Acoustic wave filter and high-frequency module

Abstract

To provide an acoustic wave filter and a high-frequency module that ensure DC cut and impedance matching in a passband.SOLUTION: An acoustic wave filter 1 includes a plurality of series arm resonators including series arm resonators 12 and 13 arranged in a series arm path connecting input / output terminals 110 and 120, one or more parallel arm resonators including a parallel arm resonator 21 connected between the series arm path and ground, and an inductor 31 connected between a first path connecting the series arm resonators 12 and 13 and ground, and the series arm resonator 13 is connected closest to the input / output terminal 120 among the plurality of series arm resonators, the one or more parallel arm resonators, and the inductor 31, and has the highest resonant frequency among the plurality of series arm resonators.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Patent Document 1 (FIG. 13) discloses a high-frequency front-end circuit that includes a low-noise amplifier that amplifies a high-frequency received signal, and a band-pass filter connected to the input end of the low-noise amplifier. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 064990 Summary of the Invention [Problem to be solved by the invention]

[0004] Because a low-noise amplifier has capacitive input impedance, connecting an inductor between the path connecting the low-noise amplifier and the band-pass filter and ground is effective in achieving impedance matching between the low-noise amplifier and the band-pass filter in, for example, the high-frequency front-end circuit disclosed in Patent Document 1. However, when such an inductor is connected, a DC-blocking capacitor must be placed in series in the path to prevent leakage of the DC bias current supplied to the low-noise amplifier.

[0005] However, when a DC-blocking capacitor is placed in series with the input terminal of a low-noise amplifier, impedance mismatch occurs in the frequency band of the high-frequency received signal, resulting in transmission loss and, as a result, a deterioration in the noise figure of the low-noise amplifier.

[0006] Therefore, 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 and a high-frequency module that ensure DC cutoff and impedance matching in the passband. [Means for solving the problem]

[0007] In order to achieve the above object, an acoustic wave filter according to one aspect of the present invention includes a plurality of series arm resonators, including a first series arm resonator and a second series arm resonator, arranged in a series arm path connecting a first input / output terminal and a second input / output terminal; one or more parallel arm resonators connected between the series arm path and ground; and a first inductor connected between a first path connecting the first series arm resonator and the second series arm resonator and ground, wherein the first series arm resonator is connected closest to the first input / output terminal among the plurality of series arm resonators, the one or more parallel arm resonators, and the first inductor, and the first series arm resonator has the highest resonant frequency among the plurality of series arm resonators.

[0008] A high-frequency module according to one aspect of the present invention includes the above acoustic wave filter and a low-noise amplifier having an input terminal connected to the first input / output terminal. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an acoustic wave filter and a high-frequency module that ensure DC cutoff and impedance matching in the pass band. [Brief explanation of the drawings]

[0010] [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 3A] FIG. 2 is a circuit diagram of an acoustic wave filter according to a first comparative example. [Figure 3B] 10 is a Smith chart showing the pass characteristics and impedance of the acoustic wave filter in accordance with Comparative Example 1. [Figure 4] 4 is a Smith chart showing the pass characteristics of an acoustic wave filter according to an embodiment, the capacitance characteristics of a first series arm resonator, and the impedance of the acoustic wave filter. [Figure 5] 10 is a Smith chart showing the pass characteristics of the acoustic wave filter in accordance with Comparative Example 2, the capacitance characteristics of a first series arm resonator, and the impedance of the acoustic wave filter. [Figure 6] 10 is a Smith chart showing the pass characteristics of the acoustic wave filter in accordance with Comparative Example 3, the capacitance characteristics of the first series arm resonator, and the impedance of the acoustic wave filter. [Figure 7A] FIG. 1 is a circuit configuration diagram of an acoustic wave filter according to an embodiment. [Figure 7B] FIG. 2 is a plan view illustrating a terminal arrangement of an acoustic wave filter according to an embodiment. [Figure 7C] 10 is a plan view illustrating a terminal arrangement of an acoustic wave filter according to a first modification of the embodiment. FIG. [Figure 8A] FIG. 10 is a circuit configuration diagram of a high-frequency module according to a second modified example of the embodiment. [Figure 8B] FIG. 10 is a plan view showing a component arrangement configuration of a high-frequency module according to a second modified example of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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 substrate. Specifically, when the substrate has a rectangular shape in a plan view, the x-axis is parallel to a first side of the substrate, and the y-axis is parallel to a second side that is perpendicular to the first side of the substrate. The z-axis is an axis perpendicular to the main surface of the substrate, with its positive direction indicating an upward direction and its negative direction indicating a downward direction.

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

[0018] Furthermore, in the component placement of this invention, "when the main surface (of the substrate) is viewed in a plan view" means that the object is viewed by orthogonally projecting it onto the xy plane from the positive side of the z axis. "A overlaps with B in a plan 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.

[0019] 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.

[0020] 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.

[0021] Furthermore, an elastic wave resonator (series arm resonator and parallel arm resonator) is defined as any one 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.

[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] The capacitance of an elastic wave resonator or an elastic wave resonator can be derived by bringing probes into contact with two input and output electrodes of the elastic wave resonator or an elastic wave resonator when the elastic wave resonator or an elastic wave resonator is not connected to other circuit elements, and measuring the DC capacitance with a network analyzer, an impedance meter, etc. The capacitances of multiple surface acoustic wave resonators or multiple surface acoustic wave resonators can be compared by actually measuring the number of pairs, cross width, pitch, and duty of the IDT (InterDigital Transducer) electrodes.

