

[0054] In the electronic device 100 including the acoustic wave resonator 10B of the second modification, the surface electrode 25 and the ground terminal 67 are provided in a region overlapping with the acoustic wave excitation unit 28, and the ground terminal 67 is in contact with the module substrate 101. This forms a heat transfer path from the acoustic wave excitation unit 28 through the first acoustic reflector 31, the surface electrode 25, and the ground terminal 67 to the module substrate 101. This allows the acoustic wave resonator 10B to improve the heat dissipation performance of heat generated in the acoustic wave excitation unit 28. Furthermore, because the acoustic wave resonator 10B has good heat dissipation performance, it is possible to improve power durability.

[0055] Because the first acoustic reflecting portion 31 is made of an insulating material and does not contain a conductive material, even if the surface electrode 25 and the ground terminal 67 are provided in a region overlapping with the elastic wave exciting portion 28, it is possible to prevent unintended electromagnetic field coupling from occurring between the surface electrode 25 and the first acoustic reflecting portion 31. As a result, the elastic wave resonator 10B of the second modified example can prevent deterioration of the resonator characteristics.

[0056] (Method of Manufacturing Elastic Wave Resonator According to Second Modification) Fig. 7 is a diagram illustrating a method of manufacturing an elastic wave resonator according to a second modification of the first embodiment. Fig. 8 is a diagram illustrating a method of manufacturing an elastic wave resonator according to the second modification of the first embodiment.

[0057] In the manufacturing method of the elastic wave resonator 10B, FIG. 7 shows the process up to the step of forming the second acoustic reflecting portion 32 on the second main surface 20b of the piezoelectric layer 20, and FIG. 8 shows the process from the step of forming the first acoustic reflecting portion 31 on the first main surface 20a of the piezoelectric layer 20 onward.

[0058] 7, the piezoelectric layer 20 is bonded to a transfer substrate 200 (step ST1). The piezoelectric layer 20 is made of lithium niobate (LiNbO ３ The transfer substrate 200 is, for example, a silicon substrate. In step ST1, the piezoelectric layer 20 is thinned by processes such as grinding, lapping, and polishing. The piezoelectric layer 20 may also be formed using an ion slicing method.

[0059] The second electrode 22 and the lead wiring 23b are formed on the second main surface 20b of the piezoelectric layer 20 (step ST2).

[0060] Next, a second low acoustic impedance layer 32a constituting the second acoustic reflector 32 is formed on the second main surface 20b of the piezoelectric layer 20 (the surface opposite to the first main surface 20a on which the surface electrode 25 is provided) (step ST3). The second low acoustic impedance layer 32a is, for example, a silicon oxide film. A material with low density and low hardness is preferred for the low acoustic impedance layer.

[0061] The surface of the second low acoustic impedance layer 32a is planarized (step ST4), thereby planarizing the convex portions of the second low acoustic impedance layer 32a formed in step ST3 in correspondence with the second electrode 22 and the lead wiring 23b.

[0062] Next, the second high acoustic impedance layer 32b constituting the second acoustic reflecting portion 32 is patterned (step ST5). The second high acoustic impedance layer 32b is, for example, a tungsten film, and the tungsten film is formed in the region overlapping with the elastic wave exciting portion 28, while the tungsten film in the region not overlapping with the elastic wave exciting portion 28 is removed.

[0063] By minimizing the variation in the pattern of the second high acoustic impedance layer 32b, variation in the resonator characteristics of the elastic wave resonator 10B can be suppressed. Therefore, it is preferable to pattern the second high acoustic impedance layer 32b using processing techniques, materials, and equipment that are effective for achieving high precision. Furthermore, a material with high density and Young's modulus is preferable for the high acoustic impedance layer, and is not limited to tungsten. Molybdenum, ruthenium, platinum, etc. can also be used.

