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

Piezoelectric zinc oxide (ZnO) and its ternary alloy magnesium zinc oxide (MgxZn1-xO) films are deposited on r-plane (01 (1) over bar2) sapphire (Al2O3) 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-Al2O3 by MOCVD technique, followed by a thick piezoelectric MgxZn1-xO (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 MgxZn1-xO films have a-plane (11 (2) over bar0) orientation in a wurtzite crystal structure. The crystallinity of the films is further improved by annealing at 600-700 degrees 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 MgxZn1-xO 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 MgxZn1-xO 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 MgxZn1-xO/r-Al2O3 structure are tailored by changing the Mg mole composition in MgxZn1-xO. Simulation results of the SAW properties are found to be in close agreement with the experimental results.(c) 2007 American Vacuum Society.