JP6494447B2 - Elastic wave device - Google Patents

Description

  The present invention relates to an acoustic wave device, for example, an acoustic wave device 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 device having a surface acoustic wave (SAW) element or the like is used for a high frequency filter or the like. The SAW element is an element in which a grating electrode such as an IDT (Interdigital Transducer) is formed on a piezoelectric substrate. Some SAW elements use SH (Shear Horizontal) waves, which are a type of surface acoustic wave.

  The SH wave is a surface acoustic wave in which a stress that shears the piezoelectric substrate is applied in a direction parallel to the surface of the piezoelectric substrate and in a direction orthogonal to the propagation direction of the SH wave. The SH wave has a higher speed of sound than the bulk wave propagating in the solid of the piezoelectric substrate. For this reason, the SH wave propagates on the surface of the piezoelectric substrate while emitting a bulk wave into the piezoelectric substrate. Therefore, in an elastic wave device using SH waves, there is a limit to reducing the loss.

  In order to reduce the loss of the elastic wave device using the SH wave, the sound speed of the SH wave is slowed by attaching a substance having a slow sound speed on the piezoelectric substrate. The sound speed of the SH wave is made slower than the bulk wave propagating in the piezoelectric substrate (for example, the slowest transverse wave bulk wave). Thereby, the emission of the bulk wave at the time of SH wave propagation is suppressed, and the loss of the elastic wave device using the SH wave can be reduced. Thus, the low-loss device is commonly referred to as a love wave type SAW device.

In Patent Document 1, an Au electrode is formed on a rotating Y-cut X-propagating lithium tantalate (LiTaO ₃ ) substrate with a cut angle of 0 °, and h / λ is set to 0 when the electrode pitch λ and film thickness are h. It is described that a low loss is obtained when the value is changed from 04 to 0.08. It is described that by setting h / λ from 0.04 to 0.08, the sound speed of the SH wave (leaky wave) becomes slower than the sound speed of the slowest transverse wave, so that the loss is reduced.

  Patent Document 2 describes that when an Au electrode is formed on a rotating Y-cut X-propagating lithium tantalate substrate with a cut angle of 36 ° and h / λ is changed from 0 to 0.05, the loss is reduced. Yes.

  In addition, in an acoustic wave device having an IDT, a technique for suppressing unwanted waves in the transverse mode is known. Patent Document 3 describes that an unnecessary wave in the transverse mode is suppressed by making the electrode finger in the edge region wider than the central region in the intersecting region of the IDT. Patent Document 4 describes that an unnecessary wave in a transverse mode is suppressed by adding a dielectric film to electrode fingers in an edge region.

JP-A-10-247835 Japanese Patent Laid-Open No. 2001-77662 JP 2011-101350 A Special table 2013-540441 gazette

  However, the calculations in Patent Documents 1 and 2 assume that the electrodes are uniformly formed on the piezoelectric substrate. That is, the electrode is not a grating electrode. For example, in Patent Document 2, the electromechanical coupling coefficient and propagation loss for h / λ from 0 to 0.1 are calculated, but this is not a calculation for a grating electrode as an electrode. Thus, the range of h / λ in Patent Documents 1 and 2 does not define a low-loss range.

  The present invention has been made in view of the above problems, and an object thereof is to provide a low-loss acoustic wave device.

The present invention is formed of a Y-cut X-propagating lithium tantalate substrate having a cut angle of 20 ° or more and 48 ° or less, and one or more metal films laminated on the substrate, exciting an elastic wave, The density of each metal film among one or more metal films is ρi, the Poisson ratio of each metal film is Pi, the film thickness of each metal film is hi, the density of copper is ρ0, the Poisson ratio of copper is P0, and A grating electrode in which (hi / λ) × (ρi / ρ0) × (Pi / P0) for each metal film is greater than 0.08 when the pitch is λ. The grating electrode includes a plurality of electrodes in an intersecting region where the plurality of electrode fingers of two comb electrodes each having a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected intersect each other. a finger, the The intersection region in which rating electrode is provided, and a edge region provided in the edge center region provided at the center in the extending direction of the grating electrode and in the stretching direction of the grating electrode, wherein in the edge region velocity of acoustic waves is minor than the speed of the acoustic wave in said central area, the rate of the acoustic wave in the gap region provided between said edge region busbar that the speed is greater than the acoustic wave in said central area This is an elastic wave device characterized by the following.

  In the above structure, the one or more metal films may include a metal film containing at least one of Cu, W, Ru, Mo, Ta, and Pt as a main component.

  The said structure WHEREIN: The said total value can be set as the structure which is 0.09 or more.

The present invention is a Y-cut X-propagating lithium tantalate substrate having a cut angle of 20 ° or more and 48 ° or less, formed on the substrate, exciting an elastic wave, containing Cu as a main component, and having a film thickness of h, A grating electrode having h / λ greater than 0.08, where the pitch is λ, and the grating electrode includes two electrode fingers each having a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected. a plurality of electrode fingers crossing areas where the plurality of electrode fingers of the comb electrodes intersect, the intersection area where the grating electrodes is provided, a central area provided in the center in the extending direction of the grating electrode An edge region provided at an edge in the extending direction of the grating electrode, and the velocity of the elastic wave in the edge region is the elastic wave in the central region. Rather smaller than the speed, the speed of the acoustic waves in the gap region provided between said edge region busbar is an acoustic wave device, wherein the greater the speed of the acoustic wave in said central area.

The present invention is a Y-cut X-propagating lithium tantalate substrate having a cut angle of 20 ° or more and 48 ° or less, formed on the substrate, exciting an elastic wave, mainly containing W, having a film thickness of h, A grating electrode having h / λ greater than 0.05, where the pitch is λ, and the grating electrode includes two electrode fingers each having a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected. a plurality of electrode fingers crossing areas where the plurality of electrode fingers of the comb electrodes intersect, the intersection area where the grating electrodes is provided, a central area provided in the center in the extending direction of the grating electrode An edge region provided at an edge in the extending direction of the grating electrode, and the velocity of the elastic wave in the edge region is the speed of the elastic wave in the central region. Rather smaller than in degrees, the speed of the acoustic waves in the gap region provided between said edge region busbar is an elastic wave device, wherein a greater velocity of the acoustic wave in said central area.

