Filter and multiplexer

Abstract

To provide a filter that suppresses spurious.SOLUTION: A filter includes a supporting substrate, a piezoelectric layer provided on the supporting substrate, series resonators S1 to S5 which are provided on the piezoelectric layer, are connected in series between the input terminal Tin and the output terminal Tout, and have electrode fingers having a first average pitch, parallel resonators P1 to 4 which are provided on the piezoelectric layer, have electrode fingers having a second average pitch greater than the first average pitch, and have one ends connected to a path between the input terminal Tin and the output terminal Tout, and the other ends connected to the ground, a resonator P' which is provided on the piezoelectric layer, has a third average pitch equal to or less than an intermediate value between the first average pitch and the second average pitch, and has one end connected to the path, and an inductor L which has one end connected to the other end of the resonator P' and the other end connected to the ground, and has an inductance greater than the inductance connected between the parallel resonators P1 to P4 and the ground.SELECTED DRAWING: Figure 12

Description

Technical Field

[0001] The present invention relates to a filter and a multiplexer, for example, a filter and a multiplexer having a pair of comb-shaped electrodes.

Background Art

[0002] As a surface acoustic wave resonator used in communication devices such as smartphones, a surface acoustic wave resonator having a pair of comb-shaped electrodes provided on a piezoelectric layer is known. It is known to bond the piezoelectric layer to a support substrate (for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] By bonding the piezoelectric layer to the support substrate, the temperature-frequency coefficient can be reduced. However, spurious responses occur at frequencies higher than the response due to the elastic wave of the main mode.

[0005] The present invention has been made in view of the above problems, and an object thereof is to suppress spurious.

Means for Solving the Problems

[0006] The present invention includes a support substrate, a piezoelectric layer provided on the support substrate, a plurality of first electrode fingers each provided on the piezoelectric layer and having a first average pitch, and one or more series resonators each connected in series between an input terminal and an output terminal. Further, the present invention includes a plurality of second electrode fingers each provided on the piezoelectric layer and having a second average pitch larger than the largest first average pitch, and one or more parallel resonators each having one end connected to a path between the input terminal and the output terminal and the other end connected to ground. Still further, the present invention includes a resonator provided on the piezoelectric layer and having a plurality of third electrode fingers with a third average pitch, and an inductor having one end connected to the path and an inductance larger than the largest inductance connected between the one or more parallel resonators and ground, and having the other end connected to ground. , the The present invention further includes a resonator provided on the piezoelectric layer and having a plurality of third electrode fingers with a third average pitch, and an inductor having one end connected to the path and an inductance larger than the largest inductance connected between the one or more parallel resonators and ground, and having the other end connected to ground. , the ratio of the difference between the third average pitch and the largest first average pitch to the third average pitch is ±0.35% or less, and the inductor has an inductance such that the attenuation poles of the circuit formed by the resonator and the inductor are formed at frequencies lower and higher than the passband. The present invention is a filter.

[0011] In the above configuration, the inductance of the inductor can be set to be 5 times or more the largest inductance connected between the one or more parallel resonators and ground.

[0018] In the above configuration, an insulating layer provided between the support substrate and the piezoelectric layer can be included. In the above configuration, one end of the resonator can be connected to the path between the input terminal and the series resonator closest to the input terminal among the one or more series resonators.

[0019] The present invention is a multiplexer including the above filter.

Advantages of the Invention

[0020] According to the present invention, spurious can be suppressed.

Brief Description of the Drawings

[0021]

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Best Mode for Carrying Out the Invention

[0022] [Surface Acoustic Wave Resonator] The elastic wave resonators used in the examples and comparative examples will be described. Fig. 1(a) is a plan view of the elastic wave resonator R1 used in the filters of the examples and comparative examples, and Fig. 1(b) is a cross-sectional view taken along the line A-A of Fig. 1(a). The arrangement direction of the electrode fingers is the X direction, the extending direction of the electrode fingers is the Y direction, and the stacking direction of the support substrate and the piezoelectric layer is the Z direction. The X direction, Y direction, and Z direction do not necessarily correspond to the X-axis direction and Y-axis direction of the crystal orientation of the piezoelectric layer. When the piezoelectric layer is a rotation Y-cut X-propagation substrate, the X direction is the X-axis direction of the crystal orientation.

[0023] As shown in Figs. 1(a) and 1(b), a piezoelectric layer 14 is provided on a support substrate 10. A temperature compensation film 12 is provided between the support substrate 10 and the piezoelectric layer 14. A boundary layer 11 is provided between the support substrate 10 and the temperature compensation film 12. An elastic wave resonator 26 is provided on the piezoelectric layer 14. The elastic wave resonator 26 has an IDT 22 and reflectors 24. The reflectors 24 are provided on both sides of the IDT 22 in the X direction. The IDT 22 and the reflectors 24 are formed by a metal film 16 on the piezoelectric layer 14.

[0024] The IDT 22 includes a pair of opposing comb-shaped electrodes 20. The comb-shaped electrodes 20 include a plurality of electrode fingers 18 and a bus bar 19 to which the plurality of electrode fingers 18 are connected. The region where the electrode fingers 18 of the pair of comb-shaped electrodes 20 intersect when viewed from the X direction is the intersection region 25. The length of the intersection region 25 is the aperture length. In at least a part of the intersection region 25 of the pair of comb-shaped electrodes 20, the electrode fingers 18 are alternately provided. The elastic wave mainly excited by the plurality of electrode fingers 18 in the intersection region 25 propagates mainly in the X direction. The pitch of the electrode fingers 18 of one of the pair of comb-shaped electrodes 20 is approximately equal to the wavelength λ of the elastic wave. When the pitch of the plurality of electrode fingers 18 (the pitch between the centers of the electrode fingers 18) is D, the pitch of the electrode fingers 18 of one of the comb-shaped electrodes 20 is half of the pitch D of the electrode fingers 18. The reflector 24 reflects the elastic wave (surface elastic wave) excited by the electrode fingers 18 of the IDT 22. Thereby, the elastic wave is confined within the intersection region 25 of the IDT 22.

[0025] The piezoelectric layer 14 is, for example, a single crystal lithium tantalate (LiTaO3) layer or a single crystal lithium niobate (LiNbO3) layer, and is, for example, a rotated Y-cut X-propagation lithium tantalate layer or a rotated Y-cut X-propagation lithium niobate layer. When it is a rotated Y-cut X-propagation lithium tantalate layer of 36° or more and 48° or less, the SH (Shear Horizontal) wave becomes the main mode elastic wave. The thickness T4 of the piezoelectric layer 14 is equal to or less than the wavelength λ of the elastic wave (that is, twice the pitch D).

[0026] The support substrate 10 is, for example, a sapphire substrate, an alumina substrate, a silicon substrate, a spinel substrate, a quartz substrate, a quartz substrate or a silicon carbide substrate. The sapphire substrate is a single crystal Al2O3 substrate, the alumina substrate is a polycrystalline or amorphous Al2O3 substrate, the silicon substrate is a single crystal or polycrystalline silicon substrate, the spinel substrate is a polycrystalline or amorphous MgAl2O4 substrate, the quartz substrate is a single crystal SiO2 substrate, the quartz substrate is a polycrystalline or amorphous SiO2 substrate, and the silicon carbide substrate is a polycrystalline or single crystal SiC substrate. The linear expansion coefficient of the support substrate 10 in the X direction is smaller than the linear expansion coefficient of the piezoelectric layer 14 in the X direction. Thereby, the frequency temperature dependence of the elastic wave resonator can be reduced.

