Fabrication of high kt2and k’ 352 Sc0.4A10.6N thin films by RF magnetron sputtering

Scandium aluminum nitride (ScAlN) films are commercially used for RF filter application owing to their large thickness extensional mode electromechanical coupling coefficient
$k_{\mathrm{t}}{}^{2}$
. In addition, c-axis tilted ScAlN films are good candidates for biosensors and gyro-sensors because of their high quasi thickness shear mode
$k_{35^{2}}^{\prime}$
. In this study, we fabricated c-axis oriented (0001) Sco.4Alo.6N thin film and c-axis 34° tilted Sco.4Alo.6N thin film by RF magnetron sputtering.
$k_{\mathrm{t}}{}^{2}$
of the c-axis oriented (0001) Sco.4Alo.6N film was evaluated to be 21.4% by CL method and approximately 28% by other four kinds of
$k_{\mathrm{t}}{}^{2}$
estimation methods.
$k_{35^{2}}^{\prime}$
of the c-axis tilted Sc
0.4
Al
0.6
N film was evaluated to be at least 22.9%. These high
$k_{\mathrm{t}}{}^{2}$
and
$k_{35^{2}}^{\prime}$
of the Sco.4Alo.6N thin films can be attributed to the high crystalline orientation and the suppression of abnormally oriented grains (AOGs) at high Sc concentration.