The present invention is a Y-cut X-propagating lithium tantalate substrate having a cut angle of 20 ° or more and 48 ° or less, and formed on the substrate, exciting an elastic wave, comprising Ru as a main component, and having a film thickness of h, When the pitch is λ, h / λ is a grating electrode greater than 0.07, and the region where the grating electrode is provided is a central region provided in the center in the extending direction of the grating electrode and the region And an edge region provided at an edge in the extending direction of the grating electrode, wherein the velocity of the elastic wave in the edge region is smaller than the velocity of the elastic wave in the central region .

The present invention is a Y-cut X-propagating lithium tantalate substrate having a cut angle of 20 ° or more and 48 ° or less, formed on the substrate, exciting an elastic wave, having Mo as a main component, and having a film thickness of h, When the pitch is λ, a grating electrode having h / λ of greater than 0.08 is provided, and the region where the grating electrode is provided is a central region provided in the center in the extending direction of the grating electrode and the grating electrode. And an edge region provided at an edge in the extending direction of the grating electrode, wherein the velocity of the elastic wave in the edge region is smaller than the velocity of the elastic wave in the central region .

  In the above configuration, the elastic wave may be a SH wave.

  The said structure WHEREIN: It can be set as the structure which comprises the dielectric film formed on the said board | substrate and covering the said grating electrode.

The present invention is formed of a Y-cut X-propagating lithium tantalate substrate having a cut angle of 20 ° or more and 48 ° or less, and one or more metal films laminated on the substrate, exciting an elastic wave, The density of each metal film among one or more metal films is ρi, the Poisson ratio of each metal film is Pi, the film thickness of each metal film is hi, the density of copper is ρ0, the Poisson ratio of copper is P0, and A grating electrode in which (hi / λ) × (ρi / ρ0) × (Pi / P0) for each metal film is greater than 0.08 when the pitch is λ. , comprising a region in which the grating electrodes is provided, edge provided on the edge in the extending direction of the central area provided in the center the grating electrodes in the extending direction of the grating electrode And a region, the width of the propagation direction of the acoustic waves of the grating electrodes in the edge region of an elastic wave device, wherein the larger acoustic wave propagation direction of the width of the grating electrodes in the central region There is .

The present invention is formed of a Y-cut X-propagating lithium tantalate substrate having a cut angle of 20 ° or more and 48 ° or less, and one or more metal films laminated on the substrate, exciting an elastic wave, The density of each metal film among one or more metal films is ρi, the Poisson ratio of each metal film is Pi, the film thickness of each metal film is hi, the density of copper is ρ0, the Poisson ratio of copper is P0, and A grating electrode in which (hi / λ) × (ρi / ρ0) × (Pi / P0) for each metal film is greater than 0.08 when the pitch is λ. The grating electrode includes a plurality of electrodes in an intersecting region where the plurality of electrode fingers of two comb electrodes each having a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected intersect each other. a finger, the The intersection region in which rating electrode is provided, and a edge region provided in the edge center region provided at the center in the extending direction of the grating electrode and in the stretching direction of the grating electrodes,
An additional film is formed on the grating electrode in the edge region, and the additional film is formed on the grating electrode in the central region and on the electrode finger in a gap region provided between the edge region and the bus bar. The elastic wave device is characterized in that is not formed.

The present invention is formed of a Y-cut X-propagating lithium tantalate substrate having a cut angle of 20 ° or more and 48 ° or less, and one or more metal films laminated on the substrate, exciting an elastic wave, The density of each metal film among one or more metal films is ρi, the Poisson ratio of each metal film is Pi, the film thickness of each metal film is hi, the density of copper is ρ0, the Poisson ratio of copper is P0, and A grating electrode in which (hi / λ) × (ρi / ρ0) × (Pi / P0) for each metal film is greater than 0.08 when the pitch is λ. The grating electrode includes a plurality of electrodes in an intersecting region where the plurality of electrode fingers of two comb electrodes each having a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected intersect each other. a finger, the The intersection region in which rating electrode is provided, and a edge region provided in the edge in the extending direction of the central area provided in the center in the extending direction of the grating electrode and the grating electrode, of the edge region An additional film is formed on the substrate between the grating electrodes, and on the substrate between the grating electrodes in the central region and on the substrate in a gap region provided between the edge region and the bus bar. The elastic wave device is characterized in that no additional film is formed.

  The present invention may be configured to include a filter including the grating electrode.

  The present invention can be configured to include a duplexer including the filter.

  According to the present invention, a low-loss acoustic wave device can be provided.

FIG. 1A is a plan view of the resonator used in the simulation, and FIG. 1B is a cross-sectional view taken along the line AA in FIG. FIG. 2A to FIG. 2D are diagrams showing the results of simulating admittance with respect to the normalized frequency in the resonator. FIGS. 3A to 3C are diagrams showing the results of simulating admittance with respect to the normalized frequency in the resonator. FIG. 4 is a diagram showing ΔY with respect to h / λ of a resonator using Cu as an electrode. FIG. 5A to FIG. 5D are diagrams showing simulation results of conductance with respect to the normalized frequency in the resonator. FIG. 6A to FIG. 6C are diagrams showing the results of simulating the conductance with respect to the normalized frequency in the resonator. FIG. 7 is a diagram showing ΔY with respect to h / λ of a resonator using W as an electrode. FIG. 8 is a diagram showing ΔY with respect to h / λ of a resonator using Ru as an electrode. FIG. 9 is a diagram showing ΔY with respect to h / λ of a resonator using Mo as an electrode. FIG. 10 is a diagram illustrating ΔY with respect to the normalized h / λ of a resonator using W as an electrode. FIG. 11 is a diagram illustrating ΔY with respect to normalized h / λ of a resonator using Ru as an electrode. FIG. 12 is a diagram illustrating ΔY with respect to the normalized h / λ of a resonator using Mo as an electrode. FIG. 13A is a plan view of the resonator according to the first embodiment, and FIG. 13B is an AA cross-sectional view of FIG. 14A to 14C are cross-sectional views of the resonators according to the first to third modifications of the first embodiment, respectively. FIG. 15 is a circuit diagram illustrating a filter according to the second embodiment. FIG. 16 is a block diagram of a duplexer according to the third embodiment. FIG. 17A is a plan view of arranged electrode fingers, and FIG. 17B is a plan view of wave numbers. FIG. 18 is a diagram illustrating β _y / β _θ with _respect to β _x / β _θ . FIG. 19 is a diagram illustrating Γ with respect to h / λ of a resonator in which Mo is a metal film. FIG. 20A and FIG. 20B are diagrams showing sound speeds in the IDT for suppressing unwanted waves in the transverse mode. FIG. 21A is a plan view of a part of the acoustic wave device according to the first modification of the fourth embodiment, and FIG. 21B is a cross-sectional view taken along the line AA in FIG. FIG. 22A and FIG. 22B are diagrams showing a Smith chart of reflection characteristics and conductance with respect to frequency, respectively, in the resonators according to the first modification of the fourth embodiment and the comparative example. FIG. 23A is a plan view of a part of the acoustic wave device according to the second modification of the fourth embodiment, and FIG. 23B is a cross-sectional view taken along line AA in FIG. FIG. 24A is a plan view of a part of the acoustic wave device according to the third modification of the fourth embodiment, and FIG. 24B is a cross-sectional view taken along the line AA in FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

