Strategy to obtain epitaxial aluminum scandium nitride thin films with reduced defect densities by magnetron sputtering

AlScN-based bulk acoustic wave resonators with enhanced performance have become attractive for meeting the demanding requirements of the 5G telecommunication industry. For resonators to have better performance, AlScN films exhibiting epitaxy, high crystalline quality, high electric insultation, and low number of abnormally oriented grains are desired. In this study, we systematically change the total sputter power and investigate the structural, optical, and electrical properties of the resulting Al1−xScxN films. Our findings demonstrate that increasing the total sputter power results in Al1−xScxN films with low abnormally oriented grains, reduced sub-bandgap absorption, and lower leakage currents—predominantly due to reduced nitrogen vacancies. Based on these results, we argue that a higher growth rate promotes the growth of Al1−xScxN with reduced impurity levels. Furthermore, by depositing Al0.7Sc0.3N on epitaxial AlN, we demonstrate that epitaxial AlScN can be achieved while improving its crystal quality by ≈36%.