Ink-jet printing of Cu conductive ink on flexible substrate modified by oxygen plasma treatment

We conducted ink-jet printing of copper (Cu) conductive ink on polyimide (PI) film to form Cu conductive patterns and determine the correlation between Cu ink based on Cu complex and flexible substrate. First, the oxygen plasma treatment was performed to modify the surface property of the PI film, and contact angles were measured to confirm the change of its surface property. Thus, we confirmed the decrease of contact angles and optimized plasma treatment parameters. Then Cu conductive lines were formed on unmodified and modified PI films using ink-jet printing, and the printed lines were reduced and sintered by thermal treatment in hydrogen (H₂) atmosphere at 200°C. The formed Cu conductive lines were analyzed by an optical microscope (OM), a field emission scanning electron microscope (FE-SEM), an X-ray diffractometer (XRD), a non-contact 3D Profiler, and a four-point probe to confirm the shape, microstructure, crystal structure of conductive lines, and electrical conductivity. The continuous lines having pure Cu phase and well-sintered microstructure were successfully formed on PI substrate modified by oxygen plasma treatment and the correlation between Cu ink and substrate surface property was determined.