Elastic wave device and multiplexer

Abstract

A filter (10) is provided with a plurality of elastic wave resonance circuits, and an elastic wave resonance circuit (11) among the plurality of elastic wave resonance circuits is composed of series arm resonators (111-113) connected in series to each other. Each of the series arm resonators (111-113) has an IDT electrode that is disposed on a piezoelectric substrate (50) and has a plurality of electrode fingers that are parallel to each other. When a region in which two or more electrode fingers having the same duty are continuously arranged is defined as an electrode finger region, the IDT electrode of each of the series arm resonators (111-113) is divided into a plurality of electrode finger regions having different duties D. When the plurality of electrode finger regions are compared, the larger the duty D, the smaller an electrode finger pitch that is the interval between the adjacent electrode fingers.

Description

Acoustic wave devices and multiplexers

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

[0002] Patent Document 1 discloses a filter (acoustic wave device) having a plurality of surface acoustic wave resonators divided in series. It claims that stop band ripple can be suppressed by varying the parameters of IDT (InterDigital Transducer) electrodes that make up the plurality of surface acoustic wave resonators. Patent Document 2 also claims that stop band ripple can be suppressed by narrowing the width of the electrode fingers that make up the surface acoustic wave resonator toward the ends of the IDT electrodes.

[0003] International Publication No. 2018 / 003297 Japanese Patent Application Laid-Open No. 2005-005853

[0004] However, the acoustic wave devices disclosed in Patent Documents 1 and 2 do not sufficiently suppress Rayleigh wave ripples that occur on the low frequency side of the fundamental wave.

[0005] 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 device and a multiplexer in which Rayleigh wave ripples are suppressed.

[0006] In order to achieve the above object, an elastic wave device according to one aspect of the present invention includes a plurality of elastic wave resonant circuits, and a first elastic wave resonant circuit of the plurality of elastic wave resonant circuits is composed of a plurality of elastic wave resonators connected in series with each other. Each of the plurality of elastic wave resonators is arranged on a piezoelectric substrate and has an IDT (InterDigital Transducer) electrode having a plurality of electrode fingers parallel to each other. When an electrode finger region is defined as a region where two or more electrode fingers with equal duties are arranged consecutively, the IDT electrode of each of the plurality of elastic wave resonators is divided into a plurality of electrode finger regions with different duties. When the plurality of electrode finger regions are compared, the electrode finger pitch, which is the distance between adjacent electrode fingers, becomes smaller as the duty increases.

[0007] According to the present invention, it is possible to provide an acoustic wave device and a multiplexer in which Rayleigh wave ripples are suppressed.

[0008] FIG. 1 is a circuit diagram of a multiplexer according to an embodiment. FIG. 2 is a circuit diagram of an elastic wave device according to Example 1. FIG. 3A is a plan view and a cross-sectional view schematically illustrating a first example of an elastic wave resonator included in an elastic wave device according to an embodiment. FIG. 3B is a cross-sectional view schematically illustrating a second example of an elastic wave resonator included in an elastic wave device according to an embodiment. FIG. 4 is a plan view illustrating an electrode configuration of a first elastic wave resonator circuit according to Example 1. FIG. 5 is a plan view illustrating an electrode configuration of an elastic wave resonator included in the first elastic wave resonator circuit according to Example 1. FIG. 6 is a plan view illustrating an electrode configuration of an elastic wave resonator circuit according to Comparative Example 1. FIG. 7A is a graph illustrating the pass characteristics of filters according to Example 1 and Comparative Example 1 near the stopband. FIG. 7B is a graph illustrating the pass characteristics of filters according to Example 1 and Comparative Example 1 near the frequency band in which a Rayleigh wave mode occurs. FIG. 8 is a graph illustrating the resonance characteristics of an elastic wave resonator. FIG. 9A is a graph showing resonance characteristics in the main mode when the duty of the elastic wave resonator is changed. FIG. 9B is a graph showing resonance characteristics in the Rayleigh wave mode when the duty of the elastic wave resonator is changed. FIG. 10A is a graph showing resonance characteristics in the main mode when the electrode finger pitch is corrected in response to changes in the duty of the elastic wave resonator. FIG. 10B is a graph showing resonance characteristics in the Rayleigh wave mode when the electrode finger pitch is corrected in response to changes in the duty of the elastic wave resonator. FIG. 11 is a graph showing changes in Rayleigh wave ripple when the number of electrode fingers in each region of the elastic wave resonator is changed. FIG. 12 is a graph showing changes in Rayleigh wave ripple when the difference in duty between the regions of the elastic wave resonator is changed. FIG. 13A is a plan view showing an electrode configuration of a first elastic wave resonator circuit in accordance with Example 2. FIG. 13B is a plan view showing an electrode configuration of a first elastic wave resonator circuit in accordance with Example 3. FIG. 13C is a plan view showing an electrode configuration of an elastic wave resonator circuit in accordance with Comparative Example 2. 14 is a graph illustrating Rayleigh wave ripples in the elastic wave devices according to Example 2, Example 3, and Comparative Example 2. FIG. 15 is a plan view illustrating an electrode configuration of a first elastic wave resonant circuit according to Example 4.FIG. 16 is a plan view showing an electrode configuration of a first elastic wave resonator circuit in accordance with Example 5. FIG. 17 is a circuit configuration diagram of an elastic wave device in accordance with Example 6. FIG. 18A is a plan view showing an electrode configuration of an elastic wave resonator constituting a first elastic wave resonator circuit in accordance with Example 7. FIG. 18B is a plan view showing an electrode configuration of an elastic wave resonator constituting a first elastic wave resonator circuit in accordance with Example 8. FIG. 18C is a plan view showing an electrode configuration of an elastic wave resonator constituting a first elastic wave resonator circuit in accordance with Example 9. FIG. 19A is a plan view showing an electrode configuration of an elastic wave resonator constituting a first elastic wave resonator circuit in accordance with Modification 1. FIG. 19B is a plan view showing an electrode configuration of an elastic wave resonator constituting a first elastic wave resonator circuit in accordance with Modification 2.

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, arrangements and connection forms of the components shown in the following embodiments are merely examples and are not intended to limit the present invention.

[0010] 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.

[0011] In the circuit configuration of the present disclosure, "connected between A and B" and "connected between A and B" mean connected to both A and B between A and B.

[0012] Furthermore, in the component arrangement of the present disclosure, "component A is arranged in series on path B" means that both the signal input terminal and the signal output terminal of component A are connected to the wiring, electrode, or terminal that constitutes path B.

[0013] 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.

[0014] Also, in this disclosure, "terminal" means a point where a conductor within an element terminates, and is to be construed as any point on the conductor between elements or the entire conductor, not just a single point, provided the impedance of the conductor between elements is sufficiently low.

[0015] In the following embodiments, the passband of an acoustic wave device or a filter is defined as a frequency band between two frequencies that are 3 dB higher than the minimum insertion loss within the passband.

[0016] In the present disclosure, band A and band B refer to frequency bands predefined by standardization organizations (e.g., 3GPP (registered trademark), IEEE (Institute of Electrical and Electronics Engineers)), etc. for communication systems built using radio access technology (RAT). In this embodiment, examples of communication systems that can be used include, but are not limited to, an LTE (Long Term Evolution) system, a 5G (5th Generation)-NR (New Radio) system, and a WLAN (Wireless Local Area Network) system.

[0017] Furthermore, the uplink operating band of Band A refers to the frequency range designated for uplink use within Band A. The downlink operating band of Band A refers to the frequency range designated for downlink use within Band A.

[0018] 1 is a circuit diagram of a multiplexer 1 according to an embodiment. The multiplexer 1 includes filters 10 and 20, a common terminal 100, and input / output terminals 110 and 120. The common terminal 100 is connected to, for example, an antenna 2.

[0019] The filter 10 is an example of an acoustic wave device, and is connected to the common terminal 100. The filter 20 is connected to the common terminal 100. The filter 10 is a band-rejection filter having a stop band. The filter 20 is a band-pass filter having a pass band. In this embodiment, the stop band of the filter 10 and the pass band of the filter 20 at least partially overlap, and the multiplexer 1 forms an extractor.

[0020] In the filter 10 according to this embodiment, the acoustic wave resonators for forming the stopband have an IDT electrode configuration, which will be described later, and thus Rayleigh wave ripples can be suppressed. This can suppress deterioration of the pass characteristics in the passband of the filter 10, which is located on the low-frequency side of the stopband of the filter 10. Furthermore, since it is possible to prevent signals in the Rayleigh wave mode generated in the filter 10 from sneaking into the filter 20 via the common terminal 100, deterioration of the attenuation characteristics of the filter 20 can be suppressed.

[0021] The filter 10 is not limited to a band-elimination filter, but may also be a band-pass filter, a low-pass filter, or a high-pass filter. When the filter 10 is a band-pass filter, it is possible to suppress Rayleigh wave ripples that occur on the low-frequency side of the pass band of the filter 10. Furthermore, it is possible to prevent Rayleigh wave mode signals generated in the filter 10 from sneaking into the filter 20 via the common terminal 100, thereby suppressing deterioration of the pass characteristics or attenuation characteristics of the filter 20.

[0022] 2. Circuit Configuration of Filter 10 FIG. 2 is a circuit configuration diagram of filter 10 according to Example 1. Filter 10 shown in FIG. 2 is an example of filter 10 constituting multiplexer 1 according to an embodiment. Filter 10 according to Example 1 is an example of an acoustic wave device and includes a plurality of acoustic wave resonant circuits. Specifically, filter 10 includes series arm resonators 111, 112, and 113, parallel arm resonators 12 and 13, and terminals 130 and 140. Terminal 130 is connected to common terminal 100.

[0023] Series arm resonators 111, 112, and 113 form a first acoustic wave resonant circuit (elastic wave resonant circuit 11). Parallel arm resonator 12 forms a second acoustic wave resonant circuit, and parallel arm resonator 13 forms a third acoustic wave resonant circuit.

[0024] The series arm resonators 111, 112, and 113 are a plurality of elastic wave resonators connected in series with one another between the terminal 130 and the terminal 140, and form a split resonator group.

[0025] A split resonator group is defined as a resonant circuit consisting of multiple elastic wave resonators connected in series with each other, and has a configuration in which the connection nodes connecting the multiple elastic wave resonators are not connected to circuit elements other than the multiple elastic wave resonators and to ground.

