Acoustic wave device

Abstract

An acoustic wave filter (1) comprises: a parallel branch resonator (22) connected between ground and a series branch path connecting input / output terminals (110 and 120); a parallel branch resonator (25) connected between the aforementioned series branch path and ground; a series branch resonator (12) arranged in series in the series branch path; a capacitor (32) connected in parallel to the parallel branch resonator (22); and a capacitor (35) connected in parallel to the parallel branch resonator (25). The parallel branch resonators (22 and 25) and the series branch resonator (12) each include an IDT electrode formed on a substrate having piezoelectric properties. The capacitors (32 and 35) each include a pair of interdigital electrodes formed on a substrate having piezoelectric properties. The direction in which the electrode fingers of the IDT electrodes extend and the direction in which the electrode fingers of the pair of interdigital electrodes extend intersect. The antiresonance frequency (fa32) of the capacitor (32) and the antiresonance frequency (fa35) of the capacitor (35) are different.

Description

Elastic Wave Device

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

[0002] Patent Document 1 discloses an elastic wave device including a series arm resonator disposed in a series arm path connecting two signal terminals, a parallel arm resonator connected between the series arm path and a first reference electrode, and a capacitive element connected between the series arm path and a second reference electrode. The above configuration is said to provide an elastic wave device with low insertion loss and high attenuation in the high frequency range.

[0003] JP 2013-243570 A

[0004] However, in the elastic wave device described in Patent Document 1, depending on the structure of the piezoelectric substrate or the elastic wave mode used, higher-order mode spurious signals caused by the capacitive element may occur in a band higher than the pass band, resulting in a deterioration in attenuation characteristics.

[0005] SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an elastic wave device with improved attenuation characteristics.

[0006] In order to achieve the above object, an elastic wave device according to one aspect of the present invention includes: a first elastic wave resonator connected between a series arm path connecting a first input / output terminal and a second input / output terminal and ground; a second elastic wave resonator connected between the series arm path and ground; a third elastic wave resonator arranged in series in the series arm path; a first capacitive element connected in parallel to the first elastic wave resonator; and a second capacitive element connected in parallel to the second elastic wave resonator. Each of the first elastic wave resonator, the second elastic wave resonator, and the third elastic wave resonator includes an InterDigital Transistor (IDT) formed on a piezoelectric substrate. The first capacitance element and the second capacitance element each include a pair of comb electrodes formed on a substrate, the IDT electrode has a plurality of first electrode fingers arranged parallel to each other and a set of first bus bar electrodes arranged opposite each other with the plurality of first electrode fingers interposed therebetween, the pair of comb electrodes has a plurality of second electrode fingers arranged parallel to each other and a set of second bus bar electrodes arranged opposite each other with the plurality of second electrode fingers interposed therebetween, the extension direction of the plurality of first electrode fingers intersects the extension direction of the plurality of second electrode fingers, and the anti-resonance frequency of the first capacitance element and the anti-resonance frequency of the second capacitance element are different.

[0007] An elastic wave device according to one aspect of the present invention includes a first elastic wave resonator arranged in series in a series arm path connecting a first input / output terminal and a second input / output terminal, a second elastic wave resonator arranged in series in the series arm path, a third elastic wave resonator connected between the series arm path and ground, a first capacitive element connected in parallel to the first elastic wave resonator, and a second capacitive element connected in parallel to the second elastic wave resonator, wherein each of the first elastic wave resonator, the second elastic wave resonator, and the third elastic wave resonator includes an IDT electrode formed on a piezoelectric substrate, and the first capacitive element and the second capacitance element each includes a pair of comb-shaped electrodes formed on a substrate, the IDT electrode having a plurality of first electrode fingers arranged parallel to each other and a set of first bus bar electrodes arranged opposite each other with the plurality of first electrode fingers in between, the pair of comb-shaped electrodes having a plurality of second electrode fingers arranged parallel to each other and a set of second bus bar electrodes arranged opposite each other with the plurality of second electrode fingers in between, the extension direction of the plurality of first electrode fingers intersects with the extension direction of the plurality of second electrode fingers, and the resonant frequency of the first capacitance element and the resonant frequency of the second capacitance element are different.

[0008] An elastic wave device according to one aspect of the present invention includes a first elastic wave resonator arranged in series in a series arm path connecting a first input / output terminal and a second input / output terminal, a second elastic wave resonator connected between the series arm path and ground, a third elastic wave resonator arranged in series in the series arm path or connected between the series arm path and ground, a first capacitive element connected in parallel to the first elastic wave resonator, and a second capacitive element connected in parallel to the second elastic wave resonator, wherein each of the first elastic wave resonator, the second elastic wave resonator, and the third elastic wave resonator includes an IDT electrode formed on a piezoelectric substrate, and the first capacitive element and the second capacitive element Each of them includes a pair of comb-shaped electrodes formed on a substrate, the IDT electrode having a plurality of first electrode fingers arranged parallel to each other and a set of first bus bar electrodes arranged opposite each other with the plurality of first electrode fingers in between, the pair of comb-shaped electrodes having a plurality of second electrode fingers arranged parallel to each other and a set of second bus bar electrodes arranged opposite each other with the plurality of second electrode fingers in between, the extension direction of the plurality of first electrode fingers intersects the extension direction of the plurality of second electrode fingers, and the anti-resonance frequency of the second capacitance element is smaller than the resonance frequency of the first capacitance element, or the anti-resonance frequency of the second capacitance element is larger than the anti-resonance frequency of the first capacitance element.

[0009] An elastic wave device according to an aspect of the present invention includes a first elastic wave resonator, a second elastic wave resonator, and a third elastic wave resonator; a first capacitive element connected in parallel to the first elastic wave resonator; and a second capacitive element connected in parallel to the second elastic wave resonator. The first and second elastic wave resonators are both arranged in series in a series arm path connecting a first input / output terminal and a second input / output terminal, and the third elastic wave resonator is connected between the series arm path and ground. Alternatively, the first and second elastic wave resonators are both connected between the series arm path and ground, and the third elastic wave resonator is arranged in series in the series arm path. Each of the piezoelectric resonators includes an IDT electrode formed on a piezoelectric substrate, and each of the first capacitive element and the second capacitive element includes a pair of comb electrodes formed on the substrate, and the IDT electrodes have a plurality of first electrode fingers arranged parallel to each other and a set of first bus bar electrodes arranged opposite each other with the plurality of first electrode fingers interposed therebetween, and the pair of comb electrodes have a plurality of second electrode fingers arranged parallel to each other and a set of second bus bar electrodes arranged opposite each other with the plurality of second electrode fingers interposed therebetween, and the extension direction of the plurality of first electrode fingers intersects with the extension direction of the plurality of second electrode fingers, and the electrode finger pitch of the first capacitive element is different from the electrode finger pitch of the second capacitive element.

[0010] An elastic wave device according to an aspect of the present invention includes a first elastic wave resonator, a second elastic wave resonator, and a third elastic wave resonator; a first capacitive element connected in parallel to the first elastic wave resonator; and a second capacitive element connected in parallel to the second elastic wave resonator. The first and second elastic wave resonators are both connected in series to a series arm path connecting a first input / output terminal and a second input / output terminal, and the third elastic wave resonator is connected between the series arm path and ground. Alternatively, the first and second elastic wave resonators are both connected between the series arm path and ground, and the third elastic wave resonator is connected in series to the series arm path. Each of the acoustic wave resonators includes an IDT electrode formed on a piezoelectric substrate, and each of the first capacitive element and the second capacitive element includes a pair of comb electrodes formed on the substrate, the IDT electrodes having a plurality of first electrode fingers arranged parallel to each other and a set of first bus bar electrodes arranged opposite each other with the plurality of first electrode fingers in between, the pair of comb electrodes having a plurality of second electrode fingers arranged parallel to each other and a set of second bus bar electrodes arranged opposite each other with the plurality of second electrode fingers in between, the extension direction of the plurality of first electrode fingers intersects the extension direction of the plurality of second electrode fingers, and the electrode finger duty of the first capacitive element is different from the electrode finger duty of the second capacitive element.

[0011] According to the present invention, it is possible to provide an acoustic wave device with improved attenuation characteristics.

[0012] FIG. 1 is a circuit diagram of an acoustic wave filter according to an embodiment. FIG. 2A is a plan view and a cross-sectional view schematically illustrating a first example of an acoustic wave resonator included in an acoustic wave filter according to an embodiment. FIG. 2B is a cross-sectional view schematically illustrating a second example of an acoustic wave resonator included in an acoustic wave filter according to an embodiment. FIG. 3 is a plan view illustrating an electrode arrangement of an acoustic wave resonator and a capacitive element according to an embodiment. FIG. 4A is a graph illustrating impedance characteristics of a capacitive element included in an acoustic wave filter according to an example. FIG. 4B is a graph illustrating the relationship between resonance characteristics of two capacitive elements included in an acoustic wave filter according to an example. FIG. 4C is a graph illustrating the pass characteristics of acoustic wave filters according to an example and a comparative example. FIG. 5A is a circuit diagram of an acoustic wave filter according to a first modification of the embodiment. FIG. 5B is a graph illustrating the relationship between resonance characteristics of two capacitive elements included in an acoustic wave filter according to the first modification of the embodiment. FIG. 6A is a circuit diagram of an acoustic wave filter according to a second modification of the embodiment. FIG. 6B is a graph illustrating the relationship between resonance characteristics of two capacitive elements included in an acoustic wave filter according to the second modification of the embodiment.

[0013] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, arrangements and connection forms of the components shown in the following embodiments are merely examples and are not intended to limit the present invention.

[0014] It should be noted that the drawings are schematic diagrams in which emphasis, omission, or adjustment of proportions has been appropriately made to illustrate the present invention, and are not necessarily strictly illustrated, and may differ from the actual shapes, positional relationships, and proportions. In the drawings, the same reference numerals are used to denote substantially the same components, and redundant explanations may be omitted or simplified.

[0015] In the circuit configuration of the present disclosure, "connected between A and B" means connected to both A and B between A and B. This also includes the case where the circuit is indirectly connected to A and B.

[0016] Furthermore, in the component arrangement of the present disclosure, "component A is arranged in series on path B" means that both the signal input terminal and the signal output terminal of component A are connected to the wiring, electrode, or terminal that constitutes path B.

[0017] Furthermore, terms indicating the relationship between elements, such as "parallel" and "perpendicular," terms indicating the shape of elements, such as "rectangle," and numerical ranges do not only represent strict meanings, but also include substantially equivalent ranges, for example, including an error of a few percent.

[0018] Also, in this disclosure, "terminal" means a point where a conductor within an element terminates, and is to be construed as any point on the conductor between elements or the entire conductor, not just a single point, provided the impedance of the conductor between elements is sufficiently low.

[0019] In addition, in the disclosure, an "input / output terminal" is a terminal that has at least one of the functions of an input terminal and an output terminal.

[0020] In addition, in this disclosure, the passband of an acoustic wave device or filter is defined as the frequency band between two frequencies that are 3 dB greater than the minimum insertion loss within the passband.

[0021] Furthermore, the resonant frequency and antiresonant frequency shown in the above embodiments and modifications are derived, for example, by contacting an RF probe with two input / output electrodes of an elastic wave resonator or a capacitive element when the elastic wave resonator or capacitive element is not connected to other circuit elements, and measuring the reflection characteristics (impedance characteristics) using a network analyzer or the like.

[0022] Furthermore, "two resonant frequencies are different" and "two anti-resonant frequencies are different" are defined as the difference between two measured resonant frequencies (or two anti-resonant frequencies) being 0.1% or more. The difference includes the error of the measuring device. Furthermore, "one resonant frequency is greater than one anti-resonant frequency" and "one resonant frequency is smaller than one anti-resonant frequency" are defined as the measured one resonant frequency being 0.1% or more greater (smaller) than the measured one anti-resonant frequency. The difference between the measured one resonant frequency and the measured one anti-resonant frequency includes the error of the measuring device.

[0023] In the present disclosure, the term "band" refers to at least one of an uplink operating band and a downlink operating band of a frequency band predefined by a standardization organization (e.g., 3GPP (registered trademark), IEEE (Institute of Electrical and Electronics Engineers)), etc., for a communication system built using a radio access technology (RAT). In this embodiment, examples of communication systems that can be used include, but are not limited to, an LTE (Long Term Evolution) system, a 5G (5th Generation)-NR (New Radio) system, and a WLAN (Wireless Local Area Network) system. Note that the uplink operating band of a frequency band refers to a frequency range designated for uplink within that frequency band. Furthermore, the downlink operating band of a frequency band refers to a frequency range designated for downlink within that frequency band.

[0024] 1 is a circuit diagram of an elastic wave filter 1 according to an embodiment of the present invention. As shown in the figure, the elastic wave filter 1 is an example of an elastic wave device and includes series arm resonators 11, 12, 13, 14, and 15, parallel arm resonators 21, 22, 23, 24, 25, and 26, capacitors 32 and 35, and input / output terminals 110 and 120.

