Elastic wave device and ladder filter having the same

Abstract

An elastic wave device and a ladder filter having the same, the elastic wave device (100) includes a substrate (105), a first resonator (101) and a second resonator (102), and a common reflector (REF12). The second resonator is disposed adjacent to the first resonator, and has a different frequency characteristic from the first resonator. The first resonator includes a first IDT electrode (IDT1). The second resonator includes a second IDT electrode (IDT2). The common reflector has the same frequency characteristic as the first resonator and the second resonator or between the first resonator and the second resonator. A high-order mode frequency of the first resonator coincides with a high-order mode frequency of the second resonator. In a case where the number of electrode fingers of the common reflector is even, the electrode fingers of the first IDT electrode and the second IDT electrode facing the common reflector are of the same polarity. In a case where the number of electrode fingers of the common reflector is odd, the electrode fingers of the first IDT electrode and the second IDT electrode facing the common reflector are of opposite polarity.

Description

Technical Field

[0001] This disclosure relates to elastic wave devices and trapezoidal filters having the elastic wave devices, and more specifically, to techniques for miniaturizing elastic wave devices. Background Technology

[0002] Japanese Patent Application Publication No. 10-303691 (Patent Document 1) discloses a filter device composed of multiple surface acoustic wave (SAW) resonators. Typically, in such a filter device, reflectors are arranged on both sides of the IDT (Interdigital Transducer) electrodes forming the SAW resonators to suppress signal leakage from the resonators that are propagating in them.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 10-303691

[0006] Patent Document 2: Japanese Patent Application Publication No. 2002-176335 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] The aforementioned filter devices using surface acoustic wave resonators are sometimes used in portable terminals such as mobile phones or smartphones. In portable terminals, the demand for miniaturization and thinness remains high, and consequently, devices constituting these portable terminals, such as filter devices, also require further miniaturization and thinning.

[0009] To address this problem, for example, Japanese Patent Application Publication No. 2002-176335 (Patent Document 2) proposed the following structure: for adjacent surface acoustic wave resonators, a reflector disposed between IDT electrodes is shared, thereby achieving miniaturization of the overall elastic wave device.

[0010] On the other hand, in elastic wave devices, spurious signals of higher-order modes at frequencies different from the frequency band through which the object passes (which would help the vibration mode in the passband to become the dominant mode) are sometimes generated. These higher-order mode spurious signals are sometimes impossible to remove by reflectors, and in such cases, the signal of these higher-order modes may affect adjacent elastic wave resonators.

[0011] The present invention was made to solve the above-mentioned problems, and its purpose is to reduce the influence of spurious high-order modes of elastic wave devices formed by multiple resonators and to achieve miniaturization.

[0012] means for solving problems

[0013] The elastic wave device of the first aspect of this disclosure includes: a substrate having a piezoelectric layer; a first resonator and a second resonator disposed on the substrate; and a common reflector. The second resonator is disposed adjacent to the first resonator on the substrate, and its frequency characteristics differ from those of the first resonator. The common reflector is disposed on the substrate between the first and second resonators. The first resonator includes a first IDT electrode with electrode fingers formed at a first spacing. The second resonator includes a second IDT electrode with electrode fingers formed at a second spacing. The lower stopband frequency of the common reflector is the same as, or between, the lower stopband frequencies of the first and second resonators. The upper stopband frequency of the common reflector is the same as, or between, the upper stopband frequencies of the first and second resonators. The higher-order mode frequencies of the first and second resonators are the same. When the number of electrode fingers of the common reflector is even, the electrode fingers in the first IDT electrode that are positioned opposite the common reflector have the same polarity as the electrode fingers in the second IDT electrode that are positioned opposite the common reflector. When the number of electrode fingers of the common reflector is odd, the electrode fingers in the first IDT electrode that are positioned opposite the common reflector have the opposite polarity as the electrode fingers in the second IDT electrode that are positioned opposite the common reflector.

[0014] The elastic wave device of the second aspect of this disclosure includes: a substrate having a piezoelectric layer; a first resonator and a second resonator disposed on the substrate; and a common reflector. The second resonator is disposed adjacent to the first resonator on the substrate, and its frequency characteristics differ from those of the first resonator. The common reflector is disposed on the substrate between the first and second resonators. The first resonator includes a first IDT electrode with electrode fingers formed at a first spacing. The second resonator includes a second IDT electrode with electrode fingers formed at a second spacing. The dominant modes of the first and second resonators are vibration modes whose resonant frequencies increase with increasing piezoelectric layer thickness. Regarding the common reflector, the first resonator, and the second resonator, when the value obtained by multiplying the electrode finger spacing, the electrode finger duty cycle, the electrode finger thickness, and the reciprocal of the piezoelectric layer thickness are respectively set as a first value, a second value, and a third value, the first value is the same as the second and third values, or is between the second and third values. The higher-order mode frequencies of the first resonator and the second resonator are consistent. When the number of electrode fingers of the common reflector is even, the electrode fingers in the first IDT electrode that are positioned opposite the common reflector have the same polarity as the electrode fingers in the second IDT electrode that are positioned opposite the common reflector. When the number of electrode fingers of the common reflector is odd, the electrode fingers in the first IDT electrode that are positioned opposite the common reflector have the opposite polarity as the electrode fingers in the second IDT electrode that are positioned opposite the common reflector.

[0015] The elastic wave device of the third aspect of this disclosure includes: a substrate having a piezoelectric layer; a first resonator and a second resonator disposed on the substrate; and a common reflector. The second resonator is disposed adjacent to the first resonator on the substrate, and its frequency characteristics differ from those of the first resonator. The common reflector is disposed on the substrate between the first and second resonators. The first resonator includes a first IDT electrode with electrode fingers formed at a first spacing. The second resonator includes a second IDT electrode with electrode fingers formed at a second spacing. The dominant modes of the first and second resonators are vibration modes whose resonant frequencies decrease with increasing thickness of the piezoelectric layer. Regarding the common reflector, the first resonator, and the second resonator, when the values ​​obtained by multiplying the electrode finger spacing, the electrode finger duty cycle, the electrode finger thickness, and the piezoelectric layer thickness are respectively set as a fourth value, a fifth value, and a sixth value, the fourth value is the same as, or falls between, the fifth and sixth values. The higher-order mode frequencies of the first resonator and the second resonator are consistent. When the number of electrode fingers of the common reflector is even, the electrode fingers in the first IDT electrode that are positioned opposite the common reflector have the same polarity as the electrode fingers in the second IDT electrode that are positioned opposite the common reflector. When the number of electrode fingers of the common reflector is odd, the electrode fingers in the first IDT electrode that are positioned opposite the common reflector have the opposite polarity as the electrode fingers in the second IDT electrode that are positioned opposite the common reflector.

[0016] Invention Effects

[0017] According to the elastic wave device disclosed herein, a shared reflector, functioning as a reflector for both elastic wave resonators (a first resonator and a second resonator), is disposed between two elastic wave resonators (each including an IDT electrode). Furthermore, this shared reflector has frequency characteristics between those of the first resonator and the second resonator. Moreover, when the number of electrode fingers on the shared reflector is even, the electrode fingers of the two resonators opposite to the shared reflector are configured with the same polarity; when the number of electrode fingers on the shared reflector is odd, the electrode fingers of the two resonators opposite to the shared reflector are configured with opposite polarities. By employing such a structure, spurious higher-order modes generated by each resonator cancel each other out. Therefore, in the elastic wave device, the influence of spurious higher-order modes can be reduced, and miniaturization can be achieved. Attached Figure Description

[0018] Figure 1 This is the circuit structure of the filter device formed by the elastic wave device of Embodiment 1.

[0019] Figure 2 This is a top view used to illustrate the structure of the portion in the elastic wave device of this embodiment 1 where a common reflector is formed.

[0020] Figure 3 This is a cross-sectional view of the elastic wave device according to Embodiment 1.

[0021] Figure 4 This is a top view of a comparative example elastic wave device.

[0022] Figure 5 This is a diagram used to illustrate the frequency characteristics of the elastic wave device in Embodiment 1.

[0023] Figure 6 This is a top view of an elastic wave device with an odd number of electrodes for the shared reflector.

[0024] Figure 7 This is a top view of an elastic wave device with an even number of electrodes for the shared reflector.

[0025] Figure 8 This diagram illustrates the principle of reducing spurious signals in higher-order modes.

[0026] Figure 9 It is a graph used to illustrate the relationship between the effective propagation distance of a signal and the permissible frequency difference.

[0027] Figure 10 This is a top view of a modified elastic wave device.

[0028] Figure 11 This is a graph showing the frequency sensitivity ratio of higher-order modes relative to the construction parameters of the resonator.

[0029] Figure 12 This is a cross-sectional view of the elastic wave device of the first example of Embodiment 2.

[0030] Figure 13 This is a graph used to illustrate the relationship between the piezoelectric layer thickness and the plate wave velocity in the main mode and higher-order modes.

[0031] Figure 14 The diagram shows the specifications of the first example of the elastic wave device and the comparative example.

[0032] Figure 15 This is a cross-sectional view of the elastic wave device in the second example of Embodiment 2.

[0033] Figure 16 This is a graph used to illustrate the relationship between higher-order mode frequencies and the duty cycle of the IDT electrodes.

[0034] Figure 17 The diagram shows the specifications of the second example elastic wave device and the comparative example.

[0035] Figure 18 This is a cross-sectional view of the elastic wave device in the third example of Embodiment 2.

[0036] Figure 19 This is a graph used to illustrate the relationship between higher-order mode frequencies and the film thickness of the IDT electrode.

[0037] Figure 20 The diagram shows the specifications of the third example elastic wave device and the comparative example.

[0038] Figure 21 This is a cross-sectional view of the elastic wave device in the fourth example of Embodiment 2.

[0039] Figure 22 This is a diagram showing an example of a deformation of the dielectric layer. Detailed Implementation

[0040] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. It should be noted that the same or equivalent parts in the drawings are labeled with the same reference numerals, and their descriptions will not be repeated.

[0041] [Implementation Method 1]

[0042] (Structure of the filter device)

[0043] Figure 1 This is a diagram showing the circuit structure of the filter device 10 formed by the elastic wave device of Embodiment 1. The filter device 10 is, for example, a filter device for the transmitting side circuit of a communication device, and is a ladder filter connected between the transmitting terminal TX and the antenna terminal ANT. The filter device 10 filters the signal received by the transmitting terminal TX and outputs it from the antenna terminal ANT.

