Soft electronic vias and interconnects through rapid three-dimensional assembly of liquid metal microdroplets

Abstract

The development of soft electronics requires methods to connect flexible and stretchable circuits. With conventional rigid electronics, vias are typically used to electrically connect circuits with multilayered architectures, increasing device integration and functionality. However, creating vias using soft conductors leads to additional challenges. Here we show that soft vias and planar interconnects can be created through the directed stratification of liquid metal droplets with programmed photocuring. Abnormalities that occur at the edges of a mask during ultraviolet exposure are leveraged to create vertical stair-like architectures of liquid metal droplets within the photoresin. The liquid metal droplets in the uncured (liquid) resin rapidly settle, assemble and then are fully cured, forming electrically conductive soft vias at multiple locations throughout the circuit in a parallel and spatially tunable manner. Our three-dimensional selective stratification method can also form seamless connections with planar interconnects, for in-plane and through-plane electrical integration. Multiple stair-like structures can be created in parallel by programmed curing of a photoresin containing liquid metal droplets, which then stratify and assemble to form soft electronic vias.