Investigation of annealing effects on sol–gel deposited indium tin oxide thin films in different atmospheres

Abstract

Indium tin oxide (ITO) thin films have been deposited onto silicon and quartz glass substrates and also on titanium dioxide and tantalum oxide coated substrates by a sol–gel process, followed by annealing in air, oxygen and nitrogen. The effect of annealing in the temperature range of 400–700 °C on the electrical, optical and structural properties of ITO thin films has been studied. The starting solution was prepared by mixing indium chloride dissolved in acetylacetone and tin chloride dissolved in ethanol. Indium oxide (0–20 at.% Sn-doped) (ITO) films were prepared. X-ray diffraction measurements were performed to determine the crystallinity of the ITO films which showed that they were polycrystalline with a cubic bixbyite structure. Films with a thickness of 250 nm had an optical transparency up to 89% in the wavelength range of the visible spectrum, regardless of annealing atmospheres. The ITO thin films containing 10 at.% Sn showed minimum resistivity of 8.0×10 −4 Ω cm when annealed at 500 °C in nitrogen. The resistivity of ITO films deposited on titanium dioxide and tantalum oxide film had a minimum value of 9.5×10 −4 and 9.0×10 −4 Ω cm, respectively, when annealed at 500 °C; higher than that deposited on glass. The conductance vs. thickness relationship for ITO shows that, when it is deposited on top of titanium or tantalum oxide, there is an interdiffusion layer of approximately 40 nm thickness. These combinations of transparent conductive ITO thin films and titanium dioxide or tantalum oxide insulating layers may be useful for thin film electroluminescent devices.