[0044] The filter device 10 includes series arm resonators S1-S5 and parallel arm resonators P1-P4 connected in series between the transmitting terminal TX and the antenna terminal ANT. Each of the series arm resonators S1-S5 and the parallel arm resonators P1-P4 is configured to include at least one elastic wave resonator. Figure 1 In the example, each of the series arm resonators S1 and S5 and the parallel arm resonators P1 to P4 includes one elastic wave resonator, and each of the series arm resonators S2 to S4 includes two elastic wave resonators. Series arm resonator S2 is configured to include elastic wave resonators S21 and S22 connected in series. Series arm resonator S3 is configured to include elastic wave resonators S31 and S32 connected in series. Series arm resonator S4 is configured to include elastic wave resonators S41 and S42 connected in series. It should be noted that the number of elastic wave resonators included in each resonator is not limited to these numbers and should be appropriately selected to match the characteristics of the filter device. Surface acoustic wave (SAW) resonators can be used as elastic wave resonators.

[0045] One end of the parallel arm resonator P1 is connected to the connection point between the series arm resonators S1 and S2, and the other end is connected to the ground potential GND. One end of the parallel arm resonator P2 is connected to the connection point between the series arm resonators S2 and S3, and the other end is connected to the ground potential GND. One end of the parallel arm resonator P3 is connected to the connection point between the series arm resonators S3 and S4, and the other end is connected to the ground potential GND. One end of the parallel arm resonator P4 is connected to the connection point between the series arm resonators S4 and S5, and the other end is connected to the ground potential GND.

[0046] (Structure of elastic wave device)

[0047] Next, use Figure 2 and Figure 3 The basic structure of the elastic wave device 100 of this embodiment 1 will be described. Figure 2 This is a top view of the portion of the elastic wave device 100 where a common reflector is formed between adjacent resonators. Additionally, Figure 3 It is a cross-sectional view of the section between adjacent resonators.

[0048] Reference Figure 2 and Figure 3 The elastic wave device 100 includes two adjacent elastic wave resonators 101 (first resonator) and 102 (second resonator), and a common reflector REF12. The elastic wave resonators 101 and 102 included in the elastic wave device 100 correspond to... Figure 1 The resonator included in any one of the series arm resonant sections S1 to S5 and the parallel arm resonant sections P1 to P4 in the filter device 10 described herein.

[0049] Elastic wave resonators 101 and 102 are SAW resonators configured to include IDT electrodes. Specifically, elastic wave resonator 101 includes an IDT electrode IDT1 and reflectors REF1-1 and REF1-2 disposed on both sides of the IDT electrode IDT1. Elastic wave resonator 102 includes an IDT electrode IDT2 and reflectors REF2-1 and REF2-2 disposed on both sides of the IDT electrode IDT2.

[0050] The IDT electrode has a structure in which two comb-shaped electrodes are positioned opposite each other, and the electrode fingers of the two comb-shaped electrodes are connected to the bus bar at a predetermined interval. The IDT electrode IDT1 of the elastic wave resonator 101 includes bus bar 210 (first bus bar) and bus bar 211 (second bus bar), and the IDT electrode IDT2 of the elastic wave resonator 102 includes bus bar 220 (third bus bar) and bus bar 221 (fourth bus bar).

[0051] In the IDT electrode, the surface acoustic wave propagates in a direction orthogonal to the extension direction of the opposing electrode finger. A reflector is used to reflect and confine the surface acoustic wave leaking from the end of the IDT electrode within the electrode. This improves the Q value of the elastic wave resonator.

[0052] like Figure 3 As shown, the IDT electrodes and reflectors constituting each elastic wave resonator are formed on a substrate 105 having a piezoelectric layer 110. In addition to the piezoelectric layer 110, the substrate 105 also includes a low-velocity layer 121, a high-velocity layer 122, and a support layer 130.

[0053] The support layer 130 is, for example, a semiconductor substrate formed of silicon (Si). On the support layer 130, facing... Figure 3 The positive direction of the Z-axis is composed of a high-velocity layer 122, a low-velocity layer 121, and a piezoelectric layer 110 stacked sequentially.

[0054] The piezoelectric layer 110 is formed, for example, of a piezoelectric single-crystal material such as lithium tantalate (LiTaO3) or lithium niobate (LiNbO3), or a piezoelectric laminate material including aluminum nitride (AlN), LiTaO3, or LiNbO3. An IDT electrode and a reflector, serving as functional elements, are formed on the upper surface (the plane in the positive direction of the Z-axis) of the piezoelectric layer 110. It should be noted that... Figure 3 In the example, lithium tantalate (LT) is used as the piezoelectric layer 110.

[0055] IDT electrodes and reflectors are formed, for example, of a single metal including at least one of aluminum, copper, silver, gold, titanium, tungsten, platinum, chromium, nickel, and molybdenum, or an alloy of these as the main components.

[0056] The low-velocity layer 121 is formed of a material whose volume wave velocity propagating in this low-velocity layer 121 is lower than that propagating in the piezoelectric layer 110. Figure 3 In the example, the low-velocity layer 121 is formed of silicon dioxide (SiO2). However, the low-velocity layer 121 is not limited to silicon dioxide; for example, it can also be formed of other dielectrics such as glass, silicon oxynitride, tantalum oxide, or compounds obtained by adding fluorine, carbon, boron, etc. to silicon dioxide.

[0057] Furthermore, the hypersonic layer 122 is formed of a material whose volume wave velocity propagating in the hypersonic layer 122 is higher than that of the elastic wave velocity propagating in the piezoelectric layer 110. Figure 3 In the example, the hypersonic layer 122 is formed of silicon nitride (SiN). However, the hypersonic layer 122 is not limited to silicon nitride, and can also be formed of materials such as aluminum nitride, alumina (bauxite), silicon oxynitride, silicon carbide, diamond-like carbon (DLC), and diamond.

[0058] By employing a structure in which a low-velocity layer 121 and a high-velocity layer 122 are stacked below the piezoelectric layer 110, the low-velocity layer 121 and the high-velocity layer 122 function as a reflective layer (mirror layer) 120. That is, surface acoustic waves leaking from the piezoelectric layer 110 towards the support layer 130 are reflected by the high-velocity layer 122 and confined within the low-velocity layer 121 due to the difference in propagation speeds. In this way, the acoustic energy loss of surface acoustic waves propagating through the reflective layer 120 is suppressed, thus enabling efficient propagation of surface acoustic waves. It should be noted that in... Figure 3 In the example described, a low-speed sound layer 121 and a high-speed sound layer 122 are formed as a reflective layer 120, but the reflective layer 120 can also be a structure in which multiple low-speed sound layers 121 and high-speed sound layers 122 are arranged alternately.

[0059] Refer again Figure 2 The reflector REF1-1 of the elastic wave resonator 101 is positioned at the end facing the elastic wave resonator 102 side of the IDT electrode IDT1. The reflector REF1-2 is positioned at the end opposite to the reflector REF1-1 of the IDT electrode IDT1. The electrode fingers of the reflectors REF1-1 and REF1-2 are formed with the same spacing as the electrode fingers of the IDT electrode IDT1.

[0060] Furthermore, the reflector REF2-1 of the elastic wave resonator 102 is positioned at the end facing the elastic wave resonator 101 side of the IDT electrode IDT2. The reflector REF2-2 is positioned at the end opposite to the reflector REF2-1 relative to the IDT electrode IDT2. The electrode fingers of the reflectors REF2-1 and REF2-2 are formed with the same spacing as the electrode fingers of the IDT electrode IDT2.

[0061] A common reflector REF12 is disposed between reflector REF1-1 of elastic wave resonator 101 and reflector REF2-1 of elastic wave resonator 102. The sum of the number of electrode fingers of reflector REF1-1 and the number of electrode fingers of common reflector REF12 is set to be the same as the number of electrode fingers of reflector REF1-2. Similarly, the sum of the number of electrode fingers of reflector REF2-1 and the number of electrode fingers of common reflector REF12 is set to be the same as the number of electrode fingers of reflector REF2-2. The length of the electrode fingers of common reflector REF12 is the length above the cross width of the electrode fingers in the IDT electrodes included in elastic wave resonators 101 and 102.

[0062] The frequency characteristics of the shared reflector REF12 are intermediate between those of the elastic wave resonator 101 and the elastic wave resonator 102. By adopting such a structure, the shared reflector REF12 functions as a reflector for both the elastic wave resonator 101 and the elastic wave resonator 102.

[0063] In embodiment 1, an intermediate frequency characteristic is achieved by forming at least a portion of the electrode fingers of the common reflector REF12 with the spacing between the IDT electrode IDT1 in the elastic wave resonator 101 and the electrode fingers of reflectors REF1-1 and REF1-2 (first spacing: PT1) and the spacing between the IDT electrode IDT2 in the elastic wave resonator 102 and the electrode fingers of reflectors REF2-1 and REF2-2 (second spacing: PT2). Here, the spacing between the electrode fingers is the center-to-center distance between adjacent electrode fingers.

[0064] It should be noted that frequency characteristics can be measured by making contact with the probes connected to the network analyzer while minimizing the wiring that connects to each resonator and reflector.

[0065] It should be noted that in the shared reflector REF12, the electrode fingers can be formed with an intermediate spacing, or the spacing can be gradually changed from the elastic wave resonator 101 toward the elastic wave resonator 102. Alternatively, the spacing can be changed in stages from the elastic wave resonator 101 toward the elastic wave resonator 102.

[0066] The reflectors REF1-1 in elastic wave resonator 101 and REF2-1 in elastic wave resonator 102 are not necessarily required. Alternatively, a structure can be formed where only a shared reflector REF12 is configured between the IDT electrode IDT1 of elastic wave resonator 101 and the IDT electrode IDT2 of elastic wave resonator 102. In this case, it is preferable that the number of electrode fingers of the shared reflector REF12 is the same as the number of electrode fingers of reflectors REF1-2 and REF2-2.

[0067] Figure 4 This is a top view of adjacent resonators in the comparative example elastic wave device 100#. Elastic wave device 100# includes two adjacent elastic wave resonators 101# and 102#. In elastic wave device 100#, reflectors (REF1-2, REF2-2) of the same shape are arranged on both sides of the IDT electrode of each elastic wave resonator. That is, in each elastic wave resonator, the number of electrode fingers on the reflectors arranged on both sides is the same. Therefore, for example, if the number of electrode fingers of each reflector REF1-2 and REF2-2 is 20, the total number of electrode fingers of the reflector arranged between the two IDT electrodes becomes 40.

