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Li+ ion conducting Li3PO4 thin film electrolytes with thickness 300nm, 650nm and1.2μm were deposited on Al2O3 substrate at room temperature by thermal evaporation method.Reference and sensing electrodes were printed on Au interfaces by conventional screen printingtechnique. The overall dimension of the sensor was 3 x 3 mm and of electrodes were 1 x 1.5 mmeach. The fabricated solid state potentiometric CO2 sensors of type: CO2, O2, Au, Li2TiO3-TiO2 / Li3PO4 / Li2CO3, Au, CO2, O2 have been investigated for CO2 sensing properties. Theelectromotive force (emf) and δemf/dec values of the sensors are dependent on the thickness ofthe electrolyte film. 1.2μm thickness deposited sensor has shown good sensing behavior than thesensors with less thickness. The δemf values of the sensor are linearly increased up to 460oCoperating temperature and became stable above 460oC. Between 460-500oC temperatures regionthe sensor has reached an equilibrium state and the experimentally obtained δemf values areabout 80% of the theoretically calculated values. A Nernst’s slope of -61mV/decade has beenobtained between 250 to 5000 ppm of CO2 concentration at 500oC temperature. The sensor issuitable for ease of mass production in view of its miniaturization and cost effectiveness aftersome further improvement.