Acoustic wave filter, and high frequency module

Abstract

To provide an acoustic wave filter which secures low loss property.SOLUTION: An acoustic wave filter 1 includes a series arm resonator 14 arranged on a series arm path connecting input / output terminals 110 and 120, and a parallel arm resonator 23 connected between the series arm path and a ground, wherein each of the series arm resonator 14 and the parallel arm resonator 23 includes an acoustic wave resonator, a resonance frequency frs 14 of the series arm resonator 14 and a resonance frequency frp 23 of the parallel arm resonator 23 are equal to or less than a low frequency end of a pass band of the acoustic wave filter 1, an antiresonance frequency fas 14 of the series arm resonator 14 and an antiresonance frequency fap 23 of the parallel arm resonator 23 are equal to or more than a high frequency end of the pass bad, the resonance frequency frs 14 is higher than the resonance frequency frp 23, and the antiresonance frequency fas 14 is higher than the antiresonance frequency fap 23.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an acoustic wave filter and a high-frequency module. [Background technology]

[0002] Patent Document 1 discloses a filter module including a bandpass filter and a matching resonator. The passband of the filter is included in the range between the resonant frequency and anti-resonant frequency of the matching resonator, so that the impedance of the passband of the filter module can be made inductive. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-088675 Summary of the Invention [Problem to be solved by the invention]

[0004] In the filter module disclosed in Patent Document 1, the matching resonator can make the impedance in the passband inductive, thereby reducing the matching loss when connected to an external circuit with capacitive impedance. However, there are cases where the insertion loss of the matching resonator itself cannot be reduced, which makes it difficult to ensure low loss in the filter module.

[0005] SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an acoustic wave filter that ensures low loss and a high-frequency module including the same. [Means for solving the problem]

[0006] In order to achieve the above object, an acoustic wave filter according to one aspect of the present invention is a band-pass acoustic wave filter including: a first series arm resonator arranged in a series arm path connecting a first input / output terminal and a second input / output terminal; and a first parallel arm resonator connected between the series arm path and ground, wherein the first series arm resonator and the first parallel arm resonator each include an acoustic wave resonator, wherein a first resonance frequency that is the resonance frequency of the first series arm resonator and a second resonance frequency that is the resonance frequency of the first parallel arm resonator are equal to or lower than the low-frequency end of a pass band of the acoustic wave filter, a first anti-resonance frequency that is the anti-resonance frequency of the first series arm resonator and a second anti-resonance frequency that is the anti-resonance frequency of the first parallel arm resonator are equal to or higher than the high-frequency end of the pass band, and the first resonance frequency is higher than the second resonance frequency, and the first anti-resonance frequency is higher than the second anti-resonance frequency.

[0007] Furthermore, a high-frequency module according to one embodiment of the present invention includes a mounting substrate having a first principal surface and a second principal surface facing each other, the above-described acoustic wave filter, and a low-noise amplifier having an input terminal connected to a first input / output terminal, wherein the acoustic wave filter is disposed on the first principal surface and the low-noise amplifier is disposed on the second principal surface, and when the mounting substrate is viewed in a plan view, the acoustic wave filter and the low-noise amplifier at least partially overlap each other. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an acoustic wave filter and a high-frequency module that ensure low loss. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a circuit configuration diagram of an acoustic wave filter and a high-frequency module according to an embodiment of the present invention; [Figure 2A] 1A and 1B are 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. [Figure 2B] FIG. 4 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. [Figure 2C]FIG. 10 is a cross-sectional view schematically illustrating a third example of an acoustic wave resonator included in an acoustic wave filter according to an embodiment. [Figure 3] 4 is a graph showing the pass characteristics of an acoustic wave filter according to an embodiment and the impedance characteristics of each acoustic wave resonator. [Figure 4] 3A and 3B are diagrams schematically illustrating the passband characteristics of an acoustic wave filter according to an embodiment, and the impedance characteristics of a first series arm resonator and a first parallel arm resonator. [Figure 5A] 1 is a circuit configuration diagram of a high-frequency module according to an embodiment; [Figure 5B] FIG. 10 is a circuit configuration diagram of a high-frequency module according to a comparative example. [Figure 6A] 10 is a Smith chart showing impedances in the pass bands of high-frequency modules according to an embodiment and a comparative example. [Figure 6B] 10 is a graph showing the relationship between the inductance value and the noise figure of a matching inductor of a high-frequency module according to a comparative example. [Figure 6C] 10 is a graph showing frequency characteristics of noise figures according to an embodiment and a comparative example. [Figure 7] FIG. 10 is a circuit configuration diagram of an acoustic wave filter according to a first modification of an embodiment. [Figure 8A] FIG. 10 is a circuit diagram of an acoustic wave filter according to a second modification of the embodiment. [Figure 8B] 10 is a graph showing the pass characteristics of a band near the pass band of an acoustic wave filter according to a second modification and the impedance characteristics of a first parallel arm resonator. [Figure 8C] 10 is a graph showing the wide-band impedance characteristics of a first parallel arm resonator of an acoustic wave filter according to a second modification. [Figure 9] 1A and 1B are a plan view and a cross-sectional view of a high-frequency module according to an embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0010] 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, component arrangements, and connection forms shown in the following embodiments are merely examples and are not intended to limit the present invention. Among the components in the following embodiments, components that are not recited in independent claims will be described as optional components. Furthermore, the sizes or size ratios of the components shown in the drawings are not necessarily strict.

[0011] 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.

[0012] In the circuit configurations disclosed herein, "connected" includes not only direct connection by connection terminals and / or wiring conductors, but also electrical connection via matching elements or switch circuits. "Connected between A and B" means connected to both A and B between A and B.

[0013] In the present invention, a "terminal" refers to a point where a conductor within an element terminates. Note that a terminal is not limited to a single point, but may be any point (node) on the conductor between elements or the entire conductor, provided that the impedance of the conductor between elements is sufficiently low.

[0014] Furthermore, in the circuit element arrangement of the present disclosure, "circuit element A is arranged in series on path B" means that the signal input terminal and signal output terminal of circuit element A are connected to two wirings that form at least a part of path B, respectively. At least one of the two wirings may be an electrode or a terminal.

[0015] In the following figures, the x-axis and y-axis are axes that are perpendicular to each other on a plane parallel to the main surface of the module substrate. Specifically, if the module substrate has a rectangular shape in a plan view, the x-axis is parallel to a first side of the module substrate, and the y-axis is parallel to a second side of the module substrate that is perpendicular to the first side. The z-axis is an axis perpendicular to the main surface of the module substrate, with its positive direction indicating the upward direction and its negative direction indicating the downward direction.

[0016] 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.

[0017] Furthermore, in the component placement of this invention, "planar view of the module substrate" means viewing an object by orthogonally projecting it onto the xy plane from the positive side of the z axis. "A overlaps with B in planar view" means that at least a portion of the area of A orthogonally projected onto the xy plane overlaps with at least a portion of the area of B orthogonally projected onto the xy plane. Furthermore, "A is placed between B and C" means that at least one of multiple line segments connecting any point in B and any point in C passes through A.

[0018] In the component placement of the present invention, "components are placed on a substrate" includes components being placed on the main surface of a substrate and components being placed within a substrate. "Components are placed on the main surface of a substrate" includes components being placed in contact with the main surface of a substrate, as well as components being placed above the main surface without contacting the main surface (for example, components being stacked on top of other components placed in contact with the main surface). "Components are placed on the main surface of a substrate" may also include components being placed in recesses formed in the main surface. "Components are placed within a substrate" includes components being encapsulated within a module substrate, as well as components being entirely placed between the two main surfaces of a substrate but partially not covered by the substrate, and components being only partially placed within the substrate.

[0019] In the following embodiments, the passband of a filter is defined as a frequency band between two frequencies that are 3 dB higher than the minimum value of insertion loss within the passband.

[0020] An elastic wave resonator is defined as any of the following: (1) a resonant circuit (a parallel connection circuit of an elastic wave resonator and a circuit (or circuit element)) consisting of an elastic wave resonator and a circuit (or circuit element) connected in parallel to the elastic wave resonator; (2) a resonant circuit (a series connection circuit of an elastic wave resonator and a circuit (or circuit element)) consisting of an elastic wave resonator and a circuit (or circuit element) connected to only one of the two input / output terminals of the elastic wave resonator, where the connection node connecting the elastic wave resonator and the circuit (or circuit element) is not connected to other circuits (and other circuit elements) or ground; (3) a resonant circuit (a parallel connection circuit of split resonators) consisting of multiple elastic wave resonators connected in parallel; and (4) a resonant circuit (series connection circuit of split resonators) consisting of multiple elastic wave resonators connected in series, where the connection node connecting the multiple elastic wave resonators is not connected to circuits (and circuit elements) other than the multiple elastic wave resonators or ground.

