Elastic wave devices, filters, and multiplexers

Abstract

To provide an elastic wave device capable of improving an electromechanical coupling coefficient.SOLUTION: An acoustic wave device includes a substrate, a lower electrode provided on the substrate, a piezoelectric layer that is provided on the lower electrode, and is a single-crystal lithium niobate layer, and in which the Euler angle when the directions perpendicular to each other in the plane direction of the top surface are the X and Y directions, and the normal direction of the top surface is the Z direction in a right-handed XYZ coordinate system is (0°±5°, 105°±5°, 11° to 28°), or (90°±5°, 105°±5°, 11°to 28°), and an upper electrode provided on the piezoelectric layer so as to form a resonant region facing the lower electrode with the piezoelectric layer in between.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] As filters and duplexers for high-frequency circuits of wireless terminals such as mobile phones, filters and duplexers using piezoelectric thin-film resonators are known. Piezoelectric thin-film resonators include FBAR (Film Bulk Acoustic Resonator) type and SMR (Solidly Mounted Resonator) type. The FBAR type piezoelectric thin-film resonator includes a piezoelectric layer, a lower electrode, and an upper electrode sandwiching the piezoelectric layer on a substrate, and a gap is formed between the substrate and the lower electrode in a region where the lower electrode and the upper electrode face each other with the piezoelectric layer interposed therebetween. The SMR type piezoelectric thin-film resonator is provided with an acoustic reflection film in which high and low acoustic impedance films are alternately laminated instead of the gap. The region where the lower electrode and the upper electrode face each other with the piezoelectric layer interposed therebetween is a resonance region where elastic waves resonate.

[0003] It is known to use a lithium niobate layer or a lithium tantalate layer for the piezoelectric layer. In this case, in order to obtain a high Q value, it is known to set the Euler angle of the lithium niobate layer or the lithium tantalate layer within a specific angle range (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, there has been a strong demand for higher performance filters, such as wider bandwidth filter characteristics. Wider bandwidth filter characteristics can be achieved by using elastic wave devices with large electromechanical coupling coefficients.

[0006] This invention has been made in view of the above problems, and aims to improve the electromechanical coupling coefficient. [Means for solving the problem]

[0007] The present invention comprises a substrate, a lower electrode provided on the substrate, and a single-crystal lithium niobate layer provided on the lower electrode, wherein the Euler angles when the directions perpendicular to each other in the plane direction of the upper surface are defined as the X and Y directions and the normal direction of the upper surface is defined as the Z direction are (0°±5°, 105°±5°, 11°~28°) )in This elastic wave device comprises a piezoelectric layer and an upper electrode provided on the piezoelectric layer such that it forms a resonant region facing the lower electrode, with the piezoelectric layer in between.

[0008] In the above configuration, an acoustic reflective film is provided between the substrate and the lower electrode in the resonance region, and the Euler angle of the piezoelectric layer is (0°±5°, 105°±5°, 11°~23°). )in It can be configured in a certain way.

[0009] In the above configuration, the Euler angle of the piezoelectric layer is (0°±5°, 105°±5°, 11°~17° )in It can be configured in a certain way.

[0010] In the above configuration, in the resonance region, the lower electrode is provided on the substrate with an air gap between it and the substrate, and the Euler angle of the piezoelectric layer is (0°±5°, 105°±5°, 11°~21° )in It can be configured in a certain way.

[0011] In the above configuration, the Euler angle of the piezoelectric layer is (0°±5°, 105°±5°, 11°~16° )in It can be configured in a certain way.

[0012] In the above configuration, the lower electrode and the upper electrode can be configured to be a film containing aluminum.

[0013] The present invention is a filter that includes the elastic wave device described above.

