Elastic wave device and multiplexer

Abstract

A filter (10) comprises a piezoelectric substrate (50) and an IDT electrode (54) disposed on the piezoelectric substrate (50). The IDT electrode (54) has N (N is an integer greater than or equal to 4) electrode fingers arranged in parallel with one another. Where M1 is one of integers greater than or equal to an integer obtained by rounding off the first decimal place of 0.2 N and less than or equal to an integer obtained by rounding off the first decimal place of 0.3 N, M2 is one of integers greater than or equal to an integer obtained by rounding off the first decimal place of 0.45 N and less than or equal to an integer obtained by rounding off the first decimal place of 0.55 N, and M3 is one of integers greater than or equal to an integer obtained by rounding off the first decimal place of 0.7 N and less than or equal to an integer obtained by rounding off the first decimal place of 0.8 N, the M1-th electrode finger pitch, the M2-th electrode finger pitch and the M3-th electrode finger pitch are all larger than any of the electrode finger pitches, excluding the M1-th, M2-th and M3-th electrode finger pitches.

Description

Acoustic wave devices and multiplexers

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

[0002] Patent Document 1 discloses a multiplexer including a transmitting filter and a receiving filter connected to a common terminal. In the transmitting filter, among a plurality of electrode fingers constituting an IDT (InterDigital Transducer) electrode, the electrode finger pitch at a center in the arrangement direction of the plurality of electrode fingers is the largest among the electrode finger pitches of the IDT electrode, and the electrode finger pitch at an end in the arrangement direction is the smallest among the electrode finger pitches of the IDT electrode. This reduces signal distortion in the IDT electrode, suppresses the occurrence of intermodulation distortion, and suppresses degradation of the pass characteristics of the transmitting filter and the receiving filter (hereinafter both referred to as acoustic wave devices).

[0003] International Publication No. 2019 / 117133

[0004] However, the multiplexer disclosed in Patent Document 1 does not sufficiently suppress unwanted waves that occur at frequencies lower than the resonant frequency of the main mode of the high-frequency elastic wave device, resulting in a problem of deterioration in the attenuation characteristics of the high-frequency elastic wave device and / or the pass characteristics of the low-frequency elastic wave device.

[0005] The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an acoustic wave device and a multiplexer in which the generation of unwanted waves is suppressed.

[0006] In order to achieve the above object, an elastic wave device according to one aspect of the present invention includes a piezoelectric substrate and an IDT electrode disposed on the substrate, the IDT electrode having N (N is an integer equal to or greater than 4) electrode fingers arranged parallel to one another, the distance between the kth electrode finger and the (k+1)th electrode finger from an end of the IDT electrode (1≦k≦N−1) is defined as the kth electrode finger pitch, M1 is any one of integers equal to or greater than 0.2N rounded to one decimal place and equal to or less than 0.3N rounded to one decimal place, and M2 is any one of integers equal to or greater than 0.45N rounded to one decimal place. Let M2 be any one of integers equal to or greater than 0.7N rounded to the nearest tenth place and equal to or less than 0.8N rounded to the nearest tenth place, and let M3 be any one of integers equal to or greater than 0.7N rounded to the nearest tenth place and equal to or less than 0.8N rounded to the nearest tenth place. Each of the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch is larger than any of the electrode finger pitches excluding the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch.

[0007] According to the present invention, it is possible to provide an acoustic wave device and a multiplexer in which the generation of unwanted waves is suppressed.

[0008] FIG. 1 is a circuit diagram of a multiplexer according to an embodiment. FIG. 2A is a plan view and a cross-sectional view schematically illustrating a first example of an elastic wave resonator included in an elastic wave device according to an embodiment. FIG. 2B is a cross-sectional view schematically illustrating a second example of an elastic wave resonator included in an elastic wave device according to an embodiment. FIG. 3 is a diagram illustrating the distribution of electrode finger pitches of IDT electrodes included in an elastic wave resonator according to Example 1. FIG. 4A is a graph illustrating the impedance of elastic wave resonators according to Example 1 and a comparative example. FIG. 4B is a graph illustrating the phase and reflection loss of Rayleigh wave responses of elastic wave resonators according to Example 1 and a comparative example. FIG. 5 is a graph illustrating the vibration displacement of Rayleigh waves of elastic wave resonators according to Example 1 and a comparative example. FIG. 6 is a diagram illustrating the distribution of electrode finger pitches of IDT electrodes included in an elastic wave resonator according to Example 2. FIG. 7A is a graph illustrating the impedance of an elastic wave resonator according to Example 2. FIG. 7B is a graph illustrating the phase and reflection loss of a Rayleigh wave response of an elastic wave resonator according to Example 2. FIG. 8 is a graph showing changes in the reflection loss of the Rayleigh wave response when the pitch of the (N / 4)th, (N / 2)th, and (3N / 4)th electrode fingers of the acoustic wave resonator according to the second embodiment is changed.

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

[0010] It should be noted that the drawings are schematic diagrams in which emphasis, omission, or adjustment of proportions has been appropriately made to illustrate the present invention, and are not necessarily strictly illustrated, and may differ from the actual shapes, positional relationships, and proportions. In the drawings, the same reference numerals are used to denote substantially the same components, and redundant explanations may be omitted or simplified.

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

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

[0013] Furthermore, terms indicating the relationship between elements, such as "parallel" and "perpendicular," terms indicating the shape of elements, such as "rectangle," and numerical ranges do not only represent strict meanings, but also include substantially equivalent ranges, for example, including an error of a few percent.

[0014] In the component layout of this disclosure, "planar view of the main surface" means that the object is viewed by orthogonal projection onto the main surface from the z-axis side. "A is located between B and C" means that at least one of multiple line segments connecting any point in B and any point in C passes through A.