[0026] The parallel arm resonator 12 is an acoustic wave resonator and is connected between the connection point of the terminal 130 and the series arm resonator 111 and the ground. The parallel arm resonator 13 is an acoustic wave resonator and is connected between the connection point of the series arm resonator 113 and the terminal 140 and the ground.

[0027] In the above-described configuration of filter 10, by arranging the frequencies in the following order from the low-frequency side: (1) the resonant frequency defined by elastic wave resonant circuit 11, (2) the anti-resonant frequency defined by elastic wave resonant circuit 11 and the resonant frequency defined by parallel arm resonators 12 and 13, and (3) the anti-resonant frequency defined by parallel arm resonators 12 and 13, filter 10 becomes a band-elimination filter whose stopband includes the anti-resonant frequency defined by elastic wave resonant circuit 11 and the resonant frequency defined by parallel arm resonators 12 and 13.

[0028] Each of the series arm resonators 111 to 113 has an IDT electrode disposed on a piezoelectric substrate.

[0029] Each of the parallel arm resonators 12 and 13 does not have to be an acoustic wave resonator, but may be a resonant circuit formed of an inductor and a capacitor.

[0030] Furthermore, the circuit configuration of filter 10 shown in FIG. 2 is one example, and the number of acoustic wave resonant circuits is not limited to three, but may be one or more in the series arm path and one or more in the parallel arm path.

[0031] Furthermore, the split resonator group, which is made up of a plurality of elastic wave resonators connected in series with each other, does not necessarily have to be included in elastic wave resonator circuit 11 , but may be included in parallel arm resonator 12 or 13 .

[0032] Furthermore, the number of elastic wave resonators constituting the split resonator group is not limited to three as exemplified in elastic wave resonator circuit 11, but may be two or more.

[0033] Furthermore, an inductor may be connected between at least one of the parallel arm resonators 12 and 13 and the ground.

[0034] Furthermore, the filter 10 is not limited to being a ladder-type filter, and may be, for example, a filter including a longitudinally coupled resonator in which a plurality of acoustic wave resonators are arranged in parallel in the acoustic wave propagation direction.

[0035] 3. Structure of Elastic Wave Resonator Next, the basic structure of an elastic wave resonator constituting filter 10 will be described. Fig. 3A is a plan view and a cross-sectional view schematically illustrating a first example of an elastic wave resonator constituting filter 10 according to an embodiment. The figures illustrate the basic structure of an elastic wave resonator constituting filter 10. Note that elastic wave resonator 60 shown in Fig. 3A is intended to illustrate a typical structure of an elastic wave resonator constituting filter 10, and the number and length of electrode fingers constituting the electrodes are not limited to this.

[0036] The acoustic wave resonator 60 includes a piezoelectric substrate 50 and comb electrodes 60a and 60b. As shown in FIG. 3A (a), a pair of opposing comb electrodes 60a and 60b are formed on the piezoelectric substrate 50. The comb electrode 60a includes a plurality of parallel electrode fingers 61a and a busbar electrode 62a connecting one ends of the electrode fingers 61a. The comb electrode 60b includes a plurality of parallel electrode fingers 61b and a busbar electrode 62b connecting one ends of the electrode fingers 61b. The electrode fingers 61a and 61b are formed in a direction perpendicular to the acoustic wave propagation direction (X-axis direction). The busbar electrodes 62a and 62b are arranged opposite each other with the electrode fingers 61a and 61b interposed therebetween. The comb electrodes 60a and 60b form an IDT electrode 54.

[0037] The acoustic wave resonator 60 may have reflectors on both ends of the IDT electrode 54 in the acoustic wave propagation direction (X-axis direction).

[0038] As shown in FIG. 3A (b), the IDT electrode 54 has a laminated structure of, for example, an adhesive layer 540 and a main electrode layer 542.

[0039] 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 primarily composed of silicon dioxide.

[0040] The materials constituting the adhesion layer 540, the main electrode layer 542, and the protective layer 55 are not limited to those described above. Furthermore, the IDT electrode 54 does not have to have the laminated structure described above. The IDT electrode 54 may be made of, for example, a metal or alloy such as Ti, Al, Cu, Pt, Au, Ag, or Pd, or may be made of a laminate of multiple layers made of the above metals or alloys. Furthermore, the protective layer 55 does not necessarily have to be formed.

[0041] Next, the laminated structure of the piezoelectric substrate 50 will be described.

[0042] As shown in (c) of Figure 3A, the piezoelectric substrate 50 has a high acoustic velocity support substrate 51, a low acoustic velocity film 52, and a piezoelectric film 53, and has a structure in which the high acoustic velocity support substrate 51, the low acoustic velocity film 52, and the piezoelectric film 53 are stacked in this order.

[0043] The piezoelectric film 53 is, for example, a θ° Y-cut X-propagation LiTaO ３ It is made of a piezoelectric single crystal or piezoelectric ceramics (a lithium tantalate single crystal or ceramic cut along a plane whose normal is an axis rotated θ degrees from the Y axis around the X axis, and through which surface acoustic waves propagate in the X axis direction). The material and cut angle θ of the piezoelectric single crystal used as the piezoelectric film 53 are appropriately selected depending on the required specifications of each filter.

[0044] 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 them from leaking below the high acoustic velocity support substrate 51. Examples of materials that can be used for the high acoustic velocity support substrate 51 include 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, DLC (diamond-like carbon), and diamond; semiconductors such as silicon; and materials containing any of the above materials as a main component. The spinel includes aluminum compounds containing oxygen and one or more elements selected from Mg, Fe, Zn, Mn, etc. Examples of the spinel include MgAl ２ O ４ , FeAl ２ O ４ , ZnAl ２ O４ , MnAl ２ O ４ Examples include:

[0045] 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 a dielectric material 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.

[0046] The above-described laminated structure of piezoelectric substrate 50 makes it possible to significantly increase the Q value at the resonant frequency and antiresonant frequency compared to a conventional structure using a single-layer piezoelectric substrate. In other words, an elastic wave resonator with a high Q value can be configured, and a filter with low insertion loss can be configured using the elastic wave resonator.

[0047] The high acoustic velocity support substrate 51 may have a laminated structure of a support substrate and a high acoustic velocity film in which the acoustic velocity of the propagating bulk waves is faster than that of elastic waves such as surface waves and boundary waves that propagate through the piezoelectric film 53. In this case, the material of the high acoustic velocity film can be the same as the material of the high acoustic velocity support substrate 51. The material of the support substrate can be, for example, piezoelectrics such as aluminum nitride, lithium tantalate, lithium niobate, and quartz; ceramics such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, and forsterite; dielectrics such as diamond and glass; semiconductors such as silicon and gallium nitride; resins; or materials containing any of the above materials as a main component.

[0048] 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.

[0049] 3B is a cross-sectional view schematically illustrating a second example of an acoustic wave resonator constituting filter 10 according to an embodiment. In acoustic wave resonator 60 illustrated in FIG. 3A, IDT electrode 54 is formed on piezoelectric substrate 50 having piezoelectric film 53. However, the substrate on which IDT electrode 54 is formed may be piezoelectric single crystal substrate 57 consisting of a single piezoelectric layer, as illustrated in FIG. 3B.

[0050] The piezoelectric single crystal substrate 57 is, for example, LiTaO ３ The elastic wave resonator according to this example is made of a piezoelectric single crystal of LiTaO ３ The piezoelectric transducer 50 is composed of a 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.

[0051] 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 filter 10 and multiplexer 1 .

[0052] The piezoelectric 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 laminated in this order. The IDT electrode 54 is formed on the piezoelectric film. The piezoelectric film may be, for example, LiTaO ３ The support substrate is a substrate that supports the piezoelectric film, the energy trapping layer, and the IDT electrode 54.

[0053] 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.

[0054] 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.

[0055] Here, the electrode parameters of the IDT electrode 54 that constitutes the acoustic wave resonator 60 will be described.

[0056] The wavelength of the acoustic wave resonator 60 is defined by wavelength λ, which is the repetition period of the electrode fingers 61 a or 61 b ​​constituting the IDT electrode 54 shown in FIG. 3A (b). The electrode finger pitch is half of the wavelength λ and is the distance between (the center of) adjacent electrode fingers 61 a and 61 b. The electrode finger pitch is defined as (L + S), where L is the line width of the electrode fingers 61 a and 61 b ​​constituting the interdigital electrodes 60 a and 60 b, respectively, and S is the space width between adjacent electrode fingers 61 a and 61 b.

[0057] As shown in FIG. 3A (a), the overlap width V of the pair of interdigital transducers 60a and 60b is the length of the overlap between the electrode fingers 61a and 61b when viewed from the acoustic wave propagation direction (X-axis direction). The duty D of the electrode fingers of each acoustic wave resonator is the line width occupancy ratio of the multiple electrode fingers 61a and 61b, which is the ratio of the line width to the sum of the line width and space width of the multiple electrode fingers 61a and 61b, and is defined as L / (L+S). The height of the interdigital transducers 60a and 60b is h. The total number of electrode fingers 61a and 61b included in the IDT electrode 54 is Ni. Hereinafter, parameters related to the shape of the IDT electrodes of the acoustic wave resonators, such as the wavelength λ, the electrode finger pitch, the overlap width V, the duty D, the height h of the IDT electrode 54, and the number of electrode fingers Ni, are referred to as electrode parameters.

[0058] The duty D (= L / (L+S)) can be determined by measuring the line width L and the space width S as follows. The line width L is the length of the bonding interface between the electrode finger 61a or 61b and the piezoelectric film 53 in the X-axis direction when the bonding interface is viewed from the extension direction of the electrode fingers 61a and 61b. The space width S is the electrode finger pitch minus the line width L. The electrode finger pitch is the distance between the center of the bonding interface in the X-axis direction and the center of the bonding interface adjacent to the bonding interface in the X-axis direction when the bonding interface is viewed from the extension direction. The line width L and the space width S are measured by exposing a cross section of the elastic wave resonator 60 perpendicular to the extension direction by cutting or the like and observing the cross section using a scanning microscope or the like.

[0059] An electrode finger region is defined as a region where two or more electrode fingers having the same duty D are arranged in succession. The IDT electrode 54 is divided into a plurality of electrode finger regions each having a different duty D.

