Viscous air damping in laterally driven microresonators

A systematic experimental study of viscous air damping in laterally moving planar microstructures is reported. Previous studies indicated that Couette and Stokes flow models underestimated microstructural damping. To investigate this discrepancy, a series of lateral resonant microstructures with different damp plates and combs was fabricated with polysilicon surface micromachining. The resonant frequencies and quality factors of the structures were measured electrically. By examining these data, the damping due to different geometries were isolated and compared to theory. The results indicated that if edge and finite-size effects are included in the model, reasonably accurate prediction on the quality factors can be obtained even for small geometries and comb drives. An empirical formula was developed that predicts quality factor for a range of plate size and comb designs. The damping effects as a function of structural thickness and structure-to-substrate separation are also reported