Si-Micromachined Knudsen Pumps for High Compression Ratio and High Flow Rate
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Micromachined Knudsen pumps are potentially useful for micro mass spectrometers and micro gas chromatographs. Knudsen pumps exploit the thermal transpiration that results from the free-molecular flow in non-isothermal channels. The absence of moving parts, without frictional loss and mechanical failure, provides significantly higher reliability. In this talk, I will present my research toward the design, fabrication, and test of Si-micromachined Knudsen pumps. First, a 48-stage Knudsen pump and a two-part 168-stage Knudsen pump will be described. These pumps evacuate cavities from 760 to Â‰^0.9 Torr, resulting in a compression ratio of ‰^844 the highest in micropumps. Second, dynamic calibration of embedded Pirani gauges will be explained. This method increases the accuracy of readings in complex fluidic networks. Third, low-temperature vacuum sealing using atomic layer deposition (ALD) of Al2O3 for wafer-level vacuum packaging will be presented. Finally, a single-stage Knudsen pump designed for high flow rates will be described. A high density of channels are integrated in a single chip and result in a measured 211 sccm air flow the highest in micropumps. I will discuss the results and conclude with future research directions.