Microstructure and piezoelectric response of YxAl1−xN thin films

Abstract

Transition metal doping of aluminium nitride (AlN) type thin films was recently employed to increase the piezoelectric constants for application in micro electromechanical systems. YxAl1−xN thin films were synthesized with varying x up to 11.6% by reactive co-sputtering from elemental Al and Y targets. Ab initio density functional theory studies up to x=50% yttrium in YxAl1−xN suggest increasing piezoelectric constants d33 and d31 with increasing yttrium content. Experimental measurements of d33 yield increasing values for increasing yttrium content though, remaining below the prediction from ab initio calculations. Detailed X-ray diffraction and transmission electron microscopy studies prove that, although the thin films are highly c-axis oriented, their nucleation at the Si (100) substrates leads to the formation of an amorphous interface region with increasing Y.