Effect of thickness on the properties of ITO thin films deposited by RF-PERTE on unheated, flexible, transparent substrates

The influence of thickness on the main properties of indium tin oxide (ITO) thin films deposited onto flexible, transparent polymer substrates at room temperature was studied. The deposition technique used was radio-frequency (RF) plasma-enhanced reactive thermal evaporation (RF-PERTE) of a 90% In–10% Sn alloy in the presence of oxygen. Results show that (1) the total transmittance is always approximately 80% at a wavelength of 500 nm when the thickness of the ITO films exceeds 70 nm and (2) ITO thin films with electrical resistivity of 6.2×10−3 Ω cm, free carrier mobility of approximately 1.2 cm2 V−1 s−1 and free carrier concentration of approximately 8.6×1020 cm−3 are obtained, for films 100 nm thick. SEM investigations revealed that the surface morphology of the growing ITO thin film is dominated by the surface features of the flexible, transparent polymer substrate in the micron and submicron ranges, and does not vary significantly with thickness.