Determination of the Electromechanical Coupling Coefficient of Thin-Film Cadmium Sulphide

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Abstract
The use of transducer input admittance data for deriving the value of the electromechanical coupling coefficient of thin piezoelectric films is described. The results of admittance measurements made in the uhf frequency range have shown that partially oriented cadmium sulphide (CdS) films may have laterally clamped thickness longitudinal‐mode coupling coefficients as large as 0.15±0.01. Within the experimental accuracy this is the same as the bulk value. The admittance measurements have also shown the presence of a series resistance in the transducer. It is shown that this resistance is sufficiently large to account for most of the loss of a tuned and matched transducer.