Sputtered AlN Lateral Bimorph: Process Integration Challenges and Opportunities

A fabrication process for sputtered piezoelectric AlN lateral bimorph transducers is presented. This work focuses on challenges with the interdependencies of the sputtered AlN film texture and the process development, especially plasma etching. The AlN films with better rocking curve FWHM have higher etch rates, smoother surface, and higher etch selectivity to oxide. By controlling the surface roughness of the underlying oxide layer, between 6 to 1.7 nm, we reduced the FWHM of sputtered AlN from 3 to 1.2 degrees. We verified an independent control parameter on the AlN crystal quality without changing the sputtering parameters, and this is a potential pathway to control the AlN plasma etching process by regional adjusting the substrate surface.