[0064] Next, the second low acoustic impedance layer 32c, the second high acoustic impedance layer 32d, and the second low acoustic impedance layer 32e are formed in this order (step ST6). Specifically, a silicon oxide film is formed as the second low acoustic impedance layer 32c and planarized, a tungsten film is formed thereon as the second high acoustic impedance layer 32d and patterned, and then a second low acoustic impedance layer 32e is formed and planarized.

[0065] In the process of forming the second acoustic reflecting portion 32 shown in steps ST3 to ST6, the film properties and thicknesses of the second low acoustic impedance layers 32a, 32c, and 32e and the second high acoustic impedance layers 32b and 32d are optimized according to the desired resonance characteristics. Note that the second acoustic reflecting portion 32 tends to have higher performance as a reflector if the impedance ratio of the high acoustic impedance layer to the low acoustic impedance layer is large. For this reason, it is preferable to use the above-mentioned metal material for the second high acoustic impedance layers 32b and 32d.

[0066] Next, the second low acoustic impedance layer 32e located on the outermost surface of the second acoustic reflector 32 is planarized and smoothed, and then directly bonded to the support member 11 (step ST7). Direct bonding may be achieved by hydrophilic bonding, surface activation bonding, atomic diffusion bonding, or the like. It is preferable to use, for example, a high-resistivity Si substrate as the support member 11. A high-resistivity Si substrate is preferable in terms of its high processability and thermal conductivity, which makes it easy to reduce loss during singulation and ensures power durability. Note that steps ST7 and beyond are illustrated upside down compared to the diagrams up to step ST6.

[0067] Next, as shown in FIG. 8, the transfer substrate 200 is removed (step ST8).

[0068] The first electrode 21 and the lead wiring 23a are formed on the first main surface 20a of the piezoelectric layer 20 (step ST9).

[0069] Next, a first low acoustic impedance layer 31a, a first high acoustic impedance layer 31b, a first low acoustic impedance layer 31c, and a first high acoustic impedance layer 31d that constitute a first acoustic reflecting portion 31 are formed in this order on a first main surface 20a of the piezoelectric layer 20 (the surface on which the surface electrode 25 is provided) (step ST10). Silicon oxide films are formed as the first low acoustic impedance layers 31a and 31c, and hafnium oxide films are formed as the first high acoustic impedance layers 31b and 31d. Furthermore, unlike the second acoustic reflecting portion 32 described above, in the first acoustic reflecting portion 31, it is not necessary to pattern the first high acoustic impedance layers 31b and 31d.

[0070] Next, a high-viscoelastic layer 42 having higher viscoelasticity than the material used for the first acoustic reflector 31 is formed (step ST11). The high-viscoelastic layer 42 is made of a material having higher viscoelasticity than the sealing resin 105 (see FIG. 6 ) that covers the acoustic wave resonator 10B. An example of the high-viscoelastic layer 42 is a polyimide film. Alternatively, the high-viscoelastic layer 42 may be made of an epoxy-based material other than polyimide, an olefin-based resin, benzocyclobutene, polybenzoxazole, silicone, or a maleimide-based resin.

[0071] Next, the surface electrode 25, the connection wiring 26, and the via 24 are formed by lift-off (step ST12). In step ST12, first, through holes penetrating the high-viscoelastic layer 42 and the first acoustic reflector 31, and through holes penetrating the high-viscoelastic layer 42, the first acoustic reflector 31, and the piezoelectric layer 20 are formed by RIE (reactive ion etching) at positions overlapping with the lead-out wirings 23a and 23b. After forming a resist pattern, a Cu / Ti film is deposited, and the surface electrode 25, the connection wiring 26, and the via 24 are formed by lift-off. In step ST12, the surface electrode 25 is also provided in a region overlapping with the elastic wave excitation unit 28.