[0021] In addition, in the embodiments of the present disclosure, the resonance bandwidth refers to the frequency difference between the antiresonance frequency and the resonance frequency of an acoustic wave resonator.

[0022] The resonant frequency and anti-resonant frequency shown in the above embodiments and modifications are derived, for example, by contacting an RF probe with two input and output electrodes of an acoustic wave resonator or acoustic wave oscillator when the acoustic wave resonator or acoustic wave oscillator is not connected to other circuit elements, and measuring the reflection characteristics (impedance characteristics) using a network analyzer or the like.

[0023] Furthermore, 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 the present embodiment, examples of the communication system that can be used include, but are not limited to, a Long Term Evolution (LTE) system, a 5th Generation (5G)-New Radio (NR) system, and a Wireless Local Area Network (WLAN) system. Note that the uplink operating band of a frequency band refers to a frequency range designated for uplink within the frequency band. Furthermore, the downlink operating band of a frequency band refers to a frequency range designated for downlink within the frequency band.

[0024] (Embodiment) [1. Circuit Configuration of Acoustic Wave Filter 1 and High-Frequency Module 100] 1 is a circuit diagram of an acoustic wave filter 1 and a high-frequency module 100 according to an embodiment. As shown in the figure, the high-frequency module 100 includes an acoustic wave filter 1, a low-noise amplifier 2, and an output terminal 130.

[0025] The low-noise amplifier 2 is connected between the acoustic wave filter 1 and the output terminal 130. Specifically, the input terminal of the low-noise amplifier 2 is connected to the input / output terminal 120 of the acoustic wave filter 1. The low-noise amplifier 2 includes an amplifying transistor, such as a field effect transistor (FET) or a bipolar transistor. The gate (or base) of the amplifying transistor is connected to the input / output terminal 120, the drain (or collector) is connected to the output terminal 130, and the source (or emitter) is connected to ground. A DC bias voltage (DC bias current) is supplied to the gate (or base) of the amplifying transistor. With the above configuration, the low-noise amplifier 2 amplifies the high-frequency signal that has passed through the acoustic wave filter 1 and outputs the amplified signal to the output terminal 130 by supplying the DC bias voltage (DC bias current) to the gate (or base). The input impedance of the low-noise amplifier 2 is capacitive and high.

[0026] The acoustic wave filter 1 is a band-pass filter and includes series arm resonators 11, 12, 13, and 14, parallel arm resonators 21, 22, and 23, capacitors 15 and 24, and input / output terminals 110 and 120.

[0027] Each of the series arm resonators 11 to 14 is an example of an acoustic wave resonator including an acoustic wave resonator, and is arranged in a series arm path connecting the input / output terminal 110 (second input / output terminal) and the input / output terminal 120 (twelfth input / output terminal). The series arm resonator 11 constitutes one series arm resonator (acoustic wave resonator) by itself, the series arm resonator 12 constitutes one series arm resonator (acoustic wave resonator) by itself, the series arm resonator 13 constitutes one series arm resonator (acoustic wave resonator) by itself, and the series arm resonator 14 constitutes one series arm resonator (acoustic wave resonator) by itself. The capacitor 15 is an example of a first capacitor, and is arranged in series in the series arm path.

[0028] The series arm resonators 11 to 14 and the capacitor 15 are connected in the following order from the input / output terminal 110: series arm resonator 11, capacitor 15, series arm resonators 12, 13, and 14.

[0029] Each of the parallel arm resonators 21 to 23 is an example of an acoustic wave resonator including 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 series arm resonator 11 and the capacitor 15 and ground. The parallel arm resonator 22 is connected between the connection point of the capacitor 15 and the series arm resonator 12 and ground. The parallel arm resonator 21 constitutes one parallel arm resonator (acoustic wave resonator) by itself, the parallel arm resonator 22 constitutes one parallel arm resonator (acoustic wave resonator) by itself, and the parallel arm resonator 23 constitutes one parallel arm resonator (acoustic wave resonator) by itself. The capacitor 24 is an example of a second capacitor, and is arranged in series in the parallel arm path connecting the series arm path between the series arm resonators 12 and 13 and ground. The parallel arm resonator 23 is connected between the connection point of the series arm resonators 13 and 14 and ground.

[0030] Of the series arm resonators 11 to 14, the series arm resonator 14 is an example of a first series arm resonator, and has a resonance frequency frs14 (first resonance frequency) and an anti-resonance frequency fas14 (first anti-resonance frequency).

[0031] Of the parallel arm resonators 21 to 23, the parallel arm resonator 23 is an example of a first parallel arm resonator, and has a resonance frequency frp23 (second resonance frequency) and an anti-resonance frequency fap23 (second anti-resonance frequency).

[0032] Each of the series arm resonators 11 to 14 and the parallel arm resonators 21 to 23 (elastic wave resonators) has only one elastic wave resonator. However, each of the series arm resonators 11 to 14 and the parallel arm resonators 21 to 23 may be, for example, any of (1) a resonator configured with an elastic wave resonator and a circuit including at least one of a capacitor and an inductor connected in parallel to the elastic wave resonator, (2) a resonator configured with an elastic wave resonator and a circuit including at least one of a capacitor and an inductor connected in series to the elastic wave resonator, (3) a resonator configured with multiple elastic wave resonators connected in parallel, and (4) a resonator configured with multiple elastic wave resonators connected in series.

[0033] Furthermore, the acoustic wave filter 1 according to this preferred embodiment may include one or more series arm resonators including the series arm resonator 14 and one or more parallel arm resonators including the parallel arm resonator 23, and may not include other acoustic wave resonators or capacitors.

[0034] Furthermore, the acoustic wave filter 1 according to this preferred embodiment may include a longitudinally coupled resonator in addition to the series arm resonators and parallel arm resonators that form a ladder filter.

[0035] [2. Structure of elastic wave resonators] Next, the structures of the acoustic wave resonators (series arm resonators and parallel arm resonators) that configure the acoustic wave filter 1 will be illustrated.

[0036] 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 structures of a plurality of acoustic wave resonators that constitute 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 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.

[0037] The acoustic wave resonator 60 is composed of a piezoelectric substrate 50 and comb-shaped electrodes 60a and 60b.

[0038] 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 and a busbar electrode 62a connecting the plurality of electrode fingers 61a. The comb-shaped electrode 60b is composed of a plurality of parallel electrode fingers 61b and a busbar electrode 62b connecting the plurality of electrode fingers 61b. The plurality of electrode fingers 61a and 61b are formed along a direction perpendicular to the acoustic wave propagation direction (X-axis direction).

[0039] The IDT electrode 54, which is composed of the electrode fingers 61a and 61b and the 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).

[0040] 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. The protective layer 55 is formed to cover the comb-shaped electrodes 60a and 60b. 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 whose main component is silicon dioxide.

[0041] 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 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.

[0042] Next, the layered structure of the piezoelectric substrate 50 will be described.

[0043] As shown in (c) of Figure 2A, the piezoelectric substrate 50 includes a high acoustic speed support substrate 51, a low acoustic speed film 52, and a piezoelectric film 53, and has a structure in which the high acoustic speed support substrate 51, the low acoustic speed film 52, and the piezoelectric film 53 are stacked in this order.

[0044] The piezoelectric film 53 is made of, for example, a θ° Y-cut X-propagation LiTaO3 piezoelectric single crystal or piezoelectric ceramics (a lithium tantalate single crystal or ceramics cut along a plane whose normal is an axis rotated θ° 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 film 53 are appropriately selected depending on the required specifications of each filter.

[0045] The high acoustic velocity support substrate 51 is a substrate that supports the low acoustic velocity film 52, the piezoelectric film 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 film 53, and functions to confine the surface acoustic waves to the portion where the piezoelectric film 53 and the low acoustic velocity film 52 are laminated, preventing leakage below the high acoustic velocity support substrate 51. Examples of materials that can be used for the high acoustic velocity support substrate 51 include piezoelectric materials such as aluminum nitride, lithium tantalate, lithium niobate, and quartz; ceramics such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, spinel, and sialon; dielectrics such as aluminum oxide, silicon oxynitride, diamond-like carbon (DLC), and diamond; semiconductors such as silicon; and materials containing any of the above materials as a main component. The spinel includes an aluminum compound containing oxygen and one or more elements selected from Mg, Fe, Zn, Mn, etc. Examples of the spinel include MgAl2O4, FeAl2O4, ZnAl2O4, and MnAl2O4.

[0046] The low acoustic velocity film 52 is a film in which the acoustic velocity of the bulk waves in the low acoustic velocity film 52 is slower than that of the bulk waves propagating through the piezoelectric film 53, and is disposed between the piezoelectric film 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 film 53. The low acoustic velocity film 52 can be made of, for example, a dielectric such as glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum oxide, or a compound in which fluorine, carbon, or boron is added to silicon oxide, or a material containing any of the above materials as a main component.

