Aluminium nitride: a promising and full CMOS compatible piezoelectric material for MOEMS applications

Abstract

Aluminum nitride (AlN) is a promising piezoelectric material suitable for full CMOS compatible MEMS processes. Due to the transversal inverse piezoelectric effect the use of AlN enables quasistatic deformable mirrors by actively coupling lateral strain in micro machined membranes. In this work a fast and reliable way for reactive magnetron rf-sputtered aluminum nitride thin films with piezoelectric properties is shown. The thin AlN films were deposited on amorphous TiAl, SiO₂ and silicon substrates using an industrial PVD cluster system. The morphologies of the deposited polycrystalline AlN films are characterized by X-ray diffraction measurements and SEM images of the layer surfaces. An enhanced texture coefficient is used to demonstrate the correlation between the X-ray diffraction pattern and the surface topology. High values of this enhanced texture coefficient will guarantee piezoelectric properties. Virtual powder X-ray diffraction experiments are used to determine the relative powder intensities required for texture coefficient evaluation. The transversal inverse piezoelectric coupling coefficient d₃₁ is measured for tempered and untreated aluminum nitride thin films with high enhanced texture coefficients by quasistatic deflected wafer cantilevers.