Elastic wave devices, filters, and multiplexers

Abstract

To provide an acoustic wave device capable of suppressing the occurrence of dielectric breakdown.SOLUTION: An acoustic wave device includes a substrate 10, a piezoelectric layer 14 provided on the substrate 10, a lower electrode 12 and an upper electrode 16 provided on the substrate 10 with at least a portion of the piezoelectric layer 14 sandwiched therebetween, and an acoustic reflection film 30 provided between the substrate 10 and the lower electrode 12 and having a first layer 32 including a resonance region 50 in which the lower electrode 12 and the upper electrode 16 overlap with each other with the piezoelectric layer 14 sandwiched therebetween, and a metal film 36 at least a portion of which is provided outside the resonance region 50, and a second layer 34 made of an insulating material having acoustic properties different from those of the first layer 32, which are alternately stacked, where the metal film 36 included in at least a top layer 32a of the first layer 32 closest to the piezoelectric layer 14 has a length L1 from the resonance region 50 at a first extraction region 52 where the upper electrode 16 is extracted from the resonance region 50 shorter than a length L2 from the resonance region 50 at a second extraction region 54 where the lower electrode 12 is extracted from the resonance region 50.SELECTED DRAWING: Figure 5

Description

Technical Field

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

Background Art

[0002] Filters and duplexers using piezoelectric thin film resonators are known as filters and duplexers for high-frequency circuits of wireless terminals such as mobile terminals. The piezoelectric thin film resonator includes a piezoelectric layer provided on a substrate, and a lower electrode and an upper electrode provided on the substrate with the piezoelectric layer interposed therebetween. A configuration is known in which an acoustic reflection film in which two types of layers having different acoustic characteristics are laminated is provided between the substrate and the lower electrode in a resonance region where the lower electrode and the upper electrode overlap with the piezoelectric layer interposed therebetween (for example, Patent Documents 1 to 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] The acoustic reflection film is formed to be larger than the resonance region in plan view. In general, the acoustic reflection film uses a first layer formed of a metal material and a second layer formed of an insulating material as the two types of layers having different acoustic characteristics. When a power durability test was performed on the elastic wave device having such an acoustic reflection film, dielectric breakdown sometimes occurred between the upper electrode and the first layer made of a metal material.

[0005] The present invention has been made in view of the above problems, and an object thereof is to suppress the occurrence of dielectric breakdown. [Means for solving the problem]

[0006] The present invention relates to an elastic wave device comprising: a substrate; a piezoelectric layer provided on the substrate; a lower electrode and an upper electrode provided on the substrate with at least a portion of the piezoelectric layer in between; one or more first layers provided between the substrate and the lower electrode, each containing a metal film that includes a resonant region where the lower electrode and the upper electrode overlap with the piezoelectric layer in between, and at least a portion of which is located outside the resonant region; and one or more second layers made of an insulating material having different acoustic properties from the one or more first layers, which are alternately laminated, wherein the metal film included in at least the uppermost layer closest to the piezoelectric layer among the one or more first layers is an acoustic reflective film in which the first length from the resonant region in the first extraction region where the upper electrode is drawn out from the resonant region is shorter than the second length from the resonant region in the second extraction region where the lower electrode is drawn out from the resonant region.

[0007] In the above configuration, the end face of the metal film included in the uppermost layer closest to the piezoelectric layer, on the first extraction region side, can be configured to be located at the boundary between the resonance region and the first extraction region.

[0008] In the above configuration, the one or more second layers can be configured to cover the end face of the metal film included in the uppermost layer closest to the piezoelectric layer in the first extraction region while in contact with it.

[0009] In the above configuration, the uppermost layer closest to the piezoelectric layer may include the metal film provided in the resonance region and an insulating film provided in the first extraction region in contact with the end face of the metal film, and made of another insulating material with a higher acoustic impedance than the insulating material.

[0010] In the above configuration, the insulating material is silicon oxide, and the other insulating material can be zinc oxide, hafnium oxide, hafnium nitride, aluminum nitride, tantalum oxide, aluminum oxide, or silicon carbide.

[0011] In the above configuration, a void in contact with the end face of the metal film included in the uppermost layer closest to the piezoelectric layer can be formed in the first extraction region.

[0012] The present invention relates to an acoustic wave device comprising: a substrate; a piezoelectric layer provided on the substrate; a lower electrode and an upper electrode provided on the substrate with at least a portion of the piezoelectric layer in between; and an acoustic reflective film provided between the substrate and the lower electrode, in which one or more first layers made of a metallic material are alternately laminated, the first layer being a first extraction region where the upper electrode is drawn out from the resonance region, and the distance between the uppermost layer closest to the piezoelectric layer and the upper electrode is longer in the first extraction region where the upper electrode is drawn out from the resonance region than in the resonance region.

[0013] In the above configuration, the distance from the surface of the piezoelectric layer in contact with the lower electrode to the upper electrode can be configured to be longer in the first extraction region than in the resonance region.

[0014] In the above configuration, the distance from the uppermost layer closest to the piezoelectric layer to the piezoelectric layer can be configured such that the distance from the first extraction region is longer than the distance from the second extraction region where the lower electrode is drawn out from the resonance region.

[0015] In the above configuration, the piezoelectric layer may be a lithium tantalate layer or a lithium niobate layer.

[0016] The present invention is a filter comprising the elastic wave device described above.

[0017] The present invention is a multiplexer equipped with the filter described above. [Effects of the Invention]

