Optimization of RF Sputtered Ag-Doped BaTiO 3-CuO Mixed Oxide Thin Film as Carbon Dioxide Sensor for Environmental Pollution Monitoring Application

Thin films of BaTiO₃-CuO doped with Ag have been evaluated for their carbon dioxide sensing characteristics. The effect of various parameters, such as Ag doping, annealing conditions, film thickness, electrode dimensions, and operating temperature on sensitivity has been explored. The thin films in the range of 250 nm, with 1% Ag doping and no post-deposition annealing, display the best sensitivity at an optimum operating temperature of 250 °C. We correlate sensitivity with material characteristics as determined by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope, and electron probe microscopic analysis. Sensitivity to CO₂ increases with the reduction in electrode dimensions, with 500 nm electrodes giving the best sensitivity of 19% for 350 ppm and 80% for 1000 ppm of CO₂. The sensor shows very low cross sensitivity to CO, NO₂, and SO₂.