Air damping analysis in resonating micro-mirrors

The maximum scanning amplitude achievable by resonating micro-mirrors intended for micro-projection display applications is a function of air damping. Simplified analytical damping calculations can be employed in order to determine the damping moment of electrostatically actuated micro-mirrors however, their accuracy is limited. Three-dimensional computational fluid dynamic models are therefore presented to simulate the interaction of air with a MEMS micro-mirror oscillating at high frequency and large scan angles. Transient analyses were performed using the sliding mesh technique available in ANSYS Fluent to evaluate the dynamic fluid flow conditions present in vertical comb structures. The time- dependent damping moment contributions due to viscous shear and pressure drag are subsequently computed for both mirror plate and comb drive structures. Good agreement in the overall quality factor is achieved between simulation and measurement results.