Elastic wave device using SH surface acoustic wave
An elastic wave device includes a lithium niobate film, a supporting substrate, a high-acoustic-velocity film located on the supporting substrate and configured so that the acoustic velocity of a propagating bulk wave is higher than the acoustic velocity of an elastic wave that propagates on the lithium niobate film, a low-acoustic-velocity film stacked on the high-acoustic-velocity film and configured so that the acoustic velocity of the propagating bulk wave is lower than the acoustic velocity of the bulk wave that propagates in the lithium niobate film, the lithium niobate film being stacked on the low-acoustic-velocity film, and an IDT electrode located on either side of the lithium niobate film. When the lithium niobate film has Euler angles of (0°±5°, θ, 0°), θ is in the range of about 0° to about 8° and about 57° to about 180°.
1. An elastic wave device configured to use an SH surface acoustic wave comprising:
a lithium niobate film;
a supporting substrate;
a high-acoustic-velocity film located on the supporting substrate and configured so that an acoustic velocity of a propagating bulk wave is higher than an acoustic velocity of an elastic wave that propagates on the lithium niobate film;
a low-acoustic-velocity film stacked on the high-acoustic-velocity film and configured so that an acoustic velocity of a propagating bulk wave is lower than an acoustic velocity of a bulk wave that propagates in the lithium niobate film, the lithium niobate film being stacked on the low-acoustic-velocity film; and
an IDT electrode located on either side of the lithium niobate film; wherein
when the lithium niobate film has Euler angles of (0°±5°, θ,0°), the Euler angle θ is in a range of about 0° to about 8° and about 57° to about 180°; and
the high-acoustic-velocity film has a thickness of about 0.3λ to about 1λ, where λ is a wavelength of a fundamental mode of the SH surface acoustic wave.
2. The elastic wave device according to claim 1 , wherein the Euler angle θ of the lithium niobate film is in a range of about 83° to about 145°.
3. The elastic wave device according to claim 1 , wherein the Euler angle θ of the lithium niobate film is in a range of about 100° to about 160°.
4. The elastic wave device according to claim 1 , wherein the low-acoustic-velocity film is made of silicon oxide.
5. The elastic wave device according to claim 4 , wherein (x, y) in xy coordinates is in an area defined by connecting points (0.023λ, 0.3λ), (0.05λ, 0.20λ), (0.10λ, 0.14λ), (0.20λ, 0.125λ), (0.44λ, 0.14λ), (0.47λ, 0.20λ), (0.435λ, 0.25λ), (0.3λ, 0.36λ), (0.15λ, 0.42λ), (0.08λ, 0.42λ), (0.05λ, 0.40λ), and (0.23λ, 0.3λ) in this order where x is a film thickness of the silicon oxide, y is a thickness of the lithium niobate film, and λ is a wavelength of a fundamental mode of the SH surface acoustic wave.
6. The elastic wave device according to claim 1 , wherein the high-acoustic-velocity film is a film made of a material selected from the group consisting of aluminum nitride, silicon nitride, and aluminum oxide or a multilayer film made of at least two of aluminum nitride, silicon nitride, and aluminum oxide.
7. The elastic wave device according to claim 1 , wherein the IDT electrode is made of Au, and the IDT electrode made of Au has a thickness of about 0.01λ to about 0.03λ, where λ is a wavelength of the fundamental mode of the SH surface acoustic wave.
8. The elastic wave device according to claim 1 , wherein the supporting substrate has a coefficient of linear expansion smaller than a coefficient of linear expansion of the lithium niobate film.
9. The elastic wave device according to claim 1 , wherein the low-acoustic-velocity film has a specific acoustic impedance smaller than a specific acoustic impedance of the lithium niobate film.