Multiplexer

Abstract

To provide a multiplexer in which an insertion loss in a passband of a filter to be connected in common is reduced.SOLUTION: A multiplexer 1 comprises: a filter 10 having a first passband; and a filter 20 that includes a second passband on the side of a frequency that is higher than that of the first passband. The filter 10 includes series arm resonators s11 to s14 and parallel arm resonators p11 to p14. At least one resonance base band width of the series arm resonators s11 to s14 is larger than the first passband, and the series arm resonator s11 is most close to a common terminal 100 of the series arm resonators s11 to s14 and the parallel arm resonators p11 to p14, and an antiresonance frequency fas11 of the series arm resonator s11 is lower than a high frequency end of the second passband, and is lowest of antiresonance frequencies fas11 to fas14 of the series arm resonators s11 to s14.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a multiplexer including an acoustic wave filter. [Background technology]

[0002] Patent Document 1 discloses a multiplexer in which a first filter and a second filter each including an acoustic wave resonator are connected to a common terminal. Specifically, the multiplexer is formed using an acoustic wave resonator having a wide resonance bandwidth (e.g., 45 MHz) relative to the bandwidth of the two filters (e.g., 35 MHz+α) and the gap between the passbands of the two filters (e.g., 10 MHz or less). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 188007 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the first filter is configured using an acoustic wave resonator having a wide resonance bandwidth relative to the passband bandwidth and the passband gap, the impedance in the passband of the second filter is influenced by the impedance of the acoustic wave resonator and is likely to deviate from the reference impedance, which may result in large insertion loss of the multiplexer.

[0005] SUMMARY OF THE PRESENT DISCLOSURE The present invention has been made to solve the above-mentioned problems, and has an object to provide a multiplexer in which the insertion loss in the passband of commonly connected filters is reduced. [Means for solving the problem]

[0006] In order to achieve the above object, a multiplexer according to one embodiment of the present invention includes a first filter having a first passband and a second filter having a second passband on the higher frequency side than the first passband, the first filter and the second filter being connected to a common terminal, the first filter having two or more series arm resonators, each including an acoustic wave resonator, arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators, each including an acoustic wave resonator, connected between the series arm path and ground, at least one of the two or more series arm resonators of the first filter has a resonance bandwidth greater than the first passband, and a first series arm resonator of the two or more series arm resonators of the first filter is connected closest to the common terminal among the two or more series arm resonators and the one or more parallel arm resonators of the first filter, and an anti-resonance frequency of the first series arm resonator is lower than the high frequency end of the second passband and is the lowest anti-resonance frequency located on the higher frequency side than the first passband among the anti-resonance frequencies of the two or more series arm resonators of the first filter.

[0007] Furthermore, a multiplexer according to one embodiment of the present invention includes a first filter having a first passband and a second filter having a second passband on the higher frequency side than the first passband, the first filter and the second filter being connected to a common terminal, the second filter having two or more series arm resonators, each including an acoustic wave resonator, arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators, each including an acoustic wave resonator, connected between the series arm path and ground, the second filter having a resonant bandwidth greater than the second passband, a second series arm resonator of the two or more series arm resonators of the second filter being connected closest to the common terminal among the two or more series arm resonators and the one or more parallel arm resonators of the second filter, and a resonant frequency of the second series arm resonator is higher than the high frequency end of the first passband and is the highest resonant frequency located on the higher frequency side than the first passband among the resonant frequencies of the two or more series arm resonators of the second filter.

[0008] According to another aspect of the present invention, a multiplexer includes a first filter having a first passband and a second filter having a second passband on the higher frequency side than the first passband, the first filter and the second filter being connected to a common terminal. The first filter includes two or more series arm resonators, each including an elastic wave resonator, arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators, each including an elastic wave resonator, connected between the series arm path and a ground. The second filter includes two or more series arm resonators, each including an elastic wave resonator, arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators, each including an elastic wave resonator, connected between the series arm path and a ground. Each of the elastic wave resonators constituting the first filter and the second filter is an IDT (InterDigital Transistor). the first filter has an IDT electrode, an electrode finger pitch of an IDT electrode constituting at least one of the two or more series arm resonators of the first filter is smaller than an electrode finger pitch of an IDT electrode constituting at least one of the one or more parallel arm resonators of the second filter, a first series arm resonator of the two or more series arm resonators of the first filter is connected closest to a common terminal among the two or more series arm resonators and the one or more parallel arm resonators of the first filter, and an anti-resonance frequency of the first series arm resonator is lower than the high frequency end of the second passband and is the lowest among the anti-resonance frequencies of the two or more series arm resonators of the first filter that are located on the higher frequency side of the first passband.

[0009] A multiplexer according to one aspect of the present invention includes a first filter having a first passband and a second filter having a second passband on the higher frequency side than the first passband, the first filter and the second filter being connected to a common terminal, the first filter having two or more series arm resonators including an elastic wave resonator and arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators including an elastic wave resonator and connected between the series arm path and ground, and the second filter having two or more series arm resonators including an elastic wave resonator and arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators including an elastic wave resonator and connected between the series arm path and ground. The acoustic wave resonators constituting the first filter and the second filter each have an IDT electrode, and the IDT electrode constituting at least one of the two or more series arm resonators of the first filter has a smaller electrode finger pitch than the IDT electrode constituting at least one of the one or more parallel arm resonators of the second filter, and a second series arm resonator of the two or more series arm resonators of the second filter is connected closest to the common terminal among the two or more series arm resonators and the one or more parallel arm resonators of the second filter, and the IDT electrode constituting the second series arm resonator has the smallest electrode finger pitch among the IDT electrodes constituting the two or more series arm resonators of the second filter. Effect of the Invention

[0010] According to the present invention, it is possible to provide a multiplexer in which the insertion loss in the passband of commonly connected filters is reduced. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a circuit configuration diagram of a multiplexer according to an embodiment. [Figure 2A] 1A and 1B are a plan view and a cross-sectional view illustrating a first example of an acoustic wave resonator that constitutes a multiplexer according to an embodiment of the present invention. [Figure 2B] 10 is a cross-sectional view illustrating a schematic diagram of a second example of an acoustic wave resonator that constitutes a multiplexer according to an embodiment. FIG. [Figure 2C]FIG. 11 is a cross-sectional view illustrating a schematic diagram of a third example of an acoustic wave resonator that constitutes a multiplexer according to an embodiment. [Diagram 3] 5 is a graph showing the pass characteristic of a multiplexer and the impedance characteristic of a series arm resonator of a first filter according to the embodiment. [Figure 4A] 6 is a graph showing pass characteristics of a second filter in multiplexers according to the embodiment and the comparative example. [Figure 4B] 11 is an immittance chart showing the impedance of a second passband when multiplexers according to an embodiment and a comparative example are viewed from a common terminal. [Diagram 5] 6 is a graph showing impedance characteristics and susceptance characteristics of first series arm resonators according to an embodiment and a comparative example. [Figure 6A] FIG. 2 is a schematic plan view showing the configuration of an IDT electrode including a floating withdrawal electrode. [Figure 6B] FIG. 2 is a schematic plan view showing a configuration of an IDT electrode including polarity-inverting withdrawal electrodes. [Figure 6C] FIG. 11 is a schematic plan view showing the configuration of an IDT electrode including a fill-in thinning-out electrode. [Figure 7] 6 is a graph showing the pass characteristic of a multiplexer and the impedance characteristic of a series arm resonator of a second filter according to the embodiment. [Figure 8A] 6 is a graph showing pass characteristics of a first filter in multiplexers according to an embodiment and a comparative example. [Figure 8B] 11 is an immittance chart showing impedance of a first passband when multiplexers according to an embodiment and a comparative example are viewed from a common terminal. [Figure 9] 6 is a graph showing impedance characteristics and susceptance characteristics of second series arm resonators according to an embodiment and a comparative example. [Figure 10] 6 is a graph showing the pass characteristic of a multiplexer and the impedance characteristic of a parallel arm resonator of a second filter according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the 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. Among the components in the following embodiments, components that are not described in the independent claims are described as optional components. Also, the size or size ratio of the components shown in the drawings is not necessarily strict.

[0013] In addition, each figure is a schematic diagram in which emphasis, omission, or adjustment of the ratio is appropriately performed in order to illustrate the present invention, and is not necessarily a strict illustration, and may differ from the actual shape, positional relationship, and ratio. In each figure, the same reference numerals are given to substantially the same configurations, and duplicated explanations may be omitted or simplified.

[0014] In the circuit configuration of the present disclosure, "connected" includes not only direct connection by a connection terminal and / or a wiring conductor, but also electrical connection via matching elements such as inductors and capacitors, and switch circuits. "Connected between A and B" means connected to both A and B between A and B.

[0015] In addition, terms indicating the relationship between elements, such as "parallel" and "perpendicular," terms indicating the shape of an element, such as "rectangle," and numerical ranges do not only indicate the strict meaning, but also include a substantially equivalent range, for example, an error of about a few percent.

[0016] In the following embodiments, the passband of a filter is defined as a frequency band between two frequencies that are 3 dB higher than the minimum value of the insertion loss in the passband.

[0017] In addition, in the embodiments of the present disclosure, the resonance bandwidth refers to the frequency difference between the antiresonance frequency and the resonance frequency of an elastic wave resonator.

[0018] In addition, in the present disclosure, band A refers to a frequency band defined in advance by a standardization organization (e.g., 3GPP (registered trademark), IEEE (Institute of Electrical and Electronics Engineers), etc.) for a communication system built using a radio access technology (RAT). In this embodiment, the communication system may be, for example, a Long Term Evolution (LTE) system, a 5th Generation (5G)-New Radio (NR) system, and a Wireless Local Area Network (WLAN) system, but is not limited thereto.

[0019] Additionally, the uplink operating band of Band A refers to the frequency range of Band A designated for uplink use, and the downlink operating band of Band A refers to the frequency range of Band A designated for downlink use.

[0020] (Embodiment) [1 Circuit configuration of multiplexer 1] 1 is a circuit diagram of a multiplexer 1 according to an embodiment of the present invention. As shown in the figure, the multiplexer 1 includes filters 10 and 20, a common terminal 100, an input terminal 101, and an output terminal .

[0021] The common terminal 100 is connected to, for example, an antenna.

[0022] Filter 10 is an example of a first filter and has a first passband that includes an uplink operating band of Band A. An output end of filter 10 is connected to a common terminal 100, and an input end is connected to an input terminal 101. Filter 10 includes a plurality of acoustic wave resonators.

[0023] The filter 20 is an example of a second filter, and has a second passband including the downlink operation band of band A. The input end of the filter 20 is connected to a common terminal 100, and the output end is connected to an output terminal 102. That is, the filters 10 and 20 are commonly connected. The filter 20 includes a plurality of acoustic wave resonators. In this embodiment, the second passband of the filter 20 is located at a higher frequency than the first passband of the filter 10.

[0024] As band A, for example, LTE Band 30 (uplink operating band: 2305-2315 MHz, downlink operating band: 2350-2360 MHz) is applied.

[0025] The second passband of filter 20 only needs to be located at a higher frequency than the first passband of filter 10, and the passbands of filters 10 and 20 do not necessarily have to include the same uplink and downlink operating bands. For example, the second passband of filter 20 may include band B, and the first passband of filter 10 may include band C, which is lower in frequency than band B.

