Physics of very thin ITO conducting films with high transparency prepared by DC magnetron sputtering

The preparation of very thin indium tin oxide (ITO) films with extremely high transparency and suitable resistivity, as well as resistivity stability for long term use, is described. In order to obtain these properties, amorphous suboxide films were first prepared and then annealed. Suboxide films with a thickness of 20 to 30 nm were prepared on PET film and glass substrates at a temperature of 60 °C using In₂O₃---SnO₂ targets with a SnO₂ content of 0 to 10 wt% by DC magnetron sputtering in a pure argon gas atmosphere. The films were annealed at a temperature of 150 °C for 1 to 100 h in air. The resistivity of films on PET films was, depending on the SnO₂ content, on the order of 10⁻³ ω cm. An average transmittance above 97% in the visible wavelength range and a resistivity of about 4 × 10⁻³ ω cm, as well as resistivity stability, were attained in ITO films with a SnO₂ content of about 1 wt% prepared on PET films by the low-temperature process. It is thought that these properties result from crystallization which occurred during the annealing, duration up to about 25 h.