[0025] Each of the series arm resonators 11 to 15 includes an acoustic wave resonator and is arranged in series in a series arm path connecting the input / output terminal 110 (first input / output terminal) and the input / output terminal 120 (second input / output terminal). Each of the series arm resonators 11 to 15 is an example of a third acoustic wave resonator, and the series arm resonators 11, 12, 13, 14, and 15 are connected in this order from the input / output terminal 110. Note that at least one of the series arm resonators 11 to 15 does not necessarily have to be included in the acoustic wave filter 1.

[0026] Each of the parallel arm resonators 21 to 26 includes an acoustic wave resonator and is connected between the series arm path and ground. The parallel arm resonator 21 is connected between the connection point of the input / output terminal 110 and the series arm resonator 11 and ground. The parallel arm resonator 22 is an example of a first acoustic wave resonator and is connected between the connection point of the series arm resonators 11 and 12 and ground. The parallel arm resonator 23 is connected between the connection point of the series arm resonators 12 and 13 and ground. The parallel arm resonator 24 is connected between the connection point of the series arm resonators 13 and 14 and ground. The parallel arm resonator 25 is an example of a second acoustic wave resonator and is connected between the connection point of the series arm resonators 14 and 15 and ground. The parallel arm resonator 26 is connected between the connection point of the series arm resonator 15 and the input / output terminal 120 and ground. At least one of the parallel arm resonators 21, 23, 24, and 26 does not have to be included in the acoustic wave filter 1.

[0027] Each of the series arm resonators 11 to 15 and the parallel arm resonators 21 to 26 includes an IDT electrode formed on a piezoelectric substrate.

[0028] The capacitor 32 is an example of a first capacitance element, and is connected in parallel to the parallel arm resonator 22. Specifically, one end of the capacitor 32 is connected to a connection node n1 between the series arm resonator 11, the series arm resonator 12, and the parallel arm resonator 22, and the other end of the capacitor 32 is connected to a connection node n2 between the parallel arm resonator 22 and ground. The capacitor 32 is a so-called bridging capacitance connected in parallel to the parallel arm resonator 22.

[0029] The capacitor 35 is an example of a second capacitance element, and is connected in parallel to the parallel arm resonator 25. Specifically, one end of the capacitor 35 is connected to a connection node n3 between the series arm resonator 14, the series arm resonator 15, and the parallel arm resonator 25, and the other end of the capacitor 35 is connected to a connection node n4 between the parallel arm resonator 25 and ground. The capacitor 35 is a so-called bridging capacitance connected in parallel to the parallel arm resonator 25.

[0030] Each of the capacitors 32 and 35 includes a pair of comb electrodes formed on a piezoelectric substrate, and resonates with the pair of comb electrodes and the substrate. As a result, each of the capacitors 32 and 35 has a resonant frequency at which the impedance is minimized and an anti-resonant frequency at which the impedance is maximized.

[0031] Here, the anti-resonance frequency fa32 of the capacitor 32 and the anti-resonance frequency fa35 of the capacitor 35 are different.

[0032] This makes it possible to suppress higher-order mode spurious responses caused by capacitors 32 and 35 in the attenuation band higher than the pass band of elastic wave filter 1, thereby making it possible to provide elastic wave filter 1 with improved attenuation characteristics higher than the pass band.

[0033] In this embodiment, "the anti-resonant frequency of the first capacitance element is different from the anti-resonant frequency of the second capacitance element" means that the first-order anti-resonant frequency of the first capacitance element is different from the first-order anti-resonant frequency of the second capacitance element. In other words, the orders of the anti-resonant frequencies of the first capacitance element and the second capacitance element to be compared are the same.

[0034] By measuring the material, film thickness, and dimensions of the elastic wave resonator and analyzing it using the finite element method, it is possible to determine whether the anti-resonance frequency is in a higher order mode and what order it is.

[0035] The capacitor 32 does not have to be connected in parallel to the parallel arm resonator 22, but may be connected in parallel to any of the parallel arm resonators 21, 23, 24, and 26. The capacitor 35 does not have to be connected in parallel to the parallel arm resonator 25, but may be connected in parallel to any of the parallel arm resonators 21, 23, 24, and 26.

[0036] In this embodiment, no capacitor is connected in parallel to each of the series arm resonators 11 to 15.

[0037] The number of series arm resonators included in the acoustic wave filter 1 may be six or more, and the number of parallel arm resonators may be seven or more.

[0038] Furthermore, longitudinally coupled resonators, inductors, capacitors, switches, etc. may be connected between the series arm resonators 11 to 15, the parallel arm resonators 21 to 26, the ground, and the input / output terminals 110 and 120. The inductors may include wiring inductors formed by wiring connecting the components, wiring within the packaging member, and conductive vias.

[0039] The structure and resonance characteristics of the acoustic wave filter 1 will be described in detail below.

[0040] [2. Structures of Acoustic Wave Resonators and Capacitor Elements] Next, examples of structures of the acoustic wave resonators (series arm resonators and parallel arm resonators) and capacitor elements that constitute the acoustic wave filter 1 will be described.

[0041] 2A is a plan view and a cross-sectional view schematically illustrating a first example of an acoustic wave resonator that constitutes the acoustic wave filter 1 according to an embodiment. The drawings illustrate the basic structure of an acoustic wave resonator that constitutes the acoustic wave filter 1. Note that the acoustic wave resonator 60 shown in FIG. 2A is intended to illustrate a typical structure of a surface acoustic wave (SAW) resonator that constitutes the acoustic wave filter 1, and the number and length of electrode fingers that constitute the electrodes are not limited to this example.

[0042] The acoustic wave resonator 60 is composed of a piezoelectric substrate 50 and comb-shaped electrodes 60a and 60b.

[0043] 2A (a), a pair of comb-shaped electrodes 60a and 60b facing each other is formed on a piezoelectric substrate 50. The comb-shaped electrode 60a is composed of a plurality of parallel electrode fingers 61a (first electrode fingers) and a busbar electrode 62a (first busbar electrode) connecting the plurality of electrode fingers 61a. The comb-shaped electrode 60b is composed of a plurality of parallel electrode fingers 61b (first electrode fingers) and a busbar electrode 62b (first busbar electrode) connecting the plurality of electrode fingers 61b. When the elastic wave resonator 60 is composed of the series arm resonators 11 to 15 and the parallel arm resonators 21 to 26, the plurality of electrode fingers 61a and 61b are formed in a direction perpendicular to the elastic wave propagation direction (X-axis direction).

[0044] As shown in FIG. 2A(c), the acoustic wave resonator in this example includes an IDT electrode 54, a protective layer 55, and a piezoelectric substrate 50.

[0045] The IDT electrode 54, which is composed of a plurality of electrode fingers 61a and 61b and bus bar electrodes 62a and 62b, has a laminated structure of an adhesive layer 540 and a main electrode layer 542, as shown in FIG. 2A(b).

[0046] The adhesion layer 540 is a layer for improving adhesion between the piezoelectric substrate 50 and the main electrode layer 542, and is made of, for example, Ti. The main electrode layer 542 is made of, for example, Al containing 1% Cu.

[0047] The protective layer 55 is formed to cover the IDT electrode 54. The protective layer 55 is a layer intended to protect the main electrode layer 542 from the external environment, adjust the frequency-temperature characteristics, and increase moisture resistance, and is, for example, a dielectric film containing silicon dioxide as its main component.

[0048] The materials constituting the adhesion layer 540, the main electrode layer 542, and the protective layer 55 are not limited to those described above. Furthermore, the IDT electrode 54 does not have to have the laminated structure described above. The IDT electrode 54 may be made of, for example, a metal or alloy such as Ti, Al, Cu, Pt, Au, Ag, or Pd, or may be made of a laminate of multiple layers made of the above metals or alloys. Furthermore, the protective layer 55 does not necessarily have to be formed.

[0049] Next, the laminated structure of the piezoelectric substrate 50 will be described.

[0050] As shown in (c) of FIG. 2A, the piezoelectric substrate 50 includes a high acoustic velocity support substrate 51, a low acoustic velocity layer 52, and a piezoelectric layer 53, and has a structure in which the high acoustic velocity support substrate 51, the low acoustic velocity layer 52, and the piezoelectric layer 53 are laminated in this order.

[0051] The piezoelectric layer 53 is, for example, a θ° Y-cut X-propagation LiTaO ３ It is made of a piezoelectric single crystal or piezoelectric ceramics (a lithium tantalate single crystal or ceramics cut along a plane whose normal is an axis rotated θ degrees from the Y axis around the X axis, and through which surface acoustic waves propagate in the X axis direction). The material and cut angle θ of the piezoelectric single crystal used as the piezoelectric layer 53 are appropriately selected depending on the required specifications of each filter.

[0052] The high acoustic velocity support substrate 51 is a substrate that supports the low acoustic velocity layer 52, the piezoelectric layer 53, and the IDT electrode 54. The high acoustic velocity support substrate 51 is also a substrate in which the acoustic velocity of bulk waves in the high acoustic velocity support substrate 51 is faster than that of acoustic waves such as surface waves and boundary waves that propagate through the piezoelectric layer 53, and functions to confine the surface acoustic waves to the portion where the piezoelectric layer 53 and the low acoustic velocity layer 52 are stacked, preventing them from leaking below the high acoustic velocity support substrate 51. Examples of materials that can be used for the high acoustic velocity support substrate 51 include piezoelectrics 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; dielectrics such as aluminum oxide, silicon oxynitride, DLC (diamond-like carbon), and diamond; semiconductors such as silicon; and materials containing any of the above materials as a main component. The spinel includes aluminum compounds containing oxygen and one or more elements selected from Mg, Fe, Zn, Mn, etc. Examples of the spinel include MgAl ２ O ４ , FeAl ２ O ４ , ZnAl ２ O ４ , MnAl ２ O ４ Examples include:

[0053] The low acoustic velocity layer 52 is a film in which the acoustic velocity of the bulk waves in the low acoustic velocity layer 52 is slower than that of the bulk waves propagating through the piezoelectric layer 53, and is disposed between the piezoelectric layer 53 and the high acoustic velocity support substrate 51. This structure and the property of the acoustic waves that energy is concentrated in a medium with an essentially low acoustic velocity suppress leakage of surface acoustic wave energy out of the piezoelectric layer 53. Examples of materials that can be used for the low acoustic velocity layer 52 include dielectrics such as glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum oxide, and compounds in which fluorine, carbon, or boron is added to silicon oxide, as well as materials containing any of the above materials as their main components.

[0054] The above-described laminated structure of piezoelectric substrate 50 makes it possible to significantly increase the Q value at the resonant frequency and antiresonant frequency compared to a conventional structure using a single-layer piezoelectric substrate. In other words, an elastic wave resonator with a high Q value can be configured, and a filter with low insertion loss can be configured using the elastic wave resonator.

[0055] The high acoustic velocity support substrate 51 may have a laminated structure of a support substrate and a high acoustic velocity film in which the acoustic velocity of the propagating bulk waves is faster than that of elastic waves such as surface waves and boundary waves that propagate through the piezoelectric layer 53. In this case, the material of the high acoustic velocity film can be the same as the material of the high acoustic velocity support substrate 51. The material of the support substrate can be, for example, piezoelectrics such as aluminum nitride, lithium tantalate, lithium niobate, and quartz; ceramics such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, and forsterite; dielectrics such as diamond and glass; semiconductors such as silicon and gallium nitride; resins; or materials containing any of the above materials as a main component.

[0056] In this specification, the term "major component of a material" refers to a component that accounts for more than 50% by weight of the material. The major component may be in a single crystal, polycrystalline, or amorphous state, or a mixture of these.

[0057] 2B is a cross-sectional view schematically illustrating a second example of an acoustic wave resonator constituting the acoustic wave filter 1 according to the embodiment. In the acoustic wave resonator 60 illustrated in FIG. 2A , the IDT electrode 54 is formed on the piezoelectric substrate 50 having the piezoelectric layer 53. However, the substrate on which the IDT electrode 54 is formed may be a piezoelectric single crystal substrate 57 having a single piezoelectric layer, as illustrated in FIG. 2B .

[0058] The acoustic wave resonator constituting the acoustic wave filter 1 includes an IDT electrode 54 , a protective layer 55 , and a piezoelectric substrate 50 .

[0059] As shown in FIG. 2B, the acoustic wave resonator in this example includes an IDT electrode 54, a dielectric layer 58, an adjustment film 59, and a piezoelectric single crystal substrate 57.

[0060] The piezoelectric single crystal substrate 57 is an example of a substrate having piezoelectric properties, and is made of, for example, a piezoelectric single crystal of lithium niobate or lithium tantalate.

