Characterization of NiO thin films for gas sensor

Nickel oxide thin films were prepared by dc reactive magnetron sputtering from a nickel metal target in an Ar-O-2 mixed atmosphere in two sputtering modes. The oxygen content in the gas mixture varied from 15 to 45%. The films deposited in the metal-sputtering mode at high target voltage (320-326 V) resulted in a polycrystalline (fcc) NiO phase with nearly stoichiometric composition. On contrary, the films prepared in the oxide-sputtering mode at low target voltage (293-298 V) were amorphous and oxygen rich. All examined NiO films were semiconductors and their conductance increased by four orders of magnitude between 25 and 350 degrees C. Finally, NiO films were tested in order their response to CO and NH3 at various operating temperatures.