JP2017112603A - Acoustic wave resonator, filter and duplexer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acoustic wave resonator which suppresses transverse mode spurious and reduces a loss, a filter and a duplexer.SOLUTION: The acoustic wave resonator comprises: a piezoelectric substrate; and an IDT which is formed on the piezoelectric substrate and in which paired interdigital electrodes oppose each other, each of the interdigital electrodes including a grating electrode which excites an acoustic wave, and a bus bar for connecting the grating electrode. An anisotropy coefficient γ0 in a crossover region 15 where the grating electrodes of the paired interdigital electrodes cross each other, is positive. An anisotropy coefficient γg in a gap region 17 that is positioned between a distal end of the grating electrode of one interdigital electrode and the bus bar of the other interdigital electrode is smaller than the anisotropy coefficient in the crossover region. A sonic velocity Vg of an acoustic wave that is propagated in the gap region is equal to or lower than a sonic velocity Vfa in an anti-resonant frequency of an acoustic wave that is propagated in the crossover region.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an acoustic wave resonator, a filter, and a duplexer, for example, an acoustic wave resonator, a filter, and a duplexer having a grating electrode formed on a piezoelectric substrate.

In a high-frequency communication system typified by a cellular phone, a high-frequency filter or the like is used to remove unnecessary signals other than the frequency band used for communication. An elastic wave resonator such as a surface acoustic wave (SAW) resonator is used for a high-frequency filter or the like. In the SAW resonator, a metal grating electrode is formed on a piezoelectric substrate such as a lithium tantalate (LiTaO ₃ ) substrate or a lithium niobate (LiNbO ₃ ) substrate.

  The grating electrode excites a SH (Shear Horizontal) wave, a Rayleigh wave, a boundary acoustic wave or the like, which is a kind of surface acoustic wave. By providing reflectors on both sides in the main propagation direction of the elastic wave excited by the grating electrode, these elastic waves are confined in the vicinity of the grating electrode. Ladder type filters and multimode felts can be realized using elastic wave resonators. In the grating electrode, an acoustic wave resonator is known in which the width in the direction perpendicular to the propagation direction of the acoustic wave is weighted (Patent Documents 1 and 2).

JP-A-9-270667 JP 2008-78883 A

  In an acoustic wave resonator having a grating electrode, a transverse mode spurious which is an unnecessary response occurs. The transverse mode spurious is generated when an elastic wave having a component in a direction perpendicular to the propagation direction of the elastic wave strengthens at a certain wavelength. In Patent Documents 1 and 2, since the cross width changes with respect to the propagation direction of the elastic wave, the frequency at which the transverse mode spurious changes changes with respect to the propagation direction. For this reason, the frequencies at which the elastic waves in the transverse mode are strengthened are averaged, and transverse mode spurious is suppressed. However, the generation of transverse mode elastic waves is not suppressed. For this reason, elastic waves in the transverse mode leak out of the grating electrode. Therefore, loss occurs.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an elastic wave resonator, a filter, and a duplexer that suppress transverse mode spurious and has low loss.

  The present invention includes a piezoelectric substrate, and an IDT formed on the piezoelectric substrate and having a pair of comb electrodes facing each other and having a grating electrode that excites an acoustic wave and a bus bar that connects the grating electrode, A gap located between the tip of the grating electrode of one comb electrode and the bus bar of the other comb electrode is positive in the crossing region where the grating electrodes of the pair of comb electrodes intersect An elastic wave resonator in which the anisotropy coefficient in the region is smaller than the anisotropy coefficient in the crossing region, and the sound velocity of the elastic wave propagating through the gap region is equal to or lower than the sound velocity at the antiresonance frequency of the elastic wave propagating through the crossing region It is.

  The said structure WHEREIN: The sound speed of the elastic wave which propagates the said gap area | region can be set as the structure more than the sound speed in the resonant frequency of the elastic wave which propagates the said cross | intersection area | region.

  In the above configuration, when the anisotropy coefficient in the gap region is γg and the anisotropy coefficient in the crossing region is γ0, γg / γ0 is −0.35 or more and +0.35 or less. it can.

  The said structure WHEREIN: The anisotropy coefficient in the said gap area | region can be set as the structure which decreases gradually from the said crossing area side to the said bus-bar side.

  The said structure WHEREIN: It can be set as the structure which comprises the additional film | membrane provided on the said piezoelectric substrate in the said gap area | region.

  The present invention includes a piezoelectric substrate, and an IDT formed on the piezoelectric substrate and having a pair of comb electrodes facing each other and having a grating electrode that excites an acoustic wave and a bus bar that connects the grating electrode, The anisotropy coefficient in the crossing region where the grating electrodes of the pair of comb electrodes cross is positive, and the anisotropy coefficient in the region adjacent to the crossing region side in the bus bar is different in the crossing region. The isotropic coefficient, the anisotropy coefficient in the gap region located between the tip of the grating electrode of one comb electrode and the bus bar of the other comb electrode, and smaller, the gap region and the inside of the bus bar The acoustic wave resonance that propagates through the region adjacent to the side on the crossing region side is less than the sound velocity of the antiresonance frequency of the elastic wave that propagates through the crossing region. It is.

  The said structure WHEREIN: The anisotropy coefficient in the said gap area | region can be set as the structure smaller than the anisotropy coefficient in the said crossing area | region.

  In the above configuration, the acoustic velocity of the elastic wave propagating in the gap region and the region adjacent to the crossing region side in the bus bar is configured to be equal to or higher than the acoustic velocity at the resonance frequency of the elastic wave propagating in the intersecting region. Can do.

  The said structure WHEREIN: The anisotropy coefficient in the said gap area | region can be set as the structure which decreases gradually from the said crossing area side to the said bus-bar side.

  In the above configuration, an additional film provided on the bus bar in a region adjacent to the side on the grating electrode side is provided, and a recess is provided on the upper surface of the piezoelectric substrate in the gap region. it can.

  The present invention includes a piezoelectric substrate, and an IDT formed on the piezoelectric substrate and having a pair of comb electrodes facing each other and having a grating electrode that excites an acoustic wave and a bus bar that connects the grating electrode, A gap located between the tip of the grating electrode of one comb electrode and the bus bar of the other comb electrode is positive in the crossing region where the grating electrodes of the pair of comb electrodes intersect The anisotropy coefficient in the region is smaller than the anisotropy coefficient in the crossing region, and the sound velocity of the elastic wave propagating in the gap region is the central region that is the crossing region other than the edge region adjacent to the gap region in the crossing region. Is larger than the acoustic velocity of the elastic wave propagating through the edge region, and the acoustic velocity of the elastic wave propagating through the edge region is smaller than the acoustic velocity of the elastic wave propagating through the central region. A sexual wave resonator.

  In the above configuration, the sound velocity of the elastic wave propagating through the gap region may be smaller than the sound velocity at the resonance frequency of the elastic wave propagating through the bus bar.

  In the above configuration, the sound velocity of the elastic wave propagating through the edge region may be 0.995 or less of the sound velocity of the elastic wave propagating through the central region.

  The said structure WHEREIN: It can be set as the structure which comprises the additional film | membrane provided on the said piezoelectric substrate in the said gap area | region.

  In the above configuration, the piezoelectric substrate may be a lithium tantalate substrate or a lithium niobate substrate.

  The present invention is a filter including the elastic wave resonator.

  The present invention is a duplexer including the filter.

  According to the present invention, it is possible to provide an elastic wave resonator, a filter, and a duplexer that suppress transverse mode spurious and has low loss.

