Investigation of thin-film ultrasonic transducers for high-temperature applications

摘要

Ultrasonic transducers based on aluminium nitride (AIN) piezoelectric thin films have been proposed for high-temperature (>400℃) defect monitoring of industrial plants and components. To form the transducers, c-axis oriented AIN films, 6 μm thick, were grown on carbon steel substrates by RF sputter deposition. If the films are deposited directly onto components, then the problems of high-temperature couplant layers can be avoided. Two approaches were taken to testing the devices. In the first method, the devices were heated on a hot plate up to 400-500℃ and tested by pulse-echo measurements at high temperature and on returning to room temperature. It was shown that AIN thin-film transducers could maintain their performance in pulse-echo mode at temperatures approaching 500℃. A deterioration in performance below 500℃ was attributed mainly to degradation of the top electrode.