[0072] Next, a protective layer 41 is formed to cover the surface electrodes 25 and the connection wiring 26, and openings are formed in the protective layer 41 in areas where terminals such as the input terminal 60A, the output terminal 60B, and the ground terminal 67 will be provided. Solder bumps are formed on the multiple surface electrodes 25 as the input terminals 60A, the output terminals 60B, and the ground terminal 67 (step ST13). At this time, the ground terminal 67 is provided on the surface electrodes 25 in an area overlapping with the elastic wave excitation unit 28.

[0073] Next, the piezoelectric layer 20 is singulated into individual pieces to manufacture the elastic wave resonators 10B. Through the above-described process, the first acoustic reflector 31 made of an insulating material is formed on the surface electrode 25 side of the piezoelectric layer 20, and the second acoustic reflector 32 containing a metal material is formed on the support member 11 side opposite the surface electrode 25.

[0074] 7 and 8, the method for manufacturing the elastic wave resonator 10B according to the second modified example has been described. However, by omitting step ST11 or by modifying a part of step ST12, the elastic wave resonators 10 and 10A according to the first embodiment and the first modified example can be manufactured.

[0075] 9 is a cross-sectional view showing the configuration of an elastic wave resonator according to a third modification of the first embodiment. As shown in FIG. 9, an elastic wave resonator 10C according to the third modification of the first embodiment differs from the first embodiment in that the support member 11 is provided on the surface electrode 25 side. That is, the support member 11 is provided opposite the first main surface 20a of the piezoelectric layer 20.

[0076] In the third modified example, the first acoustic reflector 31 is disposed between the piezoelectric layer 20 and the support member 11. Furthermore, the plurality of surface electrodes 25 are provided on the surface of the support member 11 opposite to the first acoustic reflector 31. On the opposite side of the support member 11, a protective layer 43 is provided to cover the second low acoustic impedance layer 32e located on the outermost surface of the second acoustic reflector 32.

[0077] In the elastic wave resonator 10C of the third modification, the support member 11 is provided on the surface electrode 25 side, and therefore when the elastic wave resonator 10C is mounted on the module substrate 101 (see FIG. 6 ) as the electronic device 100, the thickness of the support member 11 increases the distance between the module substrate 101 and the first acoustic reflecting portion 31, the second acoustic reflecting portion 32, and the elastic wave exciting portion 28. This reduces the influence of the wiring pattern on the module substrate 101, and the elastic wave resonator 10C can suppress deterioration of the resonator characteristics.

[0078] 10 is a cross-sectional view showing the configuration of an elastic wave resonator according to a second embodiment. As shown in FIG. 10 , an elastic wave resonator 10D according to the second embodiment differs from the first embodiment in that a cavity 12 that opens to the piezoelectric layer 20 side is provided in the support member 11 instead of the second acoustic reflecting portion 32.

[0079] The cavity 12 is provided in a region that overlaps with the elastic wave excitation portion 28 in a plan view. At least a portion of the second electrode 22 and the lead wiring 23b is disposed within the cavity 12. A portion of the support member 11 where the cavity 12 is not formed is in contact with the second main surface 20b of the piezoelectric layer 20. In the second embodiment, the cavity 12 is provided on the second main surface 20b of the piezoelectric layer 20. Therefore, compared to, for example, a case where the second acoustic reflecting portion 32 is made only of the same insulating material as the first acoustic reflecting portion 31, the energy trapping effect of the elastic wave resonator 10D is enhanced and favorable resonator characteristics are obtained.

[0080] The elastic wave resonator 10D according to the second preferred embodiment also includes a high-viscoelastic layer 42 and a high Young's modulus layer 44. The high-viscoelastic layer 42 is similar to that in the first modified example (see FIG. 4 ) described above, and therefore a repeated description will be omitted.