[0061] The dielectric layer 58 is formed to cover the surfaces of the IDT electrode 54 and the piezoelectric single crystal substrate 57. The thickness of the dielectric layer 58 is greater than the height (film thickness) of the IDT electrode 54. The dielectric layer 58 is a layer intended to protect the main electrode layer 542 from the external environment, adjust the frequency-temperature characteristics, and increase moisture resistance, and is, for example, a dielectric film whose main component is silicon dioxide.

[0062] The adjustment film 59 is formed on the surface of the dielectric layer 58. The adjustment film 59 is a layer intended to adjust the frequency, such as the pass band, of the acoustic wave filter 1, and is a film whose main component is, for example, silicon nitride. Note that the adjustment film 59 is not necessarily required.

[0063] The laminate structure, material, cut angle, and thickness of the piezoelectric layer 53 and the piezoelectric single crystal substrate 57 may be changed as appropriate depending on the required pass characteristics of the acoustic wave filter 1 .

[0064] The substrate on which the IDT electrode 54 is formed may be the piezoelectric substrate 50 shown in FIG. 2A or the piezoelectric single crystal substrate 57 shown in FIG. 2B, or may have a structure in which a support substrate, an energy trapping layer, and a piezoelectric film are laminated in this order. In this case, the IDT electrode 54 is formed on the piezoelectric film. The piezoelectric film may be, for example, LiTaO ３ The support substrate is a substrate that supports the piezoelectric film, the energy trapping layer, and the IDT electrode 54.

[0065] The energy trapping layer is composed of one or more layers, and the velocity of the bulk acoustic waves propagating through at least one of the layers is greater than the velocity of the acoustic waves propagating near the piezoelectric film. For example, the energy trapping layer may have a laminated structure of a low acoustic velocity layer and a high acoustic velocity layer. The low acoustic velocity layer is a film in which the acoustic velocity of the bulk waves in the low acoustic velocity layer is slower than the acoustic velocity of the acoustic waves propagating through the piezoelectric film. The high acoustic velocity layer is a film in which the acoustic velocity of the bulk waves in the high acoustic velocity layer is faster than the acoustic velocity of the acoustic waves propagating through the piezoelectric film. The support substrate may also be the high acoustic velocity layer.

[0066] The energy trapping layer may also be an acoustic impedance layer having a configuration in which low acoustic impedance layers with a relatively low acoustic impedance and high acoustic impedance layers with a relatively high acoustic impedance are alternately stacked.

[0067] Furthermore, elastic wave device 1 according to this embodiment is not limited to a structure having a SAW resonator, but may also be applied to a structure having a laterally excited bulk acoustic resonator (XBAR). An XBAR has a membrane structure in which an IDT electrode is formed on a first main surface of a piezoelectric layer and a cavity is formed on a second main surface of the piezoelectric layer opposite the first main surface. That is, in elastic wave device 1 according to this embodiment, each of series arm resonators 11 to 15 and parallel arm resonators 21 to 26 may have an XBAR structure.

[0068] Next, the structure of the capacitive elements (capacitors 32 and 35) that constitute acoustic wave filter 1 will be described.

[0069] 3 is a plan view showing the electrode arrangement of an acoustic wave resonator and a capacitance element according to an embodiment. This drawing illustrates an example of the layout of the IDT electrodes of the parallel arm resonator 22 and the pair of interdigital electrodes of the capacitor 32 that constitute the acoustic wave filter 1 according to the embodiment. As shown in FIG. 3 , the IDT electrodes (and reflectors) of the parallel arm resonator 22 and the interdigital electrodes of the capacitor 32 are formed on a main surface of a piezoelectric substrate 50.

[0070] Capacitor 32 is composed of a piezoelectric substrate 50 and a pair of comb-shaped electrodes. Each of the pair of comb-shaped electrodes of capacitor 32 is composed of a plurality of second electrode fingers (electrode fingers 71 a and 71 b) that are parallel to each other, and second bus bar electrodes (72 a and 72 b) that connect the plurality of second electrode fingers. Capacitor 35 also has an electrode configuration similar to that of capacitor 32. The plurality of second electrode fingers that constitute capacitors 32 and 35 are formed along a direction that intersects the acoustic wave propagation direction (X-axis direction).

[0071] As shown in FIG. 3 , one busbar electrode 62a of the IDT electrode of the parallel arm resonator 22 and one busbar electrode 72a of the pair of comb-shaped electrodes of the capacitor 32 are connected at a connection node n1. The other busbar electrode 62b of the IDT electrode of the parallel arm resonator 22 and the other busbar electrode 72b of the pair of comb-shaped electrodes of the capacitor 32 are connected at a connection node n2. A first extension direction of the electrode fingers 61a and 61b of the IDT electrode of the parallel arm resonator 22 intersects with a second extension direction of the electrode fingers 71a and 71b of the pair of comb-shaped electrodes of the capacitor 32. This configuration can suppress interference between an acoustic wave propagating through the parallel arm resonator 22 and a high frequency wave propagating through the capacitor 32. Furthermore, a first extension direction of the electrode fingers of the IDT electrode of the parallel arm resonator 25 intersects with a second extension direction of the electrode fingers of the pair of comb-shaped electrodes of the capacitor 35. This makes it possible to prevent interference between the acoustic wave propagating through the parallel arm resonator 25 and the high frequency wave propagating through the capacitor 35 .

[0072] The electrode fingers of the IDT electrodes of the series arm resonators 11 to 15 and the parallel arm resonators 21 to 26 extend in the same direction, ie, in the first extension direction.

[0073] When the series arm resonators 11 to 15 and the parallel arm resonators 21 to 26 are formed on the piezoelectric single crystal substrate 57 shown in FIG. 2B, the capacitors 32 and 35 are formed on the piezoelectric single crystal substrate 57 .

[0074] Alternatively, the piezoelectric substrate 50 may include a first piezoelectric layer and a second piezoelectric layer, the IDT electrode of the parallel arm resonator 22 and the pair of comb electrodes of the capacitor 32 may be formed on the first piezoelectric layer, and the IDT electrode of the parallel arm resonator 25 and the pair of comb electrodes of the capacitor 35 may be formed on the second piezoelectric layer.

[0075] Here, the electrode parameters of the IDT electrode 54 that constitutes the acoustic wave resonator 60 and the electrode parameters of the comb-shaped electrodes that constitute the capacitive elements (capacitors 32 and 35) will be described.

[0076] The wavelength λ of the elastic wave resonator 60 and the capacitor element is defined by the repetition period of the electrode fingers 61 a or 61 b ​​constituting the IDT electrode 54 shown in FIG. 2A (b). The electrode finger pitch P is half the wavelength λ and is defined as (L + S), where L is the line width of the electrode fingers 61 a and 61 b ​​constituting the interdigital transducers 60 a and 60 b, and S is the space width between adjacent electrode fingers 61 a and 61 b. The electrode finger duty D of the interdigital transducers of the IDT electrode 54 of the elastic wave resonator 60 and the capacitor element is the line width occupancy rate of the electrode fingers 61 a and 61 b, which is the ratio of the line width L to the sum of the line width L and the space width S of each of the electrode fingers 61 a and 61 b, and is defined as L / (L + S). The overlap width V of the IDT electrode 54 is the length of the overlapping electrode fingers 61 a and 61 b ​​when viewed from a direction perpendicular to the electrode fingers 61 a and 61 b ​​and parallel to the main surface of the piezoelectric substrate 50. The height (film thickness) of the comb-shaped electrodes 60 a and 60 b (IDT electrode 54) is defined as h.

[0077] In the IDT electrode 54, when the interval between adjacent electrode fingers is not constant, the electrode finger pitch P of the IDT electrode 54 is set to the average electrode finger pitch P ＡＶＥ The average electrode finger pitch P of the IDT electrode 54 is defined as ＡＶＥ is defined as Di / (Ni-1), where Ni is the total number of electrode fingers 61a, 61b included in the IDT electrode 54, and Di is the center-to-center distance between the electrode finger located at one end of the IDT electrode 54 and the electrode finger located at the other end in the elastic wave propagation direction.

[0078] In addition, even when the interval between adjacent electrode fingers is not constant in the comb-shaped electrode of the capacitance element, the average electrode finger pitch P ＡＶＥ That is, the average electrode finger pitch P ＡＶＥ is defined as Di / (Ni-1), where Ni is the total number of second electrode fingers included in the comb-shaped electrode of the capacitance element, and Di is the center-to-center distance between the second electrode finger located at one end of the comb-shaped electrode of the capacitance element and the second electrode finger located at the other end.

[0079] In addition, when the electrode finger duty D of the IDT electrode 54 is not constant, the electrode finger duty D of the IDT electrode 54 is equal to the average electrode finger duty D of the IDT electrode 54. ＡＶＥ The average electrode finger duty D of the IDT electrode 54 is defined as ＡＶＥ The total number of electrode fingers 61a and 61b included in the IDT electrode 54 is Ni, and the total line width obtained by adding the line width L of (Ni-1) electrode fingers is L. ＡＬＬ The total space width obtained by adding up the (Ni-1) space widths S included in the IDT electrode 54 is S ＡＬＬ In this case, L ＡＬＬ / (L ＡＬＬ +S ＡＬＬ ) is defined as

[0080] In addition, even when the electrode finger duty D is not constant in the comb-shaped electrode of the capacitance element, the average electrode finger duty D of the IDT electrode 54 ＡＶＥ That is, the average electrode finger duty D ＡＶＥ The total number of second electrode fingers included in the comb-shaped electrode is Ni, and the total line width obtained by adding the line width L of (Ni-1) electrode fingers is L. ＡＬＬ The total space width obtained by adding up the (Ni-1) space widths S included in the comb-shaped electrode is S ＡＬＬ In this case, L ＡＬＬ / (L ＡＬＬ +S ＡＬＬ ) is defined as

[0081] The electrode finger pitch P and electrode finger duty D of the IDT electrode 54 and the comb-shaped electrode of the capacitance element can be measured by using a scanning electron microscope (SEM), a scanning transmission electron microscope (STEM), or a transmission electron microscope (TEM) to view the main surface of the substrate on which the IDT electrode 54 and the comb-shaped electrode of the capacitance element are formed in a plan view and / or a cross-section perpendicular to the extension direction of the electrode fingers, and measuring the line width L and space width S.

[0082] [3. Resonance Characteristics and Pass Characteristics of Acoustic Wave Filter 1 According to the Preferred Embodiment] First, the basic operating principle of a ladder-type bandpass filter configured with one series arm resonator and one parallel arm resonator will be described.

[0083] The parallel arm resonator has a resonance frequency frp and an antiresonance frequency fap (>frp), while the series arm resonator has a resonance frequency frs and an antiresonance frequency fas (>frs>frp). In series arm and parallel arm resonators having the above resonance characteristics, the antiresonance frequency fap of the parallel arm resonator and the resonance frequency frs of the series arm resonator are generally set close to each other. This results in a low-frequency stopband near the resonance frequency frp, where the impedance of the parallel arm resonator approaches zero. Furthermore, as the frequency increases, the impedance of the parallel arm resonator increases near the antiresonance frequency fap, and the impedance of the series arm resonator approaches zero near the resonance frequency frs. This results in a signal passband in the signal path, which is the series arm path, near the antiresonance frequency fap to the resonance frequency frs. This makes it possible to form a passband that reflects the electrode parameters and electromechanical coupling coefficient of the elastic wave resonator. Furthermore, when the frequency increases and approaches the anti-resonance frequency fas, the impedance of the series arm resonator increases, resulting in a high-frequency stopband.

[0084] Next, the resonance characteristics and pass characteristics of the acoustic wave filter 1 according to the example will be described. The acoustic wave filter 1 according to the example is different from the acoustic wave filter 1 according to the embodiment in that specific values ​​of the wavelength λ (electrode finger pitch×2) and electrode finger duty D of each acoustic wave resonator (series arm resonator, parallel arm resonator) and capacitance element are specified.

[0085] Table 1 shows data of the acoustic wave resonators and capacitance elements constituting the acoustic wave filter 1 according to the example. Note that the data of the acoustic wave filter 1 shown in Table 1 is merely example data and can be changed as appropriate depending on the required pass band of the acoustic wave filter 1.

[0086]

[0087] In the acoustic wave filter 1 according to the embodiment, capacitive elements (capacitors 32 and 35) are connected in parallel to the series arm resonators 11 to 15 and the parallel arm resonators 22 and 25 of the parallel arm resonators 21 to 26. This reduces the relative resonance band width (the value obtained by dividing the frequency difference between the antiresonance frequency and the resonance frequency by the center frequency of the antiresonance frequency and the resonance frequency) of the parallel arm resonator formed by the parallel arm resonator 22 and the capacitor 32 and the parallel arm resonator formed by the parallel arm resonator 25 and the capacitor 35. This enables the steepness of the passband edges of the acoustic wave filter 1 to be improved.

