Electrical Engineering and Computer Science



The market is burgeoning in the area of flexible and wearable electronics. They are not only incorporated into a wide array of electronic devices such as displays, solar cells, automotive systems, and cell phones, they are being exploited in the fashion world. Flexible electronics also have enormous potential in wearable health monitoring devices and medical implants.

But if you wanted to communicate information efficiently from these electronic devices while retaining their flexible and sometimes transparent qualities, you were stuck - until now. Prof. Zhaohui Zhong and his team of graduate students, Seunghyun Lee, Kyunghoon Lee, Chang-Hua Liu, and Girish S. Kulkarni, have built the first flexible, transparent digital modulator for high speed communications, made solely out of graphene.

"One of the most important elements in communications is modulating the signal," stated Prof. Zhong. "If you want to broadcast music on a radio station, or send information electronically, you have to modulate and encode information into a carrier wave, and that's done by modulators."

Existing digital modulators are typically made from silicon, which is rigid and non-transparent, and therefore not suitable for applications where you want the electronics to be flexible. Graphene has previously been investigated for use in high speed communications because it's fast (it can operate up to 300 GHz) and it's reliable.

"Graphene is unique," explains Zhong. "It’s comprised of only one layer of carbon so it’s flexible. Because it’s only one layer, it has low absorption – making it transparent as well. We show that we can make the entire circuit out of graphene, making it flexible, transparent, and high speed."

Compounding the importance of Zhong's work is the fact that this is the first time anyone has shown quaternary modulation with a graphene circuit. Why is this important? It results in 2x the speed of binary modulation, which was the former state of the art. Zhong's group demonstrated a quaternary modulation scheme called Quadrature Phase-Shift Keying (QPSK) modulation on their all-graphene circuits. QPSK modulation is the building block for more complicated modulation schemes found in current telecommunication standards.

Their device is also relatively simple, thanks to graphene's unique quality of being nonlinear and ambipolar (normal transistors are unipolar). Their QPSK modulation uses only two transistors to accomplish the same amount of work accomplished with a multitude of circuits in other methods.

"We’ll continue to make improvements," stated Prof. Zhong. "In this work we demonstrated that the modulators work within the KHz range. We want to push it to GHz, which is entirely possible based on the device itself."

Prof. Zhong has applied for patent protection on this technology.

Original publication

"Flexible and transparent all-graphene circuits for quaternary digital modulations," by Seunghyun Lee, Kyunghoon Lee, Chang-Hua Liu, Girish S. Kulkarni and Prof. Zhaohui Zhong, Nature Communications 3, Article number 1018, August 21, 2012.

In the News

"Flexible and Fast," Science Vol. 227, September 7, 2012. Editor's Choice.

"Digital modulator goes transparent," Belle Dume, Nanotechweb.org, August 23, 2012.

September 20, 2012
Catharine June
EECS/ECE Communications Coordinator
cmsj@umich.edu or 734-936-2965

Related Topics:    Flexible electronics    Graphene     LNF    Solid-State Devices and Nanotechnology