AVS 57th International Symposium & Exhibition
    MEMS and NEMS Thursday Sessions
       Session MN-ThM

Paper MN-ThM9
Parametric Excitation of Large Amplitude Out-of-Plane Vibrations of Micro Beams By Fringing Electrostatic Fields

Thursday, October 21, 2010, 10:40 am, Room Santo Domingo

Session: Multi-scale Interactions of Materials at the Micro- and Nano-scale
Presenter: S.L. Krylov, Tel Aviv University, Israel
Authors: S.L. Krylov, Tel Aviv University, Israel
N. Molinazzi, Medica Group, Italy
T. Shmilovich, Tel Aviv University, Israel
U. Pomerantz, Tel Aviv University, Israel
S. Lulinsky, Tel Aviv University, Israel
Correspondent: Click to Email
We report on an approach for efficient parametric excitation of large amplitude flexural out-of-plane vibrations of cantilever and double-clamped micro beams and present results of theoretical and experimental study of the suggested principle. An actuating electrode is located symmetrically at the two sides of the beam and is fabricated from the same layer of the wafer. The beam is free to deflect in the out-of-plane direction, whereas its stiffness in the lateral in-plane direction is significantly higher. The distributed electrostatic force, which is zero in the initial configuration, is engendered by the asymmetry of the fringing fields in the deformed state and acts in the direction opposite to the deflection.

The force can be effectively viewed as a reaction of an elastic foundation, which increases the stiffness of the system. The time-varying voltage applied to the electrode results in the modulation of this electrostatic stiffness and consequently in the parametric excitation of the structure. The device is distinguished by a simple single-layer architecture and may exhibit large vibrational amplitudes, which are not limited by the pull-in instability common in close-gap actuators. In contrast to previously reported devices excited by the fringing fields, the force considered here is of distributed character. The reduced order model was built using the Galerkin decomposition with undamped linear modes as base functions and the resulting system of nonlinear differential equations was solved numerically. The electrostatic forces were approximated by means of fitting the results of three-dimensional numerical solution for the electric fields. The devices fabricated from a silicon on insulator (SOI) substrate using deep reactive ion etching (DRIE) based process combined with the critically timed etching were operated in ambient air conditions and the responses were registered by means of Laser Doppler Vibrometry. The experimental resonant curves were consistent with those predicted by the model. Theoretical and preliminary experimental results illustrated the feasibility of the suggested approach.