[0024] 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.

[0025] (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 inductor 32.

[0026] The low-noise amplifier 2 has an input terminal 130 and an output terminal 140, and the input terminal 130 is connected to the input / output terminal 120 of the acoustic wave filter 1 via an inductor 32. 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 terminal 130 without a capacitive element, the drain (or collector) is connected to the output terminal 140, 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 by supplying the DC bias voltage (DC bias current) to the gate (or base), and outputs the amplified signal to the output terminal 140. The input impedance of the low-noise amplifier 2 is capacitive and high.

[0027] The inductor 32 is an example of a second inductor, and is arranged in series in a path connecting the input / output terminal 120 and the input terminal 130. The inductor 32 is a circuit element for achieving impedance matching between the low-noise amplifier 2, which has a capacitive input impedance, and the acoustic wave filter 1. Note that the inductor 32 may be omitted.

[0028] The acoustic wave filter 1 is a band-pass filter and includes series arm resonators 11, 12, and 13, a parallel arm resonator 21, an inductor 31, and input / output terminals 110 and 120.

[0029] Each of the series arm resonators 11 to 13 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 (first input / output terminal). The series arm resonators 11 to 13 constitute a plurality of series arm resonators included in the acoustic wave filter 1.

[0030] The series arm resonator 11 constitutes one series arm resonator (acoustic wave resonator) by itself. The series arm resonator 12 is an example of a second series arm resonator, and constitutes one series arm resonator (acoustic wave resonator) by itself. The series arm resonator 13 is an example of a first series arm resonator, and constitutes one series arm resonator (acoustic wave resonator) by itself. The series arm resonators 11 to 13 are connected in this order from the input / output terminal 110.

[0031] The parallel arm resonator 21 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 constitutes one or more parallel arm resonators included in the acoustic wave filter 1. The parallel arm resonator 21 is connected between the connection point of the series arm resonators 11 and 12 and ground. The parallel arm resonator 21 alone constitutes one parallel arm resonator (acoustic wave resonator).

[0032] The inductor 31 is an example of a first inductor, and is connected between the first path connecting the series arm resonators 12 and 13 and the ground.

[0033] The series arm resonator 13 is connected closest to the input / output terminal 120 among the series arm resonators 11 to 13 , the parallel arm resonator 21 , and the inductor 31 .

[0034] Furthermore, the series arm resonator 13 has the largest capacitance among the series arm resonators 11 to 13 and the parallel arm resonator 21, and also has the highest resonance frequency among the series arm resonators 11 to 13.

[0035] The acoustic wave filter 1 according to this preferred embodiment may include at least the series arm resonators 12 and 13 as the multiple series arm resonators, or may include four or more series arm resonators including the series arm resonators 12 and 13. The acoustic wave filter 1 according to this preferred embodiment may include at least the parallel arm resonator 21 as the one or more parallel arm resonators, or may include two or more parallel arm resonators including the parallel arm resonator 21. In the acoustic wave filter 1 according to this preferred embodiment, at least one of an inductor and a capacitor may be arranged in series in a series arm path connecting the input / output terminal 110 and the series arm resonator 12, and at least one of an inductor and a capacitor may be connected between the series arm path and ground. In addition, an inductor may be connected between the parallel arm resonator 21 and ground.

[0036] Each of the series arm resonators 11 to 13 and the parallel arm resonator 21 (elastic wave resonators) has only one elastic wave resonator. However, each of the series arm resonators 11 to 13 and the parallel arm resonator 21 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.

[0037] 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.

[0038] [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.

[0039] 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.

[0040] The acoustic wave resonator 60 is composed of a piezoelectric substrate 50 and comb-shaped electrodes 60a and 60b.

[0041] 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).

[0042] The IDT electrode 54, which is made up 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).

[0043] 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.

[0044] 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.

[0045] Next, the layered structure of the piezoelectric substrate 50 will be described.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] Here, the electrode parameters of the IDT electrode 54 that constitutes the acoustic wave resonator 60 will be described.

[0060] 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).

[0061] 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.

[0062] 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.

[0063] 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.

[0064] The lower electrode 66 is an example of a first planar electrode, and is formed on one surface of the support substrate 65. The upper electrode 68 is an example of a second planar electrode, and 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.

[0065] The piezoelectric layer 67 is an example of a piezoelectric thin film, and 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).

[0066] 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.

[0067] [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.

[0068] 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.

[0069] 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.

[0070] Next, the impedance characteristics and pass characteristics of the acoustic wave filter 1 according to the present embodiment and the acoustic wave filter according to the comparative example will be described.

[0071] 3A is a circuit diagram of an acoustic wave filter 200 according to Comparative Example 1. FIG. 3B is a Smith chart illustrating the pass characteristics and impedance of the acoustic wave filter 200 according to Comparative Example 1. As shown in FIG. 3A, the acoustic wave filter 200 according to Comparative Example 1 differs from the acoustic wave filter 1 according to the embodiment in that the series arm resonator 13 and the inductor 31 are not provided. In other words, the acoustic wave filter 200 according to Comparative Example 1 is a ladder-type acoustic wave filter including series arm resonators 11 and 12 and a parallel arm resonator 21.

