c-axis orientation and piezoelectric coefficients of AlN thin films sputter-deposited on titanium bottom electrodes

► The surface roughness of the titanium bottom electrode (Ti) is a dominating factor on the piezoelectric coefficients and structure of AlN thin films. ► Increasing the surface roughness of Ti bottom electrode results in open-porous surface characteristics and low piezoelectric coefficients of the AlN top layer. ► Decreasing the surface roughness of Ti bottom electrode results in a smooth and dense surface which is a necessary requirement for high piezoelectric coefficients. ► Both piezoelectric coefficients d33 and d31 were determined by comparing the experimental and simulated displacement profile of the piezoelectric film.