Low temperature NO2 sensitivity of nano-particulate SnO2 film for work function sensors

Work function based investigations of NO2 sensitivity of tin oxide (SnO2) nano-particulate films were carried out at low temperatures under different humidity conditions. A simple preparation technique was employed to obtain stoichiometric nano-particulate SnO2 films. The nano-particles size was determined by atomic force microscopy (AFM) and the work function measurements were done at 130°C by a computer controlled Kelvin probe setup. The samples were subjected to dry and wet (30, 50, and 60% r.h.) air containing different concentrations of NO2. The results suggest that the sensor films containing particles of average 15 nm size show good sensitivity to NO2, we obtain ∼100 mV work function change to 5 ppm concentration at 130°C. Also a little influence of humidity on the work function is observed. Further, during measurements base line drift was not seen which suggests that the poisoning is not occurring on the film surface due to NO2 interaction. This is an important parameter for the long term operation of a sensor. This results indicate that nano-particulate film of SnO2 is suitable for work function based NO2 sensors like field effect transistors (FET) based sensors operating at 130°C.