Cobalt oxide based gas sensors on silicon substrate for operation at low temperatures

The gas sensing characteristics and the morphology of cobalt oxide thin films have been investigated. The thin films were prepared by reactive electron beam evaporation of cobalt on “pure” and surface-oxidised silicon wafers respectively followed by an additional thermal treatment. Structural and morphological analyses of the thin Co3O4 films were performed by X-ray diffraction analysis (XRD), scanning electron microscope (SEM) and Rutherford backscattering (RBS). Two gas-sensitive parameters of the Co3O4 films were investigated: the shift of the work function and change of conductivity during gas exposure. The gas measurements were carried out with ammonia, methane, carbon monoxide, hydrogen, chlorine (only GasFET) and nitric dioxide as test gases in synthetic air at different humidities. The work function measurements were carried out with suspended gate GasFETs as transducer, the resistive measurements with single chip thin-film sensor arrays.