A flexible electronic circuit made with the new liquid metal tracks.
A flexible electronic circuit made with the new liquid metal tracks.

Conductive tracks are usually hard printed on a board, but those recently developed at the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland are altogether different. They are almost as flexible as rubber and can be stretched up to four times their original length and in all directions; they can even be stretched a million times without cracking or interrupting their conductivity. This development is reported in a paper in Advanced Materials.

Both solid and flexible, this new metallic and partially liquid film offers a wide range of possible applications. It could be used to make circuits that can be twisted and stretched – ideal for artificial skin on prosthetics or robotic machines. It could also be integrated into fabric and used to produce connected clothing. And because it can follow the shape and movements of the human body, it could be used for sensors designed to monitor particular biological functions.

"We can come up with all sorts of uses, in forms that are complex, moving or that change over time," said Hadrien Michaud, a PhD student at the EPFL’s Laboratory for Soft Bioelectronic Interfaces (LSBI) and one of the study authors.

Extensive research has gone into developing flexible electronic circuits, but it is a major challenge, as the components traditionally used to make circuits are rigid. One promising approach involves applying liquid metal to a thin film supported on a polymer with elastic properties. Owing to the high surface tension of some of these liquid metals, however, experiments conducted so far have only produced relatively broad structures.

"Using the deposition and structuring methods that we developed, it's possible to make tracks that are very narrow – several hundredths of a nanometer thick – and very reliable," said Stéphanie Lacour, who runs the LSBI.

Apart from their unique fabrication technique, the researchers' secret lies in the material used to produce the tracks: an alloy of gold and gallium. "Not only does gallium possess good electrical properties, but it also has a low melting point, around 30°C," said Arthur Hirsch, a PhD student at LSBI and co-author of the study. "So it melts in your hand, and, thanks to the process known as supercooling, it remains liquid at room temperature, even lower." The layer of gold ensures the gallium remains homogeneous, preventing it from separating into droplets when it comes into contact with the polymer, which would ruin its conductivity.

This story is adapted from material from EPFL, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.