Elastic wave device and multiplexer

Abstract

An elastic wave device (100) comprises: an elastic wave filter (1) that includes a parallel arm resonator; and another elastic wave filter (2) that includes a series arm resonator and is higher in frequency than the elastic wave filter (1). The parallel arm resonator includes a piezoelectric substrate (30) having a main surface (30a), a first IDT electrode disposed on the main surface (30a), and a first insulating layer in which the first IDT electrode is embedded. The series arm resonator includes the piezoelectric substrate (30), a second IDT electrode disposed on the main surface (30a), and a second insulating layer in which the second IDT electrode is embedded. The ratio of the wavelength of a parallel arm resonator (11P) having the lowest resonance frequency in the elastic wave filter (1) to the wavelength of a series arm resonator (21S) having the highest resonance frequency in the elastic wave filter (2) is 1.088 or more, and the electrode finger duty of the series arm resonator (21S) is greater than the electrode finger duty of the parallel arm resonator (11P).

Description

Elastic wave apparatus and multiplexer

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

[0002] Patent Document 1 discloses a surface acoustic wave apparatus having a structure in which an insulating layer is formed on a piezoelectric substrate so as to cover an IDT (InterDigital Transducer) electrode. According to the invention, this structure makes it possible to increase the reflection coefficient of the acoustic wave resonator including the IDT electrode and suppress the degradation of characteristics due to unwanted ripple.

[0003] Japanese Patent Publication No. 2004-112748

[0004] For example, in the case of the frequency difference between a series arm resonator and a parallel arm resonator in a single ladder-type filter, unwanted ripple generated near the resonance band of the series arm resonator and the parallel arm resonator can be suppressed by optimizing the IDT electrode film thickness, insulating layer film thickness, and piezoelectric substrate cut angle of the series arm resonator and the parallel arm resonator formed on the same piezoelectric substrate.

[0005] However, in the case of two elastic wave resonators formed on the same piezoelectric substrate and having a frequency difference larger than the above-mentioned frequency difference, it is difficult to sufficiently suppress the unwanted ripple simply by optimizing the IDT electrode film thickness, insulating layer film thickness, and piezoelectric substrate cut angle.

[0006] Therefore, the present invention has been made to solve the above problems, and aims to provide an elastic wave device and multiplexer in which unwanted ripple of multiple elastic wave resonators formed on the same piezoelectric substrate has a large frequency difference.

[0007] An elastic wave apparatus according to one aspect of the present invention comprises a first elastic wave filter having a first passband and including one or more parallel arm resonators, and a second elastic wave filter having a second passband on a higher frequency side than the first passband, wherein each of the one or more parallel arm resonators includes a first piezoelectric substrate having a first main surface, a first IDT electrode disposed on the first main surface and having a plurality of first electrode fingers parallel to each other, and a first insulating layer disposed on the first main surface and formed to embed the first IDT electrode, and each of the one or more series arm resonators includes a first piezoelectric substrate and on the first main surface The device includes a second IDT electrode having a plurality of second electrode fingers arranged parallel to each other, and a second insulating layer arranged on a first main surface and formed to embed the second IDT electrode, wherein the ratio of the wavelength of the first IDT electrode in the first parallel arm resonator having the lowest resonant frequency among the one or more parallel arm resonators to the wavelength of the second IDT electrode in the first series arm resonator having the highest resonant frequency among the one or more series arm resonators is 1.088 or more, and the electrode finger duty cycle of the second IDT electrode in the first series arm resonator is greater than the electrode finger duty cycle of the first IDT electrode in the first parallel arm resonator.

[0008] Furthermore, a multiplexer according to one aspect of the present invention comprises a common terminal, the first elastic wave filter described above connected to the common terminal, and the second elastic wave filter described above connected to the common terminal.

[0009] According to the present invention, it is possible to provide an elastic wave device and a multiplexer that have a large frequency difference and suppress unwanted ripple of multiple elastic wave resonators formed on the same piezoelectric substrate.

[0010] These are plan views and cross-sectional views of the elastic wave apparatus according to the embodiment. This is a circuit diagram of the first elastic wave filter according to the embodiment. This is a circuit diagram of the second elastic wave filter according to the embodiment. This is a diagram schematically showing the transmission characteristics and impedance characteristics of the first and second elastic wave filters according to the embodiment. This is a graph showing the relationship between the wavelength of the IDT electrode of the elastic wave resonator according to the embodiment and the SH mode ripple. This is a graph showing the transmission characteristics of the first and second elastic wave filters according to the embodiment and comparative example.

[0011] The embodiments of this disclosure will be described in detail below with reference to the drawings. The embodiments described below are all general or specific examples. The numerical values, shapes, materials, components, arrangement of components, and connection configurations shown in the following embodiments are examples only and are not intended to limit the present invention.

[0012] The figures are schematic diagrams that have been appropriately emphasized, omitted, or had their proportions adjusted to illustrate the present invention, and are not necessarily strictly accurate representations. Actual shapes, positional relationships, and proportions may differ. In each figure, substantially identical components are denoted by the same reference numerals, and redundant explanations may be omitted or simplified.

[0013] In the circuit configuration of this disclosure, "connected between A and B" means connected to both A and B, including cases where the connection is indirect to both A and B.

[0014] Furthermore, in the component arrangement of this disclosure, "component A is arranged in series with path B" means that both the signal input terminal and the signal output terminal of component A are connected to the wiring, electrodes, or terminals that constitute path B.

[0015] Furthermore, terms indicating the relationship between elements, such as "parallel" and "perpendicular," terms indicating the shape of elements, such as "rectangle," and numerical ranges do not represent only strict meanings, but also include substantially equivalent ranges, such as errors of a few percent. In particular, for "IDT electrodes," "electrode fingers," "insulating layers," and "dielectric films," having the same film thickness includes a difference of ±5%.

[0016] Furthermore, in this disclosure, “terminal” means the point where a conductor within an element terminates. However, if the impedance of the conductors between elements is sufficiently low, a terminal is interpreted not only as a single point, but as any point on the conductor between elements or the entire conductor.

[0017] Furthermore, in the disclosure, "input / output terminal" refers to a terminal having at least one of the functions of an input terminal and an output terminal.

[0018] Furthermore, in this disclosure, the passband of an elastic wave filter is defined as the frequency band between two frequencies that are 3 dB greater than the minimum insertion loss within the passband.

[0019] Furthermore, the resonant frequency and anti-resonant frequency shown in the above embodiment can be derived, for example, by contacting an RF probe with the input and output electrodes of the elastic wave resonator while the elastic wave resonator is not connected to any other circuit elements, and measuring the reflection characteristics (impedance characteristics) with a network analyzer or the like.

[0020] Furthermore, "two different resonant frequencies" and "two different anti-resonant frequencies" are defined as having a difference of 0.1% or more between the two measured resonant frequencies (or two anti-resonant frequencies). This difference includes the error of the measuring device.

