Preparation and characterization of ito thin films on glass by a sol-gel process using metal salts

Indium-tin-oxide (ITO) thin film is one of the indispensable materials for advanced optoelectric technologies. In this work, uniform and transparent ITO films were deposited onto glass substrates using a sol gel method. The initial sols were prepared from anhydrous ethanol solutions of indium nitrate (In(NO₃)₃·1H₂O) and tin chloride (SnCl₄), with different In:Sn ratios. The sols were dip-coated on the substrates and were subjected to annealing at different temperatures. Depending on compositions, the electrical resistivity of ITO coating varied from 1.4 × 10³Ω/□ to 3.5 × 10³Ω/□, and the minimum value for the electric resistivity was observed for the films containing 8% Sn by weight. Increasing heat treatment-temperatures from 400 to 600°C led to increase in conductivity by one order of magnitude. The optical transmittance of 550°C-annealed ITO films was more than 90% in the visible region. The morphology of the ITO films was examined by scanning tunneling microscopy (STM) and scanning electron microscopy (SEM). The rms-roughness of 350 nm thick ITO film was 1.5 nm. Increasing film thickness resulted in decrease in both, surface roughness and electrical resistivity. The correlations among the film properties and the film preparation conditions are discussed in detail.