[0026] In the multiplexer 1 according to the present embodiment, a filter other than the filters 10 and 20 may be connected to the common terminal 100. An impedance matching circuit including at least one of an inductor and a capacitor may be connected to either the path connecting the common terminal 100 and the input terminal 101 or the path connecting the common terminal 100 and the output terminal 102.

[0027] It should be noted that the multiplexer 1 does not necessarily have to include the common terminal 100, the input terminal 101, and the output terminal .

[0028] [2 Circuit configuration of filters 10 and 20] Next, an example of the circuit configuration of the filters 10 and 20 that constitute the multiplexer 1 will be described.

[0029] As shown in FIG. 1, the filter 10 includes series arm resonators s11, s12, s13, and s14, and parallel arm resonators p11, p12, p13, and p14.

[0030] The series arm resonators s11 to s14 are arranged on a series arm path connecting the output terminal and input terminal of the filter 10 (connecting the common terminal 100 and the input terminal 101). Also, the parallel arm resonators p11 to p14 are connected between each connection point (point on the series arm path) of the series arm resonators s11 to s14 and the input terminal 101 and ground. With the above connection configuration, the filter 10 forms a ladder-type bandpass filter.

[0031] The series arm resonator s11 is an example of a first series arm resonator, and is connected closest to the common terminal 100 among the series arm resonators s11 to s14 and the parallel arm resonators p11 to p14 included in the filter 10. The series arm resonator s11 includes an elastic wave resonator 71 (first elastic wave resonator) and a capacitor 91 (first capacitive element) connected in parallel to the elastic wave resonator 71. The capacitor 91 is an example of a so-called bridging capacitance, and does not shift the resonance frequency frs11 of the series arm resonator s11 from the resonance frequency fr71 of the elastic wave resonator 71, but shifts the anti-resonance frequency fas11 of the series arm resonator s11 to a lower frequency side than the anti-resonance frequency fa71 of the elastic wave resonator 71. In other words, the capacitor 91 is connected in parallel to the elastic wave resonator 71, thereby making the resonance bandwidth of the series arm resonator s11 smaller than the resonance bandwidth of the elastic wave resonator 71 (anti-resonance frequency - resonance frequency).

[0032] In this embodiment, each of the series arm resonator and the parallel arm resonator is defined to include an elastic wave resonator and a means for adjusting the resonance bandwidth of the elastic wave resonator. For example, each of the series arm resonator and the parallel arm resonator includes an elastic wave resonator and a capacitance element (bridging capacitance) connected in parallel to the elastic wave resonator. In addition to the bridging capacitance, the means for adjusting the resonance bandwidth may include adjusting the thickness of a dielectric film added to the IDT electrode of the elastic wave resonator and thinning out the IDT electrode of the elastic wave resonator.

[0033] The series arm resonator s12 includes an elastic wave resonator and is connected between the series arm resonators s11 and s13. The series arm resonator s13 includes elastic wave resonators 72 and 73 connected in parallel to each other and is connected between the series arm resonator s12 and series arm resonator s14. The series arm resonator s14 includes an elastic wave resonator and is connected between the series arm resonator s13 and the input terminal 101.

[0034] The parallel arm resonator p11 includes an elastic wave resonator and is connected between the connection point of the series arm resonators s11 and s12 and ground. The parallel arm resonator p12 includes elastic wave resonators 74 and 75 connected in series to each other and is connected between the connection point of the series arm resonators s12 and s13 and ground. The parallel arm resonator p13 includes an elastic wave resonator and is connected between the connection point of the series arm resonators s13 and s14 and ground. The parallel arm resonator p14 includes an elastic wave resonator and is connected between the connection point of the series arm resonator s14 and the input terminal 101 and ground.

[0035] Note that the filter 10 only needs to have two or more series arm resonators including the series arm resonator s11 and one or more parallel arm resonators including the parallel arm resonator p11. When the filter 20 has two or more series arm resonators including the series arm resonator s21 and one or more parallel arm resonators, the filter 10 does not need to include an acoustic wave resonator and may be, for example, an LC filter constituted by an inductor and a capacitor.

[0036] As shown in FIG. 1, the filter 20 includes series arm resonators s21, s22, s23, s24, and s25, and parallel arm resonators p21, p22, p23, and p24.

[0037] The series arm resonators s21 to s25 are arranged on a series arm path connecting the input terminal and output terminal of the filter 20 (connecting the common terminal 100 and the output terminal 102). In addition, the parallel arm resonators p21 to p24 are connected between each connection point (a point on the series arm path) of the series arm resonators s21 to s25 and the output terminal 102 and ground. With the above connection configuration, the filter 20 configures a ladder-type bandpass filter.

[0038] The series arm resonator s21 is an example of a second series arm resonator, includes an acoustic wave resonator, and is connected closest to the common terminal 100 among the series arm resonators s21 to s25 and the parallel arm resonators p21 to p24 that the filter 20 has.

[0039] The series arm resonator s22 includes an elastic wave resonator and is connected between the series arm resonator s21 and the series arm resonator s23. The series arm resonator s23 includes an elastic wave resonator and is connected between the series arm resonator s22 and the series arm resonator s24. The series arm resonator s24 includes elastic wave resonators 81 and 82 connected in parallel to each other and is connected between the series arm resonator s23 and the series arm resonator s25. The series arm resonator s25 includes an elastic wave resonator and is connected between the series arm resonator s24 and the output terminal 102.

[0040] The parallel arm resonator p21 is an example of a first parallel arm resonator, includes an elastic wave resonator, and is connected between the connection point of the series arm resonators s21 and s22 and ground. The parallel arm resonator p22 includes an elastic wave resonator and is connected between the connection point of the series arm resonators s22 and s23 and ground. The parallel arm resonator p23 includes elastic wave resonators 83 and 84 connected in series with each other, and is connected between the connection point of the series arm resonators s23 and s24 and ground. The parallel arm resonator p24 includes an elastic wave resonator and is connected between the connection point of the series arm resonators s24 and s25 and ground.

[0041] The filter 20 may have two or more series arm resonators including the series arm resonator s21 and one or more parallel arm resonators. When the filter 10 has two or more series arm resonators including the series arm resonator s11 and one or more parallel arm resonators including the parallel arm resonator p11, the filter 20 does not need to include an acoustic wave resonator and may be, for example, an LC filter constituted by an inductor and a capacitor.

[0042] [3 Structure of elastic wave resonators] Next, the structure of the acoustic wave resonators included in the filters 10 and 20 constituting the multiplexer 1 will be illustrated.

[0043] 2A is a plan view and a cross-sectional view that typically illustrate a first example of an acoustic wave resonator that constitutes the multiplexer 1 according to the embodiment. The drawings illustrate basic structures of a plurality of acoustic wave resonators that constitute the filters 10 and 20. Note that the acoustic wave resonator 60 shown in FIG. 2A is intended to illustrate a typical structure of the acoustic wave resonators that constitute the filters 10 and 20, and the number and length of electrode fingers that constitute the electrodes are not limited thereto.

[0044] The acoustic wave resonator 60 is composed of a piezoelectric substrate 50 and comb-shaped electrodes 60a and 60b.

[0045] 2A(a), a pair of comb-shaped electrodes 60a and 60b facing each other are formed on a piezoelectric substrate 50. The comb-shaped electrode 60a is composed of a plurality of parallel electrode fingers 61a and a busbar electrode 62a connecting the plurality of electrode fingers 61a. The comb-shaped electrode 60b is composed of a plurality of parallel electrode fingers 61b and a busbar electrode 62b connecting the plurality of electrode fingers 61b. The plurality of electrode fingers 61a and 61b are formed along a direction perpendicular to the acoustic wave propagation direction (X-axis direction).

[0046] Moreover, the IDT electrode 54, which is constituted by the plurality of electrode fingers 61a and 61b and the bus bar electrodes 62a and 62b, has a laminated structure of an adhesive layer 540 and a main electrode layer 542, as shown in FIG. 2A(b).

[0047] 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 so as to cover the comb-shaped electrodes 60a and 60b. The protective layer 55 is a layer intended to protect the main electrode layer 542 from the external environment, adjust the frequency-temperature characteristics, and increase moisture resistance, and is, for example, a dielectric film whose main component is silicon dioxide.

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

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

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

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

[0052] The high acoustic velocity support substrate 51 is a substrate that supports the low acoustic velocity film 52, the piezoelectric film 53, and the IDT electrode 54. The high acoustic velocity support substrate 51 is a substrate in which the acoustic velocity of the bulk waves in the high acoustic velocity support substrate 51 is faster than that of the surface waves and boundary waves propagating 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, and to prevent the surface acoustic waves 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, dielectric materials such as aluminum oxide, silicon oxynitride, DLC (diamond-like carbon), and diamond, semiconductors such as silicon, and materials mainly composed of the above materials. The spinel includes aluminum compounds containing oxygen and one or more elements selected from Mg, Fe, Zn, Mn, etc. Examples of the spinel include MgAl 2 O 4 , FeAl 2 O 4 , ZnAl 2 O 4 , MnAl 2 O 4 The following can be mentioned.

[0053] 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 wave concentrating energy in a medium with an essentially low acoustic velocity suppress leakage of surface acoustic wave energy to the outside of the piezoelectric film 53. As the material for the low acoustic velocity film 52, for example, 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 mainly composed of the above materials can be used.

[0054] The laminated structure of piezoelectric substrate 50 makes it possible to significantly increase the Q value at the resonant frequency and the anti-resonant 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 therefore a filter with low insertion loss can be configured using the elastic wave resonator.

[0055] The high acoustic velocity support substrate 51 may have a structure in which a support substrate and a high acoustic velocity film in which the acoustic velocity of the propagating bulk wave is faster than that of the elastic wave such as the surface wave and boundary wave propagating through the piezoelectric film 53 are laminated. 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, a piezoelectric material such as aluminum nitride, lithium tantalate, lithium niobate, or quartz; a ceramic material such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, or forsterite; a dielectric material such as diamond or glass; a semiconductor material such as silicon or gallium nitride; or a resin; or a material mainly composed of the above-mentioned material.

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

[0057] Fig. 2B is a cross-sectional view that illustrates a second example of an acoustic wave resonator that constitutes the multiplexer 1 according to the embodiment. In the acoustic wave resonator 60 illustrated in Fig. 2A, the IDT electrode 54 is formed on the piezoelectric substrate 50 having the piezoelectric film 53. However, the substrate on which the IDT electrode 54 is formed may be a piezoelectric single crystal substrate 57 that is made of a single layer of a piezoelectric material, as illustrated in Fig. 2B.

[0058] The piezoelectric single crystal substrate 57 is, for example, LiNbO 3 The elastic wave resonator according to this embodiment is made of a piezoelectric single crystal of LiNbO 3 The piezoelectric element 50 is constituted by 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.

[0059] The laminated structure, material, cut angle, and thickness of the piezoelectric film 53 and the piezoelectric single crystal substrate 57 may be changed as appropriate depending on the required pass characteristics of the acoustic wave filter device. 3 Even if an elastic wave resonator using a piezoelectric substrate or the like is used, it is possible to achieve the same effects as those of elastic wave resonator 60 using piezoelectric film 53 described above.