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

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

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

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

[0019] Filter 10 is an example of an acoustic wave device, is connected to common terminal 100, and has a pass band that includes a downlink operating band, e.g., band A. Filter 20 is connected to common terminal 100 and has a pass band that includes an uplink operating band, e.g., band A. In this embodiment, the pass band of filter 20 is located at a lower frequency than the pass band of filter 10.

[0020] As shown in FIG. 1, a filter 10 includes series arm resonators 11 , 12 , and 13 , and parallel arm resonators 14 , 15 , and 16 .

[0021] Each of the series arm resonators 11 to 13 is an elastic wave resonator and is arranged in a series arm path connecting the common terminal 100 and the input / output terminal 110. The parallel arm resonator 14 is an elastic wave resonator and is connected between the connection point of the series arm resonators 11 and 12 and ground. The parallel arm resonator 15 is an elastic wave resonator and is connected between the connection point of the series arm resonators 12 and 13 and ground. The parallel arm resonator 16 is an elastic wave resonator and is connected between the connection point of the series arm resonator 13 and the input / output terminal 110 and ground. With the above configuration, the filter 10 constitutes, for example, a ladder-type bandpass filter.

[0022] In the filter 10, the number of series arm resonators and the number of parallel arm resonators are not limited to three, but may be equal to or greater than 1. In addition, an inductor may be connected between a parallel arm resonator and ground.

[0023] Furthermore, the filter 10 is not limited to being a ladder-type bandpass filter, but may be a filter including a longitudinally coupled resonator in which a plurality of acoustic wave resonators are arranged in parallel in the acoustic wave propagation direction.

[0024] The filter 20 may be any of a band-pass filter, a low-pass filter, and a high-pass filter, and includes at least one of an acoustic wave resonator, an inductor, and a capacitor.

[0025] [2. Structure of Acoustic Wave Resonator] Next, the basic structure of each series arm resonator and each parallel arm resonator constituting filter 10 will be described. Fig. 2A is a plan view and a cross-sectional view schematically illustrating a first example of an acoustic wave resonator constituting filter 10 according to an embodiment. The figures illustrate the basic structure of an acoustic wave resonator constituting filter 10. Note that acoustic wave resonator 60 shown in Fig. 2A is intended to illustrate a typical structure of an acoustic wave resonator constituting filter 10, and the number and length of electrode fingers constituting the electrodes are not limited to this.

[0026] The acoustic wave resonator 60 includes a piezoelectric substrate 50 and comb electrodes 60a and 60b. As shown in FIG. 2A (a), a pair of opposing comb electrodes 60a and 60b is formed on the piezoelectric substrate 50. The comb electrode 60a includes a plurality of parallel electrode fingers 61a and a busbar electrode 62a connecting one ends of the electrode fingers 61a. The comb electrode 60b includes a plurality of parallel electrode fingers 61b and a busbar electrode 62b connecting one ends of the electrode fingers 61b. The electrode fingers 61a and 61b are formed in a direction perpendicular to the acoustic wave propagation direction (X-axis direction). The busbar electrodes 62a and 62b are arranged opposite each other with the electrode fingers 61a and 61b interposed therebetween. The comb electrodes 60a and 60b form an IDT electrode 54.

[0027] The acoustic wave resonator 60 may have reflectors on both ends of the IDT electrode 54 in the acoustic wave propagation direction (X-axis direction).

[0028] As shown in FIG. 2B, the IDT electrode 54 has a laminated structure of, for example, an adhesive layer 540 and a main electrode layer 542.

[0029] The adhesion layer 540 is a layer for improving adhesion between the piezoelectric substrate 50 and the main electrode layer 542, and is made of, for example, Ti. The main electrode layer 542 is made of, for example, Al containing 1% Cu. The protective layer 55 is formed to cover the comb-shaped electrodes 60a and 60b. The protective layer 55 is a layer intended to protect the main electrode layer 542 from the external environment, adjust the frequency-temperature characteristics, and increase moisture resistance, and is, for example, a dielectric film primarily composed of silicon dioxide.

[0030] The materials constituting the adhesion layer 540, the main electrode layer 542, and the protective layer 55 are not limited to those described above. Furthermore, the IDT electrode 54 does not have to have the laminated structure described above. The IDT electrode 54 may be made of, for example, a metal or alloy such as Ti, Al, Cu, Pt, Au, Ag, or Pd, or may be made of a laminate of multiple layers made of the above metals or alloys. Furthermore, the protective layer 55 does not necessarily have to be formed.

[0031] Next, the laminated structure of the piezoelectric substrate 50 will be described.

[0032] As shown in (c) of FIG. 2A, the piezoelectric substrate 50 includes a high acoustic velocity support substrate 51, a low acoustic velocity film 52, and a piezoelectric film 53, and has a structure in which the high acoustic velocity support substrate 51, the low acoustic velocity film 52, and the piezoelectric film 53 are stacked in this order.

[0033] The piezoelectric film 53 is, for example, a θ° Y-cut X-propagation LiTaO ３ It is made of a piezoelectric single crystal or piezoelectric ceramics (a lithium tantalate single crystal or ceramic cut along a plane whose normal is an axis rotated θ degrees from the Y axis around the X axis, and through which surface acoustic waves propagate in the X axis direction). The material and cut angle θ of the piezoelectric single crystal used as the piezoelectric film 53 are appropriately selected depending on the required specifications of each filter.

