Effects of air annealing on the structure, resistivity, infrared emissivity and transmission of indium tin oxide films

Indium tin oxide (ITO) films were deposited on glass substrates at room temperature by direct current magnetron sputtering. And then the films were annealed at different temperature ranging 100-400°C for 1h in air. Phase, microstructure, resistivity, infrared emissivity and transmission of the films were characterized by X-ray powder diffraction, a scanning electron microscope, a four-point probe, an infrared emissivity measurement instrument and UV-vis-IR spectrophotometery, respectively. The results show that the crystalline phase of the ITO films transforms from amorphous state to polycrystalline cubic bixbyite In ₂O ₃ structure at 200°C; the resistivity first decreases with the increasing annealing temperature but then greatly increases; the variation of infrared emissivity with the annealing temperature is same with that of electrical resistivity, which is in consistent with the Hagen-Rubens relation. The film annealed at 200°C shows the lowest resistivity of 6.0×10 ^-4Ωcm, the lowest infrared emissivity and higher transparency. In addition, in order to study further the effect of annealing on the infrared emissivity, the mean infrared emissivity of the films as a function of temperature were discussed in detail in the process of heating and cooling between room temperature and 350°C.