Influence of uniaxial stretching on the Joule effect induced heating of liquid metal based stretchable electronic devices

Abstract

Liquid metals (LM), such as Galinstan (an alloy of GaInSn), make an excellent conductor with high conductivity and freedom of movement in stretchable electronics (SE). However, the combined effect of stretching and current passing through the circuit on the thermal behavior needs to be understood. In this work, we investigate the impact of the changing device parameters due to applied strain on the generated Joule heat and resulting temperature change. A fully automated spray-coating based stencil-printing method of Galinstan is used to achieve reproducible and reliable devices. Results show the combined effects of the decreasing trace cross-section, the reducing distance between wires and the decreasing thermal resistance of encap-sulant results in a linear increase in the surface temperature and internal temperature when stretching. Finally, using custom cyclic stretch testers, we report the robustness of stretchable devices surviving at least 400 000 cycles at 25% strain. Several prototypes of wearable devices, smart patches and sensors are presented. Our automated fabrication process and operando analysis provides insights into the thermal behavior of stretchable electronics subject to combined electrical current flow and mechanical stretching, with applications in wearable electronics and soft robotics in mind.