Graphene has presented all sorts of barriers for efforts to apply the material to electronics. It lacks a band gap, so research has focused on engineering one into it. Then even if you could engineer a band gap into the material, its challenging to manufacture at a high quality and high volume.
Another big obstacle is that graphene does not lend itself to being stacked with other materials, something that could be important to making graphene ICs. The reason is that electrical contacts have to be placed on the top surface of the graphene, making the layering of another material on top of those contacts complicated.
Now researchers at Columbia University have developed a way to contact 2-D graphene from its 1-D side.
"No other group has been able to successfully achieve a pure edge-contact geometry to 2-D materials such as graphene," said Columbia electrical engineering professor Ken Shepard in a press release. "This is an exciting new paradigm in materials engineering where instead of the conventional approach of layer by layer growth, hybrid materials can now be fabricated by mechanical assembly of constituent 2-D crystals."
In a research published this week in the journal Science (“One-Dimensional Electrical Contact to a Two-Dimensional Material”), the Shepard and his colleagues created a stack of graphene with boron nitride (which is itself an intensively studied 2-D material, especially in combination with graphene). After they created a boron-nitride-graphene-boron-nitride sandwich, they etched the stack to expose the edge of the graphene. They then evaporated metal onto those graphene edges to make an electrical contact.
While there was some concern that the electrical contact between the 3-D metal electrode and the one dimensional edge of the graphene would result in high contact resistance, it didn’t happen. Instead the researchers report that contact resistance was in fact lower than what can currently be achieved by making those contacts at the top of the graphene surface.
"Our novel edge-contact geometry provides more efficient contact than the conventional geometry without the need for further complex processing. There are now many more possibilities in the pursuit of both device applications and fundamental physics explorations,” said Shepard in the press release.
To start pursuing those new possibilities, the researchers are applying the techniques they developed for creating new hybrid materials of all the 2D materials that are gaining such interest of late.
"We are taking advantage of the unprecedented performance we now routinely achieve in graphene-based devices to explore effects and applications related to ballistic electron transport over fantastically large length scales," Cory Dean, who led the research as a postdoc at Columbia, said in the press release. "With so much current research focused on developing new devices by integrating layered 2D systems, potential applications are incredible, from vertically structured transistors, tunneling based devices and sensors, photoactive hybrid materials, to flexible and transparent electronics."
Illustration: Cory Dean/Columbia Engineering