Filter device

Abstract

In a filter device in which a piezoelectric layer, and a first resonator and a second resonator provided with a functional electrode are mounted on a support substrate via a support so a space is configured in which the surfaces of the functional electrodes face each other, the thickness of the piezoelectric layer of the resonator on the side having a through electrode connected to an external electrode is made thinner than the thickness of the piezoelectric layer of the other resonator, so that wear of an electrode pad due to etching at the time of through hole formation is reduced and deterioration of reliability is suppressed.

Description

Filter Device

[0001] The present invention relates to a filter device having a plurality of acoustic wave resonators.

[0002] Conventionally, filter devices having acoustic wave resonators have been widely used as filters for mobile phones, etc. Patent Document 1 below discloses an example of a piezoelectric filter as a filter device. In this piezoelectric filter, a pair of piezoelectric substrates are bonded together by a bonding layer. A gap is formed between the pair of piezoelectric substrates. An IDT (Interdigital Transducer) and an electrode pad are provided on a main surface of each piezoelectric substrate so as to be positioned within the gap.

[0003] One of the substrates has a through hole formed therethrough, one end of the through hole connected to an external electrode, and the other end of the through hole connected to an electrode pad.

[0004] WO 2006 / 008940

[0005] When manufacturing the piezoelectric filter described in Patent Document 1, through-holes are provided in the piezoelectric substrate to form the through-holes. When providing the through-holes, electrode pads serve as stoppers. However, in reality, the electrode pads tend to be worn away by the processing used to provide the through-holes. This can result in a deterioration in the reliability of the piezoelectric filter.

[0006] An object of the present invention is to provide a filter device capable of suppressing deterioration in reliability.

[0007] A filter device according to the present invention includes a first piezoelectric substrate having a first main surface and a second main surface facing each other, at least one first resonator including a functional electrode provided on the first main surface, a second piezoelectric substrate having a third main surface located on the first piezoelectric substrate side and a fourth main surface facing the third main surface, at least one second resonator including a functional electrode provided on the third main surface, a support provided between the first main surface and the third main surface so as to define a space between the first main surface and the third main surface, and the first piezoelectric substrate. the first piezoelectric substrate has a first support substrate and a first piezoelectric layer laminated with the first support substrate, the first main surface including the main surface of the first piezoelectric layer; the second piezoelectric substrate has a second support substrate and a second piezoelectric layer laminated with the second support substrate, the third main surface including the main surface of the second piezoelectric layer; and the thickness of the first piezoelectric layer is thinner than the thickness of the second piezoelectric layer.

[0008] According to the filter device of the present invention, deterioration of reliability can be suppressed.

[0009] FIG. 1 is a schematic front cross-sectional view of a filter device according to a first embodiment of the present invention. FIGS. 2(a) and 2(b) are schematic front cross-sectional views illustrating a process for providing a through electrode in a piezoelectric substrate according to the first embodiment of the present invention. FIGS. 3(a) and 3(b) are schematic front cross-sectional views illustrating a process for forming a through hole in a piezoelectric substrate in order to provide a through electrode in the piezoelectric substrate according to the first embodiment of the present invention. FIG. 4 is a schematic plan view of a first resonator according to the first embodiment of the present invention. FIG. 5 is a schematic plan view illustrating the width of the through electrode, etc. FIG. 6 is a diagram illustrating the relationship between the thickness of the piezoelectric layer and the TCFa of the resonator according to the first embodiment of the present invention. FIG. 7 is a diagram illustrating the relationship between the thickness of the piezoelectric layer and the TCFr of the resonator according to the first embodiment of the present invention. FIG. 8 is a schematic diagram of the impedance-frequency characteristics of a series arm resonator and a parallel arm resonator. FIG. 9 is a schematic diagram of the attenuation-frequency characteristics of a bandpass filter. FIG. 10 is a schematic plan view of a first resonator according to a first modification of the first embodiment of the present invention. FIG. 11 is a schematic plan view of a through hole in a second modified example of the first embodiment of the present invention. FIGS. 12(a) to 12(c) are schematic cross-sectional front views showing a process for providing a through electrode in a piezoelectric substrate in a second modified example of the first embodiment of the present invention. FIGS. 13(a) and 13(b) are schematic cross-sectional front views showing an example of a process after providing a through electrode in a piezoelectric substrate in a second modified example of the first embodiment of the present invention. FIG. 14 is a schematic cross-sectional front view of a filter device in a third modified example of the first embodiment of the present invention. FIG. 15 is a schematic cross-sectional front view of a filter device in a fourth modified example of the first embodiment of the present invention. FIG. 16 is a schematic view of VSWR in a second embodiment of the present invention. FIG. 17 is a schematic cross-sectional front view of a filter device in a third embodiment of the present invention. FIG. 18 is a diagram showing the relationship between the cut angle in the piezoelectric layer and the fractional bandwidth of a resonator in a third embodiment of the present invention. FIG. 19 is a schematic view of the impedance-frequency characteristics of a series arm resonator and a parallel arm resonator in a third embodiment of the present invention. Fig. 20 is a schematic diagram of the attenuation frequency characteristics of a filter device according to a third embodiment of the present invention, and Fig. 21 is a schematic front cross-sectional view of a filter device according to a fifth embodiment of the present invention.FIG. 22 is a diagram showing the relationship between the thickness of the intermediate layer and the relative bandwidth of a resonator according to the fifth embodiment of the present invention. FIG. 23 is a diagram showing the relationship between the thickness of the piezoelectric layer and the thickness of the intermediate layer and the phase of harmonics. FIG. 24 is a schematic front cross-sectional view of a filter device according to a sixth embodiment of the present invention. FIG. 25 is a schematic front cross-sectional view for explaining the effects of the sixth embodiment of the present invention. FIG. 26 is a schematic front cross-sectional view of a filter device according to a seventh embodiment of the present invention. FIG. 27 is a schematic front cross-sectional view for explaining the effects of the seventh embodiment of the present invention. FIG. 28 is a schematic front cross-sectional view of a filter device according to an eighth embodiment of the present invention. FIG. 29 is a diagram showing the relationship between ψ in the Euler angles (φ, θ, ψ) of the support substrate and the phases of Rayleigh waves and harmonics. FIG. 30 is a diagram showing a case where the phase is −60° or less in the relationship shown in FIG. 29. FIG. 31 is a schematic front cross-sectional view of a filter device according to a tenth embodiment of the present invention. FIG. 32 is a diagram showing the relationship between the thickness of the IDT electrode and TCFa. FIG. 33 is a diagram showing the relationship between the thickness of the IDT electrode and TCFr. FIG. 34 is a schematic plan view showing the arrangement of resonators on a first main surface of a first piezoelectric substrate in a twelfth preferred embodiment of the present invention. FIG. 35 is a schematic perspective plan view showing the arrangement of resonators on a third main surface of a second piezoelectric substrate in a twelfth preferred embodiment of the present invention. FIG. 36 is a schematic front cross-sectional view of a filter device according to a thirteenth preferred embodiment of the present invention. FIG. 37 is a diagram showing the relationship between the thickness of a dielectric film and the fractional bandwidth. FIG. 38 is a schematic front cross-sectional view of a filter device according to a fourteenth preferred embodiment of the present invention. FIG. 39 is a schematic front cross-sectional view of an elastic wave device according to a fifteenth preferred embodiment of the present invention. FIG. 40 is a schematic front cross-sectional view of an elastic wave device according to a sixteenth preferred embodiment of the present invention. FIG. 41 is a schematic front cross-sectional view of an elastic wave device according to a seventeenth preferred embodiment of the present invention. FIG. 42 is a schematic front cross-sectional view of an elastic wave device according to an eighteenth preferred embodiment of the present invention. FIG. 43 is a schematic front cross-sectional view of an elastic wave device according to a nineteenth preferred embodiment of the present invention.

[0010] The present invention will be clarified below by describing specific embodiments of the present invention with reference to the drawings.

[0011] It should be noted that the embodiments described in this specification are merely examples, and partial substitution or combination of configurations is possible between different embodiments.

[0012] The filter device according to the present invention may be a bandpass filter having one passband or a composite filter device having multiple passbands. If the filter device is a bandpass filter, the filter device may be, for example, a transmit filter or a receive filter. If the filter device is a composite filter device, the filter device may be, for example, a multiplexer such as a duplexer, triplexer, or quadplexer.

[0013] Fig. 1 is a schematic cross-sectional front view of a filter device according to a first embodiment of the present invention. A reflector, which will be described later, is omitted from Fig. 1. The same applies to the other schematic cross-sectional front views.

[0014] The filter device 1 in this embodiment is a band-pass filter. Specifically, the filter device 1 is a ladder filter. The filter device 1 has a plurality of series arm resonators and a plurality of parallel arm resonators. However, when the filter device 1 is a ladder filter, it is sufficient that the filter device 1 has at least one series arm resonator and at least one parallel arm resonator.

[0015] As shown in Fig. 1, the filter device 1 has a first piezoelectric substrate 2A and a second piezoelectric substrate 2B. A piezoelectric substrate is a substrate that has piezoelectric properties. The first piezoelectric substrate 2A has a first support substrate 3A, a first intermediate layer 4A, and a first piezoelectric layer 5A. The first intermediate layer 4A is provided on the first support substrate 3A. The first piezoelectric layer 5A is provided on the first intermediate layer 4A.

[0016] The first piezoelectric substrate 2A has a first main surface 2a and a second main surface 2b. The first main surface 2a and the second main surface 2b face each other. Specifically, the first main surface 2a is the main surface of the first piezoelectric substrate 2A that is located closest to the second piezoelectric substrate 2B. In this embodiment, the main surface of the first piezoelectric layer 5A is the first main surface 2a. However, it is sufficient that the first main surface 2a includes at least the main surface of the first piezoelectric layer 5A. For example, the first main surface 2a may include the main surface of the first piezoelectric layer 5A, as well as the main surface of the first intermediate layer 4A or the main surface of the first support substrate 3A.

[0017] On the other hand, the second main surface 2b of the first piezoelectric substrate 2A faces the first main surface 2a and is the outermost main surface of the first piezoelectric substrate 2A. Therefore, the second main surface 2b is the outermost main surface of the first support substrate 3A on the first piezoelectric substrate 2A.

[0018] Similarly, the second piezoelectric substrate 2B is a laminated substrate of a second support substrate 3B, a second intermediate layer 4B, and a second piezoelectric layer 5B. The third main surface 2c of the second piezoelectric substrate 2B is the main surface of the second piezoelectric substrate 2B that is located closest to the first piezoelectric substrate 2A. In this embodiment, the main surface of the second piezoelectric layer 5B is the third main surface 2c. However, it is sufficient that the third main surface 2c includes at least the main surface of the second piezoelectric layer 5B. For example, the third main surface 2c may include the main surface of the second piezoelectric layer 5B, as well as the main surface of the second intermediate layer 4B or the main surface of the second support substrate 3B.

[0019] On the other hand, the fourth main surface 2d of the second piezoelectric substrate 2B faces the third main surface 2c and is the outermost main surface of the second piezoelectric substrate 2B. Therefore, the fourth main surface 2d is the outermost main surface of the second piezoelectric substrate 2B of the second support substrate 3B.

[0020] In this embodiment, silicon is used as the material of the first support substrate 3A and the second support substrate 3B, and silicon oxide is used as the material of the first intermediate layer 4A and the second intermediate layer 4B, although the materials of the above layers are not limited to those mentioned above.

