Fabrication of flexible electronic devices by printing conductive interconnections is of growing research interest, including by many global electronic companies. The main objective is to find ways to fabricate these connections at low cost, by simple processes, including those suitable for plastic substrates. Therefore, during the last decade, several approaches for the sintering of metallic nanoparticles (NPs), mainly silver, at low temperatures, were developed. However, the high cost of silver based nano-inks limits fabrication of low cost plastic devices and therefore inks with other metals, such as copper, are required. However, inks containing copper NPs suffer from stability problems, as these NPs are quickly oxidised, and so lose their conductivity. Therefore, there is an unmet need for a copper ink with a low sintering temperature.
We are researching a new copper ink that will allow the printing of conductors at low temperature. The ink contains a copper salt in the form of oxidation stable nano and sub-micron particles that decomposes at a temperature below 200C. Requirements for a printable ink include small particle size, dispersion stability and viscosity tailored for the printing method. The nanoparticles are formed by a top-down approach: wet ultrafine grinding with a bead mill of the copper salt in presence of a stabilizing polymer. By this process, the size of the particles can be reduced by 3-4 orders of magnitude. Several factors influence the particle size distribution obtained, including the bead size used, milling time, ratios of solids, liquid and dispersing agent.
We have investigated the process of forming the ink, printing it, and finally decomposing the copper salt to obtain a conductive copper pattern.
rosenyitzchak@gmail.com