[0027] The temperature compensation film 12 has a temperature coefficient of elastic constant with a sign opposite to the sign of the temperature coefficient of the elastic constant of the piezoelectric layer 14. For example, the temperature coefficient of the elastic constant of the piezoelectric layer 14 is negative, and the temperature coefficient of the elastic constant of the temperature compensation film 12 is positive. The temperature compensation film 12 is an insulating film mainly composed of silicon oxide (SiO2), and is, for example, a silicon oxide (SiO2) film without addition or containing an additive element such as fluorine, and is, for example, polycrystalline or amorphous. Thereby, the frequency temperature coefficient of the elastic wave resonator can be reduced. When the temperature compensation film 12 is a silicon oxide film, the sound velocity of the bulk wave propagating through the temperature compensation film 12 is slower than the bulk wave sound velocity propagating through the piezoelectric layer 14.

[0028] For the temperature compensation film 12 to have the function of temperature compensation, it is required that a certain amount of the energy of the elastic wave in the main mode exists in the temperature compensation film 12. Although the range where the energy of the surface elastic wave concentrates depends on the type of the surface elastic wave, typically, the energy of the surface elastic wave concentrates in the range of 2λ (λ is the wavelength of the elastic wave) from the upper surface of the piezoelectric layer 14, and particularly concentrates in the range of λ from the upper surface of the piezoelectric layer 14. Therefore, the distance (thickness T2 + T4) from the lower surface of the temperature compensation film 12 to the upper surface of the piezoelectric layer 14 is preferably 2λ or less, more preferably 1λ or less, and still more preferably 0.6λ or less.

[0029] The sound velocity of the bulk wave in the boundary layer 11 is faster than that of the bulk wave in the temperature compensation film 12. The boundary layer 11 is a polycrystalline film or an amorphous film such as aluminum oxide, aluminum nitride, silicon, silicon nitride, or silicon carbide. By providing the boundary layer 11, the elastic wave in the main mode can be confined in the piezoelectric layer 14 and the temperature compensation film 12, and unnecessary waves such as bulk waves can be attenuated in the boundary layer 11. Therefore, spurious caused by unnecessary waves can be suppressed. The thickness T1 of the boundary layer 11 is, for example, 1λ to 5λ.

[0030] The metal film 16 is a film mainly composed of, for example, aluminum (Al), copper (Cu), or molybdenum (Mo). An adhesion film such as a titanium (Ti) film or a chromium (Cr) film may be provided between the electrode finger 18 and the piezoelectric layer 14. The adhesion film is thinner than the electrode finger 18. An insulating film thinner than the electrode finger 18 may be provided so as to cover the electrode finger 18. The insulating film functions as a protective film.

[0031] [High-frequency spurious] The high-frequency spurious will be described. FIGS. 2(a) and 2(b) are cross-sectional views of the surface elastic wave resonators R2 and R3. The plan views of the surface elastic wave resonators R2 and R3 are the same as those of the surface elastic wave resonator R1 in FIG. 1(a).

[0032] As shown in Fig. 2(a), in the elastic wave resonator R2, the piezoelectric layer 14 is a piezoelectric substrate, and no support substrate is provided. The thickness of the piezoelectric layer 14 is 100 μm or more. As shown in Fig. 2(b), in the elastic wave resonator R3, the piezoelectric layer 14 is provided on the support substrate 10. The thickness T4 of the piezoelectric layer 14 is 10 times or more the wavelength λ of the elastic wave.

[0033] The spurious of the elastic wave resonators R1 to R3 will be described. Figs. 3(a) to 3(c) are schematic diagrams showing |Y| with respect to the frequency in the elastic wave resonators R2, R3, and R1, respectively. It is assumed that a 42° rotated Y-cut X-propagating lithium tantalate layer is used as the piezoelectric layer 14. |Y| is the absolute value of the admittance.

[0034] As shown in Fig. 3(a), as the main response due to the elastic wave of the main mode, |Y| becomes maximum at the resonance frequency fr and minimum at the anti-resonance frequency fa. In the elastic wave resonator R2 without using the support substrate 10, almost no spurious response is observed at frequencies higher than the anti-resonance frequency fa. In the elastic wave resonator R2, since the linear expansion coefficient of the piezoelectric layer 14 is large, the frequency temperature coefficient such as the resonance frequency becomes large. In the elastic wave resonator R3, since the piezoelectric layer 14 is bonded onto the support substrate 10 having a smaller linear expansion coefficient than the piezoelectric layer 14, the frequency temperature coefficient becomes small.

[0035] As shown in Fig. 3(b), in the elastic wave resonator R3 in which the piezoelectric layer 14 is bonded onto the support substrate 10, a spurious response Sp0 is observed at a frequency higher than the anti-resonance frequency fa. The spurious response Sp0 is observed in a wide frequency range. The spurious response Sp0 occurs because unnecessary waves such as bulk waves are trapped in the piezoelectric layer 14 together with the elastic wave of the main mode.

[0036] As shown in Fig. 3(c), in the elastic wave resonator R1 where the thickness T4 of the piezoelectric layer 14 is set to be equal to or less than the wavelength λ of the elastic wave, the difference between the resonance frequency fr and the anti-resonance frequency fa is larger than that in the elastic wave resonator R3. This indicates that the electromechanical coupling coefficient of the elastic wave resonator R1 is larger than that of the elastic wave resonator R3. Also, the resonance frequency fr and the anti-resonance frequency fa are steeper than those in the elastic wave resonator R3. This indicates that the Q value of the elastic wave resonator R1 is higher than that of the elastic wave resonator R3. A spurious response Sp is observed in a frequency range narrower than that of the elastic wave resonator R3. The magnitude of the spurious response Sp is larger than Sp0 of the elastic wave resonator R3.

[0037] As described above, when the piezoelectric layer 14 is bonded onto the support substrate 10, the frequency temperature coefficient becomes small, but spurious responses Sp0 and Sp occur at frequencies higher than the anti-resonance frequency fa. When the thickness T4 of the piezoelectric layer 14 is set to be equal to or less than the wavelength λ of the elastic wave as in the elastic wave resonator R1, the Q value and the electromechanical coupling coefficient increase. A large spurious response Sp occurs in the higher frequency range within the frequency range of the spurious response Sp0 of the elastic wave resonator R3. Such a spurious response is called a high-frequency spurious.

[0038] The passing characteristics of a ladder-type filter using the elastic wave resonator R1 will be described. Fig. 4 is a circuit diagram of the ladder-type filter F. As shown in Fig. 4, the ladder-type filter F is an eight-stage ladder-type filter including series resonators S1 to S5 and parallel resonators P1 to P4. The series resonators S1 to S5 are connected in series between the input terminal Tin and the output terminal Tout. The series resonators S2 to S4 are each divided into two resonators in series. The parallel resonators P1 to P4 are connected in parallel between the input terminal Tin and the output terminal Tout. One end of the parallel resonators P1 to P4 is connected to the path between the input terminal Tin and the output terminal Tout, and the other end is connected to the ground terminal Tg. The parallel resonators P1 and P2 are connected to the ground terminal Tg via the inductor L1, and the parallel resonators P3 and P4 are connected to the ground terminal Tg via the inductor L2. The inductors L1 and L2 correspond to parasitic inductances and are 0.1 nH or less. An inductor Lin is connected between the input terminal Tin and the ground terminal Tg, and an inductor Lout is connected between the output terminal Tout and the ground terminal Tg. The inductors Lin and Lout are inductors for matching and may not be connected.

[0039] Figs. 5(a) to 5(c) are schematic diagrams showing the passing characteristics of the ladder-type filter F, the series resonator S, and the parallel resonator P. Fig. 5(b) is an enlarged view near the spurious response in Fig. 5(a), and Fig. 5(c) is an enlarged view of the passing characteristics of the series resonator S and the parallel resonator P in Fig. 5(b). F shows the passing characteristics of the ladder-type filter F, S shows the passing characteristics of the series resonators S1 to S5, and P shows the passing characteristics with the parallel resonators P1 to P4 connected in shunt. The passing characteristics of the series resonators S1 to S5 are all the same, and the passing characteristics of the parallel resonators P1 to P4 are all the same.