[0060] The substrate on which the IDT electrode 54 is formed may have a structure in which a support substrate, an energy trapping layer, and a piezoelectric film are laminated in this order. The IDT electrode 54 is formed on the piezoelectric film. The piezoelectric film is made of, for example, LiTaO 3 A piezoelectric single crystal or a piezoelectric ceramic is used. The supporting substrate is a substrate that supports the piezoelectric film, the energy trapping layer, and the IDT electrode 54.

[0061] The energy trapping layer is composed of one or more layers, and the speed of the bulk acoustic wave propagating through at least one of the layers is greater than the speed of the acoustic wave 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 wave in the low acoustic velocity layer is slower than the acoustic velocity of the acoustic wave propagating through the piezoelectric film. The high acoustic velocity layer is a film in which the acoustic velocity of the bulk wave in the high acoustic velocity layer is faster than the acoustic velocity of the acoustic wave propagating through the piezoelectric film. The support substrate may be the high acoustic velocity layer.

[0062] The energy trapping layer may be an acoustic impedance layer having a configuration in which low acoustic impedance layers having a relatively low acoustic impedance and high acoustic impedance layers having a relatively high acoustic impedance are alternately laminated.

[0063] Here, the electrode parameters of the IDT electrode 54 constituting the acoustic wave resonator 60 will be described.

[0064] The wavelength of the acoustic wave resonator is defined as wavelength λ, which is the repetition period of multiple electrode fingers 61a or 61b constituting IDT electrode 54 shown in Fig. 2A(b). The electrode finger pitch is 1 / 2 of wavelength λ, and is defined as (W+S), where W is the line width of electrode fingers 61a and 61b constituting comb-shaped electrodes 60a and 60b, respectively, and S is the space width between adjacent electrode fingers 61a and 61b.

[0065] In the case where the interval between adjacent electrode fingers in IDT electrode 54 is not constant, the electrode finger pitch of IDT electrode 54 is defined as the average electrode finger pitch of IDT electrode 54. The average electrode finger pitch of IDT electrode 54 is defined as Di / (Ni-1), where the total number of electrode fingers 61a, 61b included in IDT electrode 54 is Ni, and the center-to-center distance between the electrode finger located at one end and the electrode finger located at the other end of IDT electrode 54 in the acoustic wave propagation direction is Di.

[0066] 2C is a cross-sectional view that typically illustrates a third example of an acoustic wave resonator that constitutes the multiplexer 1 according to the embodiment. In FIG. 2C, a bulk acoustic wave resonator is illustrated as the acoustic wave resonator of the multiplexer 1. As illustrated in the figure, the bulk acoustic wave resonator has, for example, a support substrate 65, a lower electrode 66, a piezoelectric layer 67, and an upper electrode 68, and is configured such that the support substrate 65, the lower electrode 66, the piezoelectric layer 67, and the upper electrode 68 are laminated in this order.

[0067] The support substrate 65 is a substrate for supporting the lower electrode 66, the piezoelectric layer 67, and the upper electrode 68, and is, for example, a silicon substrate. The support substrate 65 has a cavity in an area in contact with the lower electrode 66. This allows the piezoelectric layer 67 to vibrate freely.

[0068] The lower electrode 66 is formed on one surface of the support substrate 65. The upper electrode 68 is formed on one surface of the support substrate 65. The lower electrode 66 and the upper electrode 68 are made of a material such as Al containing 1% Cu.

[0069] The piezoelectric layer 67 is formed between the lower electrode 66 and the upper electrode 68. The piezoelectric layer 67 is mainly composed of at least one of ZnO (zinc oxide), AlN (aluminum nitride), PZT (lead zirconate titanate), KN (potassium niobate), LN (lithium niobate), LT (lithium tantalate), quartz crystal, and LiBO (lithium borate).

[0070] A bulk acoustic wave resonator having the above-described laminated structure generates resonance by inducing bulk acoustic waves in the piezoelectric layer 67 by applying electrical energy between the lower electrode 66 and the upper electrode 68. The bulk acoustic waves generated by this bulk acoustic wave resonator propagate between the lower electrode 66 and the upper electrode 68 in a direction perpendicular to the film surface of the piezoelectric layer 67. In other words, the bulk acoustic wave resonator is a resonator that utilizes bulk acoustic waves.

[0071] [4. Resonance characteristics of filter 10 and pass characteristics of filter 20] First, the basic operating principle of a ladder-type bandpass filter composed of one series arm resonator and one parallel arm resonator will be explained.

[0072] The parallel arm resonator has a resonance frequency frp and an anti-resonance frequency fap (>frp), and the series arm resonator has a resonance frequency frs and an anti-resonance frequency fas (>frs>frp). In the series arm resonator and the parallel arm resonator having the above resonance characteristics, the anti-resonance frequency fap of the parallel arm resonator and the resonance frequency frs of the series arm resonator are generally made close to each other. As a result, the vicinity of the resonance frequency frp where the impedance of the parallel arm resonator approaches 0 becomes a low-frequency stopband. Furthermore, when the frequency increases from this frequency, the impedance of the parallel arm resonator increases near the anti-resonance frequency fap, and the impedance of the series arm resonator approaches 0 near the resonance frequency frs. As a result, the vicinity of the anti-resonance frequency fap to the resonance frequency frs becomes a signal passband in the signal path, which is the series arm path. This makes it possible to form a passband that reflects the electrode parameters and the electromechanical coupling coefficient of the elastic wave resonator. Furthermore, as the frequency increases and approaches the anti-resonance frequency fas, the impedance of the series arm resonator increases, and becomes a high-frequency stopband.

[0073] In each of the series arm resonators and the parallel arm resonators, in the frequency band lower than the resonant frequency, the impedance of the resonator is capacitive (C-type), and in the frequency band higher than the resonant frequency and lower than the anti-resonant frequency, the impedance of the resonator is inductive (L-type). Also, in the frequency band higher than the anti-resonant frequency, the impedance of the resonator is capacitive.

[0074] Based on the basic operating principle described above, it is possible to configure a multiplexer that meets the required specifications of a narrow band and a small interband gap by adjusting the resonant frequencies and anti-resonant frequencies of multiple elastic wave resonators that have a relatively large resonant bandwidth.

[0075] Next, the resonance characteristics of the series arm resonators constituting the filter 10 and the pass characteristics of the multiplexer 1 (filter 20) reflecting the resonance characteristics will be described.

[0076] Table 1 shows the wavelength λ (electrode finger pitch×2) of each resonator constituting the multiplexer 1 according to the embodiment.

[0077] [Table 1]

[0078] FIG. 3 is a graph showing (a) the pass characteristic of the multiplexer 1 and (b) the impedance characteristic of the series arm resonators s11 to s14 constituting the filter 10 according to the embodiment.

[0079] 3B, the resonant frequency frs11 of the series arm resonator s11, the resonant frequency frs12 of the series arm resonator s12, the resonant frequency frs13 of the series arm resonator s13, and the resonant frequency frs14 of the series arm resonator s14 are located within the first passband of the filter 10. On the other hand, the anti-resonant frequency fas11 of the series arm resonator s11, the anti-resonant frequency fas12 of the series arm resonator s12, the anti-resonant frequency fas13 of the series arm resonator s13, and the anti-resonant frequency fas14 of the series arm resonator s14 are located on the higher frequency side of the high frequency end of the first passband of the filter 10.

[0080] Since the series arm resonator s13 is composed of elastic wave resonators 72 and 73 connected in parallel, it has two resonant frequencies and two anti-resonant frequencies; however, the resonant frequency frs13 is defined as the higher frequency of the two resonant frequencies, and the anti-resonant frequency fas13 is defined as the higher frequency of the two anti-resonant frequencies.

[0081] Here, the resonance bandwidth of at least one of the series arm resonators s11 to s14 of the filter 10 is larger than the first passband.

[0082] Alternatively, the electrode finger pitch of the IDT electrode constituting at least one of the series arm resonators s11 to s14 of the filter 10 is smaller than the electrode finger pitch of the IDT electrode constituting at least one of the parallel arm resonators p21 to p24 of the filter 20. In other words, the resonant frequency of at least one of the series arm resonators s11 to s14 of the filter 10 is higher than the resonant frequency of at least one of the parallel arm resonators p21 to p24 of the filter 20. That is, the inter-passband gap between the first passband and the second passband is smaller than the resonant bandwidth of at least one of the series arm resonators s11 to s14 of the filter 10. As shown in Table 1, in this embodiment, the wavelength λ (electrode finger pitch×2) of the series arm resonators s11 and s14 is smaller than the wavelength λ (electrode finger pitch×2) of the parallel arm resonators p21 to p24.

[0083] In contrast, the anti-resonant frequency fas11 of the series arm resonator s11 is lower than the high frequency end of the second passband, and is the lowest among the anti-resonant frequencies fas11 to fas14 of the series arm resonators s11 to s14 that the filter 10 has.

[0084] The resonant frequency frs11 of the series arm resonator s11 is higher than the low frequency end of the first passband. As a result, in the series arm resonator s11, instead of increasing the electrode finger pitch to shift both the resonant frequency frs11 and the anti-resonant frequency fas11 to the low frequency side, only the anti-resonant frequency fas11 is shifted to the low frequency side by decreasing the resonant bandwidth. This makes it possible to position the resonant frequency frs11 within the first passband, thereby reducing the insertion loss in the first passband of the filter 10.

[0085] The series arm resonators s11 to s14 of the filter 10 are resonators that contribute to the formation of the first pass band, and more specifically, are resonators whose frequency range between a resonant frequency and an anti-resonant frequency at least partially overlaps with the first pass band. In other words, the multiple series arm resonators of the filter 10 are resonators that contribute to the formation of the first pass band, and do not include resonators whose frequency range between a resonant frequency and an anti-resonant frequency at least partially does not overlap with the first pass band.

[0086] Fig. 4A is a graph showing the pass characteristics of the filter 20 (filter 520) in the multiplexers according to the embodiment and the comparative example. Fig. 4B is an immittance chart showing the impedance of the second passband when the multiplexers according to the embodiment and the comparative example are viewed from the common terminal 100. Fig. 5 is a graph showing the impedance characteristics and susceptance characteristics of the first series arm resonator according to the embodiment and the comparative example.

[0087] The multiplexer according to the comparative example includes filters 510 and 520 instead of filters 10 and 20. The multiplexer according to the comparative example differs from the multiplexer 1 according to the embodiment in the configurations of filters 510 and 520. Filter 510 differs from filter 10 only in that capacitor 91 is not connected in parallel to acoustic wave resonator 71. Filter 520 differs from filter 20 only in that acoustic wave resonator 80 is provided instead of series arm resonator s21.

[0088] Specifically, in the multiplexer according to the comparative example, the first series arm resonator connected closest to the common terminal 100 is the acoustic wave resonator 71, and the anti-resonance frequency fa71 of the acoustic wave resonator 71 is located on the higher frequency side than the high frequency end of the second passband, as shown in Fig. 5(a). In addition, in the multiplexer according to the comparative example, the second series arm resonator connected closest to the common terminal 100 is the acoustic wave resonator 80, and the resonant frequency fr80 of the acoustic wave resonator 80 is lower than the resonant frequency frs22 of the series arm resonator s22, the resonant frequency frs24 of the series arm resonator s24, and the resonant frequency frs25 of the series arm resonator s25, as shown in Fig. 9(a) and Fig. 7(b) described later.