[0021] (Embodiment) [1 Structure of the elastic wave apparatus 100] Figure 1 is a plan view and a cross-sectional view of the elastic wave apparatus 100 according to an embodiment. Figure 1(a) is a plan view of the main surface 30a of the piezoelectric substrate 30 from the positive z-axis side (seeing through the insulating layer 40 and dielectric film 50). Figure 1(b) is a cross-sectional view along the line Ib-Ib in Figure 1(a). As shown in Figure 1(a), the elastic wave apparatus 100 includes elastic wave filters 1 and 2.

[0022] Elastic wave filter 1 is an example of a first elastic wave filter, and includes a parallel arm resonator 11P and has a first passband. Elastic wave filter 2 is an example of a second elastic wave filter, and includes a series arm resonator 21S and has a second passband that is higher in frequency than the first passband. In other words, the center frequency of the second passband is higher than the center frequency of the first passband.

[0023] The parallel arm resonator 11P includes a piezoelectric substrate 30, an IDT electrode 111, a reflective electrode 115, an insulating layer 40, and a dielectric film 50. The series arm resonator 21S includes a piezoelectric substrate 30, an IDT electrode 221, a reflective electrode 225, an insulating layer 40, and a dielectric film 50. The parallel arm resonator 11P and the series arm resonator 21S share the piezoelectric substrate 30, the insulating layer 40, and the dielectric film 50.

[0024] The piezoelectric substrate 30 is an example of a first piezoelectric substrate, has a main surface 30a (first main surface), and is made of a piezoelectric single crystal. The piezoelectric substrate 30 is used in common with both elastic wave filters 1 and 2. The piezoelectric substrate 30 is, for example, a 127.5° Y-cut X-propagating lithium niobate piezoelectric single crystal substrate (a lithium niobate single crystal cut by a plane whose normal axis is the axis rotated 127.5° from the Y axis with the X axis as the central axis). However, the cut angle of the piezoelectric substrate 30 is not limited to the above cut angle.

[0025] The IDT electrode 111 is an example of a first IDT electrode and has a plurality of electrode fingers 111a and 111b that are parallel to each other, and busbar electrodes 112a and 112b. The plurality of electrode fingers 111a and 111b are examples of a plurality of first electrode fingers, and the plurality of electrode fingers 111a and the plurality of electrode fingers 111b are arranged parallel to each other so as to intersect each other. The busbar electrode 112a is arranged to connect one end of the plurality of electrode fingers 111a. The busbar electrode 112a extends in a direction (x-axis direction) that intersects the extension direction (y-axis direction) of the plurality of electrode fingers 111a. The busbar electrode 112b is arranged to connect one end of the plurality of electrode fingers 111b. The busbar electrode 112b extends in a direction (x-axis direction) that intersects the extension direction (y-axis direction) of the plurality of electrode fingers 111b. Busbar electrodes 112a and 112b are positioned opposite each other, with multiple electrode fingers 111a and 111b in between. The other ends of the multiple electrode fingers 111a face the busbar electrode 112b, and the other ends of the multiple electrode fingers 111b face the busbar electrode 112a.

[0026] The reflective electrodes 115 are positioned on both sides of the IDT electrode 111, adjacent to the IDT electrode 111, in a direction perpendicular to the extension direction of the electrode fingers 111a and 111b (x-axis direction). Note that the reflective electrodes 115 are not required.

[0027] The IDT electrode 221 is an example of a second IDT electrode and has a plurality of electrode fingers 221a and 221b that are parallel to each other, and busbar electrodes 222a and 222b. The plurality of electrode fingers 221a and 221b are examples of a plurality of second electrode fingers, and the plurality of electrode fingers 221a and the plurality of electrode fingers 221b are arranged parallel to each other so as to intersect each other. The busbar electrode 222a is arranged to connect one end of the plurality of electrode fingers 221a. The busbar electrode 222a extends in a direction (x-axis direction) that intersects the extension direction (y-axis direction) of the plurality of electrode fingers 221a. The busbar electrode 222b is arranged to connect one end of the plurality of electrode fingers 221b. The busbar electrode 222b extends in a direction (x-axis direction) that intersects the extension direction (y-axis direction) of the plurality of electrode fingers 221b. Busbar electrodes 222a and 222b are positioned opposite each other, with multiple electrode fingers 221a and 221b in between. The other ends of the multiple electrode fingers 221a face the busbar electrode 222b, and the other ends of the multiple electrode fingers 221b face the busbar electrode 222a.

[0028] The reflective electrodes 225 are positioned on both sides of the IDT electrode 221, adjacent to the IDT electrode 221, in a direction perpendicular to the extension direction of the electrode fingers 221a and 221b (x-axis direction). Note that the reflective electrodes 225 are not required.

[0029] Preferably, each of the IDT electrodes 111 and 221, and the reflective electrodes 115 and 225, contains a high-density metal such as platinum (Pt), gold (Au), copper (Cu), molybdenum (Mo), and tungsten (W).

[0030] The insulating layer 40, which is an example of a first insulating layer, is disposed on the main surface 30a so as to embed the IDT electrode 111. The insulating layer 40, which is also an example of a second insulating layer, is disposed on the main surface 30a so as to embed the IDT electrode 221. More specifically, the insulating layer 40 covers the upper surfaces of the electrode fingers 111a, 111b, 221a, and 221b, and is disposed on the main surface 30a such that the film thickness t40 of the insulating layer 40 is greater than the film thickness t1 of the electrode fingers 111a, 111b, 221a, and 221b in the region between the electrode finger 111a and the electrode finger 111b and in the region between the electrode finger 221a and the electrode finger 221b. The insulating layer 40 is, for example, silicon dioxide (SiO ２ ) as a main component. By the arrangement of the insulating layer 40, spurious (unwanted ripple) generated near the resonance band of the parallel arm resonator 11P and the series arm resonator 21S can be reduced.

[0031] In the present embodiment, the first insulating layer disposed on the IDT electrode 111 and the second insulating layer disposed on the IDT electrode 221 are the common insulating layer 40, and the film thickness in the region between the electrode fingers 111a and 111b of the first insulating layer is equal to the film thickness in the region between the electrode fingers 221a and 221b of the second insulating layer. In addition, the first insulating layer and the second insulating layer are made of the same material.

[0032] The film thickness in the region between the electrode fingers 111a and 111b of the first insulating layer and the film thickness in the region between the electrode fingers 221a and 221b of the second insulating layer may be different, and the first insulating layer and the second insulating layer may be composed of different materials.

[0033] In addition, in the present embodiment, the film thickness of the electrode fingers 111a and 111b and the film thickness of the electrode fingers 221a and 221b are the same film thickness t1. The electrode fingers 111a and 111b and the electrode fingers 221a and 221b are made of the same material.

[0034] The film thickness of the electrode fingers 111a and 111b and the film thickness of the electrode fingers 221a and 221b may be different, and the electrode fingers 111a and 111b and the electrode fingers 221a and 221b may be composed of different materials.

[0035] Dielectric film 50 is arranged to cover insulating layer 40. The dielectric film 50 is preferably a layer in which the acoustic velocity of propagating bulk waves is higher than that of bulk waves propagating through the piezoelectric substrate 30, and for example, silicon nitride (SiN) or a material containing silicon nitride as a main component can be used.

