Elastic wave device and multiplexer

Abstract

An elastic wave device in which generation of useless waves caused by third harmonic excitation is suppressed is provided with: a plurality of elastic wave resonators which are connected to a path connecting a first input / output terminal and a second input / output terminal, and which have IDT electrodes disposed on a piezoelectric substrate, the elastic wave resonators being connected to the path connecting the first input / output terminal and the second input / output terminal, and the elastic wave resonators being connected to the path connecting the first input / output terminal and the second input / output terminal; the piezoelectric substrate has a laminated structure of a piezoelectric film, a low-sound-velocity film, and a high-sound-velocity film, the electrode finger wavelength of the IDT electrode is [lambda] (m), the film thickness of the piezoelectric film is t1 (m), the film thickness of the plurality of electrode fingers is t2 (m), t1 / [lambda] is the film thickness wavelength ratio A of the piezoelectric film, t2 / [lambda] is the film thickness wavelength ratio B of the plurality of electrode fingers, the density of the piezoelectric film is x (g / cm < 3 >), the density of the IDT electrode is y (g / cm < 3 >), (A / x + B / y) is a mass coefficient, and (A / x + B / y) is a mass coefficient. The elastic wave resonator connected closest to the first input / output terminal has a mass coefficient of 0.95 * 0.054 or more and 1.05 * 0.054 or less.

Description

Technical Field

[0001] The present invention relates to an elastic wave device and a multiplexer. Background Art

[0002] Patent Documents 1 and 2 disclose electrode structures and substrate stacking structures of surface acoustic wave resonators using a substrate including a piezoelectric film, a low acoustic velocity film, and a high acoustic velocity film. The surface acoustic wave resonator can improve the Q value at the resonant frequency and the anti-resonant frequency compared to a surface acoustic wave resonator using a single-layer piezoelectric substrate.

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: International Publication No. 2015 / 098756

[0006] Patent Document 2: Japanese Patent Application Publication No. 2020-48067

[0007] However, in the surface acoustic wave resonators disclosed in Patent Documents 1 and 2, suppression of unnecessary waves (third harmonic excitation) generated at a frequency three times that of the fundamental wave is not sufficient. Summary of the invention

[0008] Problem that the invention aims to solve

[0009] Therefore, the present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an elastic wave device and a multiplexer that suppress the generation of unnecessary waves caused by third-order harmonic excitation.

[0010] Technical solutions to solve problems

[0011] To achieve the above object, an elastic wave device according to one embodiment of the present invention comprises: a first input / output terminal and a second input / output terminal; and a plurality of elastic wave resonators connected to a path connecting the first input / output terminal and the second input / output terminal, wherein each of the plurality of elastic wave resonators has an IDT (InterDigital Transistor) disposed on a substrate having piezoelectricity. Transducer, interdigital transducer) electrode, the substrate has: a piezoelectric film, an IDT electrode is formed on one surface; a high-acoustic-velocity film, the velocity of the propagated body wave is higher than the velocity of the elastic wave propagating in the piezoelectric film; and a low-acoustic-velocity film, which is arranged between the high-acoustic-velocity film and the piezoelectric film, and the velocity of the propagated body wave is lower than the velocity of the propagated body wave in the piezoelectric film. The electrode finger wavelength is set to λ(m), which is twice the spacing between a plurality of electrode fingers parallel to each other of the IDT electrode, the film thickness of the piezoelectric film is set to t1(m), the film thickness of the plurality of electrode fingers is set to t2(m), t1 / λ is set to the film thickness-to-wavelength ratio A of the piezoelectric film, t2 / λ is set to the film thickness-to-wavelength ratio B of the plurality of electrode fingers, and the density of the piezoelectric film is set to x(g / cm 3 ), the density of the IDT electrode is set to y(g / cm 3 ), (A / x+B / y) is set as the quality coefficient M. In this case, the quality coefficient M of the elastic wave resonator connected closest to the first input-output terminal among the multiple elastic wave resonators is greater than 0.95×0.054 and less than 1.05×0.054.

[0012] Effects of the Invention

[0013] According to the present invention, it is possible to provide an elastic wave device and a multiplexer that suppress the generation of unnecessary waves caused by third-order harmonic excitation. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a circuit structure diagram of a multiplexer involved in an embodiment.

[0015] Figure 2A It is a circuit configuration diagram of an elastic wave device according to an embodiment.

[0016] Figure 2B It is a circuit configuration diagram of an elastic wave device according to a modification of the embodiment.

[0017] Figure 3 1 and 2 are a plan view and a cross-sectional view schematically showing an elastic wave resonator according to an embodiment.

[0018] Figure 4 This is a cross-sectional view of an elastic wave resonator for explaining the quality coefficient.

[0019] Figure 5 It is a graph showing the resonance characteristics of the elastic wave resonators according to the embodiment and the comparative example.

[0020] Figure 6 This is a graph showing the relationship between the quality coefficient of the elastic wave resonator and the phase of the third harmonic excitation signal.

[0021] Description of Reference Numerals

[0022] 1: Multiplexer;

[0023] 2: Antenna;

[0024] 10, 10A, 20: filter;

[0025] 11, 12, 13, 14: series arm resonator;

[0026] 15, 16, 17, 18: Parallel arm resonator;

[0027] 19: Longitudinal coupling resonator;

[0028] 50: piezoelectric substrate;

[0029] 51: high acoustic velocity support substrate;

[0030] 52: Low sound velocity membrane;

[0031] 53: piezoelectric film;

[0032] 54: IDT electrode;

[0033] 55: protective layer;

[0034] 60, 191, 192, 193, 194, 195, 196, 197: elastic wave resonator;

[0035] 60a, 60b: comb-shaped electrodes;

[0036] 61a, 61b: electrode fingers;

[0037] 62a, 62b: bus bar electrodes;

[0038] 100: common terminal;

[0039] 110, 120: input and output terminals;

[0040] 111, 112: terminal;

[0041] 540: close contact layer;

[0042] 542: Main electrode layer. DETAILED DESCRIPTION

[0043] Hereinafter, the embodiments of the present disclosure will be described in detail using the accompanying drawings. In addition, the embodiments described below all show general or specific examples. The numerical values, shapes, materials, components, configurations of components, and connection forms shown in the following embodiments are examples, and their purpose is not to limit the present invention.

