Knudsen force based MEMS structures

Knudsen forces are gas molecular forces which originate from the differential temperatures in rarefied gases. We report measurements of these forces at normal ambience on test structures made by surface micromachining of polysilicon. Using these results, a surface micromachined Knudsen vacuum sensor has been simulated, fabricated and characterized. The vacuum sensor has an area of 1 mm(2). The fabricated device has a sensitivity of 40 fF Pa-1 in the pressure range of 0.1-10 Pa. The measured data is analysed and the magnitude of the Knudsen's force is extracted. The paper also suggests ways to enhance the range and improve the sensitivity of such sensors.