Effect of Carboxylic Acid on Sintering of Inkjet-Printed Copper Nanoparticulate Films

The reduction effect of various carboxylic acids on inkjet-printed, copper film was investigated. Carboxylic acids were exposed to the film by nitrogen gas that was bubbled through the liquid acids during the annealing process. It was observed that in the case of saturated monocarboxylic acid (formic, acetic, propionic, butyric), the acids with shorter hydrocarbon chains perform better in reducing the surface copper oxides in the printed copper conductive film. The printed films exposed to formic acid vapor exhibited the lowest resistivity (3.10 and 2.30 mu Omega cm when annealed at 200 and 250 degrees C, respectively). In addition, the oxalic acid more effectively reduces copper oxide than formic acid and its usage can shorten the annealing time for highly conductive printed copper film. This reductive annealing process allows fabrication of copper patterns with low resistivity, (3.82 mu Omega cm annealed at 250 degrees C) comparable to the resistivity of bulk copper.