[0036] According to the arrangement of the dielectric film 50, it is possible to suppress the leakage of elastic waves propagating through the piezoelectric substrate 30 upward (in the positive y-axis direction) via the insulating layer 40, and the frequencies of the parallel arm resonator 11P and the series arm resonator 21S can be adjusted by adjusting the film thickness. Note that the dielectric film 50 may be omitted.

[0037] In the present embodiment, the first dielectric film disposed on the IDT electrode 111 and the second dielectric film disposed on the IDT electrode 221 are the common dielectric film 50, and the first dielectric film and the second dielectric film are made of the same material.

[0038] Note that the film thickness of the first dielectric film and the film thickness of the second dielectric film may be different, and the first dielectric film and the second dielectric film may be composed of different materials.

[0039] According to the above configuration of the elastic wave device 100, each of the elastic wave filters 1 and 2 can use, for example, a Rayleigh wave as a main mode.

[0040] Note that an insulating film may be disposed between the main surface 30a and the electrode fingers 111a, 111b, 221a, and 221b.

[0041] Further, each of the elastic wave filters 1 and 2 only needs to have a structure in which the IDT electrode is embedded in the insulating layer 40, and may be, for example, a structure using either a Rayleigh wave or a Love wave as a main mode, and the materials constituting the piezoelectric substrate 30, the insulating layer 40, and the dielectric film 50 are not limited to the materials described above.

[0042] [2 Wavelength of IDT Electrode and Electrode Finger Duty] Here, the wavelength and the electrode finger duty of the elastic wave device 100 are defined.

[0043] The wavelength λ1 of the IDT electrode 111 is a unit of length defined by the repetition period of the electrode fingers 111a or 111b. Furthermore, the electrode finger pitch p1 of the IDT electrode 111 is half the wavelength λ1.

[0044] The electrode finger duty cycle D1 of the IDT electrode 111 is the line width (electrode finger width) occupancy rate of the electrode fingers 111a and 111b, and is the ratio of the line width L1 to the sum of the line width L1 and the space width S1, and is defined as L1 / (L1+S1). The cross-sections of the electrode fingers 111a and 111b may be trapezoidal in shape as shown in Figure 1 due to the etching process using photolithography. Corresponding to this shape of the electrode finger, the line width L1 is defined as the line segment of the electrode finger tangent to the main surface 30a (length of the lower base of the trapezoidal shape).

[0045] Furthermore, the wavelength λ2, electrode finger pitch p2, and electrode finger duty cycle D2 of the IDT electrode 221 are defined in the same way as the wavelength λ1, electrode finger pitch p1, and electrode finger duty cycle D1 of the IDT electrode 111, respectively.

[0046] Furthermore, if the spacing between adjacent electrodes on the IDT electrode 111 is not constant, the wavelength λ1 of the IDT electrode 111 will be the average wavelength λ1 of the IDT electrode 111. ＡＶＥ Defined by: The average wavelength λ1 of the IDT electrode 111 ＡＶＥ This is defined as 2 × Di / (Ni-1), where Ni is the total number of electrode fingers 111a and 111b included in the IDT electrode 111, and Di is the distance between the centers of the electrode fingers located at one end and the other end of the IDT electrode 111 in the x-axis direction.

[0047] Furthermore, if the IDT electrode 111 includes so-called thinned electrodes, the average wavelength λ1 ＡＶＥ In calculating the total number of electrode fingers Ni, the number of thinned electrodes is excluded, and the line width L1 of the thinned electrodes and one of the two spaces adjacent to the thinned electrodes (space width S1) are excluded from the intercenter distance Di.

[0048] Note that thinned electrodes include floating thinned electrodes, polarity-reversing electrodes, and filled electrodes. A floating thinned electrode is an electrode finger that is not connected to either of the two opposing busbar electrodes and is positioned parallel to the electrode finger that is connected to one of the two busbar electrodes. A polarity-reversing electrode is an electrode finger that is connected to the same busbar electrode as the electrode fingers on either side and is positioned parallel to the electrode fingers on either side. A filled electrode is an electrode finger that has an electrode finger width of at least twice the average electrode finger width of the electrode fingers excluding the filled electrode and is positioned parallel to the electrode fingers excluding the filled electrode.

[0049] Furthermore, in the case of the IDT electrode 221, if the spacing between adjacent electrode fingers is not constant, and if the IDT electrode 221 includes thinned electrodes, the wavelength λ2 of the IDT electrode 221 is equal to the average wavelength λ2 of the IDT electrode 221. ＡＶＥ Defined by, with an average wavelength λ² ＡＶＥ The calculation method is the average wavelength λ1 of the IDT electrode 111. ＡＶＥ The calculation method is the same as for [another calculation].

[0050] Furthermore, if the IDT electrode 111 has a so-called 2D piston structure and the electrode finger width at the tip of the electrode finger is wider than the electrode finger width at the center of the electrode finger, the wavelength λ1 is defined as the wavelength at the center of the electrode finger. Also, if it has a 2D piston structure but the electrode finger width at the tip of the electrode finger is not wider than the electrode finger width at the center of the electrode finger, the wavelength λ1 is defined as the average wavelength of the area of ​​the electrode finger excluding both ends of the crossing width region. Furthermore, if the electrode finger width changes periodically in the direction of the crossing width of the electrode finger, the wavelength λ1 is defined as the average wavelength of the crossing width region of the electrode finger.

[0051] Furthermore, if the IDT electrode 221 has a 2D piston structure, the method for calculating the wavelength λ2 is the same as the method for calculating the wavelength λ1. Also, if the width of the electrode fingers changes periodically in the direction of the intersection of the electrode fingers in the IDT electrode 221, the method for calculating the wavelength λ2 is the same as the method for calculating the wavelength λ1.

[0052] Furthermore, if the electrode finger duty cycle D1 of the IDT electrode 111 is not constant, the electrode finger duty cycle D1 of the IDT electrode 111 is equal to the average electrode finger duty cycle D1 of the IDT electrode 111. ＡＶＥis defined by. Average electrode finger duty D1 of IDT electrode 111 ＡＶＥ is, where the total number of electrode fingers 111a, 111b included in IDT electrode 111 is Ni, and the total line width obtained by adding the line widths L1 of (Ni-1) electrode fingers is L1 ＡＬＬ , and the total space width obtained by adding (Ni-1) space widths S1 included in IDT electrode 111 is S1 ＡＬＬ , defined as L1 ＡＬＬ / (L1 ＡＬＬ +S1 ＡＬＬ ).

[0053] Further, in the IDT electrode 221, when the electrode finger duty D2 is not constant, the electrode finger duty D2 of the IDT electrode 221 is defined as the average electrode finger duty D2 of the IDT electrode 221 ＡＶＥ . Average electrode finger duty D2 of IDT electrode 221 ＡＶＥ is calculated in the same manner as the calculation method for the average electrode finger duty D1 of IDT electrode 111 ＡＶＥ .

