Non-Polar a-plane AlScN(1120) Thin Film Based SAW Resonantors with Significantly Improved Electromechanical Coupling

1 mm thick non-polar a-plane AlScN(1120) thin films were prepared by magnetron sputter epitaxy on r-planeAl2O3(1102) substrates. X-ray diffraction (XRD) measurements confirmed it as a single-phase wurtzite a-plane AlScN(1120).Surface acoustic wave (SAW) resonators with wavelengths l = {2,2.5, 3, 4, 5, 6, 7, 8, 10} mm were fabricated on a-planeAl0.77Sc0.23N(1120)0), a-plane Al0.68Sc0.32N(1120)0), and c-planeAl0.77Sc0.23N(0001) thin films. Compared to c-plane Al0.77Sc0.23N-based resonators, 1.85 - 10 times higher effective electromechanical coupling k2eff was observed in the whole investigated resonator wavelength range. 50 % higher figure of merit was obtained from a-plane Al0.77Sc0.23N-based highest frequency (1.71 GHz) SAW resonators and as high as 4.1 % coupling was achieved for a-plane Al0.68Sc0.32N-based resonators(1.39 GHz). Moreover, SAW propagation properties of AlScN(1120)/Al2O3(1102)02) and AlScN(0001)/Al2O3(0001) were analyzed using finite element method (FEM) simulations, theresults were compared and they confirmed the experimentally observed trends.