Microstructure of ZnO films used for acoustic surface‐wave generation

Zinc oxide, vacuum deposited as a crystalline aggregate with preferential orientation of its fiber grains, has been used extensively as a film transducer for generating micro‐acoustic waves. The orientation and size of the crystallite grains have a pronounced effect on the film’s electromechanical properties. The microstructure of dc‐triode compound sputtered ZnO films was investigated using the analytical tools of scanning electron microscopy (SEM), reflection electron diffraction (RED), and x‐ray diffraction (XRD). The ZnO films investigated had been deposited on fused quartz and oxidized silicon having surface interdigital electrode arrays from which the acoustic surface‐wave properties of coupling efficiency, velocity, and propagation loss had been determined. Optically clear films having electromechanical and propagation properties approaching those of single‐crystal zinc‐oxide layers were found to have a smooth surface, a dense, amorphous‐like vertical structure, an average crystallite size estimate...