[0089] In the multiplexer according to the comparative example, as shown in (a) of FIG. 5, the resonant bandwidth of the acoustic wave resonator 71 is large, so that the inductive region (region between the resonant frequency fr71 and the anti-resonant frequency fa71) of the acoustic wave resonator 71 overlaps with the second passband. In other words, in the multiplexer according to the comparative example, as shown in (b) of FIG. 5, the region in which the susceptance of the acoustic wave resonator 71 is small overlaps with the second passband. As a result, in the multiplexer according to the comparative example, the acoustic wave resonator 71 is connected in series with the filter 520 closest to the acoustic wave resonators constituting the filter 510. Therefore, as shown in FIG. 4B, the impedance of the second passband when the filters 510 and 520 are viewed from the common terminal 100 deviates into the inductive region from the impedance of the second passband (reference impedance) optimized for the filter 520 alone (dashed line in FIG. 4B).

[0090] In contrast, in the multiplexer 1 according to the embodiment, as shown in FIG. 5A, the resonance bandwidth of the series arm resonator s11 is smaller than that of the acoustic wave resonator 71, and therefore the overlap between the second passband and the inductive region of the series arm resonator s11 is reduced. In other words, in the multiplexer 1 according to the embodiment, as shown in FIG. 5B, the region in which the susceptance of the series arm resonator s11 is large overlaps with the second passband. As a result, in the multiplexer 1 according to the embodiment, as shown in FIG. 4B, the impedance of the second passband when the filters 10 and 20 are viewed from the common terminal 100 can be positioned closer to the impedance of the second passband optimized for the filter 20 alone (reference impedance) than in the multiplexer according to the comparative example (solid line in FIG. 4B).

[0091] As a result, as shown in FIG. 4A, the pass characteristics of the filter 20 of the multiplexer 1 according to the embodiment (pass characteristics from the common terminal 100 to the output terminal 102) can reduce the insertion loss in the second passband compared to the pass characteristics of the filter 520 of the multiplexer according to the comparative example.

[0092] In the present embodiment, the resonant bandwidth of the first series arm resonator, which is connected closest to the common terminal 100 among the series arm resonators and parallel arm resonators constituting the filter 10, is reduced by connecting the capacitor 91 in parallel; however, the means for reducing the resonant bandwidth is not limited to this.

[0093] One way to reduce the resonance bandwidth of the first series arm resonator is to include a withdrawal electrode in the IDT electrode of the first series arm resonator. The IDT electrode of the first series arm resonator may include, for example, any of the floating withdrawal electrodes shown in Fig. 6A, the polarity-reversed withdrawal electrodes shown in Fig. 6B, and the filled withdrawal electrodes shown in Fig. 6C. This makes it possible to reduce the resonance bandwidth of the first series arm resonator and lower the anti-resonance frequency.

[0094] Fig. 6A is a schematic plan view showing the configuration of an IDT electrode including a floating withdrawal electrode, Fig. 6B is a schematic plan view showing the configuration of an IDT electrode including a polarity-inverting withdrawal electrode, and Fig. 6C is a schematic plan view showing the configuration of an IDT electrode including a filled withdrawal electrode.

[0095] Acoustic wave resonator 111 shown in Fig. 6A is an example of a first series arm resonator, and illustrates an electrode finger structure of an IDT electrode including a floating withdrawal electrode. Note that acoustic wave resonator 111 shown in Fig. 6A is intended to illustrate a typical structure of a floating withdrawal electrode, and the number and length of electrode fingers constituting the electrode are not limited to this.

[0096] Acoustic wave resonator 111 is composed of piezoelectric substrate 50 , comb-shaped electrodes 111 a and 111 b formed on piezoelectric substrate 50 , and reflector 141 .

[0097] As shown in FIG. 6A, comb electrode 111a is composed of a plurality of electrode fingers 151a parallel to each other and busbar electrode 161a connecting one ends of the plurality of electrode fingers 151a. Comb electrode 111b is composed of a plurality of electrode fingers 151b parallel to each other and busbar electrode 161b connecting one ends of the plurality of electrode fingers 151b. The plurality of electrode fingers 151a and 151b are formed along a direction perpendicular to the surface acoustic wave propagation direction (X-axis direction). Comb electrodes 111a and 111b are arranged opposite to each other such that the plurality of electrode fingers 151a and 151b are interdigitated with each other. That is, the IDT electrode of acoustic wave resonator 111 has a pair of comb electrodes 111a and 111b.

[0098] Comb electrode 111a has a dummy electrode arranged to face electrode fingers 151b in the longitudinal direction, but this dummy electrode may be omitted. Comb electrode 111b has a dummy electrode arranged to face electrode fingers 151a in the longitudinal direction, but this dummy electrode may be omitted. Comb electrodes 111a and 111b may be so-called inclined IDT electrodes in which the extension direction of the busbar electrodes is inclined with respect to the surface acoustic wave propagation direction, or may have a so-called piston structure.

[0099] Reflector 141 is composed of a plurality of parallel electrode fingers and bus bar electrodes connecting the plurality of electrode fingers, and is disposed on both ends of a pair of comb-shaped electrodes 111a and 111b.

[0100] Here, electrode fingers 152 are formed discretely in the IDT electrode of acoustic wave resonator 111. Electrode finger 152 is a floating withdrawal electrode that is not connected to either bus bar electrode 161a or 161b and is arranged parallel to and at the same pitch as multiple electrode fingers 151a and 151b. Furthermore, multiple electrode fingers 151a and 151b are arranged between two adjacent electrode fingers 152. In other words, the pitch of electrode fingers 152 is larger than the pitch of multiple electrode fingers 151a and 151b.

[0101] Acoustic wave resonator 211 shown in Fig. 6B is an example of a first series arm resonator, and illustrates an electrode finger structure of an IDT electrode including a polarity-inverting thinned-out electrode. Note that acoustic wave resonator 211 shown in Fig. 6B is intended to illustrate a typical structure of a polarity-inverting thinned-out electrode, and the number and length of electrode fingers constituting the electrode are not limited thereto.

[0102] Acoustic wave resonator 211 is composed of piezoelectric substrate 50 , comb-shaped electrodes 211 a and 211 b formed on piezoelectric substrate 50 , and reflector 241 .

[0103] As shown in FIG. 6B, comb electrode 211a is composed of a plurality of electrode fingers 251a parallel to each other and busbar electrode 261a connecting one ends of electrode fingers 251a. Comb electrode 211b is composed of a plurality of electrode fingers 251b parallel to each other and busbar electrode 261b connecting one ends of electrode fingers 251b. Electrode fingers 251a and 251b are formed along a direction perpendicular to the surface acoustic wave propagation direction (X-axis direction). Comb electrodes 211a and 211b are arranged opposite to each other such that electrode fingers 251a and 251b are interdigitated with each other. That is, the IDT electrode of acoustic wave resonator 211 has a pair of comb electrodes 211a and 211b.

[0104] Comb electrode 211a has a dummy electrode arranged to face electrode fingers 251b in the longitudinal direction, but this dummy electrode may be omitted. Comb electrode 211b has a dummy electrode arranged to face electrode fingers 251a in the longitudinal direction, but this dummy electrode may be omitted. Comb electrodes 211a and 211b may be so-called inclined IDT electrodes in which the extension direction of the busbar electrodes is inclined with respect to the surface acoustic wave propagation direction, or may have a so-called piston structure.

[0105] Reflector 241 is composed of a plurality of electrode fingers parallel to one another and bus bar electrodes connecting the plurality of electrode fingers, and is disposed on both ends of a pair of comb-shaped electrodes 211a and 211b.

[0106] Here, electrode fingers 252 are formed discretely in the IDT electrode of acoustic wave resonator 211. Electrode finger 252 is a polarity-inverted withdrawal electrode in which, among all the electrode fingers constituting pair of comb-shaped electrodes 211a and 211b, both adjacent electrode fingers are connected to the same busbar electrode. In addition, a plurality of electrode fingers 251a and 251b are arranged between two adjacent electrode fingers 252. In other words, the pitch of electrode fingers 252 is larger than the pitch of electrode fingers 251a and 251b.

[0107] Acoustic wave resonator 311 shown in Fig. 6C is an example of a first series arm resonator, and illustrates an electrode finger structure of an IDT electrode including a fill-thinned-out electrode. Note that acoustic wave resonator 311 shown in Fig. 6C is intended to illustrate a typical structure of a fill-thinned-out electrode, and the number and length of electrode fingers constituting the electrode are not limited thereto.

[0108] Acoustic wave resonator 311 is composed of piezoelectric substrate 50 , comb-shaped electrodes 311 a and 311 b formed on piezoelectric substrate 50 , and reflector 341 .

[0109] As shown in FIG. 6C, comb electrode 311a is composed of a plurality of electrode fingers 351a parallel to each other and busbar electrode 361a connecting one ends of the plurality of electrode fingers 351a. Comb electrode 311b is composed of a plurality of electrode fingers 351b parallel to each other and busbar electrode 361b connecting one ends of the plurality of electrode fingers 351b. The plurality of electrode fingers 351a and 351b are formed along a direction perpendicular to the surface acoustic wave propagation direction (X-axis direction). Comb electrodes 311a and 311b are arranged opposite to each other such that the plurality of electrode fingers 351a and 351b are interdigitated with each other. That is, the IDT electrode of acoustic wave resonator 311 has a pair of comb electrodes 311a and 311b.

[0110] Comb electrode 311a has a dummy electrode arranged to face electrode fingers 351b in the longitudinal direction, but this dummy electrode may be omitted. Comb electrode 311b has a dummy electrode arranged to face electrode fingers 351a in the longitudinal direction, but this dummy electrode may be omitted. Comb electrodes 311a and 311b may be so-called inclined IDT electrodes in which the extension direction of the busbar electrodes is inclined with respect to the surface acoustic wave propagation direction, or may have a so-called piston structure.

[0111] Reflector 341 is composed of a plurality of parallel electrode fingers and bus bar electrodes connecting the plurality of electrode fingers, and is disposed on both ends of a pair of comb-shaped electrodes 311a and 311b.

[0112] Here, electrode fingers 352 are formed discretely in the IDT electrode of acoustic wave resonator 311. Electrode finger 352 is an electrode finger having the largest electrode finger width in the IDT electrode of acoustic wave resonator 311, and is a fill-in thinning electrode having an electrode finger width that is at least twice the average electrode finger width of the electrode fingers excluding electrode finger 352. In other words, electrode finger 352 is a fill-in thinning electrode in which adjacent electrode fingers 351a and 351b and the space between the adjacent electrode fingers 351a and 351b are combined into one electrode finger (three electrode fingers 351a and 351b in FIG. 6C ), which is connected to one of bus bar electrodes 361a and 361b and has a wider electrode finger width than the electrode fingers 351a and 351b. In addition, the electrode fingers 351a and 351b are arranged between two adjacent electrode fingers 352. In other words, the pitch of the electrode fingers 352 is greater than the pitch of the plurality of electrode fingers 351a and 351b.

[0113] The configuration of the withdrawal electrodes, which are means for narrowing the resonant bandwidth of the first series arm resonator, is not limited to the above-mentioned floating withdrawal electrodes, polarity inversion withdrawal electrodes, and filled withdrawal electrodes.