[0021] A plurality of first resonators 1A are formed on the first piezoelectric substrate 2A. Specifically, a plurality of functional electrodes are provided on a first main surface 2a of the first piezoelectric substrate 2A. Each of the plurality of first resonators 1A includes a functional electrode. More specifically, in this embodiment, each functional electrode provided on the first piezoelectric substrate 2A is a first IDT electrode 12A.

[0022] A first support 6A, which serves as a support in the present invention, is provided on the first main surface 2a of the first piezoelectric substrate 2A. The first support 6A has a frame shape. The first support 6A is provided so as to surround the plurality of first resonators 1A formed on the first piezoelectric substrate 2A. More specifically, the first support 6A surrounds the plurality of functional electrodes provided on the first main surface 2a.

[0023] A plurality of electrode pads 7 are provided on the first main surface 2a of the first piezoelectric substrate 2A. A second support 6B is provided on each of the plurality of electrode pads 7. Each second support 6B has a columnar shape. The plurality of second supports 6B are surrounded by the first support 6A.

[0024] A second piezoelectric substrate 2B is provided on the first support 6A and the plurality of second supports 6B. This defines a space between a first main surface 2a of the first piezoelectric substrate 2A and a third main surface 2c of the second piezoelectric substrate 2B. In this embodiment, the space is sealed by the first piezoelectric substrate 2A, the second piezoelectric substrate 2B, and the first support 6A.

[0025] A plurality of second resonators 1B are formed on the second piezoelectric substrate 2B. Specifically, a plurality of functional electrodes are provided on the third main surface 2c of the second piezoelectric substrate 2B. More specifically, in this embodiment, each functional electrode provided on the second piezoelectric substrate 2B is a second IDT electrode 12B.

[0026] The filter device 1 is a ladder-type filter having a plurality of first resonators 1A and a plurality of second resonators 1B. The plurality of first resonators 1A and the plurality of second resonators 1B may include at least one series arm resonator and at least one parallel arm resonator.

[0027] 1, the filter device 1 is configured as a two-stage stack including a first piezoelectric substrate 2A and a second piezoelectric substrate 2B. However, the filter device according to the present invention may be configured as a three-stage or more stack.

[0028] A plurality of external connection terminals 8 are provided on the second main surface 2b of the first piezoelectric substrate 2A. A plurality of through electrodes 9 are provided so as to penetrate the first piezoelectric substrate 2A. One end of each through electrode 9 is connected to a corresponding electrode pad 7. The other end of each through electrode 9 is connected to a corresponding external connection terminal 8. On the other hand, no through electrodes 9 are provided on the second piezoelectric substrate 2B.

[0029] The plurality of first resonators 1A and the plurality of second resonators 1B are each electrically connected to an electrode pad 7. The plurality of first resonators 1A and the plurality of second resonators 1B are each electrically connected to the outside via the electrode pad 7, the through electrode 9, and the external connection terminal 8. The plurality of electrode pads 7 may include an electrode pad 7 that is not connected to the through electrode 9.

[0030] A feature of this embodiment is that the first piezoelectric substrate 2A is provided with a through electrode 9, and the thickness of the first piezoelectric layer 5A of the first piezoelectric substrate 2A is thinner than the thickness of the second piezoelectric layer 5B of the second piezoelectric substrate 2B. This makes it possible to suppress deterioration in the reliability of the filter device 1. Details of the above effect will be described below, along with parts of the manufacturing method of the filter device 1 that relate to the above effect.

[0031] 2(a) and 2(b) are schematic front cross-sectional views showing a process for providing a through electrode in a piezoelectric substrate according to the first embodiment. Figures 3(a) and 3(b) are schematic front cross-sectional views showing a process for forming a through hole in a piezoelectric substrate in order to provide a through electrode in the piezoelectric substrate according to the first embodiment.

[0032] 2(a), a two-stage stack is prepared in which a first piezoelectric substrate 2A and a second piezoelectric substrate 2B are bonded together by a first support 6A. A plurality of functional electrodes are provided on the first main surface 2a of the first piezoelectric substrate 2A and the third main surface 2c of the second piezoelectric substrate 2B. A plurality of electrode pads 7 are provided on the first main surface 2a of the first piezoelectric substrate 2A.

[0033] Next, as shown in FIG. 2B, through-holes are formed in the first support substrate 3A and the first intermediate layer 4A of the first piezoelectric substrate 2A. When the first support substrate 3A is made of silicon, as in this embodiment, a Bosch process or the like is preferably used to form the through-holes in the first support substrate 3A. In the Bosch process, isotropic etching, formation of a protective film, and anisotropic etching are repeated. This increases the aspect ratio of the holes formed in the first support substrate 3A. Through-holes can also be formed in the first intermediate layer 4A by etching.

[0034] 3A, a through-hole is formed in the first piezoelectric layer 5A so as to reach the electrode pad 7. When forming the through-hole in the first piezoelectric layer 5A, dry etching using, for example, Ar as a main component is used. At this time, the electrode pad 7 functions as an etching stop layer.

[0035] 3(b), a through electrode 9 is provided in the through hole so that one end is connected to the electrode pad 7. At the same time, an external connection terminal 8 is provided on the second main surface 2b of the first piezoelectric substrate 2A. Specifically, for example, after a seed layer is formed in the through hole and on the second main surface 2b, the through electrode 9 and the external connection terminal 8 may be provided by plating.

[0036] In this embodiment, the thickness of the first piezoelectric layer 5A is thin. This shortens the etching time required to form through-holes in the first piezoelectric layer 5A. This shortens the etching time for the electrode pads 7. This reduces damage to the electrode pads 7. Specifically, for example, it reduces the occurrence of cracks in the electrode pads 7. This reduces the infiltration of moisture through the cracks into the space between the first piezoelectric substrate 2A and the second piezoelectric substrate 2B. This reduces the deterioration of the reliability of the filter device 1.

[0037] The configuration of this embodiment will be described in further detail below.

[0038] FIG. 4 is a schematic plan view of the first resonator according to the first embodiment.

[0039] The first resonator 1A has a first IDT electrode 12A and a pair of reflectors 13A and 13B. The first IDT electrode 12A and the reflectors 13A and 13B are provided on a first main surface 2a of a first piezoelectric substrate 2A.

[0040] The first IDT electrode 12A has a pair of bus bars and a plurality of electrode fingers. The pair of bus bars is specifically a first bus bar 16 and a second bus bar 17. The first bus bar 16 and the second bus bar 17 face each other. The plurality of electrode fingers is specifically a plurality of first electrode fingers 18 and a plurality of second electrode fingers 19. One ends of the plurality of first electrode fingers 18 are connected to the first bus bar 16, respectively. One ends of the plurality of second electrode fingers 19 are connected to the second bus bar 17, respectively. The plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 are interdigitated with each other. The first electrode fingers 18 and the second electrode fingers 19 are connected to different potentials.

[0041] Each of the first resonators 1A other than the first resonator 1A shown in FIG. 4 also has a first IDT electrode 12A and a pair of reflectors. Each of the second resonators 1B has a second IDT electrode 12B and a pair of reflectors. Like the first IDT electrode 12A, the second IDT electrode 12B also has a pair of bus bars and a plurality of electrode fingers. Note that each of the first IDT electrodes 12A, each of the second IDT electrodes 12B, and each of the reflectors may have appropriate design parameters depending on the desired electrical characteristics.

[0042] In the filter device 1 of this embodiment, each of the first resonators 1A and each of the second resonators 1B is a one-port surface acoustic wave resonator.

[0043] Applying an AC voltage to the first IDT electrode 12A excites an acoustic wave. In the first IDT electrode 12A, when the direction in which the multiple electrode fingers extend is defined as the electrode finger extension direction, the acoustic wave propagation direction is perpendicular to the electrode finger extension direction. This is the same for all first IDT electrodes 12A. However, in this embodiment, the acoustic wave propagation direction is the same for all first IDT electrodes 12A.

[0044] Similarly, an acoustic wave is excited by applying an AC voltage to the second IDT electrode 12B. In the second IDT electrode 12B, when the direction in which the electrode fingers extend is defined as the electrode finger extension direction, the acoustic wave propagation direction is perpendicular to the electrode finger extension direction. This is the same for all second IDT electrodes 12B. However, in this embodiment, the acoustic wave propagation direction is the same for all second IDT electrodes 12B. Furthermore, in this embodiment, the acoustic wave propagation direction is the same for all first IDT electrodes 12A and all second IDT electrodes 12B in a plan view.

[0045] In this specification, a plan view refers to a view from a direction corresponding to the top in Fig. 1. In Fig. 1, for example, of the first piezoelectric substrate 2A side and the second piezoelectric substrate 2B side, the second piezoelectric substrate 2B side is the top.

[0046] The first support 6A and the plurality of second support members 6B are made of an appropriate metal. The first resonator 1A and the second resonator 1B are electrically connected by the first support member 6A and the plurality of second support members 6B. This constitutes the circuit of the filter device 1.

[0047] In this embodiment, when the wavelength defined by the electrode finger pitch is λ, the thickness of the first piezoelectric layer 5A is 0.2λ. The thickness of the second piezoelectric layer 5B is 0.35λ. More specifically, the wavelength λ that serves as the reference for the thicknesses of the first piezoelectric layer 5A and the second piezoelectric layer 5B is the shortest wavelength λ among the wavelengths λ of all the first IDT electrodes 12A and all the second IDT electrodes 12B. The same applies to the thicknesses of the other layers of the first piezoelectric substrate 2A, the layers of the second piezoelectric substrate 2B, and the first IDT electrodes 12A and the second IDT electrodes 12B. The electrode finger pitch is the center-to-center distance in the acoustic wave propagation direction between adjacent electrode fingers that are connected to different potentials.

[0048] The thicknesses of the first piezoelectric layer 5A and the second piezoelectric layer 5B are not limited to the above. However, it is preferable that the thickness of the first piezoelectric layer 5A be less than 5 μm. This more reliably prevents cracks from occurring after the through-holes are formed in the first piezoelectric layer 5A. This effectively improves the reliability of the filter device.

[0049] FIG. 5 is a schematic plan view for explaining the width of the through electrode and the like.

[0050] In the following description, as shown by the dashed line in FIG. 5, the width of the through electrode 9 is the dimension of a straight line passing through the center O of the through electrode 9 in a plan view and two points on the outer periphery of the through electrode 9.

[0051] In this embodiment, the widest width of the through electrode 9 at the portion penetrating the first piezoelectric layer 5A is less than 100 μm. In this case, the widest width of the through hole in the first piezoelectric layer 5A is also less than 100 μm. This makes it possible to more reliably prevent cracks from occurring after the through hole is formed in the first piezoelectric layer 5A.

[0052] The widest width of the through electrode 9 at the portion penetrating the first piezoelectric layer 5A is preferably, for example, 10 μm or more. In this case, the electrical resistance of the through electrode 9 can be suitably reduced.

[0053] 3(b), the through electrode 9 is provided on the first piezoelectric substrate 2A after the first piezoelectric substrate 2A and the second piezoelectric substrate 2B are joined by the first support 6A. In this case, the difference in width between the portion of the through electrode 9 that penetrates the first support substrate 3A, the portion that penetrates the first intermediate layer 4A, and the portion that penetrates the first piezoelectric layer 5A is small.

[0054] 5, in plan view, the outer periphery of the portion of the through electrode 9 that penetrates the first piezoelectric layer 5A is defined as a first outer periphery 9a, and the outer periphery of the portion of the through electrode 9 that penetrates the first intermediate layer 4A is defined as a second outer periphery 9b. The point where a line drawn from the center O of the through electrode 9 intersects with the first outer periphery 9a is defined as a first point A, and the point where this line intersects with the second outer periphery 9b is defined as a second point B. The dimension as the distance between the first point A and the second point B is equal to or less than the dimension as the thickness of the first intermediate layer 4A.