[0044] In addition, each figure is a schematic diagram that appropriately emphasizes, omits, or adjusts the ratio in order to illustrate the present invention, and is not necessarily strictly illustrated, and sometimes differs from the actual shape, positional relationship, and ratio. In each figure, the same reference numerals are marked for substantially the same structure, and repeated descriptions are sometimes omitted or simplified.

[0045] In the circuit structure of the present disclosure, “connected between A and B” or “connected between A and B” means being connected between A and B or being connected to both A and B.

[0046] In addition, in the component arrangement of the present disclosure, “component A is arranged in series on path B” means that both the signal input terminal and the signal output terminal of component A are connected to wiring, electrodes, or terminals constituting path B.

[0047] In addition, terms such as “parallel” and “perpendicular” indicating the relationship between elements, terms such as “rectangular” indicating the shape of elements, and numerical ranges do not have strict meanings but also include substantially equivalent ranges, for example, including an error of several %.

[0048] In addition, in the present disclosure, the term "terminal" means a point where a conductor in an element terminates. In addition, when the impedance of the conductor between elements is sufficiently low, the terminal is not just a single point, but is interpreted as an arbitrary point on the conductor between elements or the entire conductor.

[0049] In the following embodiments, the passband of an elastic wave device or a filter is defined as a frequency band between two frequencies that are 3 dB higher than the minimum value of insertion loss in the passband.

[0050] In addition, in the present disclosure, Band A and Band B mean frequency bands predefined by standardization groups (e.g., 3GPP (registered trademark), IEEE (Institute of Electrical and Electronics Engineers), etc.) for communication systems constructed using radio access technology (RAT: Radio Access Technology). In the present embodiment, as a communication system, for example, an LTE (Long Term Evolution) system, a 5G (5th Generation)-NR (New Radio) system, and a WLAN (Wireless Local Area Network) system can be used, but it is not limited to these.

[0051] In addition, the uplink operating frequency band of Band A means a frequency range designated for uplink in Band A. In addition, the downlink operating frequency band of Band A means a frequency range designated for downlink in Band A.

[0052] (Implementation Method)

[0053] [1. Circuit structure of multiplexer]

[0054] Figure 1 1 is a circuit diagram of a multiplexer 1 according to the embodiment. The multiplexer 1 includes filters 10 and 20 , a common terminal 100 , and input / output terminals 110 and 120 .

[0055] The common terminal 100 is connected to, for example, the antenna 2 .

[0056] The filter 10 is an example of an elastic wave device, connected to the common terminal 100, and has a passband including, for example, the uplink operating frequency band of Band A. The filter 20 is connected to the common terminal 100, and has a passband including, for example, the downlink operating frequency band of Band A. The filters 10 and 20 constitute, for example, a duplexer for Band A.

[0057] Alternatively, the filter 10 may have a passband including at least one of an uplink operating frequency band and a downlink operating frequency band of Band A, and the filter 20 may have a passband including at least one of an uplink operating frequency band and a downlink operating frequency band of Band B that is different from Band A. In this case, the filters 10 and 20 constitute a diplexer.

[0058] In the present embodiment, the passband of the filter 10 is located on the lower frequency side than the passband of the filter 20. The quality coefficient M described later of at least one of the plurality of elastic wave resonators constituting the filter 10 is set to be greater than 0.95×0.054 and less than 1.05×0.054, thereby reducing the unnecessary waves of the third harmonic excitation. Therefore, even if the unnecessary waves of the third harmonic excitation generated by the filter 10 are included in the vicinity of the passband of the filter 20, the degradation of the pass characteristics of the filter 20 can be suppressed.

[0059] In addition, the passband of the filter 10 may be located on the high-frequency side relative to the passband of the filter 20 .

[0060] Figure 2A 1 is a circuit diagram of a filter 10 according to the embodiment. As shown in the figure, the filter 10 includes series arm resonators 11 , 12 , 13 , and 14 , parallel arm resonators 15 , 16 , 17 , and 18 , and terminals 111 and 112 .

[0061] Terminal 111 is an example of a first input / output terminal, and is connected to common terminal 100. Terminal 112 is an example of a second input / output terminal, and is connected to input / output terminal 110. Series arm resonators 11 to 14 are each elastic wave resonators, and are arranged in series on a path connecting terminal 111 and terminal 112. Parallel arm resonator 15 is an elastic wave resonator, and is connected between a connection point between series arm resonators 11 and 12 and ground. Parallel arm resonator 16 is an elastic wave resonator, and is connected between a connection point between series arm resonators 12 and 13 and ground. Parallel arm resonator 17 is an elastic wave resonator, and is connected between a connection point between series arm resonators 13 and 14 and ground. Parallel arm resonator 18 is an elastic wave resonator, and is connected between a connection point between series arm resonator 14 and terminal 112 and ground. With the above-mentioned structure, filter 10 constitutes, for example, a ladder-type bandpass filter.

[0062] The series arm resonators 11 to 14 and the parallel arm resonators 15 to 18 each have an IDT electrode disposed on a substrate having piezoelectricity.

[0063] in addition, Figure 2A The circuit configuration of the filter 10 shown is an example, and the number of series arm resonators and the number of parallel arm resonators are not limited to 4, respectively, and may be 1 or more. In addition, an inductor may be connected between the parallel arm resonator and the ground.

[0064] In addition, the filter 10 is not limited to a ladder-type bandpass filter, and for example, it may also be Figure 2B As shown, a filter includes a longitudinally coupled resonator in which a plurality of elastic wave resonators are arranged in parallel in the direction of propagation of elastic waves.

[0065] Figure 2B FIG. 1 is a circuit diagram of a filter 10A according to a modification of the embodiment. The filter 10A is an example of an elastic wave device and is connected to a common terminal 100. Figure 2B As shown, the filter 10A is a filter circuit including a longitudinally coupled resonator 19 including seven elastic wave resonators, and includes the longitudinally coupled resonator 19, series arm resonators 11, 12, and 13, parallel arm resonators 15 and 16, and terminals 111 and 112. The terminal 111 is connected to the common terminal 100, and the terminal 112 is connected to the input / output terminal 120.

