High sensitivity Pt-doped SnO2 gas sensors fabricated using sol–gel solution on micromachined (1 0 0) Si substrates

Pt-doped SnO2 gas sensors were fabricated on Si3N4 membranes using silicon micromachining process. Applying a sol–gel deposition technique, it is possible to obtain a highly porous tin-oxide layer suitable for high sensitivity sensors. The sensing material was spin-coated over contact electrodes with a thickness ranging from 100 to 500 nm and they were annealed at different temperatures. A lift-off technique was exploited to pattern the SnO2 thin film and to reach gold pads. Sensitivity measurements of the sensors were carried out for various concentrations of CO ranging from 50 to 500 ppm. Annealed sensors were found to show a high sensitivity for low temperature detection of CO (140–170 °C). SEM and XRD analyses were used to investigate the surface morphology and crystallinity of SnO2 films. A high sensitivity of 450 (Ra/Rg) was achieved for 400 ppm of CO for the films annealed at 450 °C.