[0068] On the other hand, in the elastic wave device 100 of Embodiment 1, for example, when the number of electrode fingers of each reflector REF1-1 and REF2-1 is set to 8, and the number of electrode fingers of the common reflector REF12 is set to 12, the total number of electrode fingers of reflectors REF1-1 and the common reflector REF12, as well as the total number of electrode fingers of reflectors REF2-1 and the common reflector REF12, becomes 20, which is the same number as the number of electrode fingers of reflectors REF1-2 and REF2-2. However, the total number of electrode fingers of the reflectors disposed between the two IDT electrodes is reduced to 28 (8+12+8). Therefore, the decrease in reflectivity can be suppressed by maintaining the number of electrode fingers that function as reflectors for each elastic wave resonator, and the interval between the two IDT electrodes can be narrowed. As a result, compared with the elastic wave device 100# of the comparative example, the elastic wave device 100 can be miniaturized.

[0069] In elastic wave devices, spurious signals of higher-order modes sometimes occur at frequencies higher than the frequency band (dominant mode) of the target signal. Typically, reflectors in elastic wave devices are designed to have a higher reflection coefficient for signals in the dominant mode band. However, the reflection coefficient for the higher-order mode band may not be able to be increased, thus potentially resulting in higher-order mode spurious signals not being adequately removed by the reflector. This higher-order mode spurious signal can then affect adjacent elastic wave resonators, causing ripple in the filter characteristics.

[0070] Therefore, in the elastic wave device of this embodiment 1, the following structure is adopted: the frequency bands of the higher-order modes of adjacent elastic wave resonators via a common reflector are made approximately consistent, and the phases of the signals of the higher-order modes generated from each elastic wave resonator are reversed. Normally, although multiple higher-order modes are generated, here at least one of these higher-order modes has its frequency band consistent. By adopting such a structure, the spurious signals of the higher-order modes leaking from the reflector cancel each other out, thus reducing the impact of spurious signals from the higher-order modes.

[0071] use Figure 5 The reflection characteristics are explained when a shared reflector is used in adjacent elastic wave resonators. Figure 5 In figures (a) and (b), the upper layer shows the frequency characteristics of the reflector's reflection coefficient, and the lower layer shows the frequency characteristics of the resonator's impedance. Figure 5 In the diagram, solid lines LN50 and LN60 show series arm resonators, while dashed lines LN51 and LN61 show parallel arm resonators.

[0072] Reference Figure 5 ,exist Figure 1In the trapezoidal filter shown, the resonant frequency of the series arm resonator is typically designed to be approximately the same as the anti-resonant frequency of the parallel arm resonator. That is, in the reflector of the series arm resonator, the stopband with a reflection coefficient close to 1 is between frequencies f2 and f4. Figure 5 (a) Region AR10). On the other hand, in the reflector of the parallel arm resonator, the stopband with a reflection coefficient close to 1 becomes the frequency between f1 and f3 ( Figure 5 (b) of the region AR11).

[0073] Therefore, when a reflector shares a series arm resonator and a parallel arm resonator, and the spacing of the reflector's electrode fingers is set to the same as the spacing of the IDT electrodes of either resonator, while reflectivity can be ensured for the frequency range of f2–f3 (region AR15), the reflectivity may decrease significantly for the frequency range of f1–f2 or f3–f4. In this region of decreased reflectivity, surface acoustic waves from one resonator are not reflected and leak to the other, potentially leading to deterioration of the filter characteristics.

[0074] On the other hand, when at least a portion of the electrode finger spacing of the common reflector is set to the midpoint of the electrode finger spacing of the two resonators, as in Embodiment 1, the reflection coefficient of the common reflector becomes, for example, Figure 5 Like the dashed line LN52 in the image. Thus, as... Figure 5 As shown in (a), the stopband of the series arm resonator is extended to the frequency range of f2–f31 (region AR16). Similarly, as Figure 5 As shown in (b), the stopband of the parallel arm resonator is extended to the frequency range of f11 to f3 (region AR17). That is, the lower limit frequency of the stopband of the common reflector is between the lower limit frequency of the stopband of the first resonator and the lower limit frequency of the stopband of the second resonator, and the upper limit frequency of the stopband of the common reflector is between the upper limit frequency of the stopband of the first resonator and the upper limit frequency of the stopband of the second resonator. Therefore, compared with the case where the electrode finger spacing of the common reflector is uniformly equal to the electrode finger spacing of either resonator, the blocking range in the filter device can be expanded, resulting in the suppression of filter characteristic degradation.

[0075] It should be noted that in Embodiment 1, "stopband" refers to the frequency range with a reflection coefficient higher than 70% of the peak value of the reflection coefficient. In Embodiment 1, the lower limit frequency of the stopband corresponds to the resonant frequency of each resonator. Furthermore, the upper limit frequency of the stopband corresponds to the frequency at which stopband ripple begins to appear in the impedance characteristics of each resonator. Figure 5 The frequencies of regions RG10 and RG11 in the middle.

[0076] Next, use Figures 6-9The structure used to reduce the effects of spurious signals in higher-order modes is described in more detail.

[0077] Figure 6 and Figure 7 This is a top view of the elastic wave device according to Embodiment 1. Figure 6 The diagram shows a top view of the elastic wave device 100A when the number of electrode fingers of the shared reflector is odd. Figure 7 A top view of the elastic wave device 100B is shown when the number of electrode fingers of the shared reflector is even. It should be noted that... Figure 6 and Figure 7 In this context, two adjacent elastic wave resonators can be series-arm resonators or parallel-arm resonators. Alternatively, two elastic wave resonators can be one series-arm resonator and the other parallel-arm resonator.

[0078] Reference Figure 6 The elastic wave device 100A includes elastic wave resonators 101A and 102A, and a common reflector REF12A disposed between the elastic wave resonators 101A and 102A. In the elastic wave device 100A, the bus bar 211 of the IDT electrode IDT1A in the elastic wave resonator 101A and the bus bar 221 of the IDT electrode IDT2A in the elastic wave resonator 102A are connected by a wiring pattern 200. That is, bus bar 211 and bus bar 221 are at the same potential.

[0079] In the elastic wave device 100A, the spacing, duty cycle, and electrode film thickness of the electrode fingers in the elastic wave resonators 101A, 102A, and the common reflector REF12A are all the same. Therefore, the frequency bands of the main mode and higher-order mode signals of the elastic wave resonators 101A and 102A are consistent.

[0080] A common reflector REF12A is disposed between reflector REF1A-1 of elastic wave resonator 101A and reflector REF2A-1 of elastic wave resonator 102A. The sum of the number of electrode fingers of reflector REF1A-1 and the number of electrode fingers of common reflector REF12A is the same as the number of electrode fingers of reflector REF1A-2. Furthermore, the sum of the number of electrode fingers of reflector REF2A-1 and the number of electrode fingers of common reflector REF12A is the same as the number of electrode fingers of reflector REF2A-2. As described above, the common reflector REF12A has an odd number of electrode fingers. It should be noted that the number of electrode fingers of reflector REF1A-1 of elastic wave resonator 101A and the number of electrode fingers of reflector REF2A-1 of elastic wave resonator 102A are set to be the same.

[0081] In the IDT electrode IDT1A of the elastic wave resonator 101A, the electrode finger closest to the elastic wave resonator 102A (the electrode finger within region RG1A), that is, the electrode finger opposite to the reflector REF1A-1, is connected to the bus bar 210. On the other hand, in the IDT electrode IDT2A of the elastic wave resonator 102A, the electrode finger closest to the elastic wave resonator 101A (the electrode finger within region RG2A), that is, the electrode finger opposite to the reflector REF2A-1, is connected to the bus bar 221. In other words, when the number of electrode fingers of the shared reflector is odd, the electrode fingers of the elastic wave resonators closest to each other in the IDT electrodes are configured to have opposite potentials (opposite polarities).

[0082] On the other hand, Figure 7 In the elastic wave device 100B, the number of electrode fingers of the common reflector REF12B disposed between the two elastic wave resonators 101B and 102B is even. In the IDT electrode IDT1B of the elastic wave resonator 101B, the electrode finger closest to the elastic wave resonator 102B (the electrode finger within region RG1B), that is, the electrode finger opposite to reflector REF1B-1, is connected to busbar 211. Furthermore, in the IDT electrode IDT2B of the elastic wave resonator 102B, the electrode finger closest to the elastic wave resonator 101B (the electrode finger within region RG2B), that is, the electrode finger opposite to reflector REF2B-1, is connected to busbar 221. In other words, when the number of electrode fingers of the common reflector is even, the electrode fingers of the elastic wave resonators closest to each other in the IDT electrodes are configured to have the same potential (same polarity).

[0083] use Figure 8 This illustrates the principle of reducing spurious higher-order modes through the electrode finger configuration of the IDT electrodes described above. Figure 8 In this example, we will use an elastic wave device 100B with an odd number of electrode fingers sharing a reflector as an example. It should be noted that, for ease of explanation, reflectors REF1A-1 and 2A-1 are omitted.

[0084] Reference Figure 8 In the IDT electrode IDT1A of the elastic wave resonator 101A, the electrode finger connected to the bus bar 210 is designated as electrode finger 230, and the electrode finger connected to the bus bar 211 is designated as electrode finger 231. Similarly, in the IDT electrode IDT2A of the elastic wave resonator 102A, the electrode finger connected to the bus bar 220 is designated as electrode finger 240, and the electrode finger connected to the bus bar 221 is designated as electrode finger 241.

[0085] In the elastic wave device 100A, the potentials of busbars 210 and 220 are assumed to be the positive electrodes on the high-potential side, and the potentials of busbars 211 and 221 are assumed to be the negative electrodes on the low-potential side. As described above, busbars 211 and 221 are connected by wiring pattern 200, and therefore have the same potential.

[0086] In an IDT electrode, the spacing between adjacent electrode fingers is equal to half the wavelength (λ / 2) of the propagating surface acoustic wave. That is, the surface acoustic wave propagating at each IDT electrode has a high potential at the positive electrode and a low potential at the negative electrode.

[0087] Regarding the main mode signal, a signal like line LN1 propagates from IDT electrode IDT1A in the direction of arrow AR1. Similarly, a signal like line LN2 propagates from IDT electrode IDT2A in the direction of arrow AR2. However, the main mode signal is reflected by a reflector positioned between the two IDT electrodes, and therefore cannot reach the IDT electrode on the opposite side.

