Pressure-dependence of MEMs Devices in Air, and Helium-4 Gas

Comb-actuated micro-electromechanical oscillators are efficient sensors that can be used to study the properties of liquid helium in slab geometry. Complete characterization of these devices will help us to better understand the effects of different mediums on the quality factor of the device. The eigenmodes of two different designs; H1 and H2, are simulated using COMSOL Multiphysics. A shear mode of an actual H1 device was then identified and studied. Pressure studies were conducted on this device from 6 mTorr to atmosphere in air, 6.5 mTorr to 5 Torr in helium, and 750 mTorr to 760 Torr in argon. It was shown that the quality factor of this device showed correspondence with the free molecular flow model described by Svitelskiy et al. 1 In accordance with this model, the quality factors studied at above 100mTorr were higher in helium and lower in argon than in air.