  Fueled by the 5G revolution, the demand for advanced radio frequency
micro-electromechanical systems (MEMS) based on AlScN is growing rapidly.
However, synthesizing high-quality, textured AlScN thin films is challenging.
Current approaches typically rely on high temperatures and expensive compound
targets. In this study, we demonstrate the feasibility of ionized physical
vapor deposition to deposit highly oriented AlScN films with minimal defects at
lower temperatures. Using metal-ion synchronized high-power impulse magnetron
co-sputtering (MIS-HiPIMS) we can selectively bombard the growing film with Al
and/or Sc ions to enhance the adatom mobility while simultaneously providing
the ability to tune stress and coat complex structures conformally. We find
that the Sc solubility in wurtzite AlN is slightly reduced, whereas
crystallinity and texture are markedly improved. Disoriented grains, a key
challenge in growing AlScN films, are completely removed via substrate biasing,
while the residual stress can be tailored by adjusting the same. The measured
piezoelectric response of the films is in line with DFT predictions and on par
with the current state of the art. Finally, we demonstrate conformal deposition
of c-axis textured AlScN on structured Si wafers underlining the promise of
ionized PVD for the fabrication of advanced RF filters and next-generation MEMS
devices.