[0081] The high Young's modulus layer 44 is disposed between the first acoustic reflector 31 and the plurality of surface electrodes 25, and is provided in a region overlapping at least the cavity 12 in a planar view. More specifically, the high Young's modulus layer 44 is disposed between the high viscoelastic layer 42 and the plurality of surface electrodes 25. The high Young's modulus layer 44 has a higher Young's modulus than at least the first low acoustic impedance layers 31a, 31c and the first high acoustic impedance layers 31b, 31d of the first acoustic reflector 31, among the layers disposed overlapping the cavity 12. More preferably, the high Young's modulus layer 44 has a higher Young's modulus than any of the materials of the layers disposed overlapping the elastic wave excitation unit 28 in a planar view (the first acoustic reflector 31, the high viscoelastic layer 42, the sealing resin 105, etc.).

[0082] The high Young's modulus layer 44 is formed, for example, from an insulating material or a semiconductive material. Examples of preferred materials for the high Young's modulus layer 44 include thinned, high-resistivity silicon, quartz, aluminum oxide, and silicon oxide. For example, in the case of high-resistivity silicon, its thickness is preferably approximately 0.5 μm to 10 μm. With this thickness, even when high-resistivity silicon, a semiconductive material, is selected for the high Young's modulus layer 44, its conductivity and the effect on resonance characteristics due to the increase in conductivity caused by carriers generated when heat is applied are limited. Furthermore, the high Young's modulus layer 44 is preferably made of an inorganic material. This is because, while organic materials such as resins soften and their Young's modulus decreases with increasing temperature, inorganic materials do not soften as easily as organic materials.

[0083] In the second embodiment, by providing the high Young's modulus layer 44, even in a configuration having a cavity 12, it is possible to suppress deterioration of the resonance characteristics and prevent deformation of the cavity 12 due to external pressure and damage to the piezoelectric layer 20. Furthermore, in the second embodiment, it is possible to suppress fluctuations in the resonance frequency due to deformation of the piezoelectric layer 20.

[0084] The support member 11 may include a support substrate (e.g., a silicon substrate) and an intermediate layer (insulating layer). That is, the piezoelectric layer 20 is bonded to the support substrate directly or via the intermediate (insulating) layer. The cavity 12 may be formed in the intermediate layer. In this case, the support substrate (silicon substrate) and the intermediate layer may have a frame-like shape, thereby forming the cavity 12. Alternatively, the cavity 12 may be formed in the intermediate layer.

[0085] 11 is an explanatory diagram for describing a method for manufacturing an elastic wave resonator according to a second embodiment. Note that in FIG. 11 , details common to the method for manufacturing elastic wave resonator 10B according to the second modified example described above are omitted.

[0086] As shown in FIG. 11, the piezoelectric layer 20 is bonded to the transfer substrate 200, and the second electrodes 22 and the lead wirings 23b are formed on the second main surface 20b of the piezoelectric layer 20 (step ST21).

[0087] Next, the cavity 12 is formed in the support member 11 by wet etching, and the second main surface 20b of the piezoelectric layer 20 is bonded to the support member 11 (step ST22). The bonding of the support member 11 can be performed by direct bonding such as hydrophilic bonding or surface activation bonding.

[0088] Next, the transfer substrate 200 is removed (step ST23). The transfer substrate 200 may be removed by wet etching, or may be separated at the bonding surface using a laser.

[0089] Next, similarly to steps ST10 and ST11 described above, the first acoustic reflecting portion 31 and the high-viscoelastic layer 42 are formed on the first main surface 20a of the piezoelectric layer 20 (step ST24). In step ST24, a high Young's modulus layer 44 is further formed. The high Young's modulus layer 44 has a higher Young's modulus than any of the materials of the layers, such as the first acoustic reflecting portion 31 and the high-viscoelastic layer 42, that are arranged to overlap the elastic wave exciting portion 28 in plan view.

[0090] Next, similar to steps ST12 and ST13 described above, the surface electrodes 25, connection wiring 26, and vias 24 are formed, the protective layer 41 is patterned, and solder bumps such as the input terminal 60A, output terminal 60B, and ground terminal 67 are formed (step ST25).

