High Electromechanical Coupling SAW Resonators Based on a-Plane AlScN-AlN-Sapphire Substrate

This work reports on surface acoustic wave (SAW) piezoelectric resonators with high electromechanical coupling coefficient (k
²
eff
) based on a-plane Aluminum Scandium Nitride (AlScN) films. The properties of surface acoustic wave modes were analyzed using finite element modeling (FEM) simulations. The influences of AlScN film thickness and in-plane propagation orientation on k
²
eff
were evaluated. Due to good crystallinity (FWHM < 1°) and high Sc doping, optimized design parameters from FEM simulations were adopted to realize a high k
²
eff
up to 5.17%, which is the highest among the reported AlScN SAW devices. These results demonstrate that the k
²
eff
can be improved by using a-plane AlScN when compared to c-plane AlScN, which is highly needed for radio frequency (RF) filters.