[0060] If the electrode finger pitch is not constant in each of the plurality of electrode finger regions constituting the IDT electrode 54, the electrode finger pitch of one electrode finger region is defined as the average electrode finger pitch of that electrode finger region, where Nr is the total number of electrode fingers 61 a, 61 b ​​included in that electrode finger region and Dr is the center-to-center distance between the electrode finger located at one end and the electrode finger located at the other end of the electrode finger region in the acoustic wave propagation direction.

[0061] 4. Structure of First Acoustic Wave Resonance Circuit According to First Embodiment Next, a description will be given of the electrode configuration of the acoustic wave resonator circuit 11, which is a group of split resonators of the filter 10. Fig. 4 is a plan view showing the electrode configuration of the acoustic wave resonator circuit 11 according to the first embodiment. This figure shows the planar layout of the IDT electrodes and reflective electrodes formed on the piezoelectric substrate 50 of the series arm resonators 111, 112, and 113 that constitute the acoustic wave resonator circuit 11 according to the first embodiment.

[0062] The IDT electrodes of the series arm resonators 111, 112, and 113 are arranged in this order in the y-axis direction via busbar electrodes. The reflective electrodes of the series arm resonators 111 to 113 are arranged on both ends of the IDT electrodes in the x-axis direction.

[0063] The IDT electrodes of each of the series arm resonators 111 to 113 are divided into a plurality of electrode finger regions with different duties D, assuming that an electrode finger region is a region where two or more electrode fingers with the same duty D are arranged consecutively.

[0064] 5 is a plan view showing the electrode configuration of the series arm resonator 111 constituting the acoustic wave resonator circuit 11 in accordance with the first embodiment. As shown in FIG. 5 , the IDT electrode of the series arm resonator 111 is specifically divided into a region 1 (D1, P1) having a duty D1 and an electrode finger pitch P1, a region 2 (D2, P2) having a duty D2 and an electrode finger pitch P2, and a region 3 (D3, P3) having a duty D3 and an electrode finger pitch P3. The duty D1 and the duty D2 are different. The duty D2 and the duty D3 are different. Note that the duty D1 and the duty D3 may be equal.

[0065] 4, the IDT electrode of the series arm resonator 112 is divided into a region 1 (D4, P4) having a duty D4 and an electrode finger pitch P4, a region 5 (D5, P5) having a duty D5 and an electrode finger pitch P5, and a region 6 (D6, P6) having a duty D6 and an electrode finger pitch P6. The duty D4 and the duty D5 are different. The duty D5 and the duty D6 are different. Note that the duty D4 and the duty D6 may be equal.

[0066] 4, the IDT electrode of the series arm resonator 113 is divided into a region 7 (D7, P7) having a duty D7 and an electrode finger pitch P7, a region 8 (D8, P8) having a duty D8 and an electrode finger pitch P8, and a region 9 (D9, P9) having a duty D9 and an electrode finger pitch P9. The duty D7 is different from the duty D8. The duty D8 is different from the duty D9. Note that the duty D7 and the duty D9 may be equal.

[0067] In this embodiment, the duties are D1<D2<D3, and the electrode finger pitches are P1>P2>P3. The duties are D4<D5<D6, and the electrode finger pitches are P4>P5>P6. The duties are D7<D8<D9, and the electrode finger pitches are P7>P8>P9.

[0068] That is, when comparing the plurality of electrode finger regions (region 1, region 2, region 3) that constitute the IDT electrode of the series arm resonator 111, the electrode finger pitch becomes smaller as the duty D increases.

[0069] 6 is a plan view showing the electrode configuration of elastic wave resonant circuit 91 in accordance with Comparative Example 1. Elastic wave resonant circuit 91 shown in the drawing constitutes filter 500 in accordance with Comparative Example 1. Filter 500 in accordance with Comparative Example 1 differs from filter 10 in accordance with Example 1 in that elastic wave resonant circuit 11 is replaced with elastic wave resonant circuit 91, and the other circuit configurations are the same as those of filter 10 in accordance with Example 1.

[0070] 6 , an acoustic wave resonator circuit 91 in accordance with Comparative Example 1 includes series arm resonators 911, 912, and 913 connected in series. The IDT electrode of the series arm resonator 911, the IDT electrode of the series arm resonator 912, and the IDT electrode of the series arm resonator 913 are arranged in this order in the y-axis direction via busbar electrodes. The reflective electrodes of each of the series arm resonators 911 to 913 are arranged on both ends of the IDT electrode in the x-axis direction. The IDT electrode of each of the series arm resonators 911 to 913 has only one electrode finger region (D1, P1) in which two or more electrode fingers having the same duty cycle D are arranged consecutively.

[0071] Table 1 shows electrode parameters of elastic wave resonant circuit 11 according to Example 1. Table 2 shows electrode parameters of elastic wave resonant circuit 91 according to Comparative Example 1.

[0072]

[0073]

[0074] 5. Pass Characteristics of the Elastic Wave Device According to Example 1 Next, the pass characteristics of the filter 10 according to Example 1 and the filter 500 according to Comparative Example 1 will be described. FIG. 7A is a graph showing the pass characteristics of the filters according to Example 1 and Comparative Example 1. As shown in the figure, both filters 10 and 500 have a notch filter stop band due to the main mode. FIG. 7B is a graph showing the pass characteristics near the stop band of the filters according to Example 1 and Comparative Example 1. As shown in the figure, the pass characteristics near the stop band are approximately the same between filters 10 and 500.

[0075] 7C is a graph showing the pass characteristics of the filters according to Example 1 and Comparative Example 1 in the vicinity of the frequency band in which the Rayleigh wave mode occurs. In the filter 500 according to Comparative Example 1, ripples in the Rayleigh wave mode occur in a frequency band that is approximately 0.7 times the frequency of the main mode. In contrast, in the filter 10 according to Example 1, ripples in the Rayleigh wave mode are suppressed compared to the filter 500 according to Comparative Example 1. The factors that suppress the Rayleigh wave ripples in the filter 10 according to Example 1 will be described with reference to FIGS. 8 to 10B.

[0076] 8 is a graph showing the resonance characteristics of an elastic wave resonator, which is a single elastic wave resonator having an IDT electrode with a uniform duty cycle D. The graph shows a main mode having a resonance point and an antiresonance point, and a Rayleigh wave mode occurring on the lower frequency side of the main mode.

[0077] 9A is a graph showing the resonance characteristics in the main mode when the duty cycle D of the elastic wave resonator is changed, and FIG. 9B is a graph showing the resonance characteristics in the Rayleigh wave mode when the duty cycle D of the elastic wave resonator is changed.

[0078] 9A, in an elastic wave resonator having an IDT electrode with a uniform duty ratio D, the resonance frequency and anti-resonance frequency of the main mode shift to lower frequencies as the duty ratio D increases from 0.49 to 0.51. In contrast, as shown in FIG. 9B, in an elastic wave resonator having an IDT electrode with a uniform duty ratio D, the resonance frequency and anti-resonance frequency of the Rayleigh wave mode shift to higher frequencies as the duty ratio D increases from 0.49 to 0.51.

[0079] By taking advantage of the fact that the direction of the frequency shift of the main mode and the direction of the frequency shift of the Rayleigh wave mode due to a change in duty D are opposite, and adjusting the electrode finger pitch, it is possible to significantly shift the frequency of the Rayleigh wave mode without shifting the frequency of the main mode even when duty D is changed.

[0080] 10A is a graph showing the resonance characteristics in the main mode when the electrode finger pitch is corrected in response to changes in the duty D of the elastic wave resonator. Specifically, the electrode finger pitch is made smaller as the duty D increases. As a result, as shown in FIG. 10A , the resonance frequency and antiresonance frequency of the main mode do not change even when the duty D is changed.

[0081] 10B is a graph showing the resonance characteristics in the Rayleigh wave mode when the electrode finger pitch is corrected in accordance with changes in the duty cycle D of the elastic wave resonator. As shown in FIG. 9B , increasing the duty cycle D shifts the resonance frequency and antiresonance frequency of the Rayleigh wave mode toward higher frequencies. In contrast, decreasing the electrode finger pitch shifts the resonance frequency and antiresonance frequency of the Rayleigh wave mode toward higher frequencies. Therefore, increasing the duty cycle D and decreasing the electrode finger pitch significantly shifts the resonance frequency and antiresonance frequency of the Rayleigh wave mode toward higher frequencies. In other words, by decreasing the electrode finger pitch as the duty cycle D of the elastic wave resonator increases, it is possible to distribute the resonance frequency of the Rayleigh wave mode without degrading the resonance characteristics of the main mode.

[0082] 10A and 10B, the duty cycle D and the electrode finger pitch can be adjusted between the multiple elastic wave resonators divided in series. However, in this configuration, the number of elastic wave resonators divided in series must be increased to reduce the ripple in the Rayleigh wave mode. This increases the layout area of ​​the multiple elastic wave resonators divided in series, resulting in a problem of increased filter size.

[0083] In contrast, in the filter 10 according to this embodiment, the IDT electrodes of each of the series arm resonators 111 to 113 are divided into three regions with different duties D, and as shown in Table 1, the electrode finger pitch (wavelength λ in Table 1) is made smaller as the duty D increases in the three regions.

[0084] This allows the resonance frequency and anti-resonance frequency of the main mode generated in different electrode finger regions within one IDT electrode to be matched, and the resonance frequency and anti-resonance frequency of the Rayleigh wave mode generated in the different electrode finger regions to be dispersed. This makes it possible to suppress Rayleigh wave mode ripples using a single split resonator without degrading the resonance characteristics of the main mode. Therefore, it is possible to provide a compact filter 10 with improved Rayleigh wave mode ripples without increasing the number of series divisions of elastic wave resonator circuit 11.

[0085] In the filter 10 according to this embodiment, the duties are also made different among the three series-divided series arm resonators 111 to 113. As shown in Table 1, the average duty of the series arm resonator 111 is 0.47, the average duty of the series arm resonator 112 is 0.50, and the average duty of the series arm resonator 113 is 0.53.

[0086] This allows the frequencies of the Rayleigh wave modes generated in the series arm resonators 111 to 113 to be dispersed, thereby further improving the Rayleigh wave ripples of the filter 10.