[0091] Next, the piezoelectric layer 20 is singulated into individual pieces to manufacture the elastic wave resonators 10D. Through the above-described process, a first acoustic reflector 31 made of an insulating material is formed on the surface electrode 25 side of the piezoelectric layer 20, and a cavity 12 is formed as a second acoustic reflector on the support member 11 side opposite the surface electrode 25.

[0092] 12 is a cross-sectional view showing the configuration of an elastic wave resonator according to a third embodiment. As shown in FIG. 12, an elastic wave resonator 10E according to the third embodiment differs from the first embodiment in that a second acoustic reflecting portion 32A is made of an insulating material.

[0093] The second acoustic reflector 32A is a laminate of second low acoustic impedance layers 32Aa and 32Ac, each having a relatively low acoustic impedance, and second high acoustic impedance layers 32Ab and 32Ad, each having a relatively high acoustic impedance. The second low acoustic impedance layers 32Aa and 32Ac and the second high acoustic impedance layers 32Ab and 32Ad are all made of insulating materials.

[0094] The second acoustic reflecting portion 32A is made of the same material as that of the first acoustic reflecting portion 31. That is, the second low acoustic impedance layers 32Aa and 32Ac are made of, for example, silicon oxide (SiO ２ The second high acoustic impedance layers 32Ab and 32Ad 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 ) or other dielectric layer.

[0095] In the third embodiment, the second acoustic reflecting portion 32A is made of an insulating material, and therefore, compared to the first embodiment, heat generated in the elastic wave exciting portion 28 is less likely to be transmitted to the support member 11. Therefore, even when silicon (Si), a semiconductor material, is used for the support member 11, fluctuations in the conductivity of Si due to heat from the elastic wave exciting portion 28 can be suppressed. Therefore, in the third embodiment, fluctuations in the characteristics of the support member 11 are suppressed, and good resonator characteristics can be obtained.

[0096] 13 is an explanatory diagram for describing a method for manufacturing an elastic wave resonator according to a third embodiment. Note that, in FIG. 13 , details common to the method for manufacturing elastic wave resonator 10B according to the second modified example described above are omitted.

[0097] 13, a second low acoustic impedance layer 32Aa constituting the second acoustic reflector 32A is formed on the second main surface 20b of the piezoelectric layer 20 and then planarized (step ST31). A silicon oxide film is formed as the second low acoustic impedance layer 32Aa. Note that, prior to step ST31, steps similar to steps ST1 to ST3 shown in FIG. 7 are performed.

[0098] Next, the second high acoustic impedance layer 32Ab, the second low acoustic impedance layer 32Ac, and the second high acoustic impedance layer 32Ad are formed (step ST32). A silicon oxide film is formed as the second low acoustic impedance layer 32Ac, and hafnium oxide films are formed as the second high acoustic impedance layers 32Ab and 32Ad. This forms the second acoustic reflector 32A made of an insulating material.

[0099] 8 are performed. The first acoustic reflector 31, the high-viscoelastic layer 42, the surface electrode 25, the protective layer 41, and the respective terminals are formed on the first main surface 20a of the piezoelectric layer 20.

[0100] Next, the elastic wave resonator 10E is manufactured by dividing the piezoelectric layer 20 into individual pieces. Through the above-described steps, the first acoustic reflector 31 and the second acoustic reflector 32A, both made of an insulating material, are formed on both sides of the piezoelectric layer 20 (the side facing the surface electrode 25 and the side facing the support member 11 opposite the surface electrode 25).

[0101] 14 is a cross-sectional view showing the configuration of an elastic wave resonator according to a fourth modification of the third embodiment. As shown in Fig. 14, an elastic wave resonator 10F according to the fourth modification of the third embodiment differs from the third embodiment in that the support member 11 is provided on the surface electrode 25 side. That is, the support member 11 is provided opposite the first main surface 20a of the piezoelectric layer 20.