[0072] In the following description, the acoustic wave filter 1 according to the present embodiment and the acoustic wave filter according to the comparative example have passbands that include, for example, band B40A for LTE or band n40A (2300 to 2370 MHz) for 5G-NR.

[0073] Based on the basic operating principle of a ladder-type bandpass filter, acoustic wave filter 200 achieves the pass characteristics of a bandpass filter as shown in FIG. 3B(a) by positioning the resonant frequencies of series arm resonators 11 and 12 and the anti-resonant frequency of parallel arm resonator 21 within the passband of acoustic wave filter 200. The impedance of the passband is capacitive and located on the high-impedance side. Therefore, when low-noise amplifier 2 having capacitive input impedance is connected to input / output terminal 120, a matching element having inductive impedance and low transmission loss is required between acoustic wave filter 200 and low-noise amplifier 2.

[0074] 4 is a Smith chart illustrating the pass characteristics of the acoustic wave filter 1 according to the embodiment, the capacitance characteristics of the series arm resonator 13, and the impedance of the acoustic wave filter 1. The acoustic wave filter 1 according to the embodiment has the series arm resonator 13 and an inductor 31 added to the acoustic wave filter 200 according to the first comparative example.

[0075] As shown in FIG. 4A, the series arm resonator 13 has a resonant frequency frs13 at which the impedance is minimized and an antiresonant frequency fas13 at which the impedance is maximized. The resonant frequency frs13 is located at the high-frequency end of the pass band of the acoustic wave filter 1. As a result, the impedance of the series arm resonator 13 in the pass band of the acoustic wave filter 1 and in the DC region is capacitive. The capacitance of the series arm resonator 13 in the DC region is approximately 5 pF, which is sufficiently large to block DC components. Therefore, even without placing a DC-blocking capacitor in series in the path connecting the acoustic wave filter 1 and the input terminal of the amplifying transistor of the low-noise amplifier 2, the DC bias current to be supplied to the low-noise amplifier 2 can be prevented from leaking to ground via the inductor 31.

[0076] 4(b), the capacitance of the series arm resonator 13 at the high-frequency end of the pass band of the acoustic wave filter 1 increases exponentially to 100 pF or more, and the capacitance of the series arm resonator 13 at the low-frequency end of the pass band also increases compared to the capacitance in the DC region to about 13 pF. In other words, the capacitance of the series arm resonator 13 in the pass band is much larger than the capacitance in the DC region, and the impedance defined by the reciprocal of the capacitance becomes low, resulting in a nearly short-circuited state.

[0077] In this way, in the passband frequency band, the series arm resonator 13 is substantially short-circuited, and the inductor 31 functions as a matching element having inductive impedance without being affected by the series arm resonator 13. Therefore, when an external circuit having capacitive impedance is connected to the input / output terminal 120, matching loss in the passband can be reduced, and an acoustic wave filter 1 can be provided that ensures DC cut in the DC region and impedance matching in the passband. Furthermore, a DC bias current can be supplied to the low-noise amplifier 2 connected to the input / output terminal 120 with high accuracy, and matching loss of the high-frequency received signal can be reduced, thereby providing a high-frequency module 100 in which degradation of the noise figure of the low-noise amplifier 2 is suppressed.

[0078] The resonant frequency frs13 of the series arm resonator 13 may be located above the high frequency end of the pass band. This allows the impedance of the series arm resonator 13 to be capacitive in the pass band and DC region, making the impedance in the pass band greater than the impedance in the DC region. This ensures DC blocking and impedance matching in the pass band.

[0079] In this embodiment, the series arm resonator 13 has the largest capacitance among the series arm resonators 11 to 13 and the parallel arm resonator 21.

[0080] This allows the series arm resonator 13 to have the largest capacitance in the DC region among all the elastic wave resonators constituting the elastic wave filter 1, and also allows the series arm resonator 13 to have an extremely low impedance in the pass band. This significantly reduces the matching loss in the pass band, and provides an elastic wave filter 1 that ensures DC blocking in the DC region and impedance matching in the pass band.

[0081] Furthermore, the resonant frequency frs13 of the series arm resonator 13 does not have to be located above the high-frequency end of the pass band, and may be the highest among the series arm resonators 11 to 13. This allows the impedance of the series arm resonator 13 to be capacitive in the DC region and substantially capacitive in the pass band, making the impedance in the pass band higher than the impedance in the DC region. This ensures DC blocking and impedance matching in the pass band. Furthermore, because the resonant frequency frs13 of the series arm resonator 13 is located in the high-frequency region of the pass band, insertion loss in the high-frequency region can be reduced, thereby suppressing a drop in the pass characteristics at the high-frequency end of the pass band.

[0082] 5 is a Smith chart showing the pass characteristics of an elastic wave filter 500 according to Comparative Example 2, the capacitance characteristics of a series arm resonator 513, and the impedance of the elastic wave filter 500. The elastic wave filter 500 according to Comparative Example 2 includes series arm resonators 11, 12, and 513, a parallel arm resonator 21, an inductor 31, and input / output terminals 110 and 120. The elastic wave filter 500 according to Comparative Example 2 differs from the elastic wave filter 1 according to the embodiment only in that the series arm resonator 13 is replaced with the series arm resonator 513. The following description of the elastic wave filter 500 according to Comparative Example 2 will focus on the different configurations and omit a description of the same configurations as those of the elastic wave filter 1 according to the embodiment.

