Preparation and Properties of rf Sputtered Films of ZnO as an Ultrasonic Transducer

Technique for preparation and properties of ZnO films by an r f sputtering method are described. This technique enables to obtain ultrasonic transducers for high frequencies of 300 MHz∼9 GHz, keeping the temperature of substrates between room temperature and 100°C. The films with the resistivity of 4×10 4 Ωcm are obtained without annealing. It is found that the films are preferentially oriented with the c -axis normal to the substrate at the thickness of 3000Å, but the grain size along the a -axis is estimated to be about 150Å.