[0088] On the other hand, signals concerning higher-order modes are not fully reflected in the reflector; at least a portion passes through the IDT electrode on the opposite side. Figure 8 In the diagram, a signal like line LN3 propagates from IDT electrode IDT2A along the direction of arrow AR3. Since the number of electrode fingers of the shared reflector REF12A is odd (i.e., the number of electrode fingers between resonators is odd), in IDT electrode IDT1A, the positive electrode (electrode finger 230) receives a low-potential signal from IDT electrode IDT2A, and the negative electrode (electrode finger 231) receives a high-potential signal from IDT electrode IDT2A. Conversely, the higher-order mode signals generated and propagated by IDT electrode IDT1A become high-potential at the positive electrode (electrode finger 230) and low-potential at the negative electrode (electrode finger 231). That is, in each electrode finger, a high-potential signal from one resonator and a low-potential signal from the other resonator are received; therefore, the higher-order mode signals cancel each other out in each electrode finger.

[0089] When the number of electrode fingers in the reflector between IDT electrodes is odd, for example, the higher-order mode signal generated by IDT electrode IDT1A becomes phase-reversed at the time point after passing through the reflector. Therefore, the electrode finger in IDT electrode IDT2A placed on the reflector becomes at the opposite potential (opposite polarity) to the electrode finger in IDT electrode IDT1A placed on the reflector, thereby removing the influence of the higher-order mode signal.

[0090] It should be noted that when the number of electrode fingers in the reflector between the IDT electrodes is even, the phase of the higher-order mode signal at the time point passing through the reflector becomes the same as the phase of the signal output from the IDT electrode. Therefore, in the elastic wave device 100B, the electrode fingers in IDT electrode IDT2B that are positioned opposite the reflector are set to the same potential (same polarity) as the electrode fingers in IDT electrode IDT1B that are positioned opposite the reflector, thereby eliminating the influence of the higher-order mode signal.

[0091] In this embodiment 1, as described above, the electrode fingers are designed to be the same number for the reflector disposed between the IDT electrode and the common reflector. Therefore, the number of electrode fingers in the reflector between the IDT electrodes is determined by the electrode fingers of the common reflector.

[0092] It should be noted that the above example assumes that the frequencies of the dominant modes in the two elastic wave resonators are the same (i.e., the frequencies of the higher-order modes are also the same). However, in actual designs, the frequencies of the higher-order modes of adjacent elastic wave resonators are not necessarily completely identical. The following explanation addresses the frequency difference of elastic wave resonators that can eliminate the spurious effects of higher-order modes.

[0093] As described above, to remove the influence of higher-order modes, the higher-order mode signal propagating from one elastic wave resonator needs to be out of phase with the higher-order mode signal in the other elastic wave resonator. Based on the relationship between the speed of sound v, frequency f, and wavelength λ (v = fλ), with a fixed speed of sound, the frequency difference can be expressed as a wavelength difference. In the case of a SAW resonator with IDT electrodes, the spacing between the electrode fingers is set to half the wavelength of the propagating surface acoustic wave (λ / 2). Therefore, when there is a spacing difference (i.e., a frequency difference) between the electrode fingers of the two elastic wave resonators, the longer the propagation distance in the shared reflector and the greater the number of propagating electrode fingers, the greater the phase difference between the two signals reaching the IDT electrodes on the other side. If this phase difference is less than λ / 4, it is expected that the influence of higher-order modes can be removed.

[0094] Figure 9 This is a graph showing the relationship between the effective propagation distance of a signal and the permissible frequency difference between the two elastic wave resonators. Here, "effective propagation distance" is the limiting distance at which the phase difference of the signal propagating between the two elastic wave resonators becomes less than λ / 4, denoted by the wavelength (λ). (See also...) Figure 9As can be seen from line LN10, for example, when the effective propagation distance is 10λ (i.e., there are 20 electrode fingers in the shared reflector), if the frequency difference between the two elastic wave resonators is less than 2.5%, the influence of higher-order modes can be eliminated. As mentioned above, the longer the propagation distance of the surface acoustic wave in the shared reflector (i.e., the more electrode fingers), the greater the phase difference between the two signals when they reach the IDT electrode on the other side, due to the accumulation of the difference in the spacing between the electrode fingers. Therefore, the longer the propagation distance of the shared reflector, the smaller the permissible frequency difference, requiring an increase in the frequency consistency of the two elastic wave resonators.

[0095] When the length in wavelength units is defined as "wavelength equivalent length (N)", the permissible frequency difference can be expressed as shown in equation (1) below, which corresponds to Figure 9 The line LN10.

[0096] Permissible frequency difference [%] = 25 / N...(1)

[0097] Here, when the number of electrode fingers of the common reflector is set to n, the relationship between the wavelength conversion length N and the number of electrode fingers n becomes n = 2N. Therefore, based on this relationship and equation (1), equation (2) is obtained.

[0098] Permissible frequency difference [%] = 50 / n...(2)

[0099] In this disclosure, "higher-order mode frequency consistency" means a permissible frequency difference within the range of 0% to (50 / n)%.

[0100] From a miniaturization perspective, it is preferable to increase the number of shared electrode fingers. However, as the number of shared electrode fingers increases, it is necessary to improve the frequency consistency between the resonators. Therefore, the size of the shared reflector should be appropriately selected based on the frequency difference between the two resonators and the overall size of the elastic wave device.

[0101] (Modified Example)

[0102] In the elastic wave device of Embodiment 1, a structure is described in which the electrode fingers in the IDT electrode and reflector extend in a direction orthogonal to the busbar connected to the electrode fingers. In the modified elastic wave device, a structure is described in which the electrode fingers of the IDT electrode and reflector are arranged at an angle relative to the busbar.

[0103] Figure 10 This is a top view of a modified elastic wave device 100C. The elastic wave device 100C includes elastic wave resonators 101C and 102C, and a common reflector REF12C disposed between the elastic wave resonators 101C and 102C.

[0104] The elastic wave resonator 101C includes an IDT electrode IDT1C and reflectors REF1C-1 and REF1C-2 disposed on both sides of the IDT electrode IDT1C. The elastic wave resonator 102C includes an IDT electrode IDT2C and reflectors REF2C-1 and REF2C-2 disposed on both sides of the IDT electrode IDT2C.

[0105] A common reflector REF12C is positioned between reflectors REF1C-1 and REF2C-1. The sum of the number of electrode fingers on reflector REF1C-1 and the common reflector REF12C is the same as the number of electrode fingers on reflector REF1C-2. Similarly, the sum of the number of electrode fingers on reflector REF2C-1 and the common reflector REF12C is the same as the number of electrode fingers on reflector REF2C-2. In the elastic wave device 100C, the electrode fingers of the elastic wave resonators 101C, 102C, and the common reflector REF12C are connected at an angle relative to the busbar. The angle between the electrode fingers and the busbar is greater than 0° and less than 90°.

[0106] In an elastic wave resonator, the surface acoustic wave propagates in a direction orthogonal to the electrodes. For example, in elastic wave device 100C, the signal from elastic wave resonator 101C propagates along... Figure 10 The signal from the elastic wave resonator 102C propagates in the direction of arrow AR11. Figure 10 The propagation direction is as indicated by arrow AR12. As in the modified elastic wave device 100C, for adjacent elastic wave resonators, the electrode fingers are arranged at an angle relative to the busbar. This allows the propagation direction of the surface acoustic wave in one elastic wave resonator to be outside the cross-width region of the electrode fingers in the IDT electrodes of the other elastic wave resonator. Therefore, the impact on the other elastic wave resonator in the event of surface acoustic wave leakage from the shared reflector can be further reduced.

[0107] It should be noted that, Figure 10 The elastic wave device 100C corresponds to a common reflector electrode index that is odd. Figure 6 The electrodes of the 100A elastic wave device are arranged in an inclined configuration, but the number of electrodes for the common reflector is even. Figure 7 The elastic wave device 100B can also be configured with the electrode fingers tilted.

[0108] [Implementation Method 2]

[0109] In Implementation 1, the case where the frequencies of the dominant modes in two adjacent elastic wave resonators are the same was described. However, in actual designs, the frequencies of the dominant modes in adjacent elastic wave resonators are sometimes different. Thus, when using a shared reflector, if the polarity of the electrode fingers of the IDT electrode is adjusted only according to the number of electrode fingers in the shared reflector, it may result in a situation where spurious higher-order modes cannot be removed.

[0110] In Implementation 2, the following structure is described: when the frequencies of the main modes of adjacent elastic wave resonators are different, the influence of the spurious signal is reduced by maintaining the frequency of the main mode and adjusting the frequency of the spurious signal of the higher-order mode.

[0111] Typically, in a resonator, the frequency dependence of resonator construction parameters such as wavelength, piezoelectric layer thickness, electrode film thickness, or duty cycle differs between the dominant mode and higher-order modes. Therefore, by utilizing this characteristic, it is possible to shift the frequency of higher-order modes while maintaining the frequency of the dominant mode.

[0112] Figure 11 This is a graph showing the frequency sensitivity ratio of higher-order modes relative to various structural parameters of the resonator (wavelength, piezoelectric layer thickness, electrode film thickness, duty cycle). The frequency sensitivity ratio represents the rate of change of the frequency of the higher-order modes when the rate of change of the resonant frequency of the main mode is set to 1.00. The frequency sensitivity ratio is positive when it increases with increasing resonant frequency of the main mode and / or frequency of the higher-order modes relative to increasing structural parameters of the resonator; it is negative when it decreases. A frequency sensitivity ratio greater than 1.00 indicates that the rate of change of the frequency of the higher-order modes when that structural parameter changes is greater than the rate of change of the frequency of the main mode.

[0113] It should be noted that the dependence of the main mode resonant frequency and higher-order mode frequencies on the various structural parameters of the resonator varies depending on the material and thickness of the piezoelectric layer. When the piezoelectric layer is LT or LN and its thickness is less than 2λ relative to the wavelength λ determined by the electrode finger spacing, the frequency sensitivity is as follows: That is, when the main mode is, for example, the A0 mode (0th-order antisymmetric mode) or the SH0 mode (0th-order shear level mode), the sign of the frequency sensitivity ratio is positive. On the other hand, when the main mode is, for example, the S0 mode (symmetric mode), the SH1 mode (1st-order shear level mode), the A1 mode (1st-order antisymmetric mode), and higher-order vibrational modes above these, the sign of the frequency sensitivity ratio is negative. Furthermore, when the higher-order mode is, for example, the A0 mode or the SH0 mode, the sign of the frequency sensitivity ratio is positive; when the higher-order mode is, for example, the S0 mode, the SH1 mode, the A1 mode, and higher-order vibrational modes above these, the sign of the frequency sensitivity ratio is negative. In higher-order modes, the absolute value of the frequency sensitivity ratio also varies depending on the vibrational mode. On the other hand, when the thickness of the piezoelectric layer is in the range of 2λ to 5λ, the aforementioned dependence disappears.

