Effectiveness of oxide trench array as a passive temperature compensation structure in AlN-on-silicon micromechanical resonators

This Letter presents the effectiveness of an oxide trench array (OTA) as a passive temperature compensation structure for aluminum nitride on silicon (AlN-on-Si) quasi-surface acoustic wave (SAW) micromechanical resonators over a wide temperature range. Two types of devices, namely, those with OTA and their reference counterparts without OTA, are designed, fabricated, and characterized over a wide temperature range of 360 °C. Experimental results show that the resonator with OTA has a first-order temperature coefficient of frequency (TCf1) at room temperature (20 °C) of 6.66 ppm/°C, which is lower than that of the reference device without OTA by 72% in magnitude. A high turnover temperature of 197 °C is achieved. Furthermore, the second-order temperature stability of the device has also improved. OTA is experimentally demonstrated to be an effective structure for passive temperature compensation, hence paving the way for using AlN-on-Si resonators as ultrasonic sensors or timing devices in ruggedized environments where the large fluctuation in temperature places stringent demands on temperature stability.