Permeated porous silicon suspended membrane as sub-ppm benzene sensor for air quality monitoring

To realise advanced microsensors for a reliable monitoring of very low concentrations of pollutant species such as NOx, SO2, CO, O-3 and aromatic hydrocarbons, the use of porous silicon (PS) permeated with semiconducting oxides has been explored. To reduce the power consumption and to make feasible the device to operate in a fast pulsed temperature mode, a novel sensor architecture has been designed. The main feature of the device is represented by a permeated suspended macroporous Si membrane, few tens of microns thick. In this paper the porous silicon formation through a suspended silicon membrane and the morphological characterization of the PS layer are reported. Moreover, the performance of a C6H6 gas sensor based on the suspended macroporous Si membrane (congruent to 30 mu m thick), permeated with the chemical precursor of Sn oxide is presented. The results have demonstrated the feasibility to realize a macroporous silicon suspended membrane with high specific surface area, efficient electrical insulation and negligible warpage. Furthermore, the permeation of the oxidized macroporous silicon membrane with SnO2 has been proved to be a valuable approach to fabricate gas sensors suitable to detect aromatic hydrocarbons in a sub-ppm range.