Cu/Ag Thickness Ratio–Dependent Structural and Electrical Behavior of AZO/Cu/Ag/AZO Multilayers on Flexible PET Substrates

This study investigates the AZO/Cu/Ag/AZO multilayer thin films deposited on PET substrates via RF confocal magnetron sputtering, focusing on the influence of Cu and Ag interlayer thickness ratios, while maintaining a constant total metal thickness of 10 nm, on their microstructural, optical, and electrical properties. X-ray diffraction (XRD) analysis combined with Rietveld refinement revealed that Ag-rich configurations enhance crystallinity, reduce residual stress, and promote a pronounced (002) preferential orientation in the AZO layers, which is attributed to improved nucleation behavior and reduced interfacial disorder. Atomic force microscopy (AFM) analysis demonstrated that the Cu/Ag thickness ratio effectively modulates nanoparticle coalescence and surface roughness. Optical characterization revealed that Ag-rich films exhibit higher visible transmittance owing to improved film continuity and constructive interference effects, whereas Cu-rich structures favor enhanced near-infrared (NIR) transparency. Electrical properties, evaluated using Hall effect measurements, indicated that a balanced Cu/Ag configuration (5/5 nm) delivers optimal charge transport, achieving the lowest resistivity (1.22 × 10 −3 Ω.cm), the highest carrier mobility (7.08 cm 2 .V −1 .s −1 ), and the maximum figure of merit (6.88 × 10 −5 Ω −1 ). These results demonstrate that rational Cu/Ag interlayer engineering enables an effective balance between transparency and conductivity in flexible transparent electrodes, opening viable pathways for applications in wearable electronics, flexible photovoltaics, and foldable display technologies.