Micro hot plate-based sensor array system for the detection of environmentally relevant gases

A monolithic stand-alone gas sensor system is presented, which includes on a single chip an array of three metal oxide-coated micro hot plates with integrated MOS-transistor heaters, as well as a specifically designed digital system architecture. An octagonal-shaped micro hot plate design with MOS-transistor heaters has been adopted for the three gas sensors. The integrated circuitry includes a programmable digital temperature regulation, digital sensor readout units, and a standard serial interface. The programmable digital temperature controllers enable individual regulation of the micro hot plate temperatures in constant or dynamic mode. Nanocrystalline tin oxide thick films with different Pd dopings (undoped, 0.2 and 3 wt %) were used. Gas test measurements for environmentally relevant gases were carried out and evidenced detection limits of less than 1 ppm for carbon monoxide, or 100 ppm for methane, both at 40% relative humidity. Temperature modulation techniques were successfully applied for improved analyte discrimination.