Resonant Sensing Element Realized as a Single Crystal Si Cantilever Actuated by Fringing Electrostatic Fields

We report on the fabrication and characterization of a generic, manufacturable, cantilever-type resonant sensing element, actuated by fringing electrostatic fields and fabricated from a silicon on insulator (SOI) wafer. The architecture of the electrode, designed to be thicker than the cantilever, was tailored to allow efficient electrostatic up-tuning of the beam's frequency and enhancement of the device frequency to voltage/displacement sensitivity in the initial “as fabricated” configuration. The device is not prone to undesired pull-in instability and can be operated at large deflections, which increases the dynamic range. The multilevel structure was fabricated using a two-stage critically timed deep reactive ion etching (DRIE). The device was operated statically and dynamically by a combination of dc and ac voltages, and an increase of the resonant frequency with the increasing voltage/deflection was registered. Consistently with the model predictions, the experimental results suggest that this type of sensing element can be promising for implementation in a large variety of resonant, inertial, force or pressure sensors.