[0018] According to the present invention, the occurrence of dielectric breakdown can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] [Figure 1] Figure 1 is a plan view of an acoustic wave device according to Example 1. [Figure 2] Figure 2(a) is an A-A cross-sectional view of Figure 1, and Figure 2(b) is a B-B cross-sectional view of Figure 1. [Figure 3] Figure 3(a) and Figure 3(b) are diagrams showing the relationship between the crystal orientation of the piezoelectric layer when the piezoelectric layer is a lithium niobate layer or a lithium tantalate layer, and the vibration direction of thickness shear vibration. [Figure 4] Figure 4(a) to Figure 4(c) are cross-sectional views showing a method of manufacturing the acoustic wave device according to Example 1. [Figure 5] Figure 5(a) is a cross-sectional view of an acoustic wave device according to Modification 1 of Example 1, and Figure 5(b) is a cross-sectional view of an acoustic wave device according to Modification 2 of Example 1. [Figure 6] Figure 6 is a cross-sectional view of an acoustic wave device according to a Comparative Example. [Figure 7] Figure 7 is a simulation result of the electric field distribution of the acoustic wave device according to the Comparative Example. [Figure 8] Figure 8(a) and Figure 8(b) are diagrams for explaining the mechanism of electric field concentration. [Figure 9] Figure 9(a) is a plan view of an acoustic wave device according to Example 2, and Figure 9(b) is an A-A cross-sectional view of Figure 9(a). [Figure 10] Figure 10(a) is a cross-sectional view of an acoustic wave device according to Modification 1 of Example 2, and Figure 10(b) is a cross-sectional view of an acoustic wave device according to Modification 2 of Example 2. [Figure 11] Figure 11 is a cross-sectional view of an acoustic wave device according to Modification 3 of Example 2. [Figure 12] Figure 12(a) and Figure 12(b) are simulation results of the electric field distribution of Example 2 and Modification 1 of Example 2. [Figure 13]Figures 13(a) and 13(b) show the simulation results of admittance |Y| as a function of frequency for the comparative example and Example 2. [Figure 14] Figures 14(a) and 14(b) are cross-sectional views showing parts of models A and B used in the simulation. [Figure 15] Figure 15 shows the simulation results of ΔY as a function of the length of the first layer of the acoustic reflective film for models A and B. [Figure 16] Figure 16 is a cross-sectional view of the elastic wave device according to Example 3. [Figure 17] Figure 17(a) is a cross-sectional view of the elastic wave device according to Example 4, and Figure 17(b) is a cross-sectional view of the elastic wave device according to Modification 1 of Example 4. [Figure 18] Figure 18(a) is a cross-sectional view of the elastic wave device according to Modification 2 of Example 4, and Figure 18(b) is a cross-sectional view of the elastic wave device according to Modification 3 of Example 4. [Figure 19] Figure 19 is a circuit diagram of the filter according to Example 5. [Figure 20] Figure 20 is a circuit diagram of the duplexer according to Example 6. [Modes for carrying out the invention]

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [Examples]

[0021] Figure 1 is a plan view of the elastic wave device according to Example 1. Figure 2(a) is a cross-sectional view AA of Figure 1, and Figure 2(b) is a cross-sectional view BB of Figure 1. In Figure 1, for clarity, the first layer 32 of the acoustic reflective film 30 is hatched, and the through-hole 22 is shown with a thicker line than the others (the same applies to similar figures below). The normal direction of the piezoelectric layer 14 is the Z direction, and the directions that are mutually orthogonal in the planar direction of the piezoelectric layer 14 are the X direction and the Y direction. As shown in Figures 1, 2(a), and 2(b), the elastic wave device 100 according to Example 1 is a piezoelectric thin-film resonator comprising a lower electrode 12, a piezoelectric layer 14, and an upper electrode 16.

[0022] An acoustic reflective film 30 is provided on the substrate 10. A piezoelectric layer 14 is provided on the acoustic reflective film 30. The upper and lower surfaces of the piezoelectric layer 14 are flat surfaces. An upper electrode 16 and a lower electrode 12 are provided above and below the piezoelectric layer 14. The region where the lower electrode 12 and the upper electrode 16 overlap in a plan view, with at least a portion of the piezoelectric layer 14 in between, is the resonance region 50. The planar shape of the resonance region 50 is, for example, approximately rectangular. The rectangle has four sides that are approximately straight. One pair of the four sides extends approximately along the Y direction, and the other pair of sides extends approximately along the X direction.

[0023] The substrate 10 is, for example, a silicon substrate, sapphire substrate, alumina substrate, spinel substrate, quartz substrate, crystal substrate, glass substrate, ceramic substrate, or GaAs substrate. The piezoelectric layer 14 is, for example, a single-crystal lithium niobate layer, a single-crystal lithium tantalate layer, an aluminum nitride layer, a zinc oxide layer, a lead zirconate titanate layer, or a lead titanate layer. The thickness of the piezoelectric layer 14 is, for example, about 200 nm to 1000 nm. The lower electrode 12 and upper electrode 16 are, for example, single-layer films or multilayer films of ruthenium (Ru), chromium (Cr), aluminum (Al), titanium (Ti), copper (Cu), molybdenum (Mo), tungsten (W), tantalum (Ta), platinum (Pt), rhodium (Rh), or iridium (Ir). The thickness of the lower electrode 12 and upper electrode 16 is, for example, about 20 nm to 150 nm.

[0024] When high-frequency power is applied between the lower electrode 12 and the upper electrode 16, elastic waves are excited in the piezoelectric layer 14 within the resonant region 50. The wavelength of the elastic waves is approximately twice the thickness of the piezoelectric layer 14. If the piezoelectric layer 14 is a single-crystal lithium niobate layer or a single-crystal lithium tantalate layer, elastic waves are excited in the piezoelectric layer 14 that vibrate in a direction where the displacement of the elastic waves is approximately perpendicular to the Z direction (i.e., the strain direction relative to the thickness). This vibration is called thickness-slip vibration. The direction in which the displacement of the thickness-slip vibration is greatest (the displacement direction of the thickness-slip vibration) is defined as the vibration direction 60 of the thickness-slip vibration. Here, the vibration direction 60 of the thickness-slip vibration is the Y direction. If the piezoelectric layer 14 is an aluminum nitride layer, a zinc oxide layer, a lead zirconate titanate layer, or a lead titanate layer, elastic waves of the thickness-longitudinal vibration mode are mainly excited in the piezoelectric layer 14. For example, when elastic waves of thickness-slip vibration are excited in the piezoelectric layer 14, the lower electrode 12 and the upper electrode 16 may be drawn out from the resonance region 50 in the vibration direction 60 of the thickness-slip vibration.

[0025] The acoustic reflective film 30 is constructed by alternately laminating one or more first layers 32 and one or more second layers 34. The first layers 32 and the second layers 34 are films with different acoustic properties. In Example 1, the first layer 32 is made of a metallic material. The second layer 34 is made of an insulating material. For example, the first layer 32 is a film with a higher acoustic impedance than the second layer 34. The film thickness of the first layer 32 and the second layer 34 is, for example, approximately λ / 4 (where λ is the wavelength of an elastic wave). As a result, the acoustic reflective film 30 reflects elastic waves. The number of layers of the first layer 32 and the second layer 34 can be set arbitrarily.

