On-chip vacuum generated by a micromachined Knudsen pump

This paper describes the design, fabrication, and testing of a single-chip micromachined implementation of a Knudsen pump, which uses the principle of thermal transpiration, and has no moving parts. A six-mask microfabrication process was used to fabricate the pump using a glass substrate and silicon wafer. The Knudsen pump and two integrated pressure sensors occupy an area of 1.5 mm x 2 mm. Measurements show that while operating in standard laboratory conditions this device can evacuate a cavity to 0.46 atm using 80 mW input power. The pumpdown time of an on-chip chamber and pressure sensor cavity with a total volume of 80 000 cubic micrometers is only 2 s, with a peak pump speed of 1 x [10.sup.-6] cc/min. High thermal isolation is obtained between the polysilicon heater and the rest of the device. [1073] Index Terms--High temperature, thermal isolation, thermal transpiration, thermomolecular, vacuum pump.