[0066] Longitudinal coupling resonator 19 includes elastic wave resonators 191 , 192 , 193 , 194 , 195 , 196 , and 197 , one end of which is connected to terminal 111 via series arm resonators 11 and 12 , and the other end of which is connected to terminal 112 via series arm resonator 13 .

[0067] Each of the elastic wave resonators 191 to 197 has an IDT electrode disposed on a substrate having piezoelectricity. The IDT electrodes of the elastic wave resonators 191 to 197 include two comb-shaped electrodes facing each other. One comb-shaped electrode of each of the elastic wave resonators 191, 193, 195, and 197 is connected to the terminal 111 via the series arm resonators 11 and 12, and the other comb-shaped electrode of each of the elastic wave resonators 191, 193, 195, and 197 is connected to the ground. One comb-shaped electrode of each of the elastic wave resonators 192, 194, and 196 is connected to the terminal 112 via the series arm resonator 13, and the other comb-shaped electrode of each of the elastic wave resonators 192, 194, and 196 is connected to the ground. The elastic wave resonators 191 to 197 are disposed in the order of the elastic wave resonators 191, 192, 193, 194, 195, 196, and 197 along the propagation direction of the elastic wave.

[0068] The series arm resonators 11, 12, and 13 are arranged in series on a path connecting the terminals 111 and 112. The parallel arm resonators 15 and 16 are connected between the above path and the ground, respectively.

[0069] The filter 20 may be any one of a bandpass filter, a lowpass filter, and a highpass filter, and includes at least one of an elastic wave resonator, an inductor, and a capacitor.

[0070] When the filter 20 includes an elastic wave resonator, the filters 10 and 20 may be formed on the same piezoelectric substrate. This can reduce the size of the multiplexer 1 and simplify the manufacturing process.

[0071] Furthermore, when the filter 20 includes an elastic wave resonator, the film thickness of the IDT electrode of the elastic wave resonator may be the same as the film thickness of the IDT electrode of the elastic wave resonator constituting the filter 10. This simplifies the manufacturing process of the multiplexer 1.

[0072] [2. Structure of elastic wave resonator]

[0073] Next, the basic structure of each series arm resonator and each parallel arm resonator constituting the filter 10 will be described. Figure 3 1 is a top view and a cross-sectional view schematically showing an elastic wave resonator according to the embodiment. In the same figure, a basic structure of an elastic wave resonator constituting the filter 10 is illustrated. Figure 3 The elastic wave resonator 60 shown is for explaining a typical structure of an elastic wave resonator constituting the filter 10 , and the number and length of electrode fingers constituting the electrodes are not limited thereto.

[0074] The elastic wave resonator 60 includes a piezoelectric substrate 50 and comb-shaped electrodes 60a and 60b. Figure 3 As shown in (a), 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 one ends of the plurality of electrode fingers 61a to each other. 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 one ends of the plurality of electrode fingers 61b to each other. The plurality of electrode fingers 61a and 61b are formed along a direction orthogonal to the direction of propagation of the elastic wave (X-axis direction). The bus bar electrode 62a and the bus bar electrode 62b are arranged opposite to each other with the electrode fingers 61a and 61b sandwiched therebetween. The comb-shaped electrodes 60a and 60b constitute the IDT electrode 54.

[0075] Alternatively, the elastic wave resonator 60 may include reflectors at both ends of the IDT electrode 54 in the elastic wave propagation direction (X-axis direction).

[0076] like Figure 3 As shown in (b) of FIG. 5 , the IDT electrode 54 has a stacked structure of, for example, an adhesion layer 540 and a main electrode layer 542 .

[0077] The adhesion layer 540 is a layer for improving the adhesion between the piezoelectric substrate 50 and the main electrode layer 542, and as a material, for example, Ti can be used. As a material for the main electrode layer 542, for example, Al containing 1% 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 the purpose of protecting the main electrode layer 542 from the external environment, adjusting the frequency-temperature characteristics, and improving moisture resistance, and is, for example, a dielectric film with silicon dioxide as the main component.

[0078] 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 be the above-mentioned stacked structure. The IDT electrode 54 may be composed of a metal or alloy such as Ti, Al, Cu, Pt, Au, Ag, Pd, etc., or may be composed of a plurality of stacked bodies composed of the above-mentioned metals or alloys. In addition, the protective layer 55 may not be formed.

[0079] Next, the stacked structure of the piezoelectric substrate 50 will be described. Figure 3 As shown in (c), 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 stacked in this order.

[0080] The piezoelectric film 53 is composed of, for example, a θ°Y-cut X-propagation LiTaO3 piezoelectric single crystal or a piezoelectric ceramic (a lithium tantalate single crystal or ceramic cut at a plane whose normal line is an axis rotated from the Y axis by θ° with the X axis as the center axis, and a single crystal or ceramic in which a surface acoustic wave propagates in the X-axis direction). In addition, the material of the piezoelectric single crystal used as the piezoelectric film 53 and the cutting angle θ can be appropriately selected according to the required specifications of each filter.

[0081] The high-acoustic-velocity support substrate 51 is a substrate that supports the low-acoustic-velocity film 52, the piezoelectric film 53, and the IDT electrode 54. The high-acoustic-velocity support substrate 51 is an example of a high-acoustic-velocity film, and is a substrate in which the acoustic velocity of the body wave in the high-acoustic-velocity support substrate 51 is higher than that of elastic waves such as surface waves and boundary waves propagating in the piezoelectric film 53, and the high-acoustic-velocity support 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 stacked, so that the surface acoustic wave does not leak downward from the high-acoustic-velocity support substrate 51. As the material of the high acoustic velocity support substrate 51, for example, piezoelectrics such as aluminum nitride, lithium tantalate, lithium niobate, quartz, alumina, sapphire, magnesium oxide, silicon nitride, silicon carbide, zirconium oxide, cordierite, mullite, steatite, forsterite, spinel, ceramics such as sialon, dielectrics such as aluminum oxide, silicon oxynitride, DLC (diamond-like carbon), diamond, or semiconductors such as silicon, or materials containing the above materials as main components can be used. In addition, the above spinel contains aluminum compounds containing one or more elements selected from Mg, Fe, Zn, Mn, etc. and oxygen. Examples of the above spinel include MgAl2O4, FeAl2O4, ZnAl2O4, and MnAl2O4.