[0114] Furthermore, one way to reduce the resonance bandwidth of the first series arm resonator is to adjust the thickness of a dielectric film disposed on the IDT electrode of the first series arm resonator. In the elastic wave resonator 60 shown in Fig. 2A(b), the protective layer 55 is an example of a first dielectric film, and by adjusting the thickness of the protective layer 55, it is possible to change the resonance bandwidth of the elastic wave resonator 60. Specifically, the larger the thickness of the protective layer 55, the smaller the resonance bandwidth becomes.

[0115] From the above viewpoint, the first series arm resonator may have the thickest protective layer 55 (first dielectric film) among the series arm resonators constituting the filter 10. This makes it possible to reduce the resonance bandwidth of the first series arm resonator and lower the anti-resonance frequency.

[0116] The first dielectric film does not have to be the protective layer 55 formed on the IDT electrode, and may be a dielectric film disposed between the piezoelectric substrate 50 and the IDT electrode.

[0117] [5. Resonance characteristics of filter 20 and pass characteristics of filter 10] Next, the resonance characteristics of the series arm resonators that configure the filter 20 and the pass characteristics of the multiplexer 1 (filter 10) that reflect the resonance characteristics will be described.

[0118] FIG. 7 is a graph showing (a) the pass characteristic of the multiplexer 1 and (b) the impedance characteristic of the series arm resonators s21 to s25 constituting the filter 20 according to the embodiment.

[0119] In FIG. 7(b), the resonant frequency frs21 of the series arm resonator s21, the resonant frequency frs22 of the series arm resonator s22, the resonant frequency frs23 of the series arm resonator s23, the resonant frequency frs24 of the series arm resonator s24, and the resonant frequency frs25 of the series arm resonator s25 are located within the second passband of the filter 20.

[0120] Since the series arm resonator s24 is composed of elastic wave resonators 81 and 82 connected in parallel, it has two resonant frequencies and two anti-resonant frequencies, but the resonant frequency frs24 is defined as the higher frequency resonant frequency of the two resonant frequencies.

[0121] Here, the resonance bandwidth of at least one of the series arm resonators s21 to s25 that configure the filter 20 is greater than the second passband.

[0122] Alternatively, the electrode finger pitch of the IDT electrode constituting at least one of the series arm resonators s11 to s14 of the filter 10 is smaller than the electrode finger pitch of the IDT electrode constituting at least one of the parallel arm resonators p21 to p24 of the filter 20. In other words, the resonant frequency of at least one of the series arm resonators s11 to s14 of the filter 10 is higher than the resonant frequency of at least one of the parallel arm resonators p21 to p24 of the filter 20. That is, the inter-passband gap between the first passband and the second passband is smaller than the resonant bandwidth of at least one of the series arm resonators s21 to s25 of the filter 20. As shown in Table 1, in this embodiment, the wavelength λ (electrode finger pitch×2) of the series arm resonators s11 and s14 is smaller than the wavelength λ (electrode finger pitch×2) of the parallel arm resonators p21 to p24.

[0123] In contrast, the resonant frequency frs21 of the series arm resonator s21 is higher than the high frequency end of the first passband and is the highest among the resonant frequencies frs21 to frs25 of the series arm resonators s21 to s25. Alternatively, as shown in Table 1, the IDT electrode constituting the series arm resonator s21 has the smallest electrode finger pitch among the IDT electrodes constituting the series arm resonators s21 to s25.

[0124] The series arm resonators s21 to s25 of the filter 20 are resonators that contribute to the formation of the second pass band, and more specifically, are resonators whose frequency range between a resonant frequency and an anti-resonant frequency at least partially overlaps with the second pass band. In other words, the multiple series arm resonators of the filter 20 are resonators that contribute to the formation of the second pass band, and do not include resonators whose frequency range between a resonant frequency and an anti-resonant frequency at least partially does not overlap with the second pass band.

[0125] Fig. 8A is a graph showing the pass characteristics of the filter 10 (filter 510) in the multiplexers according to the embodiment and the comparative example. Fig. 8B is an immittance chart showing the impedance of the first passband when the multiplexers according to the embodiment and the comparative example are viewed from the common terminal 100. Fig. 9 is a graph showing the impedance characteristics and susceptance characteristics of the second series arm resonator according to the embodiment and the comparative example.

[0126] The multiplexer according to the comparative example includes filters 510 and 520 instead of filters 10 and 20. The multiplexer according to the comparative example differs from the multiplexer 1 according to the embodiment in the configurations of filters 510 and 520. Filter 510 differs from filter 10 only in that capacitor 91 is not connected in parallel to acoustic wave resonator 71. Filter 520 differs from filter 20 only in that acoustic wave resonator 80 is provided instead of series arm resonator s21.

[0127] Specifically, in the multiplexer according to the comparative example, the first series arm resonator connected closest to the common terminal 100 is the acoustic wave resonator 71, and the anti-resonance frequency fa71 of the acoustic wave resonator 71 is located on the higher frequency side than the high frequency end of the second passband, as shown in Fig. 5A. In addition, in the multiplexer according to the comparative example, the second series arm resonator connected closest to the common terminal 100 is the acoustic wave resonator 80, and the resonant frequency fr80 of the acoustic wave resonator 80 is lower than the resonant frequency frs22 of the series arm resonator s22, the resonant frequency frs24 of the series arm resonator s24, and the resonant frequency frs25 of the series arm resonator s25, as shown in Fig. 9A and Fig. 7B.

[0128] In the multiplexer according to the comparative example, as shown in (a) of FIG. 9, the resonant bandwidth of the acoustic wave resonator 80 is large, so that the capacitive region of the acoustic wave resonator 80 (a region on the lower frequency side than the resonant frequency fr80) overlaps with the first passband of the filter 10. In other words, in the multiplexer according to the comparative example, as shown in (b) of FIG. 9, the region in which the susceptance of the acoustic wave resonator 80 is large overlaps with the first passband of the filter 10. As a result, in the multiplexer according to the comparative example, as shown in (b) of FIG. 8, the acoustic wave resonator 80 is the closest of the acoustic wave resonators constituting the filter 20 to be connected in series with the filter 10. Therefore, the impedance of the first passband when the filters 10 and 20 are viewed from the common terminal 100 deviates into the capacitive region from the impedance of the first passband (reference impedance) optimized for the filter 10 alone (dashed line in FIG. 8B).

[0129] In contrast, in the multiplexer 1 according to the embodiment, as shown in (a) of Fig. 9, the resonant frequency frs21 of the series arm resonator s21 is the highest among the resonant frequencies frs21 to frs25 of the series arm resonators s21 to s25, and therefore the capacitive region where the capacitive property of the series arm resonator s21 is high overlaps with the first pass band of the filter 10. In other words, in the multiplexer 1 according to the embodiment, as shown in (b) of Fig. 9, the region where the susceptance of the series arm resonator s21 is low overlaps with the first pass band of the filter 10. As a result, in the multiplexer 1 according to the embodiment, as shown in (b) of Fig. 8, the impedance of the first pass band when the filters 10 and 20 are viewed from the common terminal 100 can be positioned closer to the impedance of the first pass band optimized for the filter 10 alone (reference impedance) than in the multiplexer according to the comparative example (solid line in Fig. 8B).

[0130] As a result, as shown in FIG. 8A, the pass characteristics of the filter 10 of the multiplexer 1 according to the embodiment (pass characteristics from the input terminal 101 to the common terminal 100) can reduce the insertion loss in the first passband compared to the pass characteristics of the filter 10 of the multiplexer according to the comparative example.

[0131] In this embodiment, for the series arm resonator s21 (second series arm resonator) connected closest to the common terminal 100 among the series arm resonators and parallel arm resonators constituting the filter 20, the electrode finger pitch of the IDT electrodes of the series arm resonator s21 is set to be the smallest among the series arm resonators s21 to s25 of the filter 20, thereby making the resonant frequency frs21 the highest; however, the means for increasing the resonant frequency frs21 is not limited to this.

[0132] One way to increase the resonant frequency of the second series arm resonator is to have the second series arm resonator include a second acoustic wave element and a second capacitance element (bridging capacitance) connected in parallel to the second acoustic wave element. By adding the second capacitance element (bridging capacitance), the resonant bandwidth of the second series arm resonator becomes smaller relative to the resonant bandwidth of the second acoustic wave element, and the resonant frequency of the second series arm resonator can be increased.

[0133] As a means for increasing the resonant frequency of the second series arm resonator, the IDT electrode of the second series arm resonator may include a withdrawal electrode. The IDT electrode of the second series arm resonator may include any of the floating withdrawal electrodes shown in Fig. 6A, the polarity-reversed withdrawal electrodes shown in Fig. 6B, and the filled withdrawal electrodes shown in Fig. 6C. This makes it possible to reduce the resonant bandwidth of the second series arm resonator and increase its resonant frequency.

[0134] The configuration of the withdrawal electrodes, which are means for narrowing the resonant bandwidth of the second series arm resonator, is not limited to the above-mentioned floating withdrawal electrodes, polarity inversion withdrawal electrodes, and filled withdrawal electrodes.

[0135] As a means for narrowing the resonance bandwidth of the second series arm resonator, the thickness of a dielectric film disposed on the IDT electrode of the second series arm resonator can be adjusted. In the elastic wave resonator 60 shown in FIG. 2A(b), the protective layer 55 is an example of a second dielectric film, and the resonance bandwidth of the elastic wave resonator 60 can be changed by adjusting the thickness of the protective layer 55. Specifically, the larger the thickness of the protective layer 55, the smaller the resonance bandwidth. From the above viewpoint, the second series arm resonator may have the thickest protective layer 55 (second dielectric film) among the series arm resonators constituting the filter 20. This narrows the resonance bandwidth of the second series arm resonator and increases the resonance frequency.

[0136] The second dielectric film does not have to be the protective layer 55 formed on the IDT electrode, and may be a dielectric film disposed between the piezoelectric substrate 50 and the IDT electrode.

[0137] In the multiplexer 1 according to the present embodiment, the resonant frequency frp21 of the parallel arm resonator p21 may have the following characteristics.

[0138] FIG. 10 is a graph showing (a) the pass characteristic of the multiplexer 1 and (b) the impedance characteristic of the parallel arm resonators p21 to p24 constituting the filter 20 according to the embodiment.

[0139] In FIG. 10(b), the resonant frequency frp21 of the parallel arm resonator p21 is lower than the high frequency end of the first passband, and is the highest among the resonant frequencies frp21 to frp24 of the parallel arm resonators p21 to p24.

[0140] The parallel arm resonator p21 is an example of a first parallel arm resonator, and is connected to the series arm resonator s21 (second series arm resonator).

[0141] Since the parallel arm resonator p23 is composed of elastic wave resonators 83 and 84 connected in series, it has two resonant frequencies and two anti-resonant frequencies, but the resonant frequency frp23 is defined as the lower frequency of the two resonant frequencies.

[0142] The parallel arm resonators p21 to p24 of the filter 20 are resonators that contribute to the formation of the second pass band, and more specifically, are resonators whose frequency range between a resonant frequency and an anti-resonant frequency at least partially overlaps with the second pass band. In other words, the parallel arm resonators of the filter 20 are resonators that contribute to the formation of the second pass band, and do not include resonators whose frequency range between a resonant frequency and an anti-resonant frequency at least partially does not overlap with the second pass band.

[0143] In the multiplexer 1 according to the present embodiment, as shown in (b) of FIG. 10, the resonant bandwidth of the parallel arm resonators p21 to p24 is larger than the first passband, the second passband, and the passband gap, so that the inductive regions of the parallel arm resonators p21 to p24 overlap with the first passband of the filter 10.

