Formate-Free Metal-Organic Decomposition Inks of Copper Particles and Self-Reductive Copper Complex for the Fabrication of Conductive Copper Films

Abstract

Metal-organic decomposition (MOD) inks have been developed for printed electronics applications. Cu-based MOD inks prevent the oxidation of the metal during storage, as the Cu is already present in an oxidized form (i.e. a salt). However, usually hazardous formates such as Cu (II) formate have to be used as the copper salt in order to ensure thermal decomposition and self-reduction of the metal salt at moderate temperatures (less than 150 °C). In this study, a formate-free hybrid ink containing copper particles and a Cu/1-amino-2-propanol (AmIP)/acetate complex was developed for the fabrication of conductive copper films on flexible polymer substrates at low sintering temperatures. A hybrid ink with a weight ratio of 3:1copper particles to MOD ink produced a conductive copper film with close-packed copper particles and a low resistance of 7.3×10⁻ 5 Ω cm after sintering at a temperature of 180 °C for 60 min under a N2 gas flow. Good oxidation resistance of the copper films was observed after exposure to air at 23 °C for two months. Figure 7: FE-SEM images of a Cu film (prepared from a hybrid MOD ink with a weight ratio of 3:1, copper particles:MOD ink) on a polyimide film after sintering at (a)150 °C and (b) 200 °C for 60 min under N2 flow.

Effectiveness of Ligand Denticity-Dependent Oxidation Protection in Copper MOD Inks

“…This is mainly attributed to the convoluted chemistry involved, including the transition via a Cu­(I) intermediate, as first reported by Farraj et al Furthermore, the in situ reduction temperature and the reaction mechanism can be related to both the Cu­(II) and Cu­(I) complex geometries as the type of amine involved in the coordination . For this reason, almost all studies report on the decomposition of copper MOD inks in a nitrogen − or even reducing atmosphere (H 2 /N 2 or formic acid). , …”