[0054] Note that when the IDT electrode 111 includes a so-called thinned electrode, in calculating the average electrode finger duty D1 ＡＶＥ , the line width L1 of the thinned electrode is excluded from the total line width L1 ＡＬＬ , and one of the two spaces (space width S1) adjacent to the thinned electrode is excluded from the total space width S1 ＡＬＬ .

[0055] Further, when the IDT electrode 221 includes a thinned electrode, the calculation method for the average electrode finger duty D2 ＡＶＥ is the same as the calculation method for the average electrode finger duty D1 when the IDT electrode 111 includes a thinned electrode ＡＶＥ .

[0056] Furthermore, if the IDT electrode 111 has a 2D piston structure and the electrode finger width at the electrode fingertip is wider than the electrode finger center, the electrode finger duty cycle D1 of the IDT electrode 111 is defined as the electrode finger duty cycle at the electrode finger center. Also, if the electrode finger width at the electrode fingertip is not wider than the electrode finger center, even if it has a 2D piston structure, the electrode finger duty cycle D1 of the IDT electrode 111 is defined as the average electrode finger duty cycle of the electrode finger excluding both ends of the crossing width region. Furthermore, if the electrode finger width changes periodically in the direction of the crossing width of the electrode finger, the electrode finger duty cycle D1 of the IDT electrode 111 is defined as the average electrode finger duty cycle of the crossing width region of the electrode finger.

[0057] Furthermore, if the IDT electrode 221 has a 2D piston structure, the method for calculating the electrode finger duty cycle D2 of the IDT electrode 221 is the same as the method for calculating the electrode finger duty cycle D1. Also, if the electrode finger width of the IDT electrode 221 changes periodically in the direction of the crossover width of the electrode fingers, the method for calculating the electrode finger duty cycle D2 of the IDT electrode 221 is the same as the method for calculating the electrode finger duty cycle D1.

[0058] The wavelength λ1, electrode finger pitch p1, and electrode finger duty cycle D1 of the IDT electrode 111, and the wavelength λ2, electrode finger pitch p2, and electrode finger duty cycle D2 of the IDT electrode 221 can be measured by viewing the main surface 30a of the piezoelectric substrate 30 on which the IDT electrodes 111 and 221 are formed, and / or by viewing the cross-section of the cut surface perpendicular to the extension direction of the electrode fingers 111a, 111b, 221a, and 221b, thereby measuring the line widths L1 and L2 and space widths S1 and S2.

[0059] Furthermore, the area ratio occupied by the electrode fingers in the intersection region of the IDT electrodes 111 and 221 can be obtained by performing a binarization process on an image of the IDT electrode surface captured by an optical microscope or SEM.

[0060] [3. Circuit Configuration Examples of Elastic Wave Filters] Next, circuit configuration examples of elastic wave filters 1 and 2 will be described. Figure 2A is a circuit diagram of elastic wave filter 1 according to the embodiment. Figure 2B is a circuit diagram of elastic wave filter 2 according to the embodiment. Note that the circuit configurations of elastic wave filters 1 and 2 shown in Figures 2A and 2B are examples. In elastic wave filters 1 and 2 according to this embodiment, the number of series arm resonators, the number of parallel arm resonators, the connection configuration between each resonator, etc., are not limited to those shown in Figures 2A and 2B.

[0061] As shown in Figure 2A, the elastic wave filter 1 comprises series arm resonators 11S, 12S, and 13S, parallel arm resonators 11P, 12P, and 13P, and input / output terminals 101 and 102.

[0062] Each of the series arm resonators 11S to 13S includes an elastic wave resonator, and they are arranged in series in the order of 11S, 12S, and 13S, starting from input / output terminal 101, along the series arm path connecting input / output terminals 101 and 102. At least one of the series arm resonators 12S and 13S does not need to be included in the elastic wave filter 1. In other words, the elastic wave filter 1 includes one or more series arm resonators.

[0063] Each of the parallel arm resonators 11P to 13P includes an elastic wave resonator and is connected between the series arm path and ground. Parallel arm resonator 11P is connected between the connection point of series arm resonators 11S and 12S and ground. Parallel arm resonator 12P is connected between the connection point of series arm resonators 12S and 13S and ground. Parallel arm resonator 13P is connected between the connection point of series arm resonator 13S and input / output terminal 102 and ground. Parallel arm resonator 11P is an example of the first parallel arm resonator and has the lowest resonant frequency among the parallel arm resonators 11P to 13P. Note that at least one of the parallel arm resonators 12P and 13P does not need to be included in the elastic wave filter 1. In other words, the elastic wave filter 1 includes one or more parallel arm resonators.

[0064] As shown in Figure 2B, the elastic wave filter 2 comprises series arm resonators 21S, 22S, and 23S, parallel arm resonators 21P, 22P, and 23P, and input / output terminals 201 and 202.

[0065] Each of the series arm resonators 21S to 23S includes an elastic wave resonator, and they are arranged in series in the order of 21S, 22S, and 23S, starting from input / output terminal 201, along the series arm path connecting input / output terminals 201 and 202. Series arm resonator 21S is an example of the first series arm resonator and has the highest resonant frequency among the series arm resonators 21S to 23S. At least one of the series arm resonators 22S and 23S does not have to be included in the elastic wave filter 2. In other words, the elastic wave filter 2 includes one or more series arm resonators.

[0066] Each of the parallel arm resonators 21P to 23P includes an elastic wave resonator and is connected between the series arm path and ground. Parallel arm resonator 21P is connected between the connection point of series arm resonators 21S and 22S and ground. Parallel arm resonator 22P is connected between the connection point of series arm resonators 22S and 23S and ground. Parallel arm resonator 23P is connected between the connection point of series arm resonator 23S and input / output terminal 202 and ground. Note that at least one of the parallel arm resonators 22P and 23P does not need to be included in the elastic wave filter 2. In other words, the elastic wave filter 2 includes one or more parallel arm resonators.

[0067] Figure 3 schematically shows the passband characteristics and impedance characteristics of elastic wave filters 1 and 2 according to the embodiment. As shown in the figure, the second passband of elastic wave filter 2 is located on the higher frequency side than the first passband of elastic wave filter 1.

[0068] When constructing a bandpass filter using a ladder-type elastic wave resonator, the anti-resonance frequency fap of the parallel arm resonator and the resonant frequency frs of the series arm resonator are generally brought close together. As a result, the area near the resonant frequency frp, where the impedance of the parallel arm resonator approaches zero, becomes a low-frequency stopband. Furthermore, as the frequency increases, the impedance of the parallel arm resonator becomes high near the anti-resonance frequency fap, and the impedance of the series arm resonator approaches zero near the resonant frequency frs. As a result, the area near the anti-resonance frequency fap to the resonant frequency frs becomes a signal passband. Further increasing the frequency, near the anti-resonance frequency fas of the series arm resonator, the impedance of the series arm resonator becomes high, creating a high-frequency stopband.

