Tin oxide gas sensors: An analytical comparison of gas-sensitive and non-gas-sensitive thin films

Abstract The only difference between CO-sensitive and non-gas-sensitive tin oxide thin films is in the amount of oxygen or oxygen-containing species adsorbed on their surfaces. However, the density of negatively charged oxygen atoms on the surface of the tin oxide is decisive for the sensitivity towards CO. By means of investigations of the temperature dependence of the thin-film resistors in synthetic air without CO, adsorption and desorption processes of oxygen with acceptor characteristics could be proved for CO-sensitive tin oxide thin films. A prerequisite for the fabrication of reliable and reproducible tin oxide gas sensors is that defined adjustment of the density of adsorption sites for negatively charged oxygen must be possible.