CADMIUM SULPHIDE AND ZINC OXIDE THIN-FILM TRANSDUCERS

The excitation of longitudinal and shear waves by single-crystal transducers in class (6 mm) is analyzed using the linear piezoelectric equations. Application of the results of the analysis to the piezoelectric semiconductors CdS and ZnO shows that the shear-wave excitation greatly exceeds the longitudinal-wave excitation when the c axis is inclined at angles near 40° from the transducer normal, in agreement with previous experimental and theoretical work on CdS. Measurements of the electromechanical conversion loss and electrical admittance of thin-film CdS and ZnO transducers were made, and the conversion loss of CdS films for longitudinal waves was found to be extremely high for c-axis orientations near 40° from the normal. The conversion losses of the thin films are always somewhat higher than those calculated for single-crystal transducers, and the CdS shear-mode films exhibited anomalously wide acoustic bandwidths, probably due to nonuniformities in the thickness direction. The influence of deposition parameters on the structure and performance of deposited CdS and ZnO films is discussed in detail. Copyright © 1968 by The Institute of Electrical and Electronics Engineers, Inc.