Humidity sensing behaviors of nanocrystalline Al-doped ZnO thin films prepared by sol–gel process

Nanocrystalline Al-doped ZnO(AZO) thin films prepared by sol–gel method were used for studying the variation of resistance with humidity. The particle size of the films exhibits nanometer order with zincite structure and the thickness of the films increases linearly with the number of coatings. The AZO film coated five times and annealed at 500 °C exhibits the highest sensitivity for the humidity, which shows three order change in the resistance during the relative humidity variation from 20 to 90%. It is considered that the high humidity sensitivity is due to proton hopping between water molecules adsorbed on the film surfaces with capillary nanopores.