[0082] The low-acoustic-velocity film 52 is a film in which the acoustic velocity of the body wave in the low-acoustic-velocity film 52 becomes lower than that of the body wave propagating in the piezoelectric film 53, and the low-acoustic-velocity film 52 is arranged between the piezoelectric film 53 and the high-acoustic-velocity supporting substrate 51. Due to this structure and the property that the energy of the elastic wave is essentially concentrated in the medium of low acoustic velocity, it is possible to suppress the surface acoustic wave energy from leaking out of the piezoelectric film 53. As the material of the low-acoustic-velocity film 52, for example, a dielectric such as glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum oxide, or a compound to which fluorine, carbon, or boron is added to silicon oxide, or a material containing the above materials as a main component can be used.

[0083] In addition, according to the stacked structure of the piezoelectric substrate 50, the Q value at the resonant frequency and the anti-resonant frequency can be greatly improved compared with the conventional structure using a single-layer piezoelectric substrate. That is, an elastic wave resonator with a high Q value can be formed, and thus a filter with a small insertion loss can be formed using the elastic wave resonator.

[0084] 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 stacked, and the sound velocity of the body wave propagated by the high-acoustic-velocity film becomes higher than that of elastic waves such as surface waves and boundary waves propagated in the piezoelectric film 53. In this case, the high-acoustic-velocity film is arranged between the support substrate and the low-acoustic-velocity film 52. As a 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 a material of the support substrate, for example, piezoelectrics such as aluminum nitride, lithium tantalate, lithium niobate, and quartz, alumina, sapphire, magnesium oxide, silicon nitride, silicon carbide, zirconium oxide, ceramics such as cordierite, mullite, steatite, and forsterite, dielectrics such as diamond and glass, semiconductors such as silicon and gallium nitride, or resins, or materials having the above materials as main components can be used.

[0085] In this specification, the term "main component of a material" refers to a component that accounts for more than 50% by weight of the material. The main component may be present in any state of single crystal, polycrystalline, or amorphous, or in a mixed state thereof.

[0086] In addition, the piezoelectric substrate forming the IDT electrode 54 may also have a structure in which a supporting substrate, an energy confinement layer, and a piezoelectric film are stacked in sequence. The IDT electrode 54 is formed on the piezoelectric film. Regarding the piezoelectric film, for example, a LiTaO3 piezoelectric single crystal or a piezoelectric ceramic can be used. The supporting substrate is a substrate that supports the piezoelectric film, the energy confinement layer, and the IDT electrode 54.

[0087] The energy confinement layer includes one or more layers, and the speed of the body acoustic wave propagating in at least one of the layers is greater than the speed of the elastic wave propagating near the piezoelectric film. For example, the energy confinement layer can also be a stacked structure of a low-acoustic-velocity film and a high-acoustic-velocity film. The low-acoustic-velocity film is a film in which the sound speed of the body wave in the low-acoustic-velocity film is lower than the sound speed of the elastic wave propagating in the piezoelectric film. The high-acoustic-velocity film is a film in which the sound speed of the body wave in the high-acoustic-velocity film is higher than the sound speed of the elastic wave propagating in the piezoelectric film. In addition, the supporting substrate can also be set as a high-acoustic-velocity film.

[0088] Furthermore, the energy sealing layer may be an acoustic impedance layer having a structure in which low acoustic impedance layers having relatively low acoustic impedance and high acoustic impedance layers having relatively high acoustic impedance are alternately stacked.

[0089] Here, electrode parameters of the IDT electrode constituting the elastic wave resonator 60 will be described.

[0090] The wavelength of the elastic wave resonator 60 is given by Figure 3 The wavelength λ shown in (b) specifies that the wavelength λ is the repetition period of the multiple electrode fingers 61a or 61b constituting the IDT electrode 54. In addition, the wavelength λ is twice the electrode finger pitch, and the electrode finger pitch is the distance between the center of the adjacent electrode finger 61a and the center of the electrode finger 61b. In addition, when the line width of the electrode fingers 61a and 61b constituting the comb-shaped electrodes 60a and 60b, respectively, is set to W, and the gap width between the adjacent electrode fingers 61a and electrode fingers 61b is set to S, the electrode finger pitch is defined by (W+S). In addition, the duty cycle of the IDT electrode 54 is the line width occupancy rate of the multiple electrode fingers 61a and 61b, which is the ratio of the line width to the sum of the line width and the gap width of the multiple electrode fingers 61a and 61b, and is defined by W / (W+S). In addition, Figure 3 In (b), the height of the comb-shaped electrodes 60a and 60b is set to h.

[0091] In addition, when the intervals between adjacent electrode fingers in the IDT electrode 54 are not constant, 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 electrode fingers 61a and 61b included in the IDT electrode 54 is Ni, and the center-to-center distance between the electrode fingers at one end and the electrode fingers at the other end of the IDT electrode 54 in the elastic wave propagation direction is Di, the average electrode finger pitch of the IDT electrode 54 is defined by Di / (Ni-1).

[0092] [3. Relationship between quality factor M and third harmonic excitation]

[0093] Next, the relationship between the mass coefficient M and the third harmonic excitation response is described. The inventors first defined the mass coefficient M as a parameter that affects the resonance characteristics of the elastic wave resonator, and found that there is a strong correlation between the mass coefficient M and the third harmonic excitation response.

