Nanoprobe mechanical and piezoelectric characterization of ScxAl1-xN(0001) thin films

Nanoindentation with in-situ electrical characterization is used to investigate piezoelectric scandium aluminum nitride (ScxAl1-xN) thin films with Sc contents up to x = 0.3. The films are prepared by reactive magnetron sputtering using Al2O3 substrates with TiN seed layers as bottom electrodes at a substrate temperature of 400 degrees C. X-ray diffraction shows c-axis oriented wurtzite ScxAl1-xN, where the crystal quality decreases with increasing x. Piezoresponse force microscopy in mapping mode reveals a single piezoelectric polarization phase in all samples. The hardness decreases from 17 GPa in AlN to 11 GPa in Sc0.3Al0.7N, while reduced elastic modulus decreases from 265 GPa to 224 GPa, respectively. Both direct and converse piezoelectric measurements are demonstrated by first applying the load and generating the voltage and later by applying the voltage and measuring film displacement using a conductive boron doped diamond nanoindenter tip. The Sc0.2Al0.8N films exhibit an increase in generated voltage in comparison to AlN and a correspondingly larger displacement upon applied voltage, comparable to results obtained by double beam interferometry and piezoresponse force microscopy. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim