Technological realization of semiconducting metal oxide-based gas sensors

Oxide semiconductor chemiresistors have been widely investigated and used to detect various harmful, toxic, and explosive gases because of their unique advantages such as excellent sensitivity, cost effectiveness, simple sensing mechanism, and facile integration. Gas sensing characteristics such as gas response, selectivity, stability, and response/recovery speed are closely dependent upon transducer designs, sensing materials, and the deposition of sensing materials on transducers. This chapter will cover the development of sensors from bulky porous pellets to thick films on MEMS Based transducers. The chapter also reviews current and new strategies for synthesizing oxide nanostructures for high performance gas sensors will be investigated. The gas sensing reaction in oxide semiconductors consists of the diffusion of the analyte gas from the ambient atmosphere toward the surface of the oxide semiconductor and the charge-transferring interaction between the analyte gas and the oxide surface. The former highlights the importance of gas transfer via micro-, meso-, and nano-porous sensing films, while the latter is dominated by the gas adsorption, surface reaction, and change in charge carrier concentration near the surface of the oxide semiconductor. All the above parameters that determine the gas sensing characteristics are closely dependent upon the size, crystallinity, composition, porosity, and morphology of oxide nanostructures including nanorods (1-D), nanowires (1-D), nanosheets (2-D), nanocubes (3-D), and their assembled hierarchical, hollow, and yolk-shell structures.