[0026] The acoustic reflective film 30 is provided overlapping the resonance region 50 in a plan view. The first layer 32 overlaps with the lower electrode 12 and the through hole 22 outside the resonance region 50, but does not overlap with the upper electrode 16. That is, if the region where the upper electrode 16 is drawn out from the resonance region 50 is defined as the first extraction region 52, and the region where the lower electrode 12 is drawn out from the resonance region 50 is defined as the second extraction region 54, then the first layer 32 is provided in the resonance region 50 and the second extraction region 54, but not in the first extraction region 52. The reason for making the acoustic reflective film 30 larger than the resonance region 50 in a plan view is to enable the acoustic reflective film 30 to reflect elastic waves that leak obliquely from the resonance region 50, thereby suppressing degradation of characteristics.

[0027] Of the one or more first layers 32, the layer closest to the piezoelectric layer 14 is designated as the uppermost layer 32a, and the layers other than the uppermost layer 32a are designated as lower layers 32b. Since the first layers 32 are made of a metallic material, the uppermost layer 32a and lower layers 32b are made of a metallic film 36. The uppermost layer 32a is provided in the resonance region 50 and the second extraction region 54, but not in the first extraction region 52. Therefore, the length L1 from the resonance region 50 in the first extraction region 52 is shorter than the length L2 from the resonance region 50 in the second extraction region 54. Similarly, the lower layer 32b is provided in the resonance region 50 and the second extraction region 54, but not in the first extraction region 52. Therefore, the length L3 from the resonance region 50 in the first extraction region 52 is shorter than the length L4 from the resonance region 50 in the second extraction region 54. In other words, the metal films 36 forming the uppermost layer 32a and the lower layer 32b have lengths L1 and L3 from the resonance region 50 in the first extraction region 52 that are shorter than the lengths L2 and L4 from the resonance region 50 in the second extraction region 54. The end faces 33 on the first extraction region 52 side of the uppermost layer 32a and the lower layer 32b are located, for example, at the boundary between the resonance region 50 and the first extraction region 52. Therefore, lengths L1 and L3 are approximately zero. Lengths L2 and L4 are approximately the same.

[0028] The metal film 36 is a film mainly composed of, for example, titanium (Ti), nickel (Ni), chromium (Cr), gold (Au), molybdenum (Mo), magnesium (Mg), aluminum (Al), ruthenium (Ru), platinum (Pt), rhodium (Rh), palladium (Pd), iridium (Ir), or tungsten (W). The second layer 34 is a film mainly composed of, for example, silicon oxide (SiO2). Table 1 shows the physical properties of each material. In Table 1, the speed of sound was calculated by taking the square root of the product of density and bulk modulus. Acoustic impedance was calculated by multiplying density and speed of sound. [Table 1]

[0029] For a film to have a particular element as its main component, it is permissible for the film to contain intentional or unintentional impurities other than the main component. When a particular element is the main component in a film, its concentration is, for example, 50 atomic percent or more, or for example, 80 atomic percent or more. In cases where two elements are the main components, such as silicon oxide, the sum of the concentrations of silicon and oxygen is, for example, 50 atomic percent or more, or for example, 80 atomic percent or more, and the concentrations of silicon and oxygen are, for example, 10 atomic percent or more each.

[0030] When the first layer 32 is a film with high acoustic impedance, the metal film 36 is preferably a film mainly composed of Au, Pt, Rh, Ir, or W from the above materials, and is more preferably a film mainly composed of Pt, Ir, or W.

[0031] The piezoelectric layer 14 has a pair of through holes 22 formed in the Y direction, flanking the resonance region 50 from the X direction and aligned with the resonance region 50. The through holes 22 are provided in a region where the lower electrode 12 and upper electrode 16 are absent in a plan view, for example. For example, in a plan view, the through holes 22 are in contact with the resonance region 50 on both sides of the resonance region 50 in the X direction. That is, in a plan view, the through holes 22 define opposing sides of the rectangular resonance region 50 in the X direction. The through holes 22 may not be in contact with the resonance region 50, but may be provided at a distance from the resonance region 50. It is preferable that the through holes 22 are formed on both sides of the resonance region 50 at the same distance from the resonance region 50. The through holes 22 are, for example, rectangular in shape in a plan view. By providing the through holes 22, the elastic waves excited in the resonance region 50 are confined within the resonance region 50.

[0032] Here, we will explain the relationship between the crystal orientation of the piezoelectric layer 14 and the vibration direction 60 of the thickness shear vibration when the piezoelectric layer 14 is a lithium niobate layer or a lithium tantalate layer. First, we will explain the definition of the Euler angle (φ, θ, ψ). In a right-handed XYZ coordinate system, the normal direction to the upper surface of the piezoelectric layer 14 is the Z direction, and the directions perpendicular to the Z direction and mutually perpendicular to each other in the plane direction of the upper surface of the piezoelectric layer 14 are the X direction and the Y direction. The X direction, Y direction, and Z direction are the X-axis direction, Y-axis direction, and Z-axis direction of the crystal orientation, respectively. Next, rotate by an angle φ from the +X direction to the +Y direction around the Z direction. Rotate by an angle θ from the +Y direction to the +Z direction around the X direction after the angle φ rotation. Rotate by an angle ψ from the +X direction to the +Y direction around the Z direction after the angle θ rotation. The Euler angle when rotated in this way is (φ, θ, ψ). Note that the Euler angle expressed using (φ, θ, ψ) includes equivalent Euler angles.

[0033] Figures 3(a) and 3(b) show the relationship between the crystal orientation of the piezoelectric layer 14 and the vibration direction of the thickness shear vibration when the piezoelectric layer 14 is a lithium niobate layer or a lithium tantalate layer. In Figures 3(a) and 3(b), the dashed arrows on the left indicate the orientation of the crystal axis of the piezoelectric layer 14. The solid arrows on the right correspond to the X, Y, and Z directions in Figures 1, 2(a), and 2(b). As shown in Figure 3(a), the +X, +Y, and +Z directions are the +X axis direction, +Y axis direction, and +Z axis direction of the crystal orientation of the piezoelectric layer 14, respectively. As shown in Figure 3(b), from the state in Figure 3(a), the +Y and +Z directions are rotated by 105° from the +Y direction to the -Z direction on the YZ plane around the X direction. When rotated in this way, the direction obtained by rotating the +Z axis direction of the crystal orientation by 105° toward the +Y axis direction becomes the +Z direction. In this case, the Y direction is the vibration direction 60 for thickness shear vibration. The Euler angles are (0°, -105°, 0°). Note that if the Euler angles derived by the same method as above are (0°, -105°, 90°), the X direction is the vibration direction 60 for thickness shear vibration. Each angle of the Euler angle is allowed to be within a range of ±5°, and more preferably within a range of ±1°.

