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

Electromechanical coupling k{mathrm{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{mathrm{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{mathrm{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.