Preparation and Characterization of Flexible Gas Sensors with Nanostructured NiO-Doped SnO2 Thick Films

A NiO-doped SnO2 thick film with a pure tetragonal phase was prepared on a polyimide flexible substrate. The nanostructured NiO-doped SnO2 thick film composed of very fine grains was obtained by modified hydrazine and ink dropping methods. As the NiO doping concentration was increased, the average grain size of the SnO2 thick film decreased. However, an agglomerated surface morphology was observed on the surface of the NiO-doped SnO2 thick films with a high NiO doping concentration. The 0.5 wt% NiO-SnO2 thick film has a specific surface area of 56.50 m(2)/g. The optimized ink dropping process could make crack-free NiO-doped SnO2 thick films fill the 10 mu m gap between patterned Pt electrodes. Additionally, the pure SnO2 thick film without NiO doping showed gas responses (R-air/R-gas) of 1.19 and 1.65 at CO concentrations of 100 and 500 ppm, respectively. On the other hand, the prepared 0.5 wt% NiO-SnO2 thick film exhibited improved gas responses of 1.9 and 2.8 at the equivalent measurement conditions, respectively.