Tin oxide and zinc oxide based doped humidity sensors

The semiconducting materials such as stannic oxide (SnO2), zinc oxide (ZnO) doped with titanium oxide (TiO2) and alpha-alumina (alpha-Al2O3), are screen-printed in the form of thick film. alpha-Al2O3 and TiO2, are used as stabilizer and temperature improvement characteristic materials. DC-electrical resistance of the films is measured in presence of humidity. SnO2-5Al(2)O(3) and ZnO-5Al(2)O(3) sensors are found to be good sensing materials for humidity. Rutile and hexagonal structures of SnO2, ZnO and alpha-Al2O3 and their nano meter grain sizes are responsible for formation of nano meter sized pores, which ultimately adsorbs water. The adsorption of water (physisorbed water) on a hydroxylated surface causes electron injection. The interaction of adsorbed oxygen with water molecules or possibly with chemisorbed water causes energy level of the adsorbed oxygen ions to fluctuate, so that electrons can be more easily injected. (c) 2006 Elsevier B.V. All rights reserved.