[0047] The above-described laminated structure of piezoelectric substrate 50 makes it possible to significantly increase the Q value at the resonant frequency and anti-resonant frequency compared to a conventional structure using a single-layer piezoelectric substrate. In other words, an acoustic wave resonator with a high Q value can be configured, and a filter with low insertion loss can be configured using the acoustic wave resonator.

[0048] 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 the surface waves and boundary waves, etc., that propagate through the piezoelectric film 53. In this case, the high acoustic velocity film may be made of the same material as the high acoustic velocity support substrate 51. The support substrate may be made of, for example, piezoelectric materials such as aluminum nitride, lithium tantalate, lithium niobate, and quartz; ceramics such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, and forsterite; dielectric materials 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.

[0049] 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.

[0050] 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 film 53. However, the substrate on which the IDT electrode 54 is formed may be a piezoelectric single crystal substrate 57 made of a single piezoelectric layer, as illustrated in FIG. 2B.

[0051] The piezoelectric single crystal substrate 57 is made of, for example, a piezoelectric single crystal of LiNbO3. The elastic wave resonator according to this example is made up of the LiNbO3 piezoelectric single crystal substrate 57, an IDT electrode 54, and a protective layer 58 formed on the piezoelectric single crystal substrate 57 and the IDT electrode 54.

[0052] The laminate structure, material, cut angle, and thickness of the piezoelectric film 53 and piezoelectric single crystal substrate 57 may be changed as appropriate depending on the required pass characteristics of the acoustic wave filter device, etc. An acoustic wave resonator using a LiTaO piezoelectric substrate having a cut angle other than the above-mentioned cut angle can also achieve the same effects as the acoustic wave resonator 60 using the piezoelectric film 53.

[0053] Alternatively, the substrate on which the IDT electrode 54 is formed may have a structure in which a support substrate, an energy trapping layer, and a piezoelectric film are stacked in this order. The IDT electrode 54 is formed on the piezoelectric film. The piezoelectric film may be made of, for example, a LiTaO3 piezoelectric single crystal or a piezoelectric ceramic. The support substrate is a substrate that supports the piezoelectric film, the energy trapping layer, and the IDT electrode 54.

[0054] 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.

[0055] 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.

[0056] Here, the electrode parameters of the IDT electrode 54 that constitutes the acoustic wave resonator 60 will be described.

[0057] The wavelength of the acoustic wave resonator is defined by wavelength λ, which is the repetition period of the electrode fingers 61a or 61b constituting the IDT electrode 54 shown in FIG. 2A (b). The electrode finger pitch is half of the wavelength λ and is defined as (W+S), where W is the line width of the electrode fingers 61a and 61b constituting the interdigital transducers 60a and 60b, respectively, and S is the space width between adjacent electrode fingers 61a and 61b. The duty of the IDT electrode 54 is the line width occupancy rate of the electrode fingers 61a and 61b, which is the ratio of the line width to the sum of the line width and space width of each of the electrode fingers 61a and 61b, and is defined as W / (W+S). The overlap width of the IDT electrode 54 is the length of the overlapping electrode fingers 61a and 61b when viewed from the acoustic wave propagation direction (X-axis direction).

[0058] In the IDT electrode 54, when the interval between adjacent electrode fingers is not constant, the electrode finger pitch of the IDT electrode 54 is defined as the average electrode finger pitch of the IDT electrode 54. The average electrode finger pitch of the IDT electrode 54 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 acoustic wave propagation direction.

[0059] 2C is a cross-sectional view schematically illustrating a third example of an acoustic wave resonator included in the acoustic wave filter 1 according to the embodiment. Fig. 2C illustrates a bulk acoustic wave resonator as the acoustic wave resonator of the acoustic wave filter 1. As shown in the figure, the bulk acoustic wave resonator includes, for example, a support substrate 65, a lower electrode 66, a piezoelectric layer 67, and an upper electrode 68, and is configured such that the support substrate 65, the lower electrode 66, the piezoelectric layer 67, and the upper electrode 68 are layered in this order.

[0060] The support substrate 65 is a substrate, such as a silicon substrate, for supporting the lower electrode 66, the piezoelectric layer 67, and the upper electrode 68. The support substrate 65 has a cavity in the region that contacts the lower electrode 66. This allows the piezoelectric layer 67 to vibrate freely.

[0061] The lower electrode 66 is formed on one surface of the support substrate 65. The upper electrode 68 is formed on one surface of the support substrate 65. The lower electrode 66 and the upper electrode 68 are made of a material such as Al containing 1% Cu.

[0062] The piezoelectric layer 67 is formed between the lower electrode 66 and the upper electrode 68. The piezoelectric layer 67 is mainly composed of at least one of ZnO (zinc oxide), AlN (aluminum nitride), PZT (lead zirconate titanate), KN (potassium niobate), LN (lithium niobate), LT (lithium tantalate), quartz crystal, and LiBO (lithium borate).

[0063] A bulk acoustic wave resonator having the above-described layered structure generates resonance by inducing bulk acoustic waves in the piezoelectric layer 67 when electrical energy is applied between the lower electrode 66 and the upper electrode 68. The bulk acoustic waves generated by this bulk acoustic wave resonator propagate between the lower electrode 66 and the upper electrode 68 in a direction perpendicular to the film surface of the piezoelectric layer 67. In other words, a bulk acoustic wave resonator is a resonator that utilizes bulk acoustic waves.

[0064] [3 Resonance and pass characteristics of acoustic wave filter 1] First, the basic operating principle of a ladder-type bandpass filter composed of one series arm resonator and one parallel arm resonator will be explained.

[0065] 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 series arm signal 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, as the frequency increases and approaches the antiresonance frequency fas, the impedance of the series arm resonator increases, resulting in a high-frequency stopband.

[0066] In addition, in each of the series arm resonators and the parallel arm resonators, the impedance of the resonators is capacitive (C-type) in the frequency band lower than the resonant frequency, and is inductive (L-type) in the frequency band higher than the resonant frequency and lower than the anti-resonant frequency. In addition, the impedance of the resonators is capacitive in the frequency band higher than the anti-resonant frequency.

[0067] When the resonant bandwidth is wider than the desired passband bandwidth, the antiresonant frequency of the parallel arm resonator may be higher than the high-frequency end of the passband, and the resonant frequency of the series arm resonator may be lower than the low-frequency end of the passband. A resonator whose resonant bandwidth, which is the frequency range from the resonant frequency to the antiresonant frequency, at least partially overlaps with the passband of the acoustic wave filter 1 is defined as a resonator that contributes to forming the passband of the acoustic wave filter 1.

[0068] Next, the impedance characteristics and pass characteristics of the acoustic wave filter 1 will be described.

[0069] 3 is a graph showing the passband characteristics of the acoustic wave filter 1 according to the embodiment and the impedance characteristics of each acoustic wave resonator. As shown in the figure, the passband width (10 MHz) of the acoustic wave filter 1 is narrower than the resonance bandwidth (80-100 MHz) of each acoustic wave resonator. The acoustic wave filter 1 has a passband that includes, for example, the downlink operating band (2350-2360 MHz) of band B30 for LTE or band n30 for 5G-NR.

[0070] The passband (2350 to 2360 MHz) of the acoustic wave filter 1 according to this embodiment is located between the resonant frequencies and anti-resonant frequencies of the series arm resonators 12 to 14, and is also located between the resonant frequencies and anti-resonant frequencies of the parallel arm resonators 21 to 23.

[0071] That is, the series arm resonators 12 to 14 and the parallel arm resonators 21 to 23 have resonance bands that at least partially overlap with the pass band of the acoustic wave filter 1, and therefore contribute to forming the pass band of the acoustic wave filter 1.

[0072] On the other hand, the series arm resonator 11 is a resonator that does not contribute to the formation of the pass band of the acoustic wave filter 1 because both the resonant frequency and the anti-resonant frequency are higher than the high-frequency end of the pass band.

[0073] Note that acoustic wave resonators may be provided instead of the capacitors 15 and 24. The resonance bandwidths of the series arm resonators 12 to 14 and the parallel arm resonators 21 to 23 are wider than the desired pass band of the acoustic wave filter 1. In contrast, in the acoustic wave filter 1 according to this embodiment, the capacitors 15 and 24 are provided, which makes it easier to form a narrow pass band using acoustic wave resonators having a wide resonance bandwidth.

[0074] Furthermore, because the acoustic wave resonators have the same resonance bandwidth (80-100 MHz), all of the acoustic wave resonators constituting the acoustic wave filter 1 can be formed on a single piezoelectric substrate, which allows the acoustic wave filter 1 to be miniaturized.

