Ex-situ AlN seed layer for (0001)-textured Al0.85Sc0.15N thin films grown on SiO2 substrates for shear mode resonators

Partial substitution of Al by Sc in AlN wurtzite films leads to a strong enhancement of the piezoelectric properties as long as the wurtzite phase is maintained. This is very promising for improving piezoelectric MEMS devices and enlarging their application range. Nucleation of (0001)-AlScN works particularly well on Pt (111) thin films. However, in some applications, the growth on insulating substrates may be required. Even though AlN can be grown well oriented on smooth amorphous surfaces of SiO 2 , it is not the case for AlScN. AlN seed layers are an evident solution when there is no vacuum break between the AlN and AlScN growth. However, when a vacuum break is unavoidable, an oxide layer is formed on AlN, which makes the “regrowth” difficult. In this contribution we show that a mild RF etch can solve the problem.