[0040] As shown in Fig. 5(a), a passband Pass of the ladder filter F is formed near 2600 MHz. The attenuation band on the low-frequency side of the passband Pass is formed by the resonance frequency frp of the parallel resonator P, and the attenuation band on the high-frequency side of the passband Pass is formed by the anti-resonance frequency fas of the series resonator S. A spurious response Sp due to high-frequency spurs occurs from 3500 MHz to near 4200 MHz. Comparing Fig. 5(b) and Fig. 5(c), the spurious response Sp of the filter F is formed at frequencies corresponding to the spurious responses of the series resonator S and the parallel resonator P. For example, the peaks Pk1 to Pk3 of the spurious response of the filter F in Fig. 5(b) correspond to the peak Pp1 of the spurious response of the parallel resonator P, and the peaks Ps1 and Ps2 of the spurious response of the series resonator S in Fig. 5(c). Thus, in the ladder filter F, since the series resonators S1 to S5 and the parallel resonators P1 to P4 are connected in multiple stages, the spurious responses of the single series resonator S overlap and the spurious responses of the single parallel resonator P overlap, resulting in a large spurious response. When peaks of the spurious response are formed in the attenuation band, the attenuation amount becomes small, which is a problem.

[0041] [Simulation 1] In a single-stage ladder filter, a simulation was performed to suppress spurs. Fig. 6 is a circuit diagram of the ladder filter used in Simulation 1. As shown in Fig. 6, a series resonator S is connected in series and a parallel resonator P is connected in parallel between the input terminal Tin and the output terminal Tout.

[0042] The simulation conditions are as follows. Support substrate 10: Sapphire substrate with a thickness of 30 μm Boundary layer 11: Aluminum oxide layer with a thickness of 6 μm Temperature compensation film 12: Silicon oxide film with a thickness of 0.4 μm Piezoelectric layer 14: 42°Y-cut X-propagation lithium tantalate layer with a thickness of 0.5 μm Metal film 16: Titanium film with a thickness of 40 nm and aluminum film with a thickness of 117 nm from the piezoelectric layer 14 side The interface between the support substrate 10 and the boundary layer 11 is a mirror surface Filter F01 2×pitch Dp of series resonator S: 1.39 μm 2×pitch Ds of parallel resonator P: 1.50 μm Filter F02 2×pitch Dp of series resonator S: 1.39 μm 2×pitch Ds of parallel resonator P: 1.39 μm

[0043] Figures 7(a) to 7(c) are diagrams showing the passing characteristics of filters F01 and F02 in Simulation 1. S and P are the passing characteristics of the series resonator S and the parallel resonator P in filter F02. Figure 7(b) is an enlarged view near the spurious response of Figure 7(a), and Figure 7(c) is an enlarged view of the passing characteristics of the series resonator S and the parallel resonator P of Figure 7(b).

[0044] As shown in Figure 7(a), in filter F01, the pitch Dp of the parallel resonator P is made larger than the pitch Ds of the series resonator S. As a result, a passband Pass is formed between the resonance frequency frp of the parallel resonator P and the anti-resonance frequency fas of the parallel resonator P. In filter F02, since the pitch Dp of the parallel resonator P and the pitch Ds of the series resonator S are the same, no passband is formed.

[0045] As shown in Figure 7(b), filter F02 has a larger attenuation amount at the peak of the spurious response Sp compared to filter F01. As shown in Figure 7(c), at the frequencies f1 and f2 of the peaks of the series resonator S, the attenuation amount of the parallel resonator P becomes larger. At the frequencies f3 and f4 of the peaks of the parallel resonator P, the attenuation amount of the series resonator S becomes larger. Thus, when the pitch Ds of the series resonator S and the pitch Dp of the parallel resonator P are made the same, the spurious peaks of the series resonator S and the parallel resonator P cancel each other out with notches. As a result, as shown in Figure 7(b), the attenuation amount of the peak of the spurious response Sp of filter F02 becomes larger than that of filter F01.

[0046] [Simulation 2] A simulation was performed on the passing characteristics of the circuit for suppressing spurious. Fig. 8 is the circuit diagram of the circuit used in Simulation 2. As shown in Fig. 8, in circuit 46, one end of resonator P´ is connected to the path between input terminal Tin and output terminal Tout, and the other end is connected to ground terminal Tg via inductor L.

[0047] First, the 2×pitch Dp´ of resonator P´ was fixed at 1.39 μm, the inductance of inductor L was changed, and the passing characteristics of circuit 46 were simulated. Other simulation conditions are the same as those in Simulation 1.

[0048] Figs. 9(a) and 9(b) are diagrams showing the passing characteristics of circuit 46 in Simulation 2. Fig. 9(b) is an enlarged view near the spurious response in Fig. 9(a). The inductances of inductor L are 0.1 nH, 3.0 nH, and 6.0 nH.

[0049] As shown in Fig. 9(a), inductor L with an inductance of 0.1 nH corresponds to parasitic inductance. When the inductance of inductor L is 0.1 nH, one attenuation pole corresponding to the resonance frequency fr of resonator P´ is formed. When the inductance of inductor L is 3.0 nH, the attenuation pole is separated into two. One attenuation pole A1 becomes lower than the resonance frequency fr, and the other attenuation pole A2 becomes higher than the resonance frequency fr. When the inductance of inductor L is 6.0 nH, attenuation pole A1 becomes lower than attenuation pole A1 at 3.0 nH. Attenuation pole A2 becomes lower than attenuation pole A2 at 3.0 nH and higher than the resonance frequency fr.

[0050] As shown in Fig. 9(b), let the three poles of the spurious response Sp be At1 to At3. As the inductance of inductor L increases, the attenuation amounts of poles At1 to At3 decrease and shift to lower frequencies. The shift amounts of poles At1 to At3 are smaller compared to the shift amounts of attenuation poles A1 and A2.

[0051] Figures 10(a) and 10(b) are diagrams showing the attenuation amount and frequency of each of the poles At1 to At3 with respect to the inductance of the inductor L in Simulation 2. As shown in Fig. 10(a), when the inductance increases from 0.1 nH, the attenuation amount of the poles At1 to At3 increases. The attenuation amount becomes maximum when the inductance is around about 1 nH. When the inductance increases from 1 nH, the attenuation amount decreases. When the inductance is 6 nH, the attenuation amount is approximately -0.1 dB. In order to ensure the attenuation amount of the poles At1 to At3, the inductance of the inductor L is preferably 6.0 nH or less, and more preferably 3.0 nH or less.

[0052] As shown in Fig. 10(b), when the inductance increases from 0.1 nH and becomes about 0.5 nH or more, the frequencies of the poles At1 to At3 start to decrease. When the inductance exceeds about 2 nH, even if the inductance increases, the frequencies of the poles At1 to At3 hardly change. In order to change the frequencies of the poles At1 to At3, the inductance of the inductor L is preferably 0.5 nH or more, and more preferably 0.7 nH or more. As described above, by changing the inductance of the inductor L, the attenuation amount and frequency of the poles At1 to At3 can be changed.

[0053] Next, with the inductance of the inductor L set to 0 nH, the 2× pitch Dp' of the resonator P' was changed, and the passing characteristics of the circuit 46 were simulated. Other simulation conditions are the same as those in Simulation 1.

[0054] Figures 11(a) and 11(b) are diagrams showing the passing characteristics of the circuit 46 in Simulation 2, and Fig. 11(c) is a diagram showing the frequency of the pole At1 with respect to the 2× pitch Dp'. Fig. 11(b) is an enlarged view near the spurious response in Fig. 11(a). The 2× pitch Dp' of the resonator P' is 1.36 μm, 1.43 μm, and 1.51 μm. The dots in Fig. 11(c) are simulation points, and the straight line is an approximate straight line using the least squares method.

