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

We present empirical results showing that the quality factors (Q) of 48 MHz 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 Qu leads to a corresponding 5 dB reduction in insertion loss (IL) and a motional resistance as low as 154Ω. This temperature scaling effect on Q is however absent at shorter acoustic wavelengths (λ) for the same resonators vibrating at higher order modes (143 MHz). 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 λ (107 MHz). These results suggest that reducing the ratio of λ to the resonator thickness (h) strongly determines the dominance of anchor losses that do not scale with temperature.