  A simulation was performed for a case where a grating electrode formed on a piezoelectric substrate excites an SH wave. By using a material having a slow sound speed as the grating electrode, if the sound speed of the SH wave becomes smaller than the transverse bulk wave, it is considered that the emission of the bulk wave does not occur and the loss can be reduced. Therefore, attention has been paid to Cu (copper), W (tungsten), Ru (ruthenium), and Mo (molybdenum) as substances that have a slow sound speed and are heavy and can be deposited on the piezoelectric substrate. When these metal films were used for the grating electrode, the relationship between the film thickness of the metal film and the loss of the acoustic wave resonator was simulated using the finite element method.

  FIG. 1A is a plan view of the resonator used in the simulation, and FIG. 1B is a cross-sectional view taken along the line AA in FIG. As shown in FIGS. 1A and 1B, an IDT 12 and a reflector 14 are formed on a piezoelectric substrate 10. The piezoelectric substrate 10 is a rotating Y-cut X-propagating lithium tantalate substrate. The IDT 12 and the reflector 14 are formed of a metal film 16. The IDT 12 has a pair of comb electrodes 12a and 12b. Each of the pair of comb-shaped electrodes 12a and 12b has a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected. The electrode fingers of the pair of comb electrodes 12a and 12b form a grating electrode. Reflectors 14 are formed on both sides of the IDT 12 in the propagation direction of the elastic wave. The reflector 14 reflects elastic waves. The thickness of the metal film 16 is h, and the pitch of the grating electrodes (electrode fingers of the IDT 12) is λ. λ corresponds to the wavelength of the SH wave excited by the IDT 12.

The structure of the simulated resonator is shown below.
Pitch λ: 4 μm
Electrode finger duty ratio: 50%
Number of IDT electrode finger pairs: 55.5 pairs Reflector electrode index: 20 Aperture length: 35λ

Table 1 is a table showing physical property values of metals used for the simulation as the material of the metal film 16. As shown in Table 1, a Cu film, a W film, a Ru film, and a Mo film were used as the metal film. Density, Young's modulus and Poisson's ratio were used as physical property values.

  First, a simulation was performed using the metal film 16 as a Cu film.

  FIG. 2A to FIG. 3C are diagrams showing the results of simulating admittance with respect to the normalized frequency in the resonator. The specific thickness (h / λ), which is the ratio of the thickness h of the metal film 16 to the pitch (that is, the wavelength of the SH wave) λ of the IDT 16 is changed from 0.02 to 0.11. The horizontal axis is the normalized frequency, and the vertical axis is admittance. The metal film 16 is a Cu film, and the piezoelectric substrate 10 is a 36 ° rotated Y-cut X-propagating lithium tantalate substrate.

  An admittance difference ΔY between the resonance point and the antiresonance point of the resonator is used as a scale for evaluating the degree of loss of the resonator. At the resonance point of the resonator, the larger the admittance, the smaller the loss. At the antiresonance point of the resonator, the smaller the admittance, the smaller the loss. Therefore, the larger the ΔY, the larger the Q value of the resonator and the lower the loss.

  As shown in FIGS. 2A to 3C, ΔY is relatively small when h / λ is 0.02 to 0.08, but ΔY when h / λ is 0.09 to 0.11. Is relatively large. As described above, a resonator having a ΔY of 0.09 or more is a resonator having a large ΔY and a low loss compared with a resonator having an h / λ of 0.08 or less. Further, when h / λ is 0.02 to 0.06, the peak of the resonance point and the antiresonance point is not sharp. When h / λ is 0.08, the peak of the resonance point is sharp and the Q value is high. When h / λ is 0.09 to 0.11, the peak of the resonance point and the antiresonance point are sharp and the Q value is high.

  FIG. 4 is a diagram showing ΔY with respect to h / λ of a resonator using Cu as an electrode. The Y cut angles of the piezoelectric substrate 10 were 20 °, 30 °, 36 °, 42 °, and 48 °. When the Y cut angle is smaller than 20 °, the electromechanical coupling coefficient becomes small. When the Y-cut angle is larger than 48 °, the temperature coefficient of frequency increases. Therefore, the range where the Y cut angle is 20 ° to 48 ° is a practical range.

  As shown in FIG. 4, in the range 30 where h / λ is 0.08 or less, there is a maximum point of ΔY with respect to h / λ. This shows the optimum film thickness of the SH wave, not because the speed of sound of the SH wave is slower than that of the transverse bulk wave. In the range 32 where h / λ is greater than 0.08, ΔY is significantly increased.

  FIG. 5A to FIG. 6C are diagrams showing simulation results of conductance with respect to the normalized frequency in the resonator. The metal film 16 is a Cu film, and the piezoelectric substrate 10 is a 36 ° rotated Y-cut X-propagating lithium tantalate substrate. The conductance excluding the peak of the resonance point is approximated by a broken straight line. When h / λ is 0.09 to 0.11, a region 40 where the conductance is lower than the broken line is generated between the resonance point and the antiresonance point. The region 40 is considered to be a region where there is no emission of bulk waves and the conductance is lowered. As described above, the behavior of ΔY and conductance changes greatly with h / λ = 0.08 as a boundary. If h / λ is larger than 0.08, the sound speed of the SH wave becomes slower than the transverse bulk wave, the emission of the bulk wave is suppressed, and a low-loss resonator can be realized.

