A novel porous silicon sensor for detection of sub-ppm NO2 concentrations

We developed a new technique for the deposition of free-standing porous silicon (PS) on alumina substrate with interdigital contacts (Italian Patent ENEA-INFM), thus removing the silicon substrate, that is inactive in gas detection and is much more conductive than PS. The dc and ac electrical measurements in a controlled atmosphere were performed to test the sensor response towards NO2 (0.1–10 ppm), O3 (200 ppb), CO (1000 ppm), benzene (20 ppm), organic vapours and humidity. The device was able to detect very low concentrations of nitrogen dioxide (100 ppb) with no interference from ozone, benzene, CO and organic vapours. Indeed humidity interferes with nitrogen dioxide detection and must be kept under control. Since PS showed great response to NO2 at room temperature (RT), no heating of the sensor is required.