[0087] Next, the number of electrode fingers in the electrode finger regions necessary to effectively reduce ripple in the Rayleigh wave mode will be described. FIG. 11 is a graph showing the change in Rayleigh wave ripple when the number of electrode fingers in each region of an acoustic wave resonator is changed. FIG. 11B shows the Rayleigh wave ripple of the filter 10 when the acoustic wave resonator circuit 11 of the filter 10 is replaced with the single acoustic wave resonator shown in FIG. 11A. As shown in FIG. 11A, the IDT electrode of the acoustic wave resonator is configured with a region 1 having a duty D1 and a number of electrode fingers N1, and a region 2 having a duty D2 and a number of electrode fingers (N-N1). The number of electrode fingers N is the total number of electrode fingers in the IDT electrode. FIG. 11B shows the relationship between the duty change region ratio (N1 / N), which is the ratio of the number of electrode fingers in region 1, and the Rayleigh wave ripple (dB) generated in the acoustic wave resonator.

[0088] Table 3 shows the duty change region ratio and electrode parameters for each region.

[0089]

[0090] 11(b), when the duty change area ratio (N1 / N) of area 1 is 8% or less, the Rayleigh wave ripple is not reduced compared to when the IDT electrode is composed of only one electrode finger area (duty change area ratio = 0%). On the other hand, when the duty change area ratio (N1 / N) of area 1 is 10% or more, it can be seen that the Rayleigh wave ripple can be reduced.

[0091] Next, the duty difference between regions that can stably reduce the ripple in the Rayleigh wave mode will be described. Fig. 12 is a graph showing the change in Rayleigh wave ripple when the difference in duty D between the regions of an elastic wave resonator is changed. Fig. 12 also shows the Rayleigh wave ripple of filter 10 when elastic wave resonator circuit 11 of filter 10 is replaced with one of the elastic wave resonators shown in Table 4. More specifically, Fig. 12 shows the relationship between the duty difference between the regions of an elastic wave resonator having an IDT electrode configured with region 1 having duty D1 and region 2 having duty D2, and the Rayleigh wave ripple (dB) of filter 10.

[0092] Table 4 shows the duty difference between the regions and the electrode parameters for each region.

[0093]

[0094] As shown in Fig. 12, when the duty difference between the regions is small, the frequencies of the Rayleigh wave modes generated by each region become closer, resulting in a smaller dispersion effect. On the other hand, as the duty difference between the regions increases, the Rayleigh wave ripple is reduced, and when the duty difference between the regions becomes 1.0% or more, the Rayleigh wave ripple improvement effect saturates. Therefore, to obtain a stable and large improvement effect on the Rayleigh wave ripple, it is desirable to set the duty difference between the regions to 1.0% or more.

[0095] In acoustic wave resonator circuit 11 according to this embodiment, the distance between the IDT electrode and the reflective electrode of series arm resonator 111 (hereinafter referred to as the I-R gap) is preferably different from the distance between adjacent electrode fingers of the IDT electrode (electrode finger pitch). Furthermore, the distance between adjacent electrode fingers of the reflective electrode (hereinafter referred to as the reflective electrode finger pitch) is preferably different from the electrode finger pitch of the IDT electrode. In this embodiment, longitudinal mode ripple can be reduced by, for example, making the I-R gap smaller than the electrode finger pitch of the IDT electrode and making the reflective electrode finger pitch smaller than the electrode finger pitch of the IDT electrode.

[0096] This can improve Rayleigh wave ripples and longitudinal mode ripples.

[0097] In this embodiment, the first acoustic wave resonator circuit (acoustic wave resonator circuit 11), which has a configuration in which multiple split resonators having multiple electrode finger regions with different duties are connected in series, is connected closest to the common terminal 100 among the multiple acoustic wave resonator circuits that make up the filter 10.

[0098] This effectively reduces the reflection loss at the frequency at which the spurious Rayleigh waves occur when the filter 10 is viewed from the common terminal 100. This makes it possible to suppress deterioration of the pass characteristics of the filter 20 connected to the common terminal 100 at the frequency at which the spurious Rayleigh waves occur.

[0099] The first acoustic wave resonant circuit does not have to be applied to the acoustic wave resonant circuit connected closest to the common terminal 100, but may be applied to at least one of the multiple acoustic wave resonant circuits that make up the filter 10. Even in this case, it is possible to provide a compact filter 10 with improved Rayleigh wave mode ripple without increasing the number of first acoustic wave resonant circuits divided in series.

[0100] 13A is a plan view showing the electrode configuration of an elastic wave resonator circuit 11A according to Example 2. The elastic wave resonator circuit 11A according to Example 2 has series arm resonators 111A and 112A connected in series. The elastic wave resonator circuit 11A according to Example 2 differs from the elastic wave resonator circuit 11 according to Example 1 in the number of series-connected elastic wave resonators and the duty configuration of each electrode finger region. The filter according to Example 2 differs from the filter 10 according to Example 1 only in that the elastic wave resonator circuit 11 is replaced with the elastic wave resonator circuit 11A. Table 5 shows electrode parameters of the elastic wave resonator circuit 11A according to Example 2.

[0101]

[0102] 13A and Table 5, the series arm resonator 111A has two electrode finger regions (region 1 and region 2), and the series arm resonator 112A has two electrode finger regions (region 3 and region 4). The duty D of region 1 is 0.48, the duty D of region 2 is 0.49, the duty D of region 3 is 0.51, and the duty D of region 4 is 0.52. In other words, the duties D of all the electrode finger regions that make up the acoustic wave resonator circuit 11A are different.

[0103] 13B is a plan view showing the electrode configuration of an elastic wave resonator circuit 11B according to the third embodiment. The elastic wave resonator circuit 11B according to the third embodiment has series arm resonators 111B and 112B connected in series. The elastic wave resonator circuit 11B according to the third embodiment differs from the elastic wave resonator circuit 11 according to the first embodiment in the number of series-connected elastic wave resonators and the duty configuration of each electrode finger region. The filter according to the third embodiment differs from the filter 10 according to the first embodiment only in that the elastic wave resonator circuit 11 is replaced with an elastic wave resonator circuit 11B. Table 6 shows electrode parameters of the elastic wave resonator circuit 11B according to the third embodiment.

[0104]

[0105] As shown in FIG. 13B and Table 6, the series arm resonator 111B has two electrode finger regions (region 1 and region 2), and the series arm resonator 112B has two electrode finger regions (region 3 and region 4). The duty D of region 1 is 0.50, the duty D of region 2 is 0.49, the duty D of region 3 is 0.51, and the duty D of region 4 is 0.50. The duty D of regions 1 and 2 constituting the series arm resonator 111B is different from each other, and the duty D of regions 3 and 4 constituting the series arm resonator 112B is different from each other. Furthermore, the duty D of region 1 and the duty D of region 4 are equal.

[0106] 13C is a plan view showing the electrode configuration of elastic wave resonator circuit 91A in accordance with Comparative Example 2. Elastic wave resonator circuit 91A in accordance with Comparative Example 2 has series arm resonators 911A and 912A connected in series. Elastic wave resonator circuit 91A in accordance with Comparative Example 2 differs from elastic wave resonator circuit 91 in accordance with Comparative Example 1 in the number of series-connected elastic wave resonators. Note that the filter in accordance with Comparative Example 2 differs from filter 500 in accordance with Comparative Example 1 only in that elastic wave resonator circuit 91 is replaced with elastic wave resonator circuit 91A. Table 7 shows electrode parameters of elastic wave resonator circuit 91A in accordance with Comparative Example 2.

[0107]

[0108] 13C and Table 7, the series arm resonator 911A has one electrode finger region (region 1), and the series arm resonator 912A has one electrode finger region (region 2). The duty cycle D of region 1 is 0.50, and the duty cycle D of region 2 is 0.50.

[0109] 14 is a graph showing Rayleigh wave ripples of the filters according to Example 2, Example 3, and Comparative Example 2. As shown in the figure, the filters according to Example 2 and Example 3 have reduced Rayleigh wave ripples compared to the filter according to Comparative Example 2.

[0110] This is because in the filters of Examples 2 and 3, the resonant frequencies and anti-resonant frequencies of the main mode generated in different electrode finger regions within one IDT electrode are matched, and the resonant frequencies and anti-resonant frequencies of the Rayleigh wave mode generated in the different electrode finger regions are dispersed.

[0111] Furthermore, the filter according to Example 2 has a reduced Rayleigh wave ripple compared to the filter according to Example 3. This is because the duty cycles D of all the electrode finger regions (regions 1 to 4) constituting elastic wave resonant circuit 11A according to Example 2 are made different, thereby maximizing the dispersion effect of the resonant frequency and antiresonant frequency of the Rayleigh wave mode generated in the four electrode finger regions.

[0112] 15 is a plan view showing the electrode configuration of an elastic wave resonator circuit 11C according to the fourth embodiment. The elastic wave resonator circuit 11C according to the fourth embodiment has series arm resonators 111C and 112C connected in series. The elastic wave resonator circuit 11C according to the fourth embodiment differs from the elastic wave resonator circuit 11 according to the first embodiment in the number of series-connected elastic wave resonators and the duty configuration of each electrode finger region. The filter according to the fourth embodiment differs from the filter 10 according to the first embodiment only in that the elastic wave resonator circuit 11 is replaced with the elastic wave resonator circuit 11C.

[0113] 15 , the series arm resonator 111C has three electrode finger regions (regions 1, 2, and 3), and the series arm resonator 112B has three electrode finger regions (regions 4, 5, and 6). The duty D of region 1 is 0.40, the duty D of region 2 is 0.42, and the duty D of region 3 is 0.44. The duty D of region 4 is 0.50, the duty D of region 5 is 0.48, and the duty D of region 6 is 0.46.

[0114] Here, the series arm resonator 111C is an example of a first acoustic wave resonator, and the series arm resonator 112C is an example of a second acoustic wave resonator. The IDT electrodes of the series arm resonators 111C and 112C are arranged adjacent to each other in a first direction (y-axis direction) that is the extension direction of the electrode fingers on the main surface of the piezoelectric substrate 50. Among regions 1 to 3 constituting the series arm resonator 111C, region 3 is the electrode finger region with the largest duty D, and region 4 is the electrode finger region with the largest duty D among regions 4 to 6 constituting the series arm resonator 112C. These regions do not overlap with each other in the extension direction (y-axis direction).