[0055] As shown in FIGS. 11(a) and 11(b), when the 2×pitch Dp' of the resonator P' increases, the resonance frequency fr decreases, and the frequency of the pole At1 of the spurious response Sp decreases. Even if the 2×pitch Dp' is changed, the attenuation amount of the pole At1 hardly changes. The shift amount of the resonance frequency fr and the shift amount of the pole At1 with respect to the change in the 2×pitch Dp' of the resonator P' are of the same degree.

[0056] As shown in FIG. 11(c), when the 2×pitch Dp' of the resonator P' increases, the frequency of the pole At1 decreases. The approximate straight line is that the frequency of the pole At1 = -1971.2×2×Dp' + 6660.3. When the 2×pitch Dp' is increased by 0.005 μm, the frequency of the pole At1 shifts by about 10 MHz. Thus, when the 2×pitch Dp' of the resonator P' is changed, the attenuation amount of the pole At1 hardly changes, but the frequency of the pole At1 can be shifted to the same extent as the resonance frequency fr.

[0057] Examples based on the above findings will be described.

Example

[0058] FIG. 12 is a circuit diagram of a filter according to Example 1. As shown in FIG. 12, a ladder filter 44 is connected between an input terminal Tin and an output terminal Tout. The ladder filter 44 includes series resonators S1 to S5, parallel resonators P1 to P4, and inductors L1 and L2, similar to the ladder filter F in FIG. 4. The inductors L1 and L2 are parasitic inductances. A circuit 46 is connected between the ladder filter 44 and the input terminal Tin. The circuit 46 includes a resonator P' and an inductor L, similar to FIG. 8.

[0059] FIG. 13 is a plan view showing a part of the filter according to Embodiment 1 formed on a chip. As shown in FIG. 13, an elastic wave resonator 26 having an IDT 22 and a reflector 24 is provided on a support substrate 10. The elastic wave resonator 26 includes series resonators S1 to S5, parallel resonators P1 to P4, and a resonator P'. Wiring 32 and pads 34 are provided on the support substrate 10. The wiring 32 connects between the elastic wave resonators 26 and connects the elastic wave resonator 26 and the pads. The wiring 32 and the pads 34 are metal layers such as a gold layer, a copper layer, or an aluminum layer. The pad 34 is electrically connected to an input terminal Tin, an output terminal Tout, a ground terminal Tg, and an inductor terminal TL. The inductor terminal TL corresponds to a node between the resonator P' and the inductor L in the circuit 46. The inductor L is provided outside the chip. The inductor L is formed, for example, by wiring provided on a mounting substrate on which the chip is mounted. The inductor L may be a chip component.

[0060] [Simulation 3] The passing characteristics of the filter according to Embodiment 1 were simulated. The simulation conditions are as follows. Filter F1 2×pitch Ds of series resonator S: 1.390 μm 2×pitch Dp of parallel resonator P: 1.500 μm 2×pitch Dp' of resonator P': 1.395 μm Inductors L1, L2: 0.1 nH Inductor L: 3.0 nH Filter F2 2×pitch Ds of series resonator S: 1.390 μm 2×pitch Dp of parallel resonator P: 1.500 μm 2×pitch Dp' of resonator P': 1.500 μm Inductors L1, L2: 0.1 nH Inductor L: 3.0 nH Other simulation conditions are the same as those in Simulation 1.

[0061] Filter F1 corresponds to Example 1, where the pitch Dp' of resonator P' is approximately the same as the pitch Ds of series resonator S. Filter F2 corresponds to Comparative Example 1, where the pitch Dp' of resonator P' is approximately the same as the pitch Dp of parallel resonator P.

[0062] Figures 14(a) and 14(b) are diagrams showing the passing characteristics of filters F1, F2, and circuit 46 in Simulation 3. Figure 14(b) is an enlarged view near the spurious response in Figure 14(a). Also shown are the passing characteristics of circuit 46 with an inductance of 0.1 nH and circuit 46 with an inductance of 3.0 nH for resonator P' with a 2×pitch Dp' of 1.395 μm.

[0063] As shown in Figure 14(a), filters F1 and F2 have a passband Pass at approximately 2600 MHz. A spurious response Sp occurs at 3400 MHz to 4200 MHz. As shown in Figure 14(b), in filters F1 and F2, three peaks Pk1 to Pk3 are formed in the spurious response Sp. Peak Pk1 is mainly formed by the spurious response of parallel resonator P, and peaks Pk2 and Pk3 are mainly formed by the spurious response of series resonator S. In filter F1, the attenuation amounts of peaks Pk2 and Pk3 can be made larger than in filter F2. For example, in filter F1, as indicated by the downward arrow, the attenuation amount of peak Pk3 is approximately 3.0 dB larger than in filter F2.

[0064] In filter F1 of Example 1, the pitch Dp' of resonator P' is made approximately the same as the pitch Ds of series resonator S. Thereby, as shown in Figure 7(c) of Simulation 1, the peak of the spurious response of series resonator S can be compensated by the notch of the spurious response of resonator P'. Thereby, the peak of the spurious response can be made smaller compared to the case where the pitch Dp' of resonator P' is made the same as the pitch Dp of parallel resonator P as in filter F02.

[0065] When the inductance of the inductor L is on the order of parasitic inductance, such as L = 0.1 nH in FIG. 14(a), the resonance frequency fr of the resonator P' is located within the passband Pass, and a notch is formed in the passband Pass. Therefore, the inductance of the inductor L is increased. As a result, the attenuation poles A1 and A2 of the circuit 46 are formed at frequencies lower and higher than the passband Pass, as in L = 3.0 nH in FIG. 14(a). Therefore, it is possible to suppress the formation of a notch due to the circuit 46 within the passband Pass.

[0066] As shown in FIG. 10(b) of Simulation 1, when the inductance of the inductor L increases, the frequency of the spurious response of the resonator P' changes. Therefore, as shown in FIG. 11(c), by changing the pitch Dp' of the resonator P', the peak of the spurious response of the series resonator S is adjusted to be compensated by the notch of the spurious response of the resonator P'. As shown in FIG. 10(b), when the inductance of the inductor L is increased, the spurious response shifts to the low-frequency side. To compensate for this, as shown in FIG. 11(c), it is considered that the pitch Dp' of the resonator P' is made smaller than the pitch Ds of the series resonator S. However, in reality, the pitch Dp' of the resonator P' is adjusted such that the peak of the spurious response in the filter F01 is lowered in the vicinity of the pitch Ds of the series resonator S. Therefore, the pitch Dp' of the resonator P' may be larger than the pitch Ds of the series resonator S.

[0067] According to Embodiment 1, the average pitch Ds (first average pitch) of the electrode fingers 18 (first electrode fingers) in the series resonators S1 to S5 is made larger than the average pitch Dp (second average pitch) of the electrode fingers 18 (second electrode fingers) in the parallel resonators P1 to P4. When the average pitch Ds is different within the series resonators S1 to S5 and the average pitch Dp is different within the parallel resonators P1 to P4, the smallest average pitch Dpmin is larger than the largest average pitch Dsmax. Thereby, a bandpass filter is formed by the series resonators S1 to S5 and the parallel resonators P1 to P4. When the piezoelectric layer 14 is provided on the support substrate 10, spurious responses Sp0 and Sp occur as shown in FIGS. 3(b) and 3(c). Note that the average pitch D of the surface acoustic wave resonator 26 can be calculated by dividing the width in the X direction of the IDT 22 by the number of electrode fingers 18.

[0068] Therefore, the average pitch Dp' of the electrode fingers 18 of the resonator P' is made close to the average pitch Ds of the series resonators S1 to S4. That is, the average pitch Dp' of the resonator P' is set to be equal to or less than the intermediate value (Dpmin + Dsmax) / 2 between the largest average pitch Dsmax among the series resonators S1 to S4 and the smallest average pitch Dpmin among the parallel resonators P1 to P4. Thereby, the notch of the spurious response of the resonator P' compensates for the peak of the spurious response of the series resonators S1 to S5. However, a notch due to the resonance frequency fr of the resonator P' is formed within the passband Pass.

