Multiplexer

Abstract

Provided is a multiplexer (1) in which the insertion loss in the passband of a common-connected filter is reduced, the multiplexer (1) being provided with: a filter (10) having a first passband; and a filter (20) having a second passband closer to the higher frequency side than the first passband, the filter (10) having series arm resonators (s11-s14) and parallel arm resonators (p11-p14), the resonance frequency band width of at least one of the series arm resonators (s11-s14) being larger than that of the first passband, the series arm resonator (s11) being connected closest to the common terminal (100) among the series arm resonators (s11-s14) and the parallel arm resonators (p11-p14), and the series arm resonator (s11) being connected closest to the common terminal (100) among the series arm resonators (s11-s14) and the parallel arm resonators (p11-p14). The anti-resonance frequency (fast 11) 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 (fast 11 to fast 14) of the series arm resonators (s11 to s14).

Description

Technical Field

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

[0002] Patent Document 1 discloses a multiplexer in which a first filter and a second filter each including a surface acoustic wave resonator are connected to a common terminal. Specifically, the multiplexer is formed using a surface acoustic wave resonator having a wide resonance bandwidth (e.g., 45 MHz) with respect to the bandwidths 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).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: WO 2019 / 188007

[0006] However, when the first filter is formed using a surface acoustic wave resonator having a wide resonance bandwidth with respect to the passband width and the gap between the passbands, the impedance in the passband of the second filter may be affected by the impedance of the surface acoustic wave resonator and may deviate easily from the reference impedance, resulting in an increase in the insertion loss of the multiplexer. Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] Accordingly, the present invention has been made to solve the above problems, and an object thereof is to provide a multiplexer with reduced insertion loss in the passband of filters commonly connected.

[0009] Means for Solving the Problems

[0010] To achieve the above object, 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 high-frequency side of 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 including surface acoustic wave resonators and disposed in a series-arm path connecting an input terminal and an output terminal; and one or more shunt-arm resonators including surface acoustic wave resonators and connected between the series-arm path and ground. The resonance bandwidth of at least one of the two or more series-arm resonators of the first filter is greater than the first passband. Among the two or more series-arm resonators and the one or more shunt-arm resonators of the first filter, the first series-arm resonator among the two or more series-arm resonators of the first filter is connected closest to the common terminal. The 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 on the high-frequency side of the first passband.

[0011] In addition, 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 high-frequency side of 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 including surface acoustic wave resonators and disposed in a series-arm path connecting an input terminal and an output terminal; and one or more shunt-arm resonators including surface acoustic wave resonators and connected between the series-arm path and ground. The resonance bandwidth of at least one of the two or more series-arm resonators of the second filter is greater than the second passband. Among the two or more series-arm resonators and the one or more shunt-arm resonators of the second filter, the second series-arm resonator among the two or more series-arm resonators of the second filter is connected closest to the common terminal. The resonance frequency of the second series-arm resonator is higher than the high-frequency end of the first passband and is the highest among the resonance frequencies of the two or more series-arm resonators of the second filter that are on the high-frequency side of the first passband.

[0012] In addition, 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 are connected to a common terminal. The first filter includes: two or more series-arm resonators including surface acoustic wave resonators and disposed in a series-arm path connecting an input terminal and an output terminal; and one or more shunt-arm resonators including surface acoustic wave resonators and connected between the series-arm path and ground. The second filter includes: two or more series-arm resonators including surface acoustic wave resonators and disposed in a series-arm path connecting an input terminal and an output terminal; and one or more shunt-arm resonators including surface acoustic wave resonators and connected between the series-arm path and ground. The surface acoustic wave resonators constituting the first filter and the second filter each have an IDT (InterDigital Transducer) electrode. The 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 the electrode finger pitch of the IDT electrode constituting at least one of the one or more shunt-arm resonators of the second filter. Among the two or more series-arm resonators and the one or more shunt-arm resonators of the first filter, the first series-arm resonator among the two or more series-arm resonators of the first filter is connected closest to the common terminal. The anti-resonant 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-resonant frequencies of the two or more series-arm resonators of the first filter that are on the higher-frequency side than the first passband.

[0013] In addition, 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 high-frequency side of 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 including surface acoustic wave (SAW) resonators and disposed in a series-arm path connecting an input terminal and an output terminal; and one or more shunt-arm resonators including SAW resonators and connected between the series-arm path and ground. The second filter includes: two or more series-arm resonators including SAW resonators and disposed in a series-arm path connecting an input terminal and an output terminal; and one or more shunt-arm resonators including SAW resonators and connected between the series-arm path and ground. The SAW resonators constituting the first filter and the second filter each have an interdigital transducer (IDT) electrode. The IDT electrode of 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 of at least one of the one or more shunt-arm resonators of the second filter. Among the two or more series-arm resonators and the one or more shunt-arm resonators of the second filter, the 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 IDT electrodes of the two or more series-arm resonators of the second filter, the IDT electrode of the second series-arm resonator has the smallest electrode finger pitch.

[0014] Advantages of the Invention

[0015] According to the present invention, it is possible to provide a multiplexer with reduced insertion loss in the passband of filters connected in common. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a circuit configuration diagram of the multiplexer according to the embodiment.

[0017] Figure 2A is a top view and a cross-sectional view schematically showing a first example of the SAW resonator constituting the multiplexer according to the embodiment.

[0018] Figure 2B is a cross-sectional view schematically showing a second example of the SAW resonator constituting the multiplexer according to the embodiment.

[0019] Figure 2C is a cross-sectional view schematically showing a third example of the SAW resonator constituting the multiplexer according to the embodiment.

[0020] Figure 3 is a graph showing the pass characteristics of the multiplexer according to the embodiment and the impedance characteristics of the series-arm resonator of the first filter.

[0021] Figure 4A It is a graph showing the pass characteristics of the second filter in the multiplexer related to the embodiment and the comparative example.

[0022] Figure 4B It is an admittance circle diagram showing the impedance of the second passband when observing the multiplexer related to the embodiment and the comparative example from the common terminal.

[0023] Figure 5 It is a graph showing the impedance characteristics and susceptance characteristics of the first series arm resonator related to the embodiment and the comparative example.

[0024] Figure 6A It is a schematic top view showing the structure of the IDT electrode including the floating gap removal electrode.

[0025] Figure 6B It is a schematic top view showing the structure of the IDT electrode including the polarity inversion gap removal electrode.

[0026] Figure 6C It is a schematic top view showing the structure of the IDT electrode including the filled gap removal electrode.

[0027] Figure 7 It is a graph showing the pass characteristics of the multiplexer related to the embodiment and the impedance characteristics of the series arm resonator of the second filter.

[0028] Figure 8A It is a graph showing the pass characteristics of the first filter in the multiplexer related to the embodiment and the comparative example.

[0029] Figure 8B It is an admittance circle diagram showing the impedance of the first passband when observing the multiplexer related to the embodiment and the comparative example from the common terminal.

[0030] Figure 9 It is a graph showing the impedance characteristics and susceptance characteristics of the second series arm resonator related to the embodiment and the comparative example.

[0031] Figure 10 It is a graph showing the pass characteristics of the multiplexer related to the embodiment and the impedance characteristics of the parallel arm resonator of the second filter.

[0032] Description of Reference Numerals

[0033] 1: Multiplexer;

[0034] 10, 20, 510, 520: Filter;

[0035] 50: Piezoelectric substrate;

[0036] 51: High acoustic velocity supporting substrate;

[0037] 52: Low sound velocity film;

[0038] 53: Piezoelectric film;

[0039] 54: IDT electrode;

[0040] 55, 58: Protective layer;

[0041] 57: Piezoelectric single crystal substrate;

[0042] 60, 71, 72, 73, 74, 75, 80, 81, 82, 83, 84, 111, 211, 311: Elastic wave resonator;

[0043] 60a, 60b, 111a, 111b, 211a, 211b, 311a, 311b: Comb-shaped electrode;

[0044] 61a, 61b, 151a, 151b, 152, 251a, 251b, 252, 351a, 351b, 352: Electrode finger;

[0045] 62a, 62b, 161a, 161b, 261a, 261b, 361a, 361b: Bus bar electrode;

[0046] 65: Support substrate;

[0047] 66: Lower electrode;

[0048] 67: Piezoelectric layer;

[0049] 68: Upper electrode;

[0050] 91: Capacitor;

[0051] 100: Common terminal;

[0052] 101: Input terminal;

[0053] 102: Output terminal;

[0054] 141, 241, 341: Reflector;

[0055] p11, p12, p13, p14, p21, p22, p23, p24: Parallel arm resonator;

[0056] s11, s12, s13, s14, s21, s22, s23, s24, s25: Series arm resonator. Detailed implementation manner

[0057] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In addition, all the embodiments described below show general or specific examples. The numerical values, shapes, materials, constituent elements, arrangements of the constituent elements, connection manners, etc. shown in the following embodiments are examples, and the gist thereof is not to limit the present invention. Among the constituent elements in the following embodiments, the constituent elements not recited in the independent claims are described as optional constituent elements. In addition, the sizes or size ratios of the constituent elements shown in the drawings are not necessarily precise.

[0058] In addition, each drawing is a schematic diagram appropriately emphasized, omitted, or adjusted in ratio for showing the present invention, and is not necessarily drawn precisely, and sometimes differs from the actual shape, positional relationship, and ratio. In each drawing, the same reference numerals are given to substantially the same structures, and the repeated descriptions may be omitted or simplified.

[0059] In the circuit structure of the present disclosure, the term "connection" includes not only the case of directly connecting through connection terminals and / or wiring conductors, but also the case of electrically connecting via matching elements such as inductors and capacitors, and switch circuits. The phrase "connected between A and B" means connected to both A and B between A and B.

[0060] In addition, terms indicating the relationality between elements such as "parallel" and "perpendicular", terms indicating the shape of elements such as "rectangle", and numerical ranges do not only represent strict meanings, but mean substantially equivalent ranges, for example, also include an error of about several percent.

[0061] In addition, in the following embodiments, the passband of the filter is defined as the frequency band between two frequencies that are 3 dB greater than the minimum value of the insertion loss within the passband.

[0062] In addition, in the embodiments of the present disclosure, the resonance bandwidth means the frequency difference between the anti-resonance frequency and the resonance frequency of the surface acoustic wave resonator.

[0063] In addition, in the present disclosure, frequency band A means a frequency band predefined for a communication system constructed using a radio access technology (RAT) by a standardization organization or the like (e.g., 3GPP (registered trademark), IEEE (Institute of Electrical and Electronics Engineers), etc.). In the present embodiment, as the communication system, for example, an LTE (Long Term Evolution) system, a 5G (5th Generation)-NR (New Radio) system, a WLAN (Wireless Local Area Network) system, etc. can be used, but it is not limited to these.

[0064] In addition, the uplink operating frequency band of frequency band A means the frequency range designated for uplink use in frequency band A. In addition, the downlink operating frequency band of frequency band A means the frequency range designated for downlink use in frequency band A.

[0065] (Embodiment)

[0066] [1. Circuit Structure of Multiplexer 1]

[0067] Figure 1 It is a circuit structure diagram of multiplexer 1 according to the embodiment. As shown in the figure, multiplexer 1 includes filters 10 and 20, a common terminal 100, and input terminals 101 and output terminals 102.

[0068] The common terminal 100 is connected to an antenna, for example.

[0069] Filter 10 is an example of a first filter and has a first passband including the uplink operating frequency band of frequency band A. The output terminal of filter 10 is connected to the common terminal 100, and the input terminal is connected to the input terminal 101. Filter 10 includes a plurality of surface acoustic wave resonators.

