Metal films manufactured with a new method can be stretched to twice their size without breaking, promising a breakthrough in flexible electronics.
The discovery by a team from Washington State University could pave the way for a wide range of devices including bendable batteries, robotic skins, wearable monitoring devices or sensors and connected fabrics.
The study, led by Rahul Panat and Indranath Dutta from the Voiland College's School of Mechanical and Materials Engineering, was described in an article in the latest issue of Applied Physics Letters.
The team used indium, a rather inexpensive metal, and periodically bonded it to a plastic layer commonly used in electronics. The researchers were able to stretch the resulting metal film to twice its original length. When the pieces eventually broke, it was actually the plastic layer that failed, not the metal.
"This is a quantum improvement in stretchable electronics and wearable devices," said Panat. "A metal film doubling its size and not failing is very unusual. We have proposed a model for the stretchy metal but much work is needed to validate it. It's a good situation to be in.''
Researchers have struggled for years with designing and manufacturing the tiny metal connections that go into flexible electronics. The metal has to undergo severe stretching and bending while continuing to conduct electricity.
Manufacturers have so far used tiny metal springs that can stretch and still maintain connectivity, but the springs take up space and make it difficult to design complicated, high-density circuitry. Furthermore, electricity has to travel farther in coiled springs, requiring more power and bigger batteries.
"The circuitry ends up requiring a ton of real estate and bulky batteries," said Panat.
Researchers have experimented with gold, which works better than other materials but is prohibitively expensive, and copper, which severely cracks when it is stretched by more than 30 per cent.