[0114] Figure 11 The frequency sensitivity ratios are shown when SH0 mode is used for the main mode and S0 mode is used for the higher-order modes. It should be noted that the first to fourth examples described later also show the use of these modes.

[0115] Reference Figure 11 For example, when the wavelength (i.e., the distance between the electrode fingers) is varied, the rate of change of the frequency of the higher-order mode relative to the resonant frequency of the main mode is -1.00, while the rate of change of the frequency of the higher-order mode is -0.67. That is, when the wavelength is varied, the frequency change of the higher-order mode is smaller than that of the main mode.

[0116] The frequency sensitivity ratio of higher-order modes is -2.40 when the piezoelectric layer thickness is varied. In this case, if the resonant frequency of the main mode increases, the frequency of the higher-order modes decreases by a greater extent than that of the main mode. Similarly, the frequency sensitivity ratio of higher-order modes is 0.55 when the duty cycle of the electrode fingers is varied, and 0.70 when the film thickness of the electrode fingers is varied. That is, when the duty cycle and film thickness of the electrode fingers are varied, the frequency change rate of the higher-order modes is smaller than that of the main mode.

[0117] like Figure 11As shown, the frequency sensitivity ratio of higher-order modes varies depending on the construction parameters. Therefore, if the resonant frequency of the main mode is varied by construction parameters other than the wavelength (electrode finger spacing), and then the wavelength is adjusted to return the resonant frequency of the main mode to its original resonant frequency, then the frequencies of the higher-order modes can be made different while keeping the resonant frequency of the main mode the same.

[0118] Hereinafter, the first example shows an example of changing the thickness of the piezoelectric layer, the second example shows an example of changing the duty cycle of the electrode fingers, and the third example shows an example of changing the thickness of the electrode fingers.

[0119] (first example)

[0120] In the first example, we will explain the case where the frequency of spurious higher-order modes is adjusted by changing the film thickness of the piezoelectric layer in two adjacent elastic wave resonators.

[0121] Figure 12 This is a cross-sectional view of the elastic wave device 100D, the first example of Embodiment 2. (Refer to...) Figure 12 The elastic wave device 100D includes elastic wave resonators 101D and 102D, and a common reflector REF12D disposed between the elastic wave resonators 101D and 102D.

[0122] In the first example, the frequency of the dominant mode of the elastic wave resonator 101D is set to be higher than the frequency of the dominant mode of the elastic wave resonator 102D. That is, the distance between the electrode fingers (PT1) of the IDT electrode IDT1D and the reflector REF1D in the elastic wave resonator 101D is narrower than the distance between the electrode fingers (PT2) of the IDT electrode IDT2D and the reflector REF2D in the elastic wave resonator 102D. Moreover, at least a portion of the electrode fingers of the shared reflector REF12D is formed with the distance between the electrode finger distance PT1 and the electrode finger distance PT2.

[0123] In substrate 105, the thickness of the piezoelectric layer 110 in the region where the elastic wave resonator 101D is disposed is set to BT1, and the thickness of the piezoelectric layer 110 in the region where the elastic wave resonator 102D is disposed is set to BT2 (BT1>BT2). Furthermore, at least a portion of the piezoelectric layer 110 in the region where the common reflector REF12D is disposed is set to be thinner than the thickness BT1 of the piezoelectric layer 110 in the region where the elastic wave resonator 101D is disposed, and thicker than the thickness BT2 of the piezoelectric layer 110 in the region where the elastic wave resonator 102D is disposed. Figure 12 In the common reflector REF12D, the electrode film thickness gradually decreases from the elastic wave resonator 101D toward the elastic wave resonator 102D.

[0124] Figure 13This is a graph showing the relationship between the piezoelectric layer thickness and the plate wave velocity in the main mode and higher-order modes. Figure 13 In the diagram, the horizontal axis represents the thickness (h / λ) of the piezoelectric layer 110 normalized to wavelength, and the vertical axis represents the plate wave velocity. Figure 13 In the diagram, the solid line LN20 shows the case of the main mode, and the dashed line LN21 shows an example of a higher-order mode.

[0125] Reference Figure 13 The dominant mode exhibits the following trend: as the piezoelectric layer thickness decreases, the plate wave velocity decreases; when the piezoelectric layer thickness becomes thicker than specified, the velocity becomes approximately constant. According to the relationship v = fλ, even with a fixed wavelength λ (i.e., the distance between the electrode fingers), a change in the velocity v results in a change in the frequency f. That is, a thicker piezoelectric layer leads to a higher frequency, and a thinner piezoelectric layer leads to a lower frequency. On the other hand, higher-order modes differ from the dominant mode, exhibiting the following trend: a thinner piezoelectric layer results in a higher velocity (frequency), and a thicker piezoelectric layer results in a lower velocity (frequency).

[0126] like Figure 11 and Figure 13 As shown, the degree of frequency variation relative to the piezoelectric layer thickness (the absolute value of the frequency sensitivity ratio) is greater in higher-order modes than in the main mode, while the direction of variation (the sign of the frequency sensitivity ratio) is opposite. Therefore, by reducing the piezoelectric layer thickness to lower the resonant frequency of the main mode, and then adjusting the electrode finger spacing to return the resonant frequency of the main mode to its original resonant frequency, it is possible to increase the frequency of higher-order modes while maintaining the frequency of the main mode.

[0127] exist Figure 12 In the case of the elastic wave device 100D, by making the thickness of the piezoelectric layer 110 of the elastic wave resonator 101D greater than the thickness of the piezoelectric layer 110 of the elastic wave resonator 102D, the frequency of the higher-order modes in the elastic wave resonator 101D is reduced, and brought closer to the frequency of the higher-order modes in the elastic wave resonator 102D. Conversely, by making the thickness of the piezoelectric layer 110 of the elastic wave resonator 102D less than the thickness of the piezoelectric layer 110 of the elastic wave resonator 101D, the frequency of the higher-order modes in the elastic wave resonator 102D is increased, and brought closer to the frequency of the higher-order modes in the elastic wave resonator 101D. It should be noted that sometimes changing the thickness of the piezoelectric layer 110 can cause some changes in the frequency of the main mode, but in such cases, the desired frequency can be adjusted by modifying the spacing of the elastic wave resonators to be targeted.

[0128] Thus, in an elastic wave device, when the frequencies of the main modes of two adjacent elastic wave resonators arranged via a common reflector differ, the frequencies of higher-order mode signals can be made consistent by adjusting the film thickness of the piezoelectric layer and the spacing between the electrode fingers of each elastic wave resonator. Furthermore, by changing the polarity of the electrode finger arranged closest to the common reflector in the IDT electrode according to whether the number of electrode fingers of the common reflector is odd or even, the spurious effects of higher-order modes can be reduced even when the frequencies of the main modes differ.

[0129] It should be noted that in the shared reflector REF12D, the electrode fingers can be formed with an intermediate spacing, or the spacing can be gradually changed from the elastic wave resonator 101D toward the elastic wave resonator 102D. Alternatively, the spacing can be changed in stages from the elastic wave resonator 101D toward the elastic wave resonator 102D.

[0130] Furthermore, regarding the thickness of the piezoelectric layer 110 in the region where the shared reflector REF12D is configured, the overall thickness can be the intermediate thickness, or it can be as follows: Figure 12 This allows for a structure where the thickness of the piezoelectric layer 110 gradually changes from the elastic wave resonator 101D toward the elastic wave resonator 102D. Alternatively, a structure where the thickness of the piezoelectric layer 110 changes in stages from the elastic wave resonator 101D toward the elastic wave resonator 102D is also possible. However, regarding the spacing of the electrode fingers and the thickness of the piezoelectric layer 110, the following is preferred: Figure 13 As explained in the text, the piezoelectric layer thickness (h / λ) is set to be approximately fixed by wavelength.

[0131] Figure 14 A diagram showing the specific specifications of the first example embodiment and its comparative examples is provided. Figure 14 The upper layer ( Figure 14 (a) shows a comparative example, the lower layer ( Figure 14 Example (b) is shown. It should be noted that in... Figure 14 In the examples, in the comparative examples and embodiments, the duty cycle of the electrode fingers is 0.5.

[0132] In the comparative example, the piezoelectric layer thickness of both resonator 1 and resonator 2 was set to 600 nm. In the comparative example, the main mode frequency of resonator 1 was 2464.282 MHz, and the higher-order mode frequency was 3106.941 MHz. Furthermore, the main mode frequency of resonator 2 was 2361.513 MHz, and the higher-order mode frequency was 3019.257 MHz.

[0133] On the other hand, in this embodiment, the piezoelectric layer thickness of resonator 2 is changed to 500 nm, and the wavelength is adjusted to 1.607 μm. That is, by thinning the piezoelectric layer thickness of resonator 2, the resonant frequency of the main mode is reduced, and the wavelength is shortened, thereby bringing the resonant frequency of the main mode back to its original resonant frequency. Thus, in this embodiment, the frequency of the main mode of resonator 2 becomes 2361.312 MHz, and the frequency of the higher-order modes of resonator 2 reaches 3017.580 MHz. Therefore, regarding resonator 2, it is possible to maintain the frequency of the main mode while ensuring that the frequency of the higher-order modes is consistent with that of resonator 1. In this way, even when the frequency of the main mode differs, the influence of spurious emissions from higher-order modes can be removed by adjusting the piezoelectric layer thickness.

[0134] (Second example)

[0135] In the second example, we will explain the case where the frequency of spurious higher-order modes is adjusted by changing the duty cycle of the electrode fingers in two adjacent elastic wave resonators.

[0136] Figure 15 This is a cross-sectional view of the elastic wave device 100E in the second example of Embodiment 2. (Refer to...) Figure 15 The elastic wave device 100E includes elastic wave resonators 101E and 102E, and a common reflector REF12E disposed between the elastic wave resonators 101E and 102E.