[0088] However, when a piezoelectric substrate 50 having a multilayer substrate structure with high acoustic velocity layers and low acoustic velocity layers is applied to an acoustic wave filter, or when a piezoelectric single crystal substrate 57 made of lithium niobate or lithium tantalate is used to utilize Rayleigh waves, Love waves, leaky waves, or Lamb waves, higher-order mode spurious responses may occur in bands higher than the pass band due to the capacitive element connected in parallel to the acoustic wave resonator, thereby deteriorating the attenuation characteristics.

[0089] In contrast, in the acoustic wave filter 1 according to this preferred embodiment, the wavelength λ32 of the capacitor 32 (electrode finger pitch P32×2) and the wavelength λ35 of the capacitor 35 (electrode finger pitch P35×2) are made different from each other.

[0090] The wavelength λ32 (electrode finger pitch P32×2) of the capacitor 32 is smaller than the wavelengths λ of the series arm resonators 11 to 15 and the parallel arm resonators 21 to 26, and the wavelength λ35 (electrode finger pitch P35×2) of the capacitor 35 is smaller than the wavelengths λ of the series arm resonators 11 to 15 and the parallel arm resonators 21 to 26.

[0091] As a result, the spurious response of the higher order mode caused by the capacitors 32 and 35 occurs on the higher frequency side than the pass band of the acoustic wave filter 1 .

[0092] 4A is a graph showing the impedance characteristics of the capacitance elements included in the elastic wave filter 1 according to the example. The graph shows the impedance characteristics of the capacitance elements included in the elastic wave filters according to the example and the comparative example. The elastic wave filter according to the comparative example has the same circuit configuration as the elastic wave filter 1 according to the embodiment. That is, the elastic wave filter according to the comparative example includes series arm resonators 11, 12, 13, 14, and 15, parallel arm resonators 21, 22, 23, 24, 25, and 26, capacitors 32 and 35, and input / output terminals 110 and 120. However, in the elastic wave filter according to the comparative example, the wavelength λ32 of capacitor 32 (electrode finger pitch P32×2) is equal to the wavelength λ35 of capacitor 35 (electrode finger pitch P35×2).

[0093] As shown in FIG. 4A , in the acoustic wave filter according to the comparative example, the wavelength λ32 of capacitor 32 is equal to the wavelength λ35 of capacitor 35, and therefore the antiresonant frequency fa320 of capacitor 32 is equal to the antiresonant frequency fa350 of capacitor 35, and the maximum impedance values ​​at the antiresonant frequencies fa320 and fa350 are large.

[0094] In contrast, in the elastic wave filter 1 according to the example, the anti-resonance frequency fa32 of the capacitor 32 is different from the anti-resonance frequency fa35 of the capacitor 35. Specifically, the wavelength λ32 (=1.200 μm) of the capacitor 32 is smaller than the wavelength λ35 (=1.250 μm) of the capacitor 35, and therefore the anti-resonance frequency fa32 is located on the higher frequency side than the anti-resonance frequency fa35. As a result, the maximum impedance values ​​at the anti-resonance frequencies fa32 and fa35 are smaller than the maximum impedance values ​​at the anti-resonance frequencies fa320 and fa350 of the elastic wave filter according to the comparative example.

[0095] 4B is a diagram illustrating the relationship between the resonance characteristics of the capacitors 32 and 35 included in the acoustic wave filter 1 according to the embodiment. As shown in the diagram, by making the anti-resonance frequency fa32 of the capacitor 32 and the anti-resonance frequency fa35 of the capacitor 35 different from each other, the maximum value of the impedance of the capacitors arranged in the parallel arm path of the acoustic wave filter 1 is reduced, thereby ensuring large attenuation (insertion loss) at the anti-resonance frequencies fa32 and fa35 in the pass characteristics from the input / output terminal 110 to the input / output terminal 120.

[0096] 4C is a graph showing the pass characteristics of the acoustic wave filters according to the example and the comparative example. As shown in the figure, the acoustic wave filter 1 according to the example has improved attenuation characteristics in the frequency band (3 GHz-4 GHz) higher than the pass band without increasing the insertion loss in the pass band, compared to the acoustic wave filter according to the comparative example. This is due to the fact that the antiresonant frequency fa32 of capacitor 32 and the antiresonant frequency fa35 of capacitor 35 are different from each other.

[0097] In the acoustic wave filter 1 according to the embodiment, instead of differentiating the wavelength λ32 (electrode finger pitch P32×2) of the capacitor 32 from the wavelength λ35 (electrode finger pitch P35×2) of the capacitor 35, the electrode finger duty D32 of the capacitor 32 may be different from the electrode finger duty D35 of the capacitor 35. Specifically, for example, by making the electrode finger duty D32 of the capacitor 32 smaller than the electrode finger duty D35 of the capacitor 35, the anti-resonance frequency fa32 can be positioned higher than the anti-resonance frequency fa35. In this way, the anti-resonance frequency fa32 of the capacitor 32 is different from the anti-resonance frequency fa35 of the capacitor 35. This reduces the maximum impedance value of the capacitors arranged in the parallel arm path of the acoustic wave filter 1, thereby ensuring large attenuation (insertion loss) at the anti-resonance frequencies fa32 and fa35 in the pass characteristics from the input / output terminal 110 to the input / output terminal 120.

[0098] Alternatively, the wavelength λ32 (electrode finger pitch P32×2) of capacitor 32 may be made different from the wavelength λ35 (electrode finger pitch P35×2) of capacitor 35, and the electrode finger duty D32 of capacitor 32 may be made different from the electrode finger duty D35 of capacitor 35. This allows the anti-resonant frequency fa32 of capacitor 32 and the anti-resonant frequency fa35 of capacitor 35 to be made different with high precision, thereby making it possible to suppress with high precision the deterioration of the attenuation (insertion loss) of the anti-resonant frequencies fa32 and fa35 in the pass characteristics from input / output terminal 110 to input / output terminal 120.

[0099] Furthermore, in the acoustic wave filter 1 according to the embodiment, the electrode film thickness of the capacitor 32 may be different from that of the capacitor 35. Specifically, for example, by making the electrode film thickness of the capacitor 32 smaller than that of the capacitor 35, it is possible to position the anti-resonance frequency fa32 higher than the anti-resonance frequency fa35. In this way, the anti-resonance frequency fa32 of the capacitor 32 is different from the anti-resonance frequency fa35 of the capacitor 35. This reduces the maximum value of the impedance of the capacitors arranged in the parallel arm path of the acoustic wave filter 1, thereby ensuring large attenuation (insertion loss) at the anti-resonance frequencies fa32 and fa35 in the pass characteristics from the input / output terminal 110 to the input / output terminal 120.

[0100] The resonant frequency and the anti-resonant frequency are approximately inversely proportional to the product of the electrode finger pitch and the electrode finger duty (where the electrode finger duty is in the range of approximately 0.65 or less). From this perspective, in the acoustic wave filter 1 according to this embodiment, instead of making the anti-resonant frequency fa32 of the capacitor 32 and the anti-resonant frequency fa35 of the capacitor 35 different from each other, the product of the electrode finger duty D32 of the capacitor 32 and the wavelength λ32 (electrode finger pitch P32×2) may be made different from the product of the electrode finger duty D35 of the capacitor 35 and the wavelength λ35 (electrode finger pitch P35×2).

[0101] [4. Resonance Characteristics and Pass Characteristics of Elastic Wave Filter 1A According to Modification 1] Next, the circuit configuration and resonance characteristics of elastic wave filter 1A according to Modification 1 of the embodiment will be described.

[0102] 5A is a circuit diagram of an elastic wave filter 1A according to a first modification of the embodiment. As shown in the figure, the elastic wave filter 1A is an example of an elastic wave device and includes series arm resonators 11, 12, 13, 14, and 15, parallel arm resonators 21, 22, 23, 24, 25, and 26, capacitors 42 and 44, and input / output terminals 110 and 120. The elastic wave filter 1A according to this modification differs from the elastic wave filter 1 according to the embodiment in the connection configuration of the capacitive elements (capacitors 42 and 44). Therefore, the following description of the elastic wave filter 1A according to this modification will focus on the different configurations and omit a description of the same configurations as those of the elastic wave filter 1 according to the embodiment.

[0103] Each of the series arm resonators 11 to 15 includes an acoustic wave resonator and is arranged in series on a series arm path connecting the input / output terminal 110 (first input / output terminal) and the input / output terminal 120 (second input / output terminal). The series arm resonator 12 is an example of a first acoustic wave resonator, and the series arm resonator 14 is an example of a second acoustic wave resonator.

[0104] Each of the parallel arm resonators 21 to 26 is an example of a third acoustic wave resonator, and is connected between the series arm path and ground.

[0105] The capacitor 42 is an example of a first capacitance element, and is connected in parallel to the series arm resonator 12. Specifically, one end of the capacitor 42 is connected to the connection node between the series arm resonator 11, the series arm resonator 12, and the parallel arm resonator 22, and the other end of the capacitor 42 is connected to the connection node between the series arm resonator 12, the series arm resonator 13, and the parallel arm resonator 23. The capacitor 42 is a so-called bridging capacitance connected in parallel to the series arm resonator 12.

[0106] The capacitor 44 is an example of a second capacitance element, and is connected in parallel to the series arm resonator 14. Specifically, one end of the capacitor 44 is connected to the connection node between the series arm resonator 13, the series arm resonator 14, and the parallel arm resonator 24, and the other end of the capacitor 44 is connected to the connection node between the series arm resonator 14, the series arm resonator 15, and the parallel arm resonator 25. The capacitor 44 is a so-called bridging capacitance connected in parallel to the series arm resonator 14.

[0107] Each of the capacitors 42 and 44 includes an interdigital electrode formed on a piezoelectric substrate, and resonates with the substrate, thereby having a resonant frequency at which the impedance is minimized and an anti-resonant frequency at which the impedance is maximized.

[0108] Although not shown, the extension directions of the electrode fingers of the IDT electrodes of the series arm resonators 11 to 15 and the parallel arm resonators 21 to 26 are aligned in a first extension direction, the first extension direction intersects with the second extension direction of the electrode fingers of the IDT electrode of the capacitor 42, and the first extension direction intersects with the extension direction of the electrode fingers of the IDT electrode of the capacitor 44.

[0109] Here, the resonant frequency fr42 of the capacitor 42 and the resonant frequency fr44 of the capacitor 44 are different.

[0110] This makes it possible to suppress spurious responses of higher modes in the attenuation band higher than the pass band of the elastic wave filter 1A, thereby making it possible to provide an elastic wave filter 1A with improved attenuation characteristics higher than the pass band.

[0111] In this modification, "the resonant frequency of the first capacitive element is different from the resonant frequency of the second capacitive element" means that the first-order resonant frequency of the first capacitive element is different from the first-order resonant frequency of the second capacitive element. In other words, the resonant frequencies of the first capacitive element and the second capacitive element, which are compared, are of the same order.

[0112] The wavelength λ42 (electrode finger pitch P42×2) of the capacitor 42 is smaller than the wavelengths λ of the series arm resonators 11 to 15 and the parallel arm resonators 21 to 26, and the wavelength λ44 (electrode finger pitch P44×2) of the capacitor 44 is smaller than the wavelengths λ of the series arm resonators 11 to 15 and the parallel arm resonators 21 to 26.

[0113] As a result, the spurious response of the higher order mode caused by the capacitors 42 and 44 occurs on the higher frequency side than the pass band of the acoustic wave filter 1A.

[0114] At least one of the series arm resonators 11, 13, and 15 may not be included in the acoustic wave filter 1A, and at least one of the parallel arm resonators 21 to 26 may not be included in the acoustic wave filter 1A.

[0115] The capacitor 42 does not have to be connected in parallel to the series arm resonator 12, but may be connected in parallel to any of the series arm resonators 11, 13, and 15. The capacitor 44 does not have to be connected in parallel to the series arm resonator 14, but may be connected in parallel to any of the series arm resonators 11, 13, and 15.

[0116] In this modification, no capacitor is connected in parallel to each of the parallel arm resonators 21 to 26.

[0117] Alternatively, the piezoelectric substrate 50 may include a first piezoelectric layer and a second piezoelectric layer, with the IDT electrode of the series arm resonator 12 and the pair of comb electrodes of the capacitor 42 formed on the first piezoelectric layer, and the IDT electrode of the series arm resonator 14 and the pair of comb electrodes of the capacitor 44 formed on the second piezoelectric layer.

[0118] The acoustic wave filter 1A may include six or more series arm resonators, and seven or more parallel arm resonators.

[0119] Furthermore, longitudinally coupled resonators, inductors, capacitors, switches, etc. may be connected between the series arm resonators 11 to 15, the parallel arm resonators 21 to 26, the ground, and the input / output terminals 110 and 120. The inductors may include wiring inductors formed by wiring connecting the components, wiring within the packaging member, and conductive vias.

