Sputtered nickel oxide films for NO_2 gas sensors

摘要

In recent years, lot of efforts was made to develop many types of nitrogen oxide gas sensors. Among them, most interesting are WO_3, V_2O_5, TiO_2, SnO_2 and NiO thin films as gas sensing layers. Relatively small effort has been done to examine nickel oxide. But reasonably good electrical properties and stability in air make it feasible for the fabrication of nickel oxide thin film based gas sensors. Hence, in the present study NiO thin films were deposited by dc reactive magnetron sputtering technique from a nickel metal target in argon and oxygen mixed atmosphere and studied its gas sensing properties towards NO_2 gas. The effect of process parameters on the structural, morphological and electrical properties of NiO was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and Hall effect studies respectively. The films prepared at optimum conditions showed superior electrical properties and exhibited fine and uniform grains with RMS roughness 9.4 nm. These films were tested for gas sensing characteristics of NO_2 gas. The sensitivity of NiO thin film was investigated in the temperature range of 373 to 573 K. The dynamic response for the NiO films was observed at an operating temperature of 473 K, with gas concentration of 50 ppm for NO_2 gas.