[0069] Therefore, an inductor L is provided, one end of which is connected to the ground side end of the resonator P', and the other end of which is connected to the ground. The inductance of the inductor L is larger than the larger inductance of the largest inductors L1 and L2 connected between the parallel resonators P1 to P4 and the ground. Thereby, the attenuation poles A1 and A2 caused by the resonance frequency fr of the resonator P' are formed on both sides of the passband Pass, and it is suppressed that notches are formed in the passband Pass. As shown in Fig. 10(b), the frequency of the high-frequency spurious of the resonator P' is changed by the inductor L. Therefore, by finely adjusting the average pitch Dp' of the resonator P', the notch of the spurious response of the resonator P' is adjusted to compensate for the peak of the spurious response of the series resonators S1 to S5. Thereby, a decrease in the attenuation amount due to the spurious response of the series resonators S1 to S5 can be suppressed.

[0070] In order to make the average pitch Dp' of the resonator P' near the average pitch Ds of the series resonators S1 to S5, the average pitch Dp' of the resonator P' is preferably Dsmax+(Dpmin-Dsmax) / 3 or less. Also, the average pitch Dp' of the resonator P' is preferably Dsmin-(Dpmin-Dsmax) / 2 or more, and more preferably Dsmin-(Dpmin-Dsmax) / 3 or more.

[0071] As shown in Fig. 10(b), the frequency change of the spurious response due to the inductor L is very small. Therefore, the average pitch Dp' of the resonator P' is preferably 1.02 times or less of the largest average pitch Dsmax and 0.98 times or more of the smallest average pitch Dsmin, more preferably 1.015 times or less of the largest average pitch Dsmax, and even more preferably 1.01 times or less. The average pitch Dp' is more preferably 0.985 times or more of the smallest average pitch Dsmin, and even more preferably 0.99 times or more.

[0072] As shown in Fig. 14(a), in order to position the attenuation poles A1 and A2 due to the resonance frequency fr of the resonator P' outside the passband Pass, the inductance of the inductor L is preferably 5 times or more, more preferably 10 times or more, the largest inductance among the inductors L1 and L2. Thereby, even when the resonance frequency fr of the resonator P' alone is located within the passband Pass, the attenuation poles A1 and A2 due to the resonance frequency of the resonator P' to which the inductor L is connected do not locate within the passband Pass. When the inductors L1 and L2 are parasitic inductances, the inductances of the inductors L1 and L2 are 0.1 nH. Therefore, the inductance of the inductor L is preferably 0.5 nH or more, more preferably 1.0 nH or more.

[0073] As shown in Fig. 10(a), when the inductance of the inductor L is too large, the notch of the spurious response of the resonator P' becomes small. From this point of view, the inductance of the inductor L is preferably 100 times or less, more preferably 50 times or less, still more preferably 20 times or less, the largest inductance among the inductors L1 and L2.

[0074] When the average pitches Ds of the series resonators S1 to S5 are substantially equal, the spurious responses of the series resonators S1 to S5 overlap each other, and the peak of the spurious response becomes large. Therefore, when the largest average pitch Ds is Dsmax and the smallest average pitch Ds is Dsmin, it is preferable to provide the circuit 46 when (Dsmax - Dsmin) / (Dsmax + Dsmin) is 0.01 or less or 0.005 or less.

Example

[0075] Fig. 15 is a circuit diagram of a filter according to Example 2. As shown in Fig. 15, a ladder filter 44 is connected between the input terminal Tin and the output terminal Tout. The ladder filter 44 includes series resonators S1 to S6, parallel resonators P1 to P4, and inductors L1 and L2. A circuit 46 is connected between the series resonators S5 and S6. The circuit 46 includes a resonator P' and an inductor L, similar to Fig. 8.

[0076] [Simulation 4] The passing characteristics of the filter according to Example 2 were simulated. The simulation conditions are as follows. Filter F3 2×pitch Ds of series resonator S: 1.400 μm 2×pitch Dp of parallel resonator P: 1.500 μm 2×pitch Dp' of resonator P': 1.490 μm Inductors L1, L2: 0.1 nH Inductor L: 0.9 nH Filter F4 2×pitch Ds of series resonator S: 1.400 μm 2×pitch Dp of parallel resonator P: 1.500 μm 2×pitch Dp' of resonator P': 1.500 μm Inductors L1, L2: 0.1 nH Inductor L: 0.9 nH Other simulation conditions are the same as those in Simulation 1.

[0077] Filter F3 corresponds to Example 2 where the pitch Dp' of resonator P' is slightly smaller than the pitch Dp of parallel resonator P. Filter F4 corresponds to Comparative Example 2 where the pitch Dp' of resonator P' is the same as the pitch Dp of parallel resonator P.

[0078] Figures 16(a) to 17 are diagrams showing the passing characteristics of filters F3, F4, and circuit 46 in Simulation 4. Figure 16(b) is an enlarged view near the spurious response in Figure 16(a), and Figure 17 is an enlarged view near the low-frequency end of the passband Pass in Figure 16(a). The passing characteristics of circuit 46 with an inductance of 0.1 nH and 0.9 nH for inductor L in resonator P' with a 2×pitch Dp' of 1.490 μm are illustrated.

[0079] As shown in Fig. 16(a), filters F3 and F4 have a passband Pass at approximately 2600 MHz. A spurious response Sp occurs at 3400 MHz to 4200 MHz. As shown in Fig. 16(a) and Fig. 17, the resonance frequency fr of resonator P´ with L = 0.1 nH is located at the low-frequency end of the passband Pass. Attenuation poles A1 and A2 caused by the resonance frequency fr of resonator P´ with L = 0.9 nH are located at frequencies lower and higher than the passband Pass. As shown in Fig. 16(b), in filter F3, the peak Pk1 formed by the spurious response of parallel resonators P1 to P4 can be made lower than that in filter F4. For example, in filter F3, as indicated by the downward arrow, the attenuation amount of peak Pk1 is approximately 8.2 dB greater than that in filter F4.

[0080] In filter F3 of Example 2, the pitch Dp´ of resonator P´ is made slightly different from the pitch Dp of parallel resonator P. As a result, the notch of the spurious response of resonator P´ overlaps with the peak of the spurious response of parallel resonators P1 to P4. Thereby, the peak Pk1 formed by the spurious response of parallel resonators P1 to P4 can be made lower, as in filter F3 of Fig. 16(b).

[0081] However, if the pitch Dp´ of resonator P´ is made smaller than the pitch Dp of parallel resonator P, when the inductance of inductor L is on the order of parasitic inductance, as in L = 0.1 nH in Fig. 17, the resonance frequency fr of resonator P´ overlaps with the low-frequency end of the passband Pass. Thereby, the passband Pass may become narrower. Therefore, the inductance of inductor L is increased. As a result, attenuation poles A1 and A2 of circuit 46, as in L = 0.9 nH in Fig. 16(a) and Fig. 17, are formed at frequencies lower and higher than the passband Pass. Thus, it is possible to suppress the formation of a notch caused by circuit 46 within the passband Pass.

[0082] According to Example 2, the average pitch Dp´ (the third average pitch) of the electrode fingers 18 of the resonator P´ is made smaller than the smallest average pitch Dsmin among the parallel resonators P1 to P4, and is made equal to or greater than the intermediate value (Dpmin + Dsmax) / 2 between the average pitch Dsmax and the average pitch Dpmin. Thereby, the peak Pk1 mainly formed by the spurious response of the parallel resonators P1 to P4 can be lowered. However, the attenuation poles caused by the resonance frequency fr of the resonator P´ are located within the passband Pass. Therefore, the inductance of the inductor L is made greater than the largest inductance of the inductors L1 and L2 connected between the parallel resonators P1 to P4 and the ground. Thereby, even when the resonance frequency fr of the resonator P´ alone is located within the passband Pass, the attenuation poles A1 and A2 caused by the resonance frequency of the resonator P´ to which the inductor L is connected are not located within the passband Pass.