[0034] The high acoustic velocity support substrate 51 is a substrate that supports the low acoustic velocity film 52, the piezoelectric film 53, and the IDT electrode 54. The high acoustic velocity support substrate 51 is also a substrate in which the acoustic velocity of bulk waves in the high acoustic velocity support substrate 51 is faster than that of acoustic waves such as surface waves and boundary waves that propagate through the piezoelectric film 53, and functions to confine the surface acoustic waves to the portion where the piezoelectric film 53 and the low acoustic velocity film 52 are laminated, preventing them from leaking below the high acoustic velocity support substrate 51. Examples of materials that can be used for the high acoustic velocity support substrate 51 include piezoelectric materials such as aluminum nitride, lithium tantalate, lithium niobate, and quartz; ceramics such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, spinel, and sialon; dielectrics such as aluminum oxide, silicon oxynitride, DLC (diamond-like carbon), and diamond; semiconductors such as silicon; and materials containing any of the above materials as a main component. The spinel includes aluminum compounds containing oxygen and one or more elements selected from Mg, Fe, Zn, Mn, etc. Examples of the spinel include MgAl ２ O ４ , FeAl ２ O ４ , ZnAl ２ O ４ , MnAl ２ O ４ Examples include:

[0035] The low acoustic velocity film 52 is a film in which the acoustic velocity of the bulk waves in the low acoustic velocity film 52 is slower than that of the bulk waves propagating through the piezoelectric film 53, and is disposed between the piezoelectric film 53 and the high acoustic velocity support substrate 51. This structure and the property of the acoustic waves that energy is concentrated in a medium with an essentially low acoustic velocity suppress leakage of surface acoustic wave energy out of the piezoelectric film 53. The low acoustic velocity film 52 can be made of a dielectric material such as glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum oxide, or a compound in which fluorine, carbon, or boron is added to silicon oxide, or a material containing any of the above materials as a main component.

[0036] The above-described laminated structure of piezoelectric substrate 50 makes it possible to significantly increase the Q value at the resonant frequency and antiresonant frequency compared to a conventional structure using a single-layer piezoelectric substrate. In other words, an elastic wave resonator with a high Q value can be configured, and a filter with low insertion loss can be configured using the elastic wave resonator.

[0037] The high acoustic velocity support substrate 51 may have a laminated structure of a support substrate and a high acoustic velocity film in which the acoustic velocity of the propagating bulk waves is faster than that of elastic waves such as surface waves and boundary waves that propagate through the piezoelectric film 53. In this case, the material of the high acoustic velocity film can be the same as the material of the high acoustic velocity support substrate 51. The material of the support substrate can be, for example, piezoelectrics such as aluminum nitride, lithium tantalate, lithium niobate, and quartz; ceramics such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, and forsterite; dielectrics such as diamond and glass; semiconductors such as silicon and gallium nitride; resins; or materials containing any of the above materials as a main component.

[0038] In this specification, the term "major component of a material" refers to a component that accounts for more than 50% by weight of the material. The major component may be in a single crystal, polycrystalline, or amorphous state, or a mixture of these.

[0039] 2B is a cross-sectional view schematically illustrating a second example of an acoustic wave resonator constituting filter 10 according to an embodiment. In acoustic wave resonator 60 illustrated in FIG. 2A , IDT electrode 54 is formed on piezoelectric substrate 50 having piezoelectric film 53. However, the substrate on which IDT electrode 54 is formed may be piezoelectric single crystal substrate 57 consisting of a single piezoelectric layer, as illustrated in FIG. 2B .

[0040] The piezoelectric single crystal substrate 57 is, for example, LiTaO ３ The elastic wave resonator according to this example is made of a piezoelectric single crystal of LiTaO ３The piezoelectric transducer 50 is composed of a piezoelectric single crystal substrate 57, an IDT electrode 54, and a protective layer 58 formed on the piezoelectric single crystal substrate 57 and the IDT electrode 54.

[0041] The laminate structure, material, cut angle, and thickness of the piezoelectric film 53 and piezoelectric single crystal substrate 57 may be changed as appropriate depending on the required pass characteristics of the filter 10 and multiplexer 1 .

[0042] The piezoelectric substrate on which the IDT electrode 54 is formed may have a structure in which a support substrate, an energy trapping layer, and a piezoelectric film are laminated in this order. The IDT electrode 54 is formed on the piezoelectric film. The piezoelectric film may be, for example, LiTaO ３ The support substrate is a substrate that supports the piezoelectric film, the energy trapping layer, and the IDT electrode 54.

[0043] The energy trapping layer is composed of one or more layers, and the velocity of the bulk acoustic waves propagating through at least one of the layers is greater than the velocity of the acoustic waves propagating near the piezoelectric film. For example, the energy trapping layer may have a laminated structure of a low acoustic velocity layer and a high acoustic velocity layer. The low acoustic velocity layer is a film in which the acoustic velocity of the bulk waves in the low acoustic velocity layer is slower than the acoustic velocity of the acoustic waves propagating through the piezoelectric film. The high acoustic velocity layer is a film in which the acoustic velocity of the bulk waves in the high acoustic velocity layer is faster than the acoustic velocity of the acoustic waves propagating through the piezoelectric film. The support substrate may also be the high acoustic velocity layer.

[0044] The energy trapping layer may also be an acoustic impedance layer having a configuration in which low acoustic impedance layers with a relatively low acoustic impedance and high acoustic impedance layers with a relatively high acoustic impedance are alternately stacked.

[0045] Here, the electrode parameters of the IDT electrode 54 that constitutes the acoustic wave resonator 60 will be described.

[0046] The wavelength of the acoustic wave resonator 60 is defined by wavelength λ, which is the repetition period of the electrode fingers 61 a or 61 b ​​that constitute the IDT electrode 54 shown in FIG. 2A (b). The electrode finger pitch is half of the wavelength λ and is the distance between adjacent electrode fingers 61 a and 61 b. The electrode finger pitch is defined as (W+S), where W is the line width of the electrode fingers 61 a and 61 b ​​that constitute the interdigital electrodes 60 a and 60 b, respectively, and S is the space width between adjacent electrode fingers 61 a and 61 b.

[0047] In the IDT electrode 54, when the interval between adjacent electrode fingers is not constant, the electrode finger pitch of the IDT electrode 54 is defined as the average electrode finger pitch of the IDT electrode 54. The average electrode finger pitch of the IDT electrode 54 is defined as Di / (Ni-1), where Ni is the total number of electrode fingers 61a, 61b included in the IDT electrode 54, and Di is the center-to-center distance between the electrode finger located at one end of the IDT electrode 54 and the electrode finger located at the other end in the acoustic wave propagation direction.