[0137] In the second example, the frequency of the main mode of the elastic wave resonator 101E is set lower than the frequency of the main mode of the elastic wave resonator 102E. That is, the distance between the electrode fingers (PT1) of the IDT electrode IDT1E and the reflector REF1E in the elastic wave resonator 101E is wider than the distance between the electrode fingers (PT2) of the IDT electrode IDT2E and the reflector REF2E in the elastic wave resonator 102E. Moreover, at least a portion of the electrode fingers of the shared reflector REF12E is formed by the distance between the electrode finger distance PT1 and the electrode finger distance PT2.

[0138] It should be noted that in the shared reflector REF12E, the electrode fingers can be formed with a central spacing, or the spacing can be gradually changed from the elastic wave resonator 101E toward the elastic wave resonator 102E. Alternatively, the spacing can be changed in stages from the elastic wave resonator 101E toward the elastic wave resonator 102E.

[0139] In the elastic wave device 100E, the duty cycle (first duty cycle) of the electrode fingers in the elastic wave resonator 101E is set to DT1, and the duty cycle (second duty cycle) of the electrode fingers in the elastic wave resonator 102E is set to DT2 (DT1 > DT2). Furthermore, at least a portion of the electrode fingers in the common reflector REF12E is formed with a duty cycle intermediate between the first duty cycle DT1 and the second duty cycle DT2. In other words, at least a portion of the electrode fingers in the common reflector REF12E is formed to be smaller than the first duty cycle DT1 and larger than the second duty cycle DT2. For example, preferably, the duty cycle of the electrode fingers in the common reflector REF12E is set to gradually or progressively decrease from the elastic wave resonator 101E toward the elastic wave resonator 102E.

[0140] Figure 16 This is a graph used to illustrate the relationship between higher-order mode frequencies and the duty cycle of the IDT electrodes. In Figure 16 In the diagram, the horizontal axis represents the wavelength of the dominant mode, and the vertical axis represents the frequencies of higher-order modes. Figure 16 In the diagram, line LN30 shows the case where the duty cycle of the IDT electrode is 0.4, line LN31 shows the case where the duty cycle of the IDT electrode is 0.5, and line LN32 shows the case where the duty cycle of the IDT electrode is 0.6. This shows that even with the same main mode frequency, a larger duty cycle tends to decrease the frequency of higher-order modes.

[0141] The resonant frequency of the main mode is primarily determined by the spacing between the electrode fingers. However, even with the same finger spacing, the resonant frequency of the main mode can change due to the mass-added effect when the mass of the electrode fingers increases or decreases. Specifically, the resonant frequency decreases when the mass of the electrode fingers increases, and increases when the mass of the electrode fingers decreases. Therefore, when the duty cycle changes, the electrode width of the electrode fingers changes, and the mass increases or decreases, the resonant frequency of the main mode changes. Moreover, as... Figure 11 As shown, the frequency sensitivity relative to duty cycle is smaller in higher-order modes than in the main mode. Therefore, by reducing the duty cycle of the electrode fingers to increase the resonant frequency of the main mode, and then adjusting the electrode finger spacing to return the resonant frequency of the main mode to its original resonant frequency, it is possible to reduce the frequency of higher-order modes while maintaining the frequency of the main mode.

[0142] In this way, by adjusting the duty cycle and electrode finger spacing in adjacent elastic wave resonators, the frequencies of higher-order modes can be adjusted to be consistent without changing the frequency of the dominant mode. Therefore, even when the frequencies of the dominant modes in the elastic wave resonators are different, spurious signals from higher-order modes can be removed.

[0143] Figure 17 A diagram showing the specific specifications of the second example embodiment and its comparative example is provided. Figure 17 The upper layer ( Figure 17 (a) shows a comparative example, the lower layer ( Figure 17 Example (b) is shown.

[0144] In the comparative example, the duty cycle of both resonator 1 and resonator 2 was set to 0.5. In the comparative example, the frequency of the main mode of resonator 1 was 2464.282 MHz, and the frequency of its higher-order mode was 3106.941 MHz. Similarly, the frequency of the main mode of resonator 2 was 2469.837 MHz, and the frequency of its higher-order mode was 3111.626 MHz.

[0145] On the other hand, in this embodiment, the duty cycle of resonator 2 is set to 0.4, and the wavelength is set to 1.559226 μm. In the common reflector, the duty cycle of the electrode fingers gradually changes from 0.5 to 0.4 from resonator 1 toward resonator 2. That is, by reducing the duty cycle of resonator 2, the resonant frequency of the main mode is increased, and the wavelength is adjusted to be longer, thereby bringing the resonant frequency of the main mode back to its original resonant frequency. Thus, in this embodiment, the frequency of the main mode of resonator 2 becomes 2469.837 MHz, and the frequency of the higher-order mode of resonator 2 is as low as 3106.941 MHz. Therefore, with respect to resonator 2, it is possible to maintain the frequency of the main mode while making the frequency of the higher-order mode consistent with that of resonator 1. In this way, even when the frequency of the main mode is different, the influence of spurious signals from the higher-order mode can be removed by adjusting the duty cycle of the electrode fingers of the elastic wave resonator.

[0146] (Third case)

[0147] In the third example, we will explain the case where the frequency of spurious higher-order modes is adjusted by changing the film thickness of the electrode fingers in two adjacent elastic wave resonators.

[0148] Figure 18 This is a cross-sectional view of the elastic wave device 100F in the third example of Embodiment 2. (Refer to...) Figure 18 The elastic wave device 100F includes elastic wave resonators 101F and 102F, and a common reflector REF12F disposed between the elastic wave resonators 101F and 102F.

[0149] In the third example, the frequency of the dominant mode of the elastic wave resonator 101F is set to be lower than the frequency of the dominant mode of the elastic wave resonator 102F. That is, the distance between the electrode fingers (PT1) of the IDT electrode IDT1F and the reflector REF1F in the elastic wave resonator 101F is wider than the distance between the electrode fingers (PT2) of the IDT electrode IDT2F and the reflector REF2F in the elastic wave resonator 102F. Moreover, at least a portion of the electrode fingers of the shared reflector REF12F is formed by the distance between the electrode finger distance PT1 and the electrode finger distance PT2.

[0150] It should be noted that in the shared reflector REF12F, the electrode fingers can be formed with a central spacing, or the spacing can be gradually changed from the elastic wave resonator 101F toward the elastic wave resonator 102F. Alternatively, the spacing can be changed in stages from the elastic wave resonator 101F toward the elastic wave resonator 102F.

[0151] In the elastic wave device 100F, the film thickness of the electrode fingers in the elastic wave resonator 101F is set to ET1, and the film thickness of the electrode fingers in the elastic wave resonator 102F is set to ET2 (ET1 < ET2). Furthermore, at least a portion of the electrode fingers in the common reflector REF12F is formed with a film thickness intermediate between the aforementioned film thicknesses ET1 and ET2. In other words, at least a portion of the electrode fingers in the common reflector REF12F is thicker than the film thickness ET1 of the electrode fingers in the elastic wave resonator 101F, and thinner than the film thickness ET2 of the electrode fingers in the elastic wave resonator 102F. Preferably, the film thickness of the electrode fingers in the common reflector REF12F is set to gradually or progressively increase in thickness from the elastic wave resonator 101F toward the elastic wave resonator 102F.

[0152] Figure 19 This is a graph used to illustrate the relationship between higher-order mode frequencies and the film thickness of the IDT electrode. In Figure 19 In the diagram, the horizontal axis represents the wavelength of the dominant mode, and the vertical axis represents the frequencies of higher-order modes. Figure 19 In the diagram, line LN40 shows the case where the IDT electrode film thickness is 111 nm, line LN41 shows the case where the IDT electrode film thickness is 121 nm, and line LN42 shows the case where the IDT electrode film thickness is 131 nm. This indicates that even with the same main mode frequency, a thicker IDT electrode film tends to decrease the frequency of higher-order modes.

[0153] Similar to the second example where the duty cycle is changed, increasing the thickness of the IDT electrode increases the electrode's mass; therefore, the resonant frequency of the main mode decreases due to the mass-added effect. Furthermore, as... Figure 11As shown, the frequency sensitivity relative to the IDT electrode film thickness is lower in higher-order modes than in the main mode. Therefore, by increasing the IDT electrode film thickness to reduce the main mode resonant frequency, and then adjusting the electrode finger spacing to return the main mode resonant frequency to its original value, it is possible to reduce the frequency of higher-order modes while maintaining the main mode frequency.

[0154] In this way, by adjusting the film thickness and finger spacing of the IDT electrodes in adjacent elastic wave resonators, the frequencies of higher-order modes can be adjusted to be consistent without changing the frequency of the dominant mode. Therefore, even when the frequencies of the dominant modes of the elastic wave resonators are different, spurious signals from higher-order modes can be removed.

[0155] Figure 20 The figure shows the specific specifications of the third example embodiment and its comparative example. Figure 20 The upper layer ( Figure 20 (a) shows a comparative example, the lower layer ( Figure 20 Example (b) is shown.

[0156] In the comparative example, the electrode film thickness of both resonator 1 and resonator 2 was set to 121 nm. In the comparative example, the main mode frequency of resonator 1 was 2464.282 MHz, and the higher-order mode frequency was 3106.941 MHz. Furthermore, the main mode frequency of resonator 2 was 2468.655 MHz, and the higher-order mode frequency was 3110.626 MHz.

[0157] On the other hand, in this embodiment, the electrode film thickness of resonator 2 is set to 191 nm, and the wavelength is set to 1.48439 μm. In the shared reflector, the electrode film thickness gradually changes from 121 nm to 191 nm from resonator 1 toward resonator 2. That is, by increasing the electrode film thickness of resonator 2, the resonant frequency of the main mode is reduced, and the wavelength is adjusted to be shorter, thereby bringing the resonant frequency of the main mode back to its original resonant frequency. Thus, in this embodiment, the frequency of the main mode of resonator 2 becomes 2468.227 MHz, and the frequency of the higher-order mode of resonator 2 is as low as 3107.036 MHz. Therefore, with respect to resonator 2, it is possible to maintain the frequency of the main mode while making the frequency of the higher-order mode consistent with that of resonator 1. In this way, even when the frequency of the main mode is different, the influence of spurious signals from the higher-order mode can be removed by adjusting the duty cycle of the electrode fingers of the elastic wave resonator.