[0014] The present invention is a multiplexer comprising the filter described above. [Effects of the Invention]

[0015] According to the present invention, the electromechanical coupling coefficient can be improved. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1(a) is a plan view of the elastic wave device according to Example 1, and Figure 1(b) is a cross-sectional view AA of Figure 1(a). [Figure 2] Figures 2(a) to 2(c) illustrate the crystal orientation of the piezoelectric layer, which is expressed in Euler angles as (0°, 105°, 11°~28°). [Figure 3] Figures 3(a) to 3(d) illustrate the crystal orientation of the piezoelectric layer, which is expressed in Euler angles as (90°, 105°, 11°~28°). [Figure 4] Figures 4(a) and 4(b) show the simulation results of the real part Real(Y) and absolute value |Y| of the admittance as a function of frequency for the elastic wave device according to Example 1. [Figure 5] Figure 5 shows the simulation results of the electromechanical coupling coefficient k2 and spurious intensity with respect to the Euler angle γ of a piezoelectric layer whose crystal orientation is represented by the Euler angles (0°, 105°, γ) in Example 1. [Figure 6] Figure 6 is a cross-sectional view of the elastic wave device according to Example 2. [Figure 7]FIG. 7 shows the simulation results of the electromechanical coupling coefficient k2 and the spurious intensity with respect to the Euler angle γ of the piezoelectric layer whose crystal orientation is represented by the Euler angles (90°, 105°, γ) in Example 2. [Figure 8] FIG. 8 shows the simulation results of the electromechanical coupling coefficient k2 and the spurious intensity with respect to the Euler angle γ of the piezoelectric layer whose crystal orientation is represented by the Euler angles (0°, 105°, γ) in Example 2. [Figure 9] FIG. 9 is a circuit diagram of the filter according to Example 3. [Figure 10] FIG. 10 is a block diagram of the duplexer according to Example 4.

Embodiments for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Examples

[0018] FIG. 1(a) is a plan view of the elastic wave device 100 according to Example 1, and FIG. 1(b) is a cross-sectional view taken along the line A-A of FIG. 1(a). In FIG. 1(a), for clarity of the figure, the additional film 28 is hatched. As shown in FIGS. 1(a) and 1(b), the elastic wave device 100 is a piezoelectric thin film resonator, in which an acoustic reflection film 31 is provided on a substrate 10, and a piezoelectric layer 14 is provided on the acoustic reflection film 31. The upper and lower surfaces of the piezoelectric layer 14 are substantially flat. An upper electrode 16 and a lower electrode 12 are provided above and below the piezoelectric layer 14. The region where at least a part of the piezoelectric layer 14 is sandwiched and the lower electrode 12 and the upper electrode 16 overlap in a plan view is the resonance region 50.

[0019] The planar shape of the resonance region 50 is substantially rectangular. The rectangle has four substantially straight sides. The extending directions of the four sides are defined as the X direction and the Y direction. The direction in which the acoustic reflection film 31, the lower electrode 12, the piezoelectric layer 14, and the upper electrode 16 are stacked is defined as the Z direction.

[0020] 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, vibrating in a direction where the displacement of the elastic wave intersects the Z direction (i.e., the strain direction relative to the thickness direction). This vibration is called thickness-slip vibration. The direction in which the displacement of the thickness-slip vibration is greatest (the direction of displacement of the thickness-slip vibration) is defined as the thickness-slip vibration direction 60. For example, the thickness-slip vibration direction 60 is a direction slightly tilted from the Y direction to the Z direction. The wavelength of the elastic wave is approximately twice the thickness of the piezoelectric layer 14. The lower electrode 12 and the upper electrode 16 are drawn out of the resonant region 50 in a direction intersecting (e.g., perpendicular to) the thickness-slip vibration direction 60.

[0021] The resonant region 50 has a central region 54 and edge regions 52 on both sides of the central region 54 in the X direction. The edge regions 52 extend almost in the Y direction. The width of the edge region 52 in the X direction is almost constant in the Y direction. An additional film 28 is provided on the upper electrode 16 of the edge region 52. The additional film 28 is not provided in the central region 54 of the resonant region 50, which is sandwiched between the edge regions 52.

[0022] The thicknesses of the added film 28, upper electrode 16, piezoelectric layer 14, and lower electrode 12 are T28, T16, T14, and T12, respectively.