[0048] 3. Distribution of Electrode Finger Pitch in Elastic Wave Resonator According to First Example Next, the distribution of electrode finger pitch in the IDT electrode 54 constituting the elastic wave resonator 60 according to the first example will be described.

[0049] 3 is a diagram showing the distribution of electrode finger pitches of the IDT electrode 54 constituting the acoustic wave resonator 60 included in the filter 10 according to the first embodiment. The upper part of the figure shows a schematic plan view of the IDT electrode 54 constituting the acoustic wave resonator 60 according to the first embodiment, and the lower part of the figure shows a graph showing the distribution of the electrode finger pitches of the IDT electrode 54. The acoustic wave resonator 60 according to the first embodiment is formed using the piezoelectric substrate 50 shown in FIG. 2A.

[0050] 3, the IDT electrode 54 of the acoustic wave resonator 60 has (N+1) electrode fingers (N is an integer equal to or greater than 4). The distance between the kth (1≦k≦N) electrode finger and the (k+1)th electrode finger from the end (left end in FIG. 3) of the IDT electrode 54 is defined as the kth electrode finger pitch pk.

[0051] Here, the (N / 2)th electrode finger pitch p(N / 2) is larger than any of the other electrode finger pitches. In this embodiment, the ratio of the (N / 2)th electrode finger pitch p(N / 2) to the electrode finger pitch Pave is set to 1.15. Note that the electrode finger pitch Pave is the average of the electrode finger pitches excluding the (N / 2)th electrode finger pitch p(N / 2). Furthermore, all of the electrode finger pitches excluding the (N / 2)th electrode finger pitch p(N / 2) are equal to or larger than 0.98×Pave and equal to or smaller than 1.02×Pave.

[0052] The (N / 2)th electrode finger pitch p(N / 2) is defined as the M2nd electrode finger pitch pM2, where Q1 is the integer obtained by rounding off (0.45N (= N / 2 - 0.05N)) to one decimal place, Q2 is the integer obtained by rounding off (0.55N (= N / 2 + 0.05N)) to one decimal place, and M2 is any one of the integers between Q1 and Q2. For example, if N = 30, then Q1 = 14 and Q2 = 17. Therefore, M2 is any one of 14, 15, 16, and 17, and the (N / 2)th electrode finger pitch p(N / 2) is any one of the 14th electrode finger pitch p14, the 15th electrode finger pitch p15, the 16th electrode finger pitch p16, and the 17th electrode finger pitch p17.

[0053] 4A is a graph showing the impedance of elastic wave resonators according to Example 1 and a comparative example. Elastic wave resonator 60 according to Example 1 is configured with piezoelectric substrate 50 shown in FIG. 2A and IDT electrode 54 shown in FIG. 3. The elastic wave resonator according to the comparative example differs from elastic wave resonator 60 according to Example 1 only in that all of the first to Nth electrode finger pitches in the IDT electrode are equal to or greater than 0.98×Pave and equal to or less than 1.02×Pave.

[0054] 4A (a) shows the resonance (impedance) characteristics of the main mode of the elastic wave resonators according to Example 1 and the comparative example. The resonant frequency f1r and anti-resonant frequency f1a in the main mode, as well as the impedance values ​​at these frequencies, are substantially the same in both the elastic wave resonators according to Example 1 and the comparative example.

[0055] In contrast, (b) of FIG. 4A shows the resonance (impedance) characteristics of the submodes of the elastic wave resonators according to Example 1 and the comparative example. In this embodiment, the submode is a Rayleigh wave response caused by a Rayleigh wave, and occurs in a frequency band approximately 0.75 times that of the main mode. The resonance signal, which is this Rayleigh wave response, is an unwanted signal compared to the resonance signal of the main mode. In the elastic wave resonator according to the comparative example, a Rayleigh wave response (resonance signal A) having a low-impedance resonance frequency f2r and a high-impedance anti-resonance frequency f2a is generated.

[0056] On the other hand, the elastic wave resonator 60 according to the first embodiment generates a resonance signal B1, which is a Rayleigh wave response having a low-impedance resonance frequency f3r and a high-impedance anti-resonance frequency f3a, and a resonance signal B2, which is a Rayleigh wave response having a low-impedance resonance frequency f4r and a high-impedance anti-resonance frequency f4a. The resonance signals B1 and B2 have a smaller impedance difference between the resonance frequency and the anti-resonance frequency than the resonance signal A.

[0057] 4B is a graph showing the phase and return loss of the Rayleigh wave response of the elastic wave resonators according to Example 1 and the comparative example. (a) of FIG. 4B shows the phase characteristics of the Rayleigh wave response of the elastic wave resonators according to Example 1 and the comparative example. In the elastic wave resonator according to the comparative example, the phase of resonance signal A is −30° or greater, whereas in the elastic wave resonator 60 according to Example 1, the phase of resonance signals B1 and B2 is −60° or less. Note that in (a) of FIG. 4B, a larger phase (approaching 0°) indicates a higher intensity of the Rayleigh wave response, and a smaller phase (approaching −90°) indicates a lower intensity of the Rayleigh wave response.

[0058] 4B(b) shows the reflection characteristics of the Rayleigh wave response of the elastic wave resonators according to Example 1 and the comparative example. The reflection characteristics in FIG. 4B(b) reflect the impedance characteristics of the Rayleigh wave response of the elastic wave resonator shown in FIG. 4A(b) and the phase characteristics of the Rayleigh wave response of the elastic wave resonator shown in FIG. 4B(a). In other words, as shown in FIG. 4B(b), the reflection loss of the Rayleigh wave response (resonance signals B1 and B2) in elastic wave resonator 60 according to Example 1 is smaller than the reflection loss of the Rayleigh wave response (resonance signal A) in the elastic wave resonator according to the comparative example.

