ScAlN nano-rods structure thin film grown by a self-shadowing oblique sputtering for high electromechanical coupling transducer applications

Electromechanical coupling k
_t
for laterally clamped thin PZT plate is smaller than k
₃₃
for the rod type PZT which is free from lateral clamping [1]. PZT rod and polymer composite plate transducer makes it possible to enhance the coupling near k
₃₃
rather than k
_t
because of lateral unclamping due to the soft polymer. In this study, we propose the ScAlN nano-rods transducers, which is free from lateral clamping to obtain k
₃₃
mode operation rather than usual k
_t
mode operation. In the oblique sputtering growth, porous nano- rods structure forms because the side of crystal grain shadows the opposite of the crystal grain (which is so called self-shadowing effect) [2]. Using this effect, we aimed to obtain nano-rods structure with c-axis perpendicular to the substrate. We obtained desired perpendicular nano-rods structure by RF magnetron sputtering with substrate rotation. However, only a weak k
₃₃
²
was observed because of low degrees of crystallization of ScAlN. This lead free flexible ScAlN nano-rods are expected to be substitute for PVDF polymers when the highly crystalline ScAlN film is achieved.