[0070] Filter 20 is an example of a second filter and has a second passband including the downlink operating frequency band of frequency band A. The input terminal of filter 20 is connected to the common terminal 100, and the output terminal is connected to the output terminal 102. That is, filters 10 and 20 are commonly connected. Filter 20 includes a plurality of surface acoustic wave resonators. In the present embodiment, the second passband of filter 20 is located on the higher frequency side than the first passband of filter 10.

[0071] As the frequency band A, for example, Band30 of LTE can be applied (uplink operating frequency band: 2305 to 2315 MHz, downlink operating frequency band: 2350 to 2360 MHz).

[0072] In addition, as long as the second passband of the filter 20 is located on the higher frequency side than the first passband of the filter 10, the passbands of the filters 10 and 20 may not be passbands that respectively include the uplink operating frequency band and the downlink operating frequency band of the same frequency band. For example, it may also be that the second passband of the filter 20 includes the frequency band B, and the first passband of the filter 10 includes the frequency band C on the lower frequency side than the frequency band B.

[0073] In addition, in the multiplexer 1 according to the present embodiment, filters other than the filters 10 and 20 may be connected to the common terminal 100. Further, 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.

[0074] In addition, the multiplexer 1 may not include the common terminal 100, the input terminal 101, and the output terminal 102.

[0075] [2. Circuit structures of the filters 10 and 20]

[0076] Next, the circuit structures of the filters 10 and 20 that constitute the multiplexer 1 will be illustrated.

[0077] As Figure 1 shown, the filter 10 includes series arm resonators s11, s12, s13, and s14 and shunt arm resonators p11, p12, p13, and p14.

[0078] The series arm resonators s11 to s14 are arranged on a series arm path that connects the output end and the input end of the filter 10 (connects the common terminal 100 and the input terminal 101). In addition, the shunt arm resonators p11 to p14 are respectively connected between each connection point (points on the series arm path) of the series arm resonators s11 to s14 and the input terminal 101 and the ground. With the above connection structure, the filter 10 constitutes a ladder-type band-pass filter.

[0079] The series-arm resonator s11 is an example of the 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 that the filter 10 has. The series-arm resonator s11 has an elastic-wave resonator 71 (first elastic-wave resonator) and a capacitor 91 (first capacitive element) connected in parallel with the elastic-wave resonator 71. The capacitor 91 is an example of a so-called bridging capacitor, which does not shift the resonance frequency frs11 of the series-arm resonator s11 from the resonance frequency fr71 of the elastic-wave resonator 71 and shifts the anti-resonance frequency fas11 of the series-arm resonator s11 to the lower-frequency side compared to the anti-resonance frequency fa71 of the elastic-wave resonator 71. That is, by connecting the capacitor 91 in parallel with the elastic-wave resonator 71, the resonance bandwidth of the series-arm resonator s11 becomes smaller than the resonance bandwidth (anti-resonance frequency - resonance frequency) of the elastic-wave resonator 71.

[0080] In addition, in the present embodiment, the series-arm resonator and the parallel-arm resonator are each defined as a resonator including an elastic-wave resonator and means for adjusting the resonance bandwidth of the elastic-wave resonator. For example, the series-arm resonator and the parallel-arm resonator each include an elastic-wave resonator and a capacitive element (bridging capacitor) connected in parallel with the elastic-wave resonator. In addition, as means for adjusting the resonance bandwidth, in addition to the bridging capacitor, examples include adjusting the film thickness of the dielectric film of the IDT electrode attached to the elastic-wave resonator and a process of removing the interval of the IDT electrode of the elastic-wave resonator.

[0081] The series-arm resonator s12 includes an elastic-wave resonator and is connected between the series-arm resonator s11 and the series-arm resonator s13. The series-arm resonator s13 includes elastic-wave resonators 72 and 73 connected in parallel with each other and is connected between the series-arm resonator s12 and the 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.

[0082] 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 the ground. The parallel-arm resonator p12 includes elastic-wave resonators 74 and 75 connected in series with each other and is connected between the connection point of the series-arm resonators s12 and s13 and the 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 the ground. The parallel-arm resonator p14 includes an elastic-wave resonator and is connected between the connection point of the series-arm resonators s14 and the input terminal 101 and the ground.

[0083] In addition, the filter 10 only needs to have two or more series-arm resonators including the series-arm resonator s11 and one or more shunt-arm resonators including the shunt-arm resonator p11. Further, in the case where the filter 20 has two or more series-arm resonators including the series-arm resonator s21 and one or more shunt-arm resonators, the filter 10 may not include a surface acoustic wave resonator. For example, it may be an LC filter including an inductor and a capacitor.

[0084] As Figure 1 shown, the filter 20 includes series-arm resonators s21, s22, s23, s24, and s25 and shunt-arm resonators p21, p22, p23, and p24.

[0085] The series-arm resonators s21 to s25 are arranged on a series-arm path connecting the input terminal and the output terminal of the filter 20 (connecting the common terminal 100 and the output terminal 102). Further, the shunt-arm resonators p21 to p24 are respectively 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 the ground. With the above connection structure, the filter 20 constitutes a ladder-type band-pass filter.

[0086] The series-arm resonator s21 is an example of the second series-arm resonator, includes a surface acoustic wave resonator, and is connected closest to the common terminal 100 among the series-arm resonators s21 to s25 and the shunt-arm resonators p21 to p24 included in the filter 20.

[0087] The series-arm resonator s22 includes a surface acoustic wave resonator and is connected between the series-arm resonator s21 and the series-arm resonator s23. The series-arm resonator s23 includes a surface acoustic wave resonator and is connected between the series-arm resonator s22 and the series-arm resonator s24. The series-arm resonator s24 includes surface acoustic wave resonators 81 and 82 connected in parallel with each other and is connected between the series-arm resonator s23 and the series-arm resonator s25. The series-arm resonator s25 includes a surface acoustic wave resonator and is connected between the series-arm resonator s24 and the output terminal 102.

[0088] The shunt-arm resonator p21 is an example of the first shunt-arm resonator, includes a surface acoustic wave resonator, and is connected between the connection point of the series-arm resonators s21 and s22 and the ground. The shunt-arm resonator p22 includes a surface acoustic wave resonator and is connected between the connection point of the series-arm resonators s22 and s23 and the ground. The shunt-arm resonator p23 includes surface acoustic 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 the ground. The shunt-arm resonator p24 includes a surface acoustic wave resonator and is connected between the connection point of the series-arm resonators s24 and s25 and the ground.

[0089] In addition, the filter 20 only needs to have two or more series-arm resonators including the series-arm resonator s21 and one or more shunt-arm resonators. Further, when the filter 10 has two or more series-arm resonators including the series-arm resonator s11 and one or more shunt-arm resonators including the shunt-arm resonator p11, the filter 20 may not include a surface acoustic wave resonator. For example, it may be an LC filter including an inductor and a capacitor.

[0090] [3. Structure of Surface Acoustic Wave Resonator]

[0091] Next, the structures of the surface acoustic wave resonators included in the filters 10 and 20 constituting the multiplexer 1 will be illustrated.

[0092] Figure 2A FIGS. are a top view and a cross-sectional view schematically showing a first example of the surface acoustic wave resonator constituting the multiplexer 1 according to the embodiment. In the figure, the basic structures of the plurality of surface acoustic wave resonators constituting the filters 10 and 20 are illustrated. In addition, Figure 2A the surface acoustic wave resonator 60 shown is used to explain a typical structure of the surface acoustic wave resonators constituting the filters 10 and 20, and the number and length of electrode fingers constituting the electrodes are not limited thereto.

[0093] The surface acoustic wave resonator 60 includes a piezoelectric substrate 50 and comb-shaped electrodes 60a and 60b.

[0094] As shown in (a) of Figure 2A , a pair of comb-shaped electrodes 60a and 60b facing each other are formed on the piezoelectric substrate 50. The comb-shaped electrode 60a includes a plurality of electrode fingers 61a parallel to each other and a bus-bar electrode 62a connecting the plurality of electrode fingers 61a. In addition, the comb-shaped electrode 60b includes a plurality of electrode fingers 61b parallel to each other and a bus-bar electrode 62b connecting the plurality of electrode fingers 61b. The plurality of electrode fingers 61a and 61b are formed along a direction orthogonal to the surface acoustic wave propagation direction (X-axis direction).

[0095] In addition, as shown in (b) of Figure 2A , the IDT electrode 54 including the plurality of electrode fingers 61a and 61b and the bus-bar electrodes 62a and 62b has a laminated structure of a close contact layer 540 and a main electrode layer 542.

[0096] The adhesion layer 540 is a layer for improving the adhesion between the piezoelectric substrate 50 and the main electrode layer 542. As a material, for example, Ti can be used. Regarding the main electrode layer 542, as a material, for example, Al containing 1% of Cu can be used. The protective layer 55 is formed to cover the comb-shaped electrodes 60a and 60b. The protective layer 55 is a layer for protecting the main electrode layer 542 from the external environment, adjusting the frequency-temperature characteristics, and improving the moisture resistance, etc. For example, it is a dielectric film mainly composed of silicon dioxide.

[0097] In addition, 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 may not have the above-mentioned laminated structure. The IDT electrode 54 may, for example, also contain metals or alloys such as Ti, Al, Cu, Pt, Au, Ag, Pd, etc., and in addition, may also be composed of a plurality of laminates containing the above-mentioned metals or alloys. In addition, the protective layer 55 may not be formed.

[0098] Next, the laminated structure of the piezoelectric substrate 50 will be described.

[0099] As Figure 2A shown in (c) of, the piezoelectric substrate 50 includes a high acoustic velocity supporting substrate 51, a low acoustic velocity film 52, and a piezoelectric film 53, and has a structure in which the high acoustic velocity supporting substrate 51, the low acoustic velocity film 52, and the piezoelectric film 53 are laminated in sequence.

[0100] The piezoelectric film 53 contains, for example, a θ° Y-cut X-propagating LiTaO 3 piezoelectric single crystal or piezoelectric ceramic (a lithium tantalate single crystal or ceramic cut at a plane with an axis rotated by θ° from the Y-axis with the X-axis as the central axis as the normal, and a single crystal or ceramic in which surface acoustic waves propagate in the X-axis direction). In addition, the material and the cut angle θ of the piezoelectric single crystal used as the piezoelectric film 53 can be appropriately selected according to the required specifications of each filter.

[0101] The high acoustic velocity supporting substrate 51 is a substrate that supports the low acoustic velocity film 52, the piezoelectric film 53, and the IDT electrode 54. Furthermore, the high acoustic velocity supporting substrate 51 is a substrate in which the acoustic velocity of the bulk wave in the high acoustic velocity supporting substrate 51 is higher than that of the elastic waves such as surface waves and boundary waves propagating in the piezoelectric film 53, and the high acoustic velocity supporting substrate 51 functions to confine the surface acoustic wave in the portion where the piezoelectric film 53 and the low acoustic velocity film 52 are laminated and prevent it from leaking below the high acoustic velocity supporting substrate 51. As the material of the high acoustic velocity supporting substrate 51, for example, piezoelectric materials such as aluminum nitride, lithium tantalate, lithium niobate, and quartz, ceramics such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, spinel, and sialon, dielectrics such as aluminum oxide, silicon oxynitride, DLC (diamond-like carbon), and diamond, or semiconductors such as silicon, or materials mainly composed of the above materials can be used. In addition, the above spinel contains an aluminum compound containing one or more elements selected from Mg, Fe, Zn, Mn, etc. and oxygen. As an example of the above spinel, MgAl 2 O 4 、FeAl 2 O 4 、ZnAl 2 O 4 、MnAl 2 O 4 can be cited.