[0102] In the fourth modification, the first acoustic reflector 31 is disposed between the piezoelectric layer 20 and the support member 11. Furthermore, the plurality of surface electrodes 25 are provided on the surface of the support member 11 opposite to the first acoustic reflector 31. On the opposite side of the support member 11, a protective layer 43 is provided to cover the second high acoustic impedance layer 32Ad located on the outermost surface of the second acoustic reflector 32A.

[0103] In the fourth modification, the support member 11 is provided on the surface electrode 25 side, and therefore when the electronic device 100 is mounted on the module substrate 101 (see FIG. 6 ), the distance between the module substrate 101 and the first acoustic reflector 31, the second acoustic reflector 32A, and the elastic wave excitation portion 28 is increased. This reduces the influence of the wiring pattern on the module substrate 101, and the elastic wave resonator 10F can suppress deterioration of the resonator characteristics.

[0104] 15 is a cross-sectional view showing an electronic device according to a fourth embodiment. The electronic device 100 according to the fourth embodiment is a communication module used in, for example, a mobile terminal such as a mobile phone, a smartphone, or a tablet terminal, or a personal computer with a communication function. Alternatively, the electronic device 100 may be used for backhaul communication between base stations and between a base station and a core network.

[0105] As shown in FIG. 15, the electronic device 100 includes a module substrate 101, acoustic wave filters 51 and 52, a power amplifier 102, a high-frequency switch 103, surface-mounted components 104 (such as inductors and coils), and a sealing resin 105.

[0106] The module substrate 101 may be, for example, a printed circuit board made of resin or a ceramic substrate such as LTCC (Low Temperature Co-fired Ceramics) or HTCC (High Temperature Co-fired Ceramics).The module substrate 101 may be a single-layer substrate or a multi-layer substrate in which multiple dielectric layers are stacked.

[0107] The acoustic wave filters 51 and 52 include at least one of the acoustic wave resonators 10, 10A-10F of the first to third embodiments described above. The acoustic wave filter 52 may have a configuration similar to or different from that of the acoustic wave filter 51. The acoustic wave filters 51 and 52 including the acoustic wave resonator 10 have a first acoustic reflector 31 made of an insulating material on the surface electrode 25 side (the module substrate 101 side), thereby preventing electromagnetic field coupling from occurring between the first acoustic reflector 31 and the wiring pattern of the module substrate 101. Therefore, the acoustic wave filters 51 and 52 including the acoustic wave resonator 10 have excellent filter characteristics.

[0108] The sealing resin 105 is formed by transfer molding to cover the acoustic wave filters 51 and 52, the power amplifier 102, the high-frequency switch 103, and the surface-mounted components 104. As described above, the sealing resin 105 covers the side surfaces of the support member 11, the first acoustic reflecting portion 31, and the second acoustic reflecting portion 32 of the acoustic wave resonator 10. In other words, no other package or connecting member is present between the acoustic wave resonator 10 and the module substrate 101 or the sealing resin 105. This allows the electronic device 100 to be miniaturized.

[0109] It should be noted that the electronic device 100 shown in FIG. 15 is merely a schematic illustration, and the types, number, arrangement, etc. of the components mounted on the electronic device 100 can be changed as appropriate.

[0110] 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.

[0111] The present disclosure may also have the following configurations.