[0144] On the other hand, since the resonant frequency frp21 of the parallel arm resonator p21 is the highest among the resonant frequencies frp21 to frp24 of the parallel arm resonators p21 to p24, the inductance of the parallel arm resonator p21 in the first passband can be reduced. This makes it possible to shift the impedance of the first passband, when the filter 20 alone is viewed from the common terminal 100 side, further toward the open side.

[0145] This makes it possible to reduce the deviation of the impedance of the first passband when the filters 10 and 20 are viewed from the common terminal 100 from the impedance (reference impedance) of the first passband optimized for the filter 10 alone. Therefore, in the pass characteristics (pass characteristics from the input terminal 101 to the common terminal 100) of the filter 10 of the multiplexer 1 according to the embodiment, the insertion loss of the first passband can be further reduced.

[0146] [6 Configuration of the multiplexer according to the present invention] The multiplexer 1 according to the present embodiment is characterized in that (1) the anti-resonance frequency fas11 of the first series arm resonator (series arm resonator s11) is lower than the high frequency end of the second pass band and is the lowest among the anti-resonance frequencies fas11 to fas14 of the series arm resonators s11 to s14 of the filter 10, and (2) the resonant frequency frs21 of the second series arm resonator (series arm resonator s21) is higher than the high frequency end of the first pass band and is the highest among the resonant frequencies frs21 to frs25 of the series arm resonators s21 to s25 of the filter 20, but the multiplexer according to the present invention is not limited to this.

[0147] The multiplexer of the present invention is characterized in at least one of the following: (1) the anti-resonance frequency fas11 of the first series arm resonator (series arm resonator s11) is lower than the high frequency end of the second pass band and is the lowest among the anti-resonance frequencies fas11 to fas14 of the series arm resonators s11 to s14 of the filter 10; and (2) the resonant frequency frs21 of the second series arm resonator (series arm resonator s21) is higher than the high frequency end of the first pass band and is the highest among the resonant frequencies frs21 to frs25 of the series arm resonators s21 to s25 of the filter 20.

[0148] According to this, since the multiplexer 1 has the above feature (1), it is possible to position the impedance of the second passband when the filters 10 and 20 are viewed from the common terminal 100 closer to the impedance (reference impedance) of the second passband optimized for the filter 20 alone than in the multiplexer according to the comparative example. Therefore, the insertion loss in the second passband of the multiplexer 1 can be reduced more than the insertion loss in the second passband of the multiplexer according to the comparative example.

[0149] Furthermore, because the multiplexer 1 has the above feature (2), it is possible to position the impedance of the first passband when the filters 10 and 20 are viewed from the common terminal 100 closer to the impedance (reference impedance) of the first passband optimized for the filter 10 alone than in the multiplexer according to the comparative example. Therefore, the insertion loss in the first passband of the multiplexer 1 can be reduced more than the insertion loss in the first passband of the multiplexer according to the comparative example.

[0150] [7 Effects, etc.] As described above, the multiplexer 1 according to the present embodiment includes the filter 10 having the first pass band and the filter 20 having the second pass band on the higher frequency side than the first pass band. The filters 10 and 20 are connected to the common terminal 100. The filter 10 includes two or more series arm resonators s11 to s14, which include acoustic wave resonators and are arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators p11 to p14, which include acoustic wave resonators and are connected between the series arm path and ground. The resonance bandwidth of at least one of the arm resonators s11 to s14 is larger than the first passband, the series arm resonator s11 (first series arm resonator) is connected closest to the common terminal 100 among the series arm resonators s11 to s14 and the parallel arm resonators p11 to p14, and the anti-resonance frequency fas11 of the series arm resonator s11 is lower than the high frequency end of the second passband and is the lowest among the anti-resonance frequencies fas11 to fas14 of the series arm resonators s11 to s14 that are located on the higher frequency side than the first passband.

[0151] This reduces the overlap between the second passband and the inductive region of the series arm resonator s11, so that the impedance of the second passband when the filters 10 and 20 are viewed from the common terminal 100 can be shifted from the inductive region toward the capacitive region. This makes it possible to position the impedance of the second passband close to the impedance (reference impedance) of the filter 20 that was optimized by itself. This makes it possible to reduce the insertion loss in the second passband of the multiplexer 1.

[0152] Also, for example, in the multiplexer 1, the resonant frequency frs11 of the series arm resonator s11 is higher than the low frequency end of the first passband.

[0153] According to this, in the series arm resonator s11, instead of increasing the electrode finger pitch to shift both the resonance frequency frs11 and the anti-resonance frequency fas11 to the lower frequency side, the resonance bandwidth is reduced to shift only the anti-resonance frequency fas11 to the lower frequency side. This makes it possible to reduce the overlap between the second passband and the inductive region of the series arm resonator s11 without increasing the insertion loss of the filter 10.

[0154] For example, in the multiplexer 1, the series arm resonator s11 includes an acoustic wave resonator 71 and a capacitor 91 connected in parallel to the acoustic wave resonator 71.

[0155] According to this, the anti-resonance frequency fas11 of the series arm resonator s11 can be shifted to a lower frequency side than the anti-resonance frequency fa71 of the elastic wave resonator 71 without shifting the resonant frequency frs11 of the series arm resonator s11 from the resonant frequency fr71 of the elastic wave resonator 71. Therefore, the resonant bandwidth of the series arm resonator s11 can be made smaller than the resonant bandwidth of the elastic wave resonator 71.

[0156] Furthermore, for example, in the multiplexer 1, the elastic wave resonator constituting the series arm resonator s11 has an IDT electrode, and the IDT electrode has a pair of comb-shaped electrodes each composed of a plurality of electrode fingers extending in a direction intersecting the elastic wave propagation direction and arranged parallel to each other, and a bus bar electrode connecting one ends of the plurality of electrode fingers to each other. In this case, an electrode finger among the plurality of electrode fingers that is not connected to any of the bus bar electrodes constituting the pair of comb-shaped electrodes is defined as a floating withdrawal electrode, an electrode finger among the plurality of electrode fingers that is connected to the same bus bar electrode as the bus bar electrodes to which the adjacent electrode fingers are connected is defined as a polarity-inversion thinning electrode, and an electrode finger among the plurality of electrode fingers that has the largest electrode finger width and has an electrode finger width that is twice or more the average electrode finger width of the electrode fingers excluding the largest electrode finger is defined as a solid thinning electrode. In this case, the IDT electrode of the series arm resonator s11 includes any of a floating thinning electrode, a polarity-inversion thinning electrode, and a solid thinning electrode.

[0157] This makes it possible to reduce the resonant bandwidth of the series arm resonator s11 and to lower the anti-resonant frequency fas11.

[0158] Also, for example, in the multiplexer 1, each of the multiple acoustic wave resonators included in the filter 10 has a piezoelectric substrate 50, an IDT electrode arranged on the piezoelectric substrate 50, and a first dielectric film arranged between the piezoelectric substrate 50 and the IDT electrode or on the IDT electrode, and the series arm resonator s11 has the thickest first dielectric film among the series arm resonators s11 to s14.

[0159] This makes it possible to reduce the resonant bandwidth of the series arm resonator s11 and to lower the anti-resonant frequency fas11.

[0160] Moreover, the multiplexer 1 according to the present embodiment includes a filter 10 having a first pass band and a filter 20 having a second pass band on the higher frequency side than the first pass band. The filters 10 and 20 are connected to a common terminal 100. The filter 20 includes two or more series arm resonators s21 to s25, each of which includes an acoustic wave resonator and is arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators p21 to p24, each of which includes an acoustic wave resonator and is connected between the series arm path and ground. The resonance bandwidth of at least one of the resonators s21 to s24 is larger than the second passband, the series arm resonator s21 (second series arm resonator) is connected closest to the common terminal 100 among the series arm resonators s21 to s25 and the parallel arm resonators p21 to p24, and the resonant frequency frs21 of the series arm resonator s21 is higher than the high frequency end of the first passband and is the highest among the resonant frequencies frs21 to frs25 of the series arm resonators s21 to s25 that are located on the higher frequency side than the first passband.

[0161] According to this, the capacitive region where the capacitance of the series arm resonator s21 is small overlaps with the first passband of the filter 10, so that the impedance of the first passband when the filters 10 and 20 are viewed from the common terminal 100 can be shifted from the capacitive region toward the inductive region. This makes it possible to position the impedance of the first passband close to the impedance (reference impedance) of the filter 10 alone that was optimized. Therefore, the insertion loss in the first passband of the multiplexer 1 can be reduced.

[0162] Also, for example, in the multiplexer 1, the parallel arm resonator p21 (first parallel arm resonator) is connected to the series arm resonator s21, and the resonant frequency frp21 of the parallel arm resonator p21 is lower than the high frequency end of the first pass band and is the highest resonant frequency among the resonant frequencies frp21 to frp24 of the parallel arm resonators p21 to p24 that are located on the lower frequency side of the second pass band.

[0163] This can reduce the shift amount of the impedance of the first passband when the filters 10 and 20 are viewed from the common terminal 100 from the impedance (reference impedance) of the first passband optimized for the filter 10 alone. This can further reduce the insertion loss of the first passband of the multiplexer 1.

[0164] Furthermore, for example, in the multiplexer 1, the series arm resonator s21 includes a second acoustic wave resonator and a second capacitive element connected in parallel to the second acoustic wave resonator.

[0165] According to this, by adjusting the electrode finger pitch, the resonant frequency frs21 of the series arm resonator s21 can be shifted to a higher frequency than the resonant frequency of the second acoustic wave resonator.

[0166] For example, in the multiplexer 1, the IDT electrode of the series arm resonator s21 includes any one of a floating withdrawal electrode, a polarity inversion withdrawal electrode, and a fill-in withdrawal electrode.

[0167] This makes it possible to reduce the resonant bandwidth of the series arm resonator s21 and to increase the resonant frequency frs21.

[0168] Also, for example, in the multiplexer 1, each of the multiple acoustic wave resonators included in the filter 20 has a piezoelectric substrate 50, an IDT electrode arranged on the piezoelectric substrate 50, and a second dielectric film arranged between the piezoelectric substrate 50 and the IDT electrode or on the IDT electrode, and the series arm resonator s21 has the thickest second dielectric film among the series arm resonators s21 to s25.

[0169] This makes it possible to reduce the resonant bandwidth of the series arm resonator s21 and to lower the anti-resonant frequency fas21.

[0170] Moreover, the multiplexer 1 according to the present embodiment includes a filter 10 having a first pass band and a filter 20 having a second pass band on the higher frequency side than the first pass band. The filters 10 and 20 are connected to a common terminal 100. The filter 10 has two or more series arm resonators s11 to s14, which include elastic wave resonators and are arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators p11 to p14, which include elastic wave resonators and are connected between the series arm path and ground. The filter 20 has two or more series arm resonators s21 to s25, which include elastic wave resonators and are arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators p11 to p14, which include elastic wave resonators and are connected between the series arm path and ground. Each of the acoustic wave resonators constituting the filters 10 and 20 has an IDT electrode, the electrode finger pitch of the IDT electrode constituting at least one of the series arm resonators s11 to s14 is smaller than the electrode finger pitch of the IDT electrode constituting at least one of the parallel arm resonators p21 to p24, the series arm resonator s11 (first series arm resonator) is connected closest to the common terminal 100 among the series arm resonators s11 to s14 and the parallel arm resonators p11 to p14, and the anti-resonance frequency fas11 of the series arm resonator s11 is lower than the high frequency end of the second pass band and is the lowest among the anti-resonance frequencies fas11 to fas14 of the series arm resonators s11 to s14 that are located on the higher frequency side of the first pass band.

