Piezoelectricity in thin film materials

Abstract

The need for efficient ultrasonic transducers in the 100 MHz to several GHz frequency range, for materials studies and for microwave device applications, has stimulated the development of a number of transducer structures. Perhaps the most versatile of those has been the thin film piezoelectric transducer. Starting in the early 1960's with primarily longitudinal bulk mode transduction in CdS films, the piezoelectric thin film transducer technology has progressed over the years, through the controlled generation and detection of both longitudinal and shear waves in CdS films, to the similar use of the higher coupling ZnO films with parallel investigations using other materials—including ZnS, AIN, and LiNbO3. While most of the early work was directed towards bulk wave generation and detection, the more recent strong interest in SAW devices has encouraged the use of piezoelectric thin films, primarily ZnO, in this arena also. As in many newly developing fields, the experimental work (film fabrication and testing) has stimulated relevant theoretical studies, and a rather comprehensive understanding of piezoelectric thin film structure and behavior has now been developed for both bulk and surface wave applications.