Effect of sputtering conditions on the gas sensitivity of copper oxide thin films

Copper Oxide (CuO) thin films were deposited on conductive glass substrates using DC reactive sputtering in a mixture of Argon and Oxygen gases. The sputtering pressure and the substrate temperature were increased from 6 to 8.5 mbar and from 70 to 192 0C, respectively. All the synthesized films contain single phase of CuO in this range of pressure and substrate temperature. According to Scherrer formula, the crystallite sizes vary from 9.03 to 22.47 nm as sputtering pressure is varied from 8.5 to 6 mbar. The crystallites favoring perpendicular orientations dominate at higher deposition pressures due to higher deposition rates. Due to smaller crystallite sizes, the film deposited at 192 0C under 8.5 mbar pressure provides a gas sensitivity as high as 19.26 after keeping10 minutes in CO2 gas at room temperature. The sample fabricated at 192 0C and 9 mbar indicates a sharp drop of CO2 gas sensitivity from 3.67 to 0.84 at operating temperature 75 0C. All theses samples are not sensitive to N2 gas according to cross-sensitivity measured in N2 gas.