  Next, a simulation was performed when the metal film 16 was a W film, a Ru film, and a Mo film. FIG. 7 is a diagram showing ΔY with respect to h / λ of a resonator using W as an electrode. As shown in FIG. 7, the behavior of ΔY with respect to h / λ is the same as in the case of Cu. The boundary point where the behavior of ΔY changes is h / λ of about 0.05.

  FIG. 8 is a diagram showing ΔY with respect to h / λ of a resonator using Ru as an electrode. As shown in FIG. 8, the behavior of ΔY with respect to h / λ is the same as in the case of Cu. The boundary point where the behavior of ΔY changes is h / λ is about 0.07.

  FIG. 9 is a diagram showing ΔY with respect to h / λ of a resonator using Mo as an electrode. As shown in FIG. 9, the behavior of ΔY with respect to h / λ is the same as in the case of Cu. The boundary point where the behavior of ΔY changes is h / λ of about 0.08.

  H / λ was normalized for W, Ru and Mo. The density of the metal film 16 is ρ, the density of Cu is ρ0, the Poisson ratio of the metal film 16 is P, and the Poisson ratio of Cu is P0. At this time, normalized h / λ = (h / λ) × (ρ / ρ0) × (P / P0). In the case of Cu, the normalized h / λ is the same as h / λ.

  FIG. 10 is a diagram illustrating ΔY with respect to the normalized h / λ of a resonator using W as an electrode. FIG. 11 is a diagram illustrating ΔY with respect to normalized h / λ of a resonator using Ru as an electrode. FIG. 12 is a diagram illustrating ΔY with respect to the normalized h / λ of a resonator using Mo as an electrode. As shown in FIGS. 10 to 12, in the range 32 where the normalized h / λ is larger than 0.08, it is possible to suppress the emission of the bulk wave and to reduce the loss. Thus, by using the normalized h / λ, the boundary between the ranges 30 and 32 can be generalized regardless of the material of the metal film 16.

  FIG. 13A is a plan view of the resonator according to the first embodiment, and FIG. 13B is an AA cross-sectional view of FIG. As shown in FIGS. 13A and 13B, in the resonator 100, an IDT 12 and a reflector 14 are formed on a piezoelectric substrate 10 that is a rotating Y-cut X-propagating lithium tantalate substrate. The IDT 12 and the reflector 14 are formed of a metal film 16. The Y cut angle of the piezoelectric substrate 10 is not less than 20 ° and not more than 48 °. The Y cut angle may be 25 ° or more or 30 ° or more, and may be 45 ° or less or 40 ° or less. The electrode fingers of the IDT 12 form a grating electrode. The grating electrode is formed by the metal film 16. The normalized film thickness h / λ of the metal film 16 is greater than 0.08. When the Y cut angle is set to 20 ° or more and 48 ° or less and the normalized h / λ is greater than 0.08, the main mode of the elastic wave excited by the IDT 12 is an SH wave.

  As a result, as shown in FIGS. 4 and 11 to 12, it is possible to suppress the emission of bulk waves and reduce the loss. In order to reduce the loss, the normalized h / λ is preferably 0.09 or more, and more preferably 0.10 or more. When the normalized h / λ is greater than 0.14, the Rayleigh wave having the same frequency as the SH wave is increased. For this reason, spurious becomes large. Therefore, the normalized h / λ is preferably 0.14 or less, more preferably 0.13 or less, and further preferably 0.12 or less.

  The main component of the metal film 16 is preferably a heavy material having a slow sound speed. Furthermore, it is preferable that deposition on the piezoelectric substrate 10 is possible. The main component of the metal film 16 is preferably at least one of, for example, Cu, W, Ru, Mo, Ta (tantalum), and Pt (platinum).

  As shown in FIG. 4, when the main component of the metal film 16 is Cu, h / λ is preferably larger than 0.08, more preferably 0.09 or more, and further preferably 0.10 or more. As shown in FIG. 7, when the main component of the metal film 16 is W, h / λ is preferably larger than 0.05, more preferably 0.055 or more, and further preferably 0.06 or more. As shown in FIG. 8, when the main component of the metal film 16 is Ru, h / λ is preferably larger than 0.07, more preferably 0.08 or more, and further preferably 0.09 or more. As shown in FIG. 9, when the main component of the metal film 16 is Mo, h / λ is preferably larger than 0.08, more preferably 0.09 or more, and further preferably 0.10 or more. The main component is a component excluding unintended impurities and impurities intentionally added for improving characteristics, for example, a component containing 50 atomic% or more. Further, for example, other elements may be included in such a range that the Poisson's ratio / density is within ± 10% with respect to a pure metal.

  The pitch of the electrode fingers may be different between the grating electrode (IDT 12) and the reflector 14 within a range of 10% or less, preferably 5% or less. Further, the pitch may be modulated within a range of 10% or less, preferably 5% or less in the grating electrode. In this case, the h / λ error is 10% or less, or 5% or less, even if the pitch in any of the grating electrodes is used as λ of h / λ, and the result is hardly affected.

  14A to 14C are cross-sectional views of the resonators according to the first to third modifications of the first embodiment, respectively. As shown in FIG. 14A, a dielectric film 18 is formed on the piezoelectric substrate 10 so as to cover the metal film 16. The dielectric film 18 is a film for frequency adjustment and / or temperature change compensation. As the dielectric film 18, for example, a silicon oxide film, a silicon nitride film, or an aluminum oxide film can be used. The dielectric film 18 is a lighter film than the metal film 16. For this reason, the presence or absence of the dielectric film 18 has little influence on the result of the simulation.

  As shown in FIG. 14B, an adhesion layer 17 may be formed between the metal film 16 and the piezoelectric substrate 10. The adhesion layer 17 is a film for improving the adhesion between the metal film 16 and the piezoelectric substrate 10. As the adhesion layer 17, for example, Ti (titanium) or Cr (chromium) can be used. The material of the adhesion layer 17 is lighter and thinner than the metal film 16. For this reason, the presence or absence of the adhesion layer 17 hardly affects the result of the simulation.

