Direct Writing of Gallium-Indium Alloy for Stretchable Electronics

In this paper, a direct writing method for gallium-indium alloys is presented. The relationships between nozzle inner diameter, standoff distance, flow rate, and the resulting trace geometry are demonstrated. The interaction between the gallium oxide layer and the substrate is critically important in understanding the printing behavior of the liquid metal. The difference between receding and advancing contact angles demonstrates that the adhesion of the oxide layer to the substrate surface is stronger than the wetting of the surface by the gallium-indium alloy. This further demonstrates why free-standing structures such as the traces described herein can be realized. In addition to the basic characterization of the direct writing process, a design algorithm that is generalizable to a range of trace geometries is developed. This method is applied to the fabrication of an elastomer-encapsulated strain gauge that displays an approximately linear behavior through 50% strain with a gauge factor of 1.5.