[0055] The outer periphery of the portion of the through electrode 9 that penetrates the first support substrate 3A is defined as a third outer periphery 9c. The point where a line drawn from the center O of the through electrode 9 intersects with the first outer periphery 9a is defined as a first point A, and the point where the line intersects with the third outer periphery 9c is defined as a third point C. The dimension as the distance between the first point A and the third point C is equal to or less than the dimension as the sum of the thickness of the first piezoelectric layer 5A and the thickness of the first intermediate layer 4A.

[0056] In this embodiment, all of the first resonators 1A included in the filter device 1 are series arm resonators. At the same time, all of the series arm resonators of the filter device 1 are first resonators 1A. The thickness of the piezoelectric layer in these series arm resonators is thin. This can suppress deterioration of the filter characteristics. This will be described in detail below.

[0057] In this specification, the first resonator 1A and the second resonator 1B may be collectively referred to simply as "resonators." The first piezoelectric layer 5A and the second piezoelectric layer 5B may be collectively referred to simply as "piezoelectric layers." The first intermediate layer 4A and the second intermediate layer 4B may be collectively referred to simply as "intermediate layers." The first support substrate 3A and the second support substrate 3B may be collectively referred to simply as "support substrates." The first IDT electrode 12A and the second IDT electrode 12B may be collectively referred to simply as "IDT electrodes." Hereinafter, the frequency temperature coefficient at the resonant frequency is referred to as TCFr. The frequency temperature coefficient at the anti-resonant frequency is referred to as TCFa.

[0058] Fig. 6 is a diagram showing the relationship between the thickness of the piezoelectric layer and TCFa of the resonator according to the first embodiment. Fig. 7 is a diagram showing the relationship between the thickness of the piezoelectric layer and TCFr of the resonator according to the first embodiment. Note that in Figs. 6 and 7, the thickness of the piezoelectric layer is shown as a standard value. In this specification, the standard value refers to a value standardized with a certain reference value set to 1.

[0059] 6, the thicker the piezoelectric layer, the larger the TCFa in the negative direction. Since the thickness of the first piezoelectric layer 5A in the first resonator 1A is thin, the TCFa can be set to approximately 0 ppm / °C.

[0060] 7, the thicker the piezoelectric layer, the larger the TCFr becomes in the negative direction. Since the second piezoelectric layer 5B in the second resonator 1B is thick, the TCFr can be set to a value close to 0 ppm / °C.

[0061] 8 is a schematic diagram of the impedance frequency characteristics of the series arm resonator and the parallel arm resonator, and FIG. 9 is a schematic diagram of the attenuation frequency characteristics of the bandpass filter.

[0062] As shown in Figures 8 and 9, the resonant frequency of the series arm resonator constitutes the pass band of the bandpass filter. On the other hand, the antiresonant frequency of the series arm resonator is a frequency higher than the pass band. However, if the antiresonant frequency is close to the pass band, the insertion loss of the bandpass filter may increase. When the series arm resonator operates, its temperature increases. When the TCFa of the series arm resonator is a negative value, the higher the temperature, the closer the antiresonant frequency of the series arm resonator approaches the pass band of the bandpass filter.

[0063] In contrast, in this embodiment, the TCFa of the first resonator 1A serving as a series arm resonator is approximately 0 ppm / °C. As a result, even if the series arm resonator operates and the temperature rises, the anti-resonance frequency is unlikely to approach the pass band of the filter device 1 serving as a band-pass filter. Therefore, even if the temperature rises, the insertion loss of the filter device 1 is unlikely to increase, and deterioration of the filter characteristics of the filter device 1 can be suppressed.

[0064] The thickness of the first piezoelectric layer 5A is preferably 0.05λ or more and 0.5λ or less. When the thickness of the first piezoelectric layer 5A is 0.05λ or more, deterioration of the resonance characteristics of the first resonator 1A can be suppressed. When the thickness of the first piezoelectric layer 5A is 0.5λ or less, the insertion loss of the filter device 1 is further prevented from increasing.

[0065] At least one first resonator 1A may be a series arm resonator. In this case, too, it is possible to suppress deterioration of the filter characteristics of the filter device 1. Alternatively, for example, the filter device 1 may be a multiplexer including at least one ladder filter. At least one ladder filter may include at least one first resonator 1A and at least one second resonator 1B. At least one first resonator 1A included in the ladder filter may be a series arm resonator. Furthermore, the ladder filter may include a plurality of first resonators 1A, and the plurality of first resonators 1A may be series arm resonators. In these cases, it is possible to suppress deterioration of the filter characteristics of the ladder filter in the filter device.

[0066] On the other hand, as shown in Figures 8 and 9, the anti-resonance frequency of the parallel arm resonator constitutes the pass band of the bandpass filter. On the other hand, the resonant frequency of the parallel arm resonator is a frequency lower than the pass band. However, if the resonant frequency is close to the pass band, the insertion loss of the bandpass filter may increase. When the parallel arm resonator operates, the temperature of the parallel arm resonator increases. Furthermore, when the TCFr of the parallel arm resonator is a positive value, the higher the temperature, the closer the resonant frequency of the parallel arm resonator approaches the pass band of the bandpass filter.

[0067] In contrast, in this embodiment, the TCFr of the second resonator 1B serving as a parallel arm resonator is close to 0 ppm / °C. As a result, even when the parallel arm resonator operates and the temperature rises, the resonant frequency is unlikely to approach the passband of the filter device 1 serving as a bandpass filter. Therefore, even when the temperature rises, the insertion loss of the filter device 1 is unlikely to increase, and degradation of the filter characteristics of the filter device 1 can be suppressed. For example, the filter device 1 may be a multiplexer including at least one ladder filter. At least one ladder filter may include at least one first resonator 1A and at least one second resonator 1B. At least one first resonator 1A included in the ladder filter may be a parallel arm resonator. Furthermore, the ladder filter may include a plurality of first resonators 1A, and the plurality of first resonators 1A may be parallel arm resonators. In these cases, degradation of the filter characteristics of the ladder filter in the filter device can also be suppressed. However, even in these cases, at least one first resonator 1A of the ladder-type filter may be a series arm resonator.

[0068] In this embodiment, the first resonators 1A and the second resonators 1B are both surface acoustic wave resonators. However, at least one of the first resonators 1A and the second resonators 1B may be configured to use a thickness-shear bulk wave as its main mode. In this case, the resonator may satisfy the relationship d / p≦0.5, where d is the thickness of the piezoelectric layer and p is the electrode finger pitch.

[0069] Alternatively, at least one of the first resonators 1A and the second resonators 1B may be a BAW (Bulk Acoustic Wave) element, in which case the functional electrodes of the resonator are a pair of excitation electrodes facing each other with a piezoelectric layer sandwiched therebetween.

[0070] Examples of materials for each member in the present invention are shown below.

[0071] The first piezoelectric layer 5A and the second piezoelectric layer 5B may be made of, for example, lithium tantalate, lithium niobate, zinc oxide, aluminum nitride, scandium aluminum nitride, etc. Preferably, the first piezoelectric layer 5A and the second piezoelectric layer 5B are made of rotated Y-cut lithium tantalate or lithium niobate.

[0072] The first intermediate layer 4A and the second intermediate layer 4B may be made of, for example, a dielectric material such as glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum oxide, or a compound of silicon oxide with fluorine, carbon, or boron, or a material containing any of the above materials as its main component. In this specification, the term "main component" refers to a component that accounts for more than 50 wt%. The main component material may be in a single crystal, polycrystalline, or amorphous state, or a mixture of these.

[0073] Materials for the first support substrate 3A and the second support substrate 3B can include, for example, piezoelectric materials such as aluminum nitride, lithium tantalate, lithium niobate, and quartz; ceramics such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, spinel, and sialon; dielectric materials such as aluminum oxide, silicon oxynitride, DLC (diamond-like carbon), and diamond; semiconductors such as silicon and gallium arsenide; or materials containing the above materials as their main components. The spinel includes aluminum compounds containing oxygen and one or more elements selected from Mg, Fe, Zn, Mn, and the like. Examples of the spinel include MgAl ２ O ４ , FeAl ２ O ４ , ZnAl ２ O ４ , MnAl ２ O ４ Examples include:

[0074] The first IDT electrode 12A and the second IDT electrode 12B may be made of, for example, Al, Cu, Pt, Ti, Mo, W, Ru, Au, Ag, or an alloy containing any of these metals as a main component. Note that even when the first resonator 1A or the second resonator 1B is a BAW element, the functional electrodes may be made of the same material as the first IDT electrode 12A and the second IDT electrode 12B.

[0075] The first resonator 1A may be a longitudinally coupled resonator type acoustic wave resonator. A first resonator 1C in a first modification of the first embodiment shown in FIG. 10 is a five-IDT type longitudinally coupled resonator type acoustic wave resonator. That is, the first resonator 1C has five first IDT electrodes: 12C, 12D, 12E, 12F, and 12G. Note that the number of first IDT electrodes in the first resonator 1C is not limited to five. The first resonator 1C may be, for example, a three-IDT type, seven-IDT type, or nine-IDT type longitudinally coupled resonator type acoustic wave filter. In this modification, as in the first embodiment, deterioration of the reliability of the filter device can be suppressed.

[0076] FIG. 10 shows a schematic diagram of the wiring of the first resonator 1C. The first resonator 1C is connected to a wiring connected to a signal potential and a wiring connected to a ground potential. For example, an insulating film may be provided on the first piezoelectric layer 5A so as to cover a portion of the wiring connected to the signal potential or the wiring connected to the ground potential. A three-dimensional wiring section may be formed by stacking the wiring connected to the signal potential, the insulating film, and the wiring connected to the ground potential. This allows the above-mentioned two wirings to be electrically insulated from each other without increasing the area of ​​the first piezoelectric layer 5A. This prevents the area of ​​the filter device from increasing.

[0077] Alternatively, at least one of the wiring connected to the signal potential and the wiring connected to the ground potential may be connected to the electrode pad 7 that is not connected to the through electrode 9 shown in Fig. 1. Then, it may be electrically connected to the wiring provided on the second piezoelectric substrate 2B via the electrode pad 7 and the second support 6B. In this case, the two wirings can be electrically insulated from each other even if an insulating film is not provided.

[0078] The second resonator 1B may be a longitudinally coupled resonator type acoustic wave filter.

[0079] In the first embodiment, an example has been shown in which through holes are formed in the first piezoelectric substrate 2A from the first support substrate 3A side, and through electrodes 9 are provided therein. However, the through holes may be formed from the first piezoelectric layer 5A side after the first piezoelectric substrate 2A is prepared. In this case, as in the second modified example of the first embodiment shown in FIG. 11 , the width of the portion of the through electrode 9A provided in the first piezoelectric layer 5A is wider than the width of the portion of the through electrode 9A provided in the first intermediate layer 4A. The first outer periphery 9a of the portion of the through electrode 9A provided in the first piezoelectric layer 5A is located outward in plan view from the second outer periphery 9b of the portion of the through electrode 9A provided in the first intermediate layer 4A.

[0080] Similarly, in a plan view, the first outer peripheral edge 9a is located further outward than the third outer peripheral edge 9c of the portion of the through electrode 9A that is provided on the first support substrate 3A. This is because the through holes are formed in the first piezoelectric layer 5A first, and therefore the width of the through holes in the first piezoelectric layer 5A is wider than the widths of the through holes in the first intermediate layer 4A and the first support substrate 3A. Note that the shape of the portion of the through electrode 9A that is provided on the first piezoelectric layer 5A in a plan view may be different from the shape of the portion of the through electrode 9A that is provided on the first intermediate layer 4A or the first support substrate 3A in a plan view.