[0034] [Manufacturing method] Figures 4(a) to 4(c) are cross-sectional views showing a method for manufacturing an elastic wave device according to Example 1. Figures 4(a) to 4(c) are cross-sectional views corresponding to the area between A and B in Figure 1. As shown in Figure 4(a), a piezoelectric substrate is prepared as the piezoelectric layer 14. A lower electrode 12 is formed on the piezoelectric layer 14. The lower electrode 12 is formed by depositing a metal film using, for example, a sputtering method, a vacuum deposition method, or a CVD (Chemical Vapor Deposition) method, and then patterning the metal film into a desired shape using, for example, a photolithography method and an etching method. The lower electrode 12 may also be formed using a lift-off method.

[0035] As shown in Figure 4(b), an acoustic reflective film 30 is formed on the piezoelectric layer 14 so as to cover the lower electrode 12. The acoustic reflective film 30 is formed by alternately depositing a first layer 32 and a second layer 34, and patterning the first layer 32 into a desired shape. The deposit of the first layer 32 and the second layer 34 is performed using, for example, sputtering or CVD, and the patterning is performed using, for example, photolithography or etching. Subsequently, the upper surface of the acoustic reflective film 30 is planarized using, for example, CMP (Chemical Mechanical Polishing).

[0036] As shown in Figure 4(c), the acoustic reflective film 30 is bonded to the substrate 10. For bonding, for example, a surface activation method is used. A bonding layer such as a silicon film may be provided between the substrate 10 and the acoustic reflective film 30. Next, the piezoelectric layer 14 is thinned to a desired thickness. For thinning, for example, a grinding method and / or a CMP method is used. For example, the piezoelectric layer 14 is made to approximately the desired thickness using a grinding method, and the upper surface is flattened using a CMP method. As a result, the upper surface of the piezoelectric layer 14 becomes flat to the extent of manufacturing tolerance. After that, an upper electrode 16 is formed on the piezoelectric layer 14. The upper electrode 16 is formed by depositing a metal film using, for example, a sputtering method, a vacuum deposition method, or a CVD method, and then patterning the metal film into a desired shape using, for example, a photolithography method and an etching method. The upper electrode 16 may also be formed using a lift-off method.

[0037] Subsequently, as shown in Figure 2(b), through-holes 22 are formed that penetrate the piezoelectric layer 14. The through-holes 22 are formed using, for example, photolithography and etching. Through these steps, the elastic wave device according to Example 1 is formed.

[0038] [Differentiation] Figure 5(a) is a cross-sectional view of the elastic wave device according to Modification 1 of Example 1, and Figure 5(b) is a cross-sectional view of the elastic wave device according to Modification 2 of Example 1. As shown in Figure 5(a), in the elastic wave device 110 according to Modification 1 of Example 1, the uppermost layer 32a and the lower layer 32b are provided in the resonance region 50, the first extraction region 52, and the second extraction region 54, but the lengths L1 and L3 from the resonance region 50 in the first extraction region 52 are shorter than the lengths L2 and L4 from the resonance region 50 in the second extraction region 54. Therefore, as in Example 1, the metal films 36 forming the uppermost layer 32a and the lower layer 32b, respectively, have lengths L1 and L3 from the resonance region 50 in the first extraction region 52 that are shorter than the lengths L2 and L4 from the resonance region 50 in the second extraction region 54. Lengths L1 and L3 are approximately the same. The other configurations are the same as in Example 1, so their explanation is omitted.

[0039] As shown in Figure 5(b), in the elastic wave device 120 according to the modified example 2 of Example 1, the uppermost layer 32a is provided in the resonance region 50 and the second extraction region 54, as in Example 1, but not in the first extraction region 52, and its end face 33 is located at the boundary between the resonance region 50 and the first extraction region 52. Therefore, as in Example 1, the length L1 of the metal film 36 forming the uppermost layer 32a from the resonance region 50 in the first extraction region 52 is shorter than the length L2 of the metal film 36 from the resonance region 50 in the second extraction region 54. The lower layer 32b is provided in the resonance region 50, the first extraction region 52, and the second extraction region 54, and the length L3 from the resonance region 50 in the first extraction region 52 and the length L4 from the resonance region 50 in the second extraction region 54 are approximately the same. In other words, the metal film 36 forming the lower layer 32b has a length L3 from the resonance region 50 in the first extraction region 52 and a length L4 from the resonance region 50 in the second extraction region 54 that are approximately the same. The other components are the same as in Example 1, so their description is omitted.

[0040] [Comparative Example] Figure 6 is a cross-sectional view of an elastic wave device according to a comparative example. As shown in Figure 6, in the elastic wave device 1000 according to the comparative example, the uppermost layer 32a and the lower layer 32b are provided in the resonant region 50, the first extraction region 52, and the second extraction region 54, and the lengths L1 and L3 from the resonant region 50 in the first extraction region 52 are approximately the same as the lengths L2 and L4 from the resonant region 50 in the second extraction region 54. That is, the metal films 36 forming the uppermost layer 32a and the lower layer 32b have approximately the same lengths L1 and L3 from the resonant region 50 in the first extraction region 52 and L2 and L4 from the resonant region 50 in the second extraction region 54. The other configurations are the same as in Example 1, so their description is omitted.

[0041] [simulation] A simulation was performed on the electric field distribution generated when high-frequency power is applied between the lower electrode 12 and the upper electrode 16 of the elastic wave device according to the comparative example. The simulation conditions are as follows. Substrate 10: Silicon substrate Layer 1, 32: Tungsten film with a thickness of 152 nm Second layer 34: Silicon oxide film with a thickness of 194 nm Lower electrode 12: Aluminum film with a thickness of 46 nm Piezoelectric layer 14: A lithium niobate layer with a thickness of 460 nm, where the vibration direction of the thickness-slip vibration is the Y direction. Upper electrode 16: Aluminum film with a thickness of 46 nm Lengths L1, L2, L3, L4: 1000nm Wavelength of elastic waves λ: 920 μm Conditions in the X direction: The width of the resonant region 50 in the X direction is 27λ Conditions in the Y direction: The width of the resonant region 50 in the Y direction is 0.5λ, and the boundary conditions are infinitely continuous.