FIG. 1A is a plan view of an acoustic wave resonator according to a comparative example and an example, and FIG. 1B is a cross-sectional view taken along line AA in FIG. 2A is a plan view of wave numbers in the X direction and the Y direction, and FIG. 2B is a diagram showing β _y / β ₀ with respect to β _x / β ₀ . FIG. 3A is a diagram showing sound velocity and anisotropy coefficient with respect to the Y direction in the elastic wave resonator according to Comparative Example 1, and FIG. 3B is a simulation of the elastic wave resonator according to Comparative Example 1. It is a figure which shows the conductance with respect to the measured frequency. FIG. 4A is a plan view of the acoustic wave resonator according to the comparative example 2, and FIG. 4B is a diagram illustrating conductance with respect to the frequency simulated for the acoustic wave resonator according to the comparative example 2. FIG. 5 is a diagram illustrating sound velocity and anisotropy coefficient with respect to the Y direction in the acoustic wave resonator according to the first embodiment. FIG. 6A to FIG. 6D are diagrams (part 1) illustrating conductance with respect to frequency simulated for the acoustic wave resonator according to the first embodiment. FIG. 7A to FIG. 7C are diagrams (part 2) illustrating conductance with respect to frequency simulated for the acoustic wave resonator according to the first embodiment. FIG. 8A is a diagram showing sound velocity and anisotropy coefficient in the Y direction in the elastic wave resonator according to Comparative Example 3, and FIG. 8B is a simulation of the elastic wave resonator according to Comparative Example 3. It is a figure which shows the conductance with respect to the measured frequency. FIG. 9 is a diagram illustrating sound velocity and anisotropy coefficient with respect to the Y direction in the acoustic wave resonator according to the second embodiment. FIG. 10A and FIG. 10B are diagrams showing sound velocity and anisotropy coefficient with respect to the Y direction in the elastic wave resonator according to the third embodiment and the first modification of the third embodiment. FIG. 11A is a plan view of the acoustic wave resonator according to the fourth embodiment, and FIG. 11B is a cross-sectional view taken along the line AA of FIG. FIG. 12 is a diagram illustrating a dispersion curve of the crossing region in the fourth embodiment. FIG. 13A and FIG. 13B are diagrams showing dispersion curves in the gap region. FIG. 14A is a plan view of the acoustic wave resonator according to the fifth embodiment, FIG. 14B is a cross-sectional view taken along the line AA of FIG. 14A, and FIG. FIG. 14B is a cross-sectional view taken along the line BB in FIG. FIG. 15A and FIG. 15B are diagrams showing dispersion curves in the gap region. FIG. 16A and FIG. 16B are diagrams showing a dispersion curve of a bus bar. FIG. 17A to FIG. 17D are cross-sectional views of the crossing regions of the fourth and fifth embodiments. FIG. 18A is a circuit diagram of a filter according to the sixth embodiment, and FIG. 18B is a circuit diagram of a duplexer according to a modification of the sixth embodiment. FIG. 19 is a diagram illustrating sound velocity and anisotropy coefficient with respect to the Y direction in the acoustic wave resonator according to the seventh embodiment. FIG. 20A and FIG. 20B are diagrams illustrating conductance with respect to frequency simulated for the acoustic wave resonator according to the seventh embodiment. FIG. 21 is a diagram illustrating a range in which the transverse mode spurious is less than or equal to the base level of Comparative Example 1 in the acoustic wave resonator according to the seventh embodiment. FIG. 22A to FIG. 22D are diagrams illustrating conductance with respect to frequency simulated for the acoustic wave resonator according to the seventh embodiment. FIG. 23 is a diagram illustrating a range in which the transverse mode spurious is equal to or lower than the base level of Comparative Example 1 in the acoustic wave resonator according to the seventh embodiment. FIG. 24A is a plan view of the acoustic wave resonator according to the eighth embodiment, and FIG. 24B is a cross-sectional view taken along the line AA in FIG. FIG. 25A and FIG. 25B are diagrams showing dispersion curves of the central region and the edge region in the crossing region in the eighth embodiment. FIG. 26 is a diagram showing a dispersion curve of the gap region in the eighth embodiment. FIGS. 27A and 27B are diagrams showing measurement results of conductance and admittance with respect to frequency in Comparative Example 1 and Example 8. FIG. FIG. 28A to FIG. 28C are plan views of the acoustic wave resonator according to the first modification of the eighth embodiment. 29 (a) to 29 (f) are cross-sectional views taken along line AA of FIGS. 28 (a) and 28 (b). 30 (a) to 30 (f) are cross-sectional views taken along line AA of FIG. 28 (c). FIG. 31A is a plan view of the acoustic wave resonator according to the second modification of the eighth embodiment, and FIG. 31B is a cross-sectional view taken along the line AA of FIG. is there. FIG. 32A to FIG. 32C are cross-sectional views of the gap region of the second modification of the eighth embodiment.

  The structure of the acoustic wave resonator according to the comparative example and the example of the present invention will be described. FIG. 1A is a plan view of an acoustic wave resonator according to a comparative example and an example, and FIG. 1B is a cross-sectional view taken along line AA in FIG. As shown in FIGS. 1A and 1B, an IDT 21 and a reflector 22 are formed on the piezoelectric substrate 10. The IDT 21 and the reflector 22 are formed by the metal film 12 formed on the piezoelectric substrate 10. The IDT 21 includes a pair of opposing comb electrodes 20. The comb electrode 20 includes a plurality of electrode fingers 14 and a bus bar 18 to which the plurality of electrode fingers 14 are connected. The plurality of electrode fingers 14 form a grating electrode 16. The pair of comb-shaped electrodes 20 are provided to face each other so that the electrode fingers 14 are substantially staggered.

  A region where the grating electrodes 16 of the pair of comb-shaped electrodes 20 intersect is a cross region 15. The elastic wave excited by the grating electrode 16 in the crossing region 15 propagates mainly in the arrangement direction of the electrode fingers 14. The period of the grating electrode 16 is substantially the wavelength λ of the elastic wave. A region between the tip of the grating electrode 16 of one comb electrode 20 and the bus bar 18 of the other comb electrode 20 is a gap region 17. When the dummy electrode finger is provided, the gap region is a region between the tip of the electrode finger and the tip of the dummy electrode finger. The propagation direction of the elastic wave is the X direction, and the direction orthogonal to the propagation direction is the Y direction. The X direction and the Y direction do not necessarily correspond to the X axis direction and the Y axis direction of the crystal orientation of the piezoelectric substrate 10. The piezoelectric substrate 10 is, for example, a lithium tantalate substrate or a lithium niobate substrate. The metal film 12 is, for example, an aluminum film or a copper film.

Next, the anisotropy coefficient will be described. 2A is a plan view of wave numbers in the X direction and the Y direction, and FIG. 2B is a diagram showing β _y / β ₀ with respect to β _x / β ₀ . As shown in FIG. 2A, the wave number in the X direction of the elastic wave is β _x , and the wave number in the Y direction of the elastic wave is β _y . Assuming that the wave number β ₀ of the elastic wave in the direction of the angle θ from the X direction to the angle θ can be parabolically approximated to the angle θ, the wave number β ₀ uses the anisotropy coefficient γ, and β _x ² + γ · β _y ² = β represented by ₀ ^2.

In FIG. 2B, β _x / β ₀ corresponds to the inverse velocity (slowness) of the phase velocity in the X direction of the elastic wave, and β _y / β ₀ corresponds to the inverse velocity of the phase velocity in the Y direction of the elastic wave. To do. The reverse speed surface 60 when the anisotropy coefficient γ is positive is convex when viewed from the origin. For this reason, the case where γ> 0 is also referred to as a convex type. When the anisotropy coefficient γ is negative, the reverse speed surface 62 is concave when viewed from the origin. For this reason, the case where γ <0 is also referred to as a concave type.

  The anisotropy coefficient γ is determined by the material of the piezoelectric substrate 10, the material of the grating electrode 16, the film thickness, and the pitch. For example, when a rotating Y-cut X-propagating lithium niobate substrate is used as the piezoelectric substrate 10, the anisotropy coefficient γ is positive. If a rotating Y-cut X-propagating lithium tantalate substrate is used as the piezoelectric substrate 10, the anisotropy coefficient γ is negative. If a rotating Y-cut X-propagating lithium tantalate substrate is used, the grating electrode 16 is made of a heavy material, and the film thickness is increased, the anisotropy coefficient γ may become positive.

[Comparative Example 1]
Next, the simulation of Comparative Example 1 will be described. A cross-sectional view and a plan view of an acoustic wave resonator according to Comparative Example 1 are the same as those in FIGS. 1 (a) and 1 (b). FIG. 3A is a diagram illustrating the sound velocity and the anisotropy coefficient with respect to the Y direction in the elastic wave resonator according to the first comparative example.