[0069] As shown in Figure 3, the resonant frequency fr11P of the parallel arm resonator 11P of the elastic wave filter 1 is the lowest among the resonant frequencies of the parallel arm resonators 11P to 13P. Also, the resonant frequency fr21S of the series arm resonator 21S of the elastic wave filter 2 is the highest among the resonant frequencies of the series arm resonators 21S to 23S.

[0070] In elastic wave filter 1, the elastic wave resonator with the largest wavelength λ is the parallel arm resonator 11P, and in elastic wave filter 2, the elastic wave resonator with the smallest wavelength λ is the series arm resonator 21S. Therefore, in the elastic wave device 100, the combination of two elastic wave resonators that yields the largest wavelength difference (wavelength ratio) is the parallel arm resonator 11P and the series arm resonator 21S.

[0071] When forming elastic wave filters 1 and 2 using a common piezoelectric substrate 30, a common electrode finger thickness, and a common insulating layer 40, the larger the wavelength difference (wavelength ratio), the more difficult it becomes to reduce unwanted ripple generated in both elastic wave filters 1 and 2 by adjusting the thickness of the common electrode finger thickness and the common insulating layer 40.

[0072] Furthermore, the parallel arm resonators 11P to 13P of the elastic wave filter 1 are defined as elastic wave resonators that constitute the first passband of the elastic wave filter 1, and whose anti-resonant frequencies are included in the first passband. Therefore, a parallel arm resonator whose anti-resonant frequency is not included in the first passband is not included in the one or more parallel arm resonators of the elastic wave filter 1.

[0073] Furthermore, the series arm resonators 21S to 23S of the elastic wave filter 2 are defined as elastic wave resonators that constitute the second passband of the elastic wave filter 2, and whose resonant frequencies are included in the second passband. Therefore, a series arm resonator whose resonant frequency is not included in the second passband is not included in the one or more series arm resonators of the elastic wave filter 2.

[0074] Furthermore, the elastic wave filters 1 and 2 according to this embodiment may include a longitudinally coupled resonator in addition to one or more series arm resonators and one or more parallel arm resonators, and an inductor, capacitor, switch, etc. may be connected between the input / output terminals, the series arm resonators, the parallel arm resonators, and the ground.

[0075] Furthermore, the elastic wave device 100 may be a multiplexer. That is, the elastic wave device 100 may include a common terminal, an elastic wave filter 1 connected to the common terminal, and an elastic wave filter 2 connected to the common terminal.

[0076] [4 Relationship between IDT electrode wavelength and unwanted mode ripple] Next, the relationship between the wavelength λ of the IDT electrode and unwanted mode ripple will be explained. Figure 4 is a graph showing the relationship between the wavelength λ of the IDT electrode of an elastic wave resonator according to the embodiment and the SH mode ripple. The horizontal axis of the figure shows the wavelength λ (2.55 μm to 2.00 μm) of the IDT electrode in an elastic wave resonator having a structure similar to the parallel arm resonator 11P of the elastic wave device 100, and the vertical axis of the figure shows the maximum value of the SH mode ripple in the reflection characteristics of the elastic wave resonator. In the elastic wave resonator, the piezoelectric substrate 30 is a 127.5° Y-cut X-propagating lithium niobate piezoelectric single crystal substrate, the electrode fingers of the IDT electrode contain platinum (Pt), the film thickness t1 is 265 nm, and the film thickness t40 of the insulating layer 40 is 730 nm.

[0077] As shown in Figure 4, when the electrode finger duty cycle (labeled "Duty" in Figure 4) is 0.5, the wavelength λ range of the IDT electrode that can suppress the SH mode ripple to the ripple value required by the bandpass filter (0.3 dB or less) (labeled "ripple reduction range" in Figure 4) is 2.48 μm to 2.28 μm. Furthermore, when the electrode finger duty cycle (Duty) is 0.6, the wavelength λ range of the IDT electrode that can suppress the SH mode ripple to 0.3 dB or less (ripple reduction range) is 2.32 μm to 2.16 μm. Furthermore, when the electrode finger duty cycle (Duty) is 0.7, the wavelength λ range of the IDT electrode that can suppress the SH mode ripple to 0.3 dB or less (ripple reduction range) is 2.23 μm to 2.06 μm.

[0078] In other words, for example, if the wavelength ratio of the IDT electrodes between the series arm resonator and the parallel arm resonator constituting a single ladder-type filter is approximately (<1.088 (=2.48 / 2.28)), then even if the series arm resonator and the parallel arm resonator are constructed with a common piezoelectric substrate 30, a common electrode finger thickness t1, a common insulating layer 40 thickness t40, and a common electrode finger duty cycle (0.5), the SH ripple generated in both the series arm resonator and the parallel arm resonator can be suppressed.

[0079] On the other hand, when the wavelength ratio of the two IDT electrodes is 1.088 (= 2.48 / 2.28) or higher, if two elastic wave resonators are constructed with a common piezoelectric substrate 30, a common electrode finger thickness t1, a common insulating layer 40 thickness t40, and a common electrode finger duty cycle (0.5), it becomes difficult to suppress the SH ripple generated in both of the elastic wave resonators.

[0080] In contrast, when constructing two elastic wave resonators with a common piezoelectric substrate 30, a common electrode finger thickness t1, and a common insulating layer 40 thickness t40, and a wavelength ratio of 1.088 (= 2.48 / 2.28) or higher, for example, by setting the electrode finger duty cycle of the elastic wave resonator with the lower resonant frequency (larger wavelength λ) to 0.5 and increasing the electrode finger duty cycle of the elastic wave resonator with the higher resonant frequency (smaller wavelength λ) to 0.6 or 0.7, it becomes possible to suppress the SH ripple generated in both elastic wave resonators to 0.3 dB or less.

[0081] [5. Structural Data of the Elastic Wave Apparatus 100] Next, we will describe the structural data and transmission characteristics of the elastic wave filters 1 and 2, which are formed on the same piezoelectric substrate 30 and have significantly different center frequencies, in order to reduce unwanted ripple.

[0082] Table 1 shows the structural data for elastic wave filters 1 and 2. In Table 1, the electrode finger duty cycle is the average value of the electrode finger duty cycles of all parallel arm resonators in elastic wave filter 1, or the average value of the electrode finger duty cycles of all series arm resonators in elastic wave filter 2. The wavelength λ of the series arm resonator is the average value of the wavelength λ of all series arm resonators in elastic wave filter 1 or 2. The wavelength λ of the parallel arm resonator is the average value of the wavelength λ of all parallel arm resonators in elastic wave filter 1 or 2. Note that the structural data for elastic wave filters 1 and 2 shown in Table 1 are illustrative data and can be appropriately modified according to the required passband of elastic wave filters 1 and 2.