[0094] Figure 4 : is a cross-sectional view of the elastic wave resonator 60 for illustrating the quality coefficient M. As shown in the figure, the electrode finger wavelength is set to λ(m), and the electrode finger wavelength is twice the pitch of the plurality of electrode fingers (electrode fingers 61a and 61b) parallel to each other that constitute the IDT electrode 54. In addition, the film thickness of the piezoelectric film 53 is set to t1(m), and the film thickness of the electrode fingers 61a and 61b is set to t2(m). In addition, t1 / λ is set to the film thickness-to-wavelength ratio A of the piezoelectric film 53, and t2 / λ is set to the film thickness-to-wavelength ratio B of the IDT electrode 54 (electrode fingers 61a and 61b). In addition, the density of the piezoelectric film 53 is set to x(g / cm 3 ), the density of the IDT electrode 54 is set to y (g / cm 3 Here, (A / x+B / y) is defined as the quality coefficient M.

[0095] The mass coefficient M is effective as a parameter for optimizing the mass distribution of the elastic wave resonator 60 in the direction perpendicular to the main surface of the piezoelectric substrate 50 by adjusting the film thickness t1 of the piezoelectric film 53 and the film thickness t2 of the IDT electrode 54 .

[0096] Table 1 shows the structures and parameters of the elastic wave resonators according to the examples and comparative examples.

[0097] [Table 1]

[0098]

[0099] In Table 1, the mass coefficient M of the elastic wave resonator according to the embodiment is 0.053, and the mass coefficient M of the elastic wave resonator according to the comparative example is 0.044.

[0100] Figure 5 1 is a graph showing the resonance characteristics of the elastic wave resonator involved in the embodiment and the comparative example. As shown in the graph, the resonance characteristics (resonance frequency, anti-resonance frequency and impedance) of the fundamental wave are substantially the same in the elastic wave resonator involved in the embodiment and the elastic wave resonator involved in the comparative example. In contrast, the intensity of the third harmonic excitation response (the difference between the impedance of the resonant frequency and the anti-resonance frequency) is lower in the elastic wave resonator involved in the embodiment than in the elastic wave resonator involved in the comparative example.

[0101] Table 2 shows the phase of the third harmonic excitation signal of the elastic wave resonator 60 when the film thickness-to-wavelength ratio A of the piezoelectric film 53 and the film thickness-to-wavelength ratio B of the IDT electrode 54 are changed. More specifically, Table 2 shows the phase of the third harmonic excitation signal of the elastic wave resonator 60 when the film thickness t1 of the piezoelectric film 53 and the film thickness t2 of the IDT electrode 54 are changed. In addition, Table 2 shows that the larger the phase of the third harmonic excitation signal (the closer to +90°), the higher the intensity of the third harmonic excitation signal, and the smaller the phase of the third harmonic excitation signal (the closer to -90°), the lower the intensity of the third harmonic excitation signal.

[0102] [Table 2]

[0103]

[0104] In addition, when calculating the film thickness wavelength ratios A and B in Table 2, the electrode finger wavelength λ is 4.15 (μm). In addition, the density y of the IDT electrode 54 is 2.7 (g / cm 3 ), the electrode duty ratio is 0.625, and the density x of the piezoelectric film 53 is 7.45 (g / cm 3 ). In addition, the material composition of the IDT electrode 54 and the piezoelectric substrate 50 is the same as the material composition shown in Table 1.

[0105] According to Table 2, when the film thickness t1 of the piezoelectric film 53 and the film thickness t2 of the IDT electrode 54 are changed, the combination of t1 and t2 at which the phase of the third harmonic excitation signal becomes minimum (bold characters in Table 2) is different.

[0106] Figure 6 : is a graph showing the relationship between the mass coefficient M of the elastic wave resonator and the phase of the third harmonic excitation signal. In the same figure, the relationship between the mass coefficient M and the phase of the third harmonic excitation signal is shown when the film thickness t1 of the piezoelectric film 53 in Table 2 is 700nm, 800nm, and 900nm. Even if the film thickness t1 of the piezoelectric film 53 is changed, the phase of the third harmonic excitation signal is minimized when the mass coefficient M is approximately 0.054.

[0107] Furthermore, the quality factor M when the phase of the third harmonic excitation signal is -45° or less is within the range of 0.054±5%. In other words, the quality factor M when the phase of the third harmonic excitation signal is -45° or less is 0.95×0.054 or more and 1.05×0.054 or less.

[0108] Thus, the characteristic degradation of the filter 10 caused by the third harmonic excitation response can be suppressed to a level that does not cause a problem in practical use.

[0109] The elastic wave resonator involved in this embodiment is equivalent to the series arm resonator 11 among the plurality of elastic wave resonators constituting the filter 10 involved in the embodiment. That is, the quality coefficient M of the series arm resonator 11 connected closest to the terminal 111 among the plurality of elastic wave resonators constituting the filter 10 is greater than or equal to 0.95×0.054 and less than or equal to 1.05×0.054.

[0110] Thus, it is possible to effectively suppress the adverse effects of the third harmonic excitation signal generated in the filter 10 on other filter circuits connected to the filter 10 at the terminal 111. In the multiplexer 1 involved in the embodiment, for example, the reflection loss at the frequency of the third harmonic excitation generated in the filter 10 can be effectively reduced, so the degradation of the characteristics of the filter 20 at this frequency can be effectively suppressed.

[0111] This can be explained as being caused by the fact that, by optimizing the mass coefficient M, the mass distribution of the series arm resonator 11 in the direction perpendicular to the main surface of the piezoelectric substrate 50 is optimized.

[0112] In addition, when optimizing the quality coefficient M, the film thickness t1 of the piezoelectric film 53 and the film thickness t2 of the IDT electrode 54 may be adjusted.

[0113] As a first example of the optimization of the quality coefficient M, in order to adjust the relative bandwidth (resonance bandwidth) and high-order modes of the elastic wave resonator, first, the film thickness t1 of the piezoelectric film 53 is optimized. Corresponding to the optimized film thickness t1, the film thickness t2 of the IDT electrode 54 is optimized, thereby adjusting the relative bandwidth (resonance bandwidth) and high-order modes, and suppressing the third harmonic excitation response.

[0114] Furthermore, as a second example of the optimization of the quality coefficient M, in order to adjust the stopband width and power handling of the elastic wave resonator, first, the film thickness t2 of the IDT electrode 54 is optimized. Corresponding to the optimized film thickness t2, the film thickness t1 of the piezoelectric film 53 is optimized, thereby adjusting the stopband width and power handling, and suppressing the third harmonic excitation response.