The structure used for the simulation of Comparative Example 1 is as follows.
Piezoelectric substrate: rotating 42 ° Y-cut X-propagating lithium tantalate substrate Metal film 12 thickness: 0.1λ
Pitch λ: 4.4 μm
Duty ratio: 50%
Cross width: 20λ
Logarithm: 100 pairs Gap width: 0.5λ
Reflector electrode index: 10 The pitch λ is the pitch of the grating electrode 16 and corresponds to the wavelength of the elastic wave excited by the grating electrode 16. The duty ratio indicates the ratio of the width to the pitch of the grating electrode 16. The crossing width indicates the width of the crossing region 15 in the Y direction (width at which the electrode fingers 14 cross). The logarithm is the logarithm of the electrode finger 14 in the grating electrode 16. The gap width indicates the width of the gap region 17 in the Y direction. The reflector electrode index indicates the number of electrode fingers of the reflector 22.

  As shown in FIG. 3A, the sound velocity Vb in the bus bar 18 is 3900 m / s, the sound velocity Vg in the gap region 17 is 3700 m / s, and the sound velocity V0 in the crossing region 15 is 3170 m / s. The sound speed V0 in the crossing region 15 corresponds to the sound speed Vfr at the resonance frequency. 1.05 times the sound velocity Vfr corresponds to the sound velocity Vfa at the antiresonance frequency, which is 3300 m / s. The anisotropy coefficient γb in the bus bar 18 was +0.1, the anisotropy coefficient γg in the gap region 17 was −0.3, and the anisotropy coefficient γ0 in the crossing region 15 was +1.4.

  FIG. 3B is a diagram illustrating the conductance with respect to the frequency simulated for the acoustic wave resonator according to the first comparative example. In FIG. 3B, the solid line shows the simulation result of the conductance Re | Y | When the base level is large, it is indicated that the energy of the elastic wave leaks from the crossing region toward the bus bar 18. The frequency with the largest conductance is the resonance frequency. A plurality of transverse mode spurs 50 are generated on the high frequency side of the resonance frequency.

  In Comparative Example 1, the sound speed Vg in the gap region 17 is larger than the sound speed V0 in the crossing region 15 as shown in FIG. Therefore, an elastic wave having a component in the Y direction as a propagation direction among the elastic waves excited by the crossing region 15 is reflected at the boundary between the crossing region 15 and the gap region 17. Thereby, the energy of the elastic wave is confined in the crossover region 15. However, an unnecessary transverse mode spurious 50 is generated due to the elastic wave propagating with a component in the Y direction.

[Comparative Example 2]
Next, the simulation of Comparative Example 2 will be described. FIG. 4A is a plan view of the acoustic wave resonator according to the second comparative example. The cross-sectional view is the same as FIG. As shown in FIG. 4A, a gap region 17 is formed between the electrode finger 14 of one comb electrode 20 and the dummy electrode finger 14 a of the other comb electrode 20. The position of the gap region 17 is modulated with respect to the X direction. Thereby, the crossing width is modulated with respect to the X direction. In Comparative Example 2, the maximum crossing width was set to 30λ, and the crossing width was changed by arccos (X) in the X direction. Other simulation conditions are the same as those in Comparative Example 1.

  FIG. 4B is a diagram showing the conductance with respect to the frequency simulated for the acoustic wave resonator according to the comparative example 2. In FIG. 4B, the transverse mode spurious is hardly observed. The broken line is the base level 52 of the first comparative example. The conductance is greater than the base level 52 of Comparative Example 1. In Comparative Example 2, since the cross width changes with respect to the X direction, the frequency at which the transverse mode spurious occurs changes with respect to the X direction. For this reason, the frequencies at which the elastic waves propagating in the Y direction are strengthened are averaged, and the transverse mode spurious 50 is suppressed. However, the generation of elastic waves propagating in the Y direction is not suppressed. For this reason, the elastic wave propagating in the Y direction leaks out of the crossing region 15. Therefore, the conductance becomes larger than the base level 52 of Comparative Example 1. This increases the loss.

  When the anisotropy coefficient γ is 0, in principle, an elastic wave of a transverse mode that propagates with a component in the Y direction cannot exist. Therefore, it was considered to make the anisotropy coefficient γ of the gap region 17 close to zero. In a region where the anisotropy coefficient γ is close to 0, part or all of the elastic wave propagating in the Y direction disappears without satisfying the existence condition. Therefore, the anisotropy coefficient γ of the gap region 17 is brought close to zero. Thereby, transverse mode spurious can be suppressed. Furthermore, it can suppress that the energy of an elastic wave leaks in a bus-bar direction. For this reason, loss can be suppressed and Q value becomes high.

  A plan view and a cross-sectional view of the acoustic wave resonator according to the first embodiment are the same as those in FIGS. 1A and 1B, and a description thereof will be omitted. The structure used for the simulation is the same as in Comparative Example 1. FIG. 5 is a diagram illustrating sound velocity and anisotropy coefficient with respect to the Y direction in the acoustic wave resonator according to the first embodiment. As shown in FIG. 5, the sound velocity Vg in the gap region 17 is made smaller than the sound velocity Vfa at the antiresonance frequency in the crossover region 15. The anisotropy coefficient γg in the gap region 17 is made smaller than the anisotropy coefficient γ0 in the crossover region 15. Others are the same as those in FIG.

  FIG. 6A to FIG. 7C are diagrams illustrating conductance with respect to frequency simulated for the acoustic wave resonator according to the first embodiment. The anisotropy coefficient γg of the gap region 17 was set to +1.2, +1.0, +0.5, +0.2, +0.0, −0.2, and −0.5. The sound speed of the gap region 17 is adjusted in a range between the sound speed Vfa at the anti-resonance frequency of the crossing region 15 and the sound speed Vfr at the resonance frequency. The width Wg in the Y direction of the gap region 17 is adjusted.

  As shown in FIGS. 6A to 6D, as the anisotropy coefficient γg of the gap region 17 approaches 0, the range 54 in which the generation of the transverse mode spurious 50 is suppressed increases. The base level of conductance is substantially the same as the base level 52 of Comparative Example 1.

  As shown in FIG. 7A, when the anisotropy coefficient γg of the gap region 17 becomes 0, the range 54 in which the generation of the transverse mode spurious 50 is suppressed becomes further larger, and the generated transverse mode spurious 50 is increased. Is also small. Further, the base level of conductance is equal to or lower than the base level 52 of Comparative Example 1. As shown in FIG. 7B and FIG. 7C, when the anisotropy coefficient γg of the gap region 17 becomes negative, the range 54 in which the generation of the transverse mode spurious 50 is suppressed is slightly reduced and is generated. The transverse mode spurious 50 that is present also increases. As described above, when the anisotropy coefficient γg of the gap region 17 is close to 0, a transverse mode elastic wave propagating in the Y direction cannot exist in the gap region 17. Therefore, when the elastic wave propagating in the Y direction passes through the gap region 17 from the crossover region 15, is reflected at the boundary between the gap region 17 and the bus bar 18, passes through the gap region 17 and returns to the crossover region 15, the gap region In 17, the elastic wave propagating in the Y direction is attenuated. Thereby, transverse mode spurious can be suppressed. In addition, since the elastic wave propagating in the Y direction is attenuated, the base level of conductance is small and energy loss can be suppressed.

  In the first embodiment, the sound velocity Vg in the gap region 17 is set to be equal to or lower than the sound velocity Vfa of the anti-resonance frequency in the crossing region 15. As Comparative Example 3, a simulation was performed for the case where the sound velocity Vg in the gap region 17 was the same as in Comparative Example 1.

  FIG. 8A is a diagram illustrating sound speed and anisotropy coefficient with respect to the Y direction in the acoustic wave resonator according to Comparative Example 3. As shown in FIG. 8A, the sound velocity Vg in the gap region 17 is 3700 m / s, which is the same as that in the first comparative example. The anisotropy coefficient γg of the gap region 17 is +0 as in the case of FIG. Other configurations are the same as those of the first embodiment.

