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

AIN 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 AIN 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 AIN films and release the strain in AIN films. The AIN films were epitaxially grown on ZnO buffered substrate with orientation relationship of (0001)[10 (1) over bar0]AIN//(0001)[10 (1) over bar0]ZnO//(0001)[(2) over bar 110]Al2O3. High frequency SAW devices with a center frequency of 1.4 GHz, a phase velocity of 5600 m/s were achieved on the obtained AIN films. The optimum ZnO buffer layer thickness was found to be 10 nm, resulting in high-quality epitaxial AIN films with a FWHM value of the rocking curve of 0.84 degrees, nearly zero stress and low insertion loss of SAW devices. This work offers an effective approach to achieve high-quality AIN epitaxial films on sapphire substrates for the applications of AIN-based SAW devices. (C) 2017 Elsevier B.V. All rights reserved.