JP7829370B2 - Elastic wave devices, filters, and multiplexers - Google Patents

Description

This invention relates to acoustic wave devices, filters, and multiplexers.

Piezoelectric thin-film resonators are known as filters and duplexers for high-frequency circuits in wireless terminals such as mobile phones. Piezoelectric thin-film resonators include FBAR (Film Bulk Acoustic Resonator) type and SMR (Solidly Mounted Resonator) type. An FBAR type piezoelectric thin-film resonator comprises a piezoelectric layer on a substrate, a lower electrode sandwiching the piezoelectric layer, and an upper electrode. A gap is formed between the substrate and the lower electrode in the region where the lower and upper electrodes face each other across the piezoelectric layer. In an SMR type piezoelectric thin-film resonator, instead of a gap, an acoustic reflective film is provided, consisting of alternating layers of films with high and low acoustic impedance. The region where the lower and upper electrodes face each other across the piezoelectric layer is the resonant region where elastic waves resonate.

It is known that lithium niobate or lithium tantalate layers are used as piezoelectric layers. In this case, to obtain a high Q-factor, it is known that the Euler angle of the lithium niobate or lithium tantalate layer is set within a specific angular range (for example, Patent Document 1).

International Publication No. 2020/203092

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

This invention has been made in view of the above-mentioned problems, and aims to improve the electromechanical coupling coefficient.

The present invention is an elastic wave device comprising: a substrate; a lower electrode provided on the substrate; a piezoelectric layer provided on the lower electrode, which is a single-crystal lithium niobate layer and has Euler angles of (0°±5°, 105°±5°, 11° to 28° ) when the directions of mutual orthogonality in the plane direction of the upper surface in a right-handed XYZ coordinate system are the X and Y directions, and the direction of the normal to the upper surface is the Z direction; 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.

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° to 23° ) .

In the above configuration, the Euler angle of the piezoelectric layer can be set to (0°±5°, 105°±5°, 11° to 17°) .

In the above configuration, the lower electrode is provided on the substrate with an air gap between it and the substrate in the resonance region, and the Euler angle of the piezoelectric layer can be (0°±5°, 105°±5°, 11° to 21° ) .

In the above configuration, the Euler angle of the piezoelectric layer can be set to (0°±5°, 105°±5°, 11° to 16°) .

In the above configuration, the lower electrode and the upper electrode can be configured as a film containing aluminum.

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

The present invention is a multiplexer comprising the filter described above.

According to the present invention, the electromechanical coupling coefficient can be improved.

Figure 1(a) is a plan view of the elastic wave device according to Embodiment 1, and Figure 1(b) is a cross-sectional view taken along line A-A in Figure 1(a). Figures 2(a) to 2(c) illustrate the crystal orientation of the piezoelectric layer, which is expressed in Euler angles as (0°, 105°, 11° to 28°). Figures 3(a) to 3(d) illustrate the crystal orientation of the piezoelectric layer, which is expressed in Euler angles as (90°, 105°, 11° to 28°). Figures 4(a) and 4(b) show the simulation results of the real part (Y) and absolute value |Y| of the admittance as a function of frequency for the elastic wave device according to Example 1. 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 is a cross-sectional view of the elastic wave device according to Example 2. Figure 7 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 Euler angles (90°, 105°, γ) in Example 2. Figure 8 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 2. Figure 9 is a circuit diagram of the filter according to Example 3. Figure 10 is a block diagram of the duplexer according to Example 4.

The following describes embodiments of the present invention with reference to the drawings.

Figure 1(a) is a plan view of the elastic wave device 100 according to Embodiment 1, and Figure 1(b) is a cross-sectional view taken along line A-A in Figure 1(a). In Figure 1(a), hatching is applied to the additional film 28 for clarity. As shown in Figures 1(a) and 1(b), the elastic wave device 100 is a piezoelectric thin-film resonator, with an acoustic reflective film 31 provided on the substrate 10, and a piezoelectric layer 14 provided on the acoustic reflective 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 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 approximately rectangular. The rectangle has four nearly straight sides. The extension directions of the four sides are defined as the X and Y directions. The direction in which the acoustic reflective film 31, lower electrode 12, piezoelectric layer 14, and upper electrode 16 are stacked is defined as the Z direction.