[0120] 5B is a diagram illustrating the relationship between the resonance characteristics of capacitors 42 and 44 included in elastic wave filter 1A according to Modification 1 of the embodiment. As illustrated in the diagram, by making the resonance frequency fr42 of capacitor 42 and the resonance frequency fr44 of capacitor 44 different from each other, the minimum value of the impedance of the capacitors arranged in the series arm path of elastic wave filter 1A increases, thereby ensuring large attenuation (insertion loss) at the resonance frequencies fr42 and fr44 in the pass characteristics from input / output terminal 110 to input / output terminal 120.

[0121] As a result, the acoustic wave filter 1A according to the first modification has improved attenuation characteristics in the band higher than the pass band without increasing the insertion loss in the pass band, compared to a conventional acoustic wave filter in which the resonant frequency fr42 of the capacitor 42 and the resonant frequency fr44 of the capacitor 44 are equal to each other. This is because the resonant frequency fr42 of the capacitor 42 and the resonant frequency fr44 of the capacitor 44 are different from each other.

[0122] In the acoustic wave filter 1A according to this modification, the resonant frequency fr42 of the capacitor 42 may be configured to differ from the resonant frequency fr44 of the capacitor 44 by differentiating the wavelength λ44 (electrode finger pitch P44×2) of the capacitor 42 from the wavelength λ44 (electrode finger pitch P44×2) of the capacitor 44. Specifically, by making the wavelength λ42 of the capacitor 42 larger than the wavelength λ44 of the capacitor 44, the resonant frequency fr42 is positioned at a lower frequency than the resonant frequency fr44.

[0123] Alternatively, instead of differentiating the wavelength λ42 (electrode finger pitch P42×2) of the capacitor 42 from the wavelength λ44 (electrode finger pitch P44×2) of the capacitor 44, the electrode finger duty D42 of the capacitor 42 may be different from the electrode finger duty D44 of the capacitor 44. Specifically, for example, by making the electrode finger duty D42 of the capacitor 42 larger than the electrode finger duty D44 of the capacitor 44, the resonant frequency fr42 can be positioned lower than the resonant frequency fr44. In this manner, the resonant frequencies fr42 and fr44 of the capacitor 42 and 44 are different from each other, which increases the minimum impedance value of the capacitors arranged in the series arm paths of the acoustic wave filter 1A. This ensures a large amount of attenuation (insertion loss) at the resonant frequencies fr42 and fr44 in the pass characteristics from the input / output terminal 110 to the input / output terminal 120.

[0124] Alternatively, the wavelength λ42 (electrode finger pitch P42×2) of capacitor 42 may be made different from the wavelength λ44 (electrode finger pitch P44×2) of capacitor 44, and the electrode finger duty D42 of capacitor 42 may be made different from the electrode finger duty D44 of capacitor 44. This allows the resonant frequency fr42 of capacitor 42 and the resonant frequency fr44 of capacitor 44 to be made different with high precision, thereby making it possible to suppress with high precision the deterioration of the attenuation (insertion loss) of the resonant frequencies fr42 and fr44 in the pass characteristics from input / output terminal 110 to input / output terminal 120.

[0125] Furthermore, in the acoustic wave filter 1A according to this modification, the electrode film thickness of the capacitor 42 may be different from that of the capacitor 44. Specifically, for example, by making the electrode film thickness of the capacitor 42 larger than that of the capacitor 44, the resonant frequency fr42 can be positioned lower than the resonant frequency fr44. In this manner, the resonant frequency fr42 of the capacitor 42 is different from the resonant frequency fr44 of the capacitor 44. This increases the minimum value of the impedance of the capacitor disposed in the series arm path of the acoustic wave filter 1A, thereby ensuring large attenuation (insertion loss) at the resonant frequencies fr42 and fr44 in the pass characteristics from the input / output terminal 110 to the input / output terminal 120.

[0126] In the acoustic wave filter 1A according to this modified example, instead of differentiating the resonant frequency fr42 of the capacitor 42 from the resonant frequency fr44 of the capacitor 44, the product of the electrode finger duty D42 of the capacitor 42 and the wavelength λ42 (electrode finger pitch P42×2) may be different from the product of the electrode finger duty D44 of the capacitor 44 and the wavelength λ44 (electrode finger pitch P44×2).

[0127] 5. Resonance Characteristics and Pass Characteristics of Elastic Wave Filter 1B According to Modification 2 Next, the circuit configuration and resonance characteristics of elastic wave filter 1B according to Modification 2 of the embodiment will be described.

[0128] 6A is a circuit diagram of an elastic wave filter 1B according to a second modification of the embodiment. As shown in the figure, the elastic wave filter 1B is an example of an elastic wave device and includes series arm resonators 11, 12, 13, 14, and 15, parallel arm resonators 21, 22, 23, 24, 25, and 26, capacitors 32 and 44, and input / output terminals 110 and 120. The elastic wave filter 1B according to this modification has a different connection configuration of the capacitive element (capacitor 44) from the elastic wave filter 1 according to the embodiment. Therefore, the following description of the elastic wave filter 1B according to this modification will focus on the different configuration and omit a description of the same configuration as the elastic wave filter 1 according to the embodiment.

[0129] Each of the series arm resonators 11 to 15 includes an acoustic wave resonator and is arranged in series on a series arm path connecting the input / output terminal 110 (first input / output terminal) and the input / output terminal 120 (second input / output terminal). The series arm resonator 14 is an example of a first acoustic wave resonator.

[0130] Each of the parallel arm resonators 21 to 26 includes an acoustic wave resonator and is connected between the series arm path and ground. The parallel arm resonator 22 is an example of a second acoustic wave resonator.

[0131] The series arm resonators 11 to 13 and 15 and the parallel arm resonators 21 and 23 to 26 are each an example of a third acoustic wave resonator.

[0132] The capacitor 44 is an example of a first capacitance element, and is connected in parallel to the series arm resonator 14. Specifically, one end of the capacitor 44 is connected to the connection node between the series arm resonator 13, the series arm resonator 14, and the parallel arm resonator 24, and the other end of the capacitor 44 is connected to the connection node between the series arm resonator 14, the series arm resonator 15, and the parallel arm resonator 25. The capacitor 44 is a so-called bridging capacitance connected in parallel to the series arm resonator 14.

[0133] The capacitor 32 is an example of a second capacitance element, and is connected in parallel to the parallel arm resonator 22. Specifically, one end of the capacitor 32 is connected to the connection node between the series arm resonator 11, the series arm resonator 12, and the parallel arm resonator 22, and the other end of the capacitor 32 is connected to the connection node between the parallel arm resonator 22 and ground. The capacitor 32 is a so-called bridging capacitance connected in parallel to the parallel arm resonator 22.

[0134] Each of the capacitors 32 and 44 includes an interdigital electrode formed on a piezoelectric substrate, and resonates with the substrate, so that each of the capacitors 32 and 44 has a resonant frequency at which the impedance is minimized and an anti-resonant frequency at which the impedance is maximized.

[0135] Although not shown, the extension directions of the electrode fingers of the IDT electrodes of the series arm resonators 11 to 15 and the parallel arm resonators 21 to 26 are aligned in a first extension direction, the first extension direction intersects with the second extension direction of the electrode fingers of the IDT electrode of the capacitor 32, and the first extension direction intersects with the extension direction of the electrode fingers of the IDT electrode of the capacitor 44.

[0136] Here, the anti-resonance frequency fa32 of the capacitor 32 is smaller than the resonant frequency fr44 of the capacitor 44, or the anti-resonance frequency fa32 of the capacitor 32 is larger than the anti-resonant frequency fa44 of the capacitor 44.

[0137] This makes it possible to suppress spurious responses of higher modes in the attenuation band higher than the pass band of the elastic wave filter 1B, thereby making it possible to provide an elastic wave filter 1B with improved attenuation characteristics higher than the pass band.

[0138] In this modification, "the anti-resonant frequency of the second capacitive element is lower than the resonant frequency of the first capacitive element" means that the first-order anti-resonant frequency of the second capacitive element is lower than the first-order resonant frequency of the first capacitive element. In other words, the anti-resonant frequency of the second capacitive element to be compared and the resonant frequency of the first capacitive element are of the same order. Furthermore, "the anti-resonant frequency of the second capacitive element is higher than the anti-resonant frequency of the first capacitive element" means that the first-order anti-resonant frequency of the second capacitive element is higher than the first-order anti-resonant frequency of the first capacitive element. In other words, the anti-resonant frequency of the second capacitive element to be compared and the anti-resonant frequency of the first capacitive element are of the same order.

[0139] The wavelength λ32 (electrode finger pitch P32×2) of the capacitor 32 is smaller than the wavelengths λ of the series arm resonators 11 to 15 and the parallel arm resonators 21 to 26, and the wavelength λ44 (electrode finger pitch P44×2) of the capacitor 44 is smaller than the wavelengths λ of the series arm resonators 11 to 15 and the parallel arm resonators 21 to 26.

[0140] As a result, the spurious response of the higher order mode due to the capacitors 32 and 44 occurs on the higher frequency side than the pass band of the acoustic wave filter 1B.

[0141] At least one of the series arm resonators 11, 12, 13, and 15 may not be included in the acoustic wave filter 1B, and at least one of the parallel arm resonators 21, 23, 24, 25, and 26 may not be included in the acoustic wave filter 1B.

[0142] The capacitor 44 does not have to be connected in parallel to the series arm resonator 14, but may be connected in parallel to any of the series arm resonators 11, 12, 13, and 15. The capacitor 32 does not have to be connected in parallel to the parallel arm resonator 22, but may be connected in parallel to any of the parallel arm resonators 21, 23, 24, 25, and 26.

[0143] In this modification, no capacitors are connected in parallel to the series arm resonators 11 to 13 and 15 and the parallel arm resonators 21 and 23 to 26.

[0144] Alternatively, the piezoelectric substrate 50 may include a first piezoelectric layer and a second piezoelectric layer, with the IDT electrode of the series arm resonator 14 and the pair of comb electrodes of the capacitor 44 formed on the first piezoelectric layer, and the IDT electrode of the parallel arm resonator 22 and the pair of comb electrodes of the capacitor 32 formed on the second piezoelectric layer.

[0145] Furthermore, when each of the series arm resonators 11 to 15 and the parallel arm resonators 21 to 26 has an XBAR structure, the thickness of the first piezoelectric layer may be different from the thickness of the second piezoelectric layer, which allows the Q value and relative resonance bandwidth of each resonator to be adjusted with high precision.

[0146] The acoustic wave filter 1B may include six or more series arm resonators, and seven or more parallel arm resonators.

[0147] Furthermore, longitudinally coupled resonators, inductors, capacitors, switches, etc. may be connected between the series arm resonators 11 to 15, the parallel arm resonators 21 to 26, the ground, and the input / output terminals 110 and 120. The inductors may include wiring inductors formed by wiring connecting the components, wiring within the packaging member, and conductive vias.

[0148] 6B is a diagram illustrating the relationship between the resonance characteristics of the capacitors 32 and 44 included in the elastic wave filter 1B according to the second modification of the embodiment. As shown in (b) of the figure, by setting the antiresonance frequency fa32 of the capacitor 32 lower than the resonant frequency fr44 of the capacitor 44, the elastic wave filter 1B can ensure a larger amount of attenuation (insertion loss) in the band from the antiresonance frequency fa32 to the resonant frequency fr44 in the pass characteristics from the input / output terminal 110 to the input / output terminal 120, compared to an elastic wave filter in which the antiresonance frequency fa32 and the resonant frequency fr44 are equal. Also, as shown in (c) of the figure, by setting the antiresonance frequency fa32 of the capacitor 32 higher than the antiresonant frequency fa44 of the capacitor 44, the elastic wave filter 1B can ensure a larger amount of attenuation (insertion loss) in the band from the antiresonance frequency fa44 to the antiresonant frequency fa32 in the pass characteristics from the input / output terminal 110 to the input / output terminal 120, compared to an elastic wave filter in which the antiresonance frequency fa32 and the resonant frequency fr44 are equal.

[0149] [6. Effects, etc.] As described above, the acoustic wave filter 1 according to the embodiment (and examples) includes the parallel arm resonator 22 connected between the series arm path connecting the input / output terminals 110 and 120 and the ground, the parallel arm resonator 25 connected between the series arm path and the ground, the series arm resonator 12 arranged in series with the series arm path, the capacitor 32 connected in parallel with the parallel arm resonator 22, and the capacitor 35 connected in parallel with the parallel arm resonator 25. Each of the parallel arm resonators 22 and 25 and the series arm resonator 12 includes an IDT electrode formed on a piezoelectric substrate. Each of capacitors 32 and 35 includes a pair of comb electrodes formed on a piezoelectric substrate, the IDT electrodes having a plurality of first electrode fingers arranged parallel to each other and a set of first bus bar electrodes arranged opposite each other with the plurality of first electrode fingers in between, the pair of comb electrodes having a plurality of second electrode fingers arranged parallel to each other and a set of second bus bar electrodes arranged opposite each other with the plurality of second electrode fingers in between, the extension direction of the plurality of first electrode fingers intersects the extension direction of the plurality of second electrode fingers, and the anti-resonance frequency fa32 of capacitor 32 is different from the anti-resonance frequency fa35 of capacitor 35.

