A microfabricated Pirani pressure sensor operating near atmospheric pressure

A micromachined pressure sensor based on the measurement of the pressure-dependent thermal conductivity of gaseous media (Pirani principle) is presented. The sensor consists of a freestanding microbridge with a defined distance to the substrate which acts as a heat sink. The theory to compute the necessary geometrical dimensions of the sensor element is presented. Due to a novel fabrication process, based on a sacrificial layer of ZnO, the sensor can readily be adapted to operate in different pressure ranges, even exceeding atmospheric pressure. A fully integrated bridge arrangement was used to compensate for ambient temperature changes. Experimental results for different sensor geometries are presented which correspond well with the theory. Basic design rules for micromachined Pirani pressure sensors are derived from the measurements.