  FIG. 8B is a diagram showing the conductance with respect to the frequency simulated for the acoustic wave resonator according to the third comparative example. As shown in FIG. 8B, the transverse mode spurious 50 is generated. As described above, in order to suppress the transverse mode spurious, it is preferable that the sound speed Vg of the gap region 17 is equal to or lower than the sound speed Vfa of the antiresonance frequency. This is because when the sound velocity Vg is large, the elastic wave propagating in the Y direction is reflected at the interface between the crossing region 15 and the gap region 17, and the elastic wave propagating in the Y direction from the crossing region 15 into the gap region 17 leaks. This is because it becomes difficult. For this reason, even if the anisotropy coefficient γg of the gap region 17 is close to 0, there is no elastic wave propagating in the Y direction in the gap region 17, and the transverse mode spurious cannot be suppressed.

  According to the first embodiment, when the anisotropy coefficient γ0 of the crossing region 15 is positive, the anisotropy coefficient γg in the gap region 17 is made smaller than the anisotropy coefficient γ0 in the crossing region 15. Furthermore, the sound velocity Vg of the elastic wave propagating through the gap region 17 is set to be equal to or lower than the sound velocity Vfa at the antiresonance frequency of the elastic wave propagating through the crossing region 15. Thereby, transverse mode spurious can be suppressed. Moreover, loss can be suppressed. It is only necessary that the anisotropy coefficient γg in a part of the gap region 17 is smaller than the anisotropy coefficient γ0 in the crossing region 15 as long as the transverse mode spurious can be suppressed. Further, the sound speed Vg in the partial region of the gap region 17 may be equal to or lower than the sound speed Vfa within a range in which the transverse mode spurious can be suppressed.

  The sound velocity Vg of the gap region 17 is preferably set in a range in which an elastic wave having a Y-direction component at the boundary between the crossing region 15 and the gap region 17 is not reflected. Even if the sound velocity Vg of the elastic wave propagating through the gap region 17 is smaller than the sound velocity Vfr at the resonance frequency of the elastic wave propagating through the crossover region 15, it has a component in the Y direction at the boundary between the crossover region 15 and the gap region 17. Reflection of the propagating elastic wave is suppressed. However, from the viewpoint of further suppressing the reflection of the elastic wave, the sound velocity Vg of the elastic wave propagating through the gap region 17 is preferably larger than the sound velocity Vfr at the resonance frequency of the elastic wave propagating through the crossing region 15.

  As shown in FIGS. 6A to 7C, the range 54 in which the transverse mode spurious 50 can be suppressed is particularly wide in the range of γg = + 0.5 to −0.5. Furthermore, it becomes wider at γg = + 0.2 to −0.2.

  Therefore, the anisotropy coefficient γg in the gap region 17 is preferably −0.5 or more and +0.5 or less, and more preferably −0.2 or more and +0.2 or less. When normalized by the anisotropy coefficient γ0 in the crossing region 15, γg / γ0 is preferably −0.35 or more and +0.35 or less, more preferably −0.15 or more and +0.15 or less.

  A plan view and a cross-sectional view of the acoustic wave resonator according to the second embodiment are the same as those in FIG. 1A and FIG. FIG. 9 is a diagram illustrating sound velocity and anisotropy coefficient with respect to the Y direction in the acoustic wave resonator according to the second embodiment. As shown in FIG. 9, a region 24 adjacent to the side on the crossing region 15 side in the bus bar 18 is provided. The sound speeds Vg and Vc in the gap region 17 and the region 24 are equal to or lower than the sound speed Vfa of the antiresonance frequency in the crossing region 15. The sound speed Vb of the bus bar 18 other than the region 24 is the same as that of the first embodiment. The anisotropy coefficient γc of the region 24 is smaller than the anisotropy coefficient γ0 of the crossing region 15. The anisotropy coefficient γb of the bus bar 18 other than the region 24 is the same as that of the first embodiment. Other configurations are the same as those of the first embodiment, and the description thereof is omitted.

  According to the second embodiment, the sound speeds Vg and Vc of the elastic waves propagating through the gap region 17 and the region 24 are equal to or lower than the sound velocity Vfa of the antiresonance frequency of the elastic waves propagating through the crossing region 15. Thereby, reflection of the elastic wave which has a component in the Y direction at the boundary between the crossing region 15 and the gap region 17 and the boundary between the gap region 17 and the region 24 is suppressed. Therefore, the transverse mode elastic wave reaches the leakage region 24 from the crossover region 15. It is only necessary that the sound velocities Vg and Vc in the gap region 17 and a partial region of the region 24 are equal to or lower than the sound velocity Vfa within a range in which the transverse mode spurious can be suppressed.

  The anisotropy coefficient γc in the region 24 is smaller than the anisotropy coefficient γ0 in the crossover region 15 and the anisotropy coefficient γg in the gap region 17. As described above, when the anisotropy coefficient γc of the region 24 is brought close to 0, an elastic wave of a transverse mode that propagates with a component in the Y direction cannot exist in the region 24. Therefore, the elastic wave propagating with a component in the Y direction passes through the gap region 17 and the region 24 from the crossing region 15 and is reflected at the boundary between the region 24 and the other region of the bus bar 18. When passing through 17 and returning to the crossover region 15, the elastic wave propagating with a component in the Y direction in the region 24 is attenuated. Thereby, transverse mode spurious can be suppressed. In addition, since the elastic wave propagating with the Y-direction component is attenuated, the ground level of conductance is small and energy loss can be suppressed.

  In the second embodiment, the elastic wave propagating with the component in the Y direction in the region 24 is attenuated. Therefore, the anisotropy coefficient γg in the gap region 17 may be larger than the anisotropy coefficient γ0 in the crossover region 15. However, the anisotropy coefficient γg in the gap region 17 is preferably less than or equal to the anisotropy coefficient γ0 in the crossing region 15. Thereby, also in the gap area | region 17, the elastic wave which has a component of a Y direction and can propagate can be attenuated.

  The acoustic velocities Vg and Vc of the elastic waves propagating through the gap region 17 and the region 24 are preferably equal to or higher than the sonic velocity Vfr at the resonance frequency of the elastic waves propagating through the crossing region 15. Thereby, the reflection of the elastic wave which has a Y-direction component at the boundary between the crossing region 15 and the gap region 17 and the boundary between the gap region 17 and the region 24 is further suppressed.

  6A to 7C, the anisotropy coefficient γc in the region 24 is preferably −0.5 or more and +0.5 or less, and is −0.2 or more and +0.2 or less. More preferred. When normalized by the anisotropy coefficient γ0 in the crossing region 15, γc / γ0 is preferably −0.35 or more and +0.35 or less, more preferably −0.15 or more and +0.15 or less.

  A plan view and a cross-sectional view of the acoustic wave resonator according to the third embodiment are the same as those in FIGS. 1A and 1B, and a description thereof will be omitted. FIG. 10A and FIG. 10B are diagrams showing sound velocity and anisotropy coefficient with respect to the Y direction in the elastic wave resonator according to the third embodiment and the first modification of the third embodiment. As shown in FIG. 10A, the sound velocity Vg in the gap region 17 gradually decreases from the crossing region 15 side to the bus bar 18 side. The anisotropy coefficient γg in the gap region 17 gradually decreases from the crossing region 15 side to the bus bar 18 side. Other configurations are the same as those of the first embodiment, and the description thereof is omitted.

  As shown in FIG. 10B, the sound velocity Vg in the gap region 17 gradually decreases from the crossing region 15 side to the bus bar 18 side. The anisotropy coefficient γg in the gap region 17 gradually decreases from the crossing region 15 side to the bus bar 18 side. Other configurations are the same as those of the second embodiment, and the description thereof is omitted.

  According to the third embodiment and its modification, the anisotropy coefficient γg in the gap region 17 is gradually decreased from the crossover region 15 to the bus bar 18. Thereby, the physical property change in the gap region 17 is moderated. Therefore, reflection of the elastic wave propagating in the Y direction in the gap region 17 can be further suppressed. Therefore, transverse mode spurious and loss can be further suppressed.

