FABRICATION OF CARBON-DIOXIDE GAS SENSOR AND ITS ALARM SYSTEM USING INDIUM TIN OXIDE (ITO) THIN-FILMS

Indium tin oxide (ITO) polycrystalline thin films grown on alumina substrates by thermal evaporation, followed by annealing in a humid environment, are used for fabricating a gas sensor to detect carbon dioxide (CO2) gas produced by incomplete burning in domestic combustion equipment and combustion processes. ITO thin-film gas sensors with a thickness of about 150 nm show a maximum sensitivity when operated at a temperature of 573 K for various concentrations of CO2 gas. A tentative mechanism based on molecular orbital (MO) theory is proposed for the role of CO2 gas in increasing the conductance of ITO thin-film gas sensors. This increase in conductance is utilized to initiate the triggering of an electronic alarm system.