A SOI Pirani sensor with triple heat sinks

In this paper, we present a novel MEMS Pirani sensor with triple heat sinks which was designed to measure the pressure inside thin film, wafer level packages. The sensors are made in SOI (silicon on insulator) wafers leading to a very simple fabrication process. The use of relatively thick single crystal silicon for the in plane bridges result in structures with good mechanical properties as compared to alternative surface micromachining processes and reduces problems with buckling and sticking. Since, the proposed Pirani has three heat sinks, the area of heat loss through the ambient gas is greatly enlarged as compared to Pirani sensors with one or two heat sinks, without increasing the size of the sensor. Consequently, a Pirani sensor of 336 μm in length has a pressure measurement range of 0.08–200 Torr. Alternative designs have shown measurement ranges varying between 0.02 and 500 Torr. This new type of Pirani sensor is small enough to be easily integrated in small volume wafer level packages.