Hybrid deposition of piezoelectric $(11\bar 20)$ Mg_xZn_1−xO (0≤x≤0.3) on $(01\bar 12)$ R-sapphire substrates using RF sputtering and MOCVDR-sapphire substrates using RF sputtering and MOCVD

Abstract

Mg_xZn_1−xO (0≤x≤0.3) films are deposited on R-plane $(01\bar 12)$ sapphire substrates using a hybrid deposition technique: metalorganic chemical vapor deposition and radiofrequency (RF) sputtering. Thick piezoelectric Mg_xZn_1−xO films are deposited by RF sputtering on MOCVD grown thin ZnO buffers on R-sapphire substrate. Molar ratio of ZnO and MgO powders are mixed to form Mg_xZn_1−xO (0≤x≤0.3) sputtering targets with NiO (2–3 wt.%) added for compensation doping to achieve piezoelectricity. Field emission scanning electron microscopy shows that the deposited films are dense and uniform. X-ray diffraction indicates that the sputter-deposited Mg_xZn_1−xO (0≤x≤0.3) films retain the wurtzite crystal structure. The crystallinity of the deposited films is further improved by postannealing at 700°C in oxygen. Compositional analysis of the films is carried out using Rutherford back-scattering. High-frequency and low-loss surface acoustic wave (SAW) testing devices fabricated on these films are demonstrated. The SAW properties are tailored to changing Mg compositions. In the ZnO/R-Al₂O₃ system, two types of wave modes, the Rayleigh-type and the Love-type wave modes, are investigated.