Toward Mems displacement sensor based on resonant frequency monitoring of slightly curved beams

In this work we report on operational principle, design and characterization of a generic electrostatically actuated micro displacement/acceleration sensor based on frequency monitoring of an initially curved double-clamped microbeam actuated by a close gap electrode. The displacement of the electrode attached to a proof mass results in varying electrostatic force and changing effective stiffness and frequency of the beam. The sensitivity is improved by choosing the working configurations in the vicinity of the critical snapthrough buckling points of the beam. Reduced order model of the device was built by means of Gelerkin decomposition and was used for the feasibility study, evaluation of the design parameters and comparison with the experimental data. Devices of several configurations, which included initially straight as well as curved beams were fabricated from single crystal silicon and operated in open air environment. The responses were registered optically by laser Doppler vibrometry (LDV). Consistently with the model prediction, significant reduction in the frequency in the vicinity of the critical point followed by an increase of the frequency in the post-buckling configurations was observed in the experiments. Our theoretical and experimental results collectively demonstrate the feasibility of the suggested approach.