  As shown in FIG. 14C, the metal film 16 may be formed by laminating a plurality of metal films 16a and 16b. At this time, the normalized h / λ can be the sum of the normalized h / λ calculated for the metal films 16a and 16b. The film thickness, density and Poisson's ratio of the metal film 16a are set to h1, ρ1 and P1, and the film thickness, density and Poisson's ratio of the metal film 16b are set to h2, ρ2 and P2. The normalized h1 / λ = (h1 / λ) × (ρ1 / ρ0) × (P1 / P0) of the metal film 16a, and the normalized h2 / λ = (h2 / λ) × (ρ2 / ρ0) of the metal film 16b. ) × (P2 / P0). Therefore, normalized h / λ = standardized h1 / λ + standardized h2 / λ = (h1 / λ) × (ρ1 / ρ0) × (P1 / P0) + (h2 / λ) × (ρ2 / ρ0) × ( P2 / P0). It suffices that the normalized h / λ calculated in this way is larger than 0.08.

  Thus, when a plurality of metal films are stacked on the piezoelectric substrate 10 as the grating electrode, the density of each metal film among the plurality of metal films is ρi, the Poisson's ratio of each metal film is Pi, and each metal film When the film thickness is hi, the copper density is ρ0, the Poisson's ratio of copper is P0, and the pitch is λ, there are a plurality of (hi / λ) × (ρi / ρ0) × (Pi / P0) in each metal film. The total value of the metal films should be larger than 0.08.

  Example 2 is an example of a filter as an elastic wave device. FIG. 15 is a circuit diagram illustrating a filter according to the second embodiment. As shown in FIG. 15, in the filter 102, one or a plurality of 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. At least one of the series resonators S1 to S4 and the parallel resonators P1 to P3 is the resonator according to the first embodiment or its modification. As described above, the filter 102 includes the grating electrode of the first embodiment or a modification example thereof. Thereby, the loss of the filter 102 can be suppressed.

  The number and connection of the series resonator and the parallel resonator of the filter 102 can be set as appropriate. Further, the second embodiment has been described by taking a ladder type filter as an example, but the filter may be a multimode filter or the like.

  Example 3 is an example of a duplexer as an elastic wave device. FIG. 16 is a block diagram of a duplexer according to the third embodiment. As shown in FIG. 16, in the duplexer 104, the transmission filter 22 is connected between the common terminal Ant and the transmission terminal Tx. A reception filter 24 is connected between the common terminal Ant and the reception terminal Rx. The filter 102 according to the second embodiment can be used for at least one of the transmission filter 22 and the reception filter 24. As described above, the duplexer 104 includes the filter 102 according to the second embodiment. Thereby, the loss of the duplexer 104 can be suppressed.

  Although an example in which the duplexer 104 includes the transmission filter 22 and the reception filter 24 has been described, both filters may be transmission filters or reception filters.

  Example 4 is an example in which the anisotropy coefficient is changed from negative to positive by increasing the thickness of the grating electrode. FIG. 17A is a plan view of arranged electrode fingers, and FIG. 17B is a plan view of wave numbers. 17A and 17B are directions for explaining the anisotropy coefficient, and do not necessarily correspond to the X-axis direction and the Y-axis direction of the crystal orientation of the piezoelectric substrate. .

As shown in FIG. 17A, the electrode fingers 13a of the IDT 12 are arranged in the X direction on the piezoelectric substrate. The direction orthogonal to the X direction is defined as the Y direction. The elastic wave propagates in the X direction. As shown in FIG. 17B, the wave number of the elastic wave in the X direction is β _x , and the wave number of the elastic wave in the Y direction is β _y . If the wave number β _θ of the elastic wave in the direction of the angle θ from the X direction to the Y direction can be approximated by a parabola with _respect to the angle θ, the wave number β _θ uses the anisotropy coefficient γ, and β _x ² + γ · β _y ² = β represented by _theta ^2.

FIG. 18 is a diagram illustrating β _y / β _θ with _respect to β _x / β _θ . β _x / β _θ corresponds to the inverse velocity (slowness) of the phase velocity of the elastic wave in the X direction, and β _y / β _θ corresponds to the inverse velocity of the phase velocity of the elastic wave in the Y direction. FIG. 18 shows the case where the anisotropy coefficient γ is 1, 0, and −3. The reverse speed surface 70 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 0, the reverse speed surface 71 is a flat surface. When the anisotropy coefficient γ is negative, the reverse speed surface 72 is concave when viewed from the origin. For this reason, the case where γ <0 is also referred to as a concave type.

  When a rotating Y-cut X-propagating lithium tantalate substrate is used as the piezoelectric substrate, the anisotropy coefficient γ is negative. The anisotropy coefficient γ was simulated by changing the material and film thickness of the electrode fingers.

For the simulation, the structure shown in FIGS. 1A and 1B was used. The structure of the simulated resonator is shown below.
Piezoelectric substrate 10: 42 ° Y-cut X propagation lithium tantalate substrate Pitch λ: 4 μm
Electrode finger duty ratio: 50%
IDT electrode finger pairs and aperture length: Infinite

The physical properties of the Cu film, W film, and Mo film used in the simulation were the same as those in Example 1. Table 2 shows the physical property values of the Al film and the Ti film.

  FIG. 19 is a diagram illustrating Γ with respect to h / λ of a resonator in which Mo is a metal film. Anisotropy coefficient γ = 1 + Γ. That is, when Γ is greater than −1, the anisotropy coefficient γ is positive, and when Γ is less than −1, the anisotropy coefficient is negative. As shown in FIG. 19, Γ increases as the specific thickness h / λ of the film thickness of the electrode finger 13a (metal film forming the electrode finger 13a) with respect to the wavelength of the SH wave increases. When h / λ is about 0.08 or less, Γ <−1 (that is, the anisotropy coefficient is negative), and when film thickness h / λ is greater than about 0.08, Γ> −1 (that is, the anisotropy coefficient). Is positive). Thus, the anisotropy coefficient γ changes from negative to positive as the film thickness of the electrode finger 13a increases.

Table 3 shows h / λ and Γ when a Mo film, a Cu film, an Al film, a W film, and a Ti film are used as the metal film.

  As shown in Table 3, in the Mo film, Γ> −1 when h / λ is greater than about 0.08. In the Cu film, Γ> −1 when h / λ is about 0.08 or more. In the Al film, h / λ is about 0.15 or more and Γ> −1. In the W film, Γ> −1 when h / λ is about 0.05 or more. In the Ti film, Γ> −1 when h / λ is about 0.125 or more.