[0083] The inductance of the inductor L is more preferably 5 times or more, and even more preferably 8 times or more, the largest inductance of the inductors L1 and L2. The inductance of the inductor L is preferably 0.5 nH or more, and more preferably 0.8 nH or more. Thereby, even when the resonance frequency fr of the resonator P´ alone is located within the passband Pass, the attenuation poles A1 and A2 caused by the resonance frequency of the resonator P´ to which the inductor L is connected are not located within the passband Pass.

[0084] If the inductance of the inductor L is too large, the notch of the spurious response becomes small. From this viewpoint, the inductance of the inductor L is preferably 100 times or less, more preferably 50 times or less, and even more preferably 20 times or less, the largest inductance of the inductors L1 and L2.

[0085] When the average pitches Dp of the parallel resonators P1 to P4 are approximately equal, the spurious responses of the parallel resonators P1 to P4 overlap with each other, and the peaks of the spurious responses become large. Therefore, when the largest average pitch Dp is Dpmax and the smallest average pitch Dp is Dpmin, it is preferable to provide the circuit 46 when (Dpmax - Dpmin) / (Dpmax + Dpmin) is 0.01 or less or 0.005 or less. Also, Dpmin - Dp´ is preferably larger than Dpmax - Dpmin, more preferably 2 times or more of Dpmax - Dpmin, and even more preferably 3 times or more.

[0086] Looking at the waveform of the spurious response of the parallel resonator P in FIG. 7(c), in order to shift the notch of the spurious response of the resonator P´ to the peak of the spurious response of the parallel resonator P, it is sufficient to move the notch of the spurious response of the resonator P´ to the high-frequency side by about 10 MHz to 20 MHz. As shown in FIG. 11(c), if 2 × pitch Dp´ is made 0.002 μm smaller, the notch of the spurious response of the resonator P´ shifts to the high-frequency side by 10 MHz. Therefore, the average pitch Dp´ of the resonator P´ is 0.98 times or more of Dpmin, and 0.99 times or more. Also, it is Dpmin - (Dpmin - Dsmax) / 3 or more.

[0087] In Examples 1 and 2, when the thickness T4 of the piezoelectric layer 14 is 2 times or less (i.e., 1λ or less) of the largest average pitch Dpmax among the parallel resonators P1 to P4, a strong spurious response Sp occurs at some frequencies as shown in FIG. 3(c). In this case, the spurious response can be more suppressed by providing the circuit 46. The number of series resonators may be 1 or more, and the number of parallel resonators may be 1 or more.

Example

[0088] FIG. 18 is a circuit diagram of the filter according to Embodiment 3. As shown in FIG. 18, a DMS (Double Mode Surface Acoustic Wave) filter 45 is connected between an input terminal Tin and an output terminal Tout. The DMS filter 45 is grounded via an inductor L3. The inductor L3 is a parasitic inductance and is, for example, 0.1 nH or less. A circuit 46 is connected between the DMS filter 45 and the input terminal Tin. The circuit 46 includes a resonator P' and an inductor L as in FIG. 8.

[0089] FIG. 19 is a plan view of a part of the filter according to Embodiment 3 formed on a chip. As shown in FIG. 19, a DMS filter 45 and an acoustic wave resonator 26 are provided on a support substrate 10. The DMS filter 45 has three IDTs 22 arranged, and reflectors 24 are provided on both sides of the three IDTs. The acoustic wave resonator 26 includes a resonator P'. Wires 32, 36, and pads 34 are provided on the support substrate 10. The wires 32 and 36 connect between the DMS filter 45 and the acoustic wave resonator 26, and connect the DMS filter 45 and the acoustic wave resonator 26 to the pads 34. The wire 36 is a wire that intersects the wire 32 via an insulating layer. The pads 34 are electrically connected to the input terminal Tin, the output terminal Tout, the ground terminal Tg, and the inductor terminal TL.

[0090] [Simulation 5] First, the following DMS filter 45 without the circuit 46 was fabricated and its passing characteristics were measured. Support substrate 10: Sapphire substrate with a thickness of 500 μm Boundary layer 11: Aluminum oxide layer with a thickness of 5 μm Temperature compensation film 12: None Piezoelectric layer 14: 42°Y-cut X-propagation lithium tantalate layer with a thickness of 0.9 μm Metal film 16: Titanium film with a thickness of 10 nm and aluminum film with a thickness of 129 nm from the piezoelectric layer 14 side Protective film: Silicon oxide film with a thickness of 15 μm The interface between the support substrate 10 and the boundary layer 11 is rough 2×pitch Dd of IDT22: 2.00 μm

[0091] Based on the measured passing characteristics of the DMS filter 45, the passing characteristics of the filter F5 according to Example 3 were simulated. The simulation conditions are as follows. Filter F5 Characteristics of DMS filter 45: Measured characteristics of DMS Conditions of resonator P´ Support substrate 10: Sapphire substrate with a thickness of 30 μm Boundary layer 11: Aluminum oxide layer with a thickness of 5 μm Temperature compensation film 12: None Piezoelectric layer 14: 42° Y-cut X-propagation lithium tantalate layer with a thickness of 0.9 μm Metal film 16: Titanium film with a thickness of 10 nm and aluminum film with a thickness of 129 nm from the piezoelectric layer 14 side Protective film: None The interface between the support substrate 10 and the boundary layer 11 is a mirror surface 2×pitch Dp´ of resonator P´: 2.03 μm Inductor L3: 0.1 nH or less (corresponding to the parasitic inductance during measurement) Inductor L: 3.0 nH Filter F6 Measured DMS filter 45.

[0092] Filter F5 is provided with a circuit 46 and corresponds to Example 3. Filter F6 is not provided with a circuit 46 and corresponds to Comparative Example 3.

[0093] Figures 20(a) and 20(b) are diagrams showing the passing characteristics of filters F5, F6 and circuit 46 in Simulation 5. Figure 20(b) is an enlarged view near the spurious response in Figure 20(a). The passing characteristics of circuit 46 with an inductance of 0.1 nH and circuit 46 with an inductance of 3.0 nH in resonator P´ with a 2×pitch Dp´ of 2.03 μm are also shown.

[0094] As shown in Fig. 20(a), filters F5 and F6 have a passband Pass at approximately 2000 MHz. A spurious response Sp occurs at 2500 MHz to 3000 MHz. As shown in Fig. 20(b), in filter F5, the peak of the spurious response Sp can be made lower than that of filter F6. For example, in filter F5, as indicated by the downward arrow, the attenuation of peak Pk4 is approximately 8.5 dB greater than that of filter F6.

[0095] In the filter F5 of Example 3, the pitch Dp' of the resonator P' is made slightly different from the pitch Dd of the DMS filter 45. Thereby, the notch of the spurious response of the resonator P' overlaps with the peak of the spurious response of the DMS filter 45. Thereby, as in the filter F5 of Fig. 20(b), the attenuation at the peak of the spurious response of the DMS filter 45 can be increased.

[0096] However, when the pitch Dp' of the resonator P' is set to the pitch Dd of the DMS filter 45 or in its vicinity, as in L = 0.1 nH in Fig. 20(a), when the inductance of the inductor L is on the order of parasitic inductance, the resonance frequency fr of the resonator P' overlaps with the passband Pass. Thereby, a notch is formed in the passband Pass. Therefore, the inductance of the inductor L is increased. Thereby, as in L = 3.0 nH in Fig. 20(a), the attenuation poles A1 and A2 of the circuit 46 are formed at frequencies lower and higher than the passband Pass. Therefore, it is possible to suppress the formation of a notch due to the circuit 46 within the passband Pass. In practice, the inductance of the inductor L and the pitch Dp' of the resonator P' are adjusted so that the attenuation of the peak of the spurious response increases.

