Development of high-temperature acoustic emission sensor using aluminum nitride thin film

Aluminum nitride (AIN) is a promising Acoustic Emission (AE) sensor element for high-temperature environments such as gas turbines and other plants because AIN maintains its piezoelectricity up to 1200 degrees C. Highly c-axis-oriented AIN thin-film sensor elements were prepared on silicon single crystals by rf magnetron sputtering. Both ordinary-temperature AE sensors and high-temperature AE sensors have been developed using these elements. In this paper, to study effects of d(33) and thickness of AIN elements on sensor sensitivity, AIN elements with d(33) from 2 to 7 pm/V and thickness from 3 to 9 pm were prepared. It is confirmed that the AE sensor sensitivity increased with d(33) and thickness of AIN elements. The sensitivity of the high-temperature AE sensor was also improved by a design of the sensor structure. The sensor characteristics were evaluated at elevated temperatures from 200 to 600 degrees C. It was confirmed that the AE sensor works well at 600 degrees C and does not deteriorate.