Acoustic wave devices

1. A method for fabricating an acoustic wave device, the method comprising:

providing or forming a substrate containing 70 mass % or greater of silicon dioxide (SiO2);

providing or forming a piezoelectric thin film with LiTaO3 crystal or LiNbO3 crystal on the substrate, Euler angles of the substrate and Euler angles of the piezoelectric thin film selected such that a phase velocity of a surface acoustic wave propagating along the substrate is greater than a phase velocity of the surface acoustic wave propagating along the piezoelectric thin film; and

implementing an interdigital transducer electrode to be in contact with the piezoelectric thin film.

2. The method of claim 1 further comprising implementing a Si-containing film between the substrate and the piezoelectric thin film.

3. The method of claim 2 wherein the Si-containing film contains 30% or greater of SiO 2 or SiO, and has a thickness of 0.15 times to 1 times a wavelength of the surface acoustic wave.

4. The method of claim 2 wherein the Si-containing film contains 30% or greater of SiO 2 or SiO, and has a thickness of 0.3 times to 0.5 times a wavelength of the surface acoustic wave.

5. The method of claim 1 wherein the substrate includes a quartz substrate and a phase velocity of the surface acoustic wave to propagate is 4,500 m/s or greater, 4,800 m/s or greater, or 5,000 m/s or greater.

6. The method of claim 5 wherein the substrate includes a quartz substrate, and the surface acoustic wave to propagate includes a leaky acoustic wave including primarily a SH component or an S wave having a phase velocity of 4,500 m/s or greater.

7. The method of claim 1 further comprising implementing a shunt electrode and/or an insulating boundary film between the substrate and the piezoelectric thin film.

8. The method of claim 1 wherein implementing the interdigital transducer electrode results in at least a lower portion of the interdigital transducer electrode being embedded in the piezoelectric thin film and/or at least an upper portion of the interdigital transducer electrode protruding from the piezoelectric thin film.

9. The method of claim 1 wherein providing or forming the substrate includes providing or forming a quartz substrate.

10. The method of claim 1 wherein the substrate has a shear wave phase velocity of a bulk wave of 3,400 to 4,800 m/s.

11. The method of claim 1 wherein the substrate includes an isotropic substrate, and the piezoelectric thin film has a thickness of 0.001 mm or greater and less than 0.01 mm.

12. The method of claim 1 wherein the substrate has the surface acoustic wave propagate in 4,500 m/s or greater and has Euler angles of (0°±5°, 70°-165°, 0°±5°), (0°±5°, 95°-155°, 90°±5°), or crystallographically equivalent Euler angles thereof.

13. The method of claim 1 wherein the substrate has Euler angles of (0°±5°, 0°-125°, 0°±5°), (0°±5°, 0°-36°, 90°±5°), (0°±5°, 172°-180°, 90°±5°), (0°±5°, 120°-140°, 30°-49°), (0°±5°, 25°-105°, 0°±5°), (0°±5°, 0°-45°, 15°-35°), (0°±5°, 10°-20°, 60°-70°), (0°±5°, 90°-180°, 30°-45°), (0°±5°, 0°±5°, 85°-95°), (90°±5°, 90°±5°, 25°-31°), (0°±5°, 90°±5°, −3° to 3°), or crystallographically equivalent Euler angles thereof.

14. The method of claim 1 wherein the substrate has Euler angles of (20°±5°, 120°±10°, 115°±10°), (0°±5°, 90°±5°, 0°±10°), (0°±5°, 90°±5°, 75°±10°), (0°±5°, 0°±5°, 0°±10°), (0°±5°, 0°±5°, 60°±10°), or crystallographically equivalent Euler angles thereof.

15. The method of claim 1 wherein the piezoelectric thin film includes LiTaO 3 crystal and has Euler angles of (90°±5°, 90°±5°, 33°-55°), (90°±5°, 90°±5°, 125°-155°), or crystallographically equivalent Euler angles thereof.

16. The method of claim 1 wherein the piezoelectric thin film includes LiNbO 3 crystal and has Euler angles of (90°±5°, 90°±5°, 38°-65°), (90°±5°, 90°±5°, 118°-140°), or crystallographically equivalent Euler angles thereof.

17. The method of claim 1 wherein the interdigital transducer electrode has a thickness, in fraction of a wavelength of the surface acoustic wave, of 0.005-0.32, 0.005-0.20, 0.005-0.28, or 0.005-0.20 for a density range, in kg/m 3 , of 2000-5000, 5001-9500, 9501-15000, or 15001-220000, respectively.

18. The method of claim 1 wherein the interdigital transducer electrode has a metalization ratio of 0.15-0.63, 0.15-0.63, 0.15-0.71, or 0.15-0.65 for a density range, in kg/m 3 , of 2000-5000, 5001-9500, 9501-15000, or 15001-220000, respectively.

19. The method of claim 1 further comprising implementing an insulating boundary film between the substrate and the piezoelectric thin film, the boundary film having a thickness that is greater than or equal to 0.34 times a wavelength of the surface acoustic wave.

20. The method of claim 1 further comprising implementing an insulating boundary film disposed between the substrate and the piezoelectric thin film, the boundary film having one or more layers, one layer closest to the piezoelectric thin film having a thickness T, in fraction of a wavelength of the surface acoustic wave, of 0<T<=0.5, 0<T<=0.67, 0<T<=3, or 0<T<=0.6 for a shear wave phase velocity Vs, in m/s, of 1500<=Vs<=2200, 2200<Vs<=3400, 3400<Vs<=5900, or 5900<Vs<=13000, respectively.

21. The method of claim 1 wherein the surface acoustic wave has a higher order mode, and the interdigital transducer electrode has a thickness, in fraction of a wavelength of the surface acoustic wave, of 0.17-0.8, 0.08-0.44, 0.08-0.43, or 0.06-0.4 for a density range, in kg/m 3 , of 2000-5000, 5001-9500, 9501-15000, or 15001-220000, respectively.

22. The method of claim 1 wherein the surface acoustic wave has a higher order mode, and the piezoelectric thin film has a thickness of 0.35 times to 9.3 times a wavelength of the surface acoustic wave.

23. The method of claim 1 wherein the surface acoustic wave includes either or both of a leaky surface acoustic wave and a longitudinal-wave-type leaky surface acoustic wave.

24. The method of claim 1 wherein the piezoelectric thin film includes LiNbO 3 crystal, and the surface acoustic wave includes a Rayleigh wave.