Effect of Au and Ag contacts on the CO sensitivity of SnO2 thick films

Synthesized tin oxide (SnO2) nanoparticles were deposited on soda lime glass substrates, in thick films form, by means of Doctor-Blade technique. Further annealing treatment were done on all films at 250, 350, and 450 degrees C. The deposited films were characterized using X-ray diffraction, Profilometry, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). As the annealing temperature increased, the corresponding thickness of the films varied from 1319 to 538.5 nm due to the evaporation of carbon during the annealing process. SEM analysis has confirmed the formation of agglomerates consisting of SnO2 particles with average size in the range of similar to 25-60 nm, which are highly porous. At higher annealing temperatures, an increment in surface porosity resulted in pin holes-like structures. EDS analysis has confirmed the evaporation of carbon with increase in annealing temperature and homogenous distribution of Sn and O over the film surface. The films were tested as gas sensors, by detecting the resistivity change as a function of CO concentration. Two metal contacts were tested also, namely, silver and gold, deposited on tin oxide annealed at 450 degrees C. An enhanced sensing response around 100 was achieved for films with gold contacts as compared with a value of 30 found in the samples with silver contacts. The high sensing response of SnO2 films with gold contacts is due to the high contact area with SnO2, gold inertness, and chemical stability. Our findings let us suggest that SnO2 sensors with gold contacts operating at 100 degrees C will be lower power consumption sensing devices with high durability.