Effects of crystal structure and particle size on ethanol gas sensing characteristics of nanocrystalline ITO thick film

Indium tin oxide (ITO) films are widely used in optical devices for their high electrical conductivity and high transparency to visible light. Some relevant papers reported ITO thin films showed favorable sensitivity to NO ₂ and NO gases. However, researches on gas sensing with ITO films, especially thick films, had not been actively conducted until now. The crystal structure and particle size of ITO can be controlled in nanometer accuracy by coprecipitation method. To investigate the effects of crystal structure and particle size of nano-sized ITO powder on gas sensing properties, two kinds of ITO sensors, having cubic and rhombohedral crystal structures with 15 nm particle sizes, were investigated, and three kinds of ITO sensors having 15, 30, and 70 nm particle sizes, with the rhombohedral crystal structure, were investigated. Gas sensing properties were examined in a chamber with dry air (less than 1 ppm humidity concentration) or gaseous ethanol diluted in dry air. ITO gas sensors with the finer the particle sieze have better sensitivity than of large particle size. The sensitivity of ITO thick films were evaluated by sensing of gaseous ethanol.