[0081] To obtain the filter device of this modified example, first, as shown in FIG. 12( a), a first piezoelectric substrate 2A is prepared. Next, a through-hole is formed in the first piezoelectric layer 5A. Next, as shown in FIG. 12( b), a through-hole is formed in the first intermediate layer 4A and the first support substrate 3A so as to communicate with the through-hole in the first piezoelectric layer 5A. Next, as shown in FIG. 12( c), a through-electrode 9A is provided in the through-hole. Next, as shown in FIG. 13( a), a first IDT electrode 12A, an electrode pad 7, and a portion of the first support layer are provided on the first piezoelectric layer 5A. Next, an external connection terminal 8 is provided on the second main surface 2b of the first piezoelectric substrate 2A so as to connect to one end of the through-electrode 9A. Thereafter, as shown in FIG. 13( b), other layers of the first support layer 6A and a second support layer are provided, and the first piezoelectric substrate 2A and the second piezoelectric substrate 2B are bonded together. When providing the through electrodes 9A of this modified example, the etching time can be shortened even in the process of forming through holes in the first piezoelectric layer 5A because the thickness of the first piezoelectric layer 5A is thin. This shortens the time required to etch the first support substrate 3A and other components, thereby reducing damage to the first support substrate 3A and other components. For example, cracks are less likely to occur in the first support substrate 3A. This prevents deterioration of the reliability of the filter device.

[0082] The filter device according to the present invention may include a mounting substrate. For example, in a third modified example of the first embodiment shown in FIG. 14 , the filter device has a mounting substrate 11, a plurality of bumps 10, and a sealing resin layer 15. A stack including a first piezoelectric substrate 2A and a second piezoelectric substrate 2B is mounted on the mounting substrate 11. Specifically, each external connection terminal 8 is bonded to the mounting substrate 11 by the bumps 10. Note that each external connection terminal 8 may be bonded to the mounting substrate 11 by an appropriate conductive adhesive. A sealing resin layer 15 is provided on the mounting substrate 11 so as to cover the entire stack.

[0083] Alternatively, for example, in a fourth modification of the first embodiment shown in Fig. 15, the sealing resin layer 15 covers the second piezoelectric substrate 2B in the stack except for the fourth main surface 2d. On the other hand, the fourth main surface 2d is not covered with the sealing resin layer 15. A shield electrode 14 is provided on the fourth main surface 2d. This makes it possible to suppress electrical influences from the outside.

[0084] In the third and fourth modified examples, as in the first embodiment, it is possible to suppress deterioration in the reliability of the filter device.

[0085] The configurations of the second to twelfth embodiments will be described below. As with the first embodiment, the second to twelfth embodiments can also suppress deterioration in the reliability of the filter device. The configuration of the second embodiment is the same as the configuration of the first embodiment except for the circuit configuration. Therefore, the drawings and symbols used in the description of the first embodiment will be used in the description of the second embodiment.

[0086] The second embodiment differs from the first embodiment in that all of the first resonators 1A are parallel arm resonators. At the same time, in the second embodiment, all of the parallel arm resonators of the filter device are first resonators 1A. In all other respects, the filter device of the second embodiment has the same configuration as the filter device 1 of the first embodiment.

[0087] In the second embodiment, even when the resonator is operating and the temperature of the resonator rises, it is possible to suppress deterioration of the voltage standing wave ratio (VSWR), as will be described in detail below.

[0088] 16 is a schematic diagram of the VSWR in the second embodiment. In FIG. 16, the VSWR in the second embodiment is schematically shown by a solid line. The dashed line shows a conventional example in which the VSWR deteriorates as the temperature increases.

[0089] As shown in Fig. 16, in the second embodiment, the VSWR is less likely to deteriorate even when the temperature of the resonator increases. This is because the first piezoelectric layer 5A in the first resonator 1A, which is a parallel arm resonator, is thin. In the second embodiment, the first piezoelectric layer 5A is thin, as in the first embodiment. This allows the TCFa of the first resonator 1A to be approximately 0 ppm / °C.

[0090] For example, if the anti-resonant frequency of the parallel arm resonator changes, the VSWR may deteriorate. In contrast, in the second embodiment, even if the temperature of the first resonator 1A serving as the parallel arm resonator increases, the anti-resonant frequency is unlikely to change, thereby making it difficult for the VSWR to deteriorate.

[0091] In the second resonator 1B, which is a series arm resonator, the second piezoelectric layer 5B has a large thickness, which allows the TCFr of the second resonator 1B to be close to 0 ppm / °C.

[0092] For example, if the resonant frequency of the series arm resonator changes, the VSWR may deteriorate. In contrast, in the second embodiment, even if the temperature of the second resonator 1B serving as the series arm resonator increases, the resonant frequency is unlikely to change, and therefore the VSWR is unlikely to deteriorate.

[0093] FIG. 17 is a schematic cross-sectional front view of a filter device according to a third embodiment.

[0094] In this embodiment, both the first piezoelectric layer 25A and the second piezoelectric layer 25B are made of rotated Y-cut LiTaO ３ The present embodiment differs from the first embodiment in that the cut angle of the first piezoelectric layer 25A and the cut angle of the second piezoelectric layer 25B are different from each other. Except for the above, the filter device of the present embodiment has the same configuration as the filter device 1 of the first embodiment.

[0095] In this specification, the cut angle of the first piezoelectric layer and the cut angle of the second piezoelectric layer being different from each other means that the difference between these cut angles is 0.5° or more.

[0096] In this embodiment, specifically, the cut angle of the first piezoelectric layer 25A is 55°Y. The cut angle of the second piezoelectric layer 25B is 35°Y. However, the cut angles of the first piezoelectric layer 25A and the second piezoelectric layer 25B are not limited to the above. In this embodiment, the steepness of the filter device can be increased. In this specification, high steepness means that the amount of change in frequency is small for a certain amount of change in attenuation near the edge of the pass band. The above effects will be described in detail below.

[0097] Fig. 18 is a diagram showing the relationship between the cut angle of the piezoelectric layer and the bandwidth ratio of the resonator according to the third embodiment. The bandwidth ratio is expressed as (|fa-fr| / fr) x 100 [%], where fr is the resonant frequency and fa is the antiresonant frequency. In Fig. 18, the cut angle and bandwidth ratio are shown as standard values.

[0098] As shown in Figure 18, the larger the cut angle of the piezoelectric layer, the smaller the value of the fractional bandwidth. The smaller the value of the fractional bandwidth, the smaller the difference between the resonant frequency and the antiresonant frequency. In this embodiment, the cut angle of the first piezoelectric layer 25A is larger than the cut angle of the second piezoelectric layer 25B. Therefore, the value of the fractional bandwidth of the first resonator 21A is smaller than the value of the fractional bandwidth of the second resonator 21B.

[0099] Fig. 19 is a schematic diagram of the impedance frequency characteristics of the series arm resonators and the parallel arm resonators according to the third embodiment, and Fig. 20 is a schematic diagram of the attenuation frequency characteristics of the filter device according to the third embodiment.

[0100] In this embodiment, the first resonator 21A is a series arm resonator. Therefore, the fractional bandwidth of the first resonator 21A has a particularly large effect on the high-frequency side of the pass band of the filter device. As shown in FIG. 19 , the fractional bandwidth of the series arm resonator, which is the first resonator 21A, is small. Therefore, as shown in FIG. 20 , the steepness can be increased near the high-frequency end of the pass band of the filter device.

[0101] However, the first resonator 21A may be a parallel arm resonator. In this case, the fractional bandwidth of the first resonator 21A has a particularly large effect on the low-frequency end of the pass band of the filter device. Furthermore, the value of the fractional bandwidth of the first resonator 21A is small. Therefore, it is possible to increase the steepness near the low-frequency end of the pass band of the filter device.

[0102] The configuration of the fourth embodiment will be described below. The configuration of the fourth embodiment is the same as that of the first embodiment except for the material of the piezoelectric layer. Therefore, the drawings and symbols used in the description of the first embodiment will be used in the description of the fourth embodiment.

[0103] The fourth embodiment differs from the first embodiment in that the material used for the first piezoelectric layer 5 A is different from the material used for the second piezoelectric layer 5 B. Other than the above, the filter device of the fourth embodiment has the same configuration as the filter device 1 of the first embodiment.

[0104] In the fourth embodiment, similarly to the third embodiment, the fractional bandwidths of the first resonator 1A and the second resonator 1B can be suitably adjusted, thereby increasing the steepness of the filter device.

[0105] FIG. 21 is a schematic cross-sectional front view of a filter device according to a fifth embodiment.

[0106] This embodiment differs from the first embodiment in that the thickness of the first intermediate layer 24A is different from the thickness of the second intermediate layer 24B. Other than the above, the filter device of this embodiment has the same configuration as the filter device 1 of the first embodiment. Note that in this embodiment, silicon oxide is used as the material for the first intermediate layer 24A and the second intermediate layer 24B, as in the first embodiment.

[0107] In this specification, the thickness of the first intermediate layer and the thickness of the second intermediate layer being different from each other means that the difference between these thicknesses is 5% or more relative to both the thickness of the first intermediate layer and the thickness of the second intermediate layer.

[0108] In this embodiment, specifically, the thickness of the first intermediate layer 24A is 600 nm. The thickness of the second intermediate layer 24B is 300 nm. However, the thicknesses of the first intermediate layer 24A and the second intermediate layer 24B are not limited to the above. In this embodiment, similar to the third embodiment, the steepness of the filter device can be increased. The above effects will be described in detail below.

[0109] Fig. 22 is a diagram showing the relationship between the thickness of the intermediate layer and the relative bandwidth of the resonator according to the fifth embodiment, in which the thickness and the relative bandwidth of the intermediate layer are shown as standard values.

[0110] As shown in Figure 22, the thicker the intermediate layer, the smaller the value of the fractional bandwidth. In this embodiment, the thickness of the first intermediate layer 24A is thicker than the thickness of the second intermediate layer 24B. Therefore, the value of the fractional bandwidth of the first resonator 21A is smaller than the value of the fractional bandwidth of the second resonator 21B. The first resonator 21A is a series arm resonator. As a result, similar to the third embodiment, it is possible to increase the steepness near the high-frequency end of the pass band of the filter device.

[0111] However, the first resonator may be a parallel arm resonator, in which case the steepness can be increased near the lower end of the pass band of the filter device.

[0112] The thickness of the first intermediate layer 24A or the second intermediate layer 24B is preferably 350 nm or more and 500 nm or less, and more preferably 400 nm or more and 450 nm or less. This makes it possible to suppress harmonics as unwanted waves. Note that these harmonics are those generated at approximately 1.5 times the main mode. Details of this effect are described below.

[0113] 23 is a diagram showing the relationship between the thickness of the piezoelectric layer and the thickness of the intermediate layer and the phase of the harmonics, where the thickness of the piezoelectric layer is shown as a standard value.

[0114] 23, when the thickness of the intermediate layer is 350 nm or more and 500 nm or less, the phase of the harmonics is suppressed to less than 0° regardless of the thickness of the piezoelectric layer. When the thickness of the intermediate layer is 400 nm or more and 450 nm or less, the harmonics are further suppressed.

