Experimental and theoretical investigations of enhanced electromechanical properties in YbAlN and YbGaN films

Epitaxial YbAlN, YbGaN and ScAlN films were successfully fabricated by magnetron sputtering. The electromechanical coupling coefficient is 4.5% in the epitaxial Sc
0.03
Al
0.97
N film and reaches to 4.8% in the epitaxial Yb
0.27
Al
0.73
N film. Compare with the polycrystalline films, the epitaxial YbGaN films show a higher
$k_{t}^{2}$
, close to the theoretical values calculated by first principles calculations, especially at high doping Yb concentrations. This suggests that the use of epitaxial piezoelectric films in the resonator is a feasible approach to improve the performance of frequency filters.