[0059] 5 is a graph showing vibration displacements of Rayleigh waves in elastic wave resonators according to Example 1 and the comparative example. As shown in (a) of Fig. 5 , the elastic wave resonator according to the comparative example has one vibration mode in which the Rayleigh wave has the maximum vibration displacement in the (N / 2)th electrode finger. In contrast, the elastic wave resonator 60 according to Example 1 has a vibration mode in which the Rayleigh wave has the maximum vibration displacement in the (N / 2)th electrode finger, as shown in (b) of Fig. 5 , and vibration modes in which the Rayleigh wave has the maximum vibration displacement in the (N / 4)th electrode finger and the (3N / 4)th electrode finger, as shown in (c) of Fig. 5 . Furthermore, the vibration displacements of the Rayleigh waves in each vibration mode of the elastic wave resonator 60 according to Example 1 are smaller than the vibration displacements of the Rayleigh wave vibration mode of the elastic wave resonator according to the comparative example.

[0060] This allows the intensity of the Rayleigh wave response of the elastic wave resonator 60 according to the first embodiment to be smaller than the intensity of the Rayleigh wave response of the elastic wave resonator according to the comparative example, thereby providing an elastic wave resonator in which the generation of unwanted waves (Rayleigh waves) is suppressed, and a filter including the elastic wave resonator.

[0061] 4. Distribution of Electrode Finger Pitch in Elastic Wave Resonator According to Second Example Next, the distribution of electrode finger pitch in the IDT electrode 54 constituting the elastic wave resonator 60A according to the second example will be described.

[0062] 6 is a diagram showing the distribution of electrode finger pitches of the IDT electrode 54 constituting the acoustic wave resonator 60A included in the filter 10 according to Example 2. The upper part of the figure shows a schematic plan view of the IDT electrode 54 constituting the acoustic wave resonator 60A according to Example 2, and the lower part of the figure shows a graph showing the distribution of the electrode finger pitches of the IDT electrode 54. The acoustic wave resonator 60A according to Example 2 is formed using the piezoelectric substrate 50 shown in FIG.

[0063] 6, the IDT electrode 54 of the acoustic wave resonator 60A has (N+1) electrode fingers (N is an integer equal to or greater than 4). The distance between the kth (1≦k≦N) electrode finger and the (k+1)th electrode finger from the end (left end in FIG. 6) of the IDT electrode 54 is defined as the kth electrode finger pitch pk.

[0064] Here, M1 is an integer obtained by rounding off (N / 4) to one decimal place, M2 is an integer obtained by rounding off (N / 2) to one decimal place, and M3 is an integer obtained by rounding off (3N / 4) to one decimal place. In this case, the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch are each larger than any of the electrode finger pitches excluding the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch.

[0065] In this embodiment, the ratio of the (N / 4)th electrode finger pitch p(N / 4) to the electrode finger pitch Pave and the ratio of the (3N / 4)th electrode finger pitch p(3N / 4) to the electrode finger pitch Pave are set to 1.25. The ratio of the (N / 2)th electrode finger pitch p(N / 2) to the electrode finger pitch Pave is set to 1.15. The electrode finger pitch Pave is the average of the electrode finger pitches excluding the (N / 4)th electrode finger pitch p(N / 4), the (N / 2)th electrode finger pitch p(N / 2), and the (3N / 4)th electrode finger pitch p(3N / 4). In addition, the electrode finger pitches except for the (N / 4)th electrode finger pitch p(N / 4), the (N / 2)th electrode finger pitch p(N / 2), and the (3N / 4)th electrode finger pitch p(3N / 4) are all equal to or greater than 0.98×Pave and equal to or less than 1.02×Pave.

[0066] The (N / 4)th electrode finger pitch p(N / 4) is defined as the M1th electrode finger pitch pM1 when Q3 is the integer obtained by rounding off (0.20N (= N / 4 - 0.05N)) to one decimal place, Q4 is the integer obtained by rounding off (0.30N (= N / 4 + 0.05N)) to one decimal place, and M1 is any one of the integers from Q3 to Q4 inclusive. The (N / 2)th electrode finger pitch p(N / 2) is defined as the M2th electrode finger pitch pM2 when Q5 is the integer obtained by rounding off (0.45N (= N / 2 - 0.05N)) to one decimal place, Q6 is the integer obtained by rounding off (0.55N (= N / 2 + 0.05N)) to one decimal place, and M2 is any one of the integers from Q5 to Q6 inclusive. Furthermore, the (3N / 4)th electrode finger pitch p(3N / 4) is defined as the M3th electrode finger pitch pM3, where Q7 is the integer obtained by rounding off (0.70N (= 3N / 4 - 0.05N)) to one decimal place, Q8 is the integer obtained by rounding off (0.80N (= 3N / 4 + 0.05N)) to one decimal place, and M3 is any one of the integers equal to or greater than Q7 and equal to or less than Q8.

[0067] For example, if N=30, then Q3=6 and Q4=9. Therefore, M1 is any one of 6, 7, 8, and 9, and the (N / 4)th electrode finger pitch p(N / 4) is any one of the sixth electrode finger pitch p6, the seventh electrode finger pitch p7, the eighth electrode finger pitch p8, and the ninth electrode finger pitch p9. Furthermore, Q5=14 and Q6=17. Therefore, M2 is any one of 14, 15, 16, and 17, and the (N / 2)th electrode finger pitch p(N / 2) is any one of the fourteenth electrode finger pitch p14, the fifteenth electrode finger pitch p15, the sixteenth electrode finger pitch p16, and the seventeenth electrode finger pitch p17. Furthermore, Q7=21 and Q8=24. Therefore, M3 is any one of 21, 22, 23, and 24, and the (3N / 4)th electrode finger pitch p(3N / 4) is any one of the 21st electrode finger pitch p21, the 22nd electrode finger pitch p22, the 23rd electrode finger pitch p23, and the 24th electrode finger pitch p24.