[0115] The material of the first intermediate layer 24A and the material of the second intermediate layer 24B may be different from each other. In this case, it is possible to adjust the type of harmonics that are likely to be generated. Therefore, it is possible to adjust the main mode frequency of each resonator as well as the frequency at which harmonics are generated. Therefore, when the filter device is a multiplexer, it is possible to adjust the frequency at which harmonics are generated so that it is not located within the passband of any of the bandpass filters. In addition, as in this embodiment, it is also possible to suppress deterioration in the reliability of the filter device.

[0116] FIG. 24 is a schematic cross-sectional front view of a filter device according to a sixth embodiment.

[0117] This embodiment differs from the first embodiment in that the thickness of the first support substrate 23A and the thickness of the second support substrate 23B are different from each other. Specifically, the thickness of the first support substrate 23A is greater than the thickness of the second support substrate 23B. Except for the above, the filter device of this embodiment has the same configuration as the filter device 1 of the first embodiment.

[0118] In this specification, the phrase "the thickness of the first support substrate and the thickness of the second support substrate are different from each other" means that the difference between these thicknesses is 50 nm or more.

[0119] In this embodiment, when a stack including a first piezoelectric substrate and a second piezoelectric substrate is mounted on a mounting substrate, cracks are unlikely to occur in the first support substrate 23A. For example, as schematically shown by the arrows in FIG. 25 , when the stack is mounted on the mounting substrate 11, thermal stress is applied to the mounting substrate 11 and the first support substrate 23A. Alternatively, even after the stack is mounted on the mounting substrate 11, thermal stress is applied to the mounting substrate 11 and the first support substrate 23A when the filter device is in use. Even in these cases, the first support substrate 23A is unlikely to break because of its large thickness. This further increases the reliability of the filter device.

[0120] FIG. 26 is a schematic front cross-sectional view of a filter device according to a seventh embodiment.

[0121] This embodiment differs from the first embodiment in that the thickness of the second support substrate 23B is greater than the thickness of the first support substrate 23A. Except for the above, the filter device of this embodiment has the same configuration as the filter device 1 of the first embodiment.

[0122] In this embodiment, when a stack including a first piezoelectric substrate and a second piezoelectric substrate is mounted on a mounting substrate, cracks are unlikely to occur in the second support substrate 23B. For example, as schematically shown in FIG. 27 , when mounting the stack on the mounting substrate 11, the second support substrate 23B is sucked by a suction collet 100 and the stack is transported. The stack is then mounted on the mounting substrate 11. During mounting, a particularly large impact is applied to the second support substrate 23B. In contrast, in this embodiment, the second support substrate 23B is thick, making it less likely to break. This further increases the reliability of the filter device.

[0123] FIG. 28 is a schematic cross-sectional front view of a filter device according to an eighth embodiment.

[0124] This embodiment differs from the first embodiment in that the Euler angles (φ, θ, ψ) of the crystal orientations of the first support substrate 23A and the second support substrate 23B are different from each other. Except for the above, the filter device of this embodiment has the same configuration as the filter device 1 of the first embodiment. In this embodiment, silicon is used as the material for the first support substrate 23A and the second support substrate 23B.

[0125] In this specification, when the Euler angles (φ, θ, ψ) of the first support substrate and the second support substrate are different from each other, the difference between these ψ angles is 1° or more.

[0126] In this embodiment, the types of harmonics that are likely to be generated can be adjusted. Therefore, the main mode frequency of each resonator can be adjusted, and the frequencies at which harmonics are generated can also be adjusted. Therefore, when the filter device is a multiplexer, the frequencies at which harmonics are generated can be adjusted so that they are not located within the pass band of any of the bandpass filters.

[0127] Fig. 29 is a diagram showing the relationship between ψ in the Euler angles (φ, θ, ψ) of the support substrate and the phases of the Rayleigh waves and harmonics. Fig. 30 is a diagram showing a case where the phase is -60° or less in the relationship shown in Fig. 29. In Figs. 29 and 30, ψ is shown as a standard value. Note that harmonics occurring at frequencies higher than 2.2 times that of the main mode will be referred to as higher-order harmonics hereinafter.

[0128] As shown in Fig. 29, the phase of the harmonics occurring at a frequency around 2.2 times the frequency at which the main mode occurs is particularly highly dependent on ψ in the Euler angles (φ, θ, ψ) of the support substrate. However, as shown in Fig. 30, it can be seen that the phases of the harmonics occurring at a frequency around 1.5 times the frequency of the main mode, higher-order harmonics, and Rayleigh waves also depend on ψ in the Euler angles (φ, θ, ψ) of the support substrate.

[0129] The configuration of the ninth embodiment will be described below. The configuration of the ninth embodiment is the same as that of the first embodiment except for the material of the support substrate. Therefore, the drawings and reference numerals used in the description of the first embodiment will be used in the description of the ninth embodiment.

[0130] The ninth embodiment differs from the first embodiment in that the material used for the first support substrate 3 A is different from the material used for the second support substrate 3 B. Other than the above, the filter device of the ninth embodiment has the same configuration as the filter device 1 of the first embodiment.

[0131] In the configuration of the ninth embodiment, for example, the temperature coefficient of frequency (TCF) can be adjusted in each of the first support substrate 3A and the second support substrate 3B. This allows the TCF of the first resonator 1A formed on the first piezoelectric substrate 2A and the TCF of the second resonator 1B formed on the second piezoelectric substrate 2B to be adjusted. This allows, for example, the TCFr or TCFa of each resonator to approach zero. This therefore provides the effects of increasing steepness and suppressing deterioration of VSWR.

[0132] It is preferable that the heat dissipation property of the material used for the first support substrate 3A is higher than that of the material used for the second support substrate 3B, thereby increasing the power durability of the filter device.

[0133] By using a high-strength material for the first support substrate 3A, it is possible to make the first support substrate 3A less susceptible to cracking, as in the sixth embodiment. This further increases the reliability of the filter device. Note that the second support substrate 3B may be made of, for example, a material for adjusting TCFr or TCFa, or a material capable of suppressing harmonics.

[0134] Alternatively, by using a high-strength material for the second support substrate 3B, it is possible to make the second support substrate 3B less likely to crack, as in the seventh embodiment. This further increases the reliability of the filter device. Note that the first support substrate 3A may be made of, for example, a material for adjusting TCFr or TCFa, a material that can suppress harmonics, or a material with high heat dissipation properties.

[0135] FIG. 31 is a schematic cross-sectional front view of a filter device according to a tenth embodiment.

[0136] This embodiment differs from the first embodiment in that the thickness of the first IDT electrode 22A and the thickness of the second IDT electrode 22B are different from each other. Specifically, the thickness of the first IDT electrode 22A is thinner than the thickness of the second IDT electrode 22B. Except for the above, the filter device of this embodiment has the same configuration as the filter device 1 of the first embodiment. In this embodiment, Al is used as the material for the first IDT electrode 22A and the second IDT electrode 22B.

[0137] In this specification, the fact that the thickness of the first IDT electrode and the thickness of the second IDT electrode are different from each other means that the difference between these thicknesses is 5% or more with respect to both the thickness of the first IDT electrode and the thickness of the second IDT electrode.

[0138] The thickness of the first IDT electrode 22A is 0.05λ, and the thickness of the second IDT electrode 22B is 0.1λ, but the thicknesses of the first IDT electrode 22A and the second IDT electrode 22B are not limited to the above.

[0139] In this embodiment, similar to the first embodiment, the insertion loss of the filter device is unlikely to increase even when the temperature rises, and the deterioration of the filter characteristics of the filter device can be suppressed. Details of this effect will be described below.

[0140] Fig. 32 is a diagram showing the relationship between the thickness of the IDT electrode and the TCFa. Fig. 32 shows an example in which Al is used as the material of the IDT electrode. In Fig. 32, the thickness of the IDT electrode is shown as a standard value.

[0141] As shown in Figure 32, the thicker the IDT electrode, the larger the TCFa in the negative direction. Here, the first resonator 21A is a series arm resonator. In the first resonator 21A, the first IDT electrode 22A is thin. Therefore, in the first resonator 21A, which is a series arm resonator, the TCFa can approach 0 ppm / °C. As a result, even if the temperature of the first resonator 21A increases, the antiresonant frequency of the first resonator 21A is unlikely to approach the passband of the filter device.

[0142] Fig. 33 is a diagram showing the relationship between the thickness of the IDT electrode and TCFr. Fig. 33 shows an example in which Al is used as the material of the IDT electrode. In Fig. 33, the thickness of the IDT electrode is shown as a standard value.

[0143] As shown in FIG. 33 , the thicker the IDT electrode, the larger the TCFr in the negative direction. Here, the second resonator 21B is a parallel arm resonator. The second IDT electrode 22B in the second resonator 21B is thick. Therefore, the TCFr of the second resonator 21B, which is a parallel arm resonator, can approach 0 ppm / °C. This makes it difficult for the resonant frequency of the second resonator 21B to approach the passband of the filter device, even when the temperature of the second resonator 21B rises. Therefore, even when the temperature rises, the insertion loss of the filter device is unlikely to increase, and degradation of the filter characteristics of the filter device can be suppressed.

[0144] As in the second embodiment, the first resonator 21A may be a parallel arm resonator. In this case, it is preferable that the thickness of the first IDT electrode 22A is greater than the thickness of the second IDT electrode 22B. This can suppress deterioration of the VSWR.

[0145] The thickness of the first IDT electrode 22A and the second IDT electrode 22B is preferably 0.03λ or more and 0.3λ or less. When the thickness of the first IDT electrode 22A and the second IDT electrode 22B is 0.03λ or more, the insertion loss of the filter device is further prevented from increasing. When the thickness of the first IDT electrode 22A and the second IDT electrode 22B is 0.3λ or less, deterioration of power durability can be suppressed.

[0146] The configuration of the eleventh embodiment will be described below. The configuration of the eleventh embodiment is the same as that of the first embodiment except for the material of the IDT electrodes. Therefore, the drawings and symbols used in the description of the first embodiment will be used in the description of the eleventh embodiment.

[0147] The eleventh embodiment differs from the first embodiment in that the material used for the first IDT electrode 12 A is different from the material used for the second IDT electrode 12 B. Other than the above, the filter device of the eleventh embodiment has the same configuration as the filter device 1 of the first embodiment.

[0148] In this embodiment, as in the first embodiment, the first resonator 1A is a series arm resonator. The second resonator 1B is a parallel arm resonator. In this case, it is preferable that the electrical resistance of the material used for the second IDT electrode 12B is higher than the electrical resistance of the material used for the first IDT electrode 12A. Even if the electrical resistance of the parallel arm resonator is high, the filter characteristics of the filter device 1 are unlikely to deteriorate. In addition, the power durability of the parallel arm resonator can be improved.

[0149] Alternatively, it is preferable that the strength of the material used for the second IDT electrode 12B is higher than the strength of the material used for the first IDT electrode 12A, thereby increasing the power durability of the parallel arm resonator.

[0150] Alternatively, the first resonator 1A may be a parallel arm resonator, and the second resonator 1B may be a series arm resonator. In this case, it is preferable that the electrical resistance of the material used for the first IDT electrode 12A is higher than the electrical resistance of the material used for the second IDT electrode 12B. Alternatively, it is preferable that the strength of the material used for the first IDT electrode 12A is higher than the strength of the material used for the second IDT electrode 12B.

[0151] Fig. 34 is a schematic plan view showing the arrangement of resonators on the first main surface of the first piezoelectric substrate in the twelfth embodiment. Fig. 35 is a schematic perspective plan view showing the arrangement of resonators on the third main surface of the second piezoelectric substrate in the twelfth embodiment. Note that in Figs. 34 and 35, each resonator is shown as a rectangle with two diagonal lines added. The double-headed arrow F in Figs. 34 and 35 indicates the direction of elastic wave propagation.

