Flexible and Stretchable Liquid Metal Electronics

The focus of this chapter is to review the literature on flexible and stretchable electronics fabricated using gallium-based liquid metal alloys. Over the past few decades, gallium-based liquid metal alloys have gathered growing interest due to their application in various soft electronic applications as conductive yet fluidic metals that can be patterned at room temperature. Gallium-based liquid metal alloys have a melting point at or near room temperature and offer a low toxicity as opposed to the conventional liquid metal – mercury, in addition to having negligible vapor pressure and low viscosity. The surface of these metals reacts rapidly with oxygen in air to form a thin surface oxide ‘skin’ that allows these liquids to be deposited in several useful stable shapes despite the destabilizing effects of a large surface tension and gravity. There are several methods to pattern these liquid metals – traditionally using lithography-based subtractive approaches, and unconventionally using 3D printing and other additive techniques. Gallium-based liquid metal alloys have been used for fabricating various electronic structures such as ultrastretchable and self-healing wires, interconnects, and stretchable antennas. Integrating these components, many electronic components have been built such as optical and soft memory devices, reconfigurable circuits, soft diodes, microfluidic pumps, soft strain sensors, capacitors, and circuit boards.