Monitoring of environmentally monolithic metal-oxide relevant gases by a digital microsensor array

In this paper, measurements of environmentally relevant gases (CO, CH₄ and NO₂) with a novel single-chip digital microhotplate array are presented. The array consists of three tin-oxide-coated microhotplates with integrated MOS-transistor heaters and specifically designed circuitry. The programmable digital temperature controllers enable individual regulation of the microhotplate temperatures in continuous or dynamic mode. Nanocrystalline tin-oxide thick films with different Pd dopings (undoped, 0.2 wt% and 3 wt%) were tested. Excellent discrimination between the three gases was achieved with detection limits of less than 1 ppm for CO, 100 ppm for CH₄ (40% RH) and 10 ppb of NO₂ (30%/70% RH).