Fabrication of the planar-type CO2 gas sensor using an evaporated Li3PO4 film and its sensing characteristics

The CO2 gas sensor, based on the principle of electro-chemistry, was fabricated using the solid-electrolyte Li3PO4 film formed by a thermal evaporator and its sensing performances were studied. Thermal evaporated film was prepared with power of 10A, a working pressure of 10−6 mTorr and thickness of 1.2 µm. Then, it was annealed at 800 °C for 2h in air. Li2TiO3+TiO2 and Li2CO3 film were prepared using a screen printing method as the reference and the sensing electrode, respectively. Li3PO4 film showed a much denser structure than bulk-type Li3PO4 in SEM images. The response and recovery characteristics were very good at the higher CO2 concentration and its value was 280 mV and changed to 260 mV in the higher CO2 environment. It was also observed that the sensitivity decreased by 98 % when the CO2 concentration increased from 250 ppm to 5000 ppm. Response time and recovery time were measured to be 5 s and 7 s, respectively. These results showed enough potential for developing a CO2 gas sensor using Li3PO4 film instead of the bulk-type.