Large area piezoelectric ZnO film transducers produced by r.f. diode sputtering

Abstract

Large area ZnO film transducers (15mm × 45 mm) have been grown on c-cut sapphire by r.f. diode sputtering. With substrate temperature T s150°C the films grow epitaxially. Below T s = 100°C the films grow textured ( c axis perpendicular to the surface). Both textured and epitaxial films are homogeneous across the whole area and have been used for sound beam topography at freqeuncies up to 35 GHz. After annealing at 620°C, a cubic modification of ZnO is observed in a surface layer at least 5 nm thick. Its lattice parameter is a = 0.375 nm.