Permeated porous silicon for hydrocarbon sensor fabrication

To realise advanced solid-state microsensors for a reliable monitoring of very low concentrations of pollutant species such as NO,, SO2, CO, O-3 and aromatic hydrocarbons, the use of porous silicon (PS) layers permeated with mixed semiconducting oxides (Sn-V-O) has been proposed and explored. A low concentration C6H6 sensor made of a permeated macroporous silicon layer on a massive Si substrate has exhibited an excellent performance. To reduce the power consumption down to the level reported for micromachined gas sensor (0.1 W), and to make the device feasible for operation 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) on top of which a heater resistor and a temperature sensor are integrated. In this paper the PS formation and processing are presented. Results on the morphological characterization of permeated macroporous silicon membrane are also illustrated. Finally, the electrical response of the device exposed to gas mixtures of different compositions is shown. (C) 1999 Elsevier Science S.A. All rights reserved.