[0068] 7A is a graph showing the impedance of elastic wave resonators according to Example 2 and a comparative example. Elastic wave resonator 60A according to Example 2 is configured with piezoelectric substrate 50 shown in FIG. 2A and IDT electrode 54 shown in FIG. 6. The elastic wave resonator according to the comparative example differs from elastic wave resonator 60A according to Example 2 only in that all of the first to Nth electrode finger pitches in the IDT electrode are equal to or greater than 0.98×Pave and equal to or less than 1.02×Pave.

[0069] 7A (a) shows the resonance (impedance) characteristics of the main mode of the elastic wave resonators according to Example 2 and the comparative example. The resonant frequency f1r and the anti-resonant frequency f1a in the main mode differ between the elastic wave resonators according to Example 2 and the comparative example, but the impedance values ​​at the resonant frequency f1r and the anti-resonant frequency f1a are substantially the same.

[0070] In contrast, (b) of FIG. 7A shows the resonance (impedance) characteristics of the submodes of the elastic wave resonators according to Example 2 and the comparative example. In this embodiment, the submode is a Rayleigh wave response caused by a Rayleigh wave, and occurs in a frequency band approximately 0.75 times that of the main mode. The resonance signal, which is this Rayleigh wave response, is an unwanted signal compared to the main mode resonance signal. In the elastic wave resonator according to the comparative example, a Rayleigh wave response (resonance signal A) having a low-impedance resonance frequency f2r and a high-impedance anti-resonance frequency f2a is generated.

[0071] On the other hand, the elastic wave resonator 60A in accordance with the second embodiment generates a resonance signal B1, which is a Rayleigh wave response having a low-impedance resonance frequency f3r and a high-impedance anti-resonance frequency f3a, and a resonance signal B2, which is a Rayleigh wave response having a low-impedance resonance frequency f4r and a high-impedance anti-resonance frequency f4a. The resonance signals B1 and B2 have a smaller impedance difference between the resonance frequency and the anti-resonance frequency than the resonance signal A.

[0072] 7B is a graph showing the phase and return loss of the Rayleigh wave response of the elastic wave resonators according to Example 2 and the comparative example. (a) of FIG. 7B shows the phase characteristics of the Rayleigh wave response of the elastic wave resonators according to Example 2 and the comparative example. In the elastic wave resonator according to the comparative example, the phase of resonance signal A is −30° or greater, whereas in elastic wave resonator 60A according to Example 2, the phase of resonance signals B1 and B2 is −75° or less. (a) of FIG. 7B indicates that the larger the phase (approaching 0°), the higher the intensity of the Rayleigh wave response, and the smaller the phase (approaching −90°), the lower the intensity of the Rayleigh wave response.

[0073] 7B(b) shows the reflection characteristics of the Rayleigh wave response of the elastic wave resonators according to Example 2 and the comparative example. The reflection characteristics in FIG. 7B(b) reflect the impedance characteristics of the Rayleigh wave response of the elastic wave resonator shown in FIG. 7A(b) and the phase characteristics of the Rayleigh wave response of the elastic wave resonator shown in FIG. 7B(a). In other words, as shown in FIG. 7B(b), the reflection loss of the Rayleigh wave response (resonance signals B1 and B2) in elastic wave resonator 60A according to Example 2 is significantly smaller than the reflection loss of the Rayleigh wave response (resonance signal A) in the elastic wave resonator according to the comparative example.

[0074] This allows the intensity of the Rayleigh wave response of elastic wave resonator 60A in accordance with Example 2 to be smaller than the intensity of the Rayleigh wave response of the elastic wave resonator in accordance with the comparative example, thereby making it possible to provide an elastic wave resonator in which the generation of unwanted waves (Rayleigh waves) is suppressed, and a filter including the elastic wave resonator.

[0075] In acoustic wave resonator 60A according to this preferred embodiment, the (N / 4)th electrode finger pitch p(N / 4) is equal to the (3N / 4)th electrode finger pitch p(3N / 4). In other words, the M1th electrode finger pitch is equal to the M3th electrode finger pitch.

[0076] According to this, in a vibration mode in which the (N / 4)th electrode finger and the (3N / 4)th electrode finger have maximum vibration displacements, the maximum vibration displacement of the (N / 4)th electrode finger can be made equal to the maximum vibration displacement of the (3N / 4)th electrode finger, thereby enabling the maximum intensities of the resonance signals B1 and B2 according to the second embodiment to be reduced in a balanced manner relative to the resonance signal A according to the comparative example.

[0077] 8 is a diagram showing changes in the reflection loss of the Rayleigh wave response when the (N / 4)th, (N / 2)th, and (3N / 4)th electrode finger pitches of the acoustic wave resonator according to Example 2 are changed. In the table shown in FIG. 8, the (N / 4)th and (3N / 4)th electrode finger pitches increase from the top to the bottom. In other words, the ratios of the (N / 4)th and (3N / 4)th electrode finger pitches to the electrode finger pitch Pave increase from 1 to 1.25 from the top to the bottom. Furthermore, in the table shown in FIG. 8, the (N / 2)th electrode finger pitch increases from the left to the right. In other words, the ratio of the (N / 2)th electrode finger pitch to the electrode finger pitch Pave increases from 1 to 1.25 from the left to the right. 8 , the acoustic wave resonator according to the comparative example has a pitch ratio of 1 for the (N / 4)th and (3N / 4)th electrode fingers, and a pitch ratio of 1 for the (N / 2)th electrode finger. The reflection loss of the Rayleigh wave mode of the acoustic wave resonator according to the comparative example is 12.2 dB, as shown in FIG.

[0078] From FIG. 8, it is desirable that each of the (N / 4)th and (3N / 4)th electrode finger pitches is equal to or greater than the (N / 2)th electrode finger pitch.

