Factors affecting the properties of highly conductive flexible ultrathin ITO films in confined large area magnetron sputtering in three dimensions

A large area magnetron source with the strongly confined magnetic field from all direction is applied for the deposition of flexible ultrathin ITO (UT-ITO) films of thickness 30 nm at room temperature for their applications as transparent electrodes. The films show a minimum resistivity of ∼5.0 x 10-4 Ωcm and high transmittance >80% at wavelengths of 400-700 nm. Measurements and data reveal that a high plasma density, high energy flux, and a relatively low concentration of negative oxygen ions (NOIs) to the flux of positive ions (PIs) induce lower mechanical stress to the growing films, which enables a lower resistivity and superior crystallinity with the smooth surface. The capability of the magnetron source and the characteristic plasma properties are studied in light of the resulting film properties. The considerably lower resistivity with higher carrier concentration and mobility of the UT-ITO films prepared at a high power density of 3 W/cm2 and a low O2 gas flow can be attributed to the growth of crystallized UT-ITO films, resulting in the combination of the oxygen vacancy and substitution of Sn4+ to In3+ site through the deposition of a high energy flux and a low flux ratio of NOIs to PIs.