[0075] FIG. 4 is a diagram schematically illustrating the passband characteristics of the acoustic wave filter 1 according to the embodiment and the impedance characteristics of the series arm resonator 14 (first series arm resonator) and the parallel arm resonator 23 (first parallel arm resonator).

[0076] As shown in the figure, the resonant frequency frs14 (first resonant frequency) of the series arm resonator 14 (first series arm resonator) and the resonant frequency frp23 (second resonant frequency) of the parallel arm resonator 23 (first parallel arm resonator) are below the low frequency end of the pass band of the acoustic wave filter 1. In addition, the antiresonant frequency fas14 (first antiresonant frequency) of the series arm resonator 14 (first series arm resonator) and the antiresonant frequency fap23 (second antiresonant frequency) of the parallel arm resonator 23 (first parallel arm resonator) are above the high frequency end of the pass band.

[0077] That is, the resonance band of the series arm resonator 14 includes the pass band of the acoustic wave filter 1, and the impedance of the series arm resonator 14 is inductive across the pass band. Also, the resonance band of the parallel arm resonator 23 includes the pass band of the acoustic wave filter 1, and the impedance of the parallel arm resonator 23 is inductive across the pass band.

[0078] Furthermore, the resonance frequency frs14 is higher than the resonance frequency frp23, and the anti-resonance frequency fas14 is higher than the anti-resonance frequency fap23.

[0079] That is, of the resonant frequencies frs14 and frp23 at which the impedance becomes minimum, the resonant frequency frs14 is closer to the pass band, and of the antiresonant frequencies fas14 and fap23 at which the impedance becomes maximum, the antiresonant frequency fas14 is farther from the pass band. As a result, the low-impedance band of the inductive impedance band of the series arm resonator 14 overlaps with the pass band, and the high-impedance band of the inductive impedance band of the parallel arm resonator 23 overlaps with the pass band.

[0080] Fig. 5A is a circuit configuration diagram of a high-frequency module 100 according to the embodiment. Fig. 5B is a circuit configuration diagram of a high-frequency module 500 according to a comparative example. Fig. 6A is a Smith chart showing impedances in a band (1800 to 2800 MHz) that includes the passbands of the high-frequency modules according to the embodiment and the comparative example.

[0081] As shown in FIG. 5A, the high-frequency module 100 according to this embodiment may be provided with an input terminal 140 and an inductor 42 for impedance matching with an external circuit connected to the input terminal 140.

[0082] On the other hand, a high-frequency module 500 according to the comparative example includes an acoustic wave filter 501, a low-noise amplifier 2, inductors 41 and 43, an input terminal 140, and an output terminal 130. The acoustic wave filter 501 has a circuit configuration similar to that of the acoustic wave filter 1, including four series arm resonators, three parallel arm resonators, and two capacitors. However, the resonant frequencies of the four series arm resonators are located within the pass band of the acoustic wave filter 501, and the anti-resonant frequencies of the three parallel arm resonators are located within the pass band of the acoustic wave filter 501. Due to this and the structure of the acoustic wave resonators (an IDT electrode structure or a piezoelectric film laminate structure), the impedance in the pass band of the acoustic wave filter 501 tends to be capacitive. As a result, by placing an inductor 41 having an inductive impedance between the low-noise amplifier 2 having a capacitive input impedance and the acoustic wave filter 501, it is possible to match the two at a reference impedance. However, when the inductor 41 is disposed between the low-noise amplifier 2 and the acoustic wave filter 501 , a parasitic capacitance 32 due to the wiring of the inductor 41 occurs near the input terminal of the low-noise amplifier 2 .

[0083] As shown in FIG. 6A, the impedance of the pass band when the low noise amplifier 2 is viewed from the node A is a capacitive impedance (A).

[0084] In contrast, in the high-frequency module 500 according to the comparative example, the parasitic capacitance 32 is added in parallel, so that the impedance in the band (1800 to 2800 MHz) seen from the node B to the low-noise amplifier 2 shifts clockwise on an equal-conductance circle to become a higher capacitive impedance (B), as shown in Fig. 6A. Also, the impedance in the band (1800 to 2800 MHz) seen from the node C2 to the acoustic wave filter 501, the inductor 41, and the low-noise amplifier 2 shifts clockwise on an equal-resistance circle (hereinafter referred to as equal-resistance circle RB) with respect to the impedance (B), as shown in Fig. 6A.

[0085] On the other hand, in the high-frequency module 100 according to this embodiment, since the inductor 41 for impedance matching is not added, the impedance in the band (1800 to 2800 MHz) when viewing the acoustic wave filter 1 and the low-noise amplifier 2 from the node C1 moves clockwise on an equal resistance circle with a higher resistance than the equal resistance circle RB with respect to the impedance (A), as shown in FIG. 6A, and becomes impedance (C1).

[0086] As a result, as shown in FIG. 6A, in the high-frequency module 500 according to the comparative example, the impedance of the pass band viewed from the input side of the acoustic wave filter 501 becomes lower than that of the high-frequency module 100 according to the embodiment due to the parasitic capacitance 32 generated by the addition of the inductor 41, and deviates from the reference impedance.

[0087] That is, in this embodiment, the impedance in the pass band of the acoustic wave filter 1 can be made inductive, and the impedance of the high-frequency module 100 can be made closer to the reference impedance without adding the inductor 41. This reduces the matching loss of the acoustic wave filter 1 and the high-frequency module 100, and enables the high-frequency module 100 to be made more compact.

[0088] Furthermore, as described above, the resonant frequency frs14 is higher than the resonant frequency frp23, and the antiresonant frequency fas14 is higher than the antiresonant frequency fap23. As a result, the low-impedance band of the inductive impedance band of the series arm resonator 14 overlaps with the pass band, and the high-impedance band of the inductive impedance band of the parallel arm resonator 23 overlaps with the pass band. This reduces the insertion loss of the acoustic wave filter 1.

[0089] Therefore, it is possible to provide the acoustic wave filter 1 and the high-frequency module 100 that ensure low loss in terms of both matching loss and insertion loss.

[0090] In the acoustic wave filter 1 according to this embodiment, the first series arm resonator (series arm resonator 14) is connected closest to the input / output terminal 120 among the multiple series arm resonators, and the first parallel arm resonator (parallel arm resonator 23) is connected closest to the input / output terminal 120 among the multiple parallel arm resonators.

[0091] This allows the resonator, whose passband exhibits inductive impedance, to be positioned closest to the input terminal of the low-noise amplifier 2, which exhibits capacitive impedance, thereby enabling impedance matching between the acoustic wave filter 1 and the low-noise amplifier 2 with high efficiency and precision.

[0092] The first series arm resonator does not have to be the series arm resonator 14, but may be any of the series arm resonators 11 to 13. The first parallel arm resonator does not have to be the parallel arm resonator 23, but may be the parallel arm resonator 21 or 22. That is, the first series arm resonator does not have to be the one connected closest to the input / output terminal 120 among the multiple series arm resonators, and the first parallel arm resonator does not have to be the one connected closest to the input / output terminal 120 among the multiple parallel arm resonators. Even in this case, the impedance in the pass band of the acoustic wave filter 1 can be made inductive, thereby reducing the matching loss of the acoustic wave filter 1 and the high-frequency module 100 and enabling the high-frequency module 100 to be miniaturized.

[0093] Furthermore, acoustic wave filter 1 according to this preferred embodiment only needs to include at least one first series arm resonator and one first parallel arm resonator. That is, in acoustic wave filter 1 according to this preferred embodiment, the resonance bands of series arm resonators 11 to 13 and parallel arm resonators 21 to 22 do not necessarily need to include the passband.

[0094] Furthermore, in the elastic wave filter of the present invention, it is desirable that, among the multiple elastic wave resonators, the number of elastic wave resonators whose resonant frequencies are equal to or lower than the low frequency end of the pass band and whose anti-resonant frequencies are equal to or higher than the high frequency end of the pass band is greater than the number of elastic wave resonators whose resonant frequencies are higher than the low frequency end of the pass band or whose anti-resonant frequencies are lower than the high frequency end of the pass band.

[0095] In this case, the number of acoustic wave resonators whose passband impedance is inductive is greater than the number of acoustic wave resonators whose passband impedance is capacitive, so that the impedance of the entire passband of the acoustic wave filter 1 is inductive. This makes it possible to achieve more accurate impedance matching between the low-noise amplifier 2, which has a capacitive input impedance, and the acoustic wave filter 1. This makes it possible to provide an acoustic wave filter 1 and a high-frequency module 100 with reduced matching loss.

[0096] 6B is a graph showing the relationship between the inductance value Lg of the inductor 41 of the high-frequency module 500 according to the comparative example and the noise figure. As shown in the figure, the smaller the inductance value Lg, the smaller the resistance component of the inductor 41, thereby reducing the noise figure of the low-noise amplifier 2. Furthermore, when the inductor 41 is not added (the inductance value Lg is 0), as in the high-frequency module 100 according to the present embodiment, the parasitic capacitance 32 generated due to the mounting electrode of the inductor 41 and the wiring from the mounting electrode to the low-noise amplifier 2 becomes smaller, thereby significantly reducing the noise figure of the low-noise amplifier 2.

