Flexibility Enhancements of Hybrid Copper Inks with Cellulose Nanocrystals

Abstract

Increasingly, copper nanopowders are commonly used in conductive inks due to their cost-efficiency compared to silver or gold and excellent electrical conductivity. One of the challenges associated with copper inks is oxidation and to address, we have developed a hybrid copper-based ink by removing the oxide layer of copper powders and coat the powders with a silver shell to protect from oxidation. Despite the advances, the inks are prone to fatigue failures when the ink films are repeatedly bent or stretched. In order to overcome this challenge, we proposed to integrate cellulose nanocrystals (CNC) with the copper-based ink on a polymer substrate and use a sintering process based on intense pulsed light in an argon atmosphere. Sintering in argon gas environment improved in electrical conductivity that may be the result of the partial carbonization of the CNC rather than combustion. It has also been experimentally determined that CNC improved adhesion strength of the copper ink film. Moreover, the addition of CNC also reduced the damage caused by bending and stretching. The ink film containing 10% CNC increased the electrical resistance by only 3.82 times after 600 bending cycles versus the resistance increased by 34.4 times without CNC. Under the 30% strain of stretching, the change in resistance of the ink film containing 10% CNC was 1.75 times lower than without CNC. It was observed through microscopy techniques that the presence of CNC reduced the formation of cracks by enhancing mechanical strength.