Enhanced electromechanical coupling in SAW resonators based on sputtered non-polar Al0.77Sc0.23N (11(2)over-bar0) thin films

Non-polar a-plane Al0.77Sc0.23N 0 thin films were prepared by magnetron sputter epitaxy on r-plane Al2O3 substrates. Different substrate off-cut angles were compared, and the off-cut angle of 3 degrees resulted in the best structural quality of the AlScN layer. Structural characterization by x-ray diffraction confirmed that single phase, wurtzite-type, a-plane AlScN , surface acoustic wave resonators were fabricated with wavelengths lambda = 2-10 mu m (central frequency up to 1.7 GHz) with two orthogonal in-plane propagation directions. A strong dependence of electromechanical coupling on the in-plane orientation was observed. Compared to conventional c-plane AlScN based resonators, an increase of 185-1000% in the effective electromechanical coupling was achieved with only a fractional decrease of <10.5% in series resonance frequency. (C) 2020 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http:// creativecommons.org/licenses/by/4.0/).