[0115] In the case of filter 10A according to the modification of the embodiment, the quality coefficient M of series arm resonator 11 connected closest to terminal 111 among the plurality of elastic wave resonators constituting filter 10A is greater than or equal to 0.95×0.054 and less than or equal to 1.05×0.054.

[0116] In addition, in the circuit structure of filters 10 and 10A, when the elastic wave resonator connected closest to the terminal 111 is a parallel arm resonator and a series arm resonator, it is sufficient as long as the quality coefficient M of at least one of the parallel arm resonator and the series arm resonator is greater than 0.95×0.054 and less than 1.05×0.054.

[0117] The elastic wave resonator according to this embodiment may correspond to all of the plurality of elastic wave resonators constituting the filter 10 according to the embodiment. In other words, the quality coefficient M of all of the elastic wave resonators constituting the filter 10 may be greater than or equal to 0.95×0.054 and less than or equal to 1.05×0.054.

[0118] This makes it possible to suppress the third-order harmonic excitation signal generated in each elastic wave resonator constituting the filter 10 , and thus the third-order harmonic excitation signal generated from the filter 10 can be suppressed to the maximum extent.

[0119] In addition, in order to optimize the pass characteristics in filters using elastic wave resonators, a region where the duty ratio is larger than 0.5 is often used. However, in the region where the duty ratio is larger than 0.5, unnecessary waves excited by the third harmonic tend to become larger.

[0120] On the other hand, according to the filter 10 using the elastic wave resonator according to the present embodiment, even in a region where the duty ratio is larger than 0.5, it is possible to suppress unnecessary waves caused by third-order harmonic excitation.

[0121] Furthermore, all elastic wave resonators constituting the filter 10 may share a single piezoelectric substrate 50 .

[0122] This makes it possible to easily set the quality coefficient M of all elastic wave resonators constituting the filter 10 to be greater than or equal to 0.95×0.054 and less than or equal to 1.05×0.054. In addition, the filter 10 can be miniaturized.

[0123] Furthermore, the film thickness t2 of the IDT electrode 54 may be the same in all the elastic wave resonators constituting the filter 10 .

[0124] This makes it possible to easily set the quality coefficient M of all elastic wave resonators constituting the filter 10 to be greater than or equal to 0.95×0.054 and less than or equal to 1.05×0.054. In addition, the manufacturing process of the filter 10 can be simplified.

[0125] [4. Effects, etc.]

[0126] As described above, the filter 10 according to the present embodiment includes the terminals 111 and 112 and a plurality of elastic wave resonators connected to a path connecting the terminals 111 and 112. Each of the plurality of elastic wave resonators includes an IDT electrode 54 disposed on a substrate having piezoelectricity. The piezoelectric substrate includes: a piezoelectric film 53 having the IDT electrode 54 formed on one surface; a high-acoustic-velocity film having a body wave propagating at a higher speed than the elastic wave propagating on the piezoelectric film 53; and a low-acoustic-velocity film 52 disposed on the high-acoustic-velocity film. The velocity of the bulk wave propagating between the piezoelectric film 53 is lower than the velocity of the bulk wave propagating in the piezoelectric film 53, the electrode finger wavelength is set to λ(m), which is twice the pitch of the plurality of electrode fingers parallel to each other of the IDT electrode 54, the film thickness of the piezoelectric film 53 is set to t1(m), the film thickness of the plurality of electrode fingers is set to t2(m), t1 / λ is set to the film thickness-to-wavelength ratio A of the piezoelectric film 53, t2 / λ is set to the film thickness-to-wavelength ratio B of the plurality of electrode fingers, and the density of the piezoelectric film 53 is set to x(g / cm 3 ), the density of the IDT electrode 54 is set to y (g / cm 3 ), (A / x+B / y) is set as the quality coefficient M. In this case, the quality coefficient M of the first elastic wave resonator connected closest to the terminal 111 among the multiple elastic wave resonators is greater than 0.95×0.054 and less than 1.05×0.054.

[0127] This can effectively prevent the unwanted waves caused by the third harmonic excitation generated in the filter 10 from adversely affecting other filter circuits connected to the filter 10 at the terminal 111 .

[0128] Furthermore, for example, in the filter 10 , the quality coefficient M of each of the plurality of elastic wave resonators is greater than or equal to 0.95×0.054 and less than or equal to 1.05×0.054.

[0129] This makes it possible to suppress the third harmonic excitation signal generated in each elastic wave resonator constituting the filter 10 , and thus to maximally suppress unnecessary waves of the third harmonic excitation generated from the filter 10 .

[0130] Furthermore, for example, in the filter 10 , the piezoelectric substrate 50 may be shared by a plurality of elastic wave resonators.

[0131] This makes it possible to easily set the quality coefficient M of all elastic wave resonators constituting the filter 10 to be greater than or equal to 0.95×0.054 and less than or equal to 1.05×0.054. In addition, the filter 10 can be miniaturized.

[0132] Furthermore, for example, in filter 10 , the film thickness t2 of the plurality of electrode fingers is the same in the plurality of elastic wave resonators.

[0133] This makes it possible to easily set the quality coefficient M of all elastic wave resonators constituting the filter 10 to be greater than or equal to 0.95×0.054 and less than or equal to 1.05×0.054. In addition, the manufacturing process of the filter 10 can be simplified.

[0134] Furthermore, for example, in the filter 10 , the piezoelectric film 53 contains LiTaO 3 .

[0135] In the case of using an elastic wave resonator including a piezoelectric substrate 50 having a stacked structure including a piezoelectric film 53 including LiTaO3, a low-acoustic-velocity film, and a high-acoustic-velocity film, unnecessary waves of a high-order mode are easily generated. In contrast, according to the above-mentioned structure of the filter 10, even when using a piezoelectric substrate 50 having the above-mentioned stacked structure, unnecessary waves caused by third-order harmonic excitation can be suppressed.

