Ultra-High Q Self-Ovenized AlScN-on-Si X-Lamé Resonator for Stable Clock Generation

This paper presents an aluminum-scandium nitride on silicon (AlScN-on-Si) bulk acoustic wave resonator with ultra-high Q and quadratic temperature characteristic of frequency. For the first time, the piezoelectrically transduced resonator provides an f × Q approaching the phononic limit in Si, while providing higher coupling and bias-free operation that enable surpassing electrostatic counterparts for realization of stable clocks. The AlScN-on-Si resonator operates in a cross-sectional Lamé mode at 64.4 MHz, with a Q of 142,012 (f × Q ≈ 0.92 × 10
¹³
). Benefiting from doped-Si and shear nature of the mode, a temperature-stable frequency is measured with a turn-over (T
TO
) at ~47°C. Further, the resonator benefits from a novel self-ovenization approach based on Joule heating of attached phononic bandgap tethers, enabling stabilization of frequency within 0.55 part-per-billion drift over -20°C to 40°C. The resonator is used to implement an oscillator, showing three orders of magnitude reduction in Allan Deviation when applying self-ovenization for stabilization.