[0042] Figure 7 shows the simulation results of the electric field distribution of the elastic wave device in the comparative example. As shown in Figure 7, the electric field was concentrated in the second layer 34 near the end of the portion of the uppermost layer 32a that protrudes from the lower electrode 12. This is thought to be due to the following reasons.

[0043] Figures 8(a) and 8(b) are diagrams illustrating the mechanism of electric field concentration. As shown in Figure 8(a), in the portion of the uppermost layer 32a protruding from the lower electrode 12, the metal film 36 forming the uppermost layer 32a and the upper electrode 16 face each other with the second layer 34, made of insulating material, and the piezoelectric layer 14 in between. As a result, a capacitance is formed between the uppermost layer 32a and the upper electrode 16. If the capacitance between the uppermost layer 32a and the upper electrode 16 is called capacitance C, then capacitance C is divided into capacitance C1 of the piezoelectric layer 14, which has a different relative permittivity, and capacitance C2 of the second layer 34. As shown in Figure 8(b), when a voltage V is applied between the uppermost layer 32a and the upper electrode 16, if a charge +Q accumulates on one electrode of capacitance C1, then a charge -Q accumulates on the other electrode to balance it out. Consequently, a charge +Q also accumulates on one electrode of capacitance C2, and a charge -Q accumulates on the other electrode. In other words, the same charge accumulates in capacitors C1 and C2. Here, according to Coulomb's law, the strength E of the electric field created by a point charge Q at a point at a distance r is E = Q / 4πε0ε r r 2 This is expressed as follows: Relative permittivity ε when the piezoelectric layer 14 is a lithium tantalate layer r It is approximately 43, and the relative permittivity ε when the second layer 34 is a silicon oxide film r The value is approximately 3.8. Therefore, the electric field in the second layer 34 is about 11 times stronger than that in the piezoelectric layer 14. For this reason, in Figure 7, it is thought that the electric field is concentrated in the second layer 34 near the end of the portion of the uppermost layer 32a that protrudes from the lower electrode 12. Dielectric breakdown may occur due to the concentration of the electric field in the second layer 34.

[0044] In Example 1 and its modified form, the length L1 (first length) of the uppermost layer 32a metal film 36 in the first extraction region 52 is shorter than the length L2 (second length) in the second extraction region 54. As a result, the area in the first extraction region 52 where the uppermost layer 32a metal film 36 and the upper electrode 16 face each other is reduced, thereby reducing the electric field strength and suppressing dielectric breakdown. In addition, by increasing the length L2 of the uppermost layer 32a metal film 36 in the second extraction region 54, elastic waves leaking obliquely from the resonance region 50 can be effectively reflected by the acoustic reflective film 30.

[0045] Furthermore, in Example 1 and Modification 2 of Example 1, the end face 33 of the uppermost layer 32a metal film 36 is located at the boundary between the resonance region 50 and the first extraction region 52. This suppresses the opposition between the uppermost layer 32a metal film 36 and the upper electrode 16 in the first extraction region 52, thereby reducing the electric field strength and suppressing the occurrence of dielectric breakdown. The statement that the end face 33 is located at the boundary between the resonance region 50 and the first extraction region 52 means that it is acceptable if the end face 33 is shifted from the boundary towards the resonance region 50 side or the first extraction region 52 side by an amount equivalent to manufacturing tolerance.

[0046] Furthermore, in Example 1 and its modified form, the second layer 34, made of insulating material, is in contact with and covers the end face 33 of the metal film 36 of the uppermost layer 32a in the first lead-out region 52. Since capacitance is unlikely to occur between the second layer 34 and the upper electrode 16, dielectric breakdown can be suppressed.

[0047] Furthermore, in Example 1 and its modified version, the piezoelectric layer 14 is a lithium tantalate layer or a lithium niobate layer. Because the lithium tantalate layer and the lithium niobate layer have relatively high relative permittivity, the electric field strength in the second layer 34 increases due to the mechanism shown in Figures 8(a) and 8(b), making dielectric breakdown more likely. However, as in Example 1 and its modified version, by making the length L1 in the first extraction region 52 of the metal film 36 of the uppermost layer 32a shorter than the length L2 in the second extraction region 54, dielectric breakdown can be suppressed even when a lithium tantalate layer or a lithium niobate layer is used for the piezoelectric layer 14. [Examples]

[0048] Figure 9(a) is a plan view of the elastic wave device according to Example 2, and Figure 9(b) is a cross-sectional view AA of Figure 9(a). As shown in Figures 9(a) and 9(b), in the elastic wave device 200 according to Example 2, the first layer 32 of the acoustic reflective film 30 is formed of a metal film 36 and an insulating film 38. The metal films 36 of the uppermost layer 32a and the lower layer 32b are provided in the resonance region 50 and the second extraction region 54, as in Example 1, but not in the first extraction region 52. The end faces 33 of the metal films 36 of the uppermost layer 32a and the lower layer 32b are located at the boundary between the resonance region 50 and the first extraction region 52.

[0049] The insulating films 38 of the uppermost layer 32a and the lower layer 32b are provided in the first extraction region 52, in contact with the end faces 33 of the metal films 36 of the uppermost layer 32a and the lower layer 32b, respectively. Therefore, in the first extraction region 52, the insulating film 38 of the uppermost layer 32a faces the upper electrode 16 with the second layer 34 and the piezoelectric layer 14 in between. In the uppermost layer 32a, the length L5 of the insulating film 38 from the resonance region 50 in the first extraction region 52 is approximately the same as the length L2 of the metal film 36 from the resonance region 50 in the second extraction region 54. Similarly, in the lower layer 32b, the length L6 of the insulating film 38 from the resonance region 50 in the first extraction region 52 is approximately the same as the length L4 of the metal film 36 from the resonance region 50 in the second extraction region 54. Lengths L5 and L6 are approximately the same. The other configurations of Example 2 are the same as in Example 1, so their description is omitted.

