Acceleration sensitivity in silicon bulk-extensional mode oscillators is studied in this work, and a correlation between the resonator alignment to different crystalline planes of silicon and the observed acceleration sensitivity is established. It is shown that the oscillator sensitivity to the applied vibration is significantly lower when the silicon-based lateral-extensional mode resonator is aligned to the <110> plane compared to when the same resonator is aligned to <100>. A finite element model is developed that is capable of predicting the resonance frequency variation when a distributed load (i.e., acceleration) is applied to the resonator. Using this model, the orientation-dependent nature of acceleration sensitivity is confirmed, and the effect of material nonlinearity on the acceleration sensitivity is also verified. A thin-film piezoelectric-on-substrate platform is chosen for the implementation of resonators. Approximately, one order of magnitude higher acceleration sensitivity is measured for oscillators built with a resonator aligned to the <100> plane versus those with a resonator aligned to the <110> plane (an average of ~5.66 × 10−8 (1/g) vs. ~3.66 × 10−9 (1/g), respectively, for resonators on a degenerately n-type doped silicon layer).

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In this work the effect of crystalline orientation on the acceleration sensitivity of Silicon-based MEMS oscillators is experimentally studied for the first time. The thin-film piezoelectric-on-Silicon (TPoS) platform is utilized to implement the oscillators as it enables resonators with low-motional resistance and high Q. A single lateral-extensional-mode resonator design is fabricated in <100> and <110> orientations on a <100> Silicon wafer. The resonators are then used to assemble two oscillators operating at ~25MHz and ~27MHz respectively. The average acceleration sensitivity of the oscillator containing the <110> resonator is measured to be ~4×10 -10 at vibration frequencies up to 2700 Hz; an astonishing two orders of magnitude lower than that of the oscillator utilizing the <100> resonator. The acceleration sensitivity in these Silicon-based resonators is believed to stem from nonlinear elastic properties of Silicon, which is dependent on crystalline orientation as well as doping type/concentration. The Silicon substrate used in this work is Phosphorous-doped at ~5e19 cm -3 concentration.