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 fix
itself, and fix itself so fast that the user never knew there was a
problem?
A
team of University of Illinois engineers has developed a self-healing
system that restores electrical conductivity to a cracked circuit in
less time than it takes to blink. Led by aerospace engineering professor
Scott White and materials science and engineering professor Nancy
Sottos, the researchers published their results in the journal Advanced
Materials.
“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, 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 to find the source of the failure.”
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 micrometers 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
really cool about this paper is it’s the first example of taking the
microcapsule-based healing approach and applying it to a new function,”
White said. “Everything prior to this has been on structural repair.
This is on conductivity restoration. 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
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 air- 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. Co-authors of the paper included postdoctoral
researchers Benjamin Blaiszik and Sharlotte Kramer and graduate
students Martha Grady and David McIlroy.