  The fourth embodiment is a specific example of the first embodiment. FIG. 11A is a plan view of the acoustic wave resonator according to the fourth embodiment, and FIG. 11B is a cross-sectional view taken along the line AA of FIG. As shown in FIGS. 11A and 11B, in Example 4, the dielectric additional film 30 is provided on the piezoelectric substrate 10 so as to cover the electrode fingers 14 in the gap region 17. An input terminal 40 and an output terminal 42 connected to the bus bar 18 are provided. Other configurations are the same as those in FIG. 1A and FIG.

The dispersion curve of the transverse mode SH wave in Example 4 was simulated. In the simulation, the additional film 30 was a tantalum oxide (Ta ₂ O ₅ ) film having a thickness of 0.1λ. Other configurations used in the simulation are the same as those in the first embodiment.

  FIG. 12 is a diagram illustrating a dispersion curve of the crossing region in the fourth embodiment. In FIG. 12, the horizontal axis indicates the normalized wave number in the Y direction. The normalized wave number is a wave number obtained by normalizing the wave number in the Y direction with the wave number in the X direction at the resonance frequency of the crossover region 15. The vertical axis represents the frequency normalized by the resonance frequency. The frequency at which the wave number in the Y direction becomes 0 in the dispersion curve is the resonance frequency fr in the crossover region 15, and 1.0 at the normalized frequency. The dispersion curve indicates a mode mainly used for the elastic wave resonator of the SH wave. The anti-resonance frequency of the crossing region 15 is about 1.05 times the resonance frequency. In the normalized frequency, 1.05 is the antiresonance frequency fa. The anisotropy coefficient γ can be calculated from the curvature of the dispersion curve. In the crossing region 15, the anisotropy coefficient γg is about 1.4.

  FIG. 13A and FIG. 13B are diagrams showing dispersion curves in the gap region. FIG. 13A is an example in which no additional film is provided in the gap region 17, and FIG. 13B is Example 4 in which the additional film 30 is provided in the gap region 17. As shown in FIG. 13A, when the additional film 30 is not provided in the gap region 17, when the wave number in the Y direction on the dispersion curve is 0 (in this case, an elastic wave having the same mode as the crossing region 15 can propagate). ) Is about 1.18. Since the speed of sound is proportional to the normalized frequency, the speed of sound in the gap region 17 is 1.18 times that of the crossing region 15. In this case, the sound velocity in the gap region 17 is larger than the sound velocity Vfa at the antiresonance frequency fa in the crossing region 15. For this reason, the elastic wave is reflected at the boundary between the crossover region 15 and the gap region 17. Therefore, even if the anisotropy coefficient γg of the gap region 17 is −0.3 and near zero, transverse mode spurious is generated.

  As shown in FIG. 13B, when the additional film 30 is provided in the gap region 17, the normalized frequency when the wave number in the Y direction on the dispersion curve is 0 is the antiresonance frequency fa or less and the resonance frequency fr or more. Become. The anisotropy coefficient γ is +0.7. As a result, the elastic wave is not reflected at the boundary between the crossing region 15 and the gap region 17 but attenuates when passing through the gap region 17. Therefore, transverse mode spurious can be suppressed.

  According to the fourth embodiment, the additional film 30 is provided on the piezoelectric substrate 10 in the gap region 17. Thereby, the sound velocity Vg in the gap region 17 can be made equal to or lower than the sound velocity Vfa at the antiresonance frequency of the crossing region 15, and the anisotropy coefficient γg in the gap region 17 can be made smaller than the anisotropy coefficient γ0 in the crossing region 15. The material and film thickness of the additional film 30 can be appropriately selected so that the sound velocity Vg and the anisotropy coefficient γg are in the above ranges. For example, the additional film 30 may be a dielectric, but may be other than a dielectric. Further, the first embodiment may be realized by a method other than the fourth embodiment.

  The fifth embodiment is a specific example of the second embodiment. FIG. 14A is a plan view of the acoustic wave resonator according to the fifth embodiment, FIG. 14B is a cross-sectional view taken along the line AA of FIG. 14A, and FIG. FIG. 14B is a cross-sectional view taken along the line BB in FIG. As shown in FIG. 14A to FIG. 14C, in Example 5, a recess 32 is formed on the upper surface of the piezoelectric substrate 10 between the electrode fingers 14 in the gap region 17. In the region 24, an additional film 34 is formed on the metal film 12. An input terminal 40 and an output terminal 42 connected to the bus bar 18 are provided. Other configurations are the same as those in FIG. 1A and FIG.

  The dispersion curve of the transverse mode SH wave in Example 5 was simulated. In the simulation, the depth of the recess 32 was set to 0.05λ. The additional film 34 was a Ti film having a thickness of 0.05λ and an Au film having a thickness of 0.04λ from the substrate 10 side. Other configurations used in the simulation are the same as those in the first embodiment.

  FIG. 15A and FIG. 15B are diagrams showing dispersion curves in the gap region. FIG. 15A is an example in which no recess is provided in the gap region 17, and FIG. 15B is a case of Example 5 in which the recess 32 is provided in the gap region 17. As shown in FIG. 15A, the dispersion curve in which the recess 32 is not provided in the gap region 17 is the same as that in FIG.

  As shown in FIG. 15B, when the recess 32 is provided in the gap region 17, the normalized frequency when the wave number in the Y direction on the dispersion curve is 0 is equal to or lower than the antiresonance frequency fa and equal to or higher than the resonance frequency fr. . The anisotropy coefficient γ is +1.3. As a result, the elastic wave passes through the gap region 17 without being reflected at the boundary between the crossing region 15 and the gap region 17.

  FIG. 16A and FIG. 16B are diagrams showing a dispersion curve of a bus bar. FIG. 16A shows an example in which the additional film 34 is not provided on the bus bar 18, and FIG. 16B shows the case of Example 5 in which the additional film 34 is provided on the bus bar 18. As shown in FIG. 16A, when the additional film 34 is not provided on the bus bar 18, the normalized frequency when the wave number in the Y direction is 0 is 1.24 times the resonance frequency fr. Therefore, the sound speed of the bus bar 18 is 1.25 times that of the crossing region 15. Therefore, the elastic wave is reflected at the boundary between the gap region 17 and the bus bar 18.

  As shown in FIG. 16B, when the additional film 34 is provided on the bus bar 18, the normalized frequency when the wave number in the Y direction on the dispersion curve is 0 is equal to or lower than the antiresonance frequency fa and equal to or higher than the resonance frequency fr. . The anisotropy coefficient γ is +0.2. As a result, the elastic wave is not reflected at the boundary between the gap region 17 and the region 24 and is attenuated when passing through the region 24. Therefore, transverse mode spurious can be suppressed.

  According to the fifth embodiment, the additional film 34 is provided on the bus bar 18 in the region 24 adjacent to the side on the grating electrode 16 side of the side of the bus bar 18. A recess 32 is provided on the upper surface of the piezoelectric substrate 10 in the gap region 17. Thus, the sound velocity Vg in the gap region 17 and the region 24 is set to be equal to or lower than the sound velocity Vfa at the anti-resonance frequency of the crossing region 15, and the anisotropy coefficient γc in the region 24 is set to the anisotropy coefficient γ0 in the crossing region 15 and the gap region 17. It can be made smaller than the anisotropy coefficient γb. The depth of the recess 32, the region to be formed, and the material and film thickness of the additional film 34 can be appropriately selected so that the sound speeds Vg and Vc and the anisotropy coefficients γg and γc are in the above ranges. For example, the additional film 30 may be a metal film or an insulating film. The second embodiment may be realized by a method other than the fifth embodiment.

  FIG. 17A to FIG. 17D are cross-sectional views of the crossing regions of the fourth and fifth embodiments. As shown in FIG. 17A, the film covering the grating electrode 16 is not provided, and the metal film 12 may be a single layer film. As shown in FIG. 17B, an insulating film 36 may be provided on the piezoelectric substrate 10 so as to cover the grating electrode 16. The insulating film 36 is, for example, a film for adjusting the frequency or a film for compensating the temperature characteristic of the frequency. As shown in FIG. 17C, an adhesion film 38 such as Ti or Cr may be formed between the metal film 12 and the piezoelectric substrate 10. As shown in FIG. 17D, the metal film 12 may be formed by laminating a plurality of different metal films 12a and 12b.

