New Circuit Material Can Be Stretched and Twisted Like Chewing Gum

Researchers made electronics that can be stretched up to four times their original length in all directions.
February 29, 2016, 11:00am
Image: EPFL

Flexible, bendable electronics are already a real enough thing. To varying degrees, they can be found in technologies ranging from LCDs to computer keyboards to satellites. But the idea is also just getting started—a favorite trope of future consumer electronics is the integrated wearable computing device, an iPhone sewn into your sick jorts or even grafted onto skin itself.

To this end, engineers from Ecole Polytechnique Fédérale de Lausanne have made a major advance: electronics that can be stretched up to four times their original length in all directions. The material, which is described today in the journal Advanced Materials, withstands maximal stretching up to a million times without cracking or losing its conductivity properties.

The material's secret is in a layering of gold and gallium. The latter has an unusually low melting point (for a metal) or around 30 degrees Fahrenheit, e.g. it remains liquid at room temperatures. This liquid metal is patterned onto a thin polymer film, where it functions as the conductive tracks of a normal circuit board—liquid wires, basically. The gold is used to prevent the gallium from beading up and rolling away like water droplets when it comes into contact with the polymer.

The beading up of liquids has a lot to do with their surface tension. The more tension there is, or the less surface area there is per unit of volume, the less a liquid is going to spread itself around on or adhere to a flat surface. (The shape with the least amount of surface area is a sphere, not a pancake.) This is the fundamental problem in using liquid metals within circuits—they want to behave like tiny marbles rather than homogeneous wires.

So, most work with liquid metals and electronics has required the usage of very thick deposits of the metals in question, which in turn puts a prohibitive lower limit on the scale of the electronics. By using gold to lower the surface tension of the liquid gallium, the EPFL team was able to fabricate conductive tracks on the order of nanometers in width.

It's not hard to see the applications of something like this in all corners of electronics engineering, but the current research comes courtesy of EPFL's bioelectronics lab and neuroprosthetics specialist Stéphanie Lacour. So, one might start by imagining artificial skins on prosthetic limbs or robots. Where one might end, however, with a technology allowing for circuits that can be twisted up and stretched like bubble gum is anyone's guess.