[0023] The acoustic reflective film 31 is constructed by alternately laminating films 31b with low acoustic impedance and films 31a with high acoustic impedance. The film thickness of the high-acoustic-impedance film 31a and the low-acoustic-impedance film 31b is, for example, approximately λ / 4 (where λ is the wavelength of an elastic wave). As a result, the acoustic reflective film 31 reflects elastic waves. The number of layers of the high-acoustic-impedance film 31a and the low-acoustic-impedance film 31b can be set arbitrarily. The acoustic reflective film 31 only needs to consist of at least two layers with different acoustic properties. Alternatively, the substrate 10 may be one of the at least two layers with different acoustic properties of the acoustic reflective film 31. For example, the acoustic reflective film 31 may be configured such that the substrate 10 contains one layer with a different acoustic impedance. In a plan view, the acoustic reflective film 31 overlaps the resonance region 50, and the acoustic reflective film 31 is the same size as or larger than the resonance region 50.

[0024] 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 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 additional film 28 is a metal film as exemplified in the lower electrode 12 and upper electrode 16, or an insulating film such as a silicon oxide film, silicon nitride film, aluminum oxide film, tantalum oxide film, or niobium oxide film. The material of the additional film 28 may be the same as or different from the material of the lower electrode 12 and upper electrode 16.

[0025] The piezoelectric layer 14 is a single-crystal lithium niobate layer. The crystal orientation of the piezoelectric layer 14 is (0°±5°, 105°±5°, 11°~28°) or (90°±5°, 105°±5°, 11°~28°) in Euler angle notation. The reason for using these angles for the Euler angles will be explained later.

[0026] The Euler angles (α, β, γ) are defined as follows. In a right-handed XYZ coordinate system, the normal direction to the upper surface of the piezoelectric layer 14 is defined as 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 defined as the X and Y directions. First, the X, Y, and Z directions are defined as the X-axis, Y-axis, and Z-axis directions of the crystal orientation, respectively. Next, the crystal is rotated α from the +X-axis direction to the +Y-axis direction around the Z-axis direction. After the α rotation, the crystal is rotated β from the +Y-axis direction to the +Z-axis direction around the X-axis direction. After the β rotation, the crystal is rotated γ from the +X-axis direction to the +Y-axis direction around the Z-axis direction. The Euler angles of the crystal obtained by rotating the crystal orientation in this way are (α, β, γ). In this embodiment, α, β, and γ are expressed using values ​​from 0° to 180°, but the Euler angles expressed using (α, β, γ) include equivalent Euler angles.

[0027] The crystal orientation of the piezoelectric layer 14, whose Euler angles are expressed as (0°, 105°, 11°~28°), will be explained using Figures 2(a) to 2(c). Figures 2(a) to 2(c) show the lower electrode 12, the piezoelectric layer 14, and the upper electrode 16. As shown in Figure 2(a), the +X direction, +Y direction, and +Z direction 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 2(b), from the state in Figure 2(a), the +Y axis direction and +Z axis direction are rotated by 105° from the +Y axis direction to the +Z axis direction, centered on the X axis direction. Next, as shown in Figure 2(c), from the state in Figure 2(b), the +X axis direction and +Y axis direction are rotated by 11°~28° from the +X axis direction to the +Y axis direction, centered on the Z axis direction. When rotated in this way, the +Z direction becomes the direction obtained by rotating the +Z axis direction by 105°. Since the direction perpendicular to the X-axis of the piezoelectric layer 14's crystal orientation is the direction of thickness-slip vibration 60, the direction tilted 11° to 28° in the Z-direction relative to the Y-direction is the direction of thickness-slip vibration 60. In Euler angles, this corresponds to (0°, 105°, 11° to 28°).

[0028] From the perspective of exciting the piezoelectric layer 14 with thickness-sliding vibrations, the X-axis direction of the crystal orientation is preferably within ±5° from the +X direction and the plane direction of the upper surface of the piezoelectric layer 14, and preferably within ±1°. The +Z direction is preferably within ±5° from the direction rotated 105° from the +Z axis direction, and preferably within ±1°. Therefore, the crystal orientation of the piezoelectric layer 14 is (0°±5°, 105°±5°, 11°~28°).

