Combined assessment of Al1-xScxN thin films by RBS, XRD, FTIR and BAW frequency response measurements

Al
_0.7
Sc
_0.3
N films were reactively sputtered from Al-Sc segmented targets by ac powered dual-cathode S-gun magnetron. Films with homogeneous Sc concentration within 30 ± 0.5 at. % were grown at ambient temperature directly on 200-mm (100) silicon wafers and on 100-mm silicon substrates covered with SiO
₂
/Mo-based acoustic reflectors terminated by highly (110) textured Mo electrodes. The piezoelectric assessment derived from the frequency response of bulk acoustic resonators yields values of the electromechanical coupling factor k
²
up to 12.8%. Infrared absorption and X-ray diffraction measurements reveal that tiny structural changes may lead to deviation in the value of k
²
across the wafer, which can be reduced by performing a post-processing heat treatment at around 600°C.