Investigation of the optical and electrical properties of ZnO/Cu/ZnO multilayer structure for transparent conductive electrodes by magnetron sputtering

In this paper, the ZnO/Cu/ZnO multilayer structure was deposited on glass substrate by magnetron sputtering. The influence of ZnO and Cu layer thickness on optical and electrical properties of multilayer structure was investigated. The X-ray diffraction, Field Emission Scanning Electron Microscopy and Atomic Force Microscopy were used to explore the crystal structure, surface morphology, respectively. The Perkin Elmer Lambda 950 double-beam spectrophotometer and 4-point Probes Resistivity Measurement System (RTS-9) were used to investigate the optical and electrical properties. The experiment and FDTD (finite-difference time-domain) simulation results indicated that the optical transmittance increased with increase of ZnO thickness in ranging from 20 to 60 nm at fixed thickness (10 nm) of Cu layer. The RTS-9 testing showed that the sheet resistance decreased from 30 to 6.5 Ω/sq with increase of Cu layer from 6 to 20 nm. However, the sheet resistance slightly changed with increase of ZnO thickness. The Haacke’s figure of merit (FOM) for all samples with various Cu thicknesses was also calculated. The highest value of FOM was 2.95 × 10⁻³ (Ω⁻¹) in visible region (400–800 nm) when ZnO thickness was 60 nm and Cu thickness was 8 nm. In addition, the aging effect of FOM (stability) was also investigated with the changing of time in nature environment.