[0097] According to Example 3, the average pitch Dp' (second average pitch) of the electrode fingers 18 (second electrode fingers) of the resonator P' is set near the average pitch Dd (first average pitch) of the DMS filter 45 (multimode filter). Thereby, the notch of the spurious response of the resonator P' compensates for the peak of the spurious response of the DMS filter 45. However, the attenuation poles due to the resonance frequency fr of the resonator P' are located within the passband Pass. Therefore, an inductor L having an inductance larger than the inductance of the inductor L3 connected between the DMS filter 45 and the ground is provided. Thereby, even when the resonance frequency fr of the resonator P' alone is located within the passband Pass, the attenuation poles A1 and A2 due to the resonance frequency of the resonator P' to which the inductor L is connected do not locate within the passband Pass.

[0098] The frequency of the spurious response of the resonator P' is changed by the inductor L. Therefore, by finely adjusting the average pitch Dp' of the resonator P', the notch of the spurious response of the resonator P' is adjusted to compensate for the spurious response of the DMS filter 45. The average pitch Dp' of the resonator P' is preferably 1.03 times or less and 0.97 times or more of the average pitch Dd, more preferably 1.02 times or less of Dd, and even more preferably 1.015 times or less. The average pitch Dp' is more preferably 0.98 times or more of the average pitch Dd, and even more preferably 0.985 times or more.

[0099] In order to locate the attenuation poles A1 and A2 due to the resonance frequency fr of the resonator P' outside the passband Pass, the inductance of the inductor L is more preferably 5 times or more of the inductance of the inductor L3, and even more preferably 10 times or more. The inductance of the inductor L is preferably 0.5 nH or more, and more preferably 1.0 nH or more. Thereby, even when the resonance frequency fr of the resonator P' alone is located within the passband Pass, the attenuation poles A1 and A2 due to the resonance frequency of the resonator P' to which the inductor L is connected do not locate within the passband Pass.

[0100] If the inductance of the inductor L is too large, the notch of the spurious response becomes small. From this viewpoint, the inductance of the inductor L is preferably 100 times or less, more preferably 50 times or less, and even more preferably 20 times or less the inductance of the inductor L3.

[0101] When the thickness T4 of the piezoelectric layer 14 is 2 times or less (i.e., 1λ or less) of the average pitch Dd of the DMS filter 45, a strong spurious response Sp occurs at some frequencies as shown in Fig. 3(c). In this case, the spurious response can be more suppressed by providing the circuit 46.

[0102] [Modification Example 1 of Examples 1 and 2] Fig. 21(a) is a circuit diagram of a filter according to Modification Example 1 of Examples 1 and 2. As shown in Fig. 21(a), series resonators S1 to S6 and parallel resonators P1 to P4 are provided. The circuit 46 is provided between the series resonators S3 and S4. The circuit 46 can be provided at any position in the path between the input terminal Tin and the output terminal Tout. Other configurations are the same as those in Examples 1 and 2 and the description thereof is omitted.

[0103] [Modification Example 2 of Examples 1 and 2] Fig. 21(b) is a circuit diagram of a filter according to Modification Example 2 of Examples 1 and 2. As shown in Fig. 21(b), series resonators S1 to S7 and parallel resonators P1 to P4 are provided. The circuit 46a is provided between the series resonators S3 and S4, and the circuit 46b is provided between the series resonators S6 and S7. A plurality of circuits 46a and 46b can be provided at any position in the path between the input terminal Tin and the output terminal Tout. For example, the circuit 46a is used as the circuit 46 in Example 1, and the circuit 46b is used as the circuit 46 in Example 2. Thereby, both the peak due to the spurious response of the series resonators S1 to S7 and the peak of the spurious response of the parallel resonators P1 to P4 can be compensated. Other configurations are the same as those in Examples 1 and 2 and the description thereof is omitted.

[0104] [Modification Example 3 of Examples 1 and 2] Figure 21(c) is a circuit diagram of the filter according to Modification Example 3 of Embodiments 1 and 2. As shown in Figure 21(c), the inductor of circuit 46a is provided in common with the inductors L1 between the parallel resonators P1 and P2 and the ground. Other configurations are the same as those in Embodiments 1 and 2, and thus the description thereof is omitted.

[0105] [Modification Example 1 of Embodiments 1 to 3] Figure 22(a) is a cross-sectional view of the surface acoustic wave resonator in Modification Example 1 of Embodiments 1 to 3. As shown in Figure 22(a), in Modification Example 1 of Embodiments 1 to 3, a bonding layer 13 is provided between the piezoelectric layer 14 and the temperature compensation film 12. The bonding layer 13 bonds the piezoelectric layer 14 and the temperature compensation film 12. When it is difficult to directly bond the piezoelectric layer 14 and the temperature compensation film 12, the bonding layer 13 may be provided. The bonding layer 13 is, for example, an aluminum oxide film, a silicon film, an aluminum nitride film, a silicon nitride film, or a silicon carbide film. From the viewpoint of not impairing the functions of the piezoelectric layer 14 and the temperature compensation film 12, the thickness of the bonding layer 13 is preferably 20 nm or less, and more preferably 10 nm or less. From the viewpoint of not impairing the function as the bonding layer 13, the thickness of the bonding layer 13 is preferably 1 nm or more, and more preferably 2 nm or more. From the viewpoint of confining the surface acoustic wave of the main mode in the piezoelectric layer 14, the sound velocity of the bulk wave propagating through the bonding layer 13 is preferably faster than the sound velocity of the bulk wave propagating through the temperature compensation film 12. Other configurations are the same as those in Embodiments 1 to 3, and thus the description thereof is omitted.

[0106] [Modification Example 2 of Embodiments 1 to 3] Figure 22(b) is a cross-sectional view of the surface acoustic wave resonator in Modification Example 2 of Embodiments 1 to 3. As shown in Figure 22(b), in Modification Example 2 of Embodiments 1 to 3, no boundary layer is provided between the temperature compensation film 12 and the support substrate 10. Other configurations are the same as those in Modification Example 1 of Embodiments 1 to 3, and thus the description thereof is omitted. A boundary layer 11 may be provided instead of the temperature compensation film 12. That is, the temperature compensation film 12 may not be provided between the piezoelectric layer 14 and the boundary layer 11.

[0107] [Modification Example 3 of Embodiments 1 to 3] FIG. 22(c) is a cross-sectional view of the elastic wave resonator in Modification 3 of Examples 1 to 3. As shown in FIG. 22(c), in Modification 3 of Examples 1 to 3, the temperature compensation film 12 and the boundary layer 11 are not provided between the piezoelectric layer 14 and the support substrate 10, and the piezoelectric layer 14 and the support substrate 10 are directly bonded using, for example, the surface activation method. Other configurations are the same as those in Examples 1 to 3 and the description thereof is omitted.

[0108] [Modification 4 of Examples 1 to 3] FIG. 23(a) is a cross-sectional view of the elastic wave resonator in Modification 4 of Examples 1 to 3. As shown in FIG. 23(a), in Modification 4 of Examples 1 to 3, periodic or irregular unevenness is provided at the interface between the support substrate 10 and the boundary layer 11. Unwanted waves are scattered by the unevenness, and spurious can be suppressed. The interface between the boundary layer 11 and the temperature compensation film 12 is a substantially flat surface. Other configurations are the same as those in Modification 1 of Examples 1 to 3 and the description thereof is omitted.

