Sputtered AlN thin films on Si and electrodes for MEMS resonators: relationship between surface quality microstructure and film properties

Aluminum nitride thin films grown by reactive AC magnetron sputtering are characterized using several metrology techniques to examine the correlation between surface quality, microstructure and piezoelectric properties. Atomic force microscopy, X-ray diffraction and electron microscopy are employed to characterize the microstructure. A range of substrate coatings is explored to understand the impact of topography on film crystallinity and piezoelectric performance. A first order approximation model providing the piezoelectric characteristics as a function of the c-axis misorientation in the mosaic-structured wurtzite AlN films is presented. While the model predicts only a small e_{33, eff} and kt change for a misorientation distribution of FWHM of less than 5 degrees, it services as an indication of the impact of AlN crystallinity on film piezoelectric properties.