[0097] 6C is a graph showing the frequency characteristics of the noise figure of the low-noise amplifier 2 according to the embodiment and the comparative example. The low-noise amplifier 2 according to the embodiment has a lower noise figure across the entire frequency band (1800 to 2800 MHz) including the passband than the low-noise amplifier 2 according to the comparative example. Therefore, the high-frequency module 100 according to this embodiment can reduce the noise figure of the low-noise amplifier 2.

[0098] 4. Configuration of Acoustic Wave Filter 1A According to Modification 1 7 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 according to the first modification is a band-pass filter and includes series arm resonators 11, 12, 13, and 16, parallel arm resonators 21, 22, and 25, capacitors 35 and 36, 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 that the series arm resonator 14, the parallel arm resonator 23, and the capacitors 15 and 24 are not included, but the series arm resonator 16, the parallel arm resonator 25, and the capacitors 35 and 36 are included. Hereinafter, the elastic wave filter 1A according to this modification will be described mainly with reference to the different configurations, and a description of the same configurations as those of the elastic wave filter 1 according to the embodiment will be omitted.

[0099] The series arm resonator 16 and the capacitor 36 connected in parallel to each other are an example of an acoustic wave resonator including an acoustic wave resonator, and constitute a series arm resonator 16A. The series arm resonator 16A is arranged in a series arm path connecting the input / output terminal 110 (second input / output terminal) and the input / output terminal 120 (twelfth input / output terminal). By connecting the capacitor 36 in parallel to the series arm resonator 16, the resonance bandwidth of the series arm resonator 16A becomes narrower than the resonance bandwidth of the series arm resonator 16.

[0100] The series arm resonators 11 to 13 and the series arm resonator 16A are connected in this order from the input / output terminal 110: series arm resonator 11, series arm resonator 16A, series arm resonators 12 and 13.

[0101] The parallel arm resonator 25 and the capacitor 35 connected in series to each other are an example of an acoustic wave resonator including an acoustic wave resonator, and constitute the parallel arm resonator 25A. The parallel arm resonator 25A is connected between the connection point of the series arm resonators 12 and 13 and ground. By connecting the capacitor 35 in series to the parallel arm resonator 25, the resonance bandwidth of the parallel arm resonator 25A becomes narrower than the resonance bandwidth of the parallel arm resonator 25.

[0102] The series arm resonator 13 is an example of a first series arm resonator, and has a resonance frequency frs13 (first resonance frequency) and an anti-resonance frequency fas13 (first anti-resonance frequency).

[0103] The parallel arm resonator 25A is an example of a first parallel arm resonator, and has a resonance frequency frp25A (second resonance frequency) and an anti-resonance frequency fap25A (second anti-resonance frequency).

[0104] The resonant frequency frs13 (first resonant frequency) of the series arm resonator 13 (first series arm resonator) and the resonant frequency frp25A (second resonant frequency) of the parallel arm resonator 25A (first parallel arm resonator) are lower than the low frequency end of the pass band of the acoustic wave filter 1A. In addition, the antiresonant frequency fas13 (first antiresonant frequency) of the series arm resonator 13 (first series arm resonator) and the antiresonant frequency fap25A (second antiresonant frequency) of the parallel arm resonator 25A (first parallel arm resonator) are higher than the high frequency end of the pass band.

[0105] Furthermore, the resonance frequency frs13 is higher than the resonance frequency frp25A, and the anti-resonance frequency fas13 is higher than the anti-resonance frequency fap25A.

[0106] By making the impedance of the acoustic wave filter 1A according to this modification inductive in the pass band, the impedance of the high-frequency module according to this modification, which includes the acoustic wave filter 1A and the low-noise amplifier 2, can be made closer to the reference impedance without adding a matching inductor. This reduces the matching loss of the acoustic wave filter 1A and the high-frequency module according to this modification, allowing the high-frequency module to be miniaturized.

[0107] Furthermore, the low-impedance band of the inductive impedance band of the series arm resonator 13 overlaps with the pass band, and the high-impedance band of the inductive impedance band of the parallel arm resonator 25A overlaps with the pass band, thereby reducing the insertion loss of the acoustic wave filter 1A.

[0108] Therefore, it is possible to provide an acoustic wave filter 1A and a high-frequency module that ensure low loss in terms of both matching loss and insertion loss.

[0109] In this modification, the first series arm resonator is not limited to the series arm resonator 13, but may be any of the series arm resonators 11, 12, and the series arm resonator 16A. The first parallel arm resonator is not limited to the parallel arm resonator 25A, but may be any of the parallel arm resonators 21 and 22.

[0110] In the acoustic wave filter 1A according to this modification, the first series arm resonator (series arm resonator 13) is connected closest to the input / output terminal 120 among the multiple series arm resonators, and the first parallel arm resonator (parallel arm resonator 25A) is connected closest to the input / output terminal 120 among the multiple parallel arm resonators.

[0111] This allows the resonator, whose passband exhibits inductive impedance, to be positioned closest to the input terminal of the low-noise amplifier 2, which exhibits capacitive impedance, thereby enabling impedance matching between the acoustic wave filter 1A and the low-noise amplifier 2 with high efficiency and precision.

[0112] The first series arm resonator (series arm resonator 13) does not have to be connected closest to the input / output terminal 120 among the multiple series arm resonators, and the first parallel arm resonator (parallel arm resonator 25A) does not have to be connected closest to the input / output terminal 120 among the multiple parallel arm resonators. Even in this case, the impedance in the pass band of the acoustic wave filter 1A can be made inductive, thereby reducing the matching loss of the acoustic wave filter 1A and the high-frequency module.

[0113] Furthermore, the resonant bandwidth of the parallel arm resonator 25A is narrower than that of the parallel arm resonator 25, and the resonant bandwidth of the series arm resonator 16A is narrower than that of the series arm resonator 16, thereby ensuring a large amount of attenuation near the passband.

[0114] 5. Configuration of Acoustic Wave Filter 1B According to Modification 2 Fig. 8A is a circuit diagram of an acoustic wave filter 1B according to a second modification of the embodiment. Fig. 8B is a graph showing the pass characteristics of the acoustic wave filter 1B according to the second modification in a band near the pass band and the impedance characteristics of the parallel arm resonator 20. Fig. 8C is a graph showing the wide-band impedance characteristics of the parallel arm resonator 20 of the acoustic wave filter 1B according to the second modification.

[0115] 8A , an elastic wave filter 1B according to the second modification is a band-pass filter and includes series arm resonators 11, 12, 13, and 14, parallel arm resonators 21, 22, 23, and 25, an inductor 45, and input / output terminals 110 and 120. The elastic wave filter 1B according to the second modification is different in circuit configuration from the elastic wave filter 1 according to the embodiment in that the capacitors 15 and 24 are not provided, and the parallel arm resonator 25 and the inductor 45 are provided. Hereinafter, a description of the same components as those of the elastic wave filter 1B according to the embodiment will be omitted, and the different components will be mainly described.

[0116] The series arm resonators 11 to 14 are connected in this order from the input / output terminal 110: series arm resonators 11, 12, 13, and 14.

[0117] The parallel arm resonator 21 is connected between the connection point of the series arm resonators 11 and 12 and the ground. The parallel arm resonator 22 is connected between the connection point of the series arm resonators 12 and 13 and the ground. The parallel arm resonator 23 is connected between the connection point of the series arm resonators 13 and 14 and the ground.

[0118] The parallel arm resonator 25 (first acoustic wave resonator) and the inductor 45 (first inductor) connected in series to each other are an example of an acoustic wave resonator including an acoustic wave resonator, and constitute the parallel arm resonator 20. The parallel arm resonator 20 is connected between the connection point of the series arm resonator 14 and the input / output terminal 120 and ground. By connecting the inductor 45 in series to the parallel arm resonator 25, the resonant frequency frp20 of the parallel arm resonator 20 is shifted to the lower frequency side with respect to the resonant frequency frp25 of the parallel arm resonator 25. In other words, by connecting the inductor 45 in series to the parallel arm resonator 25, the resonant bandwidth of the parallel arm resonator 20 becomes wider than the resonant bandwidth of the parallel arm resonator 25.

[0119] Of the series arm resonators 11 to 14, the series arm resonator 14 is an example of a first series arm resonator, and has a resonance frequency frs14 (first resonance frequency) and an anti-resonance frequency fas14 (first anti-resonance frequency).