[0102] The low acoustic velocity film 52 is a film in which the acoustic velocity of the bulk wave in the low acoustic velocity film 52 is lower than that of the bulk wave propagating in the piezoelectric film 53, and the low acoustic velocity film 52 is disposed between the piezoelectric film 53 and the high acoustic velocity supporting substrate 51. According to this structure and the property that the energy of the elastic wave is essentially concentrated in the medium with low acoustic velocity, the leakage of the surface acoustic wave energy outside the piezoelectric film 53 can be suppressed. As the material of the low acoustic velocity film 52, for example, dielectrics such as glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum oxide, or a compound obtained by adding fluorine, carbon, or boron to silicon oxide, or materials mainly composed of the above materials can be used.

[0103] In addition, according to the above laminated structure of the piezoelectric substrate 50, compared with the conventional structure using a single-layer piezoelectric substrate, the Q values at the resonance frequency and the anti-resonance frequency can be significantly increased. That is, an elastic wave resonator with a high Q value can be formed, and therefore a filter with a small insertion loss can be formed using this elastic wave resonator.

[0104] In addition, the high acoustic velocity support substrate 51 may also have a structure in which a support substrate and a high acoustic velocity film are laminated, and the acoustic velocity of the bulk wave propagated by the high acoustic velocity film is higher than that of elastic waves such as surface waves and boundary waves propagated in the piezoelectric film 53. In this case, as the material of the high acoustic velocity film, the same material as that of the high acoustic velocity support substrate 51 can be used. In addition, as the material of the support substrate, for example, piezoelectric materials such as aluminum nitride, lithium tantalate, lithium niobate, and quartz, ceramics such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, and forsterite, dielectrics such as diamond and glass, semiconductors such as silicon and gallium nitride, or resins, or materials mainly composed of the above materials can be used.

[0105] In addition, in this specification, the so-called "main component of the material" refers to a component whose proportion in the material exceeds 50% by weight. The above main components can exist in any state of single crystal, polycrystal, and amorphous, or in a state where they are mixed.

[0106] Figure 2B is a cross-sectional view schematically showing a second example of the elastic wave resonator constituting the multiplexer 1 according to the embodiment. In Figure 2A the shown elastic wave resonator 60, an example is shown in which the IDT electrode 54 is formed on the piezoelectric substrate 50 having the piezoelectric film 53. However, as Figure 2B shown, the substrate on which the IDT electrode 54 is formed may also be a piezoelectric single crystal substrate 57 including a single-layer piezoelectric body layer.

[0107] The piezoelectric single crystal substrate 57 is composed of a piezoelectric single crystal of LiNbO 3 for example. The elastic wave resonator according to this example includes a piezoelectric single crystal substrate 57 of LiNbO 3 the IDT electrode 54, and a protective layer 58 formed on the piezoelectric single crystal substrate 57 and the IDT electrode 54.

[0108] The above piezoelectric film 53 and piezoelectric single crystal substrate 57 can also be appropriately changed in the lamination structure, material, cutting angle, and thickness according to the requirements such as characteristics of the elastic wave filter device. Even an elastic wave resonator using a LiTaO 3 piezoelectric substrate with a cutting angle other than the above cutting angle can achieve the same effect as the elastic wave resonator 60 using the above piezoelectric film 53.

[0109] In addition, the substrate on which the IDT electrode 54 is formed may also have a structure in which a support substrate, an energy confinement layer, and a piezoelectric film are laminated in sequence. The IDT electrode 54 is formed on the piezoelectric film. Regarding the piezoelectric film, for example, LiTaO 3A piezoelectric single crystal or a piezoelectric ceramic. The support substrate is a substrate that supports the piezoelectric film, the energy confinement layer, and the IDT electrode 54.

[0110] The energy confinement layer includes one or more layers, and the velocity of the bulk acoustic wave propagating in at least one of them is greater than the velocity of the elastic wave propagating near the piezoelectric film. For example, the energy confinement layer can also be 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 is lower than the acoustic velocity of the elastic wave propagating in the piezoelectric film. The high acoustic velocity layer is a film in which the acoustic velocity of the bulk wave is higher than the acoustic velocity of the elastic wave propagating in the piezoelectric film. In addition, the support substrate can be set as the high acoustic velocity layer.

[0111] In addition, the energy confinement layer can also be an acoustic impedance layer having a structure in which a low acoustic impedance layer with a relatively low acoustic impedance and a high acoustic impedance layer with a relatively high acoustic impedance are alternately laminated.

[0112] Here, the electrode parameters of the IDT electrode 54 constituting the elastic wave resonator 60 will be described.

[0113] The wavelength of the elastic wave resonator is defined by the wavelength λ which is the repetition period of the plurality of electrode fingers 61a or 61b constituting the IDT electrode 54 as shown in (b) of Figure 2A . In addition, the electrode finger pitch is 1 / 2 of the wavelength λ. When the line width of the electrode fingers 61a and 61b constituting the comb-shaped electrodes 60a and 60b is set to W and the gap width between the adjacent electrode fingers 61a and 61b is set to S, it is defined by (W + S).

[0114] In addition, in the IDT electrode 54, when the interval between adjacent electrode fingers is not fixed, the electrode finger pitch of the IDT electrode 54 is defined by the average electrode finger pitch of the IDT electrode 54. If the total number of the electrode fingers 61a and 61b included in the IDT electrode 54 is set to Ni and the distance between the centers of the electrode finger at one end and the electrode finger at the other end of the IDT electrode 54 in the elastic wave propagation direction is set to Di, the average electrode finger pitch of the IDT electrode 54 is defined as Di / (Ni - 1).

[0115] In addition, Figure 2C is a cross-sectional view schematically showing a third example of the elastic wave resonator constituting the multiplexer 1 according to the embodiment. In Figure 2C , as the elastic wave resonator of the multiplexer 1, a bulk acoustic wave resonator is shown. As shown 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 has a structure in which the support substrate 65, the lower electrode 66, the piezoelectric layer 67, and the upper electrode 68 are laminated in sequence.

[0116] The support substrate 65 is a substrate for supporting the lower electrode 66, the piezoelectric layer 67, and the upper electrode 68. For example, it is a silicon substrate. In addition, the support substrate 65 is provided with voids in the region in contact with the lower electrode 66. Thereby, the piezoelectric layer 67 can vibrate freely.

[0117] 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. Regarding the lower electrode 66 and the upper electrode 68, as the material, for example, Al containing 1% of Cu can be used.

[0118] The piezoelectric layer 67 is formed between the lower electrode 66 and the upper electrode 68. The piezoelectric layer 67 has, for example, at least one of ZnO (zinc oxide), AlN (aluminum nitride), PZT (lead zirconate titanate), KN (potassium niobate), LN (lithium niobate), LT (lithium tantalate), quartz, and LiBO (lithium borate) as the main component.

[0119] The bulk acoustic wave resonator having the above-described stacked structure generates a bulk acoustic wave in the piezoelectric layer 67 and causes it to resonate by applying electric energy between the lower electrode 66 and the upper electrode 68. The bulk acoustic wave generated by this bulk acoustic wave resonator propagates between the lower electrode 66 and the upper electrode 68 in a direction perpendicular to the film surface of the piezoelectric layer 67. That is, the bulk acoustic wave resonator is a resonator that utilizes the resonance of the bulk acoustic wave.

[0120] [4. Resonant Characteristics of Filter 10 and Pass-Through Characteristics of Filter 20]

[0121] First, the basic operating principle of a ladder-type band-pass filter including one series-arm resonator and one shunt-arm resonator will be described.

[0122] 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, generally, the anti-resonance frequency fap of the parallel-arm resonator is made close to the resonance frequency frs of the series-arm resonator. Thereby, near the resonance frequency frp where the impedance of the parallel-arm resonator approaches 0 becomes the low-frequency side stopband. Further, if the frequency increases compared thereto, the impedance of the parallel-arm resonator becomes high near the anti-resonance frequency fap, and the impedance of the series-arm resonator approaches 0 near the resonance frequency frs. Thereby, near the anti-resonance frequency fap to the resonance frequency frs, it becomes the signal passband in the signal path as the series-arm path. Thereby, a passband reflecting the electrode parameters and the electromechanical coupling coefficient of the surface acoustic wave resonator can be formed. Further, if the frequency becomes high and becomes near the anti-resonance frequency fas, the impedance of the series-arm resonator becomes high, and it becomes the high-frequency side stopband.

[0123] In addition, in each of the series-arm resonator and the parallel-arm resonator, in the frequency band on the lower frequency side than the resonance frequency, the impedance of the resonator shows capacitive (C property), and in the frequency band on the higher frequency side than the resonance frequency and on the lower frequency side than the anti-resonance frequency, the impedance of the resonator shows inductive (L property). Further, in the frequency band on the higher frequency side than the anti-resonance frequency, the impedance of the resonator shows capacitive.

[0124] Regarding the above basic operating principle, by adjusting the resonance frequencies and anti-resonance frequencies of a plurality of surface acoustic wave resonators having a relatively large resonance bandwidth, a multiplexer having required specifications such as a narrow frequency band and a small inter-band gap can be configured.

[0125] Next, the resonance characteristics of the series-arm resonator constituting the filter 10 and the passing characteristics of the multiplexer 1 (filter 20) reflecting the resonance characteristics will be described.

[0126] Table 1 shows the wavelength λ (electrode finger pitch × 2) of each resonator constituting the multiplexer 1 according to the embodiment.

[0127] [Table 1]

[0128]

[0129] Figure 3 It is a graph showing the passing characteristics of the (a) multiplexer 1 according to the embodiment and the impedance characteristics of the series-arm resonators s11 to s14 constituting the filter 10.

[0130] In Figure 3In (b) thereof, the resonance frequencies frs11, frs12, frs13, and frs14 of the series-arm resonators s11, s12, s13, and s14 are within the first passband of the filter 10. On the other hand, the anti-resonance frequencies fas11, fas12, fas13, and fas14 of the series-arm resonators s11, s12, s13, and s14 are on the high-frequency side relative to the high-frequency end of the first passband of the filter 10.

[0131] In addition, since the series-arm resonator s13 includes the surface acoustic wave resonators 72 and 73 connected in parallel, it has two resonance frequencies and two anti-resonance frequencies. The resonance frequency frs13 is defined as the resonance frequency on the high-frequency side among the two resonance frequencies, and the anti-resonance frequency fas13 is defined as the anti-resonance frequency on the high-frequency side among the two anti-resonance frequencies.

[0132] Here, the resonance bandwidth of at least one of the series-arm resonators s11 to s14 included in the filter 10 is greater than the first passband.

[0133] Alternatively, the electrode finger pitch of the IDT electrode constituting at least one of the series-arm resonators s11 to s14 included in the filter 10 is smaller than the electrode finger pitch of the IDT electrode constituting at least one of the shunt-arm resonators p21 to p24 included in the filter 20. In other words, the resonance frequency of at least one of the series-arm resonators s11 to s14 included in the filter 10 is higher than the resonance frequency of at least one of the shunt-arm resonators p21 to p24 included in the filter 20. That is, the passband gap between the first passband and the second passband is smaller than the resonance bandwidth of at least one of the series-arm resonators s11 to s14 included in the filter 10. As shown in Table 1, in the present 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 shunt-arm resonators p21 to p24.

[0134] In contrast, 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 included in the filter 10.

