Self-healing electronic chip tests may aid space travel

Enlarged view of the self-healing circuit Tests showed small microcapsules filled with liquid metal healed fractures in a gold circuit restoring conductivity

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Self-repairing electronic chips are one step closer, according to a team of US researchers.

The group has created a circuit that heals itself when cracked thanks to the release of liquid metal which restores conductivity.

The process takes less than an eye blink to bring the circuit back to use.

The researchers said that their work could eventually lead to longer-lasting gadgets as well as solving one of the big problems of interplanetary travel.

The work was carried out by a team of scientists and engineers at the University of Illinois at Urbana-Champaign and is published in the journal Advanced Materials.

The process works by exploiting the stress that causes the initial damage in the chips to break open tiny reservoirs of a healing material that fills in the resulting gaps, restoring electrical flow.

Cracked circuits

To test their theory the team patterned lines of gold onto glass to form a circuit.

They then either placed microcapsules 0.01mm wide directly onto the lines or added a thin laminate into which they embedded larger 0.2mm microcapsules.

In both cases the microcapsules contained eutectic gallium-indium - a metallic material chosen for its high conductivity and low melting point.

This device was then sandwiched between another layer of glass and acrylic and connected to electricity.

The researchers then bent the circuit until it cracked causing the monitored voltage to fall to zero.

They said the ruptured microcapsules then healed most of the test circuits within one millisecond and restored nearly all of the measured voltage.

The smaller capsules healed the device every time but were a little less conductive than the larger ones which had a slightly lower success rate. The team suggested that a mix of differently sized capsules would therefore give the best result.

The devices were then monitored for four months during which time the researchers said there was no loss of conductivity.

Safe space travel

The leader of the group said the theory could prove a boon to the space industry.

"The only avenue one has right now is to simply remove that circuitry when it fails and replace it- there is no way to manually go in and fix something like this," aerospace engineering professor Scott White told the BBC.

Graphic showing how the self-healing process works The research team hope to adapt the process to create longer lasting rechargeable batteries

"I think the real application area that you'll see for something like this is in electronics which are incredibly difficult to repair or replace - think about satellites or interplanetary travel where it's physically impossible to swap out something."

The research is an offshoot of the university's research into extending the lifetime of rechargeable batteries.

The reason current systems fail after repeated use is often because microdamage inside the devices has disrupted the conductive flow of electrons from one end of the batteries to the other.

The team said that if they could solve the problem electric car batteries might last years longer than they do at present, making the vehicles much cheaper to maintain.

Greener gadgets

The group also claimed that the technique had the potential to offer more sustainable consumer electronic devices.

Professor White gave the example of mobile phone buttons that stopped working if repeated use had caused cracks in the circuitry below. He said self-healing systems would extend handsets' lifespans.

When asked whether profit-driven electronics makers would want this he replied: "I believe any company would want to provide their customer with the best performing product and if they don't, then other companies will step into the market to provide it.

"Basically what you see is that electronics are cycled now to give you added functionality.

"Maybe the way to do this is not to physically build new circuits and packages every time, but let's have longer lasting ones.

"Then the redesigns can be more software based or functionality driven, saving us from using up our precious resources by building millions of cellphones every year."

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