[0120] Of the parallel arm resonators 21 to 23 and the parallel arm resonator 20, the parallel arm resonator 20 is an example of a first parallel arm resonator, and has a resonance frequency frp20 (second resonance frequency) and an anti-resonance frequency fap20 (second anti-resonance frequency).

[0121] The resonance frequency frs14 (first resonance frequency) of the series arm resonator 14 (first series arm resonator) and the resonance frequency frp20 (second resonance frequency) of the parallel arm resonator 20 (first parallel arm resonator) are equal to or lower than the low frequency end of the pass band of the acoustic wave filter 1B. In addition, the anti-resonance frequency fas14 (first anti-resonance frequency) of the series arm resonator 14 (first series arm resonator) and the anti-resonance frequency fap20 (second anti-resonance frequency) of the parallel arm resonator 20 (first parallel arm resonator) are equal to or higher than the high frequency end of the pass band.

[0122] According to the above configuration, by making the impedance of the acoustic wave filter 1B of this modification in the pass band inductive, it is possible to make the impedance of the high-frequency module of this modification, which includes the acoustic wave filter 1B and the low-noise amplifier 2, approach the reference impedance without adding a matching inductor, thereby reducing the matching loss of the acoustic wave filter 1B and the high-frequency module of this modification.

[0123] 8B , the frequency difference Δfa between the antiresonant frequency fap20 of the parallel arm resonator 20 and the high-frequency end of the pass band of the acoustic wave filter 1B is smaller than the frequency difference Δfr between the low-frequency end of the pass band and the resonant frequency frp20 of the parallel arm resonator 20.

[0124] As a result, the low-impedance band of the inductive impedance band of the series arm resonator 14 overlaps with the pass band, and the high-impedance band of the inductive impedance band of the parallel arm resonator 20 overlaps with the pass band, thereby reducing the insertion loss of the acoustic wave filter 1B.

[0125] In the acoustic wave filter 1B according to this modification, the first series arm resonator (series arm resonator 14) is connected closest to the input / output terminal 120 among the multiple series arm resonators, and the first parallel arm resonator (parallel arm resonator 20) is connected closest to the input / output terminal 120 among the multiple parallel arm resonators.

[0126] This allows the resonator, whose passband exhibits inductive impedance, to be positioned closest to the input terminal of the low-noise amplifier 2, which exhibits capacitive impedance, thereby enabling impedance matching between the acoustic wave filter 1B and the low-noise amplifier 2 with high efficiency and precision.

[0127] The first series arm resonator (series arm resonator 14) does not have to be connected closest to the input / output terminal 120 among the multiple series arm resonators, and the first parallel arm resonator (parallel arm resonator 20) does not have to be connected closest to the input / output terminal 120 among the multiple parallel arm resonators. Even in this case, the impedance in the pass band of the acoustic wave filter 1B can be made inductive, thereby reducing the matching loss of the acoustic wave filter 1B and the high-frequency module.

[0128] 8C , the parallel arm resonator 20 has high impedance in a DC (direct current) region. This prevents the DC bias current (DC bias voltage) supplied to the low-noise amplifier 2 from leaking to the acoustic wave filter 1B, eliminating the need to place a DC blocking capacitor between the acoustic wave filter 1B and the low-noise amplifier 2.

[0129] This allows the high-frequency module according to this modification to be miniaturized.

[0130] Furthermore, in the acoustic wave filter 1B according to this modification, all of the acoustic wave resonators included in the acoustic wave filter 1B are formed on the same piezoelectric substrate 70. This allows the resonance bands of all of the acoustic wave resonators that form the pass band of the acoustic wave filter 1B to be set to approximately the same as the pass band. In contrast, by connecting the inductor 45 in series to the parallel arm resonator 25, it is possible to set the parallel arm resonator 20 that requires a resonance band wider than the pass band. This eliminates the need to prepare an acoustic wave resonator with a wide resonance bandwidth, and allows all of the acoustic wave resonators to be integrated on a single piezoelectric substrate, thereby enabling the size of the acoustic wave filter 1B to be reduced.

[0131] Therefore, it is possible to provide a compact acoustic wave filter 1B and a high-frequency module that ensure low loss in terms of both matching loss and insertion loss.

[0132] In this modification, the first series arm resonator is not limited to the series arm resonator 14, but may be any of the series arm resonators 11 to 13. Furthermore, the first parallel arm resonator is not limited to the parallel arm resonator 20, but may be any of the parallel arm resonators 21 to 23.

[0133] In acoustic wave filter 1B according to this modification, a second inductor may be connected in parallel to any one of series arm resonators 11 to 14 (second acoustic wave resonator). In this case, a circuit in which the second acoustic wave resonator and the second inductor are connected in parallel may be a first series arm resonator.

[0134] By connecting the second inductor in parallel to the second acoustic wave resonator, the first anti-resonance frequency of the first series arm resonator is shifted to a higher frequency side relative to the anti-resonance frequency of the second acoustic wave resonator. In other words, by connecting the second inductor in parallel to the second acoustic wave resonator, the resonance bandwidth of the first series arm resonator becomes wider than the resonance bandwidth of the second acoustic wave resonator.

[0135] In this case, the first resonant frequency of the first series arm resonator and the second resonant frequency of the first parallel arm resonator are equal to or lower than the low frequency end of the pass band of the acoustic wave filter 1B, and the first anti-resonant frequency of the first series arm resonator and the second anti-resonant frequency of the first parallel arm resonator are equal to or higher than the high frequency end of the pass band.

[0136] According to the above configuration, by making the impedance of the acoustic wave filter 1B of this modification in the pass band inductive, it is possible to make the impedance of the high-frequency module of this modification, which includes the acoustic wave filter 1B and the low-noise amplifier 2, approach the reference impedance without adding a matching inductor, thereby reducing the matching loss of the acoustic wave filter 1B and the high-frequency module of this modification.

[0137] The first resonant frequency is higher than the second resonant frequency, and the first anti-resonant frequency is higher than the second anti-resonant frequency. That is, of the first resonant frequency and the second resonant frequency at which the impedance is minimized, the first resonant frequency is closer to the pass band, and of the first anti-resonant frequency and the second anti-resonant frequency at which the impedance is maximized, the first anti-resonant frequency is farther from the pass band. Furthermore, the frequency difference Δfr1 between the low-frequency end of the pass band of the acoustic wave filter 1B and the first resonant frequency is smaller than the frequency difference Δfa1 between the first anti-resonant frequency and the high-frequency end of the pass band.

[0138] As a result, the low-impedance band of the inductive impedance band of the first series arm resonator overlaps with the pass band, and the high-impedance band of the inductive impedance band of the first parallel arm resonator overlaps with the pass band, thereby reducing the insertion loss of the acoustic wave filter 1B.

[0139] [6. Component layout of high frequency module 100] Next, the arrangement of components in the high-frequency module 100 according to this embodiment will be described.

[0140] Fig. 9 shows a plan view and a cross-sectional view of a high-frequency module 100 according to an embodiment. Fig. 9(a) shows the arrangement of circuit components when a main surface 90a of a mounting board 90 is viewed from the positive side of the z-axis. Fig. 9(b) shows the arrangement of circuit components when a main surface 90b of the mounting board 90 is viewed from the positive side of the z-axis. Fig. 9(c) shows a cross-sectional view taken along line IXC-IXC in Figs. 9(a) and 9(b). Note that Fig. 9 omits some of the wiring connecting the mounting board 90 and the circuit components.

[0141] The high-frequency module 100 shown in FIG. 9 further includes a mounting substrate 90 in addition to the components of the high-frequency module 100 shown in FIG.

[0142] The mounting substrate 90 has opposing main surfaces 90a (first main surface) and 90b (second main surface). In Fig. 9, the mounting substrate 90 has a rectangular shape in plan view, but the shape of the mounting substrate 90 is not limited to this.

[0143] The mounting substrate 90 may be, for example, a low temperature co-fired ceramics (LTCC) substrate or a high temperature co-fired ceramics (HTCC) substrate having a laminated structure of multiple dielectric layers, a component-embedded substrate, a substrate having a redistribution layer (RDL), or a printed circuit board, but is not limited to these.

[0144] The acoustic wave filter 1 is disposed on the principal surface 90a of the mounting substrate 90. The low-noise amplifier 2 is disposed on the principal surface 90b of the mounting substrate 90. A resin member and a shield electrode layer may be formed on the principal surfaces 90a and 90b. In this manner, the acoustic wave filter 1 and the low-noise amplifier 2 are disposed on the principal surfaces 90a and 90b of the mounting substrate 90, respectively, which allows the high-frequency module 100 to be miniaturized.

[0145] 9(a), the acoustic wave filter 1 is formed on a single chip (hereinafter referred to as a filter chip) using, for example, a piezoelectric substrate and a package. Input / output terminals 110 (IN) and 120 (OUT) and a ground electrode (GND) are formed on the main surface of the filter chip facing the mounting substrate 90. The input / output terminals 110 and 120 and the ground electrode may be planar electrodes or bump electrodes.