[0079] This reduces the reflection loss of the Rayleigh wave response compared to when the (N / 4)th and (3N / 4)th electrode finger pitches are each smaller than the (N / 2)th electrode finger pitch, thereby providing an acoustic wave resonator in which the generation of unwanted waves is suppressed, and a filter including the acoustic wave resonator.

[0080] Furthermore, as shown in FIG. 8, it is desirable that the ratios of the (N / 4)th and (3N / 4)th electrode finger pitches to the electrode finger pitch Pave are each 1.2 or more, and that the ratio of the (N / 2)th electrode finger pitch to the electrode finger pitch Pave is 1.05 or more.

[0081] As a result, the ratio of the (N / 4)th, (N / 2)th, and (3N / 4)th electrode finger pitches falls within the range of region R1 in Figure 8, and the reflection loss of the Rayleigh wave mode can be reduced to 50% or less compared to the elastic wave resonator of the comparative example.

[0082] Furthermore, as shown in FIG. 8, it is desirable that the ratios of the (N / 4)th and (3N / 4)th electrode finger pitches to the electrode finger pitch Pave are each 1.0 or more, and that the ratio of the (N / 2)th electrode finger pitch to the electrode finger pitch Pave is 1.2 or more.

[0083] As a result, the ratio of the (N / 4)th, (N / 2)th, and (3N / 4)th electrode finger pitches falls within the range of region R2 in Figure 8, and the reflection loss of the Rayleigh wave mode can be reduced to 60% or less compared to the elastic wave resonator of the comparative example.

[0084] 5. Effects, etc. As described above, the filter 10 according to the second embodiment includes the piezoelectric substrate 50 and the IDT electrode 54 disposed on the piezoelectric substrate 50. The IDT electrode 54 has N (N is an integer equal to or greater than 3) electrode fingers arranged parallel to one another, and the distance between the k-th electrode finger and the (k+1)-th electrode finger (where 1≦k≦N−1) from the end of the IDT electrode 54 is defined as the k-th electrode finger pitch. Let M1 be one of the integers equal to or greater than 0.2N rounded to the nearest tenth place and equal to or less than 0.3N rounded to the nearest tenth place, M2 be one of the integers equal to or greater than 0.45N rounded to the nearest tenth place and equal to or less than 0.55N rounded to the nearest tenth place, and M3 be one of the integers equal to or greater than 0.7N rounded to the nearest tenth place and equal to or less than 0.8N rounded to the nearest tenth place. Each of the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch is larger than any of the electrode finger pitches excluding the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch.

[0085] This reduces the intensity of the Rayleigh wave response of the acoustic wave resonator 60A included in the filter 10. Therefore, it is possible to provide the filter 10 including the acoustic wave resonator 60A in which the generation of unwanted waves (Rayleigh waves) is suppressed.

[0086] Furthermore, for example, in the filter 10 according to the second embodiment, the M1th electrode finger pitch and the M3th electrode finger pitch are equal to or greater than the M2th electrode finger pitch.

[0087] This reduces the reflection loss in the Rayleigh wave mode compared to when the M1th and M3th electrode finger pitches are each smaller than the M2th electrode finger pitch, thereby providing a filter 10 in which the generation of unwanted waves is suppressed.

[0088] Furthermore, for example, in the filter 10 according to the second embodiment, the M1th electrode finger pitch is equal to the M3th electrode finger pitch.

[0089] This allows the maximum vibration displacement of the M1-th electrode finger and the M3-th electrode finger to be equal in a vibration mode in which the M1-th electrode finger and the M3-th electrode finger have the maximum vibration displacement, thereby enabling the maximum intensities of the resonance signals B1 and B2 according to the second embodiment to be reduced in a balanced manner relative to the resonance signal A according to the comparative example.

[0090] Furthermore, for example, in the filter 10 according to the second embodiment, the ratios of the M1th electrode finger pitch and the M3th electrode finger pitch to the average of the electrode finger pitches excluding the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch are each 1.2 or more, and the ratio of the M2th electrode finger pitch to the average of the electrode finger pitches excluding the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch is 1.05 or more.

[0091] According to this, the ratio of the pitches of the M1st, M2nd and M3th electrode fingers falls within the range of region R1 in FIG. 8, and the reflection loss in the Rayleigh wave mode can be reduced to 50% or less compared to the comparative example.

[0092] Furthermore, for example, in the filter 10 according to the second embodiment, the ratio of the M1th electrode finger pitch to the average of the electrode finger pitches excluding the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch is 1.0 or more, and the ratio of the M2th electrode finger pitch to the average of the electrode finger pitches excluding the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch is 1.2 or more.

[0093] According to this, the ratio of the electrode finger pitches of the M1th, M2th and M3th electrodes falls within the range of region R2 in FIG. 8, and the reflection loss in the Rayleigh wave mode can be reduced to 60% or less compared to the comparative example.

[0094] In addition, for example, in the filter 10 according to the second embodiment, the piezoelectric substrate 50 is made of LiTaO ３ Includes:

[0095] This makes it possible to provide a filter 10 in which the occurrence of the Rayleigh wave mode occurring in a frequency band approximately 0.75 times that of the main mode is suppressed.

[0096] For example, the multiplexer 1 according to this embodiment includes a common terminal 100, a filter 10 connected to the common terminal 100, and a filter 20 connected to the common terminal 100 and having a passband positioned on the lower frequency side than the filter 10.

[0097] This makes it possible to provide a multiplexer 1 in which deterioration of the attenuation characteristics of the filter 10 and the pass characteristics of the filter 20 is suppressed.

[0098] While the present invention has been described above with reference to exemplary embodiments and examples of the elastic wave device and multiplexer, the present invention is not limited to the exemplary embodiments and examples. The present invention also includes various modifications that can be made to the exemplary embodiments and examples without departing from the spirit of the present invention, as well as various devices incorporating the elastic wave device and multiplexer of the present invention.