  As described above, the specific film thickness h / λ at which the anisotropy coefficient γ becomes negative to positive is h / λ in which the behavior of the admittance difference changes in the first embodiment, that is, the speed of sound of the SH wave is slower than that of the transverse bulk wave. It almost coincides with h / λ. Thus, the anisotropy coefficient γ is positive in the range of h / λ where the loss is low in the first embodiment. The reason why h / λ where the anisotropy coefficient γ is positive is almost the same as h / λ where the sound velocity of the SH wave is slower than that of the transverse bulk wave is not clear. As in Example 1, it can be considered that the metal film forming the electrode finger 13a can be normalized by the Poisson's ratio and density.

  When the anisotropy coefficient γ is positive, it is easier to suppress unwanted waves in the transverse mode than when it is negative. For example, when the anisotropy coefficient γ is positive, unwanted waves in the transverse mode can be suppressed using the methods of Patent Documents 3 and 4.

  FIG. 20A and FIG. 20B are diagrams showing sound speeds in the IDT for suppressing unwanted waves in the transverse mode. 20A and 20B correspond to the cases where the anisotropy coefficient γ is positive and negative, respectively. 20A and 20B, the IDT 12 includes two comb electrodes 12a and 12b. Comb electrodes 12a and 12b have electrode fingers 13a and bus bars 13b. A plurality of electrode fingers 13a are connected to the bus bar 13b. The electrode finger 13a corresponds to a grating electrode. A region where the electrode fingers 13a intersect is an intersecting region 56 (also referred to as an opening region). Intersection region 56 has a central region 50 and an edge region 52. A gap region 54 is formed between the intersection region 56 and the bus bar 13b.

  As shown in the right diagram of FIG. 20A, when the anisotropy coefficient γ is positive, the sound speed of the gap region 54 is increased compared to the intersecting region 56. Thereby, an elastic wave is confined in the intersection region 56. The sound speed of the edge region 52 is made slower than that of the central region 50. Thereby, the unnecessary wave by transverse mode can be controlled. As shown in the right diagram of FIG. 20B, when the anisotropy coefficient γ is negative, the sound speed of the gap region 54 is made slower than the intersecting region 56. Thereby, an elastic wave is confined in the intersection region 56. The sound speed of the edge region 52 is made faster than that of the central region 50. Thereby, the unnecessary wave by transverse mode can be controlled. Such a structure is called a piston mode structure.

  In order to make the sound speed of the edge region 52 slower than the central region 50 corresponding to the case where the anisotropy coefficient is positive, the width of the electrode finger 13a of the edge region 52 is set to the electrode of the central region 50 as in Patent Document 3. It is made larger than the width of the finger 13a. On the other hand, in order to correspond to the case where the anisotropy coefficient is negative and to make the sound speed of the edge region 52 faster than the central region 50, the width of the electrode finger 13a of the edge region 52 is made larger than the width of the electrode finger 13a of the central region 50. Make it smaller. Forming the width of the electrode finger 13a narrowly places a heavy burden from the viewpoint of manufacturing. Therefore, when the anisotropy coefficient is positive, it is easier to suppress unwanted waves in the transverse mode than when it is negative. As a method of making the sound speed of the edge region 52 slower than that of the central region 50, a method of forming an additional film on the electrode finger 13a of the edge region 52 as in Patent Document 4 can be used.

  The anisotropy coefficient of the rotating Y-cut X-propagating lithium tantalate substrate is negative as shown in FIG. 20B, but the electrode film thickness is increased. Thereby, the anisotropy coefficient becomes positive as shown in FIG. Therefore, it is easy to suppress unwanted waves in the transverse mode.

  According to Example 4, the piezoelectric substrate 10 is a Y-cut X-propagating lithium tantalate substrate having a cut angle of 20 ° to 48 °. Similarly to Example 1, when a plurality of metal films are stacked on the piezoelectric substrate 10 as a grating electrode, the density of each metal film among the plurality of metal films is ρi, the Poisson's ratio of each metal film is Pi, When the thickness of each metal film is hi, the density of copper is ρ0, the Poisson's ratio of copper is P0, and the pitch is λ, (hi / λ) × (ρi / ρ0) × (Pi / P0) in each metal film ) For a plurality of metal films is made larger than 0.08. Thereby, although the anisotropy coefficient is negative in the piezoelectric substrate 10, the anisotropy coefficient can be made positive as an elastic wave device.

  The intersection region 56 provided with the grating electrode (electrode finger 13a) has a central region 50 provided at the center in the extending direction of the grating electrode and an edge region 52 provided at the edge in the extending direction of the grating electrode. The velocity of the elastic wave in the edge region 52 is made larger than the velocity of the elastic wave in the central region 50. This facilitates suppression of unwanted waves in the transverse mode.

  A method of suppressing unwanted waves in the transverse mode will be described. FIG. 21A is a plan view of a part of the acoustic wave device according to the first modification of the fourth embodiment, and FIG. 21B is a cross-sectional view taken along the line AA in FIG. As shown in FIGS. 21A and 21B, the IDT 12 is formed. The width W52 of the electrode finger 13a in the edge region 52 is wider than the width W50 of the electrode finger 13a in the central region 50. The pitch W13 between the edge region 52 and the central region 50 is the same. For this reason, the duty ratio (W52 / W13) of the edge region 52 is larger than the duty ratio (W50 / W13) of the central region 50.

A prototype of the resonator of the first modification of the fourth embodiment was actually made. The prototype structure is as follows.
Pitch λ W13: 3.84 μm
Duty ratio of central area 50: 45%
Duty ratio of edge region 52: 50%
Length L50 (opening length) of intersection region 56: 20λ
Length L52 of edge region 52: 1.5λ
Number of IDT electrode finger pairs: 100 Electrode material: Copper Electrode film thickness h / λ: 0.1λ
A comparative example in which the duty ratio of the edge region 52 was 45% was also prototyped.

  FIG. 22A and FIG. 22B are diagrams showing a Smith chart of reflection characteristics and conductance with respect to frequency, respectively, in the resonators according to the first modification of the fourth embodiment and the comparative example. As shown in FIGS. 22A and 22B, spurious is generated in the comparative example as indicated by the arrows. In the first modification of the fourth embodiment, spurious is suppressed. This is presumably because the velocity of the elastic wave in the edge region 52 is slower than the velocity of the elastic wave in the central region 50 because the duty ratio of the edge region 52 is larger than the duty ratio of the central region 50.

