Since graphene was discovered in 2004, researchers have been intent on finding ways to use it as a cheap semiconducting material given its exceptional electrical conductivity. However, as it is difficult to “switch off” the flow of electrons within graphene, it makes a poor semiconductor.
The team of researchers, based at MIT’s Research Laboratory of Electronics, instead looked at graphene’s mechanical properties. Graphene is ultra-thin and Teflon-like, and could form a useful, barely perceptible layer between two surfaces.
The engineers developed a method to place single sheets of graphene onto a semiconductor wafer – a thin semiconductor slice. They then grew semiconducting material over the graphene layer. Being just an atom thick, it was effectively electrically invisible, allowing the top layer to “see” through the graphene to the underlying crystalline wafer.
This allowed the pattern to be imprinted – as the semiconducting material’s atoms rearrange into the crystalline pattern – without being influenced by the graphene.
In conventional semiconductor manufacturing the wafer becomes strongly bonded to the semiconductor, making it almost impossible to separate afterwards and meaning that the wafer is lost. However, as graphene is slippery, the engineers found that they could peel the top semiconducting layer from the wafer after imprinting.
The researchers were successful in applying their technique to exotic semiconducting materials, including some which are 50-100 times more expensive than conventional silicon. Their results were published in Nature.
According to Professor Jeehwan Kim, an assistant professor at MIT who led the research, manufacturers could use the graphene to “copy and paste” the wafer, then remove the wafer and use it many times over. This reusability opens up the opportunity to explore more exotic semiconductor materials.
“The industry has been stuck on silicon, and even though we’ve known about better performing semiconductors, we haven’t been able to use them because of their cost,” said Professor Kim. “This gives the industry freedom in choosing semiconductor materials by performance and not cost.”
Professor Kim and his team demonstrated potential applications for the method in flexible electronics by fabricating a flexible LED display with the MIT logo with the technique. They suggest that the method could be used for installing solar cells over a car’s contoured surface.
They plan to design a reusable “mother wafer”, with regions of different exotic materials, and use graphene to create multifunctional, high-performance devices.
“Exotic materials can be popular to use,” said Professor Kim. “You don’t have to worry about the cost of the wafer. Let us give you the copy machine. You can grow your semiconductor device, peel it off, and reuse the wafer.”