Gas detection by semiconductor ceramics: Tin oxide as improved sensing material

This paper presents an overview on semiconductor ceramics for gas sensing. Conventionally used fabrication methods (sintered ceramics, thick and thin film techniques) are described and the most used materials reviewed. The use of nanostructuring techniques is also presented as one of the last advances in gas sensing devices and as a promising future research line. As long as tin oxide is the mainly used ceramic semiconductor for gas detection, a deeper revision of this material is completed in terms of its electronic and chemical behaviour in the presence of gas (receptor and transducer functions) and the most significant parameters in gas detection are also analyzed: grain size, film thickness, humidity influence, shape and material of the electrodes, etc. Special attention is paid to the way of improving selectivity in gas sensing, which is one of the major concerns in tin oxide based sensors. The main results on some of the most reported techniques to enhance selectivity such as the use of metallic additives or external and integrated filters are presented.