Development of sputtered AlN thin-film ultrasonic transducers for durable high-temperature applications

This paper presents some of the recent experimental work on developing AlN ultrasonic transducers for high-temperature NDT applications. C-axis oriented AlN films were grown on stainless steel SS316 substrate by RF sputtering deposition. The high-temperature performance and durability of the transducer were examined by pulse-echo experiments after heating to different temperatures. It can be shown that the sputtered AlN film transducer is capable of highly stable and durable performance at 400 degrees C or above, with appropriate choice of substrate, buffer layer, electroding materials and electroding approaches. Experimental evidence also indicates that transducers made of sputtered AlN film and a molybdenum buffer layer on a stainless steel substrate could potentially operate at up to 800 degrees C.