Overcoming Printing and Interfacial Challenges in Liquid Metal Direct Writing for Integrated Stretchable Electronics

Abstract

Direct writing enables rapid prototyping of liquid metal-based stretchable electronics. Challenges, such as printing on uneven surfaces, a limited understanding of the flow behavior, and interfacial issues between liquid metal and electronic terminals for reliable interconnections, remain. We innovatively utilize the kinematic bed of a 3D printer to dynamically control the stand-off distance during direct writing. This enables reliable printing on irregular surfaces and 3D structures with slopes up to 10%. We discover that the thickness of printed liquid metal is affected by a pressure-driven backflow, enabling tuning of thickness in a range of 100 . To solve interfacial challenges, we develop a novel solder-based technique that forms a liquid metal interface on metal coatings, resulting in 100% print reliability between the LM meniscus and the electronic terminal. This interface reduces contact resistance by a factor of four, and improves electrical stability during cyclic strain, with negligible resistance change up to three million cycles. These innovations are demonstrated through the fabrication of large (order of 10 cm) stretchable devices, and stretchable devices featuring integrated electronic components. Our contributions address the limitations of direct writing of liquid metal, advancing the practical realization of reliable, scalable, and fully integrated stretchable electronic systems.