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Actuation or sensing in microdevices is often achieved through electro-mechanical coupling. In practice though, the electro-mechanical system is complicated by the effects influenced by the gas surrounding the system. The gas damping may be of the same order of magnitude as the electric and mechanical forces, and thus it needs to be accounted for in the design of the devices. Notably in microsensor design, controlling the amount of damping is crucial in achieving the desired measurement accuracy and sensitivity. A certain amount of damping is required to filter out high frequency oscillations, but too heavy damping reduces the sensitivity of the device. In this paper we present a modelling method based on the finite element method to simulate the behaviour of a planar gas-damped microdevice under electrostatic loading. The transient model takes into account the true nonlinear behaviour of the damping and includes effects from non-uniform gap height. The computational cost of the simulations has been significantly reduced by various reduced-order and reduced-dimensional methods utilized in the model development. The method is used to simulate an accelerometer prototype under voltage ramp loading, up to the pull-in. The results of the simulation are compared to capacitance measurements of the real device. The method is also suitable for other types of planar microdevices, such as pressure sensors, micromirrors or microswitches.

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