Metastability and the Casimir effect in micromechanical systems

Electrostatic and Casimir interactions limit the range of positional stability of electrostatically actuated or capacitively coupled mechanical devices. We investigate this range experimentally for a generic system consisting of a doubly clamped Au suspended beam, capacitively coupled to an adjacent stationary electrode. The mechanical properties of the beam, both in the linear and nonlinear regimes, are monitored as the attractive forces are increased to the point of instability. There "pull-in" occurs, resulting in permanent adhesion between the electrodes. We investigate, experimentally and theoretically, the position-dependent lifetimes of the free state (existing prior to pull-in). We find that the data cannot be accounted for by simple theory; the discrepancy may be reflective of internal structural instabilities within the metal electrodes.