Graphene Continues Making Inroads Into Electronics
Lacking an inherent band gap is not slowing research into using graphene for electronic applications
When people look at the extraordinary properties of graphene to be a conductor, it’s hard for them to let go of the idea of using it for anything other than digital electronic applications despite it lacking an inherent band gap.
While graphene’s extraordinary electronic properties may not lend themselves to the “0” and “1” of binary electronic applications, it doesn’t mean that it can’t be used for a variety of other electronic applications outside of digital electronics. Researchers around the world are finding that graphene is demonstrating promise in electronic applications ranging from displays to random access memory.
Production Costs for Graphene-based Flexible Displays Plummet
In our previous issue, we covered the news that Plastic Logic, with assistance from the Cambridge Graphene Center located at the University of Cambridge, had developed the world’s first graphene-based flexible display.
Now researchers at the University of Surrey and AMBER, the material science center based at Trinity College Dublin, have developed a method for producing graphene-treated silver nanowires, which could significantly reduce production costs for nanowire-based displays. This could mean that graphene offers a real alternative to indium-tin oxide (ITO) in flexible low-cost touchscreen displays.
"Our work has cut the amount of expensive nanowires required to build such touchscreens by more than fifty times as well as simplifying the production process,” said Izabela Jurewicz, a researcher at the University of Surrey, in a press release. “We achieved this using graphene, a material that can conduct electricity and interpret touch commands whilst still being transparent."
The key to the new process, which is described in the journal Advanced Functional Materials, was to exploit graphene’s unmatched conducting properties. To do this, the researchers changed from using the graphene-oxide that is typically used in a solution-based process to create these nanowires to a pristine graphene. Since the pristine graphene was free of the oxygen functional groups found in graphene-oxide, it could conduct electricity without any further chemical treatment, which resulted in more than a 50-fold reduction in the number of nanowires needed to produce viable electronic electrodes.
"This is a real alternative to ITO displays and could replace existing touchscreen technologies in electronic devices,” said Jonathan Coleman of AMBER in a press release. “Even though this material is cheaper and easier to produce, it does not compromise on performance."
Novel Graphene Material Moves Electrons at Controllable Angles
Graphene is noted for the speed at which electrons pass through it. While electrons move so quickly that they appear to be massless particles, they do stay moving in the direction of the electrical current.
This basic understanding has been turned upside down recently. Researchers at MIT and the University of Manchester have reported in the journal Science that when graphene is placed on top of boron nitride, it creates a superlattice, which is a structure made of aligned, alternating layers of various nanomaterials. It turns out that the superlattice they made has the astounding ability to move electrons perpendicular to the electric field without the influence of a magnetic field.
While the Hall effect is capable of making electrons move sideways under a magnetic field, this property of graphene depends on a different principle.
What this could mean to electronic devices is that it could lead to a new kind of energy efficient transistor. While the research team has not attempted to build a transistor based on the phenomenon, the superlattice material has displayed high sensitivity to gate voltage that operates transistors.
Another implication of this discovery is that electrons in the superlattice appear to behave just like neutrinos, which are massless particles that don’t interact with most kinds of matter.
The researchers believe that this discovery could contribute to our understanding of the universe, prompting Sir Andre Geim to note: “It is very rare to come across a phenomenon that bridges materials science, particle physics, relativity, and topology.”
Random Access Memory Gets a Boost From Graphene
Researchers at the University of Nebraska at Lincoln have developed a way using graphene to improve the ferroelectric tunnel junction (FTJ) that is a component of random access memory (RAM). They have improved the FTJ by combining graphene with ammonia so that it is capable of switching on and off the flow of electrons more completely. The result is a distinct improvement in the reliability of RAM devices and the ability to read data without having to rewrite it.
“This is one of the most important differences between previous technology that has already been commercialized and this emergent ferroelectric technology,” said Alexei Gruverman, a physics professor who co-authored the study, in a press release.
In a typical FTJ design, a ferroelectric layer is placed between two electrodes so that when an electric field is applied to them the direction of the junction’s polarization is reversed. This reversal of polarization changes the alignment of positive and negative charges, which correspond to the zero and one in binary computing.
In this most recent research, which was published in the journal Nature Communications, the Nebraska team made the electrodes out of graphene.
Paradoxically the researchers didn’t want to use graphene because of its electrical conductivity, but instead because it could accommodate just about any molecule—in this case an ammonia molecule.
The ammonia molecule was positioned between the electrodes and the ferroelectric layer where it had a dramatic effect on the functioning of the FTJ. The way the system typically operates is that the polarity of the junction determines its resistance to the tunneling current so that in one direction the current is allowed to flow and in the other direction it is greatly reduced. The ammonia molecule magnified these “on” and “off” states.
“In all memory devices, there is a gradual relaxation, or decrease, of this polarization,” said Gruverman in the press release. “The thinner the ferroelectric layer is, the more difficult it is to keep these polarization charges separate, as there is a stronger driving force in the material that tries to get rid of it.”