[0115] Generally, the greater the duty D, the greater the area occupied by the electrode fingers, and the greater the heat generation area ratio. As a result, the greater the duty D, the lower the power durability of the electrode finger region. In contrast, in elastic wave resonator circuit 11C according to this embodiment, in adjacent series arm resonators 111C and 112C, regions 3 and 4, which have the largest duty D, do not overlap in the extension direction (y-axis direction). This allows the heat generated by elastic wave resonator circuit 11C to be dispersed, thereby improving the power durability of elastic wave resonator circuit 11C.

[0116] The regions 1 to 3 constituting the series arm resonator 111C are arranged in descending order of duty in a second direction (negative x-axis direction) that is parallel to the main surface of the piezoelectric substrate 50 and perpendicular to the first direction (negative x-axis direction). On the other hand, the regions 4 to 6 constituting the series arm resonator 112C are arranged in descending order of duty in a third direction (positive x-axis direction) that is opposite to the second direction.

[0117] By reversing the direction of increase and decrease of the duty D of the electrode finger regions between adjacent series arm resonators 111C and 112C, heat generation in elastic wave resonator circuit 11C can be dispersed, improving the power durability of elastic wave resonator circuit 11C. Therefore, the filter according to this embodiment can reduce Rayleigh wave ripples and improve the power durability.

[0118] 8. Electrode Configuration of Elastic Wave Resonance Circuit According to Fifth Example FIG. 16 is a plan view showing the electrode configuration of an elastic wave resonator circuit 11D according to the fifth example. The elastic wave resonator circuit 11D according to the fifth example has series arm resonators 111D, 112D, 113D, 114D, and 115D connected in series. The elastic wave resonator circuit 11D according to the fifth example differs from the elastic wave resonator circuit 11 according to the first example in the number of series-connected elastic wave resonators and the shape of each IDT electrode. The filter according to the fifth example differs from the filter 10 according to the first example only in that the elastic wave resonator circuit 11 is replaced with the elastic wave resonator circuit 11D. Table 8 shows electrode parameters of the elastic wave resonator circuit 11D according to the fifth example.

[0119]

[0120] As shown in Table 8, each of the series arm resonators 111D to 115D has a plurality of electrode finger regions with different duties D, and the larger the duty D, the smaller the electrode finger pitch.

[0121] Furthermore, the aspect ratio, which is the ratio of the cross width (vertical dimension) of the IDT electrode to the number of electrode fingers multiplied by wavelength λ (horizontal dimension), differs for each series arm resonator. Note that the number of electrode fingers multiplied by wavelength λ corresponds to the length of the IDT electrode in the direction perpendicular to the electrode fingers (x-axis direction).

[0122] In an acoustic wave resonator having an IDT electrode formed on a piezoelectric substrate 50, in addition to Rayleigh wave ripples, transverse mode ripples can occur between the resonant frequency and antiresonant frequency of the main mode. The frequency and magnitude of the transverse mode ripples depend on the aspect ratio of the IDT electrode.

[0123] In contrast, in the elastic wave resonant circuit 11D according to this embodiment, the aspect ratios of the series arm resonators 111D to 115D connected in series are different, which makes it possible to disperse the transverse mode ripples, thereby providing a filter with reduced Rayleigh wave ripples and transverse mode ripples.

[0124] In this embodiment, all of the series arm resonators 111D to 115D have different aspect ratios, but it is sufficient that two of the series arm resonators 111D to 115D constituting the acoustic wave resonator circuit 11D have different aspect ratios. As a result, the filter according to this embodiment can reduce transverse mode ripples compared to a filter having a configuration in which the aspect ratios of the multiple series arm resonators constituting the acoustic wave resonator circuit are all the same.

[0125] 17 is a circuit diagram of a filter 10A according to a sixth embodiment. The filter 10A is an example of an acoustic wave device and is disposed in place of the filter 10 in the multiplexer 1 shown in FIG. The filter 10A is connected to a common terminal 100 and is, for example, a band-pass filter having a pass band.

[0126] The filter 10A includes a plurality of acoustic wave resonant circuits. Specifically, the filter 10A includes series arm resonators 141, 142, 143, 151, and 152, parallel arm resonators 161 and 162, and terminals 130 and 140. The terminal 130 is connected to a common terminal 100.

[0127] The series arm resonators 141, 142, and 143 are an example of a first acoustic wave resonant circuit and constitute an acoustic wave resonant circuit 14. The series arm resonators 151 and 152 constitute an acoustic wave resonant circuit 15. The parallel arm resonators 161 and 162 constitute an acoustic wave resonant circuit 16.

[0128] The series arm resonators 141, 142, and 143 are a plurality of elastic wave resonators connected in series between the terminal 130 and the terminal 140, and constitute a split resonator group. The series arm resonators 151 and 152 are a plurality of elastic wave resonators connected in series between the terminal 130 and the terminal 140, and constitute a split resonator group.

[0129] Parallel arm resonators 161 and 162 are a plurality of elastic wave resonators connected in series between the path connecting elastic wave resonator circuits 14 and 15 and the ground, and form a split resonator group.

[0130] Each of the series arm resonators 141 to 143, 151 and 152 and the parallel arm resonators 161 and 162 has an IDT electrode disposed on a piezoelectric substrate.

[0131] The circuit configuration of the filter 10A shown in FIG. 17 is an example of a band-pass filter, and the number of acoustic wave resonator circuits may be one or more in the series arm path and one or more in the parallel arm path.

[0132] Furthermore, the number of elastic wave resonators constituting the split resonator group is not limited to two or three, but may be four or more.

[0133] Furthermore, an inductor may be connected between at least one of the parallel arm resonators and ground.

[0134] Furthermore, the filter 10A is not limited to being a ladder-type filter, and may be, for example, a filter including a longitudinally coupled resonator in which a plurality of acoustic wave resonators are arranged in parallel in the acoustic wave propagation direction.

[0135] The IDT electrodes of the series arm resonators 141, 142, 143, 151 and 152 and the parallel arm resonators 161 and 162 are divided into a plurality of electrode finger regions with different duties D. In addition, the electrode finger pitch is made smaller as the duty D increases in the plurality of electrode finger regions.

[0136] This allows the resonant frequency and anti-resonant frequency of the main mode generated in different electrode finger regions within one IDT electrode to be matched, and the resonant frequency and anti-resonant frequency of the Rayleigh wave mode generated in the different electrode finger regions to be dispersed. Thus, by having a single split resonator with multiple electrode finger regions as described above, it is possible to suppress the ripple in the Rayleigh wave mode without degrading the resonance characteristics of the main mode. Therefore, it is possible to provide a compact filter 10A with improved ripple in the Rayleigh wave mode without increasing the number of series divisions of the acoustic wave resonant circuit.

[0137] Here, in each of the series arm resonators 141, 142, 143, 151 and 152 and the parallel arm resonators 161 and 162, the average duty cycle D ＡＶＥ Define the average duty D ＡＶＥ is the average duty D of a plurality of electrode finger regions constituting one elastic wave resonator. When one elastic wave resonator has m electrode finger regions (R1 to Rm), the number of electrode fingers in region k is n k and the duty of region k is D k, and the total number of electrode fingers in the one elastic wave resonator is N, the average duty D of the one elastic wave resonator is ＡＶＥ is expressed by Equation 1.

[0138]

[0139] In the filter 10A according to this embodiment, as shown in FIG. 17, the average duty D ＡＶＥ is 0.51, and the average duty D ＡＶＥ is 0.50, and the average duty D ＡＶＥ That is, the series arm resonator 141 connected closest to the common terminal 100 among the series arm resonators 141 to 143 included in the acoustic wave resonator circuit 14 has the lowest average duty cycle D ＡＶＥ is the largest.

[0140] It is generally known that in a filter composed of acoustic wave resonators, the closer the acoustic wave resonator is connected to the common terminal 100, the greater the impact on intermodulation distortion, and that the greater the duty, the more intermodulation distortion is suppressed.

[0141] According to the above-described configuration of the filter 10A of this embodiment, the series arm resonator 141 connected closest to the common terminal 100 among the series arm resonators 141 to 143 included in the acoustic wave resonator circuit 14 has an average duty cycle D ＡＶＥ is the largest, the intermodulation distortion generated by the filter 10A can be effectively suppressed.

[0142] The effect of suppressing intermodulation distortion is achieved when the acoustic wave resonator circuit 14 connected closest to the common terminal 100 has the average duty D ＡＶＥ For example, the elastic wave resonator circuit 15 may include a series arm resonator 151 (D ＡＶＥ = 0.51) and 152 (D ＡＶＥ =0.50), the series arm resonator 151 connected closest to the common terminal 100 has the lowest average duty D ＡＶＥ Even if the filter 10A has a configuration in which the D is the largest, the intermodulation distortion generated by the filter 10A can be effectively suppressed. ＡＶＥ = 0.51) and 162 (D ＡＶＥ =0.50), the parallel arm resonator 161 connected closest to the common terminal 100 has the lowest average duty D ＡＶＥ Even in the configuration where the filter 10A has the largest intermodulation distortion, the intermodulation distortion generated by the filter 10A can be effectively suppressed.

[0143] 10. Elastic Wave Resonance Circuit Having IDT Electrodes with Piston Structure Next, the electrode configuration of a first elastic wave resonance circuit having IDT electrodes with a piston structure will be described.

[0144] 18A is a plan view showing the electrode configuration of a series arm resonator 111E constituting an elastic wave resonator circuit 11E according to Example 7. The elastic wave resonator circuit 11E according to Example 7 includes series arm resonators 111E and 112E connected in series to each other. The elastic wave resonator circuit 11E according to Example 7 differs from the elastic wave resonator circuit 11A according to Example 2 in that the IDT electrodes of the series arm resonators 111E and 112E each have a so-called 2D piston structure. Hereinafter, the elastic wave resonator circuit 11E according to Example 7 will be described focusing on the different configurations, and a description of the same configurations as those of the elastic wave resonator circuit 11A according to Example 2 will be omitted.

[0145] 18A , the IDT electrode of the series arm resonator 111E includes a plurality of electrode fingers 61 a (first electrode fingers) and a plurality of electrode fingers 61 b ​​(second electrode fingers) arranged parallel to each other, a busbar electrode 62 a (first busbar electrode) configured to connect one ends of the plurality of electrode fingers 61 a to each other, and a busbar electrode 62 b (second busbar electrode) configured to connect one ends of the plurality of electrode fingers 61 b ​​to each other. The plurality of electrode fingers 61 a and the plurality of electrode fingers 61 b ​​are sandwiched between the busbar electrodes 62 a and 62 b arranged opposite each other.

