High Resolution Soft and Stretchable Circuits with PVA/Liquid-Metal Mediated Printing

A novel technique that permits, for the first time, fabrication of stretchable traces with linewidths as low as 20 mu m and line-spacing of 30 mu m, based on simple coating and printing techniques, performed entirely at ambient condition, is demonstrated. By relying on existing inkjet printing technique, the proposed sinter-free method is a step toward scalable fabrication of high-resolution stretchable circuits, with application in logic gates, transparent conductors, and solar panels. This is accomplished by coating a layer of poly(vinyl alcohol) (PVA) over an elastic substrate, inkjet printing a circuit with silver nanoparticle (AgNP) ink, and then coating the printed circuit with a thin film of eutectic gallium-indium-tin (Galinstan) alloy. The Galinstan coating selectively wets to the printed AgNPs, resulting in highly conductive (6.65 x 10(6)S m(-1)) circuits that can withstand over 100% of strain with a modest gauge factor of approximate to 2.7. The process does not need thermal sintering, thanks to the Galinstan fusion with AgNPs, thus being compatible with heat-sensitive substrates. The PVA coating has a critical role as a hydrophilic surface that absorbs the water-based ink but resists wetting of the Galinstan. This method is demonstrated over a variety of substrates, including ultrasoft polyurethanes, ultra-stretchable styrene-ethylene/butylynestyrene, and polyimide.