[0029] Figures 3(a) to 3(d) illustrate the crystal orientation of the piezoelectric layer 14, whose Euler angles are expressed as (90°, 105°, 11°~28°). Figures 3(a) to 3(d) show the lower electrode 12, the piezoelectric layer 14, and the upper electrode 16. As shown in Figure 3(a), the +X direction, +Y direction, and +Z direction 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 +X axis direction and +Y axis direction are rotated 90° from the +X axis direction to the +Y axis direction around the Z axis direction. As shown in Figure 3(c), from the state in Figure 3(b), the +Y axis direction and +Z axis direction are rotated 105° from the +Y axis direction to the +Z axis direction around the X axis direction. Next, as shown in Figure 3(d), from the state in Figure 3(c), the +X axis and +Y axis are rotated by 11° to 28° from the +X axis to the +Y axis, centered on the Z axis. When rotated in this way, the +Z direction becomes the direction rotated by 105° from the +Z axis. Since the direction perpendicular to the X axis of the crystal orientation of the piezoelectric layer 14 is the direction of thickness shear vibration 60, the direction tilted 11° to 28° in the Z direction with respect to the X direction becomes the direction of thickness shear vibration 60. In Euler angles, this becomes (90°, 105°, 11° to 28°).

[0030] From the perspective of exciting the piezoelectric layer 14 with thickness-sliding vibrations, the X-axis direction of the crystal orientation is preferably within ±5° from the +X direction and the plane direction of the upper surface of the piezoelectric layer 14, and preferably within ±1°. The +Z direction is preferably within ±5° from the direction rotated 105° from the +Z axis direction, and preferably within ±1°. Therefore, the crystal orientation of the piezoelectric layer 14 is (90°±5°, 105°±5°, 11°~28°).

[0031] [simulation] For the elastic wave device 100 of Example 1, a single-crystal lithium niobate layer with a crystal orientation represented by Euler angles (0°, 105°, γ) was used as the piezoelectric layer 14, and simulations were performed to determine the changes in the electromechanical coupling coefficient k2 and spurious intensity by changing the magnitude of γ. The simulation conditions were as follows. Wavelength λ of elastic wave: Thickness T14 × 2 of piezoelectric layer 14 Conditions in the X direction: The width in the X direction is 30λ, and the boundary conditions are infinitely continuous. Conditions in the Y direction: The width of the resonant region 50 in the Y direction is set to 0.5λ. Addition film 28: Silicon oxide film with a thickness T28 of 90 nm Upper electrode 16: Aluminum film with a thickness T16 of 46 nm Piezoelectric layer 14: A single-crystal lithium niobate layer with a thickness T14 of 460 nm and a crystal orientation represented by Euler angles (0°, 105°, γ). Lower electrode 12: Aluminum film with a thickness T12 of 46 nm Acoustically high impedance film 31a: Tungsten film with a thickness of 194 nm Low acoustic impedance film 31b: Silicon oxide film with a thickness of 152 nm Substrate 10: Silicon substrate

[0032] Figures 4(a) and 4(b) show the simulation results of the real part Real(Y) and absolute value |Y| of the admittance of the elastic wave device 100 according to Example 1 as a function of frequency. Figure 4(a) shows the simulation results when a lithium niobate layer with a crystal orientation represented by Euler angles (0°, 105°, 0°) is used as the piezoelectric layer 14. Figure 4(b) shows the simulation results when a lithium niobate layer with a crystal orientation represented by Euler angles (0°, 105°, 20°) is used as the piezoelectric layer 14. Peaks at the resonant frequency fr and anti-resonant frequency fa are observed for admittance |Y|. A larger spurious response is observed for the real part Real(Y) of admittance compared to the absolute value |Y|.