[0136] In addition, for example, in the filter 10, the plurality of elastic wave resonators include series arm resonators 11 to 14 and parallel arm resonators 15 to 18, the series arm resonators 11 to 14 are arranged in series in a path connecting the terminals 111 and 112, and the parallel arm resonators 15 to 18 are connected between the above path and the ground.

[0137] This makes it possible to suppress unnecessary waves caused by third-order harmonic excitation in the ladder-type filter 10 .

[0138] Furthermore, for example, in the filter 10A, the plurality of elastic wave resonators include longitudinally coupled resonators.

[0139] This makes it possible to suppress unnecessary waves caused by third-order harmonic excitation in the filter 10A including the longitudinally coupled resonator.

[0140] Furthermore, for example, the multiplexer 1 according to the present embodiment includes the common terminal 100 , the filter 10 or 10A whose terminal 111 is connected to the common terminal 100 , and the filter 20 connected to the common terminal 100 .

[0141] This can effectively prevent the third harmonic excitation signal generated in the filter 10 from adversely affecting the filter 20 via the common terminal 100 .

[0142] Furthermore, for example, in the multiplexer 1 , the filter 20 includes an elastic wave resonator and is disposed on the piezoelectric substrate 50 .

[0143] Thus, the multiplexer 1 can be miniaturized and the manufacturing process can be simplified.

[0144] Furthermore, for example, in the multiplexer 1 , the elastic wave resonator of the filter 20 has an IDT electrode disposed on the piezoelectric substrate 50 , and the film thickness of the plurality of electrode fingers constituting the IDT electrode of the filter 20 is the same as the film thickness of the plurality of electrode fingers constituting the IDT electrode of the filter 10 .

[0145] Thus, the manufacturing process of the multiplexer 1 can be simplified.

[0146] Furthermore, for example, in the multiplexer 1 , the passband of the filter 20 is located on the high frequency side relative to the passband of the filter 10 .

[0147] Thus, even if the unnecessary waves excited by the third harmonic generated by the filter 10 are included in the vicinity of the passband of the filter 20 , it is possible to suppress the degradation of the passband characteristics of the filter 20 .

[0148] (Other Embodiments)

[0149] The elastic wave device and multiplexer according to the present invention are described above by enumerating the embodiments, examples and variations, but the present invention is not limited to the above-mentioned embodiments, examples and variations. Variations obtained by implementing various modifications that a person skilled in the art can think of to the above-mentioned embodiments, examples and variations without departing from the main purpose of the present invention, and various devices incorporating the elastic wave device and multiplexer according to the present invention are also included in the present invention.

[0150] Furthermore, for example, in the elastic wave devices and multiplexers according to the above-described embodiments, examples, and modifications, matching elements such as inductors and capacitors and switch circuits may be connected between the components.

[0151] The resonant frequency and anti-resonant frequency described in the above-described embodiment, example, and modified example can be derived by, for example, bringing an RF probe into contact with two input and output electrodes of an elastic wave resonator and measuring reflection characteristics.

[0152] Features of the elastic wave device and the multiplexer described in the above-described embodiments and examples are described below.

[0153] <1>

[0154] An elastic wave device comprising:

[0155] a first input / output terminal and a second input / output terminal; and

[0156] A plurality of elastic wave resonators are connected to a path connecting the first input / output terminal and the second input / output terminal.

[0157] Each of the plurality of elastic wave resonators includes an IDT electrode disposed on a substrate having piezoelectricity.

[0158] The substrate has:

[0159] A piezoelectric film having the IDT electrode formed on one surface;

[0160] a high acoustic velocity film in which a body wave propagates at a higher acoustic velocity than an elastic wave propagating through the piezoelectric film; and

[0161] The low-acoustic-velocity film is disposed between the high-acoustic-velocity film and the piezoelectric film, and the acoustic velocity of the bulk wave propagated therein is lower than the acoustic velocity of the bulk wave propagated in the piezoelectric film.

[0162] The electrode finger wavelength is set to λ(m), which is twice the pitch of the plurality of electrode fingers parallel to each other of the IDT electrode, the film thickness of the piezoelectric film is set to t1(m), the film thickness of the plurality of electrode fingers is set to t2(m), t1 / λ is set to the film thickness-to-wavelength ratio A of the piezoelectric film, t2 / λ is set to the film thickness-to-wavelength ratio B of the plurality of electrode fingers, and the density of the piezoelectric film is set to x(g / cm 3 ), the density of the IDT electrode is set to y(g / cm 3 ), let (A / x+B / y) be the quality coefficient M. In this case,

[0163] A quality coefficient M of a first elastic wave resonator that is connected closest to the first input / output terminal among the plurality of elastic wave resonators is greater than or equal to 0.95×0.054 and less than or equal to 1.05×0.054.

[0164] <2>

[0165] The elastic wave device according to <1>,

[0166] A quality coefficient M of each of the plurality of elastic wave resonators is greater than or equal to 0.95×0.054 and less than or equal to 1.05×0.054.

[0167] <3>

[0168] The elastic wave device according to <1> or <2>, wherein:

[0169] The substrate having piezoelectricity is shared by the plurality of elastic wave resonators.

[0170] <4>

[0171] The elastic wave device according to any one of <1> to <3>,

[0172] The film thickness t2 of the plurality of electrode fingers is the same in the plurality of elastic wave resonators.

[0173] <5>

[0174] The elastic wave device according to any one of <1> to <4>,

[0175] The piezoelectric film includes LiTaO3.

[0176] <6>

[0177] The elastic wave device according to any one of <1> to <5>,

[0178] The plurality of elastic wave resonators include:

[0179] a series arm resonator arranged in series on a path connecting the first input / output terminal and the second input / output terminal; and

[0180] The parallel arm resonator is connected between the path and the ground.

[0181] <7>

[0182] The elastic wave device according to any one of <1> to <5>,

[0183] The plurality of elastic wave resonators include longitudinally coupled resonators.

[0184] <8>

[0185] A multiplexer having:

[0186] Common terminal;

[0187] In the elastic wave device according to any one of <1> to <7>, the first input / output terminal is connected to the common terminal; and

[0188] A filter is connected to the common terminal.

