Proceedings of the
9th International Conference of Asian Society for Precision Engineering and Nanotechnology (ASPEN2022)
15 – 18 November 2022, Singapore

Eco-Friendly Direct Synthesis and Micro-Patterning of Copper on Flexible Transparent Substrates

Swami Siddhartha, Yu-Bin Chen, and Ming-Tsang Lee

Department of Power Mechanical Engineering, National Tsing Hua University, Hsinchu City, 30013 Taiwan, R.O.C.


Flexible electronics have gained significant attention in last few decades due to their applications in various devices. The liquid precursor-based laser-induced reductive technique provides a solution to a fast and low-cost fabrication of flexible conductors. In this study, we demonstrated the preparation of an eco-friendly and particle-free copper ionic solution. The solution was utilized as a precursor to fabricate copper microstructures on transparent and flexible polyethylene terephthalate (PET) using laser direct synthesis and patterning (LDSP) technique. Water was used as the solvent, while L-ascorbic acid, which is also known as Vitamin C, was used as the reducing agent. Both chemicals are environmentally benign and are not hazardous to human health. A suitable processing parameters window for fabricating Cu microlines on PET was evaluated based on the electrical resistance measurement of the copper micropatterns. We further investigated the improvement of the mechanical durability by laser reheating of copper microstructures as post-processing. Cyclic bending tests showed that the change in resistance of samples with post-processing after 1000 bending cycles was around 77% less than that of samples without post-processing. This improvement in flexibility was attributed to the enhancement in copper-PET interfacial adhesion, which was confirmed with pull-off test and SEM analysis. Apart from interfacial adhesion, post-processing also improved conductivity of the copper microstructures. Resistance of the copper microcline was reduced by up to 39% after post-processing which was attributed to grain growth during post-processing. Average grain size of copper microstructures was around 54% higher than that without post-processing. The resistivity of the fabricated copper micropattern was as low as 4.7 µΩ?cm with optimized laser parameters, which is only about three times of that for pure copper, and is among the best electrical property achieved by similar state-of-the-art micro-patterning technologies. In addition to deposition of conductive microstructures during LDSP, formation of microbubbles was found to be inevitable. In this regard, comprehensive investigation of bubble dynamics during LDSP would be useful in understanding underlying mechanism of bubble formation and its effect on properties of fabricated conductive microstructures. Therefore, in addition to investigation of conductivity and mechanical durability of fabricated Cu microstructures, preliminary results of bubble dynamics are also reported in this study. Results of this study pave the way for green and sustainable manufacturing of next generation flexible and wearable electronics with a rapid, economic, and low-energy-consumption process.

Keywords: Copper-ion liquid precursor, Flexible conductors, Laser reductive sintering, Thermal treatment

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