[0050] The metal film 36 is formed from a metal material as exemplified in Table 1, for example. The insulating film 38 is formed from an insulating material with a higher acoustic impedance than the second layer 34. For example, the insulating film 38 is a film mainly composed of zinc oxide (ZnO), hafnium oxide (HfO2), hafnium nitride (HfN), aluminum nitride (AlN), tantalum oxide (Ta2O5), aluminum oxide (Al2O3), or silicon carbide. The physical properties of each material are shown in Table 2. The physical properties of silicon oxide (SiO2) used in the second layer 34 are listed in Table 1. [Table 2]

[0051] From the viewpoint of making the first layer 32 a film with high acoustic impedance, the insulating film 38 is preferably a film mainly composed of ZnO, HfO2, HfN, AlN, or Ta2O5 from the above materials, and is more preferably a film mainly composed of HfO2 or HfN.

[0052] [Differentiation] Figure 10(a) is a cross-sectional view of the elastic wave device according to Modification 1 of Example 2, and Figure 10(b) is a cross-sectional view of the elastic wave device according to Modification 2 of Example 2. Figure 11 is a cross-sectional view of the elastic wave device according to Modification 3 of Example 2. As shown in Figure 10(a), in the elastic wave device 210 according to Modification 1 of Example 2, the uppermost layer 32a is formed by a metal film 36 provided in the resonance region 50 and the second extraction region 54, and an insulating film 38 provided in the first extraction region 52, just as in Example 2. The lower layer 32b is formed only by the metal film 36 provided in the resonance region 50, the first extraction region 52, and the second extraction region 54. The other components are the same as in Example 2, so their description is omitted.

[0053] As shown in Figure 10(b), in the elastic wave device 220 according to the modified example 2 of Example 2, the uppermost layer 32a and the lower layer 32b are formed by a metal film 36 provided in the resonant region 50 and an insulating film 38 provided in the first extraction region 52 and the second extraction region 54. The other configurations are the same as in Example 2, so their description is omitted.

[0054] As shown in Figure 11, in the elastic wave device 230 according to the modified example 3 of Example 2, the uppermost layer 32a and the lower layer 32b are formed by a metal film 36 provided in the resonant region 50 and an insulating film 38 provided in the first extraction region 52 and the second extraction region 54. The insulating film 38 provided in the first extraction region 52 and the second extraction region 54 extends to the edges of the piezoelectric layer 14. The other configurations are the same as in Example 1, so their description is omitted.

[0055] [simulation] For Example 2 and Modification 1 of Example 2, the electric field distribution generated when high-frequency power is applied between the lower electrode 12 and the upper electrode 16 was simulated. The simulation conditions were as follows. Common conditions Substrate 10: Silicon substrate Metal film 36 of the first layer 32: Tungsten film with a thickness of 152 nm Insulating film 38 of the first layer 32: Zinc oxide film with a thickness of 152 nm Second layer 34: Silicon oxide film with a thickness of 194 nm Lower electrode 12: Aluminum film with a thickness of 46 nm Piezoelectric layer 14: A lithium niobate layer with a thickness of 460 nm, where the vibration direction of the thickness-slip vibration is the Y direction. Upper electrode 16: Aluminum film with a thickness of 46 nm Wavelength of elastic waves λ: 920 μm Conditions in the X direction: The width of the resonant region 50 in the X direction is 27λ Conditions in the Y direction: The width of the resonant region 50 in the Y direction is 0.5λ, and the boundary conditions are infinitely continuous. Conditions for Example 2 Lengths L1, L3 (see Figure 9(b)): 0 nm Lengths L2, L4, L5, L6 (see Figure 9(b)): 1000 nm Conditions for Modification 1 of Example 2 Length L1 (see Figure 10(a)): 0 nm Lengths L2, L3, L4, L5 (see Figure 10(a)): 1000 nm

[0056] Figures 12(a) and 12(b) show the simulation results of the electric field distribution for Example 2 and Modification 1 of Example 2. As shown in Figures 12(a) and 12(b), in both Example 2 and Modification 1 of Example 2, the electric field strength generated in the second layer 34 was reduced. This is thought to be because, in the portion of the uppermost layer 32a that protrudes from the lower electrode 12, the insulating film 38 faces the upper electrode 16 with the second layer 34 and piezoelectric layer 14 in between. Also, as shown in Figure 12(b), since the lower layer 32b is far from the upper electrode 16, even if the metal film 36 faces the upper electrode 16 in the portion of the lower layer 32b that protrudes from the lower electrode 12, the electric field strength was reduced.

[0057] Next, the admittance characteristics were simulated for the Comparative Example and Example 2. The simulation conditions for the Comparative Example and Example 2 were the same as those for the simulations in Figures 7 and 12(a). Figures 13(a) and 13(b) show the simulation results of admittance |Y| against frequency for the Comparative Example and Example 2. As shown in Figures 13(a) and 13(b), ΔY, which is the difference between the absolute value of admittance |Y| at the resonant frequency fr and the absolute value of admittance |Y| at the anti-resonant frequency fa, was 74.47 dB for the Comparative Example and 74.78 dB for Example 2. Thus, even when an insulating film 38 was provided instead of the metal film 36, ΔY remained almost unchanged, and in fact increased slightly.

[0058] Similarly, the admittance characteristics were simulated for Modification 2 and Modification 3 of Example 2 to determine ΔY. The ΔY for Modification 2 of Example 2 was 74.75 dB, and the ΔY for Modification 3 of Example 2 was 74.46 dB.

[0059] Next, using models A and B, we simulated the relationship between the length of the first layer of the acoustic reflective film that protrudes from the resonance region and ΔY. Figures 14(a) and 14(b) are cross-sectional views showing parts of models A and B used in the simulation. In model A shown in Figure 14(a), the lengths L protruding from the resonance region 50 of the uppermost layer 32a and the lower layer 32b were made the same. In model B shown in Figure 14(b), the lower layer 32b was configured to protrude from the resonance region 50 by λ longer than the uppermost layer 32a. The simulation conditions are as follows. Substrate 10: Silicon substrate Top layer 32a, bottom layer 32b: Tungsten film with a thickness of 152 nm Second layer 34: Silicon oxide film with a thickness of 194 nm Lower electrode 12: Aluminum film with a thickness of 46 nm Piezoelectric layer 14: A lithium niobate layer with a thickness of 460 nm, where the vibration direction of the thickness-slip vibration is the Y direction. Upper electrode 16: Aluminum film with a thickness of 46 nm Length L: 0nm to 2000nm Wavelength of elastic waves λ: 920 μm Conditions in the X direction: The width of the resonant region 50 in the X direction is 27λ Conditions in the Y direction: The width of the resonant region 50 in the Y direction is 0.5λ, and the boundary conditions are infinitely continuous.