[0083]

[0084] As shown in Table 1, elastic wave filters 1 and 2 use a common piezoelectric substrate 30, a common electrode finger material and electrode finger thickness, a common insulating layer 40, and a common dielectric film 50. Furthermore, the wavelength ratio between the wavelength λ (= 2.38 μm) of the parallel arm resonator of elastic wave filter 1 and the wavelength λ (= 2.16 μm) of the series arm resonator of elastic wave filter 2 is 1.10. In this case, the wavelength ratio between the parallel arm resonator of elastic wave filter 1 and the series arm resonator of elastic wave filter 2 becomes 1.088 or higher, and when the electrode finger duty cycle of both the parallel arm resonator and the series arm resonator is set to 0.5, a problem arises in which the unwanted ripple caused by the SH mode cannot be reduced to 0.3 dB or less, as shown in Figure 4.

[0085] Figure 5 is a graph showing the transmission characteristics of elastic wave filters 1 and 2 according to the embodiment and comparative example. In the figure, the structural data of elastic wave filters 1 and 2 according to the embodiment are shown in Table 1. The structural data of elastic wave filters 1 and 2 according to the comparative example are the same as those of elastic wave filters 1 and 2 according to the embodiment, except for the electrode duty cycle (=0.5) of elastic wave filter 2.

[0086] The elastic wave filters 1 and 2, which exhibited the transmission characteristics shown in Figure 5, both have a circuit configuration including three series-arm resonators and four parallel-arm resonators.

[0087] In the comparative example of elastic wave filters 1 and 2, the structural data of elastic wave filter 1 was first optimized, and as shown in Figure 5, the passband characteristics of elastic wave filter 1 are good. However, a large ripple occurs within the passband of elastic wave filter 2, resulting in a large insertion loss in the passband. This is understood to be due to unwanted ripple caused by the SH mode occurring near the resonant frequency of the series arm resonator constituting elastic wave filter 2.

[0088] In contrast, in the elastic wave filters 1 and 2 according to the embodiment, the structural data of the elastic wave filter 1 is first optimized, and as shown in Figure 5, the transmission characteristics of the elastic wave filter 1 are good. Furthermore, by making the electrode finger duty cycle of the series arm resonator of the elastic wave filter 2 larger than the electrode finger duty cycle of the parallel arm resonator of the elastic wave filter 1 (Duty = 0.6), as shown in Figure 5, no unwanted ripple is generated within the passband of the elastic wave filter 2, and the transmission characteristics of the elastic wave filter 2 are good. Thus, an elastic wave device 100 can be provided in which unwanted ripple is suppressed in both the parallel arm resonator of the elastic wave filter 1 and the series arm resonator of the elastic wave filter 2, which have a large frequency difference.

[0089] In many cases, it is difficult to accurately adjust the frequency of two elastic wave resonators with different electrode duty cycles by adjusting the thickness of the dielectric film 50, which is commonly arranged in elastic wave filters 1 and 2. In contrast, in the elastic wave apparatus 100 according to this embodiment, the electrode duty cycle of the high-frequency elastic wave filter 2 is larger than that of the low-frequency elastic wave filter 2, so it is possible to equalize the frequency fluctuation rate with respect to changes in the thickness of the dielectric film 50 between elastic wave filter 1 and elastic wave filter 2. Therefore, frequency adjustment of elastic wave filters 1 and 2 can be easily performed.

[0090] Furthermore, if the elastic wave device 100 is a multiplexer, unwanted ripple may occur in one of the elastic wave filters 1 and 2, which may cause deterioration in the transmission characteristics of the other elastic wave filter at the frequency in which the unwanted ripple occurred. In contrast, with the elastic wave filters 1 and 2 according to this embodiment, the generation of unwanted ripple can be suppressed in both elastic wave filters 1 and 2, so even if the elastic wave device 100 constitutes a multiplexer, deterioration of the transmission characteristics can be suppressed. Therefore, a compact and low-loss multiplexer having a common piezoelectric substrate 30 and a common insulating layer 40 can be provided.

[0091] In the elastic wave apparatus 100 according to this embodiment, the electrode duty cycle of each series arm resonator in the elastic wave filter 2 does not necessarily have to be greater than the electrode duty cycle of each parallel arm resonator in the elastic wave filter 1. Specifically, the electrode duty cycle of the series arm resonator 21S, which has the highest resonant frequency among all the series arm resonators 21S to 23S in the elastic wave filter 2, may be greater than the electrode duty cycle of the parallel arm resonator 11P, which has the lowest resonant frequency among all the parallel arm resonators 11P to 13P in the elastic wave filter 1.

[0092] In other words, in the elastic wave device 100 according to this embodiment, (1) the low-frequency elastic wave filter 1 and the high-frequency elastic wave filter 2 are formed on a common piezoelectric substrate 30, (2) the ratio (wavelength ratio) of the wavelength of the parallel arm resonator 11P of the elastic wave filter 1 to the wavelength of the series arm resonator 21S of the elastic wave filter 2 is 1.088 or more, and (3) the electrode finger duty cycle of the series arm resonator 21S is made larger than the electrode finger duty cycle of the parallel arm resonator 11P.

[0093] According to this, an elastic wave device 100 can be provided in which unwanted ripple in the parallel arm resonator 11P and the series arm resonator 21S, which have a large frequency difference, is suppressed. The parallel arm resonator 11P has the lowest resonant frequency and the largest wavelength λ among the parallel arm resonators 11P to 13P of the elastic wave filter 1. The series arm resonator 21S has the highest resonant frequency and the smallest wavelength λ among the series arm resonators 21S to 23S of the elastic wave filter 2.

[0094] In the elastic wave apparatus 100 according to this embodiment, it is desirable that the ratio (wavelength ratio) of the wavelength of the parallel arm resonator 11P of the elastic wave filter 1 to the wavelength of the series arm resonator 21S of the elastic wave filter 2 is 1.33 or less.

[0095] The upper limit of the electrode finger duty cycle for forming an IDT electrode of a typical elastic wave resonator is 0.8 due to manufacturing constraints. Although not shown in Figure 4, the lower limit of the wavelength λ at which the SH mode ripple can be kept below 0.3 dB when the electrode finger duty cycle is 0.8 is 1.86 μm.

[0096] Therefore, when the electrode duty cycle of the parallel arm resonator of the low-frequency elastic wave filter 1 is set to 0.5 and the electrode duty cycle of the series arm resonator of the high-frequency elastic wave filter 2 is set to 0.8, it becomes possible to reduce the SH mode ripple of both the parallel arm resonator with an electrode duty cycle of 0.5 and the series arm resonator with an electrode duty cycle of 0.8 to 0.3 dB or less, within the range where the ratio of the wavelength of the parallel arm resonator of the elastic wave filter 1 to the wavelength of the series arm resonator of the elastic wave filter 2 (wavelength ratio) is 1.33 (2.48 μm / 1.86 μm) or less.

