Liquid-metal micro-networks with strain-induced conductivity for soft electronics and robotic skin

Abstract

Thin-film devices made of room-temperature liquid metals (LMs) have contributed to the development of electronic skin for human-robot/machine interfaces but still have limitations, including degradations of performance and robustness under repeated deformations. In this paper, we describe an interesting phenomenon of the formation of LM microscale networks (LMMNs) and propose to use the LMMNs for fabricating thin-film conductors. A simple layer-by-layer (LBL) deposition process enables the growth of a hierarchical structure of LM microdroplets that forms a conductive network (i.e., LMMN) when stretched. The strain-history behavior of LMMNs allows conductivity enhancement up to 2.37 × 106 S m−1 in response to increased tensile strains. By adjusting the number of LM layers in LBL deposition, the gauge factor (0.2 ≤ GF ≤ 1), the linearity, and the sheet resistance of LMMN films can be easily controlled, providing high potentials in various applications, including skin-mountable circuits, energy harvesters, and soft artificial skin.