[0083] The series arm resonators 11, 12, and 513 are connected in this order from the input / output terminal 110. Of the series arm resonators 11, 12, and 513, the parallel arm resonator 21, and the inductor 31, the series arm resonator 513 is connected closest to the input / output terminal 120.

[0084] 5A, the series arm resonator 513 has the largest capacitance among the series arm resonators 11, 12, and 513 and the parallel arm resonator 21. As shown in FIG. 5A, the resonant frequency frs513 of the series arm resonator 513 is located near the center of the pass band of the acoustic wave filter 500.

[0085] The series arm resonator 513 has the largest capacitance among the series arm resonators 11, 12, and 513 and the parallel arm resonator 21. As shown in FIG. 5(a), the impedance of the series arm resonator 513 in the DC region is capacitive. The capacitance of the series arm resonator 513 in the DC region is about 5 pF, which is large enough to block DC components. This prevents the bias DC to be supplied to the low-noise amplifier 2 from leaking to ground via the inductor 31.

[0086] 5(a) and 5(b), the series arm resonator 513 has capacitive impedance and a large capacitance on the low-frequency side of the pass band, but has inductive impedance and a small capacitance on the high-frequency side of the pass band. As a result, the series arm resonator 513 is short-circuited on the low-frequency side of the pass band, but is not short-circuited on the high-frequency side of the pass band. As a result, the inductor 31 is affected by the series arm resonator 13 on the high-frequency side of the pass band, and the impedance matching decreases.

[0087] Furthermore, in the acoustic wave filter 500 of Comparative Example 2, as shown in FIG. 5C, on the low-frequency side of the pass band, the series arm resonator 513 has capacitive impedance, which shifts the equal-resistance circle counterclockwise. On the high-frequency side of the pass band, the series arm resonator 513 has inductive impedance, which shifts the equal-resistance circle clockwise. As a result, the width of the impedance locus in the pass band of the acoustic wave filter 500 (R500 in FIG. 5C) is greater than the width of the impedance locus in the pass band of the acoustic wave filter 1 (R1 in FIG. 4C). In other words, the impedance concentration in the pass band of the acoustic wave filter 500 is lower than the impedance concentration in the pass band of the acoustic wave filter 1. This results in greater signal transmission loss in the pass band of the acoustic wave filter 500.

[0088] 6 is a Smith chart showing the pass characteristics of an elastic wave filter 600 according to Comparative Example 3, the capacitance characteristics of a series arm resonator 613, and the impedance of the elastic wave filter 600. The elastic wave filter 600 according to Comparative Example 3 includes series arm resonators 11, 12, and 613, a parallel arm resonator 21, an inductor 31, and input / output terminals 110 and 120. The elastic wave filter 600 according to Comparative Example 3 differs from the elastic wave filter 1 according to the embodiment only in that the series arm resonator 13 is replaced with the series arm resonator 613. The following description of the elastic wave filter 600 according to Comparative Example 3 will focus on the different configurations and omit a description of the same configurations as those of the elastic wave filter 1 according to the embodiment.

[0089] The series arm resonators 11, 12, and 613 are connected in this order from the input / output terminal 110. The series arm resonator 613 is connected closest to the input / output terminal 120 among the series arm resonators 11, 12, and 613, the parallel arm resonator 21, and the inductor 31.

[0090] 6A, the series arm resonator 613 has the largest capacitance among the series arm resonators 11, 12, and 613 and the parallel arm resonator 21. The resonant frequency frs613 and the antiresonant frequency fas613 of the series arm resonator 613 are located on the lower frequency side than the lower frequency end of the pass band of the acoustic wave filter 600.

[0091] The series arm resonator 613 has the largest capacitance among the series arm resonators 11, 12, and 613 and the parallel arm resonator 21. As shown in FIG. 6(a), the impedance of the series arm resonator 613 in the DC region is capacitive. The capacitance of the series arm resonator 613 in the DC region is 5 pF or more, which is large enough to block DC components. This prevents the bias DC to be supplied to the low-noise amplifier 2 from leaking to ground via the inductor 31.

[0092] 6(a) and 6(b), the impedance of the series arm resonator 613 in the pass band of the acoustic wave filter 600 is capacitive, but the capacitance value is small. Therefore, the impedance of the series arm resonator 613 in the pass band is large. As a result, even if the inductor 31 shifts the impedance of the acoustic wave filter 600 in the pass band to the inductive region P1, as shown in FIG. 6(c), the series arm resonator 613, which has a large capacitive impedance, shifts the impedance of the acoustic wave filter 600 in the pass band significantly counterclockwise on the equal resistance circle, resulting in a small inductive reactance. This results in insufficient impedance matching with the low-noise amplifier 2 connected to the input / output terminal 120, resulting in a large matching loss of the high-frequency received signal.

[0093] [4. Terminal arrangement of acoustic wave filter 1] Next, the terminal arrangement of the acoustic wave filter 1 according to this embodiment will be described. Fig. 7A is a circuit configuration diagram of the acoustic wave filter 1 according to this embodiment. Fig. 7B is a plan view showing the electrode arrangement of the acoustic wave filter 1 according to this embodiment.

