(Liquid) Metallic Photoresist for Monolithic Microlithography of Elastic Electronics

By offering mechanical compliance similar to biological tissue, elastic electronics show great potential in wearable and implanted electronics, interactive robots, and neural interfaces. Miniaturization of elastic electronics through advanced microfabrication is essential to increase device density for high-quality and comprehensive information processing. Cleanroom photolithography is conventionally used for micropatterning photoresists, whose patterns are then transferred to rigid metal or semiconductor materials through lift-off or etching processes. However, such delicate processes are exclusive and cannot be directly translated to fabricate elastic electronics, which are usually based on unconventional materials. Here, we developed a metallic photoresist, based on ligand-encapsulated eutectic gallium-indium liquid metal nanoparticles, and an associated microfabrication process that enables direct, single-step liquid metal microlithography across wafer-scale areas. By leveraging tunable covalent and noncovalent interactions at liquid metal nanoparticles interfaces, this method achieves 2 µm resolution, bulk-level conductivity, and 3D topology matching of liquid metal patterns, while maintaining over 750% stretchability. We demonstrate the versatility of this approach by fabricating multi-scale elastic electronics, from high-resolution liquid metal grid transparent electrodes and ECoG neural electrodes to large-area flexible printed circuit boards.