[0146] 9(b), the low-noise amplifier 2 is formed in an integrated circuit 80. An input terminal 210 (IN) and an output terminal 220 (OUT) of the low-noise amplifier 2 are formed on the main surface of the integrated circuit 80 facing the mounting substrate 90. The input terminal 210 and the output terminal 220 may be planar electrodes or bump electrodes.

[0147] The integrated circuit 80 is configured using, for example, a complementary metal oxide semiconductor (CMOS), and specifically may be manufactured by a silicon on insulator (SOI) process. Note that the integrated circuit 80 is not limited to a CMOS.

[0148] As shown in FIG. 9(c), the input / output terminal 120 and the input terminal 210 are connected by a via conductor 300 without passing through a matching circuit element.

[0149] When the mounting substrate 90 is viewed from above, the acoustic wave filter 1 and the low-noise amplifier 2 at least partially overlap each other.

[0150] This allows the wiring connecting the acoustic wave filter 1 and the low-noise amplifier 2 to be short, thereby reducing the loss of the high-frequency module 100.

[0151] Furthermore, when the mounting substrate 90 is viewed from above, the input / output terminal 120 and the input terminal 210 may at least partially overlap.

[0152] This allows the acoustic wave filter 1 and the low-noise amplifier 2 to be connected only by the via conductor 300, thereby further reducing the loss of the high-frequency module 100.

[0153] [7 Effects etc.] As described above, the acoustic wave filter 1 according to this embodiment includes the series arm resonator 14 (first series arm resonator) arranged in the series arm path connecting the input / output terminals 110 and 120, and the parallel arm resonator 23 (first parallel arm resonator) connected between the series arm path and ground. Each of the series arm resonator 14 and the parallel arm resonator 23 includes an acoustic wave resonator. The resonance frequency frs14 (first resonance frequency) of the series arm resonator 14 and the resonance frequency frp23 (second resonance frequency) of the parallel arm resonator 23 are equal to or lower than the low frequency end of the pass band of the acoustic wave filter 1. The antiresonance frequency fas14 (first antiresonance frequency) of the series arm resonator 14 and the antiresonance frequency fap23 (second antiresonance frequency) of the parallel arm resonator 23 are equal to or higher than the high frequency end of the pass band. The resonance frequency frs14 is higher than the resonance frequency frp23, and the antiresonance frequency fas14 is higher than the antiresonance frequency fap23.

[0154] This configuration makes the impedance of the series arm resonator 14 and the parallel arm resonator 23 inductive in the pass band, thereby enabling the impedance of the acoustic wave filter 1 in the pass band to be inductive. Therefore, when the acoustic wave filter 1 is connected to an external circuit having capacitive impedance, the combined impedance of the acoustic wave filter 1 and the external circuit can be made closer to a reference impedance without adding an impedance matching inductor. This reduces the matching loss of the acoustic wave filter 1 and the high-frequency module 100. Furthermore, the low-impedance band of the inductive impedance band of the series arm resonator 14 overlaps with the pass band, and the high-impedance band of the inductive impedance band of the parallel arm resonator 23 overlaps with the pass band. This configuration reduces the insertion loss of the acoustic wave filter 1. This configuration provides an acoustic wave filter 1 that ensures low loss in terms of both matching loss and insertion loss.

[0155] For example, the acoustic wave filter 1 includes a plurality of series arm resonators and a plurality of parallel arm resonators, and the series arm resonator 14 is connected closest to the input / output terminal 120 among the plurality of series arm resonators, and the parallel arm resonator 23 is connected closest to the input / output terminal 120 among the plurality of parallel arm resonators.

[0156] According to this, when the external circuit connected to the input / output terminal 120 has capacitive impedance, the acoustic wave resonator exhibiting inductive impedance in the pass band is positioned closest to the external circuit, thereby enabling impedance matching between the acoustic wave filter 1 and the external circuit with high efficiency and precision.

[0157] For example, in the elastic wave filter 1, among the multiple elastic wave resonators, the number of elastic wave resonators whose resonant frequencies are equal to or lower than the low frequency end of the pass band and whose anti-resonant frequencies are equal to or higher than the high frequency end of the pass band is greater than the number of elastic wave resonators whose resonant frequencies are higher than the low frequency end of the pass band or whose anti-resonant frequencies are lower than the high frequency end of the pass band.

[0158] In this case, the number of acoustic wave resonators whose passband impedance is inductive is greater than the number of acoustic wave resonators whose passband impedance is capacitive, so that the impedance of the entire passband of the acoustic wave filter 1 is inductive. This makes it possible to achieve more accurate impedance matching between the acoustic wave filter 1 and an external circuit having capacitive impedance. This makes it possible to provide an acoustic wave filter 1 with reduced matching loss.

[0159] For example, the acoustic wave filter 1 further includes at least one of a capacitor 15 arranged in series in the series arm path and a capacitor 24 arranged in series in a parallel arm path connecting the series arm path and ground.

[0160] This makes it easier to design an acoustic wave filter having a narrow passband using an acoustic wave resonator having a wide resonance bandwidth.

[0161] For example, in an acoustic wave filter 1B according to the second modification, the parallel arm resonator 20 includes a parallel arm resonator 25 and an inductor 45 that are connected in series.

[0162] This makes it possible to form parallel arm resonator 20 having a wide resonance band without preparing an acoustic wave resonator having a resonance band wider than the pass band.

[0163] Furthermore, for example, in the acoustic wave filter 1B, the frequency difference Δfa between the anti-resonance frequency fap20 and the high frequency end of the pass band is smaller than the frequency difference Δfr between the low frequency end of the pass band and the resonant frequency frp20.

[0164] This allows the high-impedance band of the inductive impedance band of the parallel arm resonator 20 to overlap with the passband, thereby reducing the insertion loss of the acoustic wave filter 1B.

[0165] Furthermore, for example, in the acoustic wave filter 1B, the first series arm resonator includes a second acoustic wave resonator and a second inductor connected in parallel.

[0166] This makes it possible to form a first series arm resonator with a wide resonance band without preparing an acoustic wave resonator having a resonance band wider than the pass band.

[0167] Furthermore, for example, in the acoustic wave filter 1B, the frequency difference between the first resonant frequency and the low frequency end of the pass band is smaller than the frequency difference between the high frequency end of the pass band and the first anti-resonant frequency.

[0168] This allows the low-impedance band of the inductive impedance band of the first series arm resonator to overlap with the passband, thereby reducing the insertion loss of the acoustic wave filter 1B.

[0169] Furthermore, for example, in acoustic wave filter 1B, all of the acoustic wave resonators included in acoustic wave filter 1B are formed on the same piezoelectric substrate.

[0170] This allows the resonance bandwidths of all of the acoustic wave resonators that form the pass band of the acoustic wave filter 1B to be set to approximately the same as the pass band width. On the other hand, by connecting the inductor 45 in series with the parallel arm resonator 25, it is possible to set the parallel arm resonator 20 that requires a resonance band wider than the pass band. This eliminates the need to prepare an acoustic wave resonator with a wide resonance bandwidth, and allows all of the acoustic wave resonators to be integrated on a single piezoelectric substrate, thereby enabling the size of the acoustic wave filter 1B to be reduced.

[0171] Moreover, the high-frequency module 100 according to this embodiment includes a mounting substrate 90 having opposing principal surfaces 90a and 90b, an acoustic wave filter 1 (or 1A, 1B), and a low-noise amplifier 2 having an input terminal 210 connected to an input / output terminal 120, wherein the acoustic wave filter 1 is disposed on the principal surface 90a and the low-noise amplifier 2 is disposed on the principal surface 90b, and when the mounting substrate 90 is viewed in a plan view, the acoustic wave filter 1 and the low-noise amplifier 2 at least partially overlap each other.

[0172] This allows the wiring connecting the acoustic wave filter 1 and the low-noise amplifier 2 to be short, thereby reducing the loss and size of the high-frequency module 100.

[0173] Furthermore, in the high-frequency module 100, when the mounting substrate 90 is viewed from above, the input / output terminal 120 and the input terminal 210 at least partially overlap each other.

[0174] This allows the acoustic wave filter 1 and the low-noise amplifier 2 to be connected only by the via conductor 300, thereby further reducing the loss of the high-frequency module 100.

[0175] (Other embodiments) Although the acoustic wave filter and high-frequency module according to the present invention have been described above with reference to the embodiments and modifications thereof, the present invention is not limited to the above embodiments and modifications. The present invention also includes modifications that can be made by those skilled in the art without departing from the spirit of the present invention, as well as various devices incorporating the acoustic wave filter and high-frequency module according to the present invention.