[0094] 7A, the acoustic wave filter 1 includes a substrate 70 in addition to the circuit configuration of the acoustic wave filter 1 shown in FIG. The series arm resonators 11 to 13, the parallel arm resonator 21, the input / output terminals 110 and 120, the terminal 150, and the ground terminal 160 are arranged on the substrate 70. This enables the acoustic wave filter 1 to be miniaturized.

[0095] The terminal 150 is an example of a first terminal, is a node on a path connecting the series arm resonators 12 and 13, and is connected to the inductor 31. The ground terminal 160 is connected to the parallel arm resonator 21 and is set to the ground potential.

[0096] The substrate 70 is an example of a first substrate and has principal surfaces 70a and 70b facing each other. If the series arm resonators 11 to 13 and the parallel arm resonator 21 are each surface acoustic wave resonators including an IDT electrode 54, the substrate 70 has piezoelectric properties and corresponds to the piezoelectric substrate 50 shown in Fig. 2A or the piezoelectric single crystal substrate 57 shown in Fig. 2B. If the series arm resonators 11 to 13 and the parallel arm resonator 21 are each bulk acoustic wave resonators including a stack of a bottom electrode 66, a piezoelectric layer 67, and an top electrode 68 in this order from the main surface 70a or 70b, the substrate 70 contains silicon and corresponds to the support substrate 65 shown in Fig. 2C.

[0097] 7B, the input / output terminals 110 and 120, the terminal 150, and the ground terminal 160 are arranged on the main surface 70a. The IDT electrode and the laminate may be arranged on either the main surface 70a or 70b. When the main surface 70a is viewed from above, the ground terminal 160 is arranged between the terminal 150 and the input / output terminal 110.

[0098] In this way, the ground terminal 160 is arranged between the terminal 150 and the input / output terminal 110, so that the inductor 31 connected to the terminal 150 and the input / output terminal 110 are prevented from being electromagnetically coupled (electrically coupled or magnetically coupled) to prevent the attenuation band of the acoustic wave filter 1 from deteriorating.

[0099] The ground terminal disposed between the terminal 150 and the input / output terminal 110 does not have to be the ground terminal 160, but may be another ground terminal (GND).

[0100] 7C is a plan view showing an electrode arrangement of an acoustic wave filter 1A according to a first modification of an embodiment. The acoustic wave filter 1A according to the first modification has the same circuit configuration as the acoustic wave filter 1 according to the embodiment, and differs only in its terminal arrangement. Therefore, the terminal arrangement of the acoustic wave filter 1A according to the first modification will be described below.

[0101] 7C, a plurality of ground terminals (GND) are arranged on the main surface 70a. When the main surface 70a is viewed from above, an imaginary line segment L L (First virtual line segment) and virtual line segment L connecting two of the multiple ground terminals (GND) G (Second virtual line segment) and intersects with virtual line segment L G Length D G is the imaginary line segment L L Length D L is shorter than.

[0102] This creates an electromagnetic field shielding area consisting of multiple ground terminals (GND) between terminal 150 and input / output terminal 110, thereby preventing electromagnetic field coupling between inductor 31 connected to terminal 150 and input / output terminal 110, thereby preventing deterioration of the attenuation band of elastic wave filter 1A.

[0103] The ground terminals arranged to intersect with the imaginary line segment connecting the terminal 150 and the input / output terminal 110 do not have to include the ground terminal 160, and may be other ground terminals (GND).

[0104] [5. Component layout of high-frequency module 100A] Next, a circuit configuration and component layout configuration of a high-frequency module 100A according to a second modification of the present embodiment will be described.

[0105] Fig. 8A is a circuit diagram of a high-frequency module 100A according to Modification 2 of the embodiment, and Fig. 8B is a plan view showing the component arrangement of the high-frequency module 100A according to Modification 2 of the embodiment.

[0106] As shown in FIG. 8A, a high-frequency module 100A according to this modification includes an acoustic wave filter 1, a low-noise amplifier 2, a filter 3, a switch 40, and an inductor 32.

[0107] The acoustic wave filter 1 is an acoustic wave filter 1 according to an embodiment, and is connected to an input terminal 130 of a low-noise amplifier 2 via a switch 40 and an inductor 32. The filter 3 is an example of a first filter, and has one end connected to the input terminal 130 via the switch 40 and the inductor 32 and the other end connected to an input / output terminal 170.

[0108] The switch 40 has a common terminal 40a, a selection terminal 40b (first selection terminal), and a selection terminal 40c (second selection terminal), and switches between the connection between the common terminal 40a and the selection terminal 40b and the connection between the common terminal 40a and the selection terminal 40c. The common terminal 40a is connected to the input terminal 130 via the inductor 32, the selection terminal 40b is connected to the input / output terminal 120, and the selection terminal 40c is connected to the filter 3.

[0109] According to the above configuration, the high-frequency module 100A can select either the received signal that has passed through the acoustic wave filter 1 or the received signal that has passed through the filter 3 and amplify the selected signal in the low-noise amplifier 2.

[0110] In the high-frequency module 100A, at least one of the switch 40 and the inductor 32 may be omitted.

[0111] 8B, the high-frequency module 100A further includes a mounting substrate 90. The mounting substrate 90 has an acoustic wave filter 1, a filter 3, and a low-noise amplifier 2 mounted thereon. The switch 40 and the inductor 32 may also be mounted on the mounting substrate 90.