[0152] 34 and 35 , this embodiment differs from the first embodiment in that, in a plan view, the elastic wave propagation direction in the first IDT electrode 12A intersects with the elastic wave propagation direction in the second IDT electrode 12B. The elastic wave propagation direction is perpendicular to the electrode finger extension direction. Therefore, in a plan view, the electrode finger extension direction of the first IDT electrode 12A intersects with the electrode finger extension direction of the second IDT electrode 12B. Except for the above, the filter device of this embodiment has the same configuration as the filter device 1 of the first embodiment. In this embodiment, the Euler angles (φ, θ, ψ) of the first piezoelectric layer 5A and the second piezoelectric layer 5B are the same.

[0153] The first resonator 1A and the second resonator 1B have different relationships between the acoustic wave propagation direction and the Euler angles (φ, θ, ψ) of the piezoelectric layer. This allows the first resonator 1A and the second resonator 1B to have different fractional bandwidths. In this embodiment, the first resonator 1A is a series arm resonator. Therefore, by reducing the fractional bandwidth of the first resonator 1A, it is possible to increase the steepness near the high-frequency end of the pass band of the filter device.

[0154] The first resonator 1A may be a parallel arm resonator. In this case, by reducing the value of the fractional bandwidth of the first resonator 1A, it is possible to increase the steepness near the lower end of the passband of the filter device.

[0155] FIG. 36 is a schematic cross-sectional front view of a filter device according to a thirteenth embodiment.

[0156] This embodiment differs from the first embodiment in that a first dielectric film 36A is provided on the first piezoelectric layer 5A so as to cover the plurality of first IDT electrodes 12A. This embodiment also differs from the first embodiment in that a second dielectric film 36B is provided on the second piezoelectric layer 5B so as to cover the plurality of second IDT electrodes 12B. Except for the above points, the filter device of this embodiment has the same configuration as the filter device 1 of the first embodiment.

[0157] In this embodiment, as in the first embodiment, the first piezoelectric substrate 2A is provided with the through electrodes 9, and the thickness of the first piezoelectric layer 5A of the first piezoelectric substrate 2A is thinner than the thickness of the second piezoelectric layer 5B of the second piezoelectric substrate 2B, thereby making it possible to suppress deterioration in the reliability of the filter device.

[0158] In addition, the first IDT electrodes 12A are covered with a first dielectric film 36A, and the second IDT electrodes 12B are covered with a second dielectric film 36B. This protects each IDT electrode, making it less likely to be damaged.

[0159] In this embodiment, the thickness of the first dielectric film 36A and the thickness of the second dielectric film 36B are different from each other. Specifically, the thickness of the first dielectric film 36A is thinner than the thickness of the second dielectric film 36B. More specifically, the thickness of the first dielectric film 36A is 0.015λ. The thickness of the second dielectric film 36B is 0.025λ.

[0160] More specifically, the thickness of the first dielectric film 36A is the distance from the surface of the first dielectric film 36A that is in contact with the first IDT electrode 12A to the surface of the first dielectric film 36A. Similarly, the thickness of the second dielectric film 36B is the distance from the surface of the second dielectric film 36B that is in contact with the second IDT electrode 12B to the surface of the second dielectric film 36B. The wavelength λ that serves as the reference for the thicknesses of the first dielectric film 36A and the second dielectric film 36B is the shortest wavelength λ among the wavelengths λ of all the first IDT electrodes 12A and all the second IDT electrodes 12B. However, the thicknesses of the first dielectric film 36A and the second dielectric film 36B are not limited to the above.

[0161] In this specification, the phrase "the thickness of one dielectric film is different from the thickness of the other dielectric film" means that the difference between the two thicknesses is ±5% or less. Specifically, the phrase "the difference between the two thicknesses is ±5% or less" means that the absolute value of the difference between the thickness of one dielectric film and the thickness of the other dielectric film is 5% or less relative to the thickness of either of the two dielectric films.

[0162] Silicon oxide is used as the material of the first dielectric film 36A and the second dielectric film 36B. However, the material of the first dielectric film 36A and the second dielectric film 36B is not limited to the above, and for example, dielectrics such as glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum oxide, or compounds in which fluorine, carbon, or boron is added to silicon oxide, or materials containing the above materials as a main component, can be used.

[0163] In this embodiment, the steepness of the pass band of the filter device can be increased. This will be described in detail below. Hereinafter, the first dielectric film 36A and the second dielectric film 36B may be collectively referred to simply as the dielectric film.

[0164] 37 is a diagram showing the relationship between the thickness of the dielectric film and the relative bandwidth, in which the thickness of the dielectric film and the relative bandwidth are shown as standard values.

[0165] As shown in Figure 37, the thicker the dielectric film, the smaller the value of the bandwidth ratio. In this embodiment, the second resonator 31B is a parallel arm resonator, as in the first embodiment. The second dielectric film 36B is thick. This makes it possible to reduce the bandwidth ratio of the second resonator 31B, which is a parallel arm resonator. This makes it possible to increase the steepness near the lower end of the pass band of the filter device.

[0166] However, the thickness of the first dielectric film 36A may be greater than the thickness of the second dielectric film 36B. The first resonator 31A is a series arm resonator. Therefore, the value of the bandwidth ratio can be reduced in the first resonator 31A, which is a series arm resonator. This can increase the steepness near the high-frequency end of the pass band of the filter device.

[0167] FIG. 38 is a schematic cross-sectional front view of a filter device according to a fourteenth embodiment.

[0168] This embodiment differs from the thirteenth embodiment in that the first dielectric film 46A and the second dielectric film 46B have the same thickness. This embodiment also differs from the thirteenth embodiment in that the material used for the first dielectric film 46A is different from the material used for the second dielectric film 46B. Except for the above points, the filter device of this embodiment has the same configuration as the filter device of the thirteenth embodiment.

[0169] In this embodiment, as in the thirteenth embodiment, the first piezoelectric substrate 2A is provided with the through electrodes 9, and the thickness of the first piezoelectric layer 5A of the first piezoelectric substrate 2A is thinner than the thickness of the second piezoelectric layer 5B of the second piezoelectric substrate 2B, thereby making it possible to suppress deterioration in the reliability of the filter device.

[0170] In addition, for example, the relative bandwidths of the first resonator 41A and the second resonator 41B can be adjusted by the materials used for the first dielectric film 46A and the second dielectric film 46B, thereby increasing the steepness of the passband of the filter device, as in the thirteenth embodiment.

[0171] As described above, at least one of the plurality of first resonators and the plurality of second resonators may be a BAW element. Examples of this are shown below in the fifteenth to nineteenth embodiments. In the fifteenth to nineteenth embodiments, similar to the first embodiment, a through electrode is provided in the first piezoelectric substrate, and the thickness of the first piezoelectric layer of the first piezoelectric substrate is thinner than the thickness of the second piezoelectric layer of the second piezoelectric substrate. This makes it possible to suppress deterioration in the reliability of the filter device in the fifteenth to nineteenth embodiments.

[0172] FIG. 39 is a schematic front cross-sectional view of an elastic wave device according to a fifteenth preferred embodiment of the present invention.

[0173] This embodiment differs from the first embodiment in the configuration of the first piezoelectric layer 55A and in that the plurality of first resonators include first resonators 51A that are BAW elements. This embodiment also differs from the first embodiment in that the first piezoelectric layer 55A is located inside the first support 6A in plan view. This embodiment also differs from the first embodiment in the configuration of the electrodes. Other than the above, the filter device of this embodiment has the same configuration as the filter device 1 of the first embodiment.

[0174] The first piezoelectric layer 55A has a portion that is convexly curved toward the second piezoelectric substrate 2B, and the first piezoelectric substrate 2B has a hollow portion 51a surrounded by the convexly curved portion of the first piezoelectric layer 55A and the first intermediate layer 4A.

[0175] The first functional electrode 52A of the first resonator 51A has a first excitation electrode 52a and a second excitation electrode 52b. The first excitation electrode 52a and the second excitation electrode 52b face each other with the first piezoelectric layer 5A in between. The first excitation electrode 52a is provided on the main surface of the first piezoelectric layer 5A facing the second piezoelectric substrate 2B. That is, the first excitation electrode 52a of the first functional electrode 52A is provided on the first main surface 2a of the first piezoelectric substrate.

[0176] A lead wire extends from the first excitation electrode 52a. In this embodiment, the first excitation electrode 52a and the lead wire are integrally formed from the same material. The lead wire is connected to an electrode pad 7 provided on the first piezoelectric layer 55A. Note that the first excitation electrode 52a and the lead wire may be individually formed from different materials. The lead wire may electrically connect the first excitation electrode 52a and the electrode pad 7.

[0177] On the other hand, the second excitation electrode 52b is provided on the main surface of the first piezoelectric layer 5A facing the first support substrate 3A. The second excitation electrode 52b is provided in the hollow portion 51a. A lead wire extends from the second excitation electrode 52b. In this embodiment, the second excitation electrode 52b and the lead wire are provided integrally using the same material. Note that the second excitation electrode 52b and the lead wire may be provided separately using different materials. The lead wire and the second excitation electrode 52b may be connected to each other.

[0178] A through electrode 59 other than the through electrode 9 is provided so as to penetrate the first piezoelectric layer 5A. Specifically, in this embodiment, the through electrode 59 penetrates only the first piezoelectric layer 5A among the multiple layers of the first piezoelectric substrate. An extraction wiring extending from the second excitation electrode 52b is connected to the through electrode 59. A wiring 56A is provided on the main surface of the first piezoelectric layer 55A facing the second piezoelectric substrate 2B. The wiring 56A electrically connects an electrode pad 57 provided on the first piezoelectric layer 55A to the through electrode 59. Note that the electrode pad 57 is a different electrode pad from the electrode pad 7 to which the first excitation electrode 52a is electrically connected.

[0179] The first excitation electrode 52a is electrically connected to the outside via a lead wiring, an electrode pad 7, a through electrode 9, and an external connection terminal 8. The second excitation electrode 52b is electrically connected to the outside via a lead wiring, a through electrode 59, a wiring 56A, an electrode pad 57, the through electrode 9, and an external connection terminal 8.

[0180] The first excitation electrode 52a and the second excitation electrode 52b are connected to different potentials, and bulk waves are excited by applying an AC voltage to the first excitation electrode 52a and the second excitation electrode 52b.

[0181] In this embodiment, the first piezoelectric layer 55A is located inside the first support 6A in a plan view. The first support 6A is provided on the first intermediate layer 4A of the first piezoelectric substrate. Note that the first support 6A may be provided on the first piezoelectric layer 55A.

[0182] FIG. 40 is a schematic front cross-sectional view of an elastic wave device according to a sixteenth preferred embodiment of the present invention.

[0183] This embodiment differs from the first embodiment in the configuration of the second piezoelectric layer 55B and in that the plurality of second resonators include second resonators 51B that are BAW elements. This embodiment also differs from the first embodiment in that the second piezoelectric layer 55B is located inside the first support 6A in plan view. This embodiment also differs from the first embodiment in the configuration of the electrodes. Other than the above, the filter device of this embodiment has the same configuration as the filter device 1 of the first embodiment.

[0184] The second piezoelectric layer 55B has a portion that is convexly curved toward the first piezoelectric substrate 2A, and the second piezoelectric substrate has a hollow portion 51b surrounded by the convexly curved portion of the second piezoelectric layer 55B and the second intermediate layer 4B.