[0135] In addition, the resonance frequency frs11 of the series-arm resonator s11 is higher than the low-frequency end of the first passband. Thus, regarding 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 low-frequency side, the resonance bandwidth is decreased and only the anti-resonance frequency fas11 is shifted to the low-frequency side. Therefore, the resonance frequency frs11 can be positioned within the first passband, and thus the insertion loss in the first passband of the filter 10 can be reduced.

[0136] In addition, the series-arm resonators s11 to s14 included in the filter 10 are resonators that contribute to the formation of the first passband. Specifically, they are resonators in which at least a part of the frequency region sandwiched between the resonance frequency and the anti-resonance frequency overlaps with the first passband. In other words, the multiple series-arm resonators included in the filter 10 are resonators that contribute to the formation of the first passband, and do not include resonators in which at least a part of the frequency region sandwiched between the resonance frequency and the anti-resonance frequency does not overlap with the first passband.

[0137] Figure 4A It is a graph showing the pass characteristics of the filter 20 (filter 520) in the multiplexer according to the embodiment and the comparative example. In addition, Figure 4B It is a Smith chart showing the impedance of the second passband when observing the multiplexer according to the embodiment and the comparative example from the common terminal 100. In addition, Figure 5 It is a graph showing the impedance characteristics and susceptance characteristics of the first series-arm resonator according to the embodiment and the comparative example.

[0138] In addition, the multiplexer according to the comparative example includes filters 510 and 520 instead of filters 10 and 20. Compared with the multiplexer 1 according to the embodiment, the structures of the filters 510 and 520 are different. The difference between the filter 510 and the filter 10 is only that a capacitor 91 is not connected in parallel to the surface acoustic wave resonator 71. The difference between the filter 520 and the filter 20 is only that a surface acoustic wave resonator 80 is arranged instead of the series-arm resonator s21.

[0139] Specifically, in the multiplexer according to the comparative example, the first series-arm resonator connected closest to the common terminal 100 is the surface acoustic wave resonator 71. As shown in Figure 5 (a) thereof, the anti-resonance frequency fa71 of the surface acoustic wave resonator 71 is located on the high-frequency side of the high-frequency end of the second passband. In addition, in the multiplexer according to the comparative example, the second series-arm resonator connected closest to the common terminal 100 is the surface acoustic wave resonator 80, as described later in Figure 9 (a) thereof and Figure 7As shown in (b), the resonance frequency fr80 of the elastic wave resonator 80 is lower than the resonance frequencies frs22, frs24, and frs25 of the series arm resonators s22, s24, and s25, respectively.

[0140] In the multiplexer according to the comparative example, as Figure 5 shown in (a), the resonance bandwidth of the elastic wave resonator 71 is large, so the inductive region of the elastic wave resonator 71 (the region between the resonance frequency fr71 and the anti-resonance frequency fa71) overlaps with the second passband. In other words, in the multiplexer according to the comparative example, as Figure 5 shown in (b), the region with a small susceptance of the elastic wave resonator 71 overlaps with the second passband. Thus, in the multiplexer according to the comparative example, among the elastic wave resonators constituting the filter 510, the elastic wave resonator 71 is closest to the filter 520 and is connected in series therewith. Therefore, as Figure 4B shown, when observing the filter 510 and 520 from the common terminal 100, the impedance of the second passband deviates toward the inductive region from the impedance of the second passband (reference impedance) optimized for the filter 520 alone ( Figure 4B dashed line in ).

[0141] In contrast, in the multiplexer 1 according to the embodiment, as Figure 5 shown in (a), the resonance bandwidth of the series arm resonator s11 is smaller than the resonance bandwidth of the elastic wave resonator 71, so 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 Figure 5 shown in (b), the region with a large susceptance of the series arm resonator s11 overlaps with the second passband. Thus, in the multiplexer 1 according to the embodiment, as Figure 4B shown, compared with the multiplexer according to the comparative example, it is possible to make the impedance of the second passband when observing the filter 10 and 20 from the common terminal 100 be located closer to the impedance of the second passband (reference impedance) optimized for the filter 20 alone ( Figure 4B solid line in ).

[0142] Accordingly, as Figure 4A shown, compared with the passing characteristic of the filter 520 of the multiplexer according to the comparative example, the passing characteristic (the passing characteristic from the common terminal 100 to the output terminal 102) of the filter 20 of the multiplexer 1 according to the embodiment can reduce the insertion loss of the second passband.

[0143] In addition, in the present embodiment, regarding the first series arm resonator among the series arm resonators and parallel arm resonators constituting the filter 10, which is connected closest to the common terminal 100, the resonance bandwidth is reduced by connecting the capacitor 91 in parallel. However, the means for reducing the resonance bandwidth is not limited to this.

[0144] As a means for reducing the resonance bandwidth of the first series arm resonator, it is possible to cite that the IDT electrode of the first series arm resonator includes a spacer removal electrode. For example, the IDT electrode of the first series arm resonator may also include Figure 6A the floating spacer removal electrode shown in Figure 6B the polarity inversion spacer removal electrode shown in Figure 6C or any one of the filled spacer removal electrodes shown in

[0145] Figure 6A is a schematic plan view showing the structure of the IDT electrode including the floating spacer removal electrode. Figure 6B is a schematic plan view showing the structure of the IDT electrode including the polarity inversion spacer removal electrode. Figure 6C is a schematic plan view showing the structure of the IDT electrode including the filled spacer removal electrode.

[0146] Figure 6A The surface acoustic wave resonator 111 shown in Figure 6A is an example of the first series arm resonator, and illustrates the electrode finger structure of the IDT electrode including the floating spacer removal electrode. In addition,

[0147] The surface acoustic wave resonator 111 includes a piezoelectric substrate 50, comb-shaped electrodes 111a and 111b formed on the piezoelectric substrate 50, and a reflector 141.

[0148] As shown in Figure 6A the comb-shaped electrode 111a includes a plurality of electrode fingers 151a parallel to each other and a bus bar electrode 161a connecting one ends of the plurality of electrode fingers 151a to each other. In addition, the comb-shaped electrode 111b includes a plurality of electrode fingers 151b parallel to each other and a bus bar electrode 161b connecting one ends of the plurality of electrode fingers 151b to each other. The plurality of electrode fingers 151a and 151b are formed along a direction orthogonal to the surface acoustic wave propagation direction (X-axis direction). The comb-shaped 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 the surface acoustic wave resonator 111 has a pair of comb-shaped electrodes 111a and 111b.

[0149] In addition, the comb-shaped electrode 111a has dummy electrodes disposed opposite to each other in the longitudinal direction of the plurality of electrode fingers 151b, but these dummy electrodes may be absent. Further, the comb-shaped electrode 111b has dummy electrodes disposed opposite to each other in the longitudinal direction of the plurality of electrode fingers 151a, but these dummy electrodes may be absent. Moreover, the comb-shaped electrodes 111a and 111b may be so-called inclined IDT electrodes in which the extending direction of the bus bar electrode is inclined with respect to the surface acoustic wave propagation direction. Additionally, it may have a so-called piston structure.

[0150] The reflector 141 includes a plurality of electrode fingers parallel to each other and a bus bar electrode connecting the plurality of electrode fingers, and is disposed at both ends of the pair of comb-shaped electrodes 111a and 111b.

[0151] Here, electrode fingers 152 are discretely formed on the IDT electrodes of the elastic wave resonator 111. The electrode fingers 152 are not connected to the bus bar electrodes 161a and 161b, and are floating interval removal electrodes that are parallel to the plurality of electrode fingers 151a and 151b and are arranged at the same interval. Further, between two adjacent electrode fingers 152, a plurality of electrode fingers 151a and 151b are arranged. That is, the interval between the electrode fingers 152 is larger than the interval between the plurality of electrode fingers 151a and 151b.

[0152] Figure 6B The illustrated elastic wave resonator 211 is an example of the first series arm resonator, and illustrates the electrode finger structure of the IDT electrode including the polarity inversion interval removal electrode. Additionally, Figure 6B The illustrated elastic wave resonator 211 is used to illustrate the typical structure of the polarity inversion interval removal electrode, and the number of electrode fingers, length, etc. of the electrodes constituting it are not limited thereto.

[0153] The elastic wave resonator 211 includes a piezoelectric substrate 50, comb-shaped electrodes 211a and 211b formed on the piezoelectric substrate 50, and a reflector 241.

[0154] As Figure 6B shown, the comb-shaped electrode 211a includes a plurality of electrode fingers 251a parallel to each other and a bus bar electrode 261a connecting one ends of the plurality of electrode fingers 251a to each other. Further, the comb-shaped electrode 211b includes a plurality of electrode fingers 251b parallel to each other and a bus bar electrode 261b connecting one ends of the plurality of electrode fingers 251b to each other. The plurality of electrode fingers 251a and 251b are formed along a direction orthogonal to the surface acoustic wave propagation direction (X-axis direction). The comb-shaped electrodes 211a and 211b are disposed opposite to each other such that the plurality of electrode fingers 251a and 251b are interlaced with each other. That is, the IDT electrode of the elastic wave resonator 211 has a pair of comb-shaped electrodes 211a and 211b.

[0155] In addition, the comb-shaped electrode 211a has dummy electrodes disposed opposite to each other in the long side direction of the plurality of electrode fingers 251b, but the dummy electrodes may be absent. Further, the comb-shaped electrode 211b has dummy electrodes disposed opposite to each other in the long side direction of the plurality of electrode fingers 251a, but the dummy electrodes may be absent. Moreover, the comb-shaped electrodes 211a and 211b may be so-called inclined IDT electrodes in which the extending direction of the bus bar electrode is inclined with respect to the surface acoustic wave propagation direction. In addition, it may have a so-called piston structure.

[0156] The reflector 241 includes a plurality of electrode fingers parallel to each other and a bus bar electrode connecting the plurality of electrode fingers, and is disposed at both ends of a pair of comb-shaped electrodes 211a and 211b.

[0157] Here, electrode fingers 252 are discretely formed on the IDT electrode of the elastic wave resonator 211. The electrode fingers 252 are polarity inversion interval removal electrodes that are among all the electrode fingers constituting the pair of comb-shaped electrodes 211a and 211b and are connected to the same bus bar electrode to which the adjacent electrode fingers are connected. In addition, a plurality of electrode fingers 251a and 251b are disposed between two adjacent electrode fingers 252. That is, the pitch of the electrode fingers 252 is larger than the pitch of the plurality of electrode fingers 251a and 251b.

[0158] Figure 6C The illustrated elastic wave resonator 311 is an example of a first series arm resonator and illustrates an electrode finger structure of an IDT electrode including filling interval removal electrodes. In addition, Figure 6C The illustrated elastic wave resonator 311 is used to illustrate a typical structure of the filling interval removal electrodes, and the number of electrode fingers, the length, etc. of the electrodes constituting it are not limited thereto.

[0159] The elastic wave resonator 311 includes a piezoelectric substrate 50, comb-shaped electrodes 311a and 311b formed on the piezoelectric substrate 50, and a reflector 341.

[0160] As Figure 6CAs shown, the comb-shaped electrode 311a includes a plurality of electrode fingers 351a that are parallel to each other and a bus bar electrode 361a that connects one ends of the plurality of electrode fingers 351a to each other. In addition, the comb-shaped electrode 311b includes a plurality of electrode fingers 351b that are parallel to each other and a bus bar electrode 361b that connects one ends of the plurality of electrode fingers 351b to each other. The plurality of electrode fingers 351a and 351b are formed along a direction orthogonal to the surface acoustic wave propagation direction (X-axis direction). The comb-shaped electrodes 311a and 311b are arranged opposite to each other such that the plurality of electrode fingers 351a and 351b are interlaced with each other. That is, the IDT electrode of the surface acoustic wave resonator 311 has a pair of comb-shaped electrodes 311a and 311b.