[0060] Figure 15 shows the simulation results of ΔY with respect to the length of the first layer of the acoustic reflective film for models A and B. As shown in Figure 15, for both models A and B, the decrease in ΔY was suppressed by setting the length L to λ (920 nm) or more. From these results, it is desirable that in Example 1 and its modified form, and in Example 2 and its modified form, the lengths L2 and L4 of the first layer 32 that protrude from the resonance region 50 to the second extraction region 54 be λ or more. The same applies to the length of the first layer 32 that protrudes from the resonance region 50 towards the through hole 22.

[0061] In Example 2 and its modified form, the uppermost layer 32a has a metal film 36 provided in the resonance region 50 and an insulating film 38 provided in the first extraction region 52 in contact with the end face 33 of the metal film 36. The insulating film 38 is made of an insulating material with a higher acoustic impedance than the second layer 34. As a result, in the first extraction region 52 of the uppermost layer 32a, the insulating film 38 faces the upper electrode 16, so as shown in Figures 12(a) and 12(b), the electric field strength can be reduced and the occurrence of dielectric breakdown can be suppressed. Furthermore, since the first extraction region 52 is provided with an insulating film 38 with a higher acoustic impedance than the second layer 34, elastic waves leaking obliquely from the resonance region 50 can be effectively reflected by the acoustic reflective film 30 compared to Example 1. The reason why both the uppermost layer 32a and the lower layer 32b have a metal film 36 in the resonance region 50 is to make the film high impedance in the resonance region 50 for the reflection of elastic waves. [Examples]

[0062] Figure 16 is a cross-sectional view of the elastic wave device according to Example 3. As shown in Figure 16, in the elastic wave device 300 according to Example 3, similar to Modification 2 of Example 1 shown in Figure 5(b), the uppermost layer 32a is provided in the resonance region 50 and the second extraction region 54 but not in the first extraction region 52, and the lower layer 32b is provided in the resonance region 50, the first extraction region 52 and the second extraction region 54. The difference from Modification 2 of Example 1 is that a gap 39 in contact with the end face 33 of the metal film 36 of the uppermost layer 32a is provided in the first extraction region 52. The other configurations are the same as in Example 1, so their explanation is omitted.

[0063] For Example 3, a simulation similar to the admittance characteristic simulation performed for Example 2 and its modified version was performed to determine ΔY, and the ΔY for Example 3 was 72.31 dB.

[0064] In Example 3, a gap 39 in contact with the end face 33 of the uppermost layer 32a metal film 36 is provided in the first extraction region 52. Even in this case, the metal film 36 of the uppermost layer 32a and the upper electrode 16 are prevented from facing each other in the first extraction region 52, thereby reducing the electric field strength and suppressing the occurrence of dielectric breakdown. [Examples]

[0065] Figure 17(a) is a cross-sectional view of the elastic wave device according to Example 4, and Figure 17(b) is a cross-sectional view of the elastic wave device according to Modification 1 of Example 4. Figure 18(a) is a cross-sectional view of the elastic wave device according to Modification 2 of Example 4, and Figure 18(b) is a cross-sectional view of the elastic wave device according to Modification 3 of Example 4. As shown in Figures 17(a) to 18(b), in Example 4 and its modifications, the first layer 32 is formed of a metal film 36, just as in Example 1. Also, the uppermost layer 32a and the lower layer 32b are provided in the resonance region 50, the first extraction region 52, and the second extraction region 54, just as in the comparative example, and their lengths L1 and L3 are the same as lengths L2 and L4.

[0066] As shown in Figure 17(a), in the elastic wave device 400 according to Embodiment 4, an insulating film 18 is provided between the piezoelectric layer 14 and the upper electrode 16 in the first extraction region 52. Because of the insulating film 18, the distance H1 between the uppermost layer 32a and the upper electrode 16 in the first extraction region 52 is longer than the distance H2 between the uppermost layer 32a and the upper electrode 16 in the resonance region 50. The other configurations are the same as in Embodiment 1, so their description is omitted.

[0067] As shown in Figure 17(b), in the elastic wave device 410 according to Modification 1 of Example 4, the piezoelectric layer 14 is thicker in the first extraction region 52 and the second extraction region 54 than in the resonance region 50. Therefore, the distance H1 between the uppermost layer 32a and the upper electrode 16 in the first extraction region 52 is longer than the distance H2 between the uppermost layer 32a and the upper electrode 16 in the resonance region 50. The other configurations are the same as in Example 1, so their description is omitted.

[0068] As shown in Figure 18(a), in the elastic wave device 420 according to the modified example 2 of Embodiment 4, both the uppermost layer 32a and the lower layer 32b are shifted toward the substrate 10 side in the first extraction region 52 relative to the portion 37 formed in the resonance region 50. The portion 35 is shifted toward the substrate 10 side by, for example, more than 1 / 4 and less than 1 / 2 of the thickness of the first layer 32 relative to the portion 37. Therefore, the distance H1 between the uppermost layer 32a and the upper electrode 16 in the first extraction region 52 is longer than the distance H2 between the uppermost layer 32a and the upper electrode 16 in the resonance region 50. The other configurations are the same as in Embodiment 1, so their description is omitted.

[0069] As shown in Figure 18(b), in the elastic wave device 430 according to Modification 3 of Example 4, the uppermost layer 32a and lower layer 32b have a tapered shape such that the thickness of the portion 35 formed in the first extraction region 52 decreases as it moves away from the resonance region 50. Therefore, the distance H1 between the uppermost layer 32a and the upper electrode 16 in the first extraction region 52 is longer than the distance H2 between the uppermost layer 32a and the upper electrode 16 in the resonance region 50. The other configurations are the same as in Example 1, so their description is omitted.

[0070] In Example 4 and its modified form, the distance H1 between the uppermost layer 32a and the upper electrode 16 in the first extraction region 52 is longer than the distance H2 between the uppermost layer 32a and the upper electrode 16 in the resonance region 50. As a result, the capacitance between the metal film 36 of the uppermost layer 32a and the upper electrode 16 in the first extraction region 52 is reduced, which reduces the electric field strength and suppresses the occurrence of dielectric breakdown.