[0185] The second functional electrode 52B of the second resonator 51B has a first excitation electrode 52c and a second excitation electrode 52d. The first excitation electrode 52c and the second excitation electrode 52d face each other with the second piezoelectric layer 5B interposed therebetween. The first excitation electrode 52c is provided on the main surface of the second piezoelectric layer 5B facing the first piezoelectric substrate 2A. That is, the first excitation electrode 52c of the second functional electrode 52B is provided on the third main surface 2c of the second piezoelectric substrate.

[0186] A lead wire extends from the first excitation electrode 52c. In this embodiment, the first excitation electrode 52c and the lead wire are integrally formed from the same material. The lead wire is connected to an electrode pad provided on the second piezoelectric layer 55B. Note that the first excitation electrode 52c and the lead wire may be individually formed from different materials. The lead wire may electrically connect the first excitation electrode 52c and the electrode pad.

[0187] On the other hand, the second excitation electrode 52d is provided on the main surface of the second piezoelectric layer 5B facing the second support substrate 3B. The second excitation electrode 52d is provided in the hollow portion 51b. A lead wire extends from the second excitation electrode 52d. In this embodiment, the second excitation electrode 52d and the lead wire are provided integrally using the same material. Note that the second excitation electrode 52d and the lead wire may be provided separately using different materials. The lead electrode and the second excitation electrode 52d may be connected.

[0188] A through electrode is provided so as to penetrate the second piezoelectric layer 55B. Specifically, in this embodiment, the through electrode penetrates only the second piezoelectric layer 55B among the multiple layers of the second piezoelectric substrate. An extraction wiring extending from the second excitation electrode 52d is connected to the through electrode. A wiring 56B is provided on the main surface of the second piezoelectric layer 55B facing the first piezoelectric substrate 2A. The wiring 56B electrically connects the through electrode to an electrode pad provided on the second piezoelectric layer 55B. Note that this electrode pad is different from the electrode pad electrically connected to the first excitation electrode 52c. A second support 6B is provided on the electrode pad.

[0189] A second support 6B is provided on the electrode pad to which the first excitation electrode 52c is electrically connected. Another second support 6B is also provided on the electrode pad to which the second excitation electrode 52d is electrically connected. These second supports 6B are each electrically connected to a different through electrode 9.

[0190] The first excitation electrode 52c is electrically connected to the outside via a lead-out wiring, an electrode pad, the second support 6B, the through electrode 9, and the external connection terminal 8. The second excitation electrode 52d is electrically connected to the outside via a lead-out wiring, the through electrode, a wiring 56B, an electrode pad, the second support 6B, the through electrode 9, and the external connection terminal 8.

[0191] In this embodiment, the second piezoelectric layer 55B is located inside the first support 6A in plan view. The first support 6A is provided on the second intermediate layer 4B of the second piezoelectric substrate. Note that the first support 6A may also be provided on the second piezoelectric layer 55B.

[0192] FIG. 41 is a schematic front cross-sectional view of an elastic wave device according to a seventeenth preferred embodiment of the present invention.

[0193] This embodiment differs from the fifteenth embodiment in the configuration of the second piezoelectric layer 55B and in that the plurality of second resonators include second resonators 51B that are BAW elements. This embodiment also differs from the fifteenth embodiment in that the second piezoelectric layer 55B is located inside the first support 6A in plan view. This embodiment also differs from the fifteenth embodiment in the configuration of the electrodes provided on the second piezoelectric substrate. Other than the above, the filter device of this embodiment has the same configuration as the filter device of the fifteenth embodiment.

[0194] That is, in the filter device of this embodiment, the plurality of first resonators include a first resonator 51A which is a BAW element, and the plurality of second resonators include a second resonator 51B which is a BAW element. Note that the configuration of the electrodes provided on the second piezoelectric substrate in this embodiment is the same as the configuration of the electrodes provided on the second piezoelectric substrate in the sixteenth embodiment.

[0195] FIG. 42 is a schematic front cross-sectional view of an elastic wave device according to an eighteenth preferred embodiment of the present invention.

[0196] This embodiment differs from the sixteenth embodiment in that the first intermediate layer 64A has through holes 64a, and the plurality of first resonators include a first resonator 61A configured to use a thickness-shear bulk wave as the main mode. Except for the above points, the filter device of this embodiment has the same configuration as the filter device of the sixteenth embodiment.

[0197] In the first piezoelectric substrate, one opening of the through hole 64a in the first intermediate layer 64A is blocked by the first piezoelectric layer 5A. The other opening of the through hole 64a is blocked by the first support substrate 3A. This provides a cavity in the first piezoelectric substrate. Alternatively, for example, a recess may be provided in the first intermediate layer 64A and the recess may be blocked by the first piezoelectric layer 5A. The first IDT electrode 12A of the first resonator 61A overlaps the cavity in the first piezoelectric substrate in a plan view.

[0198] In this embodiment, when the thickness of the first piezoelectric layer 5A is d and the electrode finger pitch of the first IDT electrode 12A is p, d / p≦0.5 is satisfied, which allows for suitable excitation of bulk waves in thickness-shear mode.

[0199] FIG. 43 is a schematic front cross-sectional view of an elastic wave device according to a nineteenth preferred embodiment of the present invention.

[0200] This embodiment differs from the fifteenth embodiment in that the second intermediate layer 64B has through holes 64b, and the plurality of second resonators include a second resonator 61B configured to be able to use a thickness-shear bulk wave as the main mode. Except for the above points, the filter device of this embodiment has the same configuration as the filter device of the fifteenth embodiment.

[0201] In the second piezoelectric substrate, one opening of the through hole 64b in the second intermediate layer 64B is blocked by the second piezoelectric layer 5B. The other opening of the through hole 64b is blocked by the second support substrate 3B. This provides a cavity in the second piezoelectric substrate. However, for example, a recess may be provided in the second intermediate layer 64B, and the recess may be blocked by the second piezoelectric layer 5B. The second IDT electrode 12B of the second resonator 61B overlaps the cavity in the second piezoelectric substrate in a plan view.

[0202] In this embodiment, when the thickness of the second piezoelectric layer 5B is d and the electrode finger pitch of the second IDT electrode 12B is p, d / p≦0.5 is satisfied, which allows the thickness-shear mode bulk wave to be suitably excited.

[0203] Examples of the configuration of the filter device according to the present invention will be summarized below.

[0204] <1> A piezoelectric element comprising: a first piezoelectric substrate having a first main surface and a second main surface opposed to each other; at least one first resonator including a functional electrode provided on the first main surface; a second piezoelectric substrate having a third main surface located on the first piezoelectric substrate side and a fourth main surface opposed to the third main surface; at least one second resonator including a functional electrode provided on the third main surface; a support provided between the first main surface and the third main surface so as to define a space between the first main surface and the third main surface; and a support provided so as to penetrate the first piezoelectric substrate. a through electrode electrically connected to at least one of the first resonators and at least one of the second resonators, wherein the first piezoelectric substrate has a first support substrate and a first piezoelectric layer laminated on the first support substrate, the first main surface including a main surface of the first piezoelectric layer, the second piezoelectric substrate has a second support substrate and a second piezoelectric layer laminated on the second support substrate, the third main surface including a main surface of the second piezoelectric layer, and the thickness of the first piezoelectric layer is thinner than the thickness of the second piezoelectric layer.

[0205] <2> The filter device according to <1>, wherein at least one ladder-type filter is configured including at least one of the first resonators and at least one of the second resonators, and at least one of the first resonators included in the at least one ladder-type filter is a series arm resonator of the ladder-type filter.

[0206] <3> The filter device according to <2>, comprising a plurality of the first resonators, a plurality of the first resonators among all the first resonators being included in at least one of the ladder-type filters, and all of the first resonators included in the ladder-type filter being series arm resonators of the ladder-type filter.

[0207] <4> The filter device according to <1> or <2>, wherein at least one ladder-type filter is configured including at least one of the first resonators and at least one of the second resonators, and at least one of the first resonators included in the at least one ladder-type filter is a parallel arm resonator of the ladder-type filter.

[0208] <5> The filter device according to <4>, comprising a plurality of the first resonators, a plurality of the first resonators among all the first resonators being included in at least one of the ladder-type filters, and all the first resonators included in the ladder-type filter being parallel arm resonators of the ladder-type filter.

[0209] <6> A filter device according to any one of <1> to <5>, wherein the functional electrode of the first resonator is a first IDT electrode provided on the first piezoelectric layer and having a plurality of electrode fingers, the functional electrode of the second resonator is a second IDT electrode provided on the second piezoelectric layer and having a plurality of electrode fingers, and the thickness of the first IDT electrode and the thickness of the second IDT electrode are different from each other.

[0210] <7> A filter device according to any one of <1> to <6>, wherein the functional electrode of the first resonator is a first IDT electrode provided on the first piezoelectric layer and having a plurality of electrode fingers, the functional electrode of the second resonator is a second IDT electrode provided on the second piezoelectric layer and having a plurality of electrode fingers, and a material used for the first IDT electrode is different from a material used for the second IDT electrode.

[0211] <8> A filter device according to any one of <1> to <7>, wherein the functional electrode of the first resonator is a first IDT electrode provided on the first piezoelectric layer and having a plurality of electrode fingers, the functional electrode of the second resonator is a second IDT electrode provided on the second piezoelectric layer and having a plurality of electrode fingers, and the direction in which the electrode fingers of the first IDT electrode extend intersects with the direction in which the electrode fingers of the second IDT electrode extend in a planar view.

[0212] <9> The filter device according to any one of <1> to <8>, wherein the functional electrode of the first resonator is a first IDT electrode provided on the first piezoelectric layer and having a plurality of electrode fingers, the functional electrode of the second resonator is a second IDT electrode provided on the second piezoelectric layer and having a plurality of electrode fingers, and further comprising: a first dielectric film provided on the first piezoelectric layer to cover the first IDT electrode; and a second dielectric film provided on the second piezoelectric layer to cover the second IDT electrode, wherein the thickness of the first dielectric film and the thickness of the second dielectric film are different from each other.

[0213] <10> The filter device according to any one of <1> to <9>, wherein a cut angle of the first piezoelectric layer and a cut angle of the second piezoelectric layer are different from each other.

[0214] <11> The filter device according to any one of <1> to <10>, wherein the material used for the first piezoelectric layer and the material used for the second piezoelectric layer are different from each other.

[0215] <12> A filter device described in any one of <1> to <11>, wherein the first piezoelectric substrate includes a first intermediate layer provided between the first support substrate and the first piezoelectric layer, the second piezoelectric substrate includes a second intermediate layer provided between the second support substrate and the second piezoelectric layer, and the thickness of the first intermediate layer and the thickness of the second intermediate layer are different from each other.

[0216] <13> A filter device described in any one of <1> to <12>, wherein the first piezoelectric substrate includes a first intermediate layer provided between the first support substrate and the first piezoelectric layer, the second piezoelectric substrate includes a second intermediate layer provided between the second support substrate and the second piezoelectric layer, and the material used for the first intermediate layer is different from the material used for the second intermediate layer.

[0217] <14> A filter device described in any one of <1> to <13>, wherein the first piezoelectric substrate includes a first intermediate layer provided between the first support substrate and the first piezoelectric layer, and the second piezoelectric substrate includes a second intermediate layer provided between the second support substrate and the second piezoelectric layer, and when, in a planar view, the outer circumferential edge of the portion of the through electrode that penetrates the first piezoelectric layer is defined as a first outer circumferential edge and the outer circumferential edge of the portion of the through electrode that penetrates the first intermediate layer is defined as a second outer circumferential edge, the first outer circumferential edge is located outside the second outer circumferential edge.