[0158] (Fourth case)

[0159] It should be noted that when the IDT electrode is configured with a dielectric layer as a protective film, the frequency of higher-order modes can also be adjusted according to the thickness of the dielectric layer.

[0160] Figure 21 This is a cross-sectional view of the elastic wave device 100G in the fourth example of Embodiment 2. (Refer to...) Figure 21 The elastic wave device 100G includes elastic wave resonators 101G and 102G, a common reflector REF12G disposed between the elastic wave resonators 101G and 102G, and an IDT electrode covering each resonator and a dielectric layer 140 covering the reflector.

[0161] The dielectric layer 140 may be made of materials such as silicon dioxide, glass, silicon oxynitride, tantalum oxide, silicon nitride, aluminum nitride, aluminum oxide (bauxite), silicon oxynitride, silicon carbide, diamond-like carbon (DLC), or diamond. It may also be formed from compounds obtained by adding fluorine, carbon, boron, etc. to silicon dioxide. The dielectric layer 140 is configured to cover functional elements (IDT electrodes, reflectors) disposed on the piezoelectric layer 110 of the substrate 105.

[0162] In the fourth example, the frequency of the main mode of the elastic wave resonator 101G is set to be higher than the frequency of the main mode of the elastic wave resonator 102G. That is, the distance between the electrode fingers (PT1) of the IDT electrode IDT1G and the reflector REF1G in the elastic wave resonator 101G is narrower than the distance between the electrode fingers (PT2) of the IDT electrode IDT2G and the reflector REF2G in the elastic wave resonator 102G. Moreover, at least a portion of the electrode fingers of the shared reflector REF12G is formed with the distance between the electrode finger distance PT1 and the electrode finger distance PT2.

[0163] It should be noted that in the shared reflector REF12G, the electrode fingers can be formed with a central spacing, or the spacing can be gradually changed from the elastic wave resonator 101G toward the elastic wave resonator 102G. Alternatively, the spacing can be changed in stages from the elastic wave resonator 101G toward the elastic wave resonator 102G.

[0164] In the elastic wave device 100G, the thickness of the dielectric layer 140 in the elastic wave resonator 101G is set to FT1, and the thickness of the dielectric layer 140 in the elastic wave resonator 102G is set to FT2 (FT1 < FT2). Furthermore, at least a portion of the dielectric layer in the common reflector REF12G is formed with a thickness intermediate between the aforementioned thicknesses FT1 and FT2. In other words, at least a portion of the dielectric layer in the common reflector REF12G is thicker than the dielectric layer thickness FT1 in the elastic wave resonator 101G, and thinner than the dielectric layer thickness FT2 in the elastic wave resonator 102G. Preferably, the thickness of the dielectric layer in the common reflector REF12G is set to gradually or progressively increase in thickness from the elastic wave resonator 101G toward the elastic wave resonator 102G.

[0165] When the dielectric layer 140 is formed from a material (silicon dioxide, glass, tantalum oxide, niobium oxide, tellurium oxide, etc.) with a sound velocity slower than that of the resonant frequency of the elastic wave resonator 101G or 102G, the thicker the dielectric layer 140 disposed on the electrode fingers, the greater the mass of the electrode fingers during vibration. Therefore, the resonant frequency of the resonator and the frequencies of higher-order modes decrease due to the mass-added effect. Thus, similar to the second and third examples, by adjusting the thickness of the dielectric layer 140 and the spacing of the electrode fingers, it is possible to reduce the frequencies of higher-order modes while maintaining the resonant frequency of the main mode.

[0166] On the other hand, when the dielectric layer 140 is formed from a material (glass, silicon nitride, aluminum nitride, bauxite, silicon oxynitride, silicon carbide, DLC, diamond, etc.) having a sound velocity faster than that of the resonant frequency of the elastic wave resonator 101G or 102G, the thicker the dielectric layer, the higher the resonant frequency of the resonator. In this case, by adjusting the thickness of the dielectric layer 140 and the spacing of the electrode fingers, it is possible to adjust the frequencies of higher-order modes while maintaining the resonant frequency of the main mode.

[0167] In this way, even when the frequencies of the main modes of the elastic wave resonator are different, the spurious signals of higher-order modes can be removed.

[0168] It should be noted that, in Figure 21 In the elastic wave device 100G shown, the film thicknesses FT1 and FT2 of the dielectric layer 140 are defined as the distances from the upper surface of the IDT electrode and the electrode fingers of the reflector to the surface of the dielectric layer 140. Additionally, as... Figure 22 As shown, the position of the upper surface of the dielectric layer 140 with electrode fingers can be different from the position of the upper surface of the dielectric layer without electrode fingers.

[0169] (Fifth case)

[0170] Typically, the resonant frequency, stopband frequency (upper and lower limits), and reflector frequency (upper and lower limits) of a resonator exhibit the same dependence on parameters such as the finger spacing, finger duty cycle, finger thickness, piezoelectric layer thickness, and dielectric layer thickness. As mentioned above, for the parameters of finger spacing, finger duty cycle, and finger thickness, larger values ​​tend to result in lower resonant frequencies and higher-order mode frequencies for each resonator. On the other hand, regarding the piezoelectric layer thickness, in the case of vibration modes such as A0 or SHO, larger parameter values ​​result in higher resonant frequencies for each resonator. Therefore, regarding the shared reflector REF12 and the two elastic wave resonators 101 and 102, when the value obtained by multiplying the electrode finger spacing, electrode finger duty cycle, electrode finger thickness, and the reciprocal of the piezoelectric layer thickness (= electrode finger spacing × electrode finger duty cycle × electrode finger film thickness / piezoelectric layer film thickness) is set as the first value, the second value, and the third value of the elastic wave resonator 102 are set to be between the second value of the elastic wave resonator 101 and the third value of the elastic wave resonator 102, so that even when the frequencies of the main modes of the elastic wave resonators are different, the spurious signals of higher-order modes can be removed.

[0171] Furthermore, in the case of vibration modes where the main mode is S0, SH1, A1, or higher-order vibration modes, the larger the parameter value, the smaller the resonant frequency of each resonator. Therefore, regarding the common reflector REF12 and the two elastic wave resonators 101 and 102, when the value obtained by multiplying the electrode finger spacing, electrode finger duty cycle, electrode finger thickness, and piezoelectric layer thickness (=electrode finger spacing × electrode finger duty cycle × electrode finger film thickness × piezoelectric layer film thickness) is set as the fourth, fifth, and sixth values ​​respectively, by setting the fourth value of the common reflector REF12 to be between the fifth value of the elastic wave resonator 101 and the sixth value of the elastic wave resonator 102, even when the frequencies of the main modes of the elastic wave resonators are different, spurious signals from higher-order modes can be removed. It should be noted that the main mode is not limited to the vibration modes described above, and other vibration modes can also be used.

[0172] Furthermore, when a dielectric layer is formed of a material having a volume wave velocity slower than the resonant frequency of the elastic wave resonator 101, elastic wave resonator 102, and common reflector REF12, and the dielectric layer has a thickness that increases the resonant frequency of each resonator. Therefore, regarding the common reflector REF12 and elastic wave resonators 101 and 102, when the values ​​obtained by multiplying the first, second, and third values ​​by the thickness of the dielectric layer (= electrode finger spacing × electrode finger duty cycle × electrode finger film thickness / piezoelectric layer film thickness × dielectric layer film thickness) are set as the first a value, the second a value, and the third a value, respectively, the first a value of the common reflector REF12 is set to be between the second a value of the elastic wave resonator 101 and the third a value of the elastic wave resonator 102. Furthermore, regarding the shared reflector REF12 and the elastic wave resonators 101 and 102, when the values ​​obtained by multiplying the fourth, fifth, and sixth values ​​by the thickness of the dielectric layer (= electrode finger spacing × electrode finger duty cycle × electrode finger film thickness × piezoelectric layer film thickness × dielectric layer film thickness) are set as the 4a value, 5a value, and 6a value, respectively, the 4a value of the shared reflector REF12 is set to be between the 5a value of the elastic wave resonator 101 and the 6a value of the elastic wave resonator 102.

[0173] Alternatively, when the common reflector REF12 covers the elastic wave resonator 101, elastic wave resonator 102, and common reflector REF12, and is formed of a dielectric layer made of a material having a sound velocity of volume waves that is faster than the resonant frequency of the elastic wave resonator, the greater the thickness of the dielectric layer, the higher the resonant frequency of each resonator tends to be. Therefore, regarding the common reflector REF12 and elastic wave resonators 101 and 102, when the values ​​obtained by multiplying the first, second, and third values ​​by the reciprocal of the thickness of the dielectric layer (= electrode finger spacing × electrode finger duty cycle × electrode finger film thickness / piezoelectric layer film thickness / dielectric layer film thickness) are set as the first b value, the second b value, and the third b value, respectively, the first b value of the common reflector REF12 is set to be between the second b value of the elastic wave resonator 101 and the third b value of the elastic wave resonator 102. Furthermore, regarding the shared reflector REF12 and the elastic wave resonators 101 and 102, when the values ​​obtained by multiplying the fourth, fifth, and sixth values ​​by the reciprocal of the dielectric layer thickness (= electrode finger spacing × electrode finger duty cycle × electrode finger film thickness × piezoelectric layer film thickness / dielectric layer film thickness) are set as the 4th b value, 5th b value, and 6th b value, respectively, the 4th b value of the shared reflector REF12 is set to be between the 5th b value of the elastic wave resonator 101 and the 6th b value of the elastic wave resonator 102.

[0174] It should be noted that in order for the relationships between the first to sixth values, the 1a to 6a values, and the 1b to 6b values ​​to hold true, it is necessary to use regions where each parameter changes approximately linearly. Therefore, it is necessary that the dielectric layer 140 is formed of a material having a volume sound velocity that is slower than the resonant frequency of the elastic wave resonator, and that the duty cycle of each elastic wave resonator is 0.65 or less.

[0175] The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The scope of this disclosure is set forth in the claims, rather than in the description of the embodiments above, and is intended to include all modifications within the same meaning and scope as the claims.

[0176] Explanation of reference numerals in the attached figures

[0177] 10 Filter devices; 100, 100A~100G elastic wave devices; 101, 101A~101G, 102, 102A~102G, S21, S22, S31, S32, S41, S42 elastic wave resonators; 105 substrate; 110 piezoelectric layer; 120 reflective layer; 121 low-velocity layer; 122 high-velocity layer; 130 support layer; 140 dielectric layer; 200 wiring pattern; 210, 211, 220, 221 busbars; 230, 231, 240, 241 electrode fingers; ANT antenna terminal; GND ground potential; IDT1, IDT1A~IDT1G, IDT2, IDT2A~IDT2G IDT electrodes; P1~P4 Parallel arm resonator, REF1, REF1A~REF1G, REF2, REF2A~REF2G reflectors, REF12, REF12A~REF12G shared reflector, S1~S5 series arm resonator, TX transmitting terminal.

