Vertical etching of Al0.7Sc0.3N for next generation of acoustic wave resonators

Due to their enhanced piezoelectric coefficient, aluminum scandium nitride thin films have been a promising piezoelectric material for MEMS, in particular for RF filters applications. Resonators based on this material present strong microfabrication challenges, especially in applications where partial etching of the piezoelectric AlScN is necessary, such as hybrid SAW/BAW devices. This work compares different AlScN etching techniques, with the aim of achieving smooth fully or partially etched surfaces, nearly vertical sidewalls, and high selectivity towards the mask material.