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Smoother graphene produces highly conductive wafers

Credit: MIT

Engineers at MIT claim to have found a way to make graphene with fewer wrinkles, and to iron out those that do appear. Conventional fabrication processes often generate wrinkles, which can derail an electron’s journey and limit graphene’s electrical performance.

The researchers report that their techniques successfully produce wafer-scale, ’single-domain’ graphene — single layers of graphene that are uniform in both atomic arrangement and electronic performance.

“For graphene to play as a main semiconductor material for industry, it has to be single-domain, so that the performance of all the devices is the same,” says assistant professor Jeehwan Kim. “Now we can really produce single-domain graphene at wafer scale.”

The most common way to make graphene involves chemical vapour deposition (CVD). The CVD process can produce macroscropic wrinkles in graphene, due to the roughness of the underlying copper itself and the process of pulling the graphene from the acid.

The alignment of carbon atoms is not uniform across the graphene, creating a ‘polycrystalline’ state, preventing electrons from flowing at uniform rates.

Rather than using CVD, the team produced single-crystalline graphene from a silicon carbide wafer with nanometre-level wrinkles. They then used a thin sheet of nickel to peel off the topmost graphene from the silicon carbide wafer, in a process called layer-resolved graphene transfer.

The group discovered that the layer-resolved graphene transfer irons out the wrinkles in silicon carbide-fabricated graphene.

“The CVD process creates wrinkles that are too high to be ironed out,” Kim notes. “For silicon carbide graphene, the wrinkles are short enough to be flattened out.”

To test whether the flattened, single-crystalline graphene wafers were single-domain, the researchers fabricated tiny transistors on multiple sites on each wafer, including across previously wrinkled regions.

They found each wafer exhibited uniform performance, meaning that electrons flowed freely across each wafer, at similar speeds, even across previously wrinkled regions.

Peggy Lee

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