[0033] As shown in Figures 4(a) and 4(b), the frequency interval between the resonant frequency fr and the anti-resonant frequency fa differed when a lithium niobate layer with a crystal orientation represented by Euler angles (0°, 105°, 0°) was used as the piezoelectric layer 14 (Figure 4(a)) and when a lithium niobate layer with a crystal orientation represented by (0°, 105°, 20°) was used as the piezoelectric layer 14 (Figure 4(b)). The difference between the anti-resonant frequency fa and the resonant frequency fr is proportional to the electromechanical coupling coefficient k2. When a lithium niobate layer with a crystal orientation represented by Euler angles (0°, 105°, 0°) was used as the piezoelectric layer 14 (Figure 4(a)), the electromechanical coupling coefficient k2 was 32.63%, and when a lithium niobate layer with a crystal orientation represented by Euler angles (0°, 105°, 20°) was used as the piezoelectric layer 14 (Figure 4(b)), the electromechanical coupling coefficient k2 was 34.94%. From this, it can be considered that when a lithium niobate layer with a crystal orientation represented by Euler angles (0°, 105°, γ) is used as the piezoelectric layer 14, the electromechanical coupling coefficient k2 changes by changing the magnitude of γ.

[0034] Furthermore, spurious emission 40 occurs at frequencies between the resonant frequency fr and the anti-resonant frequency fa. When a lithium niobate layer with a crystal orientation represented by Euler angles (0°, 105°, 20°) is used as the piezoelectric layer 14 (Figure 4(b)), the spurious emission 40 is larger than when a lithium niobate layer with a crystal orientation represented by Euler angles (0°, 105°, 0°) is used as the piezoelectric layer 14 (Figure 4(a)). From this, it is considered that when a lithium niobate layer with a crystal orientation represented by Euler angles (0°, 105°, γ) is used as the piezoelectric layer 14, the magnitude of spurious emission 40 changes by changing the magnitude of γ. In the following, the difference h between the maximum and minimum intensity of spurious emission 40 is defined as the spurious emission intensity.

[0035] Figure 5 shows the simulation results of the electromechanical coupling coefficient k2 and spurious intensity with respect to the Euler angle γ of the piezoelectric layer 14 in Example 1, whose crystal orientation is represented by the Euler angles (0°, 105°, γ). As shown in Figure 5, the electromechanical coupling coefficient k2 was 33.8% when the Euler angle γ was 11°, and 34.93% when the Euler angle γ was 23°, showing almost no decrease up to the Euler angle γ of 23°. When the Euler angle γ was 28°, the electromechanical coupling coefficient k2 was 34.02%, which was similar in magnitude to the electromechanical coupling coefficient k2 when the Euler angle γ was 11°. From this, it can be seen that the electromechanical coupling coefficient k2 can be improved by setting the Euler angle γ to a value within the range of 11° to 28°.

[0036] On the other hand, the spurious intensity of spurious 40 decreases as the Euler angle γ increases between 11° and 14°, reaching its lowest point at 14°, and then increasing as the angle increases beyond 14°. The spurious intensity at an Euler angle γ of 11° was 12.4 dB, and the spurious intensity at an Euler angle γ of 17° was 13.2 dB, which was the same as at an Euler angle γ of 11°. From this, it can be concluded that the increase in spurious intensity can be suppressed by setting the Euler angle γ within the range of 11° to 17°.

[0037] In the above simulation, aluminum films were used for the lower electrode 12 and the upper electrode 16. However, it is believed that the preferred range of the Euler angle γ remains unchanged even when using single-layer films or multilayer films of ruthenium, chromium, aluminum, titanium, copper, molybdenum, tungsten, tantalum, platinum, rhodium, or iridium. [Examples]

[0038] Figure 6 is a cross-sectional view of the elastic wave device 200 according to Example 2. The elastic wave device 200 of Example 2 is a piezoelectric thin-film resonator, just like the elastic wave device 100 of Example 1. As shown in Figure 6, the elastic wave device 200 has a gap 30 instead of an acoustic reflective film 31. The other components are the same as in Example 1, so their description is omitted. In Example 2 as well, the piezoelectric layer 14 is a single-crystal lithium niobate layer whose crystal orientation is expressed in Euler angles as (0°±5°, 105°±5°, 11°~28°) or (90°±5°, 105°±5°, 11°~28°).