[0150] As a result, the maximum impedance values ​​at the anti-resonance frequencies fa32 and fa35 are smaller than the maximum impedance values ​​when the anti-resonance frequencies fa32 and fa35 are the same. Therefore, higher-order mode spurious emissions can be suppressed in the attenuation band higher than the pass band of the acoustic wave filter 1, thereby providing an acoustic wave filter 1 with improved attenuation characteristics higher than the pass band. Furthermore, the first extension direction of the first electrode fingers of the IDT electrode of the parallel arm resonator 22 intersects with the second extension direction of the second electrode fingers of the pair of interdigital electrodes of the capacitor 32. This suppresses interference between acoustic waves propagating through the parallel arm resonator 22 and high-frequency waves propagating through the capacitor 32. Furthermore, the first extension direction of the first electrode fingers of the IDT electrode of the parallel arm resonator 25 intersects with the second extension direction of the second electrode fingers of the IDT electrode of the capacitor 35. This makes it possible to prevent interference between the acoustic wave propagating through the parallel arm resonator 25 and the high frequency wave propagating through the capacitor 35 .

[0151] The acoustic wave filter 1A according to the first modification of the embodiment includes a series arm resonator 12 arranged in series in a series arm path connecting the input / output terminals 110 and 120, a series arm resonator 14 arranged in series in the series arm path, a parallel arm resonator 23 connected between the series arm path and ground, a capacitor 44 connected in parallel to the series arm resonator 12, and a capacitor 44 connected in parallel to the series arm resonator 14. Each of the series arm resonators 12, 14 and the parallel arm resonator 23 includes an IDT electrode formed on a piezoelectric substrate. Each of the series arm resonators 12 includes a pair of comb electrodes formed on a piezoelectric substrate, and the IDT electrode has a plurality of first electrode fingers arranged parallel to each other and a set of first bus bar electrodes arranged opposite each other with the plurality of first electrode fingers interposed therebetween. The pair of comb electrodes has a plurality of second electrode fingers arranged parallel to each other and a set of second bus bar electrodes arranged opposite each other with the plurality of second electrode fingers interposed therebetween. The extension direction of the plurality of first electrode fingers intersects the extension direction of the plurality of second electrode fingers, and the resonant frequency fr42 of the capacitor 42 is different from the resonant frequency fr44 of the capacitor 44. Furthermore, the first extension direction of the first electrode fingers of the IDT electrode of the series arm resonator 12 intersects the second extension direction of the second electrode fingers of the pair of comb electrodes of the capacitor 42. This makes it possible to suppress interference between an acoustic wave propagating through the series arm resonator 12 and a high frequency wave propagating through the capacitor 42. Furthermore, the first extension direction of the first electrode fingers of the IDT electrode of the series arm resonator 14 intersects with the second extension direction of the second electrode fingers of the pair of interdigital electrodes of the capacitor 44. This makes it possible to suppress interference between the acoustic wave propagating through the series arm resonator 14 and the high frequency wave propagating through the capacitor 44.

[0152] As a result, the minimum impedance values ​​at the resonant frequencies fr42 and fr44 are greater than the minimum impedance values ​​when the resonant frequencies fr42 and fr44 are the same. Therefore, spurious responses of higher modes can be suppressed in the attenuation band higher than the pass band of the acoustic wave filter 1A, and it is possible to provide an acoustic wave filter 1A with improved attenuation characteristics higher than the pass band.

[0153] An acoustic wave filter 1B according to a second modification of the embodiment includes a series arm resonator 14 arranged in a series arm path connecting input / output terminals 110 and 120, a parallel arm resonator 22 connected between the series arm path and ground, a series arm resonator 12 arranged in series in the series arm path or a parallel arm resonator 23 connected between the series arm path and ground, a capacitor 44 connected in parallel to the series arm resonator 14, and a capacitor 32 connected in parallel to the parallel arm resonator 22. The series arm resonator 14, the parallel arm resonator 22, and the series arm resonator 12 or the parallel arm resonator 23 each include an IDT electrode formed on a piezoelectric substrate. It includes a pair of comb electrodes formed on a piezoelectric substrate, the IDT electrodes having a plurality of first electrode fingers arranged parallel to each other and a set of first bus bar electrodes arranged opposite each other with the plurality of first electrode fingers in between, the pair of comb electrodes having a plurality of second electrode fingers arranged parallel to each other and a set of second bus bar electrodes arranged opposite each other with the plurality of second electrode fingers in between, the extension direction of the plurality of first electrode fingers intersects the extension direction of the plurality of second electrode fingers, and the anti-resonance frequency fa32 of capacitor 32 is smaller than the resonant frequency fr44 of capacitor 44, or the anti-resonance frequency fa32 of capacitor 32 is greater than the anti-resonance frequency fa44 of capacitor 44.

[0154] By setting the anti-resonance frequency fa32 of the capacitor 32 lower than the resonant frequency fr44 of the capacitor 44, the elastic wave filter 1B can ensure a larger attenuation (insertion loss) in the band from the anti-resonance frequency fa32 to the resonant frequency fr44 in the pass characteristics from the input / output terminal 110 to the input / output terminal 120, compared to an elastic wave filter in which the anti-resonance frequency fa32 is equal to the resonant frequency fr44. Furthermore, by setting the anti-resonance frequency fa32 of the capacitor 32 higher than the anti-resonant frequency fa44 of the capacitor 44, the elastic wave filter 1B can ensure a larger attenuation (insertion loss) in the band from the anti-resonance frequency fa44 to the anti-resonant frequency fa32 in the pass characteristics from the input / output terminal 110 to the input / output terminal 120, compared to an elastic wave filter in which the anti-resonance frequency fa32 is equal to the resonant frequency fr44. Therefore, spurious signals of higher modes can be suppressed in the attenuation band higher than the pass band of the elastic wave filter 1B, making it possible to provide an elastic wave filter 1B with improved attenuation characteristics higher than the pass band. Furthermore, the first extension direction of the first electrode fingers of the IDT electrode of the series arm resonator 14 intersects with the second extension direction of the second electrode fingers of the pair of interdigital electrodes of the capacitor 44. This makes it possible to suppress interference between the acoustic wave propagating through the series arm resonator 14 and the high frequency wave propagating through the capacitor 44. Furthermore, the first extension direction of the first electrode fingers of the IDT electrode of the parallel arm resonator 22 intersects with the second extension direction of the second electrode fingers of the pair of interdigital electrodes of the capacitor 32. This makes it possible to suppress interference between the acoustic wave propagating through the parallel arm resonator 22 and the high frequency wave propagating through the capacitor 32.

[0155] Furthermore, in the acoustic wave filter 1 according to the embodiment (and the example), the IDT electrode has a plurality of first electrode fingers arranged parallel to each other and a set of first bus bar electrodes arranged opposite each other with the plurality of first electrode fingers interposed therebetween, the pair of comb electrodes has a plurality of second electrode fingers arranged parallel to each other and a set of second bus bar electrodes arranged opposite each other with the plurality of second electrode fingers interposed therebetween, the extension direction of the plurality of first electrode fingers intersects the extension direction of the plurality of second electrode fingers, and the electrode finger pitch P32 of capacitor 32 is different from the electrode finger pitch P35 of capacitor 35.

[0156] As a result, the maximum impedance values ​​at the anti-resonance frequencies fa32 and fa35 are smaller than the maximum impedance values ​​when the anti-resonance frequencies fa32 and fa35 are the same. This makes it possible to provide an acoustic wave filter 1 with improved attenuation characteristics at frequencies higher than the passband. Furthermore, the first extension direction of the first electrode fingers of the IDT electrode of the parallel arm resonator 22 intersects with the second extension direction of the second electrode fingers of the pair of interdigital electrodes of the capacitor 32. This makes it possible to suppress interference between an acoustic wave propagating through the parallel arm resonator 22 and a high-frequency wave propagating through the capacitor 32. Furthermore, the first extension direction of the first electrode fingers of the IDT electrode of the parallel arm resonator 25 intersects with the second extension direction of the second electrode fingers of the IDT electrode of the capacitor 35. This makes it possible to suppress interference between an acoustic wave propagating through the parallel arm resonator 25 and a high-frequency wave propagating through the capacitor 35.

[0157] Furthermore, in the acoustic wave filter 1A according to the first modification, the IDT electrode has a plurality of first electrode fingers arranged parallel to each other and a set of first bus bar electrodes arranged opposite each other across the plurality of first electrode fingers, and the pair of comb electrodes has a plurality of second electrode fingers arranged parallel to each other and a set of second bus bar electrodes arranged opposite each other across the plurality of second electrode fingers, the extension direction of the plurality of first electrode fingers intersects the extension direction of the plurality of second electrode fingers, and the electrode finger pitch P42 of the capacitor 42 is different from the electrode finger pitch P44 of the capacitor 44.

[0158] As a result, the minimum values ​​of the impedance at the resonant frequencies fr42 and fr44 are greater than the minimum values ​​of the impedance when the resonant frequencies fr42 and fr44 are the same. This makes it possible to provide an acoustic wave filter 1A with improved attenuation characteristics at frequencies higher than the pass band. Furthermore, the first extension direction of the first electrode fingers of the IDT electrode of the series arm resonator 12 intersects with the second extension direction of the second electrode fingers of the pair of interdigital transducers of the capacitor 42. This makes it possible to suppress interference between the acoustic wave propagating through the series arm resonator 12 and the high frequency wave propagating through the capacitor 42. Furthermore, the first extension direction of the first electrode fingers of the IDT electrode of the series arm resonator 14 intersects with the second extension direction of the second electrode fingers of the pair of interdigital transducers of the capacitor 44. This makes it possible to suppress interference between the acoustic wave propagating through the series arm resonator 14 and the high frequency wave propagating through the capacitor 44.

[0159] Furthermore, in the acoustic wave filter 1 according to the embodiment (and the example), the IDT electrode has a plurality of first electrode fingers arranged parallel to each other and a set of first bus bar electrodes arranged opposite each other with the plurality of first electrode fingers interposed therebetween, the pair of comb electrodes has a plurality of second electrode fingers arranged parallel to each other and a set of second bus bar electrodes arranged opposite each other with the plurality of second electrode fingers interposed therebetween, the extension direction of the plurality of first electrode fingers intersects the extension direction of the plurality of second electrode fingers, and the electrode finger duty D32 of capacitor 32 is different from the electrode finger duty D35 of capacitor 35.

[0160] As a result, the maximum impedance values ​​at the anti-resonance frequencies fa32 and fa35 are smaller than the maximum impedance values ​​when the anti-resonance frequencies fa32 and fa35 are the same. This makes it possible to provide an acoustic wave filter 1 with improved attenuation characteristics at frequencies higher than the passband. Furthermore, the first extension direction of the first electrode fingers of the IDT electrode of the parallel arm resonator 22 intersects with the second extension direction of the second electrode fingers of the pair of interdigital electrodes of the capacitor 32. This makes it possible to suppress interference between an acoustic wave propagating through the parallel arm resonator 22 and a high-frequency wave propagating through the capacitor 32. Furthermore, the first extension direction of the first electrode fingers of the IDT electrode of the parallel arm resonator 25 intersects with the second extension direction of the second electrode fingers of the IDT electrode of the capacitor 35. This makes it possible to suppress interference between an acoustic wave propagating through the parallel arm resonator 25 and a high-frequency wave propagating through the capacitor 35.

[0161] In addition, in the acoustic wave filter 1A according to the first modification, the IDT electrode has a plurality of first electrode fingers arranged parallel to each other and a set of first bus bar electrodes arranged opposite each other with the plurality of first electrode fingers interposed therebetween, the pair of comb electrodes has a plurality of second electrode fingers arranged parallel to each other and a set of second bus bar electrodes arranged opposite each other with the plurality of second electrode fingers interposed therebetween, the extension direction of the plurality of first electrode fingers intersects the extension direction of the plurality of second electrode fingers, and the electrode finger duty D42 of the capacitor 42 is different from the electrode finger duty D44 of the capacitor 44.

