Effect of the Cu underlayer on the optoelectrical properties of ITO/Cu thin films

Sn doped indium oxide (ITO) single layer films and ITO/Copper (Cu) bi-layer films were prepared on polycarbonate substrates by DC and RF magnetron sputtering without intentional substrate heating. In order to consider the influence of the Cu underlayer on the optoelectrical properties and microstructures of the films, the thickness of the Cu bottom layer in the ITO/Cu films was varied from 5 to 20 nm.Conventional ITO films had a constant optical transmittance of 74% and an electrical resistivity of 3.1 × 10−3 Ω cm, while ITO/Cu films had different optoelectrical properties that were influenced by the thickness of the Cu bottom layer. The lowest electrical resistivity, 5.7 × 10−5 Ω cm, was obtained from ITO 80 nm/Cu 20 nm films and the highest optical transmittance of 72%, was obtained from the ITO 95 nm/Cu 5 nm films. From the figure of merit (ϕTC) which is defined by ϕTC = T10/Rs, where T is the optical transmittance at 550 nm and Rs is the sheet resistance, it can be concluded that the most effective Cu thickness in the ITO/Cu films on the optoelectrical properties was 5 nm.