Low-temperature sintering of metallacyclic stabilized copper nanoparticles and adhesion enhancement of conductive copper film to a polyimide substrate

We report that both low electric resistivity and strong adhesion to polyimide film were attained for a conductive Cu film prepared by low-temperature sintering of 2-amino-1-butanol-protected Cu nanoparticles (AB-Cu NPs) with an average size of 4.4 nm. The sintering temperature of 60 °C for the AB-Cu NPs is the lowest ever reported for Cu NPs. A nanoink comprising these AB-Cu NPs (~35 wt% Cu) produced a conductive Cu film with resistivity of 52 μΩ cm after heating at 150 °C under a nitrogen flow. The adhesion to a polyimide film was compared for films prepared from nanoinks consisting of three different types of alkanol-amine-based Cu NPs: AB-Cu NPs, 1-amino-2-propanol-Cu NPs, and 3-amino-1-propanol-Cu NPs. Only the Cu film prepared from the AB-Cu nanoink established strong adhesion to the substrate without decreasing the electrical conductivity. The adhesiveness is attributed to residual oxidation products after thermal sintering of the Cu nanoinks.