A Monolithic High-Flow Knudsen Pump Using Vertical Al2O3 Channels in SOI.

This paper describes the analysis, design, and microfabrication of a Knudsen pump for high flow generation. The Knudsen pump generates gas streams from the cold end to the hot end using free-molecular flow without moving parts. The designed Knudsen pump has densely arrayed vertically oriented 2- \mu \textm wide rectangular channels for providing high flow. The temperature gradient is provided between a thin-film metal heater and a gridded Si heat sink in the Knudsen pump structure. The Knudsen pump is fabricated on a single silicon-on-insulator wafer using a four-mask lithographic process. The sidewalls of the rectangular channels are constructed by atomic layer deposition of Al2O3 on sacrificial Si channels and subsequent Si etching. The fabricated Knudsen pumps have designed footprints ranging from 0.4–3.2 cm ^2 . At atmospheric pressure, the fabricated Knudsen pumps provide a maximum measured air flow rate of >200 sccm with response time of <0.5 s. Experimental results have also shown that these Knudsen pumps are most suitable for pumping at moderate vacuum pressure of $\approx 200$ Torr (27 kPa). [2014-0367] [ABSTRACT FROM PUBLISHER]