[0071] In Example 4 and its Modification 1, the distance from the surface in contact with the lower electrode 12 of the piezoelectric layer 14 to the upper electrode 16 is longer in the first extraction region 52 than in the resonance region 50. This makes it possible to obtain a configuration in which the distance H1 between the uppermost layer 32a and the upper electrode 16 in the first extraction region 52 is longer than the distance H2 between the uppermost layer 32a and the upper electrode 16 in the resonance region 50.

[0072] In modified examples 2 and 3 of Example 4, the distance from the uppermost layer 32a to the piezoelectric layer 14 is longer in the first extraction region 52 than in the second extraction region 54. This makes it possible to obtain a configuration in which the distance H1 between the uppermost layer 32a and the upper electrode 16 in the first extraction region 52 is longer than the distance H2 between the uppermost layer 32a and the upper electrode 16 in the resonance region 50.

[0073] Furthermore, at least two configurations from Example 4, Modification 1 of Example 4, Modification 2 of Example 4, and Modification 3 of Example 4 may be combined. [Examples]

[0074] Figure 19 is a circuit diagram of the filter according to Example 5. As shown in Figure 19, the filter 500 according to Example 5 has one or more series resonators S1 to S4 connected in series between the input terminal Tin and the output terminal Tout. One or more parallel resonators P1 to P4 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 P4 may be an elastic wave device from Example 1, a modified example of Example 1, Example 2, a modified example of Example 2, Example 3, Example 4, and a modified example of Example 4. The number of series and parallel resonators can be set as appropriate. A ladder filter is shown as an example of the filter, but a multimode filter may also be used. [Examples]

[0075] Figure 20 is a circuit diagram of a duplexer according to Example 6. As shown in Figure 20, the duplexer 600 according to Example 6 has a transmit filter 70 connected between the common terminal Ant and the transmit terminal Tx. A receive filter 72 is connected between the common terminal Ant and the receive terminal Rx. The transmit filter 70 allows the transmit band signal from the high-frequency signal input from the transmit terminal Tx to pass to the common terminal Ant as the transmit signal, and suppresses signals of other frequencies. The receive filter 72 allows the receive band signal from the high-frequency signal input from the common terminal Ant to pass to the receive terminal Rx as the receive signal, and suppresses signals of other frequencies. At least one of the transmit filter 70 and the receive filter 72 can be the filter of Example 5. A duplexer is shown as an example of a multiplexer, but a triplexer or quadplexer may also be used.

[0076] Although embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Explanation of Symbols]

[0077] 10…Substrate, 12…Lower electrode, 14…Piezoelectric layer, 16…Upper electrode, 18…Insulating film, 22…Through hole, 30…Acoustic reflective film, 32…First layer, 32a…Uppermost layer, 32b…Lower layer, 33…End face, 34…Second layer, 35…Part, 36…Metal film, 37…Part, 38…Insulating film, 39…Gap, 50…Resonance region, 52…First extraction region, 54…Second extraction region, 70…Transmitting filter, 72…Receiving filter, 100, 110, 120, 200, 210, 220, 230, 300, 400, 410, 420, 430, 1000…Elastic wave device, 500…Filter, 600…Duplexer

Claims

1. circuit board and A piezoelectric layer provided on the substrate, A lower electrode and an upper electrode are provided on the substrate with at least a portion of the piezoelectric layer in between, An elastic wave device comprising: one or more first layers provided between the substrate and the lower electrode, each containing a metal film that includes a resonant region where the lower electrode and the upper electrode overlap with the piezoelectric layer in between, and at least a portion of which is provided outside the resonant region; and one or more second layers made of an insulating material having different acoustic properties from the one or more first layers, which are alternately laminated, wherein the metal film included in at least the uppermost layer of the one or more first layers closest to the piezoelectric layer is an acoustic reflective film in which the first length from the resonant region in the first extraction region where the upper electrode is drawn out from the resonant region is shorter than the second length from the resonant region in the second extraction region where the lower electrode is drawn out from the resonant region.

2. The elastic wave device according to claim 1, wherein the end face of the metal film included in the uppermost layer closest to the piezoelectric layer, on the first extraction region side, is located at the boundary between the resonance region and the first extraction region.

3. The elastic wave device according to claim 1 or 2, wherein the one or more second layers cover the end face of the metal film included in the uppermost layer closest to the piezoelectric layer in the first extraction region while in contact with it.

4. The elastic wave device according to claim 1 or 2, wherein the uppermost layer closest to the piezoelectric layer includes the metal film provided in the resonant region and an insulating film provided in the first extraction region in contact with the end face of the metal film, and made of another insulating material having a higher acoustic impedance than the insulating material.

5. The insulating material is silicon oxide, The elastic wave device according to claim 4, wherein the other insulating material is zinc oxide, hafnium oxide, hafnium nitride, aluminum nitride, tantalum oxide, aluminum oxide, or silicon carbide.

6. The elastic wave device according to claim 1 or 2, wherein a void in contact with the end face of the metal film included in the uppermost layer closest to the piezoelectric layer is formed in the first extraction region.

7. circuit board and A piezoelectric layer provided on the substrate, A lower electrode and an upper electrode are provided on the substrate with at least a portion of the piezoelectric layer in between, An elastic wave device comprising: an acoustic reflective film provided between the substrate and the lower electrode, comprising one or more first layers made of a metallic material provided outside the resonance region and a resonance region where the lower electrode and the upper electrode overlap with the piezoelectric layer in between, and one or more second layers made of an insulating material having different acoustic properties from the one or more first layers, wherein the distance between the uppermost layer closest to the piezoelectric layer and the upper electrode is longer in the first extraction region where the upper electrode is drawn out from the resonance region than in the resonance region.

8. The elastic wave device according to claim 7, wherein the distance from the surface of the piezoelectric layer in contact with the lower electrode to the upper electrode is longer in the first extraction region than in the resonant region.

9. The elastic wave device according to claim 7 or 8, wherein the distance from the uppermost layer closest to the piezoelectric layer to the piezoelectric layer is longer in the first extraction region than in the second extraction region from which the lower electrode is drawn out from the resonant region.

10. The elastic wave device according to claim 1 or 7, wherein the piezoelectric layer is a lithium tantalate layer or a lithium niobate layer.

11. A filter comprising the elastic wave device according to claim 1 or 7.

12. A multiplexer comprising the filter described in claim 11.

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