Improvement of characteristics of flexible Al-doped ZnO/Ag/Al-doped ZnO transparent conductive film using silver

Abstract

In recent years, transparent conductive oxide (TCO) films that can be applied to flexible devices have attracted considerable attention. Among TCOs, indium tin oxide (ITO) is frequently used, but ITO contains the rare metal In and is inflexible. Therefore, the authors focused on an Al-doped ZnO (AZO) transparent conductive film as an alternative material for ITO. The authors prepared films on polyethylene naphthalate (PEN) substrates to prepare flexible electrodes. PEN substrates are sensitive to heat and must be deposited at low temperatures. However, there is a limit to improving the conductivity of AZO film formation at low temperatures. Therefore, the authors focused on the AZO/Ag/AZO multilayer transparent conductive films. The AZO layer was deposited by RF magnetron sputtering, and the Ag layer was deposited by electron beam evaporation. The electrical and optical characteristics were evaluated by changing the deposition conditions during the AZO and Ag deposition. Thus, when the thickness of the Ag layer was changed, the maximum transmittance was obtained at a thickness of 10 nm. Next, the upper AZO film was divided into room temperature/50 °C. When the upper AZO is formed at 50 °C, the already deposited Ag is affected by thermal oxidation. Ag was protected from thermal oxidation by first depositing the upper AZO at room temperature and then applying 50 °C, resulting in improved transmittance and resistivity. Furthermore, the resistivity and transmittance were improved by increasing the deposition rate of the Ag layer due to a decrease in the oxygen content in the Ag layer. Among the formed thin films, the best obtained characteristics were the resistivity of 1.24 × 10−4 Ω cm and the transmittance of 84.8%.