[0112] (1) An elastic wave resonator comprising: a piezoelectric layer having a first main surface and a second main surface opposite to the first main surface; a first electrode provided on the first main surface of the piezoelectric layer; a second electrode provided on the second main surface of the piezoelectric layer and facing the first electrode with the piezoelectric layer in between; an external terminal provided on the first main surface side of the piezoelectric layer and electrically connecting to an external substrate; a plurality of connecting conductors connecting the first electrode and the second electrode to the external terminal; and a first acoustic reflecting portion formed on the first main surface side of the piezoelectric layer and consisting of a laminate of a first low acoustic impedance layer having a relatively low acoustic impedance and a first high acoustic impedance layer having a relatively high acoustic impedance, wherein the first high acoustic impedance layer and the first low acoustic impedance layer of the first acoustic reflecting portion are both made of an insulating material. (2) The elastic wave resonator according to (1), further comprising: a second acoustic reflecting portion provided on the second principal surface side of the piezoelectric layer and consisting of a laminate of a second low acoustic impedance layer having a relatively low acoustic impedance and a second high acoustic impedance layer having a relatively high acoustic impedance, wherein the second low acoustic impedance layer of the second acoustic reflecting portion is made of an insulating material and the second high acoustic impedance layer is made of a conductive material. (3) The elastic wave resonator according to (1), further comprising: a second acoustic reflecting portion provided on the second principal surface side of the piezoelectric layer and consisting of a laminate of a second low acoustic impedance layer having a relatively low acoustic impedance and a second high acoustic impedance layer having a relatively high acoustic impedance, wherein the second low acoustic impedance layer and the second high acoustic impedance layer of the second acoustic reflecting portion are both made of an insulating material. (4) The elastic wave resonator according to any one of (1) to (3), including: a support member provided opposite the second main surface of the piezoelectric layer; and a high viscoelastic layer arranged on the opposite side of the first acoustic reflecting portion from the piezoelectric layer, the high viscoelasticity layer having higher viscoelasticity than the first high acoustic impedance layer and the first low acoustic impedance layer of the first acoustic reflecting portion. (5) The elastic wave resonator according to any one of (1) to (3), including a support member provided opposite the first main surface of the piezoelectric layer, the first acoustic reflecting portion being arranged between the piezoelectric layer and the support member, and the external terminal being provided on a surface of the support member opposite to the first acoustic reflecting portion.(6) The elastic wave resonator according to (1), further comprising: a support member disposed opposite the second main surface of the piezoelectric layer, wherein the support member has a cavity that opens to the piezoelectric layer. (7) The elastic wave resonator according to (6), further comprising: a high viscoelastic layer disposed on the opposite side of the first acoustic reflecting section from the piezoelectric layer, the high viscoelasticity layer having higher viscoelasticity than the first high acoustic impedance layer and the first low acoustic impedance layer of the first acoustic reflecting section; and a high Young's modulus layer disposed on the opposite side of the first acoustic reflecting section from the piezoelectric layer, the high Young's modulus layer being higher than the first high acoustic impedance layer and the first low acoustic impedance layer of the first acoustic reflecting section. (8) The elastic wave resonator according to any one of (1) to (7), further comprising: when a region where the first electrode and the second electrode overlap with each other across the piezoelectric layer is defined as an elastic wave excitation section, the external terminal is disposed in a region that overlaps with the elastic wave excitation section in a planar view. (9) An electronic device comprising: an elastic wave resonator according to any one of (1) to (8); a module substrate on which the elastic wave resonator is mounted; and a sealing resin provided to cover the elastic wave resonator and in contact with at least each side surface of the piezoelectric layer and the first acoustic reflecting portion.

[0113] 10, 10A, 10B, 10C, 10D, 10E, 10F Acoustic wave resonator 11 Support member 12 Cavity 20 Piezoelectric layer 20a First main surface 20b Second main surface 21 First electrode 22 Second electrode 25 Surface electrode 28 Acoustic wave excitation portion 31 First acoustic reflection portion 31a, 31c First low acoustic impedance layer 31b, 31d First high acoustic impedance layer 32, 32A Second acoustic reflection portion 32a, 32c, 32e, 32Aa, 32Ac Second low acoustic impedance layer 32b, 32d, 32Ab, 32Ad Second high acoustic impedance layer 42 High viscoelastic layer 44 High Young's modulus layer 51, 52 Acoustic wave filter 61a, 61b, 61c, 61d, 61e Series arm resonator 62a, 62b, 62c, 62d parallel arm resonators 100 electronic device 101 module substrate 105 sealing resin

