Additive manufacturing has become a promising method for the fabrication of inexpensive, flexible sensors. Flexible electronics such as electro-optic devices, gas sensors, chemical sensors, phased-array antennas, radio frequency identification devices, and organic thin-film transistors have been demonstrated on additive technologies such as inkjet, aerosol-jet, and plasma jet printing (PJP). Silver and copper nanoparticles (NPs) and nanoflakes are commonly used in additively forming conductive traces but can suffer from oxidation and loss in performance over time. Additionally, silver is less ideal in biomedical applications compared to metals like gold and platinum, which are more biocompatible and resistant to oxidation. Gold NP inks are becoming used in additive manufacturing but have inherently poor adhesion in many cases. Even in semiconductor processes, an adhesion layer of titanium or chromium is commonly used when sputtering gold onto a substrate. The adhesion of gold printed onto smooth substrates like polyimide and glass is poor and can easily flake and scratch off. In recent experiments, we have seen that adhesion can be significantly increased with the addition of adhesion-promoting polymers to the gold ink before it is printed with PJP. PJP has an advantage over other methods because it uses a dielectric barrier discharge plasma to focus aerosolized nanoparticles onto the target substrate. The plasma can be used to tailor the properties of the printed material and sinter in situ, as has been previously shown with silver and gold nanoparticles. The technology can also be utilized in space and microgravity environments since the plasma-assisted deposition is independent of gravity. In this work, we show direct printing of flexible, conductive, gold structures onto low-temperature substrates without the need for thermal or photonic post-processing. These structures have significantly increased adhesion while maintaining similar performance to samples without added polymer.