  Thus, according to Modification 1 of Example 4, when the grating electrode is copper, the thickness h / λ of the grating electrode is set to 0.08 or more. The width W52 in the elastic wave propagation direction in the edge region 52 is made larger than the width W50 in the elastic wave propagation direction of the grating electrode in the central region 50. Thereby, unwanted waves in the transverse mode can be suppressed.

  When the film thickness of the electrode finger 13a is small and the anisotropy coefficient γ is negative, the width W52 of the electrode finger 13a in the edge region 52 is made smaller than the width W52 of the central region 50 in order to obtain a piston mode structure. It is difficult to reduce the width of the electrode finger 13a from the viewpoint of manufacturing. In Modification 1 of Embodiment 4, h / λ is increased and the anisotropy coefficient γ is positive. Accordingly, a piston mode structure can be realized by increasing the width W52 of the electrode finger 13a in the edge region 52. Therefore, it is possible to more easily suppress unnecessary waves in the transverse mode.

  FIG. 23A is a plan view of a part of the acoustic wave device according to the second modification of the fourth embodiment, and FIG. 23B is a cross-sectional view taken along line AA in FIG. As shown in FIGS. 23A and 23B, in the edge region 52, the additional film 42 is formed on the piezoelectric substrate 10 and the electrode finger 13a. The additional film 42 is formed in a band shape continuously in the propagation direction of the elastic wave.

According to the second modification of the fourth embodiment, the additional film 42 is formed on the grating electrode in the edge region 52, and the additional film 42 is not formed on the grating electrode in the central region 50. Thereby, the sound speed of the edge region 52 can be made slower than that of the central region 50. As the additional film 42, for example, a tantalum pentoxide (Ta ₂ O ₅ ) film or an aluminum oxide (Al ₂ O ₃ ) film can be used. The density of the additional film 42 is preferably 4 g / cm ³ or more, for example. The thickness of the additional film 42 is preferably 200 nm or less, for example.

  The additional film 42 may be formed at least partially on the electrode finger 13 a in the edge region 52. The additional film 42 may not be formed on the piezoelectric substrate 10 between the electrode fingers 13a. The additional film 42 formed on the electrode finger 13a can be an insulating film or a metal film. The additional film 42 formed on the piezoelectric substrate 10 between the electrode fingers 13a is preferably an insulating film.

  When the anisotropy coefficient γ is negative, the piston mode structure cannot be realized by adding the additional film 42. In the second modification of the fourth embodiment, h / λ is increased and the anisotropy coefficient γ is positive. Thereby, by forming the additional film 42 on the electrode finger 13a in the edge region 52, a piston mode structure can be easily realized.

  FIG. 24A is a plan view of a part of the acoustic wave device according to the third modification of the fourth embodiment, and FIG. 24B is a cross-sectional view taken along the line AA in FIG. As shown in FIGS. 24A and 24B, in the edge region 52, the additional film 44 is formed on the piezoelectric substrate 10 between the electrode fingers 13a. The additional film 44 is not formed on the electrode finger 13a.

According to the third modification of the fourth embodiment, the additional film 44 is formed on the piezoelectric substrate 10 between the grating electrodes in the edge region 52, and the additional film 44 is formed on the piezoelectric substrate 10 between the grating electrodes in the central region 50. Is not formed. Thereby, the sound speed of the edge region 52 can be made slower than that of the central region 50. As the additional film 44, for example, a tantalum pentoxide film or an aluminum oxide film can be used. The density of the additional film 44 is preferably 4 g / cm ³ or more, for example. The thickness of the additional film 42 is preferably 200 nm or less, for example.

  The additional film 44 may be formed at least at a part between the electrode fingers 13 a in the edge region 52. The additional film 44 is preferably an insulating film.

  When the anisotropy coefficient γ is negative, the piston mode structure cannot be obtained by adding the additional film 44. In the third modification of the fourth embodiment, h / λ is increased and the anisotropy coefficient γ is positive. Accordingly, the piston mode structure can be easily realized by forming the additional film 44 on the piezoelectric substrate 10 between the electrode fingers 13 in the edge region 52.

  In the fourth embodiment and its modification, the metal film 16 may be formed of a plurality of films as in the modification of the first embodiment. Since the central region 50 mainly contributes to the characteristics of the acoustic wave device, the length of the central region 50 is preferably larger than the length of the edge region 52. The length of the central region 50 is preferably at least twice the length of the edge region 52, and preferably at least 10 times. In the fourth embodiment and its modification, the metal film 16 may be formed of a plurality of films as in the modification of the first embodiment. The fourth embodiment and its modifications may be used for the filter of the second embodiment and the duplexer of the third embodiment.

  In Examples 1 to 4 and the modifications thereof, the surface acoustic wave device has been described as an example of the acoustic wave device. However, the acoustic wave device may be a Love wave device or a boundary acoustic wave device. The piezoelectric substrate 10 may be a piezoelectric substrate bonded to a support substrate such as a sapphire substrate.

  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.

10 Piezoelectric substrate 12 IDT
12a, 12b Comb electrode 13a Electrode finger 14 Reflector 16 Metal film 18 Dielectric film 22 Transmission filter 24 Reception filter 42, 44 Additional film 50 Central region 52 Edge region 54 Gap region 56 Crossing region

Claims (14)

