Highly conductive copper patterns on low-cost flexible substrates are obtained by inkjet printing a metal complex based ink. Upon heating the ink, the soluble complex, which is composed of copper formate and 2-amino-2-methyl-1-propanol, decomposes under nitrogen at 140 °C and is converted to pure metallic copper. The decomposition process of the complex is investigated and a suggested mechanism is presented. The ink is stable in air for prolonged periods, with no sedimentation or oxidation problems, which are usually encountered in copper nanoparticle based inks.

The use of Cu-formate-2-amino-2-methyl-1-propanol ink and low-pressure plasma for the formation of highly conductive patterns on heat sensitive plastic substrates was studied. It was found that plasma results in decomposition of copper complex to form metallic copper without heating at high temperatures. Ink composition and plasma parameters (predrying conditions, plasma treatment duration, gas type, and flow rate) were optimized to obtain uniform conductive metallic films. The morphology and electrical characteristics of these films were evaluated. Exposing the printed copper metallo-organic decomposition (MOD) ink to 160 W plasma for 8 min yielded resistivity as low as 7.3 ± 0.2 μΩ cm, which corresponds to 23% bulk copper conductivity. These results demonstrate the applicability of MOD inks and plasma treatment to obtain highly conductive printed patterns on low-cost plastic substrates and 3D printed polymers.

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COMMUNICATION (1 of 7)in general, Internet of things (IoT) applications. [5] One approach to obtaining electronics on 3D surfaces is based on printing electrical circuits on flat surface, followed by reshaping them into 3D structures. [3b] A well-known example of such process is the thermoforming of thermoplastics with embedded circuits. [6] The drawback of this method is that it is limited in its possible patterns due to the dimensional changes that take place during the thermoforming stretching process, and the limitation to thin plastic films. Another method is by direct printing of conductive inks onto the 3D surfaces, with conductive inks composed of metal NPs. [1b,5,7] However, after printing, the NPs require a sintering process to decompose the organic stabilizers and to render it electrically conductive. Typical sintering processes are based on thermal treatment at elevated temperatures, which can damage some of the polymers that are currently used in typical 3D printers (T g < 80 °C). [8] The prerequisite for low sintering temperature results in low conductivity and poor surface smoothness. For low-frequency antenna applications, the result might be satisfying. However, for highfrequency applications, high conductivity and smooth surfaces are required. Accordingly, there is still an unmet need for a new scientific approach that would result in high conductivity, high surface smoothness, as well as perform at low temperature and low cost. A suitable approach to address these obstacles is the electroless copper plating (EP), which is commonly used to form highly conductive metallic structures. A typical EP process is composed of two main steps: first, a catalyst seed is deposited onto the designated substrate, followed by immersing into a metal salt solution with a reducing agent, resulting in metal coating of the pattern composed of the catalyst. Commonly reported seeds for 2D substrate are based on palladium (Pd), silver, and poly(dopamine). However, each of these materials has its limitations. For example, Pd [9] and silver, [3a,10] which are extensively reported, are very costly materials. With seeds based on poly(dopamine), [11] the obtained bulk resistivity is six times higher than that of bulk copper, which is not sufficient for EP processes. Copper-based seeds were also reported for 2D substrate by either sequential printing of copper salt and strong reducing agents [12] or by laser-induced forward transfer (LIFT) technique. The latter resulted in poor resolution and low 3D printed electronics is an emerging field of high importance in both academic research and industrial manufacturing. It enables fabrication of 3D devices with embedded or conformal electronic circuits, which are relevant to a variety of applications, such as Internet of things, soft robotics, and medical devices. Patterning of electrical conductors with conductivity higher than 50% bulk copper is challenging and usually involves electroless or electrolytic deposition processes that require the use of very costly catalyst, ma...

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