[0112] 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.

[0113] Here, the distance D between the low-noise amplifier 2 and the acoustic wave filter 1 is 12 is the distance D between the low noise amplifier 2 and the filter 3 32 is greater than.

[0114] This allows the inductor 31 included in the acoustic wave filter 1 to cancel out the effect of parasitic capacitance occurring in the wiring, even if the wiring connecting the acoustic wave filter 1 and the low-noise amplifier 2 is long. Therefore, the filter 3, which preferably has a short wiring for connection to the low-noise amplifier 2, can be disposed between the acoustic wave filter 1 and the low-noise amplifier 2, thereby providing a compact high-frequency module 100A with reduced signal transmission loss.

[0115] [6 Effects etc.] As described above, the acoustic wave filter 1 according to this preferred embodiment includes a plurality of series arm resonators including the series arm resonators 12 and 13 arranged in a series arm path connecting the input / output terminals 110 and 120, one or more parallel arm resonators including the parallel arm resonator 21 connected between the series arm path and ground, and the inductor 31 connected between a first path connecting the series arm resonators 12 and 13 and ground. The series arm resonator 13 is connected closest to the input / output terminal 120 among the plurality of series arm resonators, the one or more parallel arm resonators, and the inductor 31, and has the highest resonant frequency among the plurality of series arm resonators.

[0116] In this configuration, the series arm resonator 13 has the highest resonant frequency, and therefore the impedance of the series arm resonator 13 in the pass band and DC region of the acoustic wave filter 1 is capacitive. Therefore, DC components can be prevented from leaking to ground via the inductor 31 without the need for a DC-blocking capacitor in series in the connection path between the input / output terminal 120 and an external circuit. Furthermore, the capacitance of the series arm resonator 13 in the pass band is significantly larger than its capacitance in the DC region, and the impedance of the series arm resonator 13 in the pass band is low, resulting in a nearly short-circuited state. As a result, the inductor 31 functions as a matching element with inductive impedance within the pass band frequency range without being affected by the series arm resonator 13. Therefore, when an external circuit with capacitive impedance is connected to the input / output terminal 120, matching loss in the pass band can be reduced, and an acoustic wave filter 1 with DC-blocking and impedance matching in the pass band can be provided. Furthermore, in the high-frequency module 100 in which the external circuit connected to the input / output terminal 120 is the low-noise amplifier 2, a DC bias current can be supplied to the low-noise amplifier 2 with high precision, and the matching loss of the high-frequency received signal can be reduced, thereby suppressing deterioration of the noise figure of the low-noise amplifier 2.

[0117] Furthermore, for example, in the acoustic wave filter 1, the series arm resonator 13 has the largest capacitance among the plurality of series arm resonators and the one or more parallel arm resonators.

[0118] This allows the series arm resonator 13 to have the largest capacitance in the DC region among all the elastic wave resonators constituting the elastic wave filter 1, and also allows the series arm resonator 13 to have an extremely low impedance in the pass band. This significantly reduces the matching loss in the pass band, and provides an elastic wave filter 1 that ensures DC blocking in the DC region and impedance matching in the pass band.

[0119] For example, in the acoustic wave filter 1, the resonant frequency frs13 of the series arm resonator 13 is located above the high frequency end of the pass band of the acoustic wave filter 1.

[0120] As a result, the impedance of the series arm resonator 13 becomes capacitive throughout the entire passband of the acoustic wave filter 1, and when an external circuit having capacitive impedance is connected to the input / output terminal 120, the matching loss in the passband can be significantly reduced.

[0121] For example, the acoustic wave filter 1 further includes a substrate 70 having principal surfaces 70a and 70b facing each other, and the acoustic wave resonators included in each of the series arm resonators 11 to 13 and the parallel arm resonator 21 are formed on the substrate 70, and the input / output terminals 110 and 120, the terminal 150 on the first path connected to the inductor 31, and the ground terminal 160 are arranged on the principal surface 70a.

[0122] In this case, the acoustic wave resonators constituting the acoustic wave filter 1 are integrated on the substrate 70, thereby enabling the acoustic wave filter 1 to be miniaturized.

[0123] Furthermore, for example, in the acoustic wave filter 1, the ground terminal 160 is disposed between the terminal 150 and the input / output terminal 110 when the main surface 70a is viewed from above.

[0124] This can prevent the attenuation band of the acoustic wave filter 1 from being deteriorated due to electromagnetic field coupling between the inductor 31 connected to the terminal 150 and the input / output terminal 110.

[0125] For example, in the acoustic wave filter 1A according to the first modification, a plurality of ground terminals are arranged on the principal surface 70a. When the principal surface 70a is viewed from above, an imaginary line segment L connecting the terminal 150 and the input / output terminal 110 is formed. L and an imaginary line segment L connecting two of the multiple ground terminals. G and intersect with the imaginary line segment L G is the virtual line segment L L is shorter than.

[0126] This allows an electromagnetic field shielding area consisting of multiple ground terminals to be formed between terminal 150 and input / output terminal 110, thereby preventing electromagnetic field coupling between inductor 31 connected to terminal 150 and input / output terminal 110 and thereby preventing deterioration of the attenuation band of elastic wave filter 1A.

[0127] Furthermore, for example, in the acoustic wave filter 1 (1A), the substrate 70 has piezoelectric properties, and the acoustic wave resonators included in each of the series arm resonators 11 to 13 and the parallel arm resonator 21 include an IDT electrode.