  As in the first and fourth embodiments, if the sound velocity Vg in the gap region 17 is set to be equal to or lower than the sound velocity Vfa at the antiresonance frequency in the crossing region 15, it becomes difficult to make the anisotropy coefficient γg in the gap region 17 close to zero. On the other hand, as in the second and fifth embodiments, in the partial region 24 of the bus bar 18, the sound speed Vg is set to be equal to or lower than the sound speed Vfa at the antiresonance frequency of the crossing region 15, and the anisotropy coefficient γg in the gap region 17 is set to zero. It is relatively easy to approach.

  In the elastic wave resonators of the first to fifth embodiments, the period of the grating electrode 16 and the electrode period in the reflector 22 may be different by about several percent. The period in the grating electrode 16 may be modulated by several percent. As the piezoelectric substrate 10, for example, a lithium niobate substrate or a lithium tantalate substrate can be used. The piezoelectric substrate 10 may be formed on a support substrate such as a sapphire substrate.

  Example 6 is an example of a filter and duplexer using the elastic resonators of Examples 1 to 5. FIG. 18A is a circuit diagram of a filter according to the sixth embodiment. As shown in FIG. 18A, one or more series resonators S1 to S4 are connected in series between the input terminal Tin and the output terminal Tout. One or a plurality of parallel resonators P1 to P3 are connected in parallel between the input terminal Tin and the output terminal Tout. The elastic wave resonators of the first to fifth embodiments can be used for at least one of the one or more series resonators S1 to S4 and the one or more parallel resonators P1 to P3. The filter including the acoustic wave resonator according to the first to fifth embodiments may be a multimode filter in addition to the ladder type filter.

  FIG. 18B is a circuit diagram of a duplexer according to a modification of the sixth embodiment. As shown in FIG. 18B, the transmission filter 44 is connected between the common terminal Ant and the transmission terminal Tx. A reception filter 46 is connected between the common terminal Ant and the reception terminal Rx. The transmission filter 44 passes a signal in the transmission band among signals input from the transmission terminal Tx as a transmission signal to the common terminal Ant, and suppresses signals of other frequencies. The reception filter 46 passes a signal in the reception band among the signals input from the common terminal Ant to the reception terminal Rx as a reception signal, and suppresses signals of other frequencies. At least one of the transmission filter 44 and the reception filter 46 may be the filter of the sixth embodiment.

  A plan view and a cross-sectional view of the acoustic wave resonator according to the seventh embodiment are the same as those in FIGS. 1A and 1B, and a description thereof will be omitted. FIG. 19 is a diagram illustrating sound velocity and anisotropy coefficient with respect to the Y direction in the acoustic wave resonator according to the seventh embodiment. As shown in FIG. 19, a central region 15 a and an edge region 15 b are provided in the crossing region 15. The edge region 15b is a region adjacent to the gap region 17 in the crossing region 15, and the central region 15a is the crossing region 15 other than the edge region 15b. The sound velocity Ve in the edge region 15b is smaller than the sound velocity V0 in the central region 15a. The speed of sound in the gap area 17 is larger than the speed of sound in the central area 15a and smaller than the speed of sound in the bus bar 18. The central region 15a and the edge region 15b have the same anisotropy coefficients γ0 and γe. The anisotropy coefficient γg of the gap region 17 is smaller than the anisotropy coefficients γ0 and γe of the crossing region 15. Other configurations are the same as those of the first embodiment, and the description thereof is omitted.

  In the first embodiment, as shown in FIG. 7A, a small transverse mode spurious 50 appears even if the anisotropy coefficient γg of the gap region 17 is zero. In the seventh embodiment, the transverse mode spurious 50 can be suppressed as compared with the first embodiment. The principle will be described. As in the first embodiment, the anisotropy coefficient γg of the gap region 17 is made closer to 0 than the anisotropy coefficients γ0 and γe of the crossing region 15. Thereby, part or all of the elastic wave propagating in the Y direction in the gap region 17 disappears without satisfying the existence condition. Thereby, the transverse mode spurious can be suppressed as in the first embodiment.

  When the anisotropy coefficient γ is positive, the elastic wave is reflected and attenuated when the elastic wave tries to propagate from the low sound velocity region to the high sound velocity region. On the other hand, it is easy to propagate an elastic wave from a high sound speed region to a low sound speed region. In the first embodiment, the sound velocity V0 in the crossing region 15 is smaller than the sound velocity Vg in the gap region 17. For this reason, the elastic wave propagating with the Y-direction component leaking into the gap region 17 from the crossover region 15 returns to the crossover region 15 before disappearing. As a result, as shown in FIG. 7A, the transverse mode spurious 50 remains in the first embodiment.

  According to the seventh embodiment, the sound velocity Vg of the elastic wave propagating through the gap region 17 is made larger than the sound velocity V0 of the elastic wave propagating through the central region 15a. Thereby, the elastic wave is confined in the crossover region 15. Furthermore, the sound velocity Ve of the elastic wave propagating through the edge region 15b is made smaller than the sound velocity V0 of the elastic wave propagating through the central region 15a. Accordingly, the elastic wave leaking from the crossing region 15 into the gap region 17 is difficult to propagate from the edge region 15b to the central region 15a. Therefore, the elastic wave propagating with the Y-direction component leaking from the crossing region 15 into the gap region 17 tends to disappear in the gap region 17. Therefore, transverse mode spurious can be suppressed.

  When the sound velocity Vg of the elastic wave propagating through the gap region 17 is made larger than the sound velocity Vfa at the antiresonance frequency of the crossover region 15 as in Comparative Example 3, the elastic wave is less likely to leak from the crossover region 15 to the gap region 17 and the transverse mode spurious is generated. growing. Therefore, in the first embodiment, the sound velocity at which the elastic wave propagates in the gap region 17 is set to be equal to or lower than the sound velocity Vfa at the antiresonance frequency of the cross region 15. However, methods for reducing the sound speed in the gap region 17 are limited and difficult.

  In the seventh embodiment, the sound velocity Vg in the gap region 17 may be larger than the sound velocity Vfa at the anti-resonance frequency in the crossing region 15. This is because the lateral elastic wave leaking from the crossing region 15 to the gap region 17 will eventually disappear in the gap region 17 unless it returns from the edge region 15b to the central region 15a.

  In Example 7, a simulation was performed for an acoustic wave resonator in which the sound velocity reduction rate dVe = (Ve−V0) / V0 × 100% in the edge region 15b is −0.5%. The simulation is performed using a two-dimensional COM equation that is a two-dimensional extension of the COM (Coupling-Of-Modes) equation used to determine the characteristics of the surface acoustic wave. The simulations in Examples 1 to 5 so far are the same.

FIG. 20A and FIG. 20B are diagrams illustrating conductance with respect to frequency simulated for the acoustic wave resonator according to the seventh embodiment. The simulation conditions in FIGS. 20A and 20B are as follows.
Length of edge region 15b: 0.75λ
FIG. 20 (a)
Anisotropy coefficient γg of gap region 17: 0.0
Speed of sound in gap region 17: 1.06 × Vfr
FIG. 20 (b)
Anisotropy coefficient γg of gap region 17: −0.1
Speed of sound in gap region 17: 1.13 × Vfr

  In FIG. 20A, the transverse mode spurious is hardly observed. In FIG. 20B, although the transverse mode spurious 50 is slightly observed, the conductance Re | Y | is equal to the base level 52 of the comparative example 1 even at the peak of the transverse mode spurious 50, and there is no practical problem. .

  The range in which the conductance Re | Y | of the peak of the transverse mode spurious is equal to or lower than the base level 52 of Comparative Example 1 was simulated by changing the anisotropy coefficient γg and the sound velocity Vg of the gap region 17. The sound velocity Vg in the gap region 17 is indicated by Vg / Vfr divided by the sound velocity Vfr at the resonance frequency of the central region 15a. dVe = −0.5%.

