Improvement of the sensitivity and operating range of MEMS-based resistive-type vacuum gauges

MEMS-based Pirani gauges consisting of 20 nm/200 nm Cr/Au meander-shaped resistor elements have been fabricated on 1 μm thick silicon nitride diaphragms. The distances d from the resistor elements to the cold junctions were 54, 340, and 1200 μm. The 54 μm device operates in a pressure range from about 0.05 to 5 Torr and the 1200 μm device from 0.003 to 0.3 Torr. By connecting the two devices in series, the combined device operates in a range from 0.005 to 5 Torr. This concept can be extended to higher operating ranges by changing the dimensions of the diaphragms. The sensitivity of the devices is strongly influenced by the thermal resistances of the metal lines and the silicon diaphragms.