A Selective Overtone MEMS-based Quartz Oscillator with Low Acceleration Sensitivity

This study investigates a MEMS-based AT-cut quartz oscillator simultaneously with selective 3
^rd
overtone oscillation and low acceleration sensitivity (G-sensitivity). We implement (i) aspect-ratio design through acoustic wave engineering to mitigate the fundamental thickness shear (TS) mode while accentuating its 3
^rd
overtone and (ii) folded structure design to alleviate inertia induced stress, thus realizing low G-sensitivity. As a result, the proposed device has a dwarfed Q-factor of 3.6k for the 1
^st
TS mode while attaining a Q-factor of 84.6k for the 3
^rd
overtone TS mode. A standard ASIC for quartz oscillator is employed to sustain the oscillation, achieving a power-frequency-normalized Figure of Merit (PFN FoM) of 228 dB at its selective 3
^rd
overtone (63 MHz). G-sensitivity is characterized through sinusoidal and random vibration test, achieving a G-sensitivity of only 0.3 ppb/g in a 200 Hz to 2 kHz range under 1g sinusoidal vibration. The proposed device exhibits more than 25% improvement on G-sensitivity in vibration frequency span of interest compared to traditional quartz oscillator designs. This work presents a selective 3
^rd
overtone oscillator with excellent PN performance, extremely low acceleration sensitivity, and a significantly reduced footprint compared to existing commercial products.