  FIG. 21 is a diagram illustrating a range in which the transverse mode spurious is less than or equal to the base level of Comparative Example 1 in the acoustic wave resonator according to the seventh embodiment. A cross region 58 in FIG. 21 is a region where the conductance of the peak of the transverse mode spurious 50 is equal to or lower than the base level 52 of the first comparative example. Black circles A and B correspond to FIGS. 20 (a) and 21 (b). As shown in FIG. 21, the anisotropy coefficient γg of the gap region 17 may not be zero. In addition, there is a region where the transverse mode spurious has no practical problem even if the sound velocity Vg in the gap region 17 is greater than the anti-resonance frequency Vfa (corresponding to Vg / Vfr = 1.05) of the crossing region 15.

A simulation was performed on an acoustic wave resonator having a sound velocity reduction rate dVe of −2.25% in the edge region 15b. FIG. 22A to FIG. 22D are diagrams illustrating conductance with respect to frequency simulated for the acoustic wave resonator according to the seventh embodiment. The simulation conditions in FIGS. 22A to 22D are as follows.
Length of edge region 15b: 0.75λ
FIG. 22 (a)
Anisotropy coefficient γg of gap region 17: +0.2
Speed of sound in gap region 17: 1.11 × Vfr
FIG. 22 (b)
Anisotropy coefficient γg of gap region 17: +0.5
Speed of sound in gap region 17: 1.06 × Vfr
FIG. 22 (c)
Anisotropy coefficient γg of gap region 17: +0.7
Speed of sound in gap region 17: 1.04 × Vfr
FIG. 22 (d)
Anisotropy coefficient γg of gap region 17: +1.0
Speed of sound in gap region 17: 1.04 × Vfr

  In FIG. 22A, the transverse mode spurious is hardly observed. In FIG. 22B, although the transverse mode spurious 50 is slightly observed, the conductance Re | Y | of the peak of the transverse mode spurious 50 is smaller than the base level 52 of the first comparative example. 22C and 22D, the peak conductance Re | Y | of the transverse mode spurious 50 is approximately the same as the base level 52 of the first comparative example. As described above, the transverse mode spurious in FIGS. 22 (a) to 22 (d) has no practical problem.

  When dVe = −2.25%, the anisotropy coefficient γg and sound velocity Vg of the gap region 17 are changed, and the conductance Re | Y | of the peak of the transverse mode spurious becomes equal to or lower than the base level 52 of the first comparative example. The range was simulated.

  FIG. 23 is a diagram illustrating a range in which the transverse mode spurious is equal to or lower than the base level of Comparative Example 1 in the acoustic wave resonator according to the seventh embodiment. Black circles A to C correspond to FIGS. 22 (a) to 22 (c). As shown in FIG. 23, the anisotropy coefficient γg of the gap region 17 may be larger than zero. In addition, there is a region where the transverse mode spurious has no practical problem even if the sound velocity Vg in the gap region 17 is larger than the sound velocity Vfa at the antiresonance frequency of the crossing region 15.

  As shown in FIGS. 21 and 23, in Example 7, the degree of freedom in designing the anisotropy coefficient γg and the sound velocity Vg in the gap region 17 is increased, and the design is facilitated.

  The sound velocity Vg in the gap region 17 may be larger than the sound velocity Vfr at the resonance frequency of the central region 15a, but Vg / Vfr is preferably 1.02 or more, and more preferably 1.04 or more. Vg / Vfr is preferably 1.13 or less. The sound speed Vg in the gap region 17 is preferably smaller than the sound speed Vb in the bus bar 18. Thereby, it is possible to suppress the elastic wave in the gap region 17 from leaking to the bus bar 18.

  The anisotropy coefficient γg in the gap region 17 is preferably +1.0 or less, and more preferably +0.5 or less.

  As shown in FIG. 22, the reduction rate dVe of the sound velocity Ve in the edge region 15b is preferably −0.5% or less, and more preferably −2.25% or less. That is, the sound velocity Ve of the elastic wave propagating through the edge region 15b is preferably 0.995 or less, and more preferably 0.9775 or less, of the sound velocity V0 of the elastic wave propagating through the central region 15a.

  Example 8 is a specific example of Example 7. FIG. 24A is a plan view of the acoustic wave resonator according to the eighth embodiment, and FIG. 24B is a cross-sectional view taken along the line AA in FIG. As shown in FIGS. 24A and 24B, in Example 8, the additional film 35 is provided on the piezoelectric substrate 10 between the electrode fingers 14 in the gap region 17. Other configurations are the same as those of the fourth embodiment, and the description thereof is omitted.

The dispersion curve of the transverse mode SH wave in Example 8 was simulated using eigenvalue analysis of the finite element method. The simulation conditions are as follows.
Additional film 35: Au film with a film thickness of 0.44λ Duty ratio of central region 15a: 50%
Duty ratio of edge region 15b: 54%
Other configurations used in the simulation are the same as those in the first embodiment.

Here, the anisotropy coefficient γ can be calculated from the curvature of the dispersion curve when the normalized wave number in the Y direction is near zero. The curvature is fitted and derived using the following equation.
f _N = (V ₀ / λ) √ (1 + γ · β _N ² −μ)
f _N is the normalized frequency, β _N is the normalized wave number, V ₀ is the acoustic wave velocity below the free surface, and μ is the reflection coefficient. As V _0, the acoustic wave velocity below the solid metal film may be used. In this case, only the value of μ as a correction coefficient is changed appropriately, and γ is not affected.

  FIG. 25A and FIG. 25B are diagrams showing dispersion curves of the central region and the edge region in the crossing region in the eighth embodiment. As shown in FIG. 25A, the dispersion curve in the central region 15a is the same as that in FIG. 12 of the fourth embodiment, and γ0 is 1.4. The standardized frequency at which the standardized wave number becomes 0 is the resonance frequency fr of the central region 15a. That is, the normalized frequency is 1.0. As shown in FIG. 25 (b), the anisotropy coefficient γg in the edge region 15b is about 1.4, which is the same as the central region 15a, and the normalized frequency at which the normalized wave number is 0 is about 0. 0 from the resonance frequency. 5% smaller.

  FIG. 26 is a diagram showing a dispersion curve of the gap region in the eighth embodiment. As shown in FIG. 26, the anisotropy coefficient γg in the gap region 17 is about 0.05, and the normalized frequency is about 1.05 (that is, Vg / Vfr = 1.05).

  As described above, in Example 8, dVe = −0.5%, γg = + 0.05, and Vg / Vf = 1.05. This corresponds to the black circle C in FIG. 21, and the transverse mode spurious should be suppressed to the base level of Comparative Example 1. Therefore, the acoustic wave resonator of Example 8 was produced. An acoustic wave resonator according to Comparative Example 1 was also produced.

  FIGS. 27A and 27B are diagrams showing measurement results of conductance Re | Y | and admittance Y with respect to frequency in Comparative Example 1 and Example 8. FIG. As shown in FIG. 27A, a large transverse mode spurious 50 is observed in Comparative Example 1. As shown in FIG. 27B, in the eighth embodiment, the transverse mode spurious 50 is suppressed to the base level of the first comparative example.

[Modification 1 of Example 8]
Modification 1 of Example 8 is an example in which the additional film 35 is a metal film. When the additional film 35 has a high density, a desired sound speed can be obtained even if the additional film 35 is thin. Further, the additional film 35 is formed after the electrode fingers 14 are formed. For this reason, it is preferable to form the additional film 35 using a sputtering method or a vapor deposition method and a lift-off method. From these viewpoints, the material of the additional film 35 is preferably Au, Pt (platinum), Mo (molybdenum), Ru (ruthenium), W (tungsten), Ta (tantalum), or Rh (rhodium). The additional film 35 may be a metal film, a multilayer film such as an adhesion film and / or a barrier film, or an alloy film of these metals. Further, the material of the additional film 35 may be the same metal material as that of the electrode fingers 14.

  FIG. 28A to FIG. 28C are plan views of the acoustic wave resonator according to the first modification of the eighth embodiment. As shown in FIG. 28A, the additional film 35 may be separated from the electrode finger 14 and the bus bar 18. As shown in FIG. 28B, the additional film 35 may be in contact with the bus bar 18 and separated from the electrode finger 14. As shown in FIG. 28 (c), the additional film 35 may be in contact with the electrode fingers 14 of the opposing comb-shaped electrode 20 even if it is in contact with the bus bar 18 and the electrode fingers 14.

