Extreme narrow gap surface micromachined, Pirani pressure sensor

This paper presents an innovative surface micromachined Pirani pressure sensor with an extreme narrow gap and with atmospheric operating pressure range. By using a very thin layer of sputtered silicon as a sacrificial layer and Xenon Difluoride (XeF2) gas phase etching technique, a 25nm gap was fabricated between a heated microbridge and the substrate (heatsink). The gas phase etching of the sacrificial layer eliminates the liquid's surface tension that may cause the microbridge to collapse onto the substrate during the releasing and drying steps, therefore, usage of Critical Point Drying (CPD) technique is not necessary. Such a narrow gap pushes the upper pressure operating range of the sensor up to several atmospheres. Experimental results show signigicant sensitivity to absolute pressure up to 94.5 psi on a device with an active area as small as 250 mu m(2).