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Micro-electromechanical systems (MEMS) components find increasing use in devices which measure and control gas flow, for medical and industrial use. Little or no information on the reliability of these devices has been published. This work reports the results of long-term performance studies of pressure-based mass flow controllers (MFCs) comprised of MEMS microvalves, pressure sensors, and critical flow orifices. Specifically, the details of long-term drift in the silicon pressure sensors (which comprise the flow sensor) are presented. Generally, pressure-based MFCs using MEMS components retain a flow accuracy of better than 1% of full scale over a 20:1 dynamic range, with response time under 0.5 sec, after more than three million operation cycles. The primary cause of inaccuracy within this dynamic range, and of inaccuracy larger than 1% of full scale beyond this range, is attributable to uncompensated zero-offset drift in the silicon pressure sensors, whose behavior is intrinsic to the flow sensor. Data is presented which details this characteristic, across many MFCs. Mechanical, thermal, fluidic, pneumatic and electronic mechanisms possibly responsible for the drift are also presented. Means to overcome this long-term drift phenomenon in silicon pressure sensors will complete the discussion.

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