  29 (a) to 29 (f) are cross-sectional views taken along line AA of FIGS. 28 (a) and 28 (b). The additional film 35 and the electrode finger 14 are separated by a distance D. 30 (a) to 30 (f) are cross-sectional views taken along line AA of FIG. 28 (c). The additional film 35 and the electrode finger 14 are in contact with each other. As shown in FIG. 29A and FIG. 30A, an insulating film 37 a may be provided between the additional film 35 and the piezoelectric substrate 10. As shown in FIGS. 29B and 30B, the insulating films 37 a to 37 c may not be provided around the additional film 35. 29C and 30C, an insulating film 37a may be provided between the additional film 35 and the piezoelectric substrate 10, and an insulating film 37b may be provided on the additional film 35.

  As shown in FIGS. 29D and 30D, an insulating film 37b may be provided on the additional film 35. 29E and 30E, an insulating film 37a may be provided between the additional film 35 and the piezoelectric substrate 10, and an insulating film 37c may be provided on the electrode finger 14. 29F and 30F, the insulating film 37b may be provided on the additional film 35, and the insulating film 37c may be provided on the electrode finger 14.

  As shown in FIGS. 29 (a) and 29 (b), the insulating film may not be embedded between the additional film 35 and the electrode finger 14, or as shown in FIGS. 29 (c) to 29 (f). In addition, an insulating film 37 b or 37 c may be embedded between the additional film 35 and the electrode finger 14. As the insulating films 37a to 37c, for example, a silicon oxide film, a silicon nitride film, an aluminum oxide film, or the like can be used.

[Modification 2 of Example 8]
The second modification of the eighth embodiment is an example in which the additional film 35 is an insulating film. In order to increase the density of the additional film 35, the material of the additional film 35 is preferably Ta oxide, Nb oxide, W oxide, Mo oxide, or the like. The additional film 35 may be a multilayer film of these insulating films or a mixed film of these oxides.

  FIG. 31A is a plan view of the acoustic wave resonator according to the second modification of the eighth embodiment, and FIG. 31B is a cross-sectional view taken along the line AA of FIG. is there. As shown in FIGS. 31A and 31B, in the second modification of the eighth embodiment, the additional film 35 is provided between the electrode fingers 14 in the gap region 17 and on the electrode fingers 14. Other configurations are the same as those of the eighth embodiment, and the description thereof is omitted.

  FIG. 32A to FIG. 32C are cross-sectional views of the gap region of the second modification of the eighth embodiment. As illustrated in FIG. 32A, the additional film 35 may not be provided on the electrode finger 14. As illustrated in FIG. 32B, an additional film 35 may be provided between the electrode fingers 14, and another insulating film 37 c may be provided on the electrode fingers 14. As shown in FIG. 32C, the electrode finger 14 and the additional film 35 may be separated from each other.

  For the filter and duplexer of the sixth embodiment, the elastic wave devices of the seventh and eighth embodiments and modifications thereof may be used.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

DESCRIPTION OF SYMBOLS 10 Piezoelectric substrate 12 Metal film 14 Electrode finger 15 Crossing region 16 Grating electrode 17 Gap region 18 Bus bar 20 Comb electrode 21 IDT
22 Reflector 30, 34, 35 Additional film 32 Recess 44 Transmitting filter 46 Receiving filter

Claims (17)

A piezoelectric substrate;
An IDT formed on the piezoelectric substrate and having a pair of comb electrodes facing each other and having a grating electrode that excites an acoustic wave and a bus bar that connects the grating electrode;
Comprising
The anisotropy coefficient in the crossing region where the grating electrodes of the pair of comb electrodes cross is positive,
The anisotropy coefficient in the gap region located between the tip of the grating electrode of one comb electrode and the bus bar of the other comb electrode is smaller than the anisotropy coefficient in the cross region,
An acoustic wave resonator in which the acoustic velocity of the elastic wave propagating in the gap region is equal to or lower than the acoustic velocity at the antiresonance frequency of the elastic wave propagating in the crossing region.   The acoustic wave resonator according to claim 1, wherein the acoustic velocity of the elastic wave propagating in the gap region is equal to or higher than the acoustic velocity at the resonance frequency of the elastic wave propagating in the crossing region.   3. The elastic wave according to claim 1, wherein γg / γ0 is not less than −0.35 and not more than +0.35, where γg is an anisotropy coefficient in the gap region and γ0 is an anisotropy coefficient in the crossing region. Resonator.   The elastic wave resonator according to any one of claims 1 to 3, wherein an anisotropy coefficient in the gap region gradually decreases from the crossing region side to the bus bar side.   The acoustic wave resonator according to any one of claims 1 to 4, further comprising an additional film provided on the piezoelectric substrate in the gap region. A piezoelectric substrate;
An IDT formed on the piezoelectric substrate and having a pair of comb electrodes facing each other and having a grating electrode that excites an acoustic wave and a bus bar that connects the grating electrode;
Comprising
The anisotropy coefficient in the crossing region where the grating electrodes of the pair of comb electrodes cross is positive,
The anisotropy coefficient in the region adjacent to the side of the crossing region in the bus bar includes the anisotropy coefficient in the crossing region, the tip of the grating electrode of one comb electrode, and the bus bar of the other comb electrode. Anisotropy coefficient in the gap region located between and smaller,
The acoustic wave resonator in which the acoustic velocity of the elastic wave propagating through the gap region and the region adjacent to the side of the crossing region in the bus bar is equal to or lower than the acoustic velocity of the antiresonance frequency of the elastic wave propagating through the intersecting region.   The elastic wave resonator according to claim 6, wherein an anisotropy coefficient in the gap region is smaller than an anisotropy coefficient in the crossing region.   The elastic velocity of the elastic wave propagating in the gap region and the region adjacent to the side of the crossing region in the bus bar is equal to or higher than the acoustic velocity at the resonance frequency of the elastic wave propagating in the crossing region. Wave resonator.   The elastic wave resonator according to any one of claims 6 to 8, wherein an anisotropy coefficient in the gap region gradually decreases from the crossing region side to the bus bar side. Comprising an additional film provided on the bus bar in a region adjacent to the side on the grating electrode side;
The acoustic wave resonator according to any one of claims 6 to 9, wherein a concave portion is provided on an upper surface of the piezoelectric substrate in the gap region. A piezoelectric substrate;
An IDT formed on the piezoelectric substrate and having a pair of comb electrodes facing each other and having a grating electrode that excites an acoustic wave and a bus bar that connects the grating electrode;
Comprising
The anisotropy coefficient in the crossing region where the grating electrodes of the pair of comb electrodes cross is positive,
The anisotropy coefficient in the gap region located between the tip of the grating electrode of one comb electrode and the bus bar of the other comb electrode is smaller than the anisotropy coefficient in the cross region,
The acoustic velocity of the elastic wave propagating in the gap region is larger than the acoustic velocity of the elastic wave propagating in the central region that is the crossing region other than the edge region adjacent to the gap region in the crossing region,
An acoustic wave resonator in which the acoustic velocity of the elastic wave propagating in the edge region is smaller than the acoustic velocity of the elastic wave propagating in the central region.   The acoustic wave resonator according to claim 11, wherein the acoustic velocity of the elastic wave propagating through the gap region is smaller than the acoustic velocity at the resonant frequency of the elastic wave propagating through the bus bar.   The acoustic wave resonator according to claim 11 or 12, wherein the acoustic velocity of the elastic wave propagating in the edge region is 0.995 or less of the acoustic velocity of the elastic wave propagating in the central region.   The acoustic wave resonator according to claim 11, further comprising an additional film provided on the piezoelectric substrate in the gap region.   The acoustic wave resonator according to claim 1, wherein the piezoelectric substrate is a lithium tantalate substrate or a lithium niobate substrate.   A filter comprising the acoustic wave resonator according to claim 1. A duplexer comprising the filter according to claim 16.

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