[0039] [simulation] For the elastic wave device 200 of Example 2, a single-crystal lithium niobate layer with a crystal orientation represented by Euler angles (0°, 105°, γ) was used as the piezoelectric layer 14, as in Example 1, and simulations were performed to determine the changes in the electromechanical coupling coefficient k2 and spurious intensity by changing the magnitude of γ. Furthermore, simulations were also performed to determine the changes in the electromechanical coupling coefficient k2 and spurious intensity by changing the magnitude of γ when a single-crystal lithium niobate layer with a crystal orientation represented by Euler angles (90°, 105°, γ) was used as the piezoelectric layer 14. The simulation conditions are as follows. Wavelength λ of elastic wave: Thickness T14 × 2 of piezoelectric layer 14 Conditions in the X direction: The width in the X direction is 30λ, and the boundary conditions are infinitely continuous. Conditions in the Y direction: The width of the resonant region 50 in the Y direction is set to 0.5λ. Addition film 28: Silicon oxide film with a thickness T28 of 70 nm Upper electrode 16: Aluminum film with a thickness T16 of 44 nm Piezoelectric layer 14: A single-crystal lithium niobate layer with a thickness T14 of 440 nm and a crystal orientation represented by Euler angles (0°, 105°, γ) or (90°, 105°, γ). Lower electrode 12: Aluminum film with a thickness T12 of 44 nm Substrate 10: Silicon substrate

[0040] Figure 7 shows the simulation results of the electromechanical coupling coefficient k2 and spurious intensity for the piezoelectric layer 14 in Example 2, where the crystal orientation is represented by Euler angles (90°, 105°, γ), with respect to the Euler angle γ. As shown in Figure 7, the electromechanical coupling coefficient k2 is 40.46% when the Euler angle γ is 11°, and 41.82% when the Euler angle γ is 21°, increasing as the angle increases up to 21°. When the Euler angle γ is 28°, the electromechanical coupling coefficient k2 is 40.68%, which is similar in magnitude to the electromechanical coupling coefficient k2 when the Euler angle γ is 11°. From this, it can be seen that the electromechanical coupling coefficient k2 can be improved by setting the Euler angle γ to a value within the range of 11° to 28°.

[0041] On the other hand, the spurious intensity of spurious 40 decreases as the Euler angle γ increases between 11° and 15°, and increases as the angle increases from 15° up to 21°. The spurious intensity at an Euler angle γ of 11° was 19.8 dB, and the spurious intensity at an Euler angle γ of 16° was similar to that at 11°. From this, it can be concluded that the increase in spurious intensity can be suppressed by setting the Euler angle γ within the range of 11° to 16°.

[0042] Figure 8 shows the simulation results of the electromechanical coupling coefficient k2 and spurious intensity for the piezoelectric layer 14 in Example 2, where the crystal orientation is represented by Euler angles (0°, 105°, γ), with respect to the Euler angle γ. As shown in Figure 8, the electromechanical coupling coefficient k2 increases as the angle increases up to Euler angle γ = 21°. The electromechanical coupling coefficient k2 is of similar magnitude when Euler angle γ = 11° and when it is = 28°. From this, it can be seen that the electromechanical coupling coefficient k2 can be improved by setting the Euler angle γ to a value within the range of 11° to 28°.

[0043] On the other hand, the spurious intensity of spurious emission 40 decreases as the Euler angle γ increases between 11° and 14°, and increases as the angle increases from 14° up to 22°. The spurious intensity when the Euler angle γ is 11° was equivalent to the spurious intensity when the Euler angle γ is slightly less than 17°. From this, it can be concluded that the increase in spurious intensity can be suppressed by setting the Euler angle γ to a value within the range of 11° to 16°.

[0044] In the above simulation, aluminum films were used for the lower electrode 12 and the upper electrode 16. However, it is believed that the preferred range of the Euler angle γ remains unchanged even when using single-layer films or multilayer films of ruthenium, chromium, aluminum, titanium, copper, molybdenum, tungsten, tantalum, platinum, rhodium, or iridium.

