Study of SnO/sub 2/ and SnO/sub 2/:CuO thin films for H/sub 2/S gas sensing applications

SnO/sub 2/:CuO thin films have been identified earlier as highly sensitive and selective H/sub 2/S gas sensors. Usually the sensors are characterized by measuring dc resistance. In the present study ac impedance spectroscopy has been used to investigate the effect of cupric oxide addition on H/sub 2/S sensing properties of polycrystalline SnO/sub 2/ based thin film sensors. For this two types of thin films-pure SnO/sub 2/ and SnO/sub 2/:(0.5 wt%)CuO, were studied. It has been observed that the total impedance of the films has two contributions: one due to grains (intragranular) and other from grain boundaries (intergranular). On exposure to H/sub 2/S gas, it was seen that for SnO/sub 2/ films, the intergranular resistance drops by a factor of 6 while for SnO/sub 2/:CuO films this reduction is by a factor of 10/sup 7/. These results support earlier studies, that high sensitivity in SnO/sub 2/:CuO films is due to destruction of p-n junctions formed at grain boundaries.