Scalable Manufacturing of Liquid Metal Circuits

Abstract

Liquid-metal (LM)-based soft and stretchable electronics (SSEs) provide unique advantages for wearable computing, soft robotics, and implantable devices applications involving physical interaction with biological tissues and delicate objects. However, the lack of scalable manufacturing techniques prevents their mainstream adoption and commercialization. This paper introduces a scalable and reproducible manufacturing technique for wafer-level fabrication of LM-based SSEs, including LM-only devices and hybrid circuits with LM and solid-state microelectronics. The approach combines selective metal-alloy wetting (SMAW) and controlled dip-coating of eutectic gallium-indium (EGaIn). The alloying of EGaIn and metal enables depositing EGaIn selectively onto the circuit layout defined by lithographically patterned copper traces on elastomer-coated wafers. An automated, wafer-level dip-coating (DC) approach is developed to enable controllable and reproducible deposition of EGaIn. Wafer-level simultaneous fabrication of many LM capacitors is demonstrated, and their geometric and electrical reproducibility is evaluated. The results indicate that the SMAW-DC process can fabricate LM circuits reproducibly and rapidly. Hybrid SSEs are demonstrated by fabricating multiple wearable patches of ultra-high frequency circuits with an LM dipole antenna, an LM strain gauge, and a solid-state temperature sensor. Importantly, the presented technique can be integrated into the standard microfabrication flow for microelectronics, ensuring a high level of scalability.