[0045] In Example 2, the preferred range of Euler angle γ from the viewpoint of electromechanical coupling coefficient k2 and spurious intensity was almost the same in Figure 7, which shows the simulation results when the Euler angle of the crystal orientation of the piezoelectric layer 14 is (90°, 105°, γ), and in Figure 8, which shows the simulation results when it is (0°, 105°, γ). Therefore, in Example 1 as well, the preferred range of the preferred Euler angle γ when the Euler angle of the crystal orientation of the piezoelectric layer 14 is (90°, 105°, γ) is considered to be almost the same as in Figure 5, which shows the simulation results when it is (0°, 105°, γ).

[0046] As described above, in Examples 1 and 2, a single-crystal lithium niobate layer with an Euler angle of (0°±5°, 105°±5°, 11°~28°) or (90°±5°, 105°±5°, 11°~28°) is used for the piezoelectric layer 14. This makes it possible to improve the electromechanical coupling coefficient k2.

[0047] As shown in Figure 5 of Example 1, in the case of a Solidly Mounted Resonator (SMR) type piezoelectric thin-film resonator in which an acoustic reflective film 31 is provided between the substrate 10 and the lower electrode 12 in the resonance region 50, the Euler angle of the single-crystal lithium niobate layer used for the piezoelectric layer 14 is preferably (0°±5°, 105°±5°, 11°~23°), more preferably (0°±5°, 105°±5°, 12°~22°), even more preferably (0°±5°, 105°±5°, 13°~22°), and even more preferably (0°±5°, 105°±5°, 14°~22°). Furthermore, as mentioned above, the preferred range of Euler angle γ when the Euler angle is (90°, 105°, γ) is considered to be approximately the same as that when it is (0°, 105°, γ). Therefore, in terms of improving the electromechanical coupling coefficient k2, the Euler angle of the single-crystal lithium niobate layer used in the piezoelectric layer 14 is preferably (90°±5°, 105°±5°, 11°~23°), more preferably (90°±5°, 105°±5°, 12°~22°), even more preferably (90°±5°, 105°±5°, 13°~22°), and still more preferably (90°±5°, 105°±5°, 14°~22°).

[0048] Furthermore, as shown in Figure 5 of Example 1, in the case of an SMR type piezoelectric thin film resonator, in order to improve the electromechanical coupling coefficient k2 while suppressing an increase in spurious intensity, the Euler angle of the single-crystal lithium niobate layer used in the piezoelectric layer 14 is preferably (0°±5°, 105°±5°, 11°~17°), more preferably (0°±5°, 105°±5°, 12°~16°), even more preferably (0°±5°, 105°±5°, 13°~15°), and even more preferably (0°±5°, 105°±5°, 14°~15°). Also, as mentioned above, the preferred range of Euler angle γ when the Euler angle is (90°, 105°, γ) is considered to be almost the same as when it is (0°, 105°, γ). Therefore, in order to suppress the increase in spurious intensity, the Euler angle of the single-crystal lithium niobate layer used in the piezoelectric layer 14 is preferably (90°±5°, 105°±5°, 11°~17°), more preferably (90°±5°, 105°±5°, 12°~16°), even more preferably (90°±5°, 105°±5°, 13°~15°), and still more preferably (90°±5°, 105°±5°, 14°~15°).

[0049] As shown in Figure 7 of Example 2, in the case of an FBAR (Film Bulk Acoustic Resonator) type piezoelectric thin-film resonator in which a gap 30 is provided between the substrate 10 and the lower electrode 12 in the resonance region 50, the Euler angle of the single-crystal lithium niobate layer used for the piezoelectric layer 14 is preferably (90°±5°, 105°±5°, 11°~21°), more preferably (90°±5°, 105°±5°, 12°~21°), even more preferably (90°±5°, 105°±5°, 13°~21°), and still more preferably (90°±5°, 105°±5°, 14°~21°). Furthermore, as shown in Figure 8 of Example 2, the case of (0°±5°, 105°±5°, 11°~21°) is preferred, the case of (0°±5°, 105°±5°, 12°~21°) is more preferred, the case of (0°±5°, 105°±5°, 13°~21°) is even more preferred, and the case of (0°±5°, 105°±5°, 14°~21°) is even more preferred.