A Y-cut X-propagating lithium tantalate substrate having a cut angle of 20 ° or more and 48 ° or less;
Formed of one or more metal films laminated on the substrate, exciting an elastic wave, wherein the density of each metal film among the one or more metal films is ρi, the Poisson's ratio of each metal film is Pi, When the thickness of each metal film is hi, the density of copper is ρ0, the Poisson's ratio of copper is P0, and the pitch is λ, (hi / λ) × (ρi / ρ0) × (Pi / P0) for the one or more metal films, a grating electrode having a value greater than 0.08,
Comprising
The grating electrodes are the plurality of electrode fingers in an intersecting region where the plurality of electrode fingers of two comb electrodes each having a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected,
The intersecting region provided with the grating electrode has a central region provided at the center in the extending direction of the grating electrode and an edge region provided at an edge in the extending direction of the grating electrode,
Velocity of the acoustic wave in the edge region is minor than the speed of the acoustic wave in said central area,
The elastic wave device according to claim 1, wherein an elastic wave velocity in a gap region provided between the edge region and the bus bar is larger than an elastic wave velocity in the central region .   2. The acoustic wave device according to claim 1, wherein the one or more metal films include a metal film containing at least one of Cu, W, Ru, Mo, Ta, and Pt as a main component.   3. The acoustic wave device according to claim 1, wherein the total value is 0.09 or more. A Y-cut X-propagating lithium tantalate substrate having a cut angle of 20 ° or more and 48 ° or less;
A grating electrode formed on the substrate, exciting an acoustic wave, comprising Cu as a main component, having a film thickness of h, and a pitch of λ, and h / λ is greater than 0.08;
Comprising
The grating electrodes are the plurality of electrode fingers in an intersecting region where the plurality of electrode fingers of two comb electrodes each having a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected,
The intersecting region provided with the grating electrode has a central region provided at the center in the extending direction of the grating electrode and an edge region provided at an edge in the extending direction of the grating electrode,
Velocity of the acoustic wave in the edge region is minor than the speed of the acoustic wave in said central area,
The elastic wave device according to claim 1, wherein an elastic wave velocity in a gap region provided between the edge region and the bus bar is larger than an elastic wave velocity in the central region . A Y-cut X-propagating lithium tantalate substrate having a cut angle of 20 ° or more and 48 ° or less;
A grating electrode formed on the substrate, exciting an elastic wave, having W as a main component, a film thickness of h, and a pitch of λ, and h / λ is greater than 0.05;
Comprising
The grating electrodes are the plurality of electrode fingers in an intersecting region where the plurality of electrode fingers of two comb electrodes each having a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected,
The intersecting region provided with the grating electrode has a central region provided at the center in the extending direction of the grating electrode and an edge region provided at an edge in the extending direction of the grating electrode,
Velocity of the acoustic wave in the edge region is minor than the speed of the acoustic wave in said central area,
The elastic wave device according to claim 1, wherein an elastic wave velocity in a gap region provided between the edge region and the bus bar is larger than an elastic wave velocity in the central region . A Y-cut X-propagating lithium tantalate substrate having a cut angle of 20 ° or more and 48 ° or less;
A grating electrode formed on the substrate, exciting an acoustic wave, having Ru as a main component, having a film thickness of h, and a pitch of λ, h / λ is greater than 0.07;
Comprising
The region where the grating electrode is provided has a central region provided at the center in the extending direction of the grating electrode and an edge region provided at an edge in the extending direction of the grating electrode,
The elastic wave device according to claim 1, wherein the velocity of the elastic wave in the edge region is smaller than the velocity of the elastic wave in the central region. A Y-cut X-propagating lithium tantalate substrate having a cut angle of 20 ° or more and 48 ° or less;
A grating electrode formed on the substrate, exciting an acoustic wave, having Mo as a main component, having a film thickness of h, and a pitch of λ, h / λ is greater than 0.08;
Comprising
The region where the grating electrode is provided has a central region provided at the center in the extending direction of the grating electrode and an edge region provided at an edge in the extending direction of the grating electrode,
The elastic wave device according to claim 1, wherein the velocity of the elastic wave in the edge region is smaller than the velocity of the elastic wave in the central region.   The elastic wave device according to claim 1, wherein the elastic wave is an SH wave.   The elastic wave device according to claim 1, further comprising a dielectric film formed on the substrate and covering the grating electrode. A Y-cut X-propagating lithium tantalate substrate having a cut angle of 20 ° or more and 48 ° or less;
Formed of one or more metal films laminated on the substrate, exciting an elastic wave, wherein the density of each metal film among the one or more metal films is ρi, the Poisson's ratio of each metal film is Pi, When the thickness of each metal film is hi, the density of copper is ρ0, the Poisson's ratio of copper is P0, and the pitch is λ, (hi / λ) × (ρi / ρ0) × (Pi / P0) for the one or more metal films, a grating electrode having a value greater than 0.08,
Comprising
The region where the grating electrode is provided has a central region provided at the center in the extending direction of the grating electrode and an edge region provided at an edge in the extending direction of the grating electrode,
The elastic wave device according to claim 1, wherein a width of the grating electrode in the edge region in the propagation direction of the elastic wave is larger than a width of the grating electrode in the propagation direction of the elastic wave in the central region. A Y-cut X-propagating lithium tantalate substrate having a cut angle of 20 ° or more and 48 ° or less;
Formed of one or more metal films laminated on the substrate, exciting an elastic wave, wherein the density of each metal film among the one or more metal films is ρi, the Poisson's ratio of each metal film is Pi, When the thickness of each metal film is hi, the density of copper is ρ0, the Poisson's ratio of copper is P0, and the pitch is λ, (hi / λ) × (ρi / ρ0) × (Pi / P0) for the one or more metal films, a grating electrode having a value greater than 0.08,
Comprising
The grating electrodes are the plurality of electrode fingers in an intersecting region where the plurality of electrode fingers of two comb electrodes each having a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected,
The intersecting region provided with the grating electrode has a central region provided at the center in the extending direction of the grating electrode and an edge region provided at an edge in the extending direction of the grating electrode,
An additional film is formed on the grating electrode in the edge region, and the additional film is formed on the grating electrode in the central region and on the electrode finger in a gap region provided between the edge region and the bus bar. An elastic wave device characterized in that is not formed. A Y-cut X-propagating lithium tantalate substrate having a cut angle of 20 ° or more and 48 ° or less;
Formed of one or more metal films laminated on the substrate, exciting an elastic wave, wherein the density of each metal film among the one or more metal films is ρi, the Poisson's ratio of each metal film is Pi, When the thickness of each metal film is hi, the density of copper is ρ0, the Poisson's ratio of copper is P0, and the pitch is λ, (hi / λ) × (ρi / ρ0) × (Pi / P0) for the one or more metal films, a grating electrode having a value greater than 0.08,
Comprising
The grating electrodes are the plurality of electrode fingers in an intersecting region where the plurality of electrode fingers of two comb electrodes each having a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected,
The intersecting region provided with the grating electrode has a central region provided at the center in the extending direction of the grating electrode and an edge region provided at an edge in the extending direction of the grating electrode,
An additional film is formed on the substrate between the grating electrodes in the edge region, and a gap region provided on the substrate between the grating electrodes in the central region and between the edge region and the bus bar. An elastic wave device, wherein an additional film is not formed on the substrate .   The acoustic wave device according to any one of claims 1 to 12, further comprising a filter including the grating electrode.   The acoustic wave device according to claim 13, further comprising a duplexer including the filter.

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