A Subtractive Method to Chemically Pattern Liquid Metal for Stretchable Circuits

Advancements in biomedical research have spurred the development of stretchable electronic devices. While soft insulators are readily available, soft conductors with metal-like electrical conductivity are rare. Gallium and its alloys, being non-toxic and intrinsically stretchable, are potentially ideal solutions. However, current additive liquid metal (LM) patterning methods face limitations in achieving high-throughput, high-resolution, and high-density LM wiring. Here, a subtractive LM patterning method has been developed to meet all these requirements simultaneously. The innovative method involves parallel filling a single continuous microfluidic mesh network with LM that short-circuits all the pins and pads of a circuit, followed by parallel cutting of the unwanted short-circuited interconnections using hydrochloric acid (HCl) vapor. Cutting locations are pre-defined by designing narrower intersecting channels, leveraging capillary force for precise filling and cutting. The process was characterized using a multi-dimensional parametric study with varying LM line widths and HCl concentrations, and in-situ impedance measurements to assess insulation performance. To showcase its high-throughput capabilities, a mock circuit was used to successfully generate complex LM interconnects that connected hundreds of electrical pads. Lastly, a stretchable LM circuit, fabricated using the subtractive LM patterning method, was integrated with a micro-LED array, highlighting the practical application of this new technology in creating massively parallel LM wirings in complex, heterogeneous, and stretchable electronic circuits.