[0050] Furthermore, as shown in Figure 7 of Example 2, in the case of an FBAR type piezoelectric thin film resonator, in order to improve the electromechanical coupling coefficient k2 while suppressing an increase in spurious intensity, the Euler angle of the single-crystal lithium niobate layer used in the piezoelectric layer 14 is preferably (90°±5°, 105°±5°, 11°~16°), more preferably (90°±5°, 105°±5°, 12°~15°), even more preferably (90°±5°, 105°±5°, 13°~15°), and even more preferably (90°±5°, 105°±5°, 14°~15°). Furthermore, as shown in Figure 8 of Example 2, the case of (0°±5°, 105°±5°, 11°~16°) is preferred, the case of (0°±5°, 105°±5°, 12°~15°) is more preferred, the case of (0°±5°, 105°±5°, 13°~15°) is even more preferred, and the case of (0°±5°, 105°±5°, 14°~15°) is even more preferred. [Examples]

[0051] Figure 9 is a circuit diagram of the filter 300 according to Embodiment 3. As shown in Figure 9, the filter 300 has one or more series resonators S1 to S3 connected in series between the input terminal Tin and the output terminal Tout. One or more parallel resonators P1 and P2 are connected in parallel between the input terminal Tin and the output terminal Tout. The parallel resonators P1 and P2 are connected between the path between the input terminal Tin and the output terminal Tout and the ground terminal. Elastic wave devices according to Embodiment 1 or Embodiment 2 can be used for one or more series resonators S1 to S3 and at least one of the one or more parallel resonators P1 and P2. The number of resonators in the ladder-type filter can be set as appropriate. [Examples]

[0052] Figure 10 is a block diagram of the duplexer 400 according to Embodiment 4. As shown in Figure 10, the duplexer 400 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 Embodiment 3. Although a duplexer has been described as an example of a multiplexer, a triplexer or quadplexer may also be used.

[0053] 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]

[0054] 10 circuit boards 12 Lower electrode 14 Piezoelectric layer 16 Upper electrode 28 Addition film 30 void 31 Acoustic reflective film 31a Film with high acoustic impedance 31b Membrane with low acoustic impedance 40 spurious 50 resonance area 52 Edge regions 54 Central area 60 Direction of shear vibration due to thickness 70 Sending Filter 72 Receiving Filter 100, 200 elastic wave devices 300 filters 400 Duplexa S1~S3 Series resonator P1 and P2 parallel resonators

Claims

1. circuit board and The lower electrode provided on the substrate, A piezoelectric layer is provided on the lower electrode, which is a single-crystal lithium niobate layer, and in a right-handed XYZ coordinate system, the Euler angles when the directions perpendicular to each other in the plane direction of the upper surface are the X and Y directions and the normal direction of the upper surface is the Z direction are (0°±5°, 105°±5°, 11° to 28°), An elastic wave device comprising: an upper electrode provided on the piezoelectric layer such as to form a resonant region opposite to the lower electrode, with the piezoelectric layer in between.

2. The resonant region includes an acoustic reflective film provided between the substrate and the lower electrode, The elastic wave device according to claim 1, wherein the Euler angle of the piezoelectric layer is (0°±5°, 105°±5°, 11° to 23°).

3. The elastic wave device according to claim 2, wherein the Euler angle of the piezoelectric layer is (0°±5°, 105°±5°, 11° to 17°).

4. In the aforementioned resonance region, the lower electrode is provided on the substrate with an air gap between it and the substrate. The elastic wave device according to claim 1, wherein the Euler angle of the piezoelectric layer is (0°±5°, 105°±5°, 11° to 21°).

5. The elastic wave device according to claim 4, wherein the Euler angle of the piezoelectric layer is (0°±5°, 105°±5°, 11° to 16°).

6. The elastic wave device according to any one of claims 1 to 5, wherein the lower electrode and the upper electrode are films containing aluminum.

7. A filter comprising an elastic wave device according to any one of claims 1 to 6.

8. A multiplexer comprising the filter described in claim 7.

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