Low Temperature Quality Factor Scaling of Laterally-vibrating AlN Piezoelectric-on-silicon Resonators

We present empirical results showing that the quality factors (Q) of 48MHz Aluminium Nitride (AlN) thin-film piezoelectric-on-silicon (TPoS) resonators double as a result of cryogenic cooling them from room temperature to 78K. The increase in Q(u) leads to a corresponding 5dB reduction in insertion loss (IL) and a motional resistance as low as 154 Omega. This temperature scaling effect on Q is however absent at shorter acoustic wavelengths (lambda) for the same resonators vibrating at higher order modes (143MHz). This absence was also found to be the case for other resonators with interdigitated electrode layouts to transduce 3rd and 5th order vibration modes of similar lambda (107MHz). These results suggest that reducing the ratio of lambda to the resonator thickness (h) strongly determines the dominance of anchor losses that do not scale with temperature. (C) 2015 The Authors. Published by Elsevier Ltd.