Acoustic Properties and Crystallographic Structure of CdS Double-Layer Acousto-Electric Transducers

Abstract

Acoustic properties and crystallographic structure of cadmium sulphide, evaporated, double-layer transducers have been investigated. The double-layer structure consists of a relatively thick, 5–20 μ, highly conducting base layer, within which the required c-axis orientation is developed. A thin 0.1–1.0 μ high resistivity film, which determines the fundamental frequency response of the transducer, is deposited on the highly conducting layer. The c-axis orientation of this top layer is determined by that of the conducting layer; the resonant mode being determined by the angle of inclination of the c-axis to the substrate normal. Operation of these transducers in the frequency range 1–3 GHz has been investigated in both modes. Tuned conversion efficiencies of less than 10dB have been observed. Crystallographic studies have been carried out in an attempt to correlate the film structure with acoustic properties. Results will also be presented on the efficiency of this technique in producing efficient acousto-electric transducers for higher microwave frequencies. The top layers of these transducers can be formed by either direct evaporation or epitaxial growth and the performance of both types has been studied.