A technology has been developed that allows drawing lines with liquid metal, as if painting, to create electronic circuits. It is expected to be useful for next-generation electronic devices such as wearables.

KAIST announced on the 15th that a research team led by Distinguished Professor Park In-Gyu in the Department of Mechanical Engineering, jointly with the team of Dr. Hye-Jin Kim at the Electronics and Telecommunications Research Institute (ETRI), has developed a new concept electronic material technology that conducts electricity wherever it is drawn, including on paper, textiles, and even leaves.

The new electronic material developed by the team is based on a fine-powder form of ‘liquid metal powder’. Although liquid metal powder is normally non-conductive, light physical stimulationsuch as rubbing with a brush or pressing with a fingerbreaks the oxide layer surrounding the particles, connecting the underlying metal so that electricity flows. Using this technology addresses the drawbacks of conventional liquid metal, which has high surface tension and does not spread well, making it hard to form precise circuits at desired locations, and which easily bleeds or agglomerates.

Liquid metal powder is characterized by having virtually no constraints on where and on what materials it can be used. Even without heat treatment, electronic circuits can be implemented not only on paper, glass, and plastic, but also on the surfaces of textiles and leaves. The team verified practical applicability by using liquid metal powder in skin-attachable wireless health-monitoring devices and in circuits for soft robots whose shapes can change freely.

The research team said, “Using liquid metal powder greatly reduces the bleeding, sedimentation, and pattern deformation issues that troubled conventional liquid-metal circuits, enabling stable circuit fabrication on a variety of surfaces,” and added, “Because precise circuits can be made on diverse surfaces without complex equipment, it is expected to be utilized in fields of next-generation electronic devices such as wearable healthcare, soft robotics, and flexible electronics.”

After use, electronic circuits based on liquid metal powder can be dissolved in water for disassembly, and with simple chemical treatment the liquid metal can be recovered, reprocessed into powder, and reused. This is an eco-friendly technology that reduces the generation of electronic waste.

Professor Park said, “This study is significant not only because it enables intuitive, drawing-like fabrication of electronic circuits, but also because the circuits can be recycled,” and added, “Liquid metal powder maintains its performance even after being stored for over a year at room temperature and is stable enough that circuits do not break even after being bent or twisted tens of thousands of times, allowing use across a wide range of fields.”

The findings, with KAIST Department of Mechanical Engineering postdoctoral researcher Gul Osman as the first author, were published as a back-cover paper in the international journal ‘Advanced Functional Materials’.