[0161] In addition, the comb-shaped electrode 311a has dummy electrodes arranged opposite to each other in the long side direction of the plurality of electrode fingers 351b, but the dummy electrodes may not be provided. In addition, the comb-shaped electrode 311b has dummy electrodes arranged opposite to each other in the long side direction of the plurality of electrode fingers 351a, but the dummy electrodes may not be provided. In addition, the comb-shaped electrodes 311a and 311b may be so-called inclined IDT electrodes in which the extending direction of the bus bar electrode is inclined with respect to the surface acoustic wave propagation direction. In addition, a so-called piston structure may be provided.

[0162] The reflector 341 includes a plurality of electrode fingers that are parallel to each other and a bus bar electrode that connects the plurality of electrode fingers, and is arranged at both ends of a pair of comb-shaped electrodes 311a and 311b.

[0163] Here, electrode fingers 352 are discretely formed on the IDT electrode of the surface acoustic wave resonator 311. The electrode fingers 352 are electrode fingers having the largest electrode finger width among the electrode fingers of the IDT electrode of the surface acoustic wave resonator 311, and are fill gap removal electrodes having an electrode finger width more than twice the average electrode finger width of the electrode fingers other than the electrode fingers 352. In other words, the electrode fingers 352 are fill gap removal electrodes such that the adjacent electrode fingers 351a and 351b and the gap between the adjacent electrode fingers 351a and 351b together form one electrode finger (in Figure 6C it is the amount of 3 of the electrode fingers 351a and 351b), are connected to either the bus bar electrodes 361a and 361b, and have an electrode finger width wider than that of the plurality of electrode fingers 351a and 351b. In addition, a plurality of electrode fingers 351a and 351b are arranged between two adjacent electrode fingers 352. That is, the pitch of the electrode fingers 352 is larger than the pitch of the plurality of electrode fingers 351a and 351b.

[0164] In addition, the structure of the gap removal electrode as a means for reducing the resonance bandwidth of the first series arm resonator is not limited to the above-mentioned floating gap removal electrode, polarity inversion gap removal electrode, and fill gap removal electrode.

[0165] In addition, as a means of reducing the resonance bandwidth of the first series arm resonator, adjustment of the film thickness of the dielectric film of the IDT electrode disposed in the first series arm resonator can be cited. In Figure 2A In the surface acoustic wave resonator 60 shown in (b) of

[0166] by adjusting the film thickness of the protective layer 55, the resonance bandwidth of the surface acoustic wave resonator 60 can be changed. Specifically, the larger the film thickness of the protective layer 55, the smaller the resonance bandwidth becomes.

[0167] From the above viewpoints, the protective layer 55 (first dielectric film) of the first series arm resonator may be the thickest among the series arm resonators constituting the filter 10. Thereby, the resonance bandwidth of the first series arm resonator becomes smaller, and the anti-resonance frequency can be reduced.

[0168] [5. Resonance characteristics of filter 20 and passing characteristics of filter 10]

[0169] Next, the resonance characteristics of the series arm resonators constituting the filter 20 and the passing characteristics of the multiplexer 1 (filter 10) reflecting the resonance characteristics will be described.

[0170] Figure 7 are graphs showing (a) the passing characteristics of the multiplexer 1 and (b) the impedance characteristics of the series arm resonators s21 to s25 constituting the filter 20 according to the embodiment.

[0171] In Figure 7 in (b) of

[0172] the resonance frequencies frs21 of the series arm resonator s21, the resonance frequencies frs22 of the series arm resonator s22, the resonance frequencies frs23 of the series arm resonator s23, the resonance frequencies frs24 of the series arm resonator s24, and the resonance frequencies frs25 of the series arm resonator s25 are within the second passband of the filter 20.

[0173] Here, the resonance bandwidth of at least one of the series arm resonators s21 to s25 constituting the filter 20 is larger than the second passband.

[0174] Alternatively, the electrode finger pitch of the IDT electrode forming 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 forming at least one of the parallel arm resonators p21 to p24 of the filter 20. In other words, the resonance frequency of at least one of the series arm resonators s11 to s14 of the filter 10 is higher than the resonance frequency of at least one of the parallel arm resonators p21 to p24 of the filter 20. That is to say, the passband gap between the first passband and the second passband is smaller than the resonance bandwidth of at least one of the series arm resonators s21 to s25 of the filter 20. As shown in Table 1, in the present 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.

[0175] In contrast, the resonance 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 resonance frequencies frs21 to frs25 of the series arm resonators s21 to s25. Alternatively, as shown in Table 1, among the IDT electrodes forming the series arm resonators s21 to s25, the electrode finger pitch of the IDT electrode forming the series arm resonator s21 is the smallest.

[0176] In addition, the series arm resonators s21 to s25 of the filter 20 are resonators that contribute to the formation of the second passband. Specifically, they are resonators in which at least a part of the frequency region sandwiched between the resonance frequency and the anti-resonance frequency overlaps with the second passband. In other words, the plurality of series arm resonators of the filter 20 are resonators that contribute to the formation of the second passband, and do not include resonators in which at least a part of the frequency region sandwiched between the resonance frequency and the anti-resonance frequency does not overlap with the second passband.

[0177] Figure 8A It is a graph showing the pass characteristics of the filter 10 (filter 510) in the multiplexer according to the embodiment and the comparative example. In addition, Figure 8B It is an admittance circle diagram showing the impedance of the first passband when observing the multiplexer according to the embodiment and the comparative example from the common terminal 100. In addition, Figure 9 It is a graph showing the impedance characteristics and susceptance characteristics of the second series arm resonator according to the embodiment and the comparative example.

[0178] In addition, the multiplexer in the comparative example includes filters 510 and 520 instead of filters 10 and 20. The structures of filters 510 and 520 are different from those of the multiplexer in the embodiment. The only difference between filter 510 and filter 10 is that a capacitor 91 is not connected in parallel to the surface acoustic wave resonator 71. The only difference between filter 520 and filter 20 is that a surface acoustic wave resonator 80 is disposed instead of the series arm resonator s21.

[0179] Specifically, in the multiplexer in the comparative example, the first series arm resonator connected closest to the common terminal 100 is the surface acoustic wave resonator 71. As shown in Figure 5 (a) thereof, the anti-resonant frequency fa71 of the surface acoustic wave resonator 71 is located on the high-frequency side of the high-frequency end of the second passband. In addition, in the multiplexer in the comparative example, the second series arm resonator connected closest to the common terminal 100 is the surface acoustic wave resonator 80. As shown in Figure 9 (a) thereof and Figure 7 (b) thereof, the resonant frequency fr80 of the surface acoustic wave resonator 80 is lower than the resonant frequencies frs22 of the series arm resonator s22, frs24 of the series arm resonator s24, and frs25 of the series arm resonator s25.

[0180] In the multiplexer in the comparative example, as shown in Figure 9 (a) thereof, the resonant bandwidth of the surface acoustic wave resonator 80 is large, so the capacitive region of the surface acoustic wave resonator 80 (the region on the low-frequency side of the resonant frequency fr80) overlaps with the first passband of filter 10. In other words, in the multiplexer in the comparative example, as shown in Figure 9 (b) thereof, the region with a large susceptance of the surface acoustic wave resonator 80 overlaps with the first passband of filter 10. Thus, in the multiplexer in the comparative example, as shown in Figure 8B it is shown that among the surface acoustic wave resonators constituting filter 20, the surface acoustic wave resonator 80 is closest to filter 10 and is connected in series therewith. Therefore, when observing filters 10 and 20 from the common terminal 100, the impedance of the first passband deviates from the impedance (reference impedance) of the first passband optimized for filter 10 alone toward the capacitive region (the dotted line in Figure 8B ).

[0181] In contrast, in the multiplexer 1 in the embodiment, as shown in Figure 9 (a) thereof, among the resonant frequencies frs21 to frs25 of the series arm resonators s21 to s25, the resonant frequency frs21 of the series arm resonator s21 is the highest. Therefore, the highly capacitive region of the series arm resonator s21 overlaps with the first passband of filter 10. In other words, in the multiplexer 1 in the embodiment, as shown inFigure 9 As shown in (b), the region with a small susceptance of the series-arm resonator s21 overlaps with the first passband of the filter 10. Thus, in the multiplexer 1 according to the embodiment, as Figure 8B shown, compared with the multiplexer according to the comparative example, the impedance of the first passband when observing the filters 10 and 20 from the common terminal 100 can be positioned closer to the impedance (reference impedance) of the first passband optimized for the filter 10 alone ( Figure 8B solid line in).

[0182] Accordingly, as Figure 8A shown, the passing characteristic (the passing characteristic from the input terminal 101 to the common terminal 100) of the filter 10 of the multiplexer 1 according to the embodiment can reduce the insertion loss of the first passband compared with the passing characteristic of the filter 510 of the multiplexer according to the comparative example.

[0183] In addition, in the present embodiment, regarding the series-arm resonator s21 (the second series-arm resonator) that is connected closest to the common terminal 100 among the series-arm resonators and shunt-arm resonators constituting the filter 20, by making the electrode finger pitch of the IDT electrode of the series-arm resonator s21 the smallest among the series-arm resonators s21 to s25 included in the filter 20, the resonance frequency frs21 is made the highest, but the means for increasing the resonance frequency frs21 is not limited thereto.

[0184] As a means for increasing the resonance frequency of the second series-arm resonator, there can be mentioned providing the second series-arm resonator with a second surface acoustic wave element and a second capacitor element (bridging capacitor) connected in parallel with the second surface acoustic wave element. By adding the second capacitor element (bridging capacitor), the resonance bandwidth of the second series-arm resonator becomes smaller than the resonance bandwidth of the second surface acoustic wave element, and the resonance frequency of the second series-arm resonator can be increased.

[0185] In addition, as a means for increasing the resonance frequency of the second series-arm resonator, there can be mentioned making the IDT electrode of the second series-arm resonator include a spaced-apart removal electrode. The IDT electrode of the second series-arm resonator may also include Figure 6A the floating spaced-apart removal electrode shown in, Figure 6B the polarity-reversed spaced-apart removal electrode shown in, and Figure 6C any one of the filled spaced-apart removal electrodes shown in. Thus, the resonance bandwidth of the second series-arm resonator becomes smaller, and the resonance frequency can be increased.

[0186] In addition, the structure of the spaced-apart removal electrode as a means for reducing the resonance bandwidth of the second series-arm resonator is not limited to the above-mentioned floating spaced-apart removal electrode, polarity-reversed spaced-apart removal electrode, and filled spaced-apart removal electrode.

[0187] In addition, as a means of reducing the resonance bandwidth of the second series arm resonator, adjustment of the film thickness of the dielectric film of the IDT electrode disposed in the second series arm resonator can be cited. In Figure 2A the surface acoustic wave resonator 60 shown in (b) of , the protective layer 55 is an example of the second dielectric film. By adjusting the film thickness of the protective layer 55, the resonance bandwidth of the surface acoustic wave resonator 60 can be changed. Specifically, the larger the film thickness of the protective layer 55, the smaller the resonance bandwidth becomes. From the above viewpoints, the protective layer 55 (second dielectric film) of the second series arm resonator can be made the thickest among the series arm resonators constituting the filter 20. Thereby, the resonance bandwidth of the second series arm resonator becomes smaller, and the resonance frequency can be increased.

