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Photoresist puts focus on laser-induced graphene

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Graphene has been patterned in high-resolution and at the micron-scale with a laser and photoresist, an advance that could lead to applications in consumer electronics.

photoresist
A laser-induced graphene Rice Owl is surrounded by photoresist material at left and stands alone at right after the excess photoresist is washed away with acetone (Credit: Tour Group/Rice University)

This is the claim of a Rice University laboratory that has demonstrated the conversion of positive photoresist (PR), frequently used in the manufacture of consumer electronics, into laser-induced graphene (LIG).

First introduced in 2014 by Rice chemist James Tour, laser-induced graphene (LIG) involves burning away everything that is not carbon from polymers or other materials, leaving the carbon atoms to reconfigure into films of hexagonal graphene.

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The process uses a commercial laser that writes graphene patterns into surfaces that have so far included wood, paper and food.

According to Rice, the new iteration writes fine patterns of graphene into photoresist polymers. Baking the film increases its carbon content, and lasing solidifies the robust graphene pattern, after which unlased photoresist is washed away. Details of the PR-LIG process appear in ACS Nano.

"This process permits the use of graphene wires and devices in a more conventional silicon-like process technology," Tour said in a statement. "It should allow a transition into mainline electronics platforms."

The Rice lab produced lines of LIG about 10 microns wide and hundreds of nanometres thick, which the team said is comparable to what can be achieved with more cumbersome processes that involve lasers attached to scanning electron microscopes.

Achieving lines of LIG small enough for circuitry prompted the lab to optimise its process, according to graduate student Jacob Beckham, lead author of the paper.

"The breakthrough was a careful control of the process parameters," Beckham said. "Small lines of photoresist absorb laser light depending on their geometry and thickness, so optimising the laser power and other parameters allowed us to get good conversion at very high resolution."

Because the positive photoresist is a liquid before being spun onto a substrate for lasing, it is a simple matter to dope the raw material with metals or other additives to customise it for applications, Tour said.

Potential applications include on-chip microsupercapacitors, functional nanocomposites and microfluidic arrays.