[0162] As a result, the minimum values ​​of the impedance at the resonant frequencies fr42 and fr44 are greater than the minimum values ​​of the impedance when the resonant frequencies fr42 and fr44 are the same. This makes it possible to provide an acoustic wave filter 1A with improved attenuation characteristics at frequencies higher than the pass band. Furthermore, the first extension direction of the first electrode fingers of the IDT electrode of the series arm resonator 12 intersects with the second extension direction of the second electrode fingers of the pair of interdigital transducers of the capacitor 42. This makes it possible to suppress interference between the acoustic wave propagating through the series arm resonator 12 and the high frequency wave propagating through the capacitor 42. Furthermore, the first extension direction of the first electrode fingers of the IDT electrode of the series arm resonator 14 intersects with the second extension direction of the second electrode fingers of the pair of interdigital transducers of the capacitor 44. This makes it possible to suppress interference between the acoustic wave propagating through the series arm resonator 14 and the high frequency wave propagating through the capacitor 44.

[0163] Furthermore, in the acoustic wave filter 1 according to the embodiment (and the example), the electrode finger duty D32 of the capacitor 32 is different from the electrode finger duty D35 of the capacitor 35, and the electrode finger pitch P32 of the capacitor 32 is different from the electrode finger pitch P35 of the capacitor 35.

[0164] This allows the anti-resonant frequency fa32 of capacitor 32 and the anti-resonant frequency fa35 of capacitor 35 to be made different with high precision, thereby enabling the deterioration of the attenuation (insertion loss) of the anti-resonant frequencies fa32 and fa35 in the pass characteristics from input / output terminal 110 to input / output terminal 120 to be suppressed with high precision.

[0165] In acoustic wave filter 1A according to the first modification, electrode finger pitch P42 of capacitor 42 is different from electrode finger pitch P44 of capacitor 44, and electrode finger duty D42 of capacitor 42 is different from electrode finger duty D44 of capacitor 44.

[0166] This allows the resonant frequency fr42 of capacitor 42 and the resonant frequency fr44 of capacitor 44 to be made different with high precision, thereby enabling the deterioration of the attenuation (insertion loss) of the resonant frequencies fr42 and fr44 in the pass characteristics from input / output terminal 110 to input / output terminal 120 to be suppressed with high precision.

[0167] Furthermore, for example, in the acoustic wave filter 1, the wavelength λ32 of the capacitor 32 is smaller than both the wavelength λ22 of the parallel arm resonator 22 and the wavelength λ25 of the parallel arm resonator 25, and the wavelength λ35 of the capacitor 35 is smaller than both the wavelength λ22 of the parallel arm resonator 22 and the wavelength λ25 of the parallel arm resonator 25.

[0168] As a result, the spurious response of the higher order mode caused by the capacitors 32 and 35 occurs on the higher frequency side than the pass band of the acoustic wave filter 1 .

[0169] Furthermore, for example, in the acoustic wave filter 1A, the wavelength λ42 of the capacitor 42 is smaller than both the wavelength λ12 of the series arm resonator 12 and the wavelength λ14 of the series arm resonator 14, and the wavelength λ44 of the capacitor 44 is smaller than both the wavelength λ12 of the series arm resonator 12 and the wavelength λ14 of the series arm resonator 14.

[0170] As a result, the spurious response of the higher order mode caused by the capacitors 42 and 44 occurs on the higher frequency side than the pass band of the acoustic wave filter 1A.

[0171] Furthermore, for example, in the acoustic wave filter 1B, the wavelength λ32 of the capacitor 32 is smaller than both the wavelength λ22 of the parallel arm resonator 22 and the wavelength λ14 of the series arm resonator 14, and the wavelength λ44 of the capacitor 44 is smaller than both the wavelength λ22 of the parallel arm resonator 22 and the wavelength λ14 of the series arm resonator 14.

[0172] As a result, the spurious response of the higher order mode due to the capacitors 32 and 44 occurs on the higher frequency side than the pass band of the acoustic wave filter 1B.

[0173] Furthermore, for example, in the acoustic wave filter 1, no capacitive element is connected in parallel to each of the series arm resonators 11 to 15.

[0174] Furthermore, for example, in the acoustic wave filter 1A, no capacitive element is connected in parallel to each of the parallel arm resonators 21 to 26.

[0175] Furthermore, for example, in the acoustic wave filter 1B, no capacitive element is connected in parallel to each of the series arm resonators 11 to 13 and 15, or the parallel arm resonators 21 and 23 to 26.

[0176] Furthermore, for example, in the acoustic wave filters 1, 1A, and 1B, the substrate includes a piezoelectric layer 53 on which an IDT electrode is arranged, a support substrate, a low acoustic velocity layer 52 arranged between the piezoelectric layer 53 and the support substrate, in which the acoustic velocity of the bulk waves is slower than that of the bulk waves propagating through the piezoelectric layer 53, and a high acoustic velocity layer arranged between the low acoustic velocity layer 52 and the support substrate, in which the acoustic velocity of the bulk waves propagating through the piezoelectric layer 53 is faster than that of the acoustic wave propagating through the piezoelectric layer 53.

[0177] This allows for the construction of an acoustic wave resonator with a high Q value, and therefore, acoustic wave filters 1, 1A, and 1B with low insertion loss can be constructed using the acoustic wave resonator.

[0178] For example, in acoustic wave filters 1, 1A, and 1B, the substrate includes lithium niobate or lithium tantalate, an IDT electrode is disposed on a first main surface of the substrate, and acoustic wave filters 1, 1A, and 1B further include a dielectric layer 58 disposed on the first main surface so as to cover the IDT electrode.

[0179] This makes it possible to provide wideband acoustic wave filters 1, 1A, and 1B that utilize Rayleigh waves, Love waves, leaky waves, or Lamb waves.

[0180] Also, for example, in the acoustic wave filters 1, 1A, and 1B, the substrate includes a first piezoelectric layer and a second piezoelectric layer, the IDT electrode of the first acoustic wave resonator and the pair of comb electrodes of the first capacitive element are formed on the first piezoelectric layer, and the IDT electrode of the second acoustic wave resonator and the pair of comb electrodes of the second capacitive element are formed on the second piezoelectric layer.

[0181] For example, in the acoustic wave filters 1, 1A, and 1B, the substrate includes a first piezoelectric layer and a second piezoelectric layer, the IDT electrode of the first acoustic wave resonator and the pair of interdigital electrodes of the first capacitive element are formed on the first piezoelectric layer, and the IDT electrode of the second acoustic wave resonator and the pair of interdigital electrodes of the second capacitive element are formed on the second piezoelectric layer, and the thickness of the first piezoelectric layer is different from the thickness of the second piezoelectric layer. (Other Modifications, etc.) While the acoustic wave device has been described above using embodiments, examples, and modifications, the acoustic wave device of the present invention is not limited to the above embodiments, examples, and modifications. The present invention also includes other embodiments realized by combining any of the components in the above embodiments, examples, and modifications, modifications obtained by applying various modifications to the above embodiments, examples, and modifications that would be conceivable to a person skilled in the art without departing from the spirit of the present invention, and various devices incorporating acoustic wave devices according to the above embodiments, examples, and modifications.

[0182] The features of the acoustic wave devices described based on the above-described embodiment, example, and modified examples will be described below.

[0183] <1> A piezoelectric resonator includes: a first acoustic wave resonator connected between a series arm path connecting a first input / output terminal and a second input / output terminal and a ground; a second acoustic wave resonator connected between the series arm path and a ground; a third acoustic wave resonator arranged in series in the series arm path; a first capacitive element connected in parallel to the first acoustic wave resonator; and a second capacitive element connected in parallel to the second acoustic wave resonator, wherein each of the first acoustic wave resonator, the second acoustic wave resonator, and the third acoustic wave resonator includes an IDT electrode formed on a piezoelectric substrate, and each of the first capacitive element and the second capacitive element includes a pair of comb-shaped electrodes formed on the substrate, and the IDT electrode includes: a plurality of first electrode fingers arranged parallel to each other; and a set of first bus bar electrodes arranged opposite each other with the plurality of first electrode fingers interposed therebetween, and the pair of comb-shaped electrodes includes: a plurality of second electrode fingers arranged parallel to each other; and a set of second bus bar electrodes arranged opposite each other with the plurality of second electrode fingers interposed therebetween, an extension direction of the first electrode fingers and an extension direction of the second electrode fingers intersect; and an anti-resonant frequency of the first capacitance element and an anti-resonant frequency of the second capacitance element are different.

[0184] <2> A piezoelectric resonator including: a first acoustic wave resonator arranged in series in a series arm path connecting a first input / output terminal and a second input / output terminal; a second acoustic wave resonator arranged in series in the series arm path; a third acoustic wave resonator connected between the series arm path and ground; a first capacitance element connected in parallel to the first acoustic wave resonator; and a second capacitance element connected in parallel to the second acoustic wave resonator, wherein each of the first acoustic wave resonator, the second acoustic wave resonator, and the third acoustic wave resonator includes an IDT electrode formed on a piezoelectric substrate, and each of the first capacitance element and the second capacitance element includes a pair of comb-shaped electrodes formed on the substrate, and the IDT electrode includes: a plurality of first electrode fingers arranged parallel to each other; and a set of first bus bar electrodes arranged opposite each other with the plurality of first electrode fingers interposed therebetween, and the pair of comb-shaped electrodes includes: a plurality of second electrode fingers arranged parallel to each other; and a set of second bus bar electrodes arranged opposite each other with the plurality of second electrode fingers interposed therebetween, an extension direction of the first electrode fingers and an extension direction of the second electrode fingers intersect; and a resonant frequency of the first capacitance element and a resonant frequency of the second capacitance element are different from each other.

[0185] <3> A piezoelectric resonator including: a first acoustic wave resonator arranged in series in a series arm path connecting a first input / output terminal and a second input / output terminal; a second acoustic wave resonator connected between the series arm path and ground; a third acoustic wave resonator arranged in series in the series arm path or connected between the series arm path and ground; a first capacitance element connected in parallel to the first acoustic wave resonator; and a second capacitance element connected in parallel to the second acoustic wave resonator, wherein each of the first acoustic wave resonator, the second acoustic wave resonator, and the third acoustic wave resonator includes an IDT electrode formed on a piezoelectric substrate, and each of the first capacitance element and the second capacitance element includes a pair of comb electrodes formed on the substrate, and the IDT electrode includes: a plurality of first electrode fingers arranged parallel to each other; and a set of first bus bar electrodes arranged opposite each other with the plurality of first electrode fingers interposed therebetween, and the pair of comb electrodes includes: a plurality of second electrode fingers arranged parallel to each other; a set of second bus bar electrodes arranged opposite each other with the plurality of second electrode fingers interposed therebetween, wherein an extension direction of the plurality of first electrode fingers intersects an extension direction of the plurality of second electrode fingers, and an anti-resonance frequency of the second capacitance element is lower than a resonant frequency of the first capacitance element, or the anti-resonance frequency of the second capacitance element is higher than the anti-resonant frequency of the first capacitance element.

[0186] <4> A piezoelectric resonator includes a first acoustic wave resonator, a second acoustic wave resonator, and a third acoustic wave resonator; a first capacitive element connected in parallel to the first acoustic wave resonator; and a second capacitive element connected in parallel to the second acoustic wave resonator, wherein the first acoustic wave resonator and the second acoustic wave resonator are both connected in series to a series arm path connecting a first input / output terminal and a second input / output terminal, and the third acoustic wave resonator is connected between the series arm path and ground, or the first acoustic wave resonator and the second acoustic wave resonator are both connected between the series arm path and ground, and the third acoustic wave resonator is connected in series to the series arm path, wherein each of the first acoustic wave resonator, the second acoustic wave resonator, and the third acoustic wave resonator includes an IDT electrode formed on a piezoelectric substrate, and each of the first capacitive element and the second capacitive element includes a pair of interdigital electrodes formed on the substrate, and the IDT electrode includes: a plurality of first electrode fingers arranged parallel to each other; an extension direction of the first electrode fingers and an extension direction of the second electrode fingers intersect, and an electrode finger pitch of the first capacitance element and an electrode finger pitch of the second capacitance element are different.

[0187] <5> A piezoelectric resonator includes a first acoustic wave resonator, a second acoustic wave resonator, and a third acoustic wave resonator; a first capacitance element connected in parallel to the first acoustic wave resonator; and a second capacitance element connected in parallel to the second acoustic wave resonator, wherein the first acoustic wave resonator and the second acoustic wave resonator are both connected in series to a series arm path connecting a first input / output terminal and a second input / output terminal, and the third acoustic wave resonator is connected between the series arm path and ground, or the first acoustic wave resonator and the second acoustic wave resonator are both connected between the series arm path and ground, and the third acoustic wave resonator is connected in series to the series arm path, wherein each of the first acoustic wave resonator, the second acoustic wave resonator, and the third acoustic wave resonator includes an IDT electrode formed on a piezoelectric substrate, and each of the first capacitance element and the second capacitance element includes a pair of interdigital electrodes formed on the substrate, and the IDT electrode includes: a plurality of first electrode fingers arranged parallel to each other; an extension direction of the first electrode fingers and an extension direction of the second electrode fingers intersect, and an electrode finger duty of the first capacitance element and an electrode finger duty of the second capacitance element are different.