[0188] In addition, the second dielectric film may not be the protective layer 55 formed on the IDT electrode, but may be a dielectric film disposed between the piezoelectric substrate 50 and the IDT electrode.

[0189] In addition, in the multiplexer 1 according to the present embodiment, the resonance frequency frp21 of the parallel arm resonator p21 may have the following characteristics.

[0190] Figure 10 are graphs showing the transmission characteristics of the multiplexer 1 in (a) according to the embodiment and the impedance characteristics of the parallel arm resonators p21 to p24 constituting the filter 20 in (b).

[0191] In Figure 10 in (b) of , the resonance 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 resonance frequencies frp21 to frp24 of the parallel arm resonators p21 to p24.

[0192] The parallel arm resonator p21 is an example of the first parallel arm resonator and is connected to the series arm resonator s21 (second series arm resonator).

[0193] In addition, since the parallel arm resonator p23 includes surface acoustic wave resonators 83 and 84 connected in series, it has two resonance frequencies and two anti-resonance frequencies, and the resonance frequency frp23 is defined as the resonance frequency on the lower frequency side of the two resonance frequencies.

[0194] In addition, the parallel-arm resonators p21 to p24 included in the filter 20 are resonators that contribute to the formation of the second passband. Specifically, they are resonators in which at least a part of the frequency region sandwiched between the resonance frequency and the anti-resonance frequency overlaps with the second passband. In other words, the plurality of parallel-arm resonators included in the filter 20 are resonators that contribute to the formation of the second passband, and do not include resonators in which at least a part of the frequency region sandwiched between the resonance frequency and the anti-resonance frequency does not overlap with the second passband.

[0195] In the multiplexer 1 according to the present embodiment, as shown in (b) of Figure 10 , the resonance bandwidths of the parallel-arm resonators p21 to p24 are larger than the first passband, the second passband, and the inter-passband gap. Therefore, the inductive regions of the parallel-arm resonators p21 to p24 overlap with the first passband of the filter 10.

[0196] In contrast, among the resonance frequencies frp21 to frp24 of the parallel-arm resonators p21 to p24, the resonance frequency frp21 of the parallel-arm resonator p21 is the highest. Therefore, the inductance of the parallel-arm resonator p21 in the first passband can be reduced. As a result, when observing the filter 20 alone from the common terminal 100 side, the impedance of the first passband can be further shifted toward the open-circuit side.

[0197] Accordingly, when observing the filters 10 and 20 from the common terminal 100, the deviation of the impedance of the first passband from the impedance (reference impedance) of the first passband optimized for the filter 10 alone can be reduced. Therefore, in the pass characteristic (the pass characteristic 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.

[0198] [6. Structure of the multiplexer according to the present invention]

[0199] In addition, 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 passband and is the lowest among the anti-resonance frequencies fas11 to fas14 of the series-arm resonators s11 to s14 included in the filter 10, and (2) the resonance frequency frs21 of the second series-arm resonator (series-arm resonator s21) is higher than the high-frequency end of the first passband and is the highest among the resonance frequencies frs21 to frs25 of the series-arm resonators s21 to s25 included in the filter 20. However, the multiplexer according to the present invention is not limited thereto.

[0200] The multiplexer according to the present invention is characterized by at least one of the following: (1) the anti-resonant frequency fas11 of the first series-arm resonator (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 included in 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 passband and is the highest among the resonant frequencies frs21 to frs25 of the series-arm resonators s21 to s25 included in the filter 20.

[0201] Accordingly, by having the characteristic of the above (1), the multiplexer 1 can make the impedance of the second passband when observing the filters 10 and 20 from the common terminal 100 closer to the impedance (reference impedance) of the second passband optimized for the filter 20 alone compared with the multiplexer according to the comparative example. Therefore, the insertion loss in the second passband of the multiplexer 1 can be reduced compared with the insertion loss in the second passband of the multiplexer according to the comparative example.

[0202] In addition, by having the characteristic of the above (2), the multiplexer 1 can make the impedance of the first passband when observing the filters 10 and 20 from the common terminal 100 closer to the impedance (reference impedance) of the first passband optimized for the filter 10 alone compared with the multiplexer according to the comparative example. Therefore, the insertion loss in the first passband of the multiplexer 1 can be reduced compared with the insertion loss in the first passband of the multiplexer according to the comparative example.

[0203] [7. Effects, etc.]

[0204] As described above, the multiplexer 1 according to the present embodiment includes: a filter 10 having a first passband; and a filter 20 having a second passband on the high-frequency side of the first passband. 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 including surface acoustic wave resonators and arranged in a series-arm path connecting an input end and an output end; and one or more shunt-arm resonators p11 to p14 including surface acoustic wave resonators and connected between the series-arm path and the ground. The resonance bandwidth of at least one of the series-arm resonators s11 to s14 is greater than the first passband. Among the series-arm resonators s11 to s14 and the shunt-arm resonators p11 to p14, the series-arm resonator s11 (the first series-arm resonator) is connected closest to the common terminal 100. 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 are on the high-frequency side of the first passband.

[0205] Accordingly, the overlap of the inductive regions of the second passband and the series-arm resonator s11 can be reduced, and thus the impedance of the second passband when observing the filters 10 and 20 from the common terminal 100 can be shifted from the inductive region toward the capacitive region. Thereby, it can be positioned closer to the impedance (reference impedance) of the second passband optimized for the filter 20 alone. Therefore, the insertion loss in the second passband of the multiplexer 1 can be reduced.

[0206] In addition, for example, in the multiplexer 1, the resonance frequency frs11 of the series-arm resonator s11 is higher than the low-frequency end of the first passband.

[0207] Accordingly, the series-arm resonator s11 does not increase the electrode finger pitch to shift both the resonance frequency frs11 and the anti-resonance frequency fas11 to the low-frequency side, but reduces the resonance bandwidth and only shifts the anti-resonance frequency fas11 to the low-frequency side. Therefore, the overlap of the inductive regions of the second passband and the series-arm resonator s11 can be reduced without increasing the insertion loss of the filter 10.

[0208] In addition, for example, in the multiplexer 1, the series-arm resonator s11 includes a surface acoustic wave resonator 71 and a capacitor 91 connected in parallel with the surface acoustic wave resonator 71.

[0209] Accordingly, the resonance frequency frs11 of the series-arm resonator s11 can be prevented from shifting from the resonance frequency fr71 of the surface acoustic wave resonator 71, and the anti-resonance frequency fas11 of the series-arm resonator s11 can be shifted to the low-frequency side relative to the anti-resonance frequency fa71 of the surface acoustic wave resonator 71. Therefore, the resonance bandwidth of the series-arm resonator s11 can be reduced relative to the resonance bandwidth of the surface acoustic wave resonator 71.

[0210] In addition, for example, in the multiplexer 1, the surface acoustic wave resonator constituting the series arm resonator s11 has an IDT electrode. The IDT electrode has a pair of comb-shaped electrodes, which include: a plurality of electrode fingers extending in a direction crossing the surface acoustic wave propagation direction and arranged in parallel with each other; and a bus bar electrode connecting one ends of the plurality of electrode fingers to each other. The electrode fingers that are not connected to any of the bus bar electrodes constituting the pair of comb-shaped electrodes are defined as floating interval elimination electrodes. The electrode fingers connected to the same bus bar electrode as the bus bar electrodes to which the adjacent electrode fingers are connected are defined as polarity inversion interval elimination electrodes. The electrode fingers having the largest electrode finger width and having an electrode finger width more than twice the average electrode finger width of the other electrode fingers are defined as filling interval elimination electrodes. In this case, the IDT electrode of the series arm resonator s11 includes any one of the floating interval elimination electrodes, the polarity inversion interval elimination electrodes, and the filling interval elimination electrodes.

[0211] Accordingly, the resonance bandwidth of the series arm resonator s11 becomes smaller, and the anti-resonance frequency fas11 can be reduced.

[0212] In addition, for example, in the multiplexer 1, each of the plurality of surface acoustic wave resonators included in the filter 10 has: a piezoelectric substrate 50; an IDT electrode disposed on the piezoelectric substrate 50; and a first dielectric film disposed between the piezoelectric substrate 50 and the IDT electrode or on the IDT electrode. Among the series arm resonators s11 to s14, the first dielectric film of the series arm resonator s11 is the thickest.

[0213] Accordingly, the resonance bandwidth of the series arm resonator s11 becomes smaller, and the anti-resonance frequency fas11 can be reduced.

[0214] In addition, the multiplexer 1 according to this embodiment includes: a filter 10 having a first passband; and a filter 20 having a second passband on the higher-frequency side than the first passband. 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, including surface acoustic wave resonators and arranged in a series-arm path connecting an input end and an output end; and one or more shunt-arm resonators p21 to p24, including surface acoustic wave resonators and connected between the series-arm path and ground. The resonance bandwidth of at least one of the series-arm resonators s21 to s24 is greater than the second passband. Among the series-arm resonators s21 to s25 and the shunt-arm resonators p21 to p24, the series-arm resonator s21 (the second series-arm resonator) is connected closest to the common terminal 100. The resonance frequency frs21 of the series-arm resonator s21 is higher than the high-frequency end of the first passband, and among the resonance frequencies frs21 to frs25 of the series-arm resonators s21 to s25, it is the highest among the resonance frequencies on the higher-frequency side than the first passband.

[0215] Accordingly, the capacitive region with a small capacitance of the series-arm resonator s21 overlaps with the first passband of the filter 10. Therefore, it is possible to shift the impedance of the first passband when observing the filters 10 and 20 from the common terminal 100 in the direction from the capacitive region to the inductive region. Thereby, it can be positioned close to the impedance (reference impedance) of the first passband optimized for the filter 10 alone. Thus, the insertion loss in the first passband of the multiplexer 1 can be reduced.

[0216] In addition, for example, in the multiplexer 1, the shunt-arm resonator p21 (the first shunt-arm resonator) is connected to the series-arm resonator s21. The resonance frequency frp21 of the shunt-arm resonator p21 is lower than the high-frequency end of the first passband, and among the resonance frequencies frp21 to frp24 of the shunt-arm resonators p21 to p24, it is the highest among the resonance frequencies on the lower-frequency side than the second passband.

[0217] Accordingly, regarding the impedance of the first passband when observing the filters 10 and 20 from the common terminal 100, the amount of shift from the impedance (reference impedance) of the first passband optimized for the filter 10 alone can be reduced. Thus, the insertion loss in the first passband of the multiplexer 1 can be further reduced.

[0218] In addition, for example, in the multiplexer 1, the series-arm resonator s21 has a second surface acoustic wave resonator and a second capacitor element connected in parallel with the second surface acoustic wave resonator.

[0219] Accordingly, by adjusting the electrode finger pitch, the resonance frequency frs21 of the series-arm resonator s21 can be shifted to the higher-frequency side than the resonance frequency of the second surface acoustic wave resonator.

[0220] In addition, for example, in multiplexer 1, the IDT electrodes of the series-arm resonator s21 include any one of a floating-gap rejection electrode, a polarity-inverted gap rejection electrode, and a filled-gap rejection electrode.

[0221] Accordingly, the resonance bandwidth of the series-arm resonator s21 becomes smaller, and the resonance frequency frs21 can be increased.

[0222] In addition, for example, in multiplexer 1, each of the plurality of surface acoustic wave resonators included in filter 20 includes: a piezoelectric substrate 50; IDT electrodes disposed on the piezoelectric substrate 50; and a second dielectric film disposed between the piezoelectric substrate 50 and the IDT electrodes or on the IDT electrodes. Among the series-arm resonators s21 to s25, the second dielectric film of the series-arm resonator s21 is the thickest.

