Fabrication of thin film potentiometric CO2 sensors on differentiate substrate surfaces and their characteristics

Two kinds of planar-type potentiometric CO2 gas sensors using thermal evaporated Li3PO4 thin film as solid electrolyte were fabricated. Alumina plates with rough and smooth surfaces were used as the substrates of the sensors. X-ray diffraction analysis, atomic force microscopy and scanning electron microscopy were used to characterise the Li3PO4 films. The sensing properties were investigated in the range of 500-5000 ppm CO2 concentrations at 480 degrees C. Both the rough substrate-based sensor (r-sensor) and the smooth substrate-based sensor (s-sensor) were sensitive to CO2 gas and showed a good Nernst behaviour. The output electromotive force (EMF) of the s-sensor showed a more stable signal than the r-senor. The EMF/decade values obtained from the r-sensor and the s-sensor were 45 and 55 mV/decade, respectively. The response and recovery time were not primarily influenced by the electrolyte film. It was found that the sensitivity of the s-sensor was closer to the theoretical value. The results revealed that the substrate surface roughness may influence the characteristics of Li3PO4 film and the response properties of the sensors to CO2.