[0146] Here, each of the multiple electrode fingers 61a has irregular portions 71a and 72a that are wider than the width of one end of the electrode finger 61a, and each of the multiple electrode fingers 61b has irregular portions 71b and 72b that are wider than the width of one end of the electrode finger 61b. The length of the irregular portion 71a in the extension direction (y-axis direction) in region 1 is different from the length of the irregular portion 72a in the extension direction (y-axis direction) in region 2. Furthermore, the length of the irregular portion 71b in the extension direction (y-axis direction) in region 1 is different from the length of the irregular portion 72b in the extension direction (y-axis direction) in region 2. Note that instead of or in addition to making the length of the irregular portion 71a in region 1 different from the length of the irregular portion 72a in region 2, the width of the irregular portion 71a in region 1 may be made different from the width of the irregular portion 72a in region 2. Furthermore, instead of or in addition to making the length of the irregular portion 71b in region 1 different from the length of the irregular portion 72b in region 2, the width of the irregular portion 71b in region 1 may be made different from the width of the irregular portion 72b in region 2.

[0147] It is generally known that when the IDT electrodes of an acoustic wave resonator have a 2D piston structure, ripples in the transverse mode can be suppressed.

[0148] According to the above-described configuration of this embodiment, the shapes of the irregular portions of the first and second regions constituting the series arm resonator 111E are different from each other, which makes it possible to disperse transverse mode ripples, thereby providing a filter with reduced Rayleigh wave ripples and transverse mode ripples.

[0149] The series arm resonator 112E may also have a structure of a variant portion similar to that of the series arm resonator 111E, which can further suppress transverse mode ripples occurring in the acoustic wave resonator circuit 11E.

[0150] Furthermore, it is sufficient that at least one of the plurality of electrode fingers 61a in region 1 has the irregular portion 71a, and it is sufficient that at least one of the plurality of electrode fingers 61a in region 2 has the irregular portion 72a. It is sufficient that at least one of the plurality of electrode fingers 61b in region 1 has the irregular portion 71b, and it is sufficient that at least one of the plurality of electrode fingers 61b in region 2 has the irregular portion 72b.

[0151] 18B is a plan view showing the electrode configuration of a series arm resonator 111F constituting an elastic wave resonator circuit 11F according to Example 8. The elastic wave resonator circuit 11F according to Example 8 includes series arm resonators 111F and 112F connected in series to each other. The elastic wave resonator circuit 11F according to Example 8 differs from the elastic wave resonator circuit 11A according to Example 2 in that the IDT electrodes of the series arm resonators 111F and 112F each have a so-called 3D piston structure. Hereinafter, a description of the same configuration as that of the elastic wave resonator circuit 11A according to Example 2 will be omitted, and the following description will focus on the different configuration.

[0152] 18B , the IDT electrode of the series arm resonator 111F includes a plurality of electrode fingers 61 a (first electrode fingers) and a plurality of electrode fingers 61 b ​​(second electrode fingers) arranged parallel to each other, a busbar electrode 62 a (first busbar electrode) configured to connect one ends of the plurality of electrode fingers 61 a to each other, and a busbar electrode 62 b (second busbar electrode) configured to connect one ends of the plurality of electrode fingers 61 b ​​to each other. The plurality of electrode fingers 61 a and the plurality of electrode fingers 61 b ​​are sandwiched between the busbar electrodes 62 a and 62 b arranged opposite each other.

[0153] Here, the IDT electrode of the series arm resonator 111F includes mass addition films 73a and 74a laminated on a portion of the extension direction of the plurality of electrode fingers 61a, and mass addition films 73b and 74b laminated on a portion of the extension direction of the plurality of electrode fingers 61b. The length of the mass addition film 73a in the extension direction (y-axis direction) in region 1 is different from the length of the mass addition film 74a in region 2 in the extension direction (y-axis direction). Furthermore, the length V1 of the mass addition film 73b in region 1 in the extension direction (y-axis direction) is different from the length V2 of the mass addition film 74b in region 2 in the extension direction (y-axis direction). Note that instead of or in addition to making the lengths of the mass addition films in region 1 and region 2 different, the thicknesses of the mass addition films in region 1 and region 2 may be made different.

[0154] According to the above-described configuration of this embodiment, the shapes of the mass-adding films in the regions 1 and 2 constituting the series arm resonator 111F are different from each other, which makes it possible to disperse transverse-mode ripples, thereby providing a filter with reduced Rayleigh-wave ripples and transverse-mode ripples.

[0155] The series arm resonator 112F may also have a mass-added film structure similar to that of the series arm resonator 111F, which can further suppress transverse mode ripples occurring in the acoustic wave resonator circuit 11F.

[0156] 18C is a plan view showing the electrode configuration of a series arm resonator 111G constituting an elastic wave resonator circuit 11G according to Example 9. The elastic wave resonator circuit 11G according to Example 9 has series arm resonators 111G and 112G connected in series to each other. The elastic wave resonator circuit 11G according to Example 9 is different from the elastic wave resonator circuit 11F according to Example 8 in the shape of the mass addition films formed on the series arm resonators 111G and 112G. Hereinafter, a description of the same configuration as that of the elastic wave resonator circuit 11F according to Example 8 will be omitted, and the following description will focus on the different configuration.

[0157] 18C , the IDT electrode of the series arm resonator 111G includes mass addition films 75a and 76a laminated along a portion of the extension direction of the electrode fingers 61a, and mass addition films 75b and 76b laminated along a portion of the extension direction of the electrode fingers 61b. The length, film thickness, and material of the mass addition film 75a in the extension direction (y-axis direction) in region 1 are the same as the length, film thickness, and material of the mass addition film 76a in region 2. Furthermore, the length V3, film thickness, and material of the mass addition film 75b in region 1 are the same as the length V4, film thickness, and material of the mass addition film 76b in region 2.

[0158] According to the above-described configuration of this embodiment, the mass addition films of the first and second regions of the series arm resonator 111G have the same shape and are made of the same material, which improves the accuracy of the lift-off process used to form the mass addition films and simplifies the manufacturing process. As a result, a filter can be provided in which Rayleigh wave ripples and transverse mode ripples are reduced and the manufacturing process is simplified.

[0159] The series arm resonator 112G may also have a mass-added film structure similar to that of the series arm resonator 111G, which can further suppress transverse mode ripples occurring in the acoustic wave resonator circuit 11G.

[0160] [11. Acoustic Wave Resonator Having Reflecting Electrodes with Different Duties] In the first acoustic wave resonator circuits according to Examples 1 to 9, at least one of the multiple acoustic wave resonators connected in series may have multiple reflecting electrodes with different reflecting electrode finger pitches and duties.

[0161] 19A is a plan view illustrating an electrode configuration of an elastic wave resonator constituting a first elastic wave resonator circuit according to Modification 1. The first elastic wave resonator circuit according to Modification 1 includes a plurality of series arm resonators connected in series, and at least one of the plurality of series arm resonators may include the series arm resonator 111H illustrated in FIG. 19A . The series arm resonator 111H includes an IDT electrode having three electrode finger regions (regions 1, 2, and 3) and a reflective electrode having two reflective electrode finger regions (regions R1 and R2). The reflective electrode is disposed at an end of the IDT electrode in the x-axis direction. For example, the duty cycle D1 of Region 1 is 0.45 (wavelength λ1 is 2.0635 μm), the duty cycle D2 of Region 2 is 0.50 (wavelength λ2 is 2.0580 μm), and the duty cycle D3 of Region 3 is 0.55 (wavelength λ3 is 2.0545 μm). The duty cycle Dr1 of the region R1 is 0.40 (the wavelength λr1 is 2.0708 μm), and the duty cycle Dr2 of the region R2 is 0.60 (the wavelength λr2 is 2.0528 μm). That is, in the series arm resonator 111H, when comparing the electrode finger regions of the IDT electrode, the larger the duty cycle D, the smaller the electrode finger pitch P, which is the distance between adjacent electrode fingers. In addition, the regions R1 and R2 of the reflective electrode have different duties Dr and different reflective electrode finger pitches Pr. This makes it possible to provide an acoustic wave device with reduced Rayleigh wave ripple. In the series arm resonator 111H, the IDT electrode may have two or more electrode finger regions, and the reflective electrode finger regions may have two or more electrode finger regions.

[0162] 19B is a plan view illustrating an electrode configuration of an elastic wave resonator constituting a first elastic wave resonator circuit according to Modification 2. The first elastic wave resonator circuit according to Modification 2 includes a plurality of series arm resonators connected in series, and at least one of the plurality of series arm resonators may include the series arm resonator 111J illustrated in FIG. 19B. The series arm resonator 111J includes an IDT electrode having three electrode finger regions (regions 1, 2, and 3) and a reflective electrode having four reflective electrode finger regions (regions R1, R2, R3, and R4). The reflective electrode is disposed at an end of the IDT electrode in the x-axis direction. For example, the duties D1 to D3 of the regions 1 to 3 are the same as the duties D1 to D3 of the regions 1 to 3 of the series arm resonator 111H. The duty cycle Dr1 of region R1 is 0.35 (wavelength λr1 is 2.0801 μm), the duty cycle Dr2 of region R2 is 0.40 (wavelength λr2 is 2.0708 μm), the duty cycle Dr3 of region R3 is 0.60 (wavelength λr2 is 2.0528 μm), and the duty cycle Dr4 of region R4 is 0.65 (wavelength λr2 is 2.0530 μm). That is, in the series arm resonator 111J, when comparing the electrode finger regions of the IDT electrode, the larger the duty cycle D, the smaller the electrode finger pitch P, which is the distance between adjacent electrode fingers. Furthermore, in the reflective electrode, the duty cycle Dr and the reflective electrode finger pitch Pr differ among the four reflective electrode finger regions R1 to R4. This makes it possible to provide an acoustic wave device with reduced Rayleigh wave ripple. In the series arm resonator 111J, the IDT electrode may have two or more electrode finger regions, and the reflective electrode finger regions may have two or more electrode finger regions.

