CO2-sensing characteristics of SnO2 thick film by coating lanthanum oxide

CO2 gas-sensor was fabricated by coating and heat-treating the drop of LaCl3⋅7H2O solution on the surface of SnO2 thick film. The effects of several factors, such as heat-treatment temperature, La concentration of coating-drop and humidity on CO2 sensitivity of thick film sensor were investigated in this work. The starting material, LaCl3⋅7H2O, for coating was phase-transformed by heat-treating, from LaCl3 to LaOCl at temperature range of 367–738°C, and from LaOCl to La2O3 over 773°C. The maximum sensitivity appeared at heat-treatment temperature of 1000°C and La concentration of 1×10−2 M La. The sensitivity showed a tendency to decrease remarkably with increasing humidity as well as with decreasing oxygen partial pressure.