[0176] Furthermore, for example, in the acoustic wave filters and high-frequency modules according to the above-described embodiments and modifications, matching elements such as inductors and capacitors, and switch circuits may be connected between the respective components.

[0177] The following describes the features of the acoustic wave filter and the high-frequency module described based on the above-described embodiment and modifications.

[0178] <1> A band-pass acoustic wave filter, a first series arm resonator disposed in a series arm path connecting the first input / output terminal and the second input / output terminal; a first parallel arm resonator connected between the series arm path and ground, each of the first series arm resonator and the first parallel arm resonator includes an acoustic wave resonator; a first resonance frequency that is a resonance frequency of the first series arm resonator and a second resonance frequency that is a resonance frequency of the first parallel arm resonator are equal to or lower than a low frequency end of a pass band of the acoustic wave filter, a first anti-resonant frequency that is an anti-resonant frequency of the first series arm resonator and a second anti-resonant frequency that is an anti-resonant frequency of the first parallel arm resonator are equal to or higher than a high frequency end of the pass band, The acoustic wave filter, wherein the first resonant frequency is higher than the second resonant frequency, and the first anti-resonant frequency is higher than the second anti-resonant frequency.

[0179] <2> a plurality of series arm resonators including the first series arm resonator; a plurality of parallel arm resonators including the first parallel arm resonator, the first series arm resonator is connected closest to the first input / output terminal among the plurality of series arm resonators; the first parallel arm resonator is connected closest to the first input / output terminal among the plurality of parallel arm resonators; <1> The acoustic wave filter according to claim 1.

[0180] <3> a plurality of acoustic wave resonators including the first series arm resonator and the first parallel arm resonator, Among the plurality of elastic wave resonators, the number of elastic wave resonators whose resonance frequency is equal to or lower than the low frequency end of the pass band and whose anti-resonance frequency is equal to or higher than the high frequency end of the pass band is greater than the number of elastic wave resonators whose resonance frequency is higher than the low frequency end of the pass band or whose anti-resonance frequency is lower than the high frequency end of the pass band. <1> The acoustic wave filter according to claim 1.

[0181] <4> moreover, the power supply includes at least one of a first capacitor arranged in series in the series arm path and a second capacitor arranged in series in a parallel arm path connecting the series arm path and ground; <1> ~ <3> 10. The acoustic wave filter according to claim 9, wherein

[0182] <5> the first parallel arm resonator includes a first acoustic wave resonator and a first inductor connected in series; <1> ~ <4> 10. The acoustic wave filter according to claim 9, wherein

[0183] <6> a frequency difference between the second anti-resonant frequency and the high frequency end of the pass band is smaller than a frequency difference between the low frequency end of the pass band and the second resonant frequency; <5> The acoustic wave filter according to claim 1.

[0184] <7> the first series arm resonator includes a second acoustic wave resonator and a second inductor connected in parallel; <1> ~ <4> 10. The acoustic wave filter according to claim 9, wherein

[0185] <8> a frequency difference between the first resonant frequency and the low frequency end of the pass band is smaller than a frequency difference between the high frequency end of the pass band and the first anti-resonant frequency; <7> The acoustic wave filter according to claim 1.

[0186] <9> a plurality of acoustic wave resonators including the first series arm resonator and the first parallel arm resonator, each of the plurality of acoustic wave resonators includes an acoustic wave resonator; all of the acoustic wave resonators included in the acoustic wave filter are formed on the same piezoelectric substrate; <1> ~ <8> 10. The acoustic wave filter according to claim 9, wherein

[0187] <10> a mounting substrate having a first main surface and a second main surface facing each other; <1> ~ <9> an acoustic wave filter according to any one of the preceding claims; a low noise amplifier having an input terminal connected to the first input / output terminal; the acoustic wave filter is disposed on the first principal surface, the low noise amplifier is disposed on the second principal surface; the acoustic wave filter and the low-noise amplifier at least partially overlap each other when the mounting substrate is viewed from above.

[0188] <11> When the mounting substrate is viewed from above, the first input / output terminal and the input terminal at least partially overlap each other. <10> The high-frequency module according to claim 1. [Industrial Applicability]

[0189] INDUSTRIAL APPLICABILITY The present invention can be widely used in communication devices such as mobile phones as a low-loss acoustic wave filter and high-frequency module that can be applied to multi-band frequency standards. [Explanation of symbols]

[0190] 1, 1A, 1B, 501 Acoustic Wave Filter 2. Low noise amplifier 11, 12, 13, 14, 16 Series arm resonators 15, 24, 35, 36 capacitors 16A Series Arm Resonator 20, 25A parallel arm resonator 21, 22, 23, 25 Parallel arm resonators 32 Parasitic capacitance 41, 42, 43, 45 Inductors 50, 70 Piezoelectric substrate 51 High-sonic support substrate 52 Low sound velocity membrane 53 Piezoelectric film 54 IDT electrode 55, 58 protective layer 57 Piezoelectric single crystal substrate 60 Elastic wave resonator 60a, 60b comb-shaped electrode 61a, 61b electrode fingers 62a, 62b Busbar electrodes 65 Support substrate 66 Lower electrode 67 Piezoelectric layer 68 Upper electrode 80 Integrated Circuits 90 Mounting board 90a, 90b main surface 100, 500 high frequency module 110, 120 input / output terminals 130, 220 output terminal 140, 210 input terminal 300 via conductor 540 Adhesion layer 542 Main electrode layer

Claims

1. A band-pass acoustic wave filter, a first series arm resonator disposed in a series arm path connecting the first input / output terminal and the second input / output terminal; a first parallel arm resonator connected between the series arm path and ground, each of the first series arm resonator and the first parallel arm resonator includes an acoustic wave resonator; a first resonance frequency that is a resonance frequency of the first series arm resonator and a second resonance frequency that is a resonance frequency of the first parallel arm resonator are equal to or lower than a low frequency end of a pass band of the acoustic wave filter, a first anti-resonant frequency that is an anti-resonant frequency of the first series arm resonator and a second anti-resonant frequency that is an anti-resonant frequency of the first parallel arm resonator are equal to or higher than a high frequency end of the pass band, the first resonant frequency is higher than the second resonant frequency, and the first anti-resonant frequency is higher than the second anti-resonant frequency; Acoustic wave filters.

2. a plurality of series arm resonators including the first series arm resonator; a plurality of parallel arm resonators including the first parallel arm resonator, the first series arm resonator is connected closest to the first input / output terminal among the plurality of series arm resonators; the first parallel arm resonator is connected closest to the first input / output terminal among the plurality of parallel arm resonators; The acoustic wave filter according to claim 1 .

3. a plurality of acoustic wave resonators including the first series arm resonator and the first parallel arm resonator, Among the plurality of elastic wave resonators, the number of elastic wave resonators whose resonance frequency is equal to or lower than the low frequency end of the pass band and whose anti-resonance frequency is equal to or higher than the high frequency end of the pass band is greater than the number of elastic wave resonators whose resonance frequency is higher than the low frequency end of the pass band or whose anti-resonance frequency is lower than the high frequency end of the pass band. The acoustic wave filter according to claim 1 .

4. moreover, the power supply includes at least one of a first capacitor arranged in series in the series arm path and a second capacitor arranged in series in a parallel arm path connecting the series arm path and ground; The acoustic wave filter according to any one of claims 1 to 3.

5. the first parallel arm resonator includes a first acoustic wave resonator and a first inductor connected in series; The acoustic wave filter according to claim 1 .

6. a frequency difference between the second anti-resonance frequency and the high frequency end of the pass band is smaller than a frequency difference between the low frequency end of the pass band and the second resonant frequency; The acoustic wave filter according to claim 5 .

7. the first series arm resonator includes a second acoustic wave resonator and a second inductor connected in parallel; The acoustic wave filter according to claim 1 .

8. a frequency difference between the first resonant frequency and the low frequency end of the pass band is smaller than a frequency difference between the high frequency end of the pass band and the first anti-resonant frequency; The acoustic wave filter according to claim 7 .

9. a plurality of acoustic wave resonators including the first series arm resonator and the first parallel arm resonator, each of the plurality of acoustic wave resonators includes an acoustic wave resonator; all of the acoustic wave resonators included in the acoustic wave filter are formed on the same piezoelectric substrate; The acoustic wave filter according to any one of claims 5 to 8.

10. a mounting substrate having a first main surface and a second main surface facing each other; The acoustic wave filter according to claim 1 ; a low noise amplifier having an input terminal connected to the first input / output terminal; the acoustic wave filter is disposed on the first principal surface, the low noise amplifier is disposed on the second principal surface; When the mounting substrate is viewed from above, the acoustic wave filter and the low-noise amplifier at least partially overlap each other. High frequency module.

11. When the mounting substrate is viewed from above, the first input / output terminal and the input terminal at least partially overlap each other. The high frequency module according to claim 10.

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