[0163] [12. Effects, etc.] As described above, filter 10 according to the present embodiment includes a plurality of elastic wave resonant circuits. Elastic wave resonant circuit 11 among the plurality of elastic wave resonant circuits is composed of series arm resonators 111 to 113 connected in series to each other. Each of series arm resonators 111 to 113 is disposed on piezoelectric substrate 50 and has an IDT electrode having a plurality of electrode fingers that are parallel to each other. When an electrode finger region is defined as a region in which two or more electrode fingers having the same duty are continuously arranged, the IDT electrode of each of series arm resonators 111 to 113 is divided into a plurality of electrode finger regions with different duties D. When the plurality of electrode finger regions are compared, the electrode finger pitch, which is the distance between adjacent electrode fingers, becomes smaller as the duty D increases.

[0164] This allows the resonance frequency and anti-resonance frequency of the main mode generated in different electrode finger regions within one IDT electrode to be matched, and the resonance frequency and anti-resonance frequency of the Rayleigh wave mode generated in the different electrode finger regions to be dispersed. This makes it possible to suppress the Rayleigh wave mode ripple without degrading the main mode resonance characteristics using a single split (series arm) resonator. Therefore, it is possible to provide a compact filter 10 with improved Rayleigh wave mode ripple without increasing the number of series splits in elastic wave resonator circuit 11.

[0165] Furthermore, for example, in the filter 10, the number of electrode fingers included in each of the plurality of electrode finger regions is 10% or more of the number of electrode fingers of the IDT electrode.

[0166] This makes it possible to reduce Rayleigh wave ripples compared to when the IDT electrode is configured with only one electrode finger region (duty change region ratio=0%).

[0167] Furthermore, for example, in the filter according to the second embodiment, the duties of all the electrode finger regions constituting the acoustic wave resonator circuit 11A are different.

[0168] This maximizes the dispersion effect of the resonant frequency and anti-resonant frequency of the Rayleigh wave mode generated in all electrode finger regions that make up elastic wave resonant circuit 11A, thereby making it possible to reduce Rayleigh wave ripples to the greatest extent.

[0169] Furthermore, for example, in the filter according to the fourth embodiment, the acoustic wave resonator circuit 11C includes series arm resonators 111C and 112C, and the IDT electrode of the series arm resonator 111C and the IDT electrode of the series arm resonator 112C are arranged adjacent to each other on the main surface of the piezoelectric substrate 50 in a first direction, which is the extension direction of the electrode fingers. Among regions 1 to 3 of the series arm resonator 111C, region 3 having the maximum duty cycle D does not overlap with region 4 of regions 4 to 6 of the series arm resonator 112C having the maximum duty cycle D in the extension direction.

[0170] This allows heat generation in elastic wave resonant circuit 11C to be dispersed, and improves the power durability of elastic wave resonant circuit 11C.

[0171] Furthermore, for example, in the filter according to the fourth embodiment, the multiple regions 1 to 3 of the series arm resonator 111C are arranged in a second direction parallel to the principal surface and perpendicular to the first direction in order of increasing duty D, and the multiple regions 4 to 6 of the series arm resonator 112C are arranged in a third direction opposite to the second direction in order of decreasing duty D.

[0172] By reversing the direction of increase and decrease of the duty D of the electrode finger regions between adjacent series arm resonators 111C and 112C, heat generated by elastic wave resonator circuit 11C can be dispersed, improving the power durability of elastic wave resonator circuit 11C.

[0173] Furthermore, for example, in the filter according to the fifth embodiment, the acoustic wave resonator circuit 11D includes series arm resonators 111D and 112D, and the ratio between the overlap width V of the IDT electrode of the series arm resonator 111D and the length of the IDT electrode in the direction perpendicular to the electrode fingers is different from the ratio between the overlap width V of the IDT electrode of the series arm resonator 112D and the length of the IDT electrode in the direction perpendicular to the electrode fingers.

[0174] In this configuration, the aspect ratios of the series arm resonators 111D and 112D connected in series are made different, which makes it possible to disperse transverse mode ripples, thereby providing a filter with reduced Rayleigh wave ripples and transverse mode ripples.

[0175] Furthermore, for example, in the filter according to the seventh embodiment, the IDT electrode of the series arm resonator 111E includes a plurality of electrode fingers 61a and a plurality of electrode fingers 61b arranged parallel to each other, a bus bar electrode 62a configured to connect one ends of the plurality of electrode fingers 61a to each other, and a bus bar electrode 62b configured to connect one ends of the plurality of electrode fingers 61b to each other and arranged opposite to the bus bar electrode 62a with the plurality of electrode fingers 61a and 61b interposed therebetween. The electrode finger 61a has irregular portions 71a and 72a having a width wider than the width of the electrode finger 61a at one end thereof, the plurality of electrode fingers 61b have irregular portions 71b and 72b having a width wider than the width of the electrode finger 61b at one end thereof, and at least one of the width and length of the irregular portion 71a in region 1 and the irregular portion 72a in region 2 differs between the regions, and at least one of the width and length of the irregular portion 71b in region 1 and the irregular portion 72b in region 2 differs between the regions.

[0176] In this way, the shapes of the irregular portions of the first and second regions constituting the series arm resonator 111E are made different, which makes it possible to disperse transverse mode ripples, thereby providing a filter with reduced Rayleigh wave ripples and transverse mode ripples.

[0177] Furthermore, for example, in the filter according to Example 8, the IDT electrode of the series arm resonator 111F further includes mass-adding films 73a and 74a laminated on a portion of the extension direction of the plurality of electrode fingers 61a, and mass-adding films 73b and 74b laminated on a portion of the extension direction of the plurality of electrode fingers 61b, and at least one of the length and film thickness in the extension direction of the mass-adding film 73a in region 1 and the mass-adding film 74a in region 2 differs between the regions, and at least one of the length and film thickness in the extension direction of the mass-adding film 73b in region 1 and the mass-adding film 74b in region 2 differs between the regions.

[0178] In this way, the shapes of the mass-adding films in the regions 1 and 2 constituting the series arm resonator 111F are made different, which makes it possible to disperse transverse mode ripples, thereby providing a filter with reduced Rayleigh wave ripples and transverse mode ripples.

[0179] For example, in the filter according to Example 9, the IDT electrode of the series arm resonator 111G further includes mass-adding films 75a and 76a laminated on a portion of the electrode fingers 61a in the extension direction, and mass-adding films 75b and 76b laminated on a portion of the electrode fingers 61b in the extension direction, and the lengths and thicknesses in the extension direction of the mass-adding film 75a in region 1 and the mass-adding film 76a in region 2 are the same between the regions, and the lengths and thicknesses in the extension direction of the mass-adding film 73b in region 1 and the mass-adding film 74b in region 2 are the same between the regions.

[0180] In this way, the mass addition films of the first and second regions constituting the series arm resonator 111G have the same shape, which improves the accuracy of the lift-off process used to form the mass addition films and simplifies the manufacturing process, thereby providing a filter with reduced Rayleigh wave ripples and transverse mode ripples and a simplified manufacturing process.

[0181] For example, the multiplexer 1 according to this embodiment includes a common terminal 100, a filter 10 connected to the common terminal 100 or a filter according to Examples 2 to 9, and a filter 20 connected to the common terminal 100.

[0182] This makes it possible to provide a multiplexer 1 in which the Rayleigh wave response generated in the filter 10 or the filters according to the second to ninth embodiments is suppressed.

[0183] Furthermore, for example, in multiplexer 1, acoustic wave resonator circuit 11 is connected closest to common terminal 100 among the plurality of acoustic wave resonator circuits that make up the filter.

[0184] This effectively reduces the reflection loss at the frequency at which the spurious Rayleigh waves occur when the filter 10 or any of the filters according to Examples 2 to 9 is viewed from the common terminal 100. This makes it possible to suppress deterioration of the pass characteristics of the filter 20 connected to the common terminal 100 at the frequency at which the spurious Rayleigh waves occur.

[0185] Furthermore, for example, in the multiplexer 1, among the series arm resonators 141 to 143 included in the acoustic wave resonator circuit 14 constituting the filter 10A, the series arm resonator 141 connected closest to the common terminal 100 has the lowest average duty cycle D ＡＶＥ is the largest.

[0186] This makes it possible to effectively suppress the intermodulation distortion generated by the filter 10A.

[0187] Also, for example, in the multiplexer 1, the filter 10 is a band-elimination filter having a stop band.

[0188] This can suppress Rayleigh wave ripples in the passband of the filter 10. Furthermore, it can prevent signals in the Rayleigh wave mode generated in the filter 10 from sneaking into the filter 20 via the common terminal 100, thereby suppressing deterioration of the attenuation characteristics of the filter 20.

[0189] Also, for example, in the multiplexer 1, the filter 10 is a band-pass filter having a pass band.

[0190] This can suppress Rayleigh wave ripples that occur on the low-frequency side of the pass band of the filter 10. Furthermore, it can prevent Rayleigh wave mode signals that occur in the filter 10 from sneaking into the filter 20 via the common terminal 100, thereby suppressing deterioration of the pass characteristics or attenuation characteristics of the filter 20.

[0191] While the present invention has been described above with reference to exemplary embodiments and examples of the elastic wave device and multiplexer, the present invention is not limited to the exemplary embodiments and examples. The present invention also includes various modifications that can be made to the exemplary embodiments and examples without departing from the spirit of the present invention, as well as various devices incorporating the elastic wave device and multiplexer of the present invention.

[0192] For example, while the above-described embodiments have been described focusing on examples in which the first acoustic wave resonant circuit is configured with a plurality of series arm resonators connected in series, in the acoustic wave device and multiplexer according to the present invention, it is sufficient that the first acoustic wave resonant circuit is configured with a plurality of series arm resonators, or the first acoustic wave resonant circuit may be configured with a plurality of parallel arm resonators connected in series. Even in this case, an acoustic wave device and multiplexer in which Rayleigh wave ripple is suppressed can be provided.

[0193] Furthermore, for example, in the acoustic wave devices and multiplexers according to the above-described embodiments and examples, matching elements such as inductors and capacitors, and switch circuits may be connected between the components.

[0194] The resonant frequency and anti-resonant frequency shown in the above-described embodiments and examples are derived, for example, by bringing an RF probe into contact with two input and output electrodes of an acoustic wave resonator and measuring the reflection characteristics.

[0195] The features of the acoustic wave devices and multiplexers described based on the above embodiments and examples will be described below.