[0189] <9>

[0190] The multiplexer according to <8>, wherein:

[0191] The filter includes an elastic wave resonator disposed on the substrate.

[0192] <10>

[0193] The multiplexer according to <9>, wherein:

[0194] The elastic wave resonator of the filter has an IDT electrode arranged on the substrate.

[0195] The film thickness of the plurality of electrode fingers of the IDT electrode constituting the filter is the same as the film thickness of the plurality of electrode fingers of the IDT electrode constituting the elastic wave device.

[0196] <11>

[0197] The multiplexer according to any one of <8> to <10>, wherein:

[0198] The passband of the filter is located on the higher frequency side than the passband of the elastic wave device.

[0199] Industrial Applicability

[0200] The present invention can be widely used as a transceiver filter and a multiplexer used at the front end of a wireless communication terminal that requires low loss within a passband and high attenuation outside the passband.

Claims

1. An elastic wave device comprising: a first input / output terminal and a second input / output terminal; and A plurality of elastic wave resonators are connected to a path connecting the first input / output terminal and the second input / output terminal. Each of the plurality of elastic wave resonators includes an IDT electrode, that is, an interdigital transducer electrode, disposed on a piezoelectric substrate. The substrate has: A piezoelectric film having the IDT electrode formed on one surface; a high acoustic velocity film in which a body wave propagates at a higher acoustic velocity than an elastic wave propagating through the piezoelectric film; and The low-acoustic-velocity film is disposed between the high-acoustic-velocity film and the piezoelectric film, and the acoustic velocity of the bulk wave propagated therein is lower than the acoustic velocity of the bulk wave propagated in the piezoelectric film. The electrode finger wavelength is set to λ, in units of m. The electrode finger wavelength is twice the pitch of the multiple electrode fingers parallel to each other of the IDT electrode. The film thickness of the piezoelectric film is set to t1, in units of m. The film thickness of the multiple electrode fingers is set to t2, in units of m. t1 / λ is set to the film thickness-to-wavelength ratio A of the piezoelectric film. t2 / λ is set to the film thickness-to-wavelength ratio B of the multiple electrode fingers. The density of the piezoelectric film is set to x, in units of g / cm 3 , the density of the IDT electrode is set to y, the unit is g / cm 3 , let (A / x+B / y) be the quality coefficient M. In this case, A quality coefficient M of an elastic wave resonator connected closest to the first input / output terminal among the plurality of elastic wave resonators is greater than or equal to 0.95×0.054 and less than or equal to 1.05×0.

054.

2. The elastic wave device according to claim 1, wherein: A quality coefficient M of each of the plurality of elastic wave resonators is greater than or equal to 0.95×0.054 and less than or equal to 1.05×0.

054.

3. The elastic wave device according to claim 1 or 2, wherein: The substrate is shared by the plurality of elastic wave resonators.

4. The elastic wave device according to any one of claims 1 to 3, wherein: The film thickness t2 of the plurality of electrode fingers is the same in the plurality of elastic wave resonators.

5. The elastic wave device according to any one of claims 1 to 4, wherein: The piezoelectric film includes LiTaO3.

6. The elastic wave device according to any one of claims 1 to 5, wherein: The plurality of elastic wave resonators include: a series arm resonator arranged in series on a path connecting the first input / output terminal and the second input / output terminal; and The parallel arm resonator is connected between the path and the ground.

7. The elastic wave device according to any one of claims 1 to 5, wherein: The plurality of elastic wave resonators include longitudinally coupled resonators.

8. A multiplexer comprising: Common terminal; The elastic wave device according to any one of claims 1 to 7, wherein the first input / output terminal is connected to the common terminal; and A filter is connected to the common terminal.

9. The multiplexer according to claim 8, wherein: The filter includes an elastic wave resonator disposed on the substrate.

10. The multiplexer according to claim 9, wherein: The elastic wave resonator of the filter has an IDT electrode arranged on the substrate. The film thickness of the plurality of electrode fingers of the IDT electrode constituting the filter is the same as the film thickness of the plurality of electrode fingers of the IDT electrode constituting the elastic wave device.

11. The multiplexer according to any one of claims 8 to 10, wherein: The passband of the filter is located on the higher frequency side than the passband of the elastic wave device.

12. An elastic wave device comprising: a first input / output terminal and a second input / output terminal; and A plurality of elastic wave resonators are connected to a path connecting the first input / output terminal and the second input / output terminal. Each of the plurality of elastic wave resonators includes an IDT electrode, that is, an interdigital transducer electrode, disposed on a piezoelectric substrate. The substrate has: A piezoelectric film having the IDT electrode formed on one surface; A high acoustic velocity membrane composed of any one of aluminum nitride, lithium tantalate, lithium niobate, quartz, alumina, sapphire, magnesium oxide, silicon nitride, silicon carbide, zirconium oxide, cordierite, mullite, steatite, forsterite, spinel, sialon, aluminum oxide, silicon oxynitride, diamond-like carbon, diamond, silicon, or a material having any of the above as a main component; and The low acoustic velocity film is disposed between the high acoustic velocity film and the piezoelectric film and is composed of any one of glass, silicon oxide, silicon oxynitride, lithium oxide, and tantalum oxide, or a material having the same as a main component. The electrode finger wavelength is set to λ, in units of m. The electrode finger wavelength is twice the pitch of the multiple electrode fingers parallel to each other of the IDT electrode. The film thickness of the piezoelectric film is set to t1, in units of m. The film thickness of the multiple electrode fingers is set to t2, in units of m. t1 / λ is set to the film thickness-to-wavelength ratio A of the piezoelectric film. t2 / λ is set to the film thickness-to-wavelength ratio B of the multiple electrode fingers. The density of the piezoelectric film is set to x, in units of g / cm 3 , the density of the IDT electrode is set to y, the unit is g / cm 3 , let (A / x+B / y) be the quality coefficient M. In this case, A quality coefficient M of an elastic wave resonator connected closest to the first input / output terminal among the plurality of elastic wave resonators is greater than or equal to 0.95×0.054 and less than or equal to 1.05×0.054.

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