Bifurcation point drift in electrostatic MEMS sensors: Strategies to mitigate against an uninvited guest

In this paper, we investigate the repeatability of bifurcation-based electrostatic MEMS sensors over prolonged excitations. The sensors used in this study were subjected to two test conditions: continuous frequency sweeps near a cyclic-fold bifurcation and long-term residence on a resonant branch beyond the cyclic-fold bifurcation point. We found that prolonged high-amplitude oscillations undermine repeatability and cause significant shifts in the bifurcation location toward lower frequencies by building up plastic deformations that reduce the capacitive gap. Biased excitation waveforms were also found to lead to charge buildup within dielectrics, exacerbating the drift in frequency of the bifurcation point. In comparison, stiffer in-plane sensors with no metallization operating under unbiased waveforms showed dramatic improvement in repeatability.