[0171] This reduces the overlap between the second passband and the inductive region of the series arm resonator s11, so that the impedance of the second passband when the filters 10 and 20 are viewed from the common terminal 100 can be shifted from the inductive region toward the capacitive region. This makes it possible to position the impedance of the second passband close to the impedance (reference impedance) of the filter 20 that was optimized by itself. This makes it possible to reduce the insertion loss in the second passband of the multiplexer 1.

[0172] Moreover, the multiplexer 1 according to the present embodiment includes a filter 10 having a first pass band and a filter 20 having a second pass band on the higher frequency side than the first pass band. The filters 10 and 20 are connected to a common terminal 100. The filter 10 has two or more series arm resonators s11 to s14, which include elastic wave resonators and are arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators p11 to p14, which include elastic wave resonators and are connected between the series arm path and ground. The filter 20 has two or more series arm resonators s21 to s25, which include elastic wave resonators and are arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators p11 to p14, which include elastic wave resonators and are connected between the series arm path and ground. The elastic wave resonators constituting the filters 10 and 20 each have an IDT electrode, and the electrode finger pitch of the IDT electrode constituting at least one of the series arm resonators s11 to s14 is smaller than the electrode finger pitch of the IDT electrode constituting at least one of the parallel arm resonators p21 to p24. The series arm resonator s21 (second series arm resonator) is connected closest to the common terminal 100 among the series arm resonators s21 to s25 and the parallel arm resonators p21 to p24, and the electrode finger pitch of the IDT electrode constituting the series arm resonator s21 is the smallest among the electrode finger pitches of the IDT electrodes constituting the series arm resonators s21 to s25.

[0173] According to this, the capacitive region where the capacitance of the series arm resonator s21 is small overlaps with the first passband of the filter 10, so that the impedance of the first passband when the filters 10 and 20 are viewed from the common terminal 100 can be shifted from the capacitive region toward the inductive region. This makes it possible to position the impedance of the first passband close to the impedance (reference impedance) of the filter 10 alone that was optimized. Therefore, the insertion loss in the first passband of the multiplexer 1 can be reduced.

[0174] (Other embodiments) Although the multiplexer according to the present invention has been described above with reference to an embodiment, the present invention is not limited to the above embodiment. The present invention also includes modifications that can be made to the above embodiment without departing from the spirit of the present invention, which may occur to those skilled in the art, and various devices incorporating the multiplexer according to the present invention.

[0175] Furthermore, for example, in the multiplexers according to the above embodiments, matching elements such as inductors and capacitors, and switch circuits may be connected between the respective components.

[0176] The resonant frequency and anti-resonant frequency shown in the above-described embodiments are derived, for example, by contacting an RF probe with two input / output electrodes of an acoustic wave resonator and measuring the reflection characteristics.

[0177] The features of the multiplexer described based on the above embodiment will be described below.

[0178] <1> a first filter having a first passband; a second filter having a second passband that is higher than the first passband; the first filter and the second filter are connected to a common terminal; the first filter includes two or more series arm resonators, each of which includes an elastic wave resonator, arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators, each of which includes an elastic wave resonator and is connected between the series arm path and a ground; a resonance bandwidth of at least one of the two or more series arm resonators of the first filter is larger than the first passband; a first series arm resonator of the two or more series arm resonators of the first filter is connected closest to the common terminal among the two or more series arm resonators and the one or more parallel arm resonators of the first filter; a multiplexer, wherein an anti-resonant frequency of the first series arm resonator is lower than a high frequency end of the second pass band, and is the lowest anti-resonant frequency located on the higher frequency side of the first pass band among the anti-resonant frequencies of the two or more series arm resonators of the first filter.

[0179] <2> the second filter includes two or more series arm resonators, each of which includes an elastic wave resonator, arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators, each of which includes an elastic wave resonator and is connected between the series arm path and a ground; a resonance bandwidth of at least one of the two or more series arm resonators of the second filter is larger than the second passband; a second series arm resonator of the two or more series arm resonators of the second filter is connected closest to the common terminal among the two or more series arm resonators and the one or more parallel arm resonators of the second filter, a resonant frequency of the second series arm resonator is higher than a high frequency end of the first pass band, and is the highest resonant frequency located on the higher frequency side of the first pass band among the resonant frequencies of the two or more series arm resonators of the second filter; <1> 2. A multiplexer according to claim 1 .

[0180] <3> a resonant frequency of the first series arm resonator is higher than a low frequency end of the first passband; <1> or <2> 2. A multiplexer according to claim 1 .

[0181] <4> The first series arm resonator includes: A first acoustic wave resonator; a first capacitive element connected in parallel to the first acoustic wave resonator; <1> ~ <3> 2. A multiplexer according to claim 1 .

[0182] <5> an elastic wave resonator constituting the first series arm resonator has an IDT electrode, the IDT electrode extends in a direction intersecting a propagation direction of an acoustic wave, and includes a pair of comb-shaped electrodes each including a plurality of electrode fingers arranged parallel to each other and a bus bar electrode connecting one ends of the electrode fingers that constitute the plurality of electrode fingers, Among the plurality of electrode fingers, an electrode finger that is not connected to any of the bus bar electrodes constituting the pair of comb-shaped electrodes is defined as a floating withdrawal electrode, Among the plurality of electrode fingers, an electrode finger connected to the same bus bar electrode as adjacent electrode fingers on both sides is defined as a polarity inversion withdrawal electrode, When an electrode finger having a maximum electrode finger width among the plurality of electrode fingers and having an electrode finger width that is twice or more the average electrode finger width of the electrode fingers other than the maximum electrode finger is defined as a fill-in thinning-out electrode, the IDT electrode of the first series arm resonator includes any one of the floating withdrawal electrode, the polarity inversion withdrawal electrode, and the filled thinning electrode. <1> ~ <3> 2. A multiplexer according to claim 1 .

[0183] <6> Each of the plurality of acoustic wave resonators included in the first filter has A piezoelectric substrate; an IDT electrode disposed on the piezoelectric substrate; a first dielectric film disposed between the piezoelectric substrate and the IDT electrode or on the IDT electrode; the first series arm resonator has the first dielectric film that is the thickest among the two or more series arm resonators included in the first filter; <1> ~ <3> 2. A multiplexer according to claim 1 .

[0184] <7> a first filter having a first passband; a second filter having a second passband that is higher than the first passband; the first filter and the second filter are connected to a common terminal; the second filter includes two or more series arm resonators, each of which includes an elastic wave resonator, arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators, each of which includes an elastic wave resonator and is connected between the series arm path and a ground; a resonance bandwidth of at least one of the two or more series arm resonators of the second filter is larger than the second passband; a second series arm resonator of the two or more series arm resonators of the second filter is connected closest to the common terminal among the two or more series arm resonators and the one or more parallel arm resonators of the second filter, a resonant frequency of the second series arm resonator is higher than a high frequency end of the first pass band, and is the highest resonant frequency located on the higher frequency side of the first pass band among the resonant frequencies of the two or more series arm resonators included in the second filter.

[0185] <8> the second filter has the two or more series arm resonators and two or more parallel arm resonators including an acoustic wave resonator connected between the series arm path and a ground, a first parallel arm resonator of the two or more parallel arm resonators of the second filter is connected to the second series arm resonator; a resonant frequency of the first parallel arm resonator is lower than a high frequency end of the first pass band, and is the highest resonant frequency located on the lower frequency side of the second pass band among the resonant frequencies of the two or more parallel arm resonators of the second filter; <7> 2. A multiplexer according to claim 1 .

[0186] <9> The second series arm resonator includes: A second acoustic wave resonator; a second capacitive element connected in parallel to the second acoustic wave resonator, <7> or <8> 2. A multiplexer according to claim 1 .

[0187] <10> an elastic wave resonator constituting the second series arm resonator has an IDT electrode, the IDT electrode extends in a direction intersecting a propagation direction of an acoustic wave, and includes a pair of comb-shaped electrodes each including a plurality of electrode fingers arranged parallel to each other and a bus bar electrode connecting one ends of the electrode fingers that constitute the plurality of electrode fingers, Among the plurality of electrode fingers, an electrode finger that is not connected to any of the bus bar electrodes constituting the pair of comb-shaped electrodes is defined as a floating withdrawal electrode, Among the plurality of electrode fingers, an electrode finger connected to the same bus bar electrode as adjacent electrode fingers on both sides is defined as a polarity inversion withdrawal electrode, When an electrode finger having a maximum electrode finger width among the plurality of electrode fingers and having an electrode finger width that is twice or more the average electrode finger width of the electrode fingers other than the maximum electrode finger is defined as a fill-in thinning-out electrode, the IDT electrode of the second series arm resonator includes any one of the floating withdrawal electrode, the polarity inversion withdrawal electrode, and the filled thinning electrode. <7> or <8> 2. A multiplexer according to claim 1 .

[0188] <11> Each of the plurality of acoustic wave resonators included in the second filter has A piezoelectric substrate; an IDT electrode disposed on the piezoelectric substrate; a second dielectric film disposed between the piezoelectric substrate and the IDT electrode or on the IDT electrode; the second series arm resonator has the second dielectric film that is the thickest among the two or more series arm resonators included in the second filter; <7> or <8> 2. A multiplexer according to claim 1 .

[0189] <12> a first filter having a first passband; a second filter having a second passband that is higher than the first passband; the first filter and the second filter are connected to a common terminal; the first filter includes two or more series arm resonators, each of which includes an elastic wave resonator, arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators, each of which includes an elastic wave resonator and is connected between the series arm path and a ground; the second filter includes two or more series arm resonators, each of which includes an elastic wave resonator, arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators, each of which includes an elastic wave resonator and is connected between the series arm path and a ground; Each of the acoustic wave resonators constituting the first filter and the second filter has an IDT (InterDigital Transducer) electrode, an electrode finger pitch of the IDT electrode constituting at least one of the two or more series arm resonators of the first filter is smaller than an electrode finger pitch of the IDT electrode constituting at least one of the one or more parallel arm resonators of the second filter; a first series arm resonator of the two or more series arm resonators of the first filter is connected closest to the common terminal among the two or more series arm resonators and the one or more parallel arm resonators of the first filter; a multiplexer, wherein an anti-resonant frequency of the first series arm resonator is lower than a high frequency end of the second pass band, and is the lowest anti-resonant frequency located on the higher frequency side of the first pass band among the anti-resonant frequencies of the two or more series arm resonators of the first filter.

[0190] <13> a second series arm resonator of the two or more series arm resonators of the second filter is connected closest to the common terminal among the two or more series arm resonators and the one or more parallel arm resonators of the second filter, an electrode finger pitch of the IDT electrode constituting the second series arm resonator is the smallest among electrode finger pitches of the IDT electrodes constituting the two or more series arm resonators of the second filter; <12> 2. A multiplexer according to claim 1 .

