Temperature-Stable AlScN-on-Si Shear-BAW Resonator with > 1.8M Quality Factor and < 1 ppb Frequency Drift enabled by Closed-loop Instinctual Self-Ovenization

To fulfill the needs of low-cost and low-SWaP (size, weight and power) requirements for micro-electromechanical system (MEMS)-based clocks, while simultaneously providing improved short-term and long-term stability, we demonstrate, for the first time, (1) a piezoelectrically transduced shear-BAW Resonator with $\gt10^{14} f_{\text {res }} \times Q$ product for good short-term stability, as well as (2) a method of instinctual closed-loop self-ovenization in the resonator for long-term stability, using a temperature controlled voltage source, for $\lt 1 \mathrm{ppb}$ frequency drift within $-20^{\circ} \mathrm{C}$ to $40^{\circ} \mathrm{C}$ in a controlled temperature chamber. An improvement of 4 orders of magnitude is observed in Allan Deviation (ADEV) as compared to the non-ovenized scenario.