SAW and BAW response of c-axis AlN thin films sputtered on platinum

We evaluate the longitudinal and transverse piezoelectric response of highly (00·2)-oriented AlN films sputtered on platinum layers. We have observed that the existence of some defects in the films, associated with the appearance of weak diffraction peaks other than the 00·2 reflection in the XRD patterns, annihilates the piezoelectric response, even in films with very large grain size. In the absence of these defects, the piezoelectric response of the AlN films is strongly dependent on the grain size of the microcrystals. The transverse and longitudinal electromechanical coupling factors (k₃₁² and k₃₃²) were evaluated from the frequency response of SAW and BAW devices, respectively. Values of k₃₁² = 2% and k₃₃² = 4.77% were obtained for the AlN films deposited on Pt.