[0128] According to this, the acoustic wave filter 1 (1A) is a ladder-type filter made up of surface acoustic wave resonators.

[0129] Also, for example, in the acoustic wave filter 1 (1A), the substrate 70 includes silicon, and the acoustic wave resonators included in each of the series arm resonators 11 to 13 and the parallel arm resonator 21 include a laminate of a lower electrode 66, a piezoelectric layer 67, and an upper electrode 68, in that order from the main surface 70a or 70b.

[0130] According to this, the acoustic wave filter 1 (1A) is a ladder-type filter configured with bulk acoustic wave resonators.

[0131] Moreover, the high-frequency module 100 according to this preferred embodiment includes an acoustic wave filter 1 and a low-noise amplifier 2 having an input terminal 130 connected to an input / output terminal 120 .

[0132] With this, the series arm resonator 13 has a DC cut function and is short-circuited in the pass band, so that a DC bias current can be supplied to the low-noise amplifier 2 with high precision and the matching loss of the high-frequency received signal in the pass band can be reduced, thereby suppressing deterioration of the noise figure of the low-noise amplifier 2.

[0133] Furthermore, for example, in the high-frequency module 100, a capacitor is not arranged in series in the path connecting the input end of the amplifying transistor included in the low-noise amplifier 2 and the input / output terminal 120.

[0134] This makes it possible to prevent the capacitor from causing impedance mismatch in the pass band and deteriorating the noise figure of the low-noise amplifier.

[0135] For example, the high-frequency module 100A according to the second modification further includes a filter 3 connected to the input terminal 130, and a mounting substrate 90 on which the acoustic wave filter 1, the filter 3, and the low-noise amplifier 2 are arranged, and the distance between the low-noise amplifier 2 and the acoustic wave filter 1 is greater than the distance between the low-noise amplifier 2 and the filter 3.

[0136] This allows the inductor 31 included in the acoustic wave filter 1 to cancel out the effect of parasitic capacitance occurring in the wiring, even if the wiring connecting the acoustic wave filter 1 and the low-noise amplifier 2 is long. Therefore, the filter 3, which preferably has a short wiring for connection to the low-noise amplifier 2, can be disposed between the acoustic wave filter 1 and the low-noise amplifier 2, thereby providing a compact high-frequency module 100A with reduced signal transmission loss.

[0137] For example, the high-frequency module 100A further has a common terminal 40a and selection terminals 40b and 40c, and is equipped with a switch 40 that switches the connection between the common terminal 40a and the selection terminal 40b and the connection between the common terminal 40a and the selection terminal 40c, where the common terminal 40a is connected to the input terminal 130, the selection terminal 40b is connected to the input / output terminal 120, and the selection terminal 40c is connected to the filter 3.

[0138] With this configuration, the high-frequency module 100A can select either the received signal that has passed through the acoustic wave filter 1 or the received signal that has passed through the filter 3 and amplify the selected signal in the low-noise amplifier 2.

[0139] (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.

[0140] 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.

[0141] The following describes the features of the acoustic wave filter and the high-frequency module described based on the above-described embodiment and modifications.

[0142] <1> a plurality of series arm resonators including a first series arm resonator and a second series arm resonator arranged in a series arm path connecting the first input / output terminal and the second input / output terminal; one or more parallel arm resonators connected between the series arm path and ground; a first inductor connected between a first path connecting the first series arm resonator and the second series arm resonator and ground, the first series arm resonator is connected closest to the first input / output terminal among the plurality of series arm resonators, the one or more parallel arm resonators, and the first inductor; an elastic wave filter, wherein the first series arm resonator has the largest capacitance among the plurality of series arm resonators and the one or more parallel arm resonators, and also has the highest resonance frequency among the plurality of series arm resonators;

[0143] <2> the first series arm resonator has the largest capacitance among the plurality of series arm resonators and the one or more parallel arm resonators; The acoustic wave filter according to claim 1.

[0144] <3> a resonant frequency of the first series arm resonator is located at or above the high frequency end of the pass band of the acoustic wave filter; <1> or <2> The acoustic wave filter according to claim 1.

[0145] <4> moreover, a first substrate having a first main surface and a second main surface facing each other; an acoustic wave resonator included in each of the plurality of series arm resonators and the one or more parallel arm resonators is formed on the first substrate; the first input / output terminal, the second input / output terminal, the first terminal on the first path connected to the first inductor, and the ground terminal are disposed on the first main surface; <1> ~ <3> 10. The acoustic wave filter according to claim 9, wherein

[0146] <5> When the first main surface is viewed in plan, the ground terminal is disposed between the first terminal and the second input / output terminal. <4> The acoustic wave filter according to claim 1.

[0147] <6> a plurality of ground terminals are arranged on the first main surface; When the first main surface is viewed in plan, a first virtual line segment connecting the first terminal and the second input / output terminal intersects with a second virtual line segment connecting two of the plurality of ground terminals, The second imaginary line segment is shorter than the first imaginary line segment. <4> The acoustic wave filter according to claim 1.

