Multiple Stable Oscillators Referenced to the Same Multimode AlN/Si MEMS Resonator with Mode-Dependent Phase Noise and Frequency Stability

We report on the first experimental demonstration of multiple self-sustaining feedback oscillators referenced to a single multimode resonator, using piezoelectric aluminum nitride on silicon (AlN/Si) microelectromechanical systems (MEMS) technology. Integrated piezoelectric transduction enables efficient readout of three resonance modes of the same AlN/Si MEMS resonator, at 10MHz, 30MHz, and 65MHz with quality (Q) factors of 18600, 4350, 4230, respectively. Three stable self-sustaining oscillators are built, each referenced to one of these high-Q modes, and their mode-dependent phase noise and frequency stability (Allan deviation) are measured and analyzed. The 10, 30 and 65MHz oscillators exhibit low phase noise of -114, -100 and -105dBc/Hz at 1kHz offset frequency, respectively. The 65MHz oscillator yields excellent Allan deviation of $4\times 10^{-9}$ and $2\times 10^{-7}$ at ls and 1000s averaging time, respectively. The 10MHz oscillator’s low phase noise holds strong promise for clock and timing applications. The three oscillators’ overall excellent performance also suggests suitability for multimode resonant sensing and tracking. This work also elucidates mode dependency in oscillator noise and stability, on key attributes of mode-engineerable resonators.