[0218] <15> A filter device described in any one of <1> to <14>, in which, in a planar view, when the outer peripheral edge of the portion of the through electrode that penetrates the first piezoelectric layer is defined as a first outer peripheral edge and the outer peripheral edge of the portion of the through electrode that penetrates the first support substrate is defined as a third outer peripheral edge, the first outer peripheral edge is located outside the third outer peripheral edge.

[0219] <16> The filter device according to any one of <1> to <13>, wherein the first piezoelectric substrate includes a first intermediate layer provided between the first support substrate and the first piezoelectric layer, and the second piezoelectric substrate includes a second intermediate layer provided between the second support substrate and the second piezoelectric layer, and when, in a planar view, the outer periphery of a portion of the through electrode that penetrates the first piezoelectric layer is defined as a first outer periphery, the outer periphery of a portion of the through electrode that penetrates the first intermediate layer is defined as a second outer periphery, the point where a straight line drawn from the center of the through electrode intersects with the first outer periphery is defined as a first point, and the point where the straight line intersects with the second outer periphery is defined as a second point, the dimension as the distance between the first point and the second point is equal to or less than the dimension as the thickness of the first intermediate layer.

[0220] <17> The filter device according to any one of <1> to <13> or <16>, wherein the first piezoelectric substrate includes a first intermediate layer provided between the first support substrate and the first piezoelectric layer, and the second piezoelectric substrate includes a second intermediate layer provided between the second support substrate and the second piezoelectric layer, and when, in a planar view, the outer periphery of a portion of the through electrode that penetrates the first piezoelectric layer is defined as a first outer periphery, the outer periphery of a portion of the through electrode that penetrates the first support substrate is defined as a third outer periphery, the point where a straight line drawn from the center of the through electrode intersects with the first outer periphery is defined as a first point, and the point where the straight line intersects with the third outer periphery is defined as a third point, the dimension as a distance between the first point and the third point is equal to or less than the dimension as a sum of the thickness of the first piezoelectric layer and the thickness of the first intermediate layer.

[0221] <18> The filter device according to any one of <1> to <17>, wherein the thickness of the first support substrate and the thickness of the second support substrate are different from each other.

[0222] <19> The filter device according to any one of <1> to <18>, wherein the first support substrate and the second support substrate have different ψ angles in the Euler angles (φ, θ, ψ).

[0223] <20> The filter device according to any one of <1> to <19>, wherein the material used for the first support substrate and the material used for the second support substrate are different from each other.

[0224] REFERENCE SIGNS LIST 1...Filter device 1A, 1B...First and second resonators 1C...First resonator 2A, 2B...First and second piezoelectric substrates 2a, 2b...First and second main surfaces 2c, 2d...Third and fourth main surfaces 3A, 3B...First and second support substrates 4A, 4B...First and second intermediate layers 5A, 5B...First and second piezoelectric layers 6A, 6B...First and second supports 7...Electrode pad 8...External connection terminal 9, 9A...Through-through electrodes 9a to 9c...First to third outer peripheries 10...Bump 11...Mounting substrate 12A, 12B...First and second IDT electrodes 12C to 12G...First IDT electrodes 13A, 13B...Reflectors 14...Shield electrode 15...Sealing resin layer REFERENCE SIGNS 16, 17... First and second bus bars 18, 19... First and second electrode fingers 21A, 21B... First and second resonators 22A, 22B... First and second IDT electrodes 23A, 23B... First and second support substrates 24A, 24B... First and second intermediate layers 25A, 25B... First and second piezoelectric layers 31A, 31B... First and second resonators 36A, 36B... First and second dielectric films 41A, 41B... First and second resonators 46A, 46B... First and second dielectric films 51A, 51B... First and second resonators 51a, 51b... Hollow portions 52A, 52B... First and second functional electrodes 52a, 52b... first and second excitation electrodes 52c, 52d... first and second excitation electrodes 55A, 55B... first and second piezoelectric layers 56A, 56B... wiring 57... electrode pad 59... through electrode 61A, 61B... first and second resonators 64A, 64B... first and second intermediate layers 64a, 64b... through holes 100... suction collet

Claims

1. A piezoelectric element comprising: a first piezoelectric substrate having a first main surface and a second main surface opposed to each other; at least one first resonator including a functional electrode provided on the first main surface; a second piezoelectric substrate having a third main surface located on the first piezoelectric substrate side and a fourth main surface opposed to the third main surface; at least one second resonator including a functional electrode provided on the third main surface; a support provided between the first main surface and the third main surface such that a space is defined between the first main surface and the third main surface; and a through electrode provided so as to penetrate the first piezoelectric substrate and electrically connected to at least one of the first resonator and at least one of the second resonators; wherein the first piezoelectric substrate has a first support substrate and a first piezoelectric layer laminated on the first support substrate, and the first main surface includes the main surface of the first piezoelectric layer; a filter device, wherein the second piezoelectric substrate has a second support substrate and a second piezoelectric layer laminated with the second support substrate, the third main surface includes a main surface of the second piezoelectric layer, and a thickness of the first piezoelectric layer is smaller than a thickness of the second piezoelectric layer.

2. The filter device according to claim 1, wherein at least one ladder-type filter is configured including at least one of the first resonators and at least one of the second resonators, and at least one of the first resonators included in the at least one ladder-type filter is a series arm resonator of the ladder-type filter.

3. The filter device according to claim 2, comprising a plurality of the first resonators, a plurality of the first resonators among all of the first resonators being included in at least one of the ladder type filters, and all of the first resonators included in the ladder type filter being series arm resonators of the ladder type filter.

4. A filter device according to claim 1 or 2, wherein at least one ladder-type filter is configured including at least one of the first resonators and at least one of the second resonators, and at least one of the first resonators included in the at least one ladder-type filter is a parallel arm resonator of the ladder-type filter.

5. The filter device according to claim 4, comprising a plurality of the first resonators, a plurality of the first resonators among all of the first resonators being included in at least one of the ladder type filters, and all of the first resonators included in the ladder type filter being parallel arm resonators of the ladder type filter.

6. A filter device as claimed in any one of claims 1 to 5, wherein the functional electrode of the first resonator is a first IDT electrode provided on the first piezoelectric layer and having a plurality of electrode fingers, the functional electrode of the second resonator is a second IDT electrode provided on the second piezoelectric layer and having a plurality of electrode fingers, and the thickness of the first IDT electrode and the thickness of the second IDT electrode are different from each other.

7. A filter device as claimed in any one of claims 1 to 6, wherein the functional electrode of the first resonator is a first IDT electrode provided on the first piezoelectric layer and having a plurality of electrode fingers, the functional electrode of the second resonator is a second IDT electrode provided on the second piezoelectric layer and having a plurality of electrode fingers, and a material used for the first IDT electrode and a material used for the second IDT electrode are different from each other.

8. A filter device as claimed in any one of claims 1 to 7, wherein the functional electrode of the first resonator is a first IDT electrode provided on the first piezoelectric layer and having a plurality of electrode fingers, the functional electrode of the second resonator is a second IDT electrode provided on the second piezoelectric layer and having a plurality of electrode fingers, and the extension direction of the plurality of electrode fingers of the first IDT electrode intersects with the extension direction of the plurality of electrode fingers of the second IDT electrode in a planar view.

9. A filter device as claimed in any one of claims 1 to 8, further comprising: the functional electrode of the first resonator is a first IDT electrode provided on the first piezoelectric layer and having a plurality of electrode fingers; the functional electrode of the second resonator is a second IDT electrode provided on the second piezoelectric layer and having a plurality of electrode fingers; a first dielectric film provided on the first piezoelectric layer so as to cover the first IDT electrode; and a second dielectric film provided on the second piezoelectric layer so as to cover the second IDT electrode; and wherein the thickness of the first dielectric film and the thickness of the second dielectric film are different from each other.

10. A filter device according to any one of claims 1 to 9, wherein a cut angle of the first piezoelectric layer and a cut angle of the second piezoelectric layer are different from each other.

11. A filter device according to any one of claims 1 to 10, wherein a material used for the first piezoelectric layer and a material used for the second piezoelectric layer are different from each other.

12. A filter device as described in any one of claims 1 to 11, wherein the first piezoelectric substrate includes a first intermediate layer provided between the first support substrate and the first piezoelectric layer, the second piezoelectric substrate includes a second intermediate layer provided between the second support substrate and the second piezoelectric layer, and the first intermediate layer and the second intermediate layer have different thicknesses.

13. A filter device as described in any one of claims 1 to 12, wherein the first piezoelectric substrate includes a first intermediate layer provided between the first support substrate and the first piezoelectric layer, the second piezoelectric substrate includes a second intermediate layer provided between the second support substrate and the second piezoelectric layer, and a material used for the first intermediate layer and a material used for the second intermediate layer are different from each other.

14. A filter device as described in any one of claims 1 to 13, wherein the first piezoelectric substrate includes a first intermediate layer provided between the first support substrate and the first piezoelectric layer, and the second piezoelectric substrate includes a second intermediate layer provided between the second support substrate and the second piezoelectric layer, and when, in a plan view, the outer periphery of a portion of the through electrode that penetrates the first piezoelectric layer is defined as a first outer periphery and the outer periphery of a portion of the through electrode that penetrates the first intermediate layer is defined as a second outer periphery, the first outer periphery is located outside the second outer periphery.

15. A filter device as described in any one of claims 1 to 14, wherein, in a plan view, when the outer periphery of the portion of the through electrode that penetrates the first piezoelectric layer is defined as a first outer periphery and the outer periphery of the portion of the through electrode that penetrates the first support substrate is defined as a third outer periphery, the first outer periphery is located outside the third outer periphery.

16. A filter device according to any one of claims 1 to 13, wherein the first piezoelectric substrate includes a first intermediate layer provided between the first support substrate and the first piezoelectric layer, and the second piezoelectric substrate includes a second intermediate layer provided between the second support substrate and the second piezoelectric layer, and wherein, in a plan view, the outer periphery of a portion of the through electrode that penetrates the first piezoelectric layer is defined as a first outer periphery, the outer periphery of a portion of the through electrode that penetrates the first intermediate layer is defined as a second outer periphery, a point where a straight line drawn from the center of the through electrode intersects with the first outer periphery is defined as a first point, and a point where the straight line intersects with the second outer periphery is defined as a second point, and the dimension as the distance between the first point and the second point is equal to or less than the dimension as the thickness of the first intermediate layer.

17. A filter device according to any one of claims 1 to 13 or 16, wherein the first piezoelectric substrate includes a first intermediate layer provided between the first support substrate and the first piezoelectric layer, and the second piezoelectric substrate includes a second intermediate layer provided between the second support substrate and the second piezoelectric layer, and wherein, in a plan view, the outer periphery of a portion of the through electrode that penetrates the first piezoelectric layer is defined as a first outer periphery, the outer periphery of a portion of the through electrode that penetrates the first support substrate is defined as a third outer periphery, a point where a straight line drawn from the center of the through electrode intersects with the first outer periphery is defined as a first point, and a point where the straight line intersects with the third outer periphery is defined as a third point, and the dimension as the distance between the first point and the third point is equal to or less than the dimension as the sum of the thickness of the first piezoelectric layer and the thickness of the first intermediate layer.

18. The filter device according to any one of claims 1 to 17, wherein the first support substrate and the second support substrate have different thicknesses.

19. A filter device according to any one of claims 1 to 18, wherein the Euler angles (φ, θ, ψ) of the first support substrate and the second support substrate are different from each other.

20. A filter device according to any one of claims 1 to 19, wherein a material used for the first support substrate and a material used for the second support substrate are different from each other.

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