Claims

1. An elastic wave resonator comprising: a piezoelectric layer having a first principal surface and a second principal surface opposite the first principal surface; a first electrode provided on the first principal surface of the piezoelectric layer; a second electrode provided on the second principal surface of the piezoelectric layer and facing the first electrode with the piezoelectric layer in between; an external terminal provided on the first principal surface side of the piezoelectric layer and electrically connecting to an external substrate; a plurality of connecting conductors connecting the first electrode and the second electrode to the external terminal; and a first acoustic reflecting portion on the first principal surface side of the piezoelectric layer, the first acoustic reflecting portion comprising a laminate of a first low acoustic impedance layer having a relatively low acoustic impedance and a first high acoustic impedance layer having a relatively high acoustic impedance, wherein the first low acoustic impedance layer and the first high acoustic impedance layer of the first acoustic reflecting portion are both made of an insulating material.

2. An elastic wave resonator according to claim 1, further comprising a second acoustic reflecting section provided on the second main surface side of the piezoelectric layer and comprising a laminate of a second low acoustic impedance layer having a relatively low acoustic impedance and a second high acoustic impedance layer having a relatively high acoustic impedance, wherein the second low acoustic impedance layer of the second acoustic reflecting section is made of an insulating material and the second high acoustic impedance layer is made of a conductive material.

3. An elastic wave resonator according to claim 1, further comprising a second acoustic reflecting portion provided on the second principal surface side of the piezoelectric layer and consisting of a laminate of a second low acoustic impedance layer having a relatively low acoustic impedance and a second high acoustic impedance layer having a relatively high acoustic impedance, wherein the second low acoustic impedance layer and the second high acoustic impedance layer of the second acoustic reflecting portion are both made of an insulating material.

4. An elastic wave resonator according to any one of claims 1 to 3, comprising: a support member provided opposite the second main surface of the piezoelectric layer; and a high-viscoelastic layer arranged on the opposite side of the first acoustic reflecting section from the piezoelectric layer, the high-viscoelastic layer having higher viscoelasticity than the first high acoustic impedance layer and the first low acoustic impedance layer of the first acoustic reflecting section.

5. An elastic wave resonator according to any one of claims 1 to 3, further comprising a support member disposed opposite the first main surface of the piezoelectric layer, the first acoustic reflection portion being disposed between the piezoelectric layer and the support member, and the external terminal being disposed on a surface of the support member opposite the first acoustic reflection portion.

6. The elastic wave resonator according to claim 1, further comprising a support member disposed opposite the second main surface of the piezoelectric layer, the support member having a cavity that opens to the piezoelectric layer side.

7. The elastic wave resonator according to claim 6, comprising: a high viscoelastic layer, disposed on the opposite side of the piezoelectric layer of the first acoustic reflecting section, and having higher viscoelasticity than the first high acoustic impedance layer and the first low acoustic impedance layer of the first acoustic reflecting section; and a high Young's modulus layer, disposed on the opposite side of the piezoelectric layer of the first acoustic reflecting section, provided in a region overlapping with at least the cavity in a plan view, and having a higher Young's modulus than the first high acoustic impedance layer and the first low acoustic impedance layer of the first acoustic reflecting section.

8. An elastic wave resonator according to any one of claims 1 to 7, wherein when an area where the first electrode and the second electrode overlap with each other across the piezoelectric layer is defined as an elastic wave excitation section, the external terminal is arranged in an area that overlaps with the elastic wave excitation section in a plan view.

9. An electronic device comprising: an elastic wave resonator according to any one of claims 1 to 8; a module substrate on which the elastic wave resonator is mounted; and a sealing resin provided to cover the elastic wave resonator and in contact with at least each side surface of the piezoelectric layer and the first acoustic reflecting portion.

Images