AlN-based surface acoustic wave resonators for temperature sensing applications

Highly c-axis oriented AlN films were sputtered on Pt coated Si substrate and surface acoustic wave (SAW) resonators with Pt/AlN/Pt/Si structure were realized by lift-off photolithographic process. Frequency-temperature performance of SAW devices has been investigated as temperature sensors operating under high temperature, which can be up to 500 degrees C. The results show that the center frequency of resonator at room temperature is 456.6 MHz. The variation of frequency with temperature is linear, and the temperature coefficient of frequency (TCF) value is -69.9 ppm/degrees C. It provides a large, quasi-constant, temperature sensitivity which is suitable for temperature sensor applications. The electromechanical coupling coefficient (K-2) increases with temperature and a linear relationship is observed. The temperature coefficient of K-2 is 821 ppm/degrees C, which is calculated from linear fitting. The K-2 value is 0.23% at room temperature, but which increases to 0.32% at 500 degrees C, with an increase of 39%.