Three-dimensional flexible electronics using solidified liquid metal with regulated plasticity

Abstract

Three-dimensional liquid metal structures can be created by manipulating ductile gallium–indium alloy wires that are then encapsulated in an elastomer and heated to recover their fluidity, and can remain in a liquid state for a range of temperatures due to a supercooling effect. Liquid metals based on gallium alloy are of potential use in the development of soft and stretchable electronics due to their intrinsic fluidity and high conductivity. However, it is challenging to build three-dimensional circuits using liquid metals, which limits the complexity and integration of the resulting devices. Here we show that a gallium–indium alloy can be used to fabricate flexible electronics with three-dimensional circuits by exploiting the solid–liquid phase transition and plastic deformation of the liquid metal. Solid but plastically deformable alloy wires are shaped into circuits at low temperatures (under 15 °C) and encapsulated in an elastomer, before being heated above their melting temperature. Subsequently, the supercooling effect allows the alloy to maintain a liquid state at a wide range of temperatures, including below the melting point. We use the technique to fabricate high-sensitivity strain sensors, three-dimensional interconnect arches for integrating an array of light-emitting diodes, and a three-dimensional wearable sensor and multilayer flexible circuit board for monitoring finger motion.