Printing of copper patterns on 2D and 3D Objects Yielding 50% Bulk Conductivity by Using a Self-Reducing Precursor

Yitzchak (Isaac) Rosen, Casali Center for Applied Chemistry, The Institute of Chemistry and Center for Nanoscience and Nanotechnology, Hebrew University of Jerusalem, Jerusalem, Israel
Michael Grouchko, Casali Center for Applied Chemistry, The Institute of Chemistry and Center for Nanoscience and Nanotechnology, Hebrew University of Jerusalem, Jerusalem, Israel
Shlomo Magdassi, Casali Center for Applied Chemistry, The Institute of Chemistry and Center for Nanoscience and Nanotechnology, Hebrew University of Jerusalem, Jerusalem, Israel

Fabrication of devices by printing conductive interconnections is of growing research interest, including by many global electronic companies. One of the main challenges in the field of flexible electronic is to find ways to fabricate connections at a low cost, by simple processes, suitable for plastic substrates. Therefore, several approaches for the sintering of metallic nanoparticles (NP), mainly silver were recently developed. However, the high cost of silver limits commercial use and therefore inks with other metals, such as copper, are required. However, inks containing copper NPs suffer from stability problems, as the NPs are quickly oxidised, and so lose their conductivity. Therefore, there is an unmet need for a copper ink with a low sintering temperature.

Two concepts for forming copper conductive patterns were examined. The first approach is based on using a new ink that contains nano and sub-micron copper salt particles which are stable to oxidation. This ink was used as a Metal Organic Decomposition ink which is printed and then heated to induce thermal decomposition. During decomposition, the organic matter is broken down to volatile species while reducing the copper, thus leaving a Cu° pattern.

Another approach is based on the use of copper precursors in a transfer printing process that results in 50% bulk copper conductivity. Two steps are involved in the process. In the first step, the mirror image of a desired pattern is printed with the ink on a “donor substrate”. In the second step, this mirror image pattern decomposes by heating under N₂ gas, and copper is transferred to a close by “acceptor substrate” through the gas phase. This approach can be used to pattern 2D substrates and performed onto 3D objects with several advantages; it is non-contact, eco-friendly, low cost, and a dense layer of copper is obtained leading to low resistivity.