[0148] <7> the first substrate has piezoelectric properties; an acoustic wave resonator included in each of the plurality of series arm resonators and the one or more parallel arm resonators includes an IDT electrode; <4> ~ <6> 10. The acoustic wave filter according to claim 9, wherein

[0149] <8> the first substrate comprises silicon; an elastic wave resonator included in each of the plurality of series arm resonators and the one or more parallel arm resonators includes a laminate of a first planar electrode, a piezoelectric thin film, and a second planar electrode, in this order from the first principal surface or the second principal surface; <4> ~ <6> 10. The acoustic wave filter according to claim 9, wherein

[0150] <9> <1> ~ <8> an acoustic wave filter according to any one of the preceding claims; A high-frequency module comprising: a low-noise amplifier having an input terminal, the input terminal being connected to the first input / output terminal.

[0151] <10> a capacitor is not arranged in series in a path connecting an input end of an amplifying transistor included in the low-noise amplifier and the first input / output terminal; <9> The high-frequency module according to claim 1.

[0152] <11> moreover, a first filter connected to the input terminal; a mounting substrate on which the acoustic wave filter, the first filter, and the low-noise amplifier are arranged, the distance between the low-noise amplifier and the acoustic wave filter is greater than the distance between the low-noise amplifier and the first filter; <9> or <10> The high-frequency module according to claim 1.

[0153] <12> moreover, a switch having a common terminal, a first selection terminal, and a second selection terminal, and switching between a connection between the common terminal and the first selection terminal and a connection between the common terminal and the second selection terminal; the common terminal is connected to the input terminal; the first selection terminal is connected to the first input / output terminal; the second selection terminal is connected to the first filter; <11> The high-frequency module according to claim 1. [Industrial Applicability]

[0154] 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]

[0155] 1, 1A, 200, 500, 600 Acoustic Wave Filter 2. Low noise amplifier 3. Filters 11, 12, 13, 513, 613 Series arm resonators 21 Parallel arm resonator 31, 32 Inductors 40 Switch 40a common terminal 40b, 40c selection terminals 50 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 70 boards 70a, 70b main surface 90 Mounting board 100, 100A high frequency module 110, 120, 170 input / output terminals 130 Input terminal 140 output terminal 150 terminals 160 Ground terminal 540 Adhesion layer 542 Main electrode layer

Claims

1. a plurality of series arm resonators including a first series arm resonator and a second series arm resonator arranged in a series arm path connecting the first input / output terminal and the second input / output terminal; one or more parallel arm resonators connected between the series arm path and ground; a first inductor connected between a first path connecting the first series arm resonator and the second series arm resonator and ground, the first series arm resonator is connected closest to the first input / output terminal among the plurality of series arm resonators, the one or more parallel arm resonators, and the first inductor; the first series arm resonator has the highest resonant frequency among the plurality of series arm resonators; Acoustic wave filters.

2. the first series arm resonator has the largest capacitance among the plurality of series arm resonators and the one or more parallel arm resonators; The acoustic wave filter according to claim 1 .

3. a resonant frequency of the first series arm resonator is located at or above the high frequency end of the pass band of the acoustic wave filter; The acoustic wave filter according to claim 1 or 2.

4. moreover, a first substrate having a first main surface and a second main surface facing each other; an acoustic wave resonator included in each of the plurality of series arm resonators and the one or more parallel arm resonators is formed on the first substrate; the first input / output terminal, the second input / output terminal, the first terminal on the first path connected to the first inductor, and the ground terminal are disposed on the first main surface; The acoustic wave filter according to claim 1 or 2.

5. When the first main surface is viewed in plan, the ground terminal is disposed between the first terminal and the second input / output terminal. The acoustic wave filter according to claim 4 .

6. a plurality of ground terminals are arranged on the first main surface; When the first main surface is viewed in a plan view, a first virtual line segment connecting the first terminal and the second input / output terminal intersects with a second virtual line segment connecting two of the plurality of ground terminals, The second imaginary line segment is shorter than the first imaginary line segment. The acoustic wave filter according to claim 4 .

7. the first substrate has piezoelectric properties; an acoustic wave resonator included in each of the plurality of series arm resonators and the one or more parallel arm resonators includes an IDT electrode; The acoustic wave filter according to claim 4 .

8. the first substrate comprises silicon; an elastic wave resonator included in each of the plurality of series arm resonators and the one or more parallel arm resonators includes a laminate of a first planar electrode, a piezoelectric thin film, and a second planar electrode, in this order from the first principal surface or the second principal surface; The acoustic wave filter according to claim 4 .

9. an acoustic wave filter according to claim 1 or 2; a low noise amplifier having an input terminal, the input terminal being connected to the first input / output terminal; High frequency module.

10. a capacitor is not arranged in series in a path connecting an input end of an amplifying transistor included in the low-noise amplifier and the first input / output terminal; The high frequency module according to claim 9 .

11. moreover, a first filter connected to the input terminal; a mounting substrate on which the acoustic wave filter, the first filter, and the low-noise amplifier are arranged, a distance between the low-noise amplifier and the acoustic wave filter is greater than a distance between the low-noise amplifier and the first filter; The high frequency module according to claim 9 .

12. moreover, a switch having a common terminal, a first selection terminal, and a second selection terminal, and switching between a connection between the common terminal and the first selection terminal and a connection between the common terminal and the second selection terminal; the common terminal is connected to the input terminal; the first selection terminal is connected to the first input / output terminal; the second selection terminal is connected to the first filter; The high frequency module according to claim 11.

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