a-plane MgxZn1−xO films deposited on r-sapphire and its surface acoustic wave characteristics

Abstract

Piezoelectric zinc oxide (ZnO) and its ternary alloy magnesium zinc oxide (Mgx Zn1-x O) films are deposited on r -plane (01 1- 2) sapphire (Al2 O3) substrates using the hybrid deposition technology by combining metal-organic chemical vapor deposition (MOCVD) and sputtering. An ultra-thin ZnO buffer is first grown on r- Al2 O3 by MOCVD technique, followed by a thick piezoelectric Mgx Zn1-x O (0≤x≤0.3) film deposited using RF sputtering. The sputtering targets are made by mixing ZnO and MgO powders in appropriate composition ratio, and nickel oxide (NiO) powder (2 wt%) is added as the compensation dopant to achieve piezoelectricity. The as-deposited Mgx Zn1-x O films have a -plane (11 2- 0) orientation in a wurtzite crystal structure. The crystallinity of the films is further improved by annealing at 600-700 °C in oxygen ambient. It is found that a ZnO thin buffer layer and post-deposition annealing process significantly improve the film's piezoelectric properties. The c -axis of the Mgx Zn1-x O film lies in the plane of the substrate, resulting in the in-plane anisotropy of the piezoelectric properties. The surface acoustic wave (SAW) devices are fabricated on the piezoelectric a -plane Mgx Zn1-x O films. The Rayleigh-type waves propagate parallel to the c -axis while the Love-type waves propagate perpendicular to the c -axis.The SAW characteristics in the Mgx Zn1-x Or- Al2 O3 structure are tailored by changing the Mg mole composition in Mgx Zn1-x O. Simulation results of the SAW properties are found to be in close agreement with the experimental results. © 2007 American Vacuum Society.