[0191] <14> a first filter having a first passband; a second filter having a second passband that is higher than the first passband; the first filter and the second filter are connected to a common terminal; the first filter includes two or more series arm resonators, each of which includes an elastic wave resonator, arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators, each of which includes an elastic wave resonator and is connected between the series arm path and a ground; the second filter includes two or more series arm resonators, each of which includes an elastic wave resonator, arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators, each of which includes an elastic wave resonator and is connected between the series arm path and a ground; each of the acoustic wave resonators constituting the first filter and the second filter has an IDT electrode; the IDT electrode constituting at least one of the two or more series arm resonators of the first filter has a smaller electrode finger pitch than the IDT electrode constituting at least one of the one or more parallel arm resonators of the second filter; a second series arm resonator of the two or more series arm resonators of the second filter is connected closest to the common terminal among the two or more series arm resonators and the one or more parallel arm resonators of the second filter, a multiplexer, wherein the IDT electrode constituting the second series arm resonator has the smallest electrode finger pitch among the IDT electrodes constituting the two or more series arm resonators of the second filter. [Industrial Applicability]

[0192] The present invention can be widely used in communication devices such as mobile phones as a low-loss multiplexer that can be applied to multi-band frequency standards. [Explanation of symbols]

[0193] 1 Multiplexer 10, 20, 510, 520 Filters 50 Piezoelectric Substrate 51 High-sonic support substrate 52 Low sound velocity membrane 53 Piezoelectric film 54 IDT electrode 55, 58 protective layer 57 Piezoelectric single crystal substrate 60, 71, 72, 73, 74, 75, 80, 81, 82, 83, 84, 111, 211, 311 Elastic wave resonators 60a, 60b, 111a, 111b, 211a, 211b, 311a, 311b comb electrode 61a, 61b, 151a, 151b, 152, 251a, 251b, 252, 351a, 351b, 352 Electrode finger 62a, 62b, 161a, 161b, 261a, 261b, 361a, 361b Busbar electrodes 65 Support substrate 66 Lower electrode 67 Piezoelectric layer 68 Upper electrode 91 Capacitor 100 Common terminal 101 Input terminal 102 Output terminal 141, 241, 341 reflector p11, p12, p13, p14, p21, p22, p23, p24 Parallel arm resonators s11, s12, s13, s14, s21, s22, s23, s24, s25 Series arm resonators

Claims

1. a first filter having a first passband; a second filter having a second passband that is higher in frequency than the first passband, the first filter and the second filter are connected to a common terminal; the first filter includes two or more series arm resonators, each of which includes an elastic wave resonator, disposed in a series arm path connecting an input end and an output end, and one or more parallel arm resonators, each of which includes an elastic wave resonator and is connected between the series arm path and a ground; a resonance bandwidth of at least one of the two or more series arm resonators of the first filter is larger than the first passband; a first series arm resonator of the two or more series arm resonators included in the first filter is connected closest to the common terminal among the two or more series arm resonators and the one or more parallel arm resonators included in the first filter; an anti-resonance frequency of the first series arm resonator is lower than a high frequency end of the second pass band, and is the lowest anti-resonance frequency located on a higher frequency side than the first pass band among the anti-resonance frequencies of the two or more series arm resonators included in the first filter; Multiplexer.

2. the second filter includes two or more series arm resonators, each of which includes an elastic wave resonator and is arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators, each of which includes an elastic wave resonator and is connected between the series arm path and a ground; a resonance bandwidth of at least one of the two or more series arm resonators of the second filter is larger than the second passband; a second series arm resonator of the two or more series arm resonators of the second filter is connected closest to the common terminal among the two or more series arm resonators and the one or more parallel arm resonators of the second filter, a resonant frequency of the second series arm resonator is higher than a high frequency end of the first pass band, and is the highest resonant frequency located on a higher frequency side than the first pass band among the resonant frequencies of the two or more series arm resonators included in the second filter; 2. The multiplexer of claim 1.

3. a resonant frequency of the first series arm resonator is higher than a low frequency end of the first passband; 3. A multiplexer according to claim 1 or 2.

4. The first series arm resonator is A first acoustic wave resonator; a first capacitance element connected in parallel to the first acoustic wave resonator, 3. A multiplexer according to claim 1 or 2.

5. an elastic wave resonator constituting the first series arm resonator has an IDT electrode, the IDT electrode extends in a direction intersecting a propagation direction of an acoustic wave, and includes a pair of comb-shaped electrodes each including a plurality of electrode fingers arranged parallel to each other and a bus bar electrode connecting one ends of the electrode fingers constituting the plurality of electrode fingers, Among the plurality of electrode fingers, an electrode finger that is not connected to any of the bus bar electrodes constituting the pair of comb-shaped electrodes is defined as a floating withdrawal electrode, Among the plurality of electrode fingers, an electrode finger connected to the same bus bar electrode as adjacent electrode fingers on both sides is defined as a polarity inversion withdrawal electrode, When an electrode finger having a maximum electrode finger width among the plurality of electrode fingers and having an electrode finger width that is at least twice the average electrode finger width of the electrode fingers other than the maximum electrode finger is defined as a fill-in thinning-out electrode, the IDT electrode of the first series arm resonator includes any one of the floating withdrawal electrode, the polarity inversion withdrawal electrode, and the filled thinning electrode.

3. A multiplexer according to claim 1 or 2.

6. Each of the plurality of acoustic wave resonators included in the first filter has A piezoelectric substrate; an IDT electrode disposed on the piezoelectric substrate; a first dielectric film disposed between the piezoelectric substrate and the IDT electrode or on the IDT electrode; the first series arm resonator has the first dielectric film that is the thickest among the two or more series arm resonators included in the first filter; 3. A multiplexer according to claim 1 or 2.

7. a first filter having a first passband; a second filter having a second passband that is higher in frequency than the first passband, the first filter and the second filter are connected to a common terminal; the second filter includes two or more series arm resonators, each of which includes an elastic wave resonator and is arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators, each of which includes an elastic wave resonator and is connected between the series arm path and a ground; a resonance bandwidth of at least one of the two or more series arm resonators of the second filter is larger than the second passband; a second series arm resonator of the two or more series arm resonators of the second filter is connected closest to the common terminal among the two or more series arm resonators and the one or more parallel arm resonators of the second filter, a resonant frequency of the second series arm resonator is higher than a high frequency end of the first pass band, and is the highest resonant frequency located on a higher frequency side than the first pass band among the resonant frequencies of the two or more series arm resonators included in the second filter; Multiplexer.

8. the second filter has the two or more series arm resonators and two or more parallel arm resonators including an acoustic wave resonator and connected between the series arm path and a ground, a first parallel arm resonator of the two or more parallel arm resonators included in the second filter is connected to the second series arm resonator; a resonant frequency of the first parallel arm resonator is lower than a high frequency end of the first pass band, and is the highest resonant frequency located on the lower frequency side of the second pass band among the resonant frequencies of the two or more parallel arm resonators of the second filter; 8. The multiplexer of claim 7.

9. The second series arm resonator is A second acoustic wave resonator; a second capacitive element connected in parallel to the second acoustic wave resonator, 9. A multiplexer according to claim 7 or 8.

10. an elastic wave resonator constituting the second series arm resonator has an IDT electrode, the IDT electrode extends in a direction intersecting a propagation direction of an acoustic wave, and includes a pair of comb-shaped electrodes each including a plurality of electrode fingers arranged parallel to each other and a bus bar electrode connecting one ends of the electrode fingers constituting the plurality of electrode fingers, Among the plurality of electrode fingers, an electrode finger that is not connected to any of the bus bar electrodes constituting the pair of comb-shaped electrodes is defined as a floating withdrawal electrode, Among the plurality of electrode fingers, an electrode finger connected to the same bus bar electrode as adjacent electrode fingers on both sides is defined as a polarity inversion withdrawal electrode, When an electrode finger having a maximum electrode finger width among the plurality of electrode fingers and having an electrode finger width that is at least twice the average electrode finger width of the electrode fingers other than the maximum electrode finger is defined as a fill-in thinning-out electrode, the IDT electrode of the second series arm resonator includes any one of the floating withdrawal electrode, the polarity inversion withdrawal electrode, and the filled thinning electrode.

9. A multiplexer according to claim 7 or 8.

11. Each of the plurality of acoustic wave resonators included in the second filter has A piezoelectric substrate; an IDT electrode disposed on the piezoelectric substrate; a second dielectric film disposed between the piezoelectric substrate and the IDT electrode or on the IDT electrode; the second series arm resonator has a second dielectric film that is thickest among the two or more series arm resonators included in the second filter; 9. A multiplexer according to claim 7 or 8.

12. a first filter having a first passband; a second filter having a second passband that is higher in frequency than the first passband, the first filter and the second filter are connected to a common terminal; the first filter includes two or more series arm resonators, each of which includes an elastic wave resonator, disposed in a series arm path connecting an input end and an output end, and one or more parallel arm resonators, each of which includes an elastic wave resonator and is connected between the series arm path and a ground; the second filter includes two or more series arm resonators, each of which includes an elastic wave resonator and is arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators, each of which includes an elastic wave resonator and is connected between the series arm path and a ground; Each of the acoustic wave resonators constituting the first filter and the second filter has an IDT (InterDigital Transducer) electrode, an electrode finger pitch of the IDT electrode constituting at least one of the two or more series arm resonators of the first filter is smaller than an electrode finger pitch of the IDT electrode constituting at least one of the one or more parallel arm resonators of the second filter; a first series arm resonator of the two or more series arm resonators included in the first filter is connected closest to the common terminal among the two or more series arm resonators and the one or more parallel arm resonators included in the first filter; an anti-resonance frequency of the first series arm resonator is lower than a high frequency end of the second pass band, and is the lowest anti-resonance frequency located on a higher frequency side than the first pass band among the anti-resonance frequencies of the two or more series arm resonators included in the first filter; Multiplexer.

13. a second series arm resonator of the two or more series arm resonators of the second filter is connected closest to the common terminal among the two or more series arm resonators and the one or more parallel arm resonators of the second filter, an electrode finger pitch of the IDT electrode constituting the second series arm resonator is smallest among electrode finger pitches of the IDT electrodes constituting the two or more series arm resonators of the second filter; 13. The multiplexer of claim 12.

14. a first filter having a first passband; a second filter having a second passband that is higher in frequency than the first passband, the first filter and the second filter are connected to a common terminal; the first filter includes two or more series arm resonators, each of which includes an elastic wave resonator, disposed in a series arm path connecting an input end and an output end, and one or more parallel arm resonators, each of which includes an elastic wave resonator and is connected between the series arm path and a ground; the second filter includes two or more series arm resonators, each of which includes an elastic wave resonator and is arranged in a series arm path connecting an input end and an output end, and one or more parallel arm resonators, each of which includes an elastic wave resonator and is connected between the series arm path and a ground; each of the acoustic wave resonators constituting the first filter and the second filter has an IDT electrode; the IDT electrode constituting at least one of the two or more series arm resonators of the first filter has a smaller electrode finger pitch than the IDT electrode constituting at least one of the one or more parallel arm resonators of the second filter; a second series arm resonator of the two or more series arm resonators of the second filter is connected closest to the common terminal among the two or more series arm resonators and the one or more parallel arm resonators of the second filter, the IDT electrode constituting the second series arm resonator has a smallest electrode finger pitch among the IDT electrodes constituting the two or more series arm resonators of the second filter; Multiplexer.

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