Measurement of the Mass Flow and Tangential Momentum Accommodation Coefficient in Silicon Micromachined Channels

Abstract

An analytic and experimental investigation into gaseous flow with slight rarefaction through long microchannels is undertaken in an attempt to obtain values of the Tangential Momentum Accommodation Coefficient (TMAC) for a common MicroElectroMechanical Systems (MEMS) surface. A set of analytic expressions is developed from the slip- flow solutions of the Navier Stokes equations which can be used to interpret the results of flow in micromachined channels and to extract TMAC values from these results. In addition to the theoretical framework, a robust microchannel fabrication procedure and a dedicated high-resolution mass flow measurement technique is developed. These are used in conjunction to obtain TMAC values for single-crystal silicon upon which a native oxide resides for gas flows of argon, nitrogen and carbon dioxide. It is shown that the TMAC for this common MEMS surface can possess a value less than unity (0.75-0.85) for the conditions which are expected to be encountered with state-of-the-art MEMS.