C-Axis Textured, 2–3 μm Thick Al(0.75)Sc(0.25)N Films Grown on Chemically Formed TiN/Ti Seeding Layers for MEMS Applications

A protocol for successfully depositing [001] textured, 2–3 µm thick films of Al(0.75)Sc(0.25)N, is proposed. The procedure relies on the fact that sputtered Ti is [001]-textured [Formula: see text]-phase (hcp). Diffusion of nitrogen ions into the α-Ti film during reactive sputtering of Al(0.75),Sc(0.25)N likely forms a [111]-oriented TiN intermediate layer. The lattice mismatch of this very thin film with Al(0.75)Sc(0.25)N is ~3.7%, providing excellent conditions for epitaxial growth. In contrast to earlier reports, the Al(0.75)Sc(0.25)N films prepared in the current study are Al-terminated. Low growth stress (<100 MPa) allows films up to 3 µm thick to be deposited without loss of orientation or decrease in piezoelectric coefficient. An advantage of the proposed technique is that it is compatible with a variety of substrates commonly used for actuators or MEMS, as demonstrated here for both Si wafers and D263 borosilicate glass. Additionally, thicker films can potentially lead to increased piezoelectric stress/strain by supporting application of higher voltage, but without increase in the magnitude of the electric field.