Claims

1. An elastic wave device, comprising: A substrate having a piezoelectric layer; A first resonator is disposed on the substrate; A second resonator, disposed on the substrate, has a different frequency response than the first resonator; and A common reflector is disposed on the substrate between the first resonator and the second resonator. The first resonator includes a first IDT electrode forming electrode fingers with a first spacing, wherein, IDT stands for interdigital transducer. The second resonator includes a second IDT electrode with electrode fingers formed at a second spacing. The lower stopband frequency of the common reflector is the same as the lower stopband frequency of the first resonator and the lower stopband frequency of the second resonator, or it is between the lower stopband frequencies of the first resonator and the second resonator. The upper limit frequency of the stopband of the common reflector is the same as the upper limit frequency of the stopband of the first resonator and the upper limit frequency of the stopband of the second resonator, or it is between the upper limit frequency of the stopband of the first resonator and the upper limit frequency of the stopband of the second resonator. The higher-order mode frequencies of the first resonator are the same as those of the second resonator. When the number of electrode fingers of the common reflector is even, the electrode fingers in the first IDT electrode that are positioned opposite the common reflector have the same polarity as the electrode fingers in the second IDT electrode that are positioned opposite the common reflector. When the number of electrode fingers of the common reflector is odd, the electrode fingers of the first IDT electrode that are opposite to the common reflector have the opposite polarity to the electrode fingers of the second IDT electrode that are opposite to the common reflector.

2. The elastic wave device according to claim 1, wherein, The electrode finger of the first IDT electrode is connected to the first busbar or the second busbar. The electrode finger of the second IDT electrode is connected to the third or fourth bus bar. The second busbar is connected to the fourth busbar. When the number of electrode fingers of the shared reflector is even. In the first IDT electrode, the electrode located on the common reflector is connected to the second busbar. In the second IDT electrode, the electrode located on the common reflector is connected to the fourth busbar. When the number of electrode fingers of the shared reflector is odd. In the first IDT electrode, the electrode located on the common reflector is connected to the first busbar. In the second IDT electrode, the electrode finger placed on the common reflector is connected to the fourth bus bar.

3. The elastic wave device according to claim 1 or 2, wherein, The frequency of the dominant mode of the first resonator is higher than the frequency of the dominant mode of the second resonator. The thickness of the piezoelectric layer in the region where the first resonator is located is greater than the thickness of the piezoelectric layer in the region where the second resonator is located. At least a portion of the piezoelectric layer in the region where the common reflector is disposed is thinner than the piezoelectric layer in the region where the first resonator is disposed, and thicker than the piezoelectric layer in the region where the second resonator is disposed.

4. The elastic wave device according to claim 1 or 2, wherein, The frequency of the dominant mode of the first resonator is lower than the frequency of the dominant mode of the second resonator. The film thickness of the electrode fingers of the first resonator is thinner than that of the electrode fingers of the second resonator. At least a portion of the electrode fingers of the common reflector have a film thickness that is thicker than the electrode fingers of the first resonator and thinner than the electrode fingers of the second resonator.

5. The elastic wave device according to claim 3, wherein, The first spacing is narrower than the second spacing. The electrodes of the shared reflector are formed at least a portion of the distance between the first spacing and the second spacing.

6. The elastic wave device according to claim 5, wherein, The spacing between the electrode fingers of the shared reflector gradually widens from the first resonator toward the second resonator.

7. The elastic wave device according to claim 5, wherein, The spacing between the electrode fingers of the shared reflector gradually widens from the first resonator toward the second resonator.

8. The elastic wave device according to claim 1 or 2, wherein, The frequency of the dominant mode of the first resonator is lower than the frequency of the dominant mode of the second resonator. The electrode fingers in the first resonator have a first duty cycle, and the electrode fingers in the second resonator have a second duty cycle, which is smaller than the first duty cycle. The electrodes of the shared reflector are formed at least a portion of the duty cycle between the first duty cycle and the second duty cycle.

9. The elastic wave device according to claim 8, wherein, The first spacing is wider than the second spacing. The electrodes of the shared reflector are formed at least a portion of the distance between the first spacing and the second spacing.

10. The elastic wave device according to claim 9, wherein, The spacing between the electrode fingers of the shared reflector gradually narrows from the first resonator toward the second resonator.

11. The elastic wave device according to claim 9, wherein, The spacing between the electrode fingers of the shared reflector narrows in stages from the first resonator toward the second resonator.

12. The elastic wave device according to claim 1 or 2, wherein, The first resonator and the second resonator each include: A first reflector, disposed between the IDT electrode included in the resonator and the common reflector; and The second reflector is positioned at the end opposite to the first reflector relative to the IDT electrode. The electrode fingers of the first reflector of the first resonator are formed with the first spacing. The electrode fingers of the first reflector of the second resonator are formed with the second spacing.

13. The elastic wave device according to claim 1 or 2, wherein, Each IDT electrode and each reflector includes the busbar connected to the electrode fingers. In each IDT electrode and each reflector, the angle between the electrode finger and the bus bar is larger than 0° and smaller than 90°.

14. The elastic wave device according to claim 1 or 2, wherein, The substrate also includes a reflective layer on which the piezoelectric layer is disposed.

15. An elastic wave device, comprising: A substrate having a piezoelectric layer; A first resonator is disposed on the substrate; A second resonator, disposed on the substrate, has a different frequency response than the first resonator; and A common reflector is disposed on the substrate between the first resonator and the second resonator. The first resonator includes a first IDT electrode forming electrode fingers with a first spacing. The second resonator includes a second IDT electrode with electrode fingers formed at a second spacing. The dominant modes of the first and second resonators are vibration modes whose resonant frequencies increase with increasing thickness of the piezoelectric layer. Regarding the shared reflector, the first resonator, and the second resonator, when the values ​​obtained by multiplying the electrode finger spacing, the electrode finger duty cycle, the electrode finger thickness, and the reciprocal of the piezoelectric layer thickness are respectively set as the first value, the second value, and the third value, the first value is the same as the second value and the third value, or is between the second value and the third value. The higher-order mode frequencies of the first resonator are the same as those of the second resonator. When the number of electrode fingers of the common reflector is even, the electrode fingers in the first IDT electrode that are positioned opposite the common reflector have the same polarity as the electrode fingers in the second IDT electrode that are positioned opposite the common reflector. When the number of electrode fingers of the common reflector is odd, the electrode fingers of the first IDT electrode that are opposite to the common reflector have the opposite polarity to the electrode fingers of the second IDT electrode that are opposite to the common reflector.

16. The elastic wave device according to claim 15, wherein, The elastic wave device further includes a dielectric layer configured to cover the first resonator, the second resonator, and the common reflector. The dielectric layer is formed of a material having a volume wave velocity that is slower than the resonant frequencies of the first and second resonators. Regarding the shared reflector, the first resonator, and the second resonator, when the values ​​obtained by multiplying the first to the third values ​​by the thickness of the dielectric layer are respectively set as values ​​1a to 3a. The first a value is the same as the second a value and the third a value, or is between the second a value and the third a value.

17. The elastic wave device according to claim 15, wherein, The elastic wave device further includes a dielectric layer configured to cover the first resonator, the second resonator, and the common reflector. The dielectric layer is formed of a material having a volume wave velocity that is faster than the resonant frequencies of the first and second resonators. Regarding the shared reflector, the first resonator, and the second resonator, when the values ​​obtained by multiplying the first value to the third value by the reciprocal of the thickness of the dielectric layer are respectively set as values ​​1b to 3b,... The first b value is the same as the second b value and the third b value, or is between the second b value and the third b value.

18. An elastic wave device, comprising: A substrate having a piezoelectric layer; A first resonator is disposed on the substrate; A second resonator, disposed on the substrate, has a different frequency response than the first resonator; and A common reflector is disposed on the substrate between the first resonator and the second resonator. The first resonator includes a first IDT electrode forming electrode fingers with a first spacing. The second resonator includes a second IDT electrode with electrode fingers formed at a second spacing. The dominant modes of the first and second resonators are vibration modes in which the resonant frequency decreases with increasing thickness of the piezoelectric layer. Regarding the shared reflector, the first resonator, and the second resonator, when the values ​​obtained by multiplying the spacing of the electrode fingers, the duty cycle of the electrode fingers, the thickness of the electrode fingers, and the thickness of the piezoelectric layer are respectively set as the fourth, fifth, and sixth values, the fourth value is the same as, or falls between, the fifth and sixth values. The higher-order mode frequencies of the first resonator are the same as those of the second resonator. When the number of electrode fingers of the common reflector is even, the electrode fingers in the first IDT electrode that are positioned opposite the common reflector have the same polarity as the electrode fingers in the second IDT electrode that are positioned opposite the common reflector. When the number of electrode fingers of the common reflector is odd, the electrode fingers of the first IDT electrode that are opposite to the common reflector have the opposite polarity to the electrode fingers of the second IDT electrode that are opposite to the common reflector.

19. The elastic wave device according to claim 18, wherein, The elastic wave device further includes a dielectric layer configured to cover the first resonator, the second resonator, and the common reflector. The dielectric layer is formed of a material having a volume wave velocity that is slower than the resonant frequencies of the first and second resonators. Regarding the shared reflector, the first resonator, and the second resonator, when the values ​​obtained by multiplying the fourth to sixth values ​​by the thickness of the dielectric layer are respectively set as values ​​4a to 6a. The 4a value is the same as or between the 5a value and the 6a value.

20. The elastic wave device according to claim 18, wherein, The elastic wave device further includes a dielectric layer configured to cover the first resonator, the second resonator, and the common reflector. The dielectric layer is formed of a material having a volume wave velocity that is faster than the resonant frequencies of the first and second resonators. Regarding the shared reflector, the first resonator, and the second resonator, when the values ​​obtained by multiplying the fourth to sixth values ​​by the reciprocal of the thickness of the dielectric layer are respectively set as the 4b to 6b values, The 4b value is the same as or between the 5b and 6b values.

21. A trapezoidal filter comprising the elastic wave device according to any one of claims 1 to 20.

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