Sputtered thin film piezoelectric aluminum nitride as a functional MEMS material

A comprehensive study on the complete process for the fabrication of AlN-based MEMS sensors and actuators is presented. Varying the bias voltage during the reactive rf sputtering enables to adjust the stress level in AlN films in the range of about 2 GPa. For the first time the influence of the rf bias power on the whole set of piezoelectric parameters was investigated. It could be shown that the dielectric permittivity, dielectric loss, rocking curve width, effective longitudinal piezoelectric coefficient d 33,f and effective transverse piezoelectric coefficient e 31,f remained unchanged. Further it was observed that piezoelectric AlN films could be deposited at low process temperatures of only 200 °C. Moreover an increase in the e 31,f coefficient with thicker films could be stated. Finally cone formation during wet etching was observed and revealed a formation of {01-12} planes which exhibit a slow etching rate. The c-textured growth of AlN starts directly at the Pt interface.