[0099] Furthermore, for example, in the acoustic wave devices and multiplexers according to the above-described embodiments and examples, matching elements such as inductors and capacitors, and switch circuits may be connected between the components.

[0100] The resonant frequency and anti-resonant frequency shown in the above-described embodiments and examples are derived, for example, by bringing an RF probe into contact with two input and output electrodes of an acoustic wave resonator and measuring the reflection characteristics.

[0101] The features of the acoustic wave devices and multiplexers described based on the above embodiments and examples will be described below.

[0102] <1> A piezoelectric piezoelectric element comprising: a piezoelectric substrate; and an IDT electrode disposed on the substrate; the IDT electrode has N (N is an integer equal to or greater than 3) electrode fingers arranged parallel to each other; the distance between the kth (1≦k≦N−1)th electrode finger and the (k+1)th electrode finger from an end of the IDT electrode is defined as the kth electrode finger pitch; when M1 is any one of integers equal to or greater than 0.2N rounded to the nearest tenth place and equal to or less than 0.3N rounded to the nearest tenth place, M2 is any one of integers equal to or greater than 0.45N rounded to the nearest tenth place and equal to or less than 0.55N rounded to the nearest tenth place, and M3 is any one of integers equal to or greater than 0.7N rounded to the nearest tenth place and equal to or less than 0.8N rounded to the nearest tenth place, An elastic wave device, wherein each of the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch is larger than any of the electrode finger pitches other than the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch.

[0103] <2> The acoustic wave device according to <1>, in which the M1th electrode finger pitch and the M3th electrode finger pitch are each equal to or greater than the M2th electrode finger pitch.

[0104] <3> The acoustic wave device according to <1> or <2>, wherein the M1th electrode finger pitch is equal to the M3th electrode finger pitch.

[0105] <4> The elastic wave device according to any one of <1> to <3>, wherein a ratio of the M1th electrode finger pitch to an average of the electrode finger pitches excluding the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch is 1.2 or more, and a ratio of the M2th electrode finger pitch to an average of the electrode finger pitches excluding the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch is 1.05 or more.

[0106] <5> The elastic wave device according to any one of <1> to <3>, wherein a ratio of the M1th electrode finger pitch to an average of the electrode finger pitches excluding the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch is 1.0 or more, and a ratio of the M2th electrode finger pitch to an average of the electrode finger pitches excluding the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch is 1.2 or more.

[0107] <6> The substrate is LiTaO ３ The acoustic wave device according to any one of <1> to <5>,

[0108] <7> A multiplexer comprising: a common terminal; the elastic wave device according to any one of <1> to <6> connected to the common terminal; and a filter connected to the common terminal and having a passband positioned at a lower frequency than the elastic wave device.

[0109] The present invention can be widely used as a transmit / receive filter and a multiplexer used in the front end of a wireless communication terminal where low loss within the passband and high attenuation outside the passband are required.

[0110] REFERENCE SIGNS LIST 1 Multiplexer 10, 20 Filter 11, 12, 13 Series arm resonator 14, 15, 16 Parallel arm resonator 50 Piezoelectric substrate 51 High acoustic velocity support substrate 52 Low acoustic velocity film 53 Piezoelectric film 54 IDT electrode 55, 58 Protective layer 57 Piezoelectric single crystal substrate 60, 60A Elastic wave resonator 60a, 60b Interdigital electrodes 61a, 61b Electrode fingers 62a, 62b Busbar electrodes 100 Common terminal 110, 120 Input / output terminal 540 Adhesion layer 542 Main electrode layer

Claims

1. A piezoelectric transducer comprising: a substrate having piezoelectricity; and an IDT (InterDigital Transducer) electrode arranged on the substrate, the IDT electrode having N (N is an integer of 4 or more) electrode fingers arranged parallel to each other; the distance between the kth electrode finger (1≦k≦N-1) and the (k+1)th electrode finger from an end of the IDT electrode is defined as the kth electrode finger pitch; M1 is any one of integers equal to or greater than 0.2N rounded off to the nearest tenth place and equal to or less than 0.3N rounded off to the nearest tenth place, M2 is any one of integers equal to or greater than 0.45N rounded off to the nearest tenth place and equal to or less than 0.55N rounded off to the nearest tenth place, and M3 is any one of integers equal to or greater than 0.7N rounded off to the nearest tenth place and equal to or less than 0.8N rounded off to the nearest tenth place, each of the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch is larger than any of the electrode finger pitches other than the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch.

2. The acoustic wave device according to claim 1, wherein each of the M1th electrode finger pitch and the M3th electrode finger pitch is equal to or greater than the M2th electrode finger pitch.

3. The acoustic wave device according to claim 1 or 2, wherein the M1th electrode finger pitch is equal to the M3th electrode finger pitch.

4. The elastic wave device according to any one of claims 1 to 3, wherein a ratio of the M1th electrode finger pitch and a ratio of the M3th electrode finger pitch to an average of the electrode finger pitches excluding the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch are each 1.2 or more, and a ratio of the M2th electrode finger pitch to an average of the electrode finger pitches excluding the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch is 1.05 or more.

5. The elastic wave device according to any one of claims 1 to 3, wherein a ratio of the M1th electrode finger pitch and a ratio of the M3th electrode finger pitch to an average of electrode finger pitches excluding the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch are each 1.0 or greater, and a ratio of the M2th electrode finger pitch to an average of electrode finger pitches excluding the M1th electrode finger pitch, the M2th electrode finger pitch, and the M3th electrode finger pitch is 1.2 or greater.

6. The substrate is LiTaO ３ The elastic wave device according to claim 1 , further comprising:

7. A multiplexer comprising: a common terminal; an elastic wave device according to any one of claims 1 to 6 connected to the common terminal; and a filter connected to the common terminal and having a passband located on the lower frequency side than the elastic wave device.

Images