[0188] <6> The acoustic wave device according to <5>, wherein the electrode finger pitch of the first capacitor element and the electrode finger pitch of the second capacitor element are different.

[0189] <7> The acoustic wave device according to any one of <1> to <6>, wherein an electrode finger pitch of the first capacitance element is smaller than both the electrode finger pitch of the first acoustic wave resonator and the electrode finger pitch of the second acoustic wave resonator, and an electrode finger pitch of the second capacitance element is smaller than both the electrode finger pitch of the first acoustic wave resonator and the electrode finger pitch of the second acoustic wave resonator.

[0190] <8> The acoustic wave device according to any one of <1> to <7>, wherein a capacitive element is not connected in parallel to the third acoustic wave resonator.

[0191] <9> The elastic wave device according to any one of <1> to <8>, wherein the substrate includes: a piezoelectric layer on which the IDT electrode is arranged; a support substrate; a low acoustic velocity layer disposed between the piezoelectric layer and the support substrate, the low acoustic velocity layer having a bulk wave acoustic velocity slower than that of a bulk wave propagating through the piezoelectric layer; and a high acoustic velocity layer disposed between the low acoustic velocity layer and the support substrate, the high acoustic velocity layer having a bulk wave acoustic velocity faster than that of an elastic wave propagating through the piezoelectric layer.

[0192] <10> The acoustic wave device according to any one of <1> to <8>, wherein the substrate includes lithium niobate or lithium tantalate, the IDT electrode is disposed on a first main surface of the substrate, and the acoustic wave device further includes a dielectric layer disposed on the first main surface to cover the IDT electrode.

[0193] <11> The elastic wave device according to any one of <1> to <10>, wherein the substrate includes a first piezoelectric layer and a second piezoelectric layer, the IDT electrode of the first elastic wave resonator and the pair of comb electrodes of the first capacitive element are formed on the first piezoelectric layer, and the IDT electrode of the second elastic wave resonator and the pair of comb electrodes of the second capacitive element are formed on the second piezoelectric layer.

[0194] <12> The elastic wave device according to <3>, wherein the substrate includes a first piezoelectric layer and a second piezoelectric layer, the IDT electrode of the first elastic wave resonator and the pair of comb electrodes of the first capacitive element are formed on the first piezoelectric layer, the IDT electrode of the second elastic wave resonator and the pair of comb electrodes of the second capacitive element are formed on the second piezoelectric layer, and a thickness of the first piezoelectric layer is different from a thickness of the second piezoelectric layer.

[0195] INDUSTRIAL APPLICABILITY The present invention is applicable to a wide range of communication devices such as mobile phones as an acoustic wave filter with low loss and high attenuation that can be applied to multi-band frequency standards.

[0196] 1, 1A, 1B Acoustic wave filter 11, 12, 13, 14, 15 Series arm resonator 21, 22, 23, 24, 25, 26 Parallel arm resonator 32, 35, 42, 44 Capacitor 50 Piezoelectric substrate 51 High acoustic velocity support substrate 52 Low acoustic velocity layer 53 Piezoelectric layer 54 IDT electrode 55 Protective layer 57 Piezoelectric single crystal substrate 58 Dielectric layer 59 Adjustment film 60a, 60b Interdigital electrodes 61a, 61b, 71a, 71b Electrode fingers 62a, 62b, 72a, 72b Bus bar electrodes 110, 120 Input / output terminal 540 Adhesion layer 542 Main electrode layer fa32, fa35, fa44, fa320, fa350 Anti-resonance frequency fr42, fr44 Resonant frequency n1, n2, n3, n4 Connection node λ32, λ35, λ42, λ44 Wavelength

Claims

1. A piezoelectric transducer comprising: a first acoustic wave resonator connected between a series arm path connecting a first input / output terminal and a second input / output terminal and ground; a second acoustic wave resonator connected between the series arm path and ground; a third acoustic wave resonator arranged in series in the series arm path; a first capacitive element connected in parallel to the first acoustic wave resonator; and a second capacitive element connected in parallel to the second acoustic wave resonator, wherein each of the first acoustic wave resonator, the second acoustic wave resonator, and the third acoustic wave resonator includes an IDT (Inter Digital Transducer) electrode formed on a piezoelectric substrate, and each of the first capacitive element and the second capacitive element includes a pair of comb-shaped electrodes formed on the substrate, and the IDT electrode has a plurality of first electrode fingers arranged parallel to each other and a set of first bus bar electrodes arranged opposite each other with the plurality of first electrode fingers interposed therebetween, and the pair of comb-shaped electrodes has a plurality of second electrode fingers arranged parallel to each other and a pair of second bus bar electrodes arranged opposite each other with the plurality of second electrode fingers interposed therebetween, wherein an extension direction of the plurality of first electrode fingers intersects an extension direction of the plurality of second electrode fingers, and an anti-resonance frequency of the first capacitance element is different from an anti-resonance frequency of the second capacitance element.

2. A piezoelectric transducer comprising: a first acoustic wave resonator arranged in series in a series arm path connecting a first input / output terminal and a second input / output terminal; a second acoustic wave resonator arranged in series in the series arm path; a third acoustic wave resonator connected between the series arm path and ground; a first capacitive element connected in parallel to the first acoustic wave resonator; and a second capacitive element connected in parallel to the second acoustic wave resonator, wherein each of the first acoustic wave resonator, the second acoustic wave resonator, and the third acoustic wave resonator includes an IDT electrode formed on a piezoelectric substrate, and each of the first capacitive element and the second capacitive element includes a pair of comb-shaped electrodes formed on the substrate, the IDT electrode including a plurality of first electrode fingers arranged parallel to each other and a set of first bus bar electrodes arranged opposite each other with the plurality of first electrode fingers interposed therebetween, and the pair of comb-shaped electrodes including a plurality of second electrode fingers arranged parallel to each other and a set of second bus bar electrodes arranged opposite each other with the plurality of second electrode fingers interposed therebetween, an extension direction of the first electrode fingers and an extension direction of the second electrode fingers intersect; and a resonant frequency of the first capacitive element and a resonant frequency of the second capacitive element are different from each other.

3. A piezoelectric transducer comprising: a first acoustic wave resonator arranged in series in a series arm path connecting a first input / output terminal and a second input / output terminal; a second acoustic wave resonator connected between the series arm path and ground; a third acoustic wave resonator arranged in series in the series arm path or connected between the series arm path and ground; a first capacitive element connected in parallel to the first acoustic wave resonator; and a second capacitive element connected in parallel to the second acoustic wave resonator, wherein each of the first acoustic wave resonator, the second acoustic wave resonator, and the third acoustic wave resonator includes an IDT electrode formed on a piezoelectric substrate, and each of the first capacitive element and the second capacitive element includes a pair of comb electrodes formed on the substrate, and the IDT electrode has a plurality of first electrode fingers arranged parallel to each other and a set of first bus bar electrodes arranged opposite each other with the plurality of first electrode fingers interposed therebetween, and the pair of comb electrodes has a plurality of second electrode fingers arranged parallel to each other and a set of second bus bar electrodes arranged opposite each other with the plurality of second electrode fingers interposed therebetween, wherein an extension direction of the plurality of first electrode fingers intersects an extension direction of the plurality of second electrode fingers, and an anti-resonance frequency of the second capacitance element is lower than a resonant frequency of the first capacitance element, or the anti-resonance frequency of the second capacitance element is higher than the anti-resonant frequency of the first capacitance element.

4. A piezoelectric resonator comprising: a first acoustic wave resonator, a second acoustic wave resonator, and a third acoustic wave resonator; a first capacitive element connected in parallel to the first acoustic wave resonator; and a second capacitive element connected in parallel to the second acoustic wave resonator, wherein the first acoustic wave resonator and the second acoustic wave resonator are both connected in series to a series arm path connecting a first input / output terminal and a second input / output terminal, and the third acoustic wave resonator is connected between the series arm path and ground, or the first acoustic wave resonator and the second acoustic wave resonator are both connected between the series arm path and ground, and the third acoustic wave resonator is connected in series to the series arm path, wherein each of the first acoustic wave resonator, the second acoustic wave resonator, and the third acoustic wave resonator includes an IDT electrode formed on a piezoelectric substrate, and each of the first capacitive element and the second capacitive element includes a pair of interdigital electrodes formed on the substrate, and the IDT electrode includes: a plurality of first electrode fingers arranged parallel to each other; a set of first bus bar electrodes arranged opposite each other with the plurality of first electrode fingers interposed therebetween, wherein the pair of comb-shaped electrodes has a plurality of second electrode fingers arranged parallel to each other and a set of second bus bar electrodes arranged opposite each other with the plurality of second electrode fingers interposed therebetween, wherein an extension direction of the plurality of first electrode fingers intersects an extension direction of the plurality of second electrode fingers, and an electrode finger pitch of the first capacitance element is different from an electrode finger pitch of the second capacitance element.

5. A piezoelectric resonator comprising: a first acoustic wave resonator, a second acoustic wave resonator, and a third acoustic wave resonator; a first capacitance element connected in parallel to the first acoustic wave resonator; and a second capacitance element connected in parallel to the second acoustic wave resonator, wherein the first acoustic wave resonator and the second acoustic wave resonator are both connected in series to a series arm path connecting a first input / output terminal and a second input / output terminal, and the third acoustic wave resonator is connected between the series arm path and ground, or the first acoustic wave resonator and the second acoustic wave resonator are both connected between the series arm path and ground, and the third acoustic wave resonator is connected in series to the series arm path, wherein each of the first acoustic wave resonator, the second acoustic wave resonator, and the third acoustic wave resonator includes an IDT electrode formed on a piezoelectric substrate, and each of the first capacitance element and the second capacitance element includes a pair of interdigital electrodes formed on the substrate, and the IDT electrode includes: a plurality of first electrode fingers arranged parallel to each other; an extension direction of the first electrode fingers intersects an extension direction of the second electrode fingers; and a set of first bus bar electrodes arranged opposite each other with the plurality of first electrode fingers interposed therebetween, wherein the pair of comb-shaped electrodes has a plurality of second electrode fingers arranged parallel to each other and a set of second bus bar electrodes arranged opposite each other with the plurality of second electrode fingers interposed therebetween, wherein an extension direction of the first electrode fingers intersects an extension direction of the second electrode fingers, and an electrode finger duty of the first capacitance element differs from an electrode finger duty of the second capacitance element.

6. The acoustic wave device according to claim 5, wherein the electrode finger pitch of the first capacitance element and the electrode finger pitch of the second capacitance element are different.

7. The acoustic wave device according to any one of claims 1 to 6, wherein the electrode finger pitch of the first capacitance element is smaller than both the electrode finger pitch of the first acoustic wave resonator and the electrode finger pitch of the second acoustic wave resonator, and the electrode finger pitch of the second capacitance element is smaller than both the electrode finger pitch of the first acoustic wave resonator and the electrode finger pitch of the second acoustic wave resonator.

8. The acoustic wave device according to any one of claims 1 to 7, wherein no capacitive element is connected in parallel to the third acoustic wave resonator.

9. The elastic wave device according to any one of claims 1 to 8, wherein the substrate includes: a piezoelectric layer on which the IDT electrode is arranged; a support substrate; a low acoustic velocity layer arranged between the piezoelectric layer and the support substrate, the low acoustic velocity layer causing a bulk wave to propagate at a slower acoustic velocity than a bulk wave propagating through the piezoelectric layer; and a high acoustic velocity layer arranged between the low acoustic velocity layer and the support substrate, causing a bulk wave to propagate at a faster acoustic velocity than a bulk wave propagating through the piezoelectric layer.

10. The acoustic wave device according to any one of claims 1 to 8, wherein the substrate contains lithium niobate or lithium tantalate, the IDT electrode is disposed on a first main surface of the substrate, and the acoustic wave device further comprises a dielectric layer disposed on the first main surface so as to cover the IDT electrode.

11. The acoustic wave device according to any one of claims 1 to 10, wherein the substrate includes a first piezoelectric layer and a second piezoelectric layer, the IDT electrode of the first acoustic wave resonator and the pair of comb electrodes of the first capacitive element are formed on the first piezoelectric layer, and the IDT electrode of the second acoustic wave resonator and the pair of comb electrodes of the second capacitive element are formed on the second piezoelectric layer.

12. The acoustic wave device according to claim 3, wherein the substrate includes a first piezoelectric layer and a second piezoelectric layer, the IDT electrode of the first acoustic wave resonator and the pair of comb electrodes of the first capacitance element are formed on the first piezoelectric layer, the IDT electrode of the second acoustic wave resonator and the pair of comb electrodes of the second capacitance element are formed on the second piezoelectric layer, and the thickness of the first piezoelectric layer is different from the thickness of the second piezoelectric layer.

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