Formation and Utilization of Copper Conductive Inks for 2D and 3D Electronics

The fabrication of electrical circuit boards on heat sensitive polymers by printing conductive inks has gained much interest. Among the printing techniques, inkjet printing has many advantages over screen and gravure, as it does not require contact with the substrate and therefore enables printings on 2D, 2.5D and 3D structures. However, printing conductive features, especially on heat sensitive substrates and objects is not widely spread yet, mainly because of the high cost of the common silver inks, which require high temperature for sintering. The best metal for low cost ink is copper, which is about hundred times cheaper than silver. However, copper tends to undergo oxidation at ambient conditions, and therefore becomes non-conductive. Therefore, there is an un-met need for copper inks that are stable to oxidation, and that can be processed at low temperatures.

To overcome these challenges, here we present the formation and utilization of an ink based on soluble copper complexes which is thermodynamically stable. The ink undergoes decomposition and self-reduction, to yield copper nanoparticles either thermally (below 150 °C), or by plasma treatment at low temperatures. The later induces self reduction of the ink, regardless to the decomposition temperature of the complex, and therefore opens the window for utilization on a wide variety of materials such as polymers which are used in 3D printings. We will demonstrate printing of copper inks on 3D objects (Figure 1) along with fabricating an Internet of Things (IoT) system, ReadSpot, that is composed of NFC tag that can communicate with an Android Application (which we developed) and gives visually impairment people an access to information on various products, such as medications (Figure 2).

Figure 1: Printed antenna on 3D printed high heat sensitive polymer (T_g=~80 °C)

Figure 2: A printed NFC antennacommunicates with ReadSpot application installed on Android based phone.