Self-healing electronic circuits. That 21st-century concept, which could extend the usable lifespan of electronic devices and batteries, has been accomplished by a team of researchers at the University of Illinois.
The researchers, who had previously created self-healing polymers, have now implemented a similar approach for circuits. Microcapsules, with diameters as small as 10 microns, reside above a gold circuit line and, when a crack appears in the circuit, the microcapsules rupture and release liquid metal that repairs the break. The research is described in a paper published in the journal Advanced Materials.
'You Can't See It'
According to the researchers, the break lasts only for about a hundred microseconds before it is healed.
"It's so fast that you can't see it," said co-team leader and aerospace engineering professor Scott White in a video 
released by the university. "You need special equipment to even detect that there was failure" and a healing process, he added.
The team reported that 90 percent of test samples were restored to 99 percent of their original conductivity with this technique.
Materials science and engineering professor and co-team leader Nancy Sottos told news media that there are an unlimited number of applications, especially for mission-critical systems. She noted that multilayer integrated circuits and batteries cannot readily be opened and repaired, and currently it's more efficient -- but more costly in time and money -- to simply replace the circuit or battery. With this self-healing technique, devices and batteries could potentially last much longer.
She pointed out that autonomous healing techniques can take care of a break that occurs in the "miles and miles of conductive wire" in a military aircraft or a spacecraft. No human intervention is required. The other strength of the technique is that it is localized, so that the microcapsules do their job only at the point of the crack, rather than throughout the entire circuit.
'What's Really Cool....'
Chemistry professor Jeffrey Moore, a co-author of the paper, noted in a statement that this approach "simplifies the system." Instead of having to build in redundancies or a sensory diagnostics system, he said, "this material is designed to take care of the problem itself."
White said that "what's really cool" about this self-healing system is that it's "the first example of taking the microcapsule-based healing approach and applying it to a new function." Previously, he said, this approach and similar ones were focused on structural repair, but this is directed at "conductivity restoration," and shows that the overall self-healing concept can be applied to other needs.
The next targets include using the microcapsules to control conductivity. In particular, the researchers want to apply the technology to batteries, in order to improve their safety and longevity.
The research was funded by U.S. Department of Energy, and key team members Moore, Sottos, and White are affiliated with the University of Illinois' Beckman Institute for Advanced Science and Technology.
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