University of Illinois engineers have developed a self-healing system that restores electrical conductivity to a cracked circuit in microseconds.

“It simplifies the system,” said chemistry professor Jeffrey Moore, a co-author of the paper. “Rather than having to build in redundancies or to build in a sensory diagnostics system, this material is designed to take care of the problem itself.”

As electronic devices are evolving to perform more sophisticated tasks, manufacturers are packing as much density onto a chip as possible. However, such density compounds reliability problems, such as failure stemming from fluctuating temperature cycles as the device operates or fatigue. A failure at any point in the circuit can shut down the whole device.

“In general, there’s not much avenue for manual repair,” Sottos said. “Sometimes you just can’t get to the inside. In a multilayer integrated circuit, or battery, there’s no opening it up. Normally you just replace the whole chip or battery.”

Most consumer devices are meant to be replaced with some frequency, adding to electronic waste issues, but in many important applications — such as instruments or vehicles for space or military functions — electrical failures cannot be replaced or repaired.

The Illinois team previously developed a system for self-healing polymer materials and decided to adapt their technique for conductive systems. They dispersed tiny microcapsules, as small as 10 microns (millionths of a meter) in diameter, on top of a gold line functioning as a circuit. As a crack propagates, the microcapsules break open and release the liquid metal contained inside. The liquid metal fills in the gap in the circuit, restoring electrical flow.

A failure interrupts current for mere microseconds as the liquid metal immediately fills the crack. The researchers demonstrated that 90 percent of their samples healed to 99 percent of original conductivity, even with a small amount of microcapsules.

The self-healing system also has the advantages of being localized and autonomous. Only the microcapsules that a crack intercepts are opened, so repair only takes place at the point of damage. Furthermore, it requires no human intervention or diagnostics, a boon for applications where accessing a break for repair is impossible, such as a battery, or finding the source of a failure is difficult, such as an aircraft or spacecraft.

“In an aircraft, especially a defense-based aircraft, there are miles and miles of conductive wire,” Sottos said. “You don’t often know where the break occurs. The autonomous part is nice — it knows where it broke, even if we don’t.”

Next, the researchers plan to further refine their system and explore other possibilities for using microcapsules to control conductivity. They are particularly interested in applying the microcapsule-based self-healing system to batteries, improving their safety and longevity.

This research was supported as part of the Center for Electrical Energy Storage, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science. Moore, Sottos and White are also affiliated with the Beckman Institute for Advanced Science and Technology at the U. of I.

Ref.: Benjamin J. Blaiszik, et al., Autonomic Restoration of Electrical Conductivity, Advanced Materials, 2011; [DOI: 10.1002/adma.201102888]