Quality-enhanced AlN epitaxial films grown on c-sapphire using ZnO buffer layer for SAW applications

Abstract

AlN epitaxial films with a thin ZnO buffer layer were successfully deposited on c-sapphire by DC magnetron sputtering for surface acoustic wave (SAW) applications. The effect of ZnO buffer layer thickness on structural properties of AlN epitaxial films and the related SAW properties were investigated systematically. The results revealed that a thin ZnO buffer layer can significantly enhance the crystalline quality of AlN films and release the strain in AlN films. The AlN films were epitaxially grown on ZnO buffered-substrate with orientation relationship of (0001)[101¯0]AlN//(0001)[101¯0]ZnO//(0001)[2¯110]Al2O3. High frequency SAW devices with a center frequency of 1.4GHz, a phase velocity of 5600m/s were achieved on the obtained AlN films. The optimum ZnO buffer layer thickness was found to be 10nm, resulting in high-quality epitaxial AlN films with a FWHM value of the rocking curve of 0.84°, nearly zero stress and low insertion loss of SAW devices. This work offers an effective approach to achieve high-quality AlN epitaxial films on sapphire substrates for the applications of AlN-based SAW devices.