[0097] [6 Effects, etc.] As described above, the elastic wave apparatus 100 according to the embodiment comprises an elastic wave filter 1 including one or more parallel arm resonators and having a first passband, and an elastic wave filter 2 including one or more series arm resonators and having a second passband on the higher frequency side than the first passband, each of the one or more parallel arm resonators includes a piezoelectric substrate 30 having a main surface 30a, a first IDT electrode arranged on the main surface 30a and having a plurality of first electrode fingers parallel to each other, and a first insulating layer arranged on the main surface 30a and formed to embed the first IDT electrode, and each of the one or more series arm resonators includes a piezoelectric substrate 30 and a main surface 30 The device includes a second IDT electrode having a plurality of parallel second electrode fingers arranged on surface a, and a second insulating layer arranged on the main surface 30a and formed to embed the second IDT electrode. The ratio of the wavelength of the first IDT electrode in the parallel arm resonator 11P with the lowest resonant frequency among the one or more parallel arm resonators to the wavelength of the second IDT electrode in the series arm resonator 21S with the highest resonant frequency among the one or more series arm resonators is 1.088 or more, and the electrode finger duty cycle of the second IDT electrode in the series arm resonator 21S is greater than the electrode finger duty cycle of the first IDT electrode in the parallel arm resonator 11P.

[0098] When forming elastic wave filters 1 and 2 using a common piezoelectric substrate 30, the larger the wavelength difference (wavelength ratio) between the IDT electrode of elastic wave filter 1 and the IDT electrode of elastic wave filter 2, the more difficult it becomes to reduce unwanted ripple generated in both elastic wave filters 1 and 2 by adjusting the common electrode film thickness and the common insulating layer thickness.

[0099] In contrast, in an elastic wave apparatus 100 formed using a common piezoelectric substrate 30, where the ratio of the wavelength of the parallel arm resonator 11P to the wavelength of the series arm resonator 21S (wavelength ratio) is 1.088 or more, by making the electrode finger duty cycle of the series arm resonator 21S of the elastic wave filter 2 larger than the electrode finger duty cycle of the parallel arm resonator 11P of the elastic wave filter 1, unwanted ripple can be suppressed in the passbands of both elastic wave filters 1 and 2. Therefore, an elastic wave apparatus 100 can be provided that has multiple elastic wave resonators with a large frequency difference, and in which unwanted ripple of the multiple elastic wave resonators is suppressed.

[0100] Furthermore, the elastic wave apparatus 100 according to the embodiment comprises an elastic wave filter 1 including one or more parallel arm resonators and having a first passband, and an elastic wave filter 2 including one or more series arm resonators and having a second passband on the higher frequency side than the first passband, each of the one or more parallel arm resonators includes a piezoelectric substrate 30 having a main surface 30a, a first IDT electrode having a plurality of first electrode fingers arranged on the main surface 30a and parallel to each other, and a first insulating layer arranged on the main surface 30a and formed to embed the first IDT electrode, and each of the one or more series arm resonators includes a piezoelectric substrate 30 and arranged on the main surface 30a and parallel to each other The device includes a second IDT electrode having a plurality of second electrode fingers parallel to the main surface 30a and a second insulating layer formed to embed the second IDT electrode, wherein the ratio of the wavelength of the first IDT electrode in the parallel arm resonator 11P, which has the largest wavelength of the first IDT electrode among the one or more parallel arm resonators, to the wavelength of the second IDT electrode in the series arm resonator 21S, which has the smallest wavelength of the second IDT electrode among the one or more series arm resonators, is 1.088 or more, and the electrode finger duty cycle of the second IDT electrode in the series arm resonator 21S is greater than the electrode finger duty cycle of the first IDT electrode in the parallel arm resonator 11P.

[0101] According to this, in an elastic wave apparatus 100 formed using a common piezoelectric substrate 30, where the ratio of the wavelength of the parallel arm resonator 11P to the wavelength of the series arm resonator 21S (wavelength ratio) is 1.088 or more, by making the electrode finger duty cycle of the series arm resonator 21S of the elastic wave filter 2 larger than the electrode finger duty cycle of the parallel arm resonator 11P of the elastic wave filter 1, it is possible to suppress the generation of unwanted ripple in the passbands of both elastic wave filters 1 and 2. Therefore, an elastic wave apparatus 100 can be provided in which unwanted ripple in the parallel arm resonator 11P and the series arm resonator 21S, which have a large frequency difference, is suppressed.

[0102] For example, in the elastic wave apparatus 100, the ratio of the wavelength of the first IDT electrode in the parallel arm resonator 11P to the wavelength of the second IDT electrode in the series arm resonator 21S is 1.33 or less.

[0103] When the electrode finger duty cycle is 0.8, which is the upper limit for manufacturing, the wavelength at which the SH mode ripple can be reduced to 0.3 dB or less is 1.86 μm or longer. Therefore, when the electrode finger duty cycle of the parallel arm resonators of elastic wave filter 1 is set to 0.5 and the electrode finger duty cycle of the series arm resonators of elastic wave filter 2 is set to 0.8, it becomes possible to reduce the SH mode ripple of both elastic wave filters 1 and 2 to 0.3 dB or less in the range where the wavelength ratio of the parallel arm resonators of elastic wave filter 1 to the parallel arm resonators of elastic wave filter 2 is 1.33 or less.

[0104] For example, in the elastic wave apparatus 100, the electrode finger duty cycle of the second IDT electrode in each of the one or more series arm resonators is greater than the electrode finger duty cycle in each of the one or more parallel arm resonators.

[0105] According to this, it is possible to provide an elastic wave apparatus 100 in which unwanted ripple in elastic wave filters 1 and 2 having a large frequency difference is suppressed.

[0106] For example, in the elastic wave apparatus 100, the thickness of the first insulating layer in the region between adjacent first electrode fingers among the plurality of first electrode fingers is equal to the thickness of the second insulating layer in the region between adjacent second electrode fingers among the plurality of second electrode fingers.

[0107] According to this, the insulating layers placed in elastic wave filters 1 and 2 can be made common, thus simplifying the manufacturing process of the elastic wave apparatus 100.

[0108] For example, in the elastic wave apparatus 100, the first insulating layer and the second insulating layer are made of the same material.

[0109] According to this, the insulating layers placed in elastic wave filters 1 and 2 can be made common, thus simplifying the manufacturing process of the elastic wave apparatus 100.

[0110] For example, in the elastic wave apparatus 100, the film thickness of the plurality of first electrode fingers and the film thickness of the plurality of second electrode fingers are equal.

[0111] According to this, the manufacturing process for the first IDT electrode and the second IDT electrode can be standardized, thus simplifying the manufacturing process for the elastic wave apparatus 100.

[0112] Furthermore, for example, in the elastic wave apparatus 100, the plurality of first electrode fingers and the plurality of second electrode fingers are made of the same material.

[0113] According to this, the manufacturing process for the first IDT electrode and the second IDT electrode can be standardized, thus simplifying the manufacturing process for the elastic wave apparatus 100.

[0114] For example, the elastic wave apparatus 100 further includes a first dielectric film arranged to cover the first insulating layer and a second dielectric film arranged to cover the second insulating layer.

[0115] According to this, the frequencies of elastic wave filters 1 and 2 can be adjusted.

[0116] Furthermore, for example, in the elastic wave apparatus 100, the first dielectric film and the second dielectric film each propagate at a speed faster than the speed of bulk sound propagating through the piezoelectric substrate 30.

[0117] According to this, it is possible to suppress the leakage of elastic waves propagating through the piezoelectric substrate 30 upward through the insulating layer.

[0118] For example, in the elastic wave apparatus 100, the first dielectric film and the second dielectric film are made of the same material.

[0119] According to this, the manufacturing process for the dielectric film can be standardized, thus simplifying the manufacturing process for the elastic wave apparatus 100.

[0120] For example, in the elastic wave apparatus 100, the elastic wave filter 1 further includes one or more series arm resonators, and the elastic wave filter 2 further includes one or more parallel arm resonators.

[0121] According to this, each of the elastic wave filters 1 and 2 functions as a ladder-type filter including a series arm resonator and a parallel arm resonator.

[0122] Furthermore, the multiplexer according to this embodiment includes a common terminal, an elastic wave filter connected to the common terminal, and an elastic wave filter 2 connected to the common terminal.

[0123] According to this, the generation of unwanted ripple can be suppressed in both elastic wave filters 1 and 2, making it possible to provide a compact and low-loss multiplexer having a common piezoelectric substrate 30.

[0124] (Other Modifications, etc.) Although embodiments and modifications of the elastic wave apparatus and multiplexer have been described above, the elastic wave apparatus and multiplexer of the present invention are not limited to the above embodiments and modifications. The present invention also includes other embodiments realized by combining any components in the above embodiments and modifications, modifications obtained by applying various modifications to the above embodiments and modifications that a person skilled in the art can conceive of without departing from the spirit of the present invention, and various devices incorporating the elastic wave apparatus or multiplexer according to the above embodiments and modifications.

[0125] For example, in the elastic wave apparatus and multiplexer according to the present invention, the electrode fingers constituting the IDT electrode and the reflective electrode fingers constituting the reflective electrode do not have to have a linear shape along the y-axis, but may have a curved shape.

[0126] The present invention, as a low-loss elastic wave filter and multiplexer applicable to multiband frequency standards, can be widely used in communication devices such as mobile phones.

[0127] 1, 2 Elastic wave filters 11P, 12P, 13P, 21P, 22P, 23P Parallel arm resonators 11S, 12S, 13S, 21S, 22S, 23S Series arm resonators 30 Piezoelectric substrate 30a Main surface 40 Insulating layer 50 Dielectric film 100 Elastic wave device 101, 102, 201, 202 Input / output terminals 111, 221 IDT electrodes 111a, 111b, 221a, 221b Electrode fingers 112a, 112b, 222a, 222b Busbar electrodes 115, 225 Reflecting electrodes

Claims

1. A first elastic wave filter comprising one or more parallel arm resonators and having a first passband, and a second elastic wave filter comprising one or more series arm resonators and having a second passband at a higher frequency than the first passband, wherein each of the one or more parallel arm resonators comprises a first piezoelectric substrate having a first main surface, a first IDT (InterDigital Transducer) electrode disposed on the first main surface and having a plurality of parallel first electrode fingers, and a first insulating layer disposed on the first main surface and formed to embed the first IDT electrode, and each of the one or more series arm resonators comprises the first piezoelectric substrate, a second IDT electrode disposed on the first main surface and having a plurality of parallel second electrode fingers, and a second insulating layer disposed on the first main surface and formed to embed the second IDT electrode, An elastic wave apparatus wherein the ratio of the wavelength of the first IDT electrode in the first parallel arm resonator, which has the lowest resonant frequency among the one or more parallel arm resonators, to the wavelength of the second IDT electrode in the first series arm resonator, which has the highest resonant frequency among the one or more series arm resonators, is 1.088 or more, and the electrode finger duty cycle of the second IDT electrode in the first series arm resonator is greater than the electrode finger duty cycle of the first IDT electrode in the first parallel arm resonator.

2. A first elastic wave filter comprising one or more parallel arm resonators and having a first passband, and a second elastic wave filter comprising one or more series arm resonators and having a second passband at a higher frequency than the first passband, wherein each of the one or more parallel arm resonators comprises a first piezoelectric substrate having a first main surface, a first IDT electrode disposed on the first main surface and having a plurality of parallel first electrode fingers, and a first insulating layer disposed on the first main surface and formed to embed the first IDT electrode, and each of the one or more series arm resonators comprises the first piezoelectric substrate, a second IDT electrode disposed on the first main surface and having a plurality of parallel second electrode fingers, and a second insulating layer disposed on the first main surface and formed to embed the second IDT electrode, An elastic wave apparatus wherein the ratio of the wavelength of the first IDT electrode in the first parallel-arm resonator, which has the largest wavelength of the first IDT electrode among the one or more parallel-arm resonators, to the wavelength of the second IDT electrode in the first series-arm resonator, which has the smallest wavelength of the second IDT electrode among the one or more series-arm resonators, is 1.088 or more, and the electrode finger duty cycle of the second IDT electrode in the first series-arm resonator is greater than the electrode finger duty cycle of the first IDT electrode in the first parallel-arm resonator.

3. The elastic wave apparatus according to claim 1 or 2, wherein the ratio of the wavelength of the first IDT electrode in the first parallel arm resonator to the wavelength of the second IDT electrode in the first series arm resonator is 1.33 or less.

4. The elastic wave apparatus according to any one of claims 1 to 3, wherein the electrode finger duty cycle of the second IDT electrode in each of the one or more series arm resonators is greater than the electrode finger duty cycle in each of the one or more parallel arm resonators.

5. The acoustic wave apparatus according to any one of claims 1 to 4, wherein the thickness of the first insulating layer in the region between adjacent first electrode fingers among the plurality of first electrode fingers is equal to the thickness of the second insulating layer in the region between adjacent second electrode fingers among the plurality of second electrode fingers.

6. The elastic wave apparatus according to any one of claims 1 to 5, wherein the first insulating layer and the second insulating layer are made of the same material.

7. The acoustic wave apparatus according to any one of claims 1 to 6, wherein the film thickness of the plurality of first electrode fingers is equal to the film thickness of the plurality of second electrode fingers.

8. The elastic wave apparatus according to any one of claims 1 to 7, wherein the plurality of first electrode fingers and the plurality of second electrode fingers are made of the same material.

9. The elastic wave apparatus according to any one of claims 1 to 8, further comprising a first dielectric film disposed to cover the first insulating layer and a second dielectric film disposed to cover the second insulating layer.

10. The elastic wave apparatus according to claim 9, wherein each of the first dielectric film and the second dielectric film has a propagating bulk wave speed faster than the bulk wave speed propagating through the first piezoelectric substrate.

11. The elastic wave apparatus according to claim 9 or 10, wherein the first dielectric film and the second dielectric film are made of the same material.

12. The elastic wave apparatus according to any one of claims 1 to 11, wherein the first elastic wave filter further includes one or more series arm resonators, and the second elastic wave filter further includes one or more parallel arm resonators.

13. A multiplexer comprising: a common terminal; a first elastic wave filter according to any one of claims 1 to 12, connected to the common terminal; and a second elastic wave filter according to any one of claims 1 to 12, connected to the common terminal.

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