Influence of O2 admixture and sputtering pressure on the properties of ITO thin films deposited on PET substrate using RF reactive magnetron sputtering

A systematic study of the growth of indium tin oxide (ITO) thin films on polyethylene terephthalate substrate was carried out using RF reactive magnetron sputtering. The effect of oxygen admixture to sputtering gas, sputtering pressure (4.5×10−1 to 6.8×10−1 Pa), RF power (30–50 W) and growth time (15–50 min) on the electrical and optical properties of ITO thin films was investigated. An indium tin alloy (90:10) of 99.999% purity was used as target. Deposition was carried out at room temperature. Cracks in the films were not observed. It is found that the increase in admixture of O2 to Ar sputtering gas decreases the growth rate. A minimum value of resistivity (7×10−3 Ω cm), decreases in the mobility, reduction in particle size, an average transmittance of ∼80% in UV–Vis range with carrier concentration of ∼5.9×1019 atmos/cm3 and mobility of ∼37 cm2/V s was found with increasing O2 admixture. The increase in sputtering pressure has less effect on growth rate, changes the distribution of particles with increase in their sizes, little variation in Sn/In ratio and a minimum resistivity of 1.9×10−3 Ω cm. The increasing pressure results in improved transmittance to above 80%. Increase in RF power results in a minimum resistivity of 1.9×10−3 Ω cm (at 50 W) and decreases the carrier mobility to 3.5 cm2/V s. A linear increase in the film thickness with increase in optical transmittance to ∼85 is found with increasing growth time. It can be concluded that the film grown at 10% of O2 admixture, 5.6×10−1 Pa sputtering pressure and RF power of 50 W, can meet the requirement of a good transparent and conducting ITO film on polymer substrate.