[0109] [Modification 5 of Examples 1 to 3] FIG. 23(b) is a cross-sectional view of the elastic wave resonator in Modification 5 of Examples 1 to 3. As shown in FIG. 23(b), in Modification 5 of Examples 1 to 3, in addition to the interface between the support substrate 10 and the boundary layer 11, periodic or irregular unevenness is provided at the interface between the boundary layer 11 and the temperature compensation film 12. Unwanted waves are scattered by the two-layer unevenness, and spurious can be suppressed. Other configurations are the same as those in Modification 4 of Examples 1 to 3 and the description thereof is omitted.

[0110] [Modification 6 of Examples 1 to 3] FIG. 23(c) is a cross-sectional view of the elastic wave resonator in Modification 6 of Examples 1 to 3. As shown in FIG. 23(c), in Modification 6 of Examples 1 to 3, periodic or irregular unevenness is provided at the interface between the support substrate 10 and the temperature compensation film 12 of Other configurations are the same as those in Modification 2 of Examples 1 to 3 and the description thereof is omitted.

[0111] Even in Modifications 1 to 6 of Examples 1 to 3, by providing the piezoelectric layer 14 on the support substrate 10, high-frequency spurs as shown in FIGS. 3(b) and 3(c) occur. Therefore, it is preferable to provide the circuit 46 as in Examples 1 to 3. As in Examples 1 to 3 and Modifications 1, 2, 4 to 6 thereof, an insulating layer may be provided between the support substrate 10 and the piezoelectric layer 14. The insulating layer may be a single layer made of a uniform material or a layer formed by laminating a plurality of layers.

[0112] [Simulation 6] In Simulations 1 to 5, the interface between the support substrate 10 and the boundary layer 11 is assumed to be a mirror surface. As shown in FIG. 23(a) of Modification 4 of Examples 1 to 3, it was examined whether the results of Simulations 1 to 5 could be applied when the interface between the support substrate 10 and the boundary layer 11 was a rough surface. The following resonator R4 was fabricated and its passing characteristics were measured. Also, the passing characteristics of resonator R5 were simulated. Resonator R4 Support substrate 10: Sapphire substrate with a thickness of 500 μm Boundary layer 11: Aluminum oxide layer with a thickness of 5.0 μm Temperature compensation film 12: None Piezoelectric layer 14: 42°Y-cut X-propagation lithium tantalate layer with a thickness of 1.2 μm Metal film 16: Titanium film with a thickness of 40 nm and aluminum film with a thickness of 130 nm from the piezoelectric layer 14 side Protective film on metal film 16: Silicon oxide film with a thickness of 15 nm The interface between the support substrate 10 and the boundary layer 11 is a rough surface with an arithmetic mean roughness Ra of 0.15 μm 2 × pitch D of electrode fingers 18: 2.0 μm Resonator R5 Support substrate 10: Sapphire substrate with a thickness of 30 μm Boundary layer 11: Aluminum oxide layer with a thickness of 5.0 μm Temperature compensation film 12: None Piezoelectric layer 14: 42°Y-cut X-propagation lithium tantalate layer with a thickness of 1.2 μm Metal film 16: Titanium film with a thickness of 40 nm and aluminum film with a thickness of 130 nm from the piezoelectric layer 14 side Protective film on metal film 16: None The interface between the support substrate 10 and the boundary layer 11 is a mirror surface.

[0113] Figures 24(a) and 24(b) are diagrams showing Real(Y) and |Y| of the resonators R4 and R5 in Simulation 6, respectively, and Figure 24(c) is a diagram showing fs / fr with respect to the thickness T4 of the piezoelectric layer 14 in the resonator R5. Real(Y) and |Y| are the real part of the admittance and the absolute value of the admittance, respectively.

[0114] As shown in Figures 24(a) and 24(b), for the resonators R4 and R5, the resonance frequency fr of the main mode, the anti-resonance frequency fa, and the frequency fs of the peak of the largest spurious response are almost the same. It is considered that the reason why the spurious response Sp is larger in the resonator R5 than in the resonator R4 is that the interface between the support substrate 10 and the boundary layer 11 is a mirror surface. The frequencies of the peaks of the spurious response Sp are almost the same between the resonators R4 and R5. As described above, it can be seen that even when the interface between the support substrate 10 and the boundary layer 11 is rough, the results of Simulations 1 to 5 can be applied.

[0115] As shown in Figure 24(c), when the thickness T4 of the piezoelectric layer 14 is 0.7λ to 0.9λ (λ = 2×D), fs / fr is approximately 1.15. When the thickness T4 becomes less than 0.7λ, fs / fr increases. When the thickness T4 is 0.2λ, fs / fr is approximately 1.45. When fs / fr is 1.1 or more, the spurious response becomes a problem, and when fs / fr is 1.2 times or more, the problem becomes even more serious. Therefore, when the thickness T4 of the piezoelectric layer 14 is 1λ (2×D) or less, the spurious response becomes a problem, when it is 0.7λ (1.4×D) or less, the spurious response becomes a more serious problem, and when it is 0.6λ (1.2×D) or less, the spurious response becomes an even more serious problem.

Example

[0116] FIG. 25 is a circuit diagram of the duplexer according to Embodiment 4. As shown in FIG. 25, a transmission filter 40 is connected between the common terminal Ant and the transmission terminal Tx. A reception filter 42 is connected between the common terminal Ant and the reception terminal Rx. The transmission filter 40 passes, as a transmission signal, a signal in the transmission band among the high-frequency signals input from the transmission terminal Tx to the common terminal Ant, and suppresses signals of other frequencies. The reception filter 42 passes, as a reception signal, a signal in the reception band among the high-frequency signals input from the common terminal Ant to the reception terminal Rx, and suppresses signals of other frequencies. At least one of the transmission filter 40 and the reception filter 42 can be the filter of Embodiment 1 and its modified example.

[0117] Although the duplexer is described as an example of the multiplexer, a triplexer or a quadplexer may also be used.

[0118] As described above in detail with respect to the embodiments of the present invention, the present invention is not limited to such specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

Explanation of Reference Numerals

[0119] 10 Support substrate 11 Boundary layer 12 Temperature compensation film 13 Bonding layer 14 Piezoelectric layer 16 Metal film 18 Electrode finger 20 Comb-shaped electrode 22 IDT 25 Intersection region 26 Surface acoustic wave resonator 40 Transmission filter 42 Reception filter 44 Ladder-type filter 45 DMS filter 46 Circuit

Claims

1. A support substrate, a piezoelectric layer provided on the support substrate, a plurality of first electrode fingers each provided on the piezoelectric layer and having a first average pitch, and one or more series resonators each serially connected between an input terminal and an output terminal, a plurality of second electrode fingers each provided on the piezoelectric layer and having a second average pitch greater than the largest first average pitch, and one or more parallel resonators each having one end connected to a path between the input terminal and the output terminal and the other end connected to ground, a resonator provided on the piezoelectric layer and having a plurality of third electrode fingers with a third average pitch, and one end of the resonator is connected to the path, an inductor having one end connected to the other end of the resonator, the other end connected to ground, and an inductance greater than the largest inductance connected between the one or more parallel resonators and ground, comprising, a ratio of a difference between the third average pitch and the largest first average pitch to the third average pitch is ±0.35% or less, the inductor has an inductance such that an attenuation pole of a circuit formed by the resonator and the inductor is formed at a frequency lower and higher than a passband.

2. The filter according to claim 1, wherein an inductance of the inductor is 5 times or more the largest inductance connected between the one or more parallel resonators and ground.

3. The filter according to claim 1 or 2, further comprising an insulating layer provided between the support substrate and the piezoelectric layer.

4. The filter according to any one of claims 1 to 3, wherein the one end of the resonator is connected to the path between the input terminal and the series resonator closest to the input terminal among the one or more series resonators.

5. A multiplexer comprising the filter according to any one of claims 1 to 4.

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