[0196] <1> An elastic wave device comprising a plurality of elastic wave resonant circuits, wherein a first elastic wave resonant circuit of the plurality of elastic wave resonant circuits is composed of a plurality of elastic wave resonators connected in series with each other, wherein each of the plurality of elastic wave resonators is disposed on a piezoelectric substrate and has an IDT (InterDigital Transducer) electrode having a plurality of electrode fingers parallel to each other, wherein the IDT electrode of each of the plurality of elastic wave resonators is divided into a plurality of electrode finger regions with different duties, where an electrode finger region is defined as a region in which two or more electrode fingers with the same duty are continuously arranged, and when the plurality of electrode finger regions are compared, the electrode finger pitch, which is the distance between adjacent electrode fingers, becomes smaller as the duty increases.

[0197] <2> The acoustic wave device according to <1>, wherein the number of electrode fingers included in each of the plurality of electrode finger regions is 10% or more of the number of electrode fingers included in the IDT electrode.

[0198] <3> The acoustic wave device according to <1> or <2>, wherein all of the electrode finger regions constituting the first acoustic wave resonator circuit have different duties.

[0199] <4> The elastic wave device according to any one of <1> to <3>, wherein the plurality of elastic wave resonators constituting the first elastic wave resonator circuit include a first elastic wave resonator and a second elastic wave resonator, the IDT electrode of the first elastic wave resonator and the IDT electrode of the second elastic wave resonator are arranged adjacent to each other on the main surface of the substrate in a first direction that is an extension direction of electrode fingers, and an electrode finger region having a maximum duty among the plurality of electrode finger regions of the first elastic wave resonator and an electrode finger region having a maximum duty among the plurality of electrode finger regions of the second elastic wave resonator do not overlap in the extension direction.

[0200] <5> The elastic wave device according to <4>, wherein the plurality of electrode finger regions of the first elastic wave resonator are arranged in a second direction parallel to the principal surface and perpendicular to the first direction in descending order of duty, and the plurality of electrode finger regions of the second elastic wave resonator are arranged in a third direction opposite to the second direction in descending order of duty.

[0201] <6> The elastic wave device according to any one of <1> to <3>, wherein the plurality of elastic wave resonators constituting the first elastic wave resonator include a first elastic wave resonator and a second elastic wave resonator, and a ratio of an overlap width of an IDT electrode of the first elastic wave resonator to a length of the IDT electrode in a direction perpendicular to the electrode fingers is different from a ratio of an overlap width of an IDT electrode of the second elastic wave resonator to a length of the IDT electrode in a direction perpendicular to the electrode fingers.

[0202] <7> The elastic wave device according to any one of <1> to <6>, wherein the IDT electrode includes: a plurality of first electrode fingers and a plurality of second electrode fingers arranged in parallel to each other; a first bus bar electrode configured to connect one ends of the plurality of first electrode fingers together; and a second bus bar electrode configured to connect one ends of the plurality of second electrode fingers together and arranged to face the first bus bar electrode across the plurality of first electrode fingers and the plurality of second electrode fingers; at least one of the plurality of first electrode fingers and the plurality of second electrode fingers has an irregular-shaped portion having a width greater than a width of the first electrode finger at one end of the plurality of first electrode fingers and a width of the second electrode finger at one end of the plurality of second electrode fingers; and at least one of the width and length of the irregular-shaped portion differs among the plurality of electrode finger regions.

[0203] <8> The acoustic wave device according to any one of <1> to <6>, wherein the IDT electrode further includes a mass-adding film laminated on a portion of the electrode fingers in an extension direction, and at least one of a length in the extension direction and a thickness of the mass-adding film differs among the electrode finger regions.

[0204] <9> The acoustic wave device according to any one of <1> to <6>, wherein the IDT electrode further includes a mass-adding film laminated on a portion of the electrode fingers in an extension direction, and the length and film thickness of the mass-adding film in the extension direction are the same across the electrode finger regions.

[0205] <10> A multiplexer comprising: a common terminal; the acoustic wave device according to any one of <1> to <9> connected to the common terminal; and a filter connected to the common terminal.

[0206] <11> The multiplexer according to <10>, wherein the first acoustic wave resonant circuit is connected closest to the common terminal among the plurality of acoustic wave resonant circuits.

[0207] <12> The multiplexer according to <10> or <11>, wherein, among the plurality of elastic wave resonators included in the first elastic wave resonator circuit, an elastic wave resonator connected closest to the common terminal has the largest average duty cycle among the plurality of elastic wave resonators.

[0208] <13> The multiplexer according to any one of <10> to <12>, wherein the acoustic wave device is a band-elimination filter having a stopband.

[0209] <14> The multiplexer according to any one of <10> to <12>, wherein the acoustic wave device is a band-pass filter having a passband.

[0210] The present invention can be widely used as a transmit / receive filter and a multiplexer used in the front end of a wireless communication terminal where low loss within the passband and high attenuation outside the passband are required.

[0211] REFERENCE SIGNS LIST 1 multiplexer 2 antenna 10, 10A, 20, 500 filter 11, 11A, 11B, 11C, 11D, 11E, 11F, 11G, 14, 15, 16, 91, 91A acoustic wave resonator circuit 12, 13, 161, 162 parallel arm resonator 50 piezoelectric substrate 51 high acoustic velocity support substrate 52 low acoustic velocity film 53 piezoelectric film 54 IDT electrode 55, 58 protective layer 57 piezoelectric single crystal substrate 60 acoustic wave resonator 60a, 60b comb-shaped electrodes 61a, 61b electrode fingers 62a, 62b busbar electrodes 71a, 71b, 72a, 72b irregular-shaped portions 73a, 73b, 74a, 74b, 75a, 75b, 76a, 76b Mass-adding film 100 common terminal 110, 120 input / output terminal 111, 111A, 111B, 111C, 111D, 111E, 111F, 111G, 112, 112A, 112B, 112C, 112D, 112E, 112F, 112G, 113, 113D, 114D, 115D, 141, 142, 143, 151, 152, 911, 911A, 912, 912A, 913 series arm resonator 130, 140 terminal 540 adhesion layer 542 main electrode layer

Claims

1. An elastic wave device comprising a plurality of elastic wave resonant circuits, wherein a first elastic wave resonant circuit of the plurality of elastic wave resonant circuits is composed of a plurality of elastic wave resonators connected in series with each other, each of the plurality of elastic wave resonators is arranged on a piezoelectric substrate and has an IDT (Inter Digital Transducer) electrode having a plurality of electrode fingers parallel to each other, the IDT electrode of each of the plurality of elastic wave resonators is divided into a plurality of electrode finger regions with different duties when an electrode finger region is defined as a region in which two or more electrode fingers with the same duty are continuously arranged, and when comparing the plurality of electrode finger regions, the electrode finger pitch, which is the distance between adjacent electrode fingers, is smaller as the duty is larger.

2. The acoustic wave device according to claim 1, wherein the number of electrode fingers included in each of the plurality of electrode finger regions is 10% or more of the number of electrode fingers in the IDT electrode.

3. The acoustic wave device according to claim 1 or 2, wherein all of the electrode finger regions constituting the first acoustic wave resonant circuit have different duties.

4. The elastic wave device according to any one of claims 1 to 3, wherein the multiple elastic wave resonators constituting the first elastic wave resonator include a first elastic wave resonator and a second elastic wave resonator, the IDT electrode of the first elastic wave resonator and the IDT electrode of the second elastic wave resonator are arranged adjacent to each other in a first direction that is an extension direction of electrode fingers on the main surface of the substrate, and an electrode finger region having a maximum duty among the multiple electrode finger regions of the first elastic wave resonator and an electrode finger region having a maximum duty among the multiple electrode finger regions of the second elastic wave resonator do not overlap in the extension direction.

5. The elastic wave device of claim 4, wherein the multiple electrode finger regions of the first elastic wave resonator are arranged in a second direction parallel to the main surface and perpendicular to the first direction in order of decreasing duty, and the multiple electrode finger regions of the second elastic wave resonator are arranged in a third direction opposite to the second direction in order of decreasing duty.

6. The elastic wave device according to any one of claims 1 to 3, wherein the multiple elastic wave resonators constituting the first elastic wave resonator include a first elastic wave resonator and a second elastic wave resonator, and a ratio of an overlap width of an IDT electrode of the first elastic wave resonator to a length of the IDT electrode in a direction perpendicular to the electrode fingers is different from a ratio of an overlap width of an IDT electrode of the second elastic wave resonator to a length of the IDT electrode in a direction perpendicular to the electrode fingers.

7. The elastic wave device according to any one of claims 1 to 6, wherein the IDT electrode comprises: a plurality of first electrode fingers and a plurality of second electrode fingers arranged in parallel to each other; a first bus bar electrode configured to connect one ends of the plurality of first electrode fingers to each other; and a second bus bar electrode configured to connect one ends of the plurality of second electrode fingers to each other and arranged opposite the first bus bar electrode across the plurality of first electrode fingers and the plurality of second electrode fingers, wherein at least one of the plurality of first electrode fingers and the plurality of second electrode fingers has an irregular portion having a width wider than the width of the first electrode finger at one end of the plurality of first electrode fingers and the width of the second electrode finger at one end of the plurality of second electrode fingers, and at least one of the width and length of the irregular portion differs among the plurality of electrode finger regions.

8. An elastic wave device according to any one of claims 1 to 6, wherein the IDT electrode further has a mass-adding film laminated in a portion of the extension direction of the plurality of electrode fingers, and at least one of the length in the extension direction and the film thickness of the mass-adding film differs among the plurality of electrode finger regions.

9. An elastic wave device according to any one of claims 1 to 6, wherein the IDT electrode further has a mass-adding film laminated in a portion of the extension direction of the plurality of electrode fingers, and the length and film thickness of the mass-adding film in the extension direction are the same among the plurality of electrode finger regions.

10. A multiplexer comprising: a common terminal; an elastic wave device according to any one of claims 1 to 3 connected to the common terminal; and a filter connected to the common terminal.

11. The multiplexer according to claim 10, wherein the first acoustic wave resonant circuit is connected closest to the common terminal among the plurality of acoustic wave resonant circuits.

12. A multiplexer as described in claim 10 or 11, wherein among the plurality of elastic wave resonators in the first elastic wave resonator circuit, the elastic wave resonator connected closest to the common terminal has the largest average duty cycle among the plurality of elastic wave resonators.

13. The multiplexer according to any one of claims 10 to 12, wherein the acoustic wave device is a band-elimination filter having a stopband.

14. The multiplexer according to any one of claims 10 to 12, wherein the acoustic wave device is a band-pass filter having a passband.

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