[0223] Accordingly, the resonance bandwidth of the series-arm resonator s21 becomes smaller, and the anti-resonance frequency fas21 can be decreased.

[0224] In addition, multiplexer 1 according to the present embodiment includes: a filter 10 having a first passband; and a filter 20 having a second passband on the higher-frequency side than the first passband. Filters 10 and 20 are connected to a common terminal 100. Filter 10 includes: two or more series-arm resonators s11 to s14 including surface acoustic wave resonators and disposed on a series-arm path connecting an input terminal and an output terminal; and one or more shunt-arm resonators p11 to p14 including surface acoustic wave resonators and connected between the series-arm path and ground. Filter 20 includes: two or more series-arm resonators s21 to s25 including surface acoustic wave resonators and disposed on a series-arm path connecting an input terminal and an output terminal; and one or more shunt-arm resonators p21 to p24 including surface acoustic wave resonators and connected between the series-arm path and ground. The surface acoustic wave resonators constituting filters 10 and 20 each have IDT electrodes. The electrode finger pitch of the IDT electrodes constituting at least one of the series-arm resonators s11 to s14 is smaller than the electrode finger pitch of the IDT electrodes constituting at least one of the shunt-arm resonators p21 to p24. Among the series-arm resonators s11 to s14 and the shunt-arm resonators p11 to p14, the series-arm resonator s11 (the first series-arm resonator) is connected closest to the common terminal 100. The anti-resonance frequency fas11 of the series-arm resonator s11 is lower than the high-frequency end of the second passband, and among the anti-resonance frequencies fas11 to fas14 of the series-arm resonators s11 to s14, it is the lowest among the anti-resonance frequencies on the higher-frequency side than the first passband.

[0225] Accordingly, the overlap between the second passband and the inductive region of the series arm resonator s11 can be reduced, and thus the impedance of the second passband when observing the filters 10 and 20 from the common terminal 100 can be shifted from the inductive region toward the capacitive region. As a result, it can be positioned closer to the impedance (reference impedance) of the second passband optimized for the filter 20 alone. Therefore, the insertion loss in the second passband of the multiplexer 1 can be reduced.

[0226] In addition, the multiplexer 1 according to the present embodiment includes: a filter 10 having a first passband; and a filter 20 having a second passband on the higher frequency side than the first passband. 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, including surface acoustic wave resonators and arranged in a series arm path connecting an input end and an output end; and one or more shunt arm resonators p11 to p14, including surface acoustic wave resonators and connected between the series arm path and the ground. The filter 20 includes: two or more series arm resonators s21 to s25, including surface acoustic wave resonators and arranged in a series arm path connecting an input end and an output end; and one or more shunt arm resonators p21 to p24, including surface acoustic wave resonators and connected between the series arm path and the ground. The surface acoustic wave resonators constituting the filters 10 and 20 each have 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 shunt arm resonators p21 to p24. Among the series arm resonators s21 to s25 and the shunt arm resonators p21 to p24, the series arm resonator s21 (the second series arm resonator) is connected closest to the common terminal 100. Among the electrode finger pitches of the IDT electrodes constituting the series arm resonators s21 to s25, the electrode finger pitch of the IDT electrode constituting the series arm resonator s21 is the smallest.

[0227] Accordingly, the capacitive region with a small capacitance of the series arm resonator s21 overlaps with the first passband of the filter 10, and thus the impedance of the first passband when observing the filters 10 and 20 from the common terminal 100 can be shifted from the capacitive region toward the inductive region. As a result, it can be positioned closer to the impedance (reference impedance) of the first passband optimized for the filter 10 alone. Therefore, the insertion loss in the first passband of the multiplexer 1 can be reduced.

[0228] (Other Embodiments)

[0229] As described above, the multiplexer according to the present invention has been described by way of embodiments. However, the present invention is not limited to the above embodiments. Variations obtained by making various modifications that occur to those skilled in the art to the above embodiments within the scope not departing from the gist of the present invention, and various devices incorporating the multiplexer according to the present invention are also included in the present invention.

[0230] In addition, for example, in the multiplexer according to the above embodiment, matching elements such as inductors and capacitors, and a switch circuit may be connected between the respective components.

[0231] Further, in the above embodiment, the resonance frequency and the anti-resonance frequency shown, for example, are derived by bringing an RF probe into contact with two input / output electrodes of the surface acoustic wave resonator and measuring the reflection characteristics.

[0232] Hereinafter, the characteristics of the multiplexer described based on the above embodiment will be shown.

[0233] <1>

[0234] A multiplexer includes:

[0235] A first filter having a first passband; and

[0236] A second filter having a second passband on the higher frequency side than the first passband,

[0237] The first filter and the second filter are connected to a common terminal,

[0238] The first filter includes: two or more series-arm resonators including surface acoustic wave resonators and arranged in a series-arm path connecting an input end and an output end; and one or more shunt-arm resonators including surface acoustic wave resonators and connected between the series-arm path and ground,

[0239] The resonance bandwidth of at least one of the two or more series-arm resonators included in the first filter is larger than the first passband,

[0240] Among the two or more series-arm resonators and the one or more shunt-arm resonators included in the first filter, the first series-arm resonator among the two or more series-arm resonators included in the first filter is connected closest to the common terminal,

[0241] The 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 included in the first filter that are on the higher frequency side than the first passband.

[0242] <2>

[0243] The multiplexer according to <1>, wherein,

[0244] The second filter has: two or more series-arm resonators including surface acoustic wave resonators and disposed in a series-arm path connecting an input end and an output end; and one or more shunt-arm resonators including surface acoustic wave resonators and connected between the series-arm path and ground,

[0245] The resonance bandwidth of at least one of the two or more series-arm resonators of the second filter is greater than the second passband,

[0246] Among the two or more series-arm resonators and the one or more shunt-arm resonators of the second filter, the second series-arm resonator of the two or more series-arm resonators of the second filter is connected closest to the common terminal,

[0247] The resonance frequency of the second series-arm resonator is higher than the high-frequency end of the first passband, and is the highest among the resonance frequencies of the two or more series-arm resonators of the second filter on the high-frequency side of the first passband.

[0248] <3>

[0249] The multiplexer according to <1> or <2>, wherein,

[0250] The resonance frequency of the first series-arm resonator is higher than the low-frequency end of the first passband.

[0251] <4>

[0252] The multiplexer according to any one of <1> to <3>, wherein,

[0253] The first series-arm resonator has:

[0254] A first surface acoustic wave resonator; and

[0255] A first capacitor element connected in parallel with the first surface acoustic wave resonator.

[0256] <5>

[0257] The multiplexer according to any one of <1> to <3>, wherein,

[0258] The surface acoustic wave resonator constituting the first series-arm resonator has an IDT electrode,

[0259] The IDT electrode has a pair of comb-shaped electrodes, and the comb-shaped electrodes include: a plurality of electrode fingers extending in a direction intersecting the elastic wave propagation direction and arranged in parallel with each other; and busbar electrodes connecting one ends of the electrode fingers constituting the plurality of electrode fingers to each other.

[0260] The electrode fingers among the plurality of electrode fingers that are not connected to any of the busbar electrodes constituting the pair of comb-shaped electrodes are defined as floating interval rejection electrodes, the electrode fingers among the plurality of electrode fingers that are connected to the same busbar electrode as the busbar electrodes to which the adjacent electrode fingers are connected are defined as polarity inversion interval rejection electrodes, and the electrode fingers among the plurality of electrode fingers that have the largest electrode finger width and have an electrode finger width more than twice the average electrode finger width of the other electrode fingers are defined as filling interval rejection electrodes. In this case,

[0261] The IDT electrode of the first series arm resonator includes any one of the floating interval rejection electrodes, the polarity inversion interval rejection electrodes, and the filling interval rejection electrodes.

[0262] <6>

[0263] The multiplexer according to any one of <1> to <3>, wherein

[0264] The plurality of elastic wave resonators included in the first filter each have:

[0265] A piezoelectric substrate;

[0266] An IDT electrode disposed on the piezoelectric substrate; and

[0267] A first dielectric film disposed between the piezoelectric substrate and the IDT electrode or on the IDT electrode,

[0268] Among the two or more series arm resonators included in the first filter, the first dielectric film of the first series arm resonator is the thickest.

[0269] <7>

[0270] A multiplexer includes:

[0271] A first filter having a first passband; and

[0272] A second filter having a second passband on the higher frequency side than the first passband,

[0273] The first filter and the second filter are connected to a common terminal,

[0274] The second filter includes: two or more series-arm resonators including surface acoustic wave resonators and arranged in a series-arm path connecting an input terminal and an output terminal; and one or more shunt-arm resonators including surface acoustic wave resonators and connected between the series-arm path and ground,

[0275] The resonance bandwidth of at least one of the two or more series-arm resonators included in the second filter is greater than the second passband,

[0276] Among the two or more series-arm resonators and the one or more shunt-arm resonators included in the second filter, the second series-arm resonator among the two or more series-arm resonators included in the second filter is connected closest to the common terminal,

[0277] The resonance frequency of the second series-arm resonator is higher than the high-frequency end of the first passband and is the highest among the resonance frequencies of the two or more series-arm resonators included in the second filter that are on the high-frequency side of the first passband.

[0278] <8>

[0279] The multiplexer according to <7>, wherein,

[0280] The second filter includes: the two or more series-arm resonators; and two or more shunt-arm resonators including surface acoustic wave resonators and connected between the series-arm path and ground,

[0281] The first shunt-arm resonator among the two or more shunt-arm resonators included in the second filter is connected to the second series-arm resonator,

[0282] The resonance frequency of the first shunt-arm resonator is lower than the high-frequency end of the first passband and is the highest among the resonance frequencies of the two or more shunt-arm resonators included in the second filter that are on the low-frequency side of the second passband.

[0283] <9>

[0284] The multiplexer according to <7> or <8>, wherein,

[0285] The second series-arm resonator includes:

[0286] A second surface acoustic wave resonator; and

[0287] A second capacitor element connected in parallel with the second surface acoustic wave resonator.

[0288] <10>

[0289] The multiplexer according to <7> or <8>, wherein,

[0290] The surface acoustic wave resonator constituting the second series arm resonator has an IDT electrode,

[0291] The IDT electrode has a pair of comb-shaped electrodes, the comb-shaped electrodes comprising: a plurality of electrode fingers extending in a direction crossing the surface acoustic wave propagation direction and arranged in parallel with each other; and a bus bar electrode connecting one ends of the electrode fingers constituting the plurality of electrode fingers to each other,

[0292] An electrode finger that is not connected to any of the bus bar electrodes constituting the pair of comb-shaped electrodes among the plurality of electrode fingers is defined as a floating interval elimination electrode, an electrode finger 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 interval elimination electrode, and an electrode finger having the largest electrode finger width and having an electrode finger width more than twice the average electrode finger width of the other electrode fingers is defined as a filling interval elimination electrode. In this case,

[0293] The IDT electrode of the second series arm resonator includes any one of the floating interval elimination electrode, the polarity inversion interval elimination electrode, and the filling interval elimination electrode.

[0294] <11>

[0295] The multiplexer according to <7> or <8>, wherein,

[0296] The plurality of surface acoustic wave resonators included in the second filter each have:

[0297] A piezoelectric substrate;

[0298] An IDT electrode disposed on the piezoelectric substrate; and

[0299] A second dielectric film disposed between the piezoelectric substrate and the IDT electrode or on the IDT electrode,

[0300] Among the two or more series arm resonators included in the second filter, the second dielectric film of the second series arm resonator is the thickest.

