Self-healing electronics could reduce waste

When one tiny circuit within an integrated chip cracks or fails, the whole chip - or even the whole device - is a loss. But what if it could repair itself, and repair itself so fast that the user never knew there was a problem?

University of Illinois professors Nancy Sottos, Scott White and Jeffery Moore applied their experience in self-healing polymers to electrical systems, developing technology that could extend the longevity of electronic devices and batteries.

The team has developed a self-healing system that restores electrical conductivity to a cracked circuit in less time than it takes to blink.

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, such as failures 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, there’s no opening it up. Normally you just replace the whole chip. It’s true for a battery too. You can’t pull a battery apart and try and find the source of the failure.”

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

The 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 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.

“What’s good about this, is it’s the first example of taking the microcapsule-based healing approach and applying it to a new function,” White said.

“Everything before has been on structural repair. This is on conductivity restoration and it shows the concept translates to other things as well.”

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

The self-healing system also has the advantages of being localised 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 air- or spacecraft.

“In an aircraft, especially a defence-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.