Researchers Use Graphene to Make Wireless Communications More Flexible

September 5, 2012

Michael Lekas and Sunwoo Lee, electrical engineering Ph.D. candidates, have been awarded a Qualcomm Innovation Fellowship (QInF) and the accompanying $100,000 prize. They were one of eight teams from across the U.S. to win the fellowship. Their project —“CMOS Compatible Graphene Nanoelectromechanical Systems for Next Generation RF Design”— focuses on addressing the increasing congestion of the wireless spectrum created by the growing number of people using wireless devices and the enormous volume of data they are moving every day.

Suspended graphene (green) over the gating electrode (blue). Information at different frequencies (red and black) come into the gate, but only the information carried at the resonant frequency (black) of the suspended graphene can go through the two readout electrodes (yellow). The polymer gasket (pink) is for structural support.

One potential solution is to make wireless devices flexible enough to operate at different frequencies throughout the wireless spectrum so that they may take advantage of unoccupied bandwidth. But that level of flexibility is very difficult to achieve in current wireless technologies, explain Lekas and Lee.

Working with Mechanical Engineering Associate Professor James Hone and Electrical Engineering Professor Ken Shepard on ways to solve this problem, the students are developing one crucial element of such a system: tunable electromechanical filters that use the vibration of graphene to pick out electrical signals only at a desired frequency. These devices will enable more versatile wireless circuits that can operate at many different frequencies while also being integrated with existing silicon chip technology.

“The device we are designing is essentially a sheet of carbon—about 10,000 times thinner than human hair—suspended like a bridge between two electrodes,” says Lee. “When electrical signals like the ones that come to and from your cell phone are applied to a third electrode located underneath the ‘bridge,’ then only the signal at a particular frequency (the resonant frequency, or RF) can make the graphene vibrate. This vibration changes the electrical properties of the graphene ‘bridge,’ in effect amplifying the desired signal and blocking out interfering signals and noise.”

Lekas adds that their device is unique because the resonant frequency of the suspended graphene can be tuned electrically by as much as 400 percent, in contrast to existing technologies which are only tunable by 1 percent. This tunability will enable wireless devices to ‘search’ over a much wider range of the spectrum to find unused bandwidth. “Plus it’s much smaller and, therefore, easier to integrate onto a conventional silicon chip, compared to the existing filter technologies,” he explains. “This device could substantially improve the flexibility, miniaturization, and integration of wireless transceivers, which would make devices such as cell phones smaller, faster, and more energy efficient.”

“Qualcomm views Graphene resonators, pioneered by the Columbia team, as an important element in next generation wireless technology,” says Abramsky, who has extensive experience in commercializing RF products and will guide the team to help take the technology closer to implementation.

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