[0301] <12>

[0302] A multiplexer, comprising:

[0303] A first filter having a first passband; and

[0304] A second filter having a second passband on the higher frequency side than the first passband,

[0305] The first filter and the second filter are connected to a common terminal.

[0306] The first filter includes: two or more series-arm resonators including surface acoustic wave resonators and disposed in a series-arm path connecting an input end and an output end; and one or more shunt-arm resonators including surface acoustic wave resonators and connected between the series-arm path and ground.

[0307] The second filter includes: two or more series-arm resonators including surface acoustic wave resonators and disposed in a series-arm path connecting an input end and an output end; and one or more shunt-arm resonators including surface acoustic wave resonators and connected between the series-arm path and ground.

[0308] The surface acoustic wave resonators constituting the first filter and the second filter each have IDT (InterDigital Transducer) electrodes.

[0309] The electrode finger pitch of the IDT electrode of at least one of the two or more series-arm resonators included in the first filter is smaller than the electrode finger pitch of the IDT electrode of at least one of the one or more shunt-arm resonators included in the second filter.

[0310] Among the two or more series-arm resonators and the one or more shunt-arm resonators included in the first filter, the first series-arm resonator among the two or more series-arm resonators included in the first filter is connected closest to the common terminal.

[0311] The anti-resonant 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-resonant frequencies of the two or more series-arm resonators included in the first filter that are on the high-frequency side of the first passband.

[0312] <13>

[0313] The multiplexer according to <12>, wherein

[0314] Among the two or more series-arm resonators and the one or more shunt-arm resonators included in the second filter, the second series-arm resonator among the two or more series-arm resonators included in the second filter is connected closest to the common terminal.

[0315] Among the electrode finger pitches of the IDT electrodes of the two or more series-arm resonators included in the second filter, the electrode finger pitch of the IDT electrode of the second series-arm resonator is the smallest.

[0316] <14>

[0317] A multiplexer, comprising:

[0318] A first filter having a first passband; and

[0319] A second filter having a second passband on the high-frequency side of the first passband,

[0320] The first filter and the second filter are connected to a common terminal,

[0321] The first filter has: two or more series-arm resonators, each including a surface acoustic wave resonator and disposed in a series-arm path connecting an input end and an output end; and one or more shunt-arm resonators, each including a surface acoustic wave resonator and connected between the series-arm path and ground,

[0322] The second filter has: two or more series-arm resonators, each including a surface acoustic wave resonator and disposed in a series-arm path connecting an input end and an output end; and one or more shunt-arm resonators, each including a surface acoustic wave resonator and connected between the series-arm path and ground,

[0323] The surface acoustic wave resonators constituting the first filter and the second filter each have an IDT electrode,

[0324] The IDT electrode of at least one of the two or more series-arm resonators constituting the first filter has a smaller electrode finger pitch than the IDT electrode of at least one of the one or more shunt-arm resonators constituting the second filter,

[0325] Among the two or more series-arm resonators and the one or more shunt-arm resonators of the second filter, the second series-arm resonator of the two or more series-arm resonators of the second filter is connected closest to the common terminal,

[0326] Among the IDT electrodes of the two or more series-arm resonators constituting the second filter, the IDT electrode of the second series-arm resonator has the smallest electrode finger pitch.

[0327] Industrial applicability

[0328] The present invention can be widely used in communication devices such as mobile phones as a low-loss multiplexer applicable to a frequency standard with multiple frequency bands.

Claims

1. A multiplexer comprising: a first filter having a first passband; and The second filter has a second passband which is closer to the high frequency side than the first passband. The first filter and the second filter are connected to a common terminal, The first filter comprises: two or more series arm resonators including an elastic wave resonator, which are 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, which are connected between the series arm path and ground. The resonance frequency bandwidth of at least one of the two or more series arm resonators of the first filter is larger than the first passband. Among the two or more series arm resonators and the one or more parallel arm resonators included in the first filter, a first series arm resonator among the two or more series arm resonators included in the first filter is connected closest to the common terminal, The antiresonance frequency of the first series arm resonator is lower than the high frequency end of the second passband, and is the lowest among the antiresonance frequencies of the two or more series arm resonators of the first filter, the antiresonance frequency located on the high frequency side of the first passband.

2. The multiplexer according to claim 1, wherein: The second filter comprises: two or more series arm resonators including an elastic wave resonator, which are 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, which are connected between the series arm path and ground. The resonance frequency bandwidth of at least one of the two or more series arm resonators of the second filter is wider than the second passband. Among the two or more series arm resonators and the one or more parallel arm resonators included in the second filter, a second series arm resonator among the two or more series arm resonators included in the second filter is connected closest to the common terminal, The resonant frequency of the second series arm resonator is higher than the high frequency end of the first passband, and is the highest among the resonant frequencies of the two or more series arm resonators of the second filter, the resonant frequencies located on the high frequency side of the first passband.

3. The multiplexer according to claim 1 or 2, wherein: The resonance frequency of the first series arm resonator is higher than a low frequency end of the first passband.

4. The multiplexer according to any one of claims 1 to 3, wherein: The first series arm resonator has: a first elastic wave resonator; and The first capacitive element is connected in parallel with the first elastic wave resonator.

5. The multiplexer according to any one of claims 1 to 3, wherein: The elastic wave resonator constituting the first series arm resonator has an IDT electrode. The IDT electrode has a pair of comb-shaped electrodes, the comb-shaped electrodes including: 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 electrode fingers constituting the plurality of electrode fingers to each other. The electrode fingers among the plurality of electrode fingers that are not connected to any of the bus bar electrodes constituting the pair of comb-shaped electrodes are defined as floating spacing elimination electrodes, the electrode fingers among the plurality of electrode fingers that are connected to the same bus bar electrodes as the bus bar electrodes connected to the electrode fingers on both sides are defined as polarity-reversed spacing elimination electrodes, and the electrode fingers among the plurality of electrode fingers that have the largest electrode finger width and have an electrode finger width that is more than twice the average electrode finger width among the electrode fingers other than the electrode finger are defined as filled spacing elimination electrodes. In this case, The IDT electrode of the first series arm resonator includes any one of the floating thinned-out electrode, the polarity-reversed thinned-out electrode, and the filled thinned-out electrode.

6. The multiplexer according to any one of claims 1 to 3, wherein: The plurality of elastic wave resonators included in the first filter each include: Piezoelectric substrate; An IDT electrode is disposed on the piezoelectric substrate; as well as a first dielectric film disposed between the piezoelectric substrate and the IDT electrode or on the IDT electrode; Among the two or more series arm resonators included in the first filter, the first dielectric film of the first series arm resonator is the thickest.

7. A multiplexer comprising: a first filter having a first passband; and The second filter has a second passband which is closer to the high frequency side than the first passband. The first filter and the second filter are connected to a common terminal, The second filter comprises: two or more series arm resonators including an elastic wave resonator, which are 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, which are connected between the series arm path and ground. The resonance frequency bandwidth of at least one of the two or more series arm resonators of the second filter is wider than the second passband. Among the two or more series arm resonators and the one or more parallel arm resonators included in the second filter, a second series arm resonator among the two or more series arm resonators included in the second filter is connected closest to the common terminal, The resonant frequency of the second series arm resonator is higher than the high frequency end of the first passband, and is the highest among the resonant frequencies of the two or more series arm resonators of the second filter, the resonant frequencies located on the high frequency side of the first passband.

8. The multiplexer according to claim 7, wherein: The second filter comprises: the two or more series arm resonators; and two or more parallel arm resonators, including elastic wave resonators, connected between the series arm path and ground. A first parallel arm resonator among the two or more parallel arm resonators included in the second filter is connected to the second series arm resonator. The resonant frequency of the first parallel arm resonator is lower than the high frequency end of the first passband, and is the highest among the resonant frequencies of the two or more parallel arm resonators of the second filter, the resonant frequency being located on the low frequency side of the second passband.

9. The multiplexer according to claim 7 or 8, wherein: The second series arm resonator has: a second elastic wave resonator; and The second capacitive element is connected in parallel with the second elastic wave resonator.

10. The multiplexer according to claim 7 or 8, wherein: The elastic wave resonator constituting the second series arm resonator has an IDT electrode. The IDT electrode has a pair of comb-shaped electrodes, the comb-shaped electrodes including: 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 electrode fingers constituting the plurality of electrode fingers to each other. The electrode fingers among the plurality of electrode fingers that are not connected to any of the bus bar electrodes constituting the pair of comb-shaped electrodes are defined as floating spacing elimination electrodes, the electrode fingers among the plurality of electrode fingers that are connected to the same bus bar electrodes as the bus bar electrodes connected to the electrode fingers on both sides are defined as polarity-reversed spacing elimination electrodes, and the electrode fingers among the plurality of electrode fingers that have the largest electrode finger width and have an electrode finger width that is more than twice the average electrode finger width among the electrode fingers other than the electrode finger are defined as filled spacing elimination electrodes. In this case, The IDT electrode of the second series arm resonator includes any one of the floating thinned-out electrode, the polarity-reversed thinned-out electrode, and the filled thinned-out electrode.

11. The multiplexer according to claim 7 or 8, wherein: The plurality of elastic wave resonators included in the second filter each include: Piezoelectric substrate; An IDT electrode is disposed on the piezoelectric substrate; as well as a second dielectric film disposed between the piezoelectric substrate and the IDT electrode or on the IDT electrode; Among the two or more series arm resonators included in the second filter, the second dielectric film of the second series arm resonator is the thickest.

12. A multiplexer comprising: a first filter having a first passband; and The second filter has a second passband which is closer to the high frequency side than the first passband. The first filter and the second filter are connected to a common terminal, The first filter comprises: two or more series arm resonators including an elastic wave resonator, which are 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, which are connected between the series arm path and ground. The second filter comprises: two or more series arm resonators including an elastic wave resonator, which are 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, which are connected between the series arm path and ground. The elastic wave resonators constituting the first filter and the second filter each have an IDT electrode, that is, an interdigital transducer electrode. The electrode finger pitch of the IDT electrode constituting at least one of the two or more series arm resonators included in the first filter is smaller than the electrode finger pitch of the IDT electrode constituting at least one of the one or more parallel arm resonators included in the second filter. Among the two or more series arm resonators and the one or more parallel arm resonators included in the first filter, a first series arm resonator among the two or more series arm resonators included in the first filter is connected closest to the common terminal, The antiresonance frequency of the first series arm resonator is lower than the high frequency end of the second passband, and is the lowest among the antiresonance frequencies of the two or more series arm resonators of the first filter, the antiresonance frequency located on the high frequency side of the first passband.

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

14. A multiplexer comprising: a first filter having a first passband; and The second filter has a second passband which is closer to the high frequency side than the first passband. The first filter and the second filter are connected to a common terminal, The first filter comprises: two or more series arm resonators including an elastic wave resonator, which are 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, which are connected between the series arm path and ground. The second filter comprises: two or more series arm resonators including an elastic wave resonator, which are 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, which are connected between the series arm path and ground. The elastic wave resonators constituting the first filter and the second filter each have an IDT electrode. The IDT electrode constituting at least one of the two or more series arm resonators included in 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 included in the second filter. Among the two or more series arm resonators and the one or more parallel arm resonators included in the second filter, a second series arm resonator among the two or more series arm resonators included in the second filter is connected closest to the common terminal, Among the IDT electrodes constituting the two or more series arm resonators included in the second filter, the electrode finger pitch of the IDT electrode constituting the second series arm resonator is the smallest.

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