Film growth of c-axis tilted ScAlN on the sapphire substrate for SAW devices

ScAlN films are attractive for SAW devices with high electromechanical coupling coefficient K
²
. In previous study, we analyzed K
²
in c-axis-tilted Sc
_0.4
Al
_0.6
N film / diamond substrate. The K
²
of c-axis-tilted film was increased, compared with that of the c-axis-normally-oriented film. However, it is difficult to perform experiments because diamond substrate are very expensive. In this study, K
²
of SAWs in c-axis tilted ScAlN film / R-sapphire substrate were theoretically analyzed. The K
²
in Rayleigh mode SAW were found to be 3.9% at Ψ = 90° and 3.7% at Ψ = 54°. Next, c-axis tilted ScAlN films were grown on sapphire substrate. c-Axis-33°-tilted ScAlN film was obtained on the R-plane sapphire. Then, IDT/ c-axis-33°-tilted ScAlN / R-sapphire structure was fabricated. The insertion loss of the structure was 34.4 dB. High K
²
was expected to improve the crystalline orientation of the ScAlN films.