When high-frequency power is applied between the lower electrode 12 and the upper electrode 16, an elastic wave is 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.

The resonant region 50 comprises 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 approximately in the Y direction. The width of the edge region 52 in the X direction is approximately constant in the Y direction. An additional film 28 is provided on the upper electrode 16 of the edge region 52. The central region 54 of the resonant region 50, sandwiched between the edge regions 52, does not have an additional film 28.

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

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-impedance film 31a and the low-impedance film 31b is, for example, approximately λ/4 (where λ is the wavelength of the elastic wave). This allows the acoustic reflective film 31 to reflect elastic waves. The number of layers of the high-impedance film 31a and the low-impedance film 31b can be arbitrarily set. The acoustic reflective film 31 only needs to consist of at least two layers with different acoustic properties. Furthermore, 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.

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 single-layer films or multilayer films thereof, such as 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 an insulating film such as the metal films exemplified for the lower electrode 12 and upper electrode 16, or 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.

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 will be explained later.

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.

The crystal orientation of the piezoelectric layer 14, whose Euler angles are expressed as (0°, 105°, 11° to 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° to 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°).

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 towards the plane 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°).

The crystal orientation of the piezoelectric layer 14, whose Euler angles are expressed as (90°, 105°, 11° to 28°), will be explained using Figures 3(a) to 3(d). 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 by 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 by 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 and +Y axes are rotated by 11° to 28° from the +X axis to the +Y axis, centered on the Z axis. With this rotation, the +Z direction becomes the direction rotated 105° from the +Z axis. Since the direction perpendicular to the X axis of the piezoelectric layer 14's crystal orientation is the direction of thickness shear vibration 60, the direction tilted 11° to 28° in the Z direction relative to the X direction becomes the direction of thickness shear vibration 60. In Euler angles, this corresponds to (90°, 105°, 11° to 28°).

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 towards 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°).

[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: Single crystal lithium niobate layer with a thickness T14 of 460 nm and a crystal orientation expressed as Euler angles (0°, 105°, γ) Lower electrode 12: Aluminum film with a thickness T12 of 46 nm Film with high acoustic impedance 31a: Tungsten film with a thickness of 194 nm Film with low acoustic impedance 31b: Silicon oxide film with a thickness of 152 nm Substrate 10: Silicon substrate

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|.

As shown in Figures 4(a) and 4(b), 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 frequency interval between the resonant frequency fr and the anti-resonant frequency fa differed depending on whether 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 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%. 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 inferred that when a lithium niobate layer with a crystal orientation represented by Euler angles (0°, 105°, γ) is used as the piezoelectric layer 14, changing the magnitude of γ alters the electromechanical coupling coefficient k2.

Furthermore, spurious emissions 40 are generated 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 emissions 40 are 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, changing the magnitude of γ will also change the magnitude of spurious emissions 40. In the following, the difference h between the maximum and minimum intensity of spurious emissions 40 will be defined as the spurious intensity.

Figure 5 shows the simulation results of the electromechanical coupling coefficient k2 and spurious intensity as a function of the Euler angle γ for the piezoelectric layer 14 in Example 1, where the crystal orientation is represented by the Euler angle (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 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°. Therefore, by setting the Euler angle γ within the range of 11° to 28°, the electromechanical coupling coefficient k2 can be improved.

On the other hand, the spurious intensity of spurious emission 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 at an Euler angle γ of 17°, it was 13.2 dB, similar to the value at 11°. Therefore, by setting the Euler angle γ within the range of 11° to 17°, the increase in spurious intensity can be suppressed.

In the above simulation, aluminum films were used for the lower electrode 12 and 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.

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, similar to the elastic wave device 100 of Example 1. As shown in Figure 6, the elastic wave device 200 has a gap 30 instead of the acoustic reflective film 31. Other configurations are the same as in Example 1, so their explanation is omitted. In Example 2, 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°).

[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: Single crystal lithium niobate layer with a thickness T14 of 440 nm and a crystal orientation represented by Euler angles as (0°, 105°, γ) or (90°, 105°, γ) Lower electrode 12: Aluminum film with a thickness T12 of 44 nm Substrate 10: Silicon substrate

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°. Therefore, by setting the Euler angle γ within the range of 11° to 28°, the electromechanical coupling coefficient k2 can be improved.

On the other hand, the spurious intensity of spurious emission 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°. Therefore, by setting the Euler angle γ within the range of 11° to 16°, the increase in spurious intensity can be suppressed.

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 similar in magnitude when Euler angle γ = 11° and when it is = 28°. Therefore, by setting the Euler angle γ within the range of 11° to 28°, the electromechanical coupling coefficient k2 can be improved.

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 at Euler angle γ of 11° was similar to that at Euler angle γ slightly less than 17°. Therefore, by setting Euler angle γ within the range of 11° to 16°, the increase in spurious intensity can be suppressed.

In the above simulation, aluminum films were used for the lower electrode 12 and 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.

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

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

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° to 23°), more preferably (0°±5°, 105°±5°, 12° to 22°), even more preferably (0°±5°, 105°±5°, 13° to 22°), and even more preferably (0°±5°, 105°±5°, 14° to 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, from the viewpoint 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° to 23°), more preferably (90°±5°, 105°±5°, 12° to 22°), even more preferably (90°±5°, 105°±5°, 13° to 22°), and still most preferably (90°±5°, 105°±5°, 14° to 22°).

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° to 17°), more preferably (0°±5°, 105°±5°, 12° to 16°), even more preferably (0°±5°, 105°±5°, 13° to 15°), and even more preferably (0°±5°, 105°±5°, 14° to 15°). Also, 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 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° to 17°), more preferably (90°±5°, 105°±5°, 12° to 16°), even more preferably (90°±5°, 105°±5°, 13° to 15°), and still most preferably (90°±5°, 105°±5°, 14° to 15°).

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° to 21°), more preferably (90°±5°, 105°±5°, 12° to 21°), even more preferably (90°±5°, 105°±5°, 13° to 21°), and still more preferably (90°±5°, 105°±5°, 14° to 21°). Furthermore, as shown in Figure 8 of Example 2, the case of (0°±5°, 105°±5°, 11° to 21°) is preferred, the case of (0°±5°, 105°±5°, 12° to 21°) is more preferred, the case of (0°±5°, 105°±5°, 13° to 21°) is even more preferred, and the case of (0°±5°, 105°±5°, 14° to 21°) is even more preferred.

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° to 16°), more preferably (90°±5°, 105°±5°, 12° to 15°), even more preferably (90°±5°, 105°±5°, 13° to 15°), and even more preferably (90°±5°, 105°±5°, 14° to 15°). Furthermore, as shown in Figure 8 of Example 2, the case of (0°±5°, 105°±5°, 11° to 16°) is preferred, the case of (0°±5°, 105°±5°, 12° to 15°) is more preferred, the case of (0°±5°, 105°±5°, 13° to 15°) is even more preferred, and the case of (0°±5°, 105°±5°, 14° to 15°) is even more preferred.

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. At least one of the series resonators S1 to S3 and the parallel resonators P1 and P2 can be elastic wave devices according to Embodiment 1 or Embodiment 2. The number of resonators in the ladder-type filter can be set as appropriate.

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 from Embodiment 3. Although a duplexer has been described as an example of a multiplexer, a triplexer or quadplexer may also be used.

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.

10 Substrate 12 Lower electrode 14 Piezoelectric layer 16 Upper electrode 28 Addition film 30 Gap 31 Acoustic reflective film 31a Film with high acoustic impedance 31b Film with low acoustic impedance 40 Spurious 50 Resonance region 52 Edge region 54 Central region 60 Direction of thickness shear vibration 70 Transmitting filter 72 Receiving filter 100, 200 Elastic wave device 300 Filter 400 Duplexer S1-S3 Series resonators P1, P2 Parallel resonators

Claims (8)

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 direction normal to 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. 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°) . The elastic wave device according to claim 2, wherein the Euler angle of the piezoelectric layer is (0°±5°, 105°±5°, 11° to 17°) . 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°) . The elastic wave device according to claim 4, wherein the Euler angle of the piezoelectric layer is (0°±5°, 105°±5°, 11° to 16°) . 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. A filter comprising an elastic wave device according to any one of claims 1 to 6. A multiplexer comprising the filter described in claim 7.