Highly reliable and highly conductive submicron Cu particle patterns fabricated by low temperature heat-welding and subsequent flash light sinter-reinforcement
Submicron Cu particle ink was developed to successfully achieve highly reliable and highly conductive Cu patterns on low-cost, transparent, and flexible substrates by an optimized two-step sintering process involving low temperature heat-welding and subsequent flash light sinter-reinforcement. The Cu ink contains a special additive of the Cu–amino complex made from copper(II) formate and 2-amino-2-methyl-1-propanol solvent. Low temperature heat-welding promotes the decomposition of the Cu–amino complex into fresh metallic Cu particles, which as nano-welders can in situ weld those big submicron Cu particles. The subsequent flash light sintering further reinforces the connection between big Cu particles with the assistance of these active nano-welders and strengthens the adhesion between sintered Cu patterns and polymer substrates due to the local soft-effect. The achieved resistivities of sintered Cu patterns on polyethylene terephthalate (PET), polyethylene naphthalate (PEN) and polyimide (PI) substrates are 26.5 μΩ cm, 15.9 μΩ cm and 7.2 μΩ cm at a low welding temperature of 140 °C for 10 min and subsequent flash light energies of 1080 mJ cm−2, 1273 mJ cm−2 and 2073 mJ cm−2, respectively, at which the same electrical properties cannot be obtained from either pure nano-Cu or submicron Cu particle ink as reported in previous research studies. Moreover, bending fatigue and oxidation-resistance tests indicate that the sintered Cu patterns have superior mechanical and environmental stability. Finally, flexible and foldable LED circuits and flexible dipole antennas were successfully fabricated to demonstrate the applicability of the sintered Cu patterns for printed electronic devices. It should be noted that this method opens a new way for making highly reliable and highly conductive Cu patterns on low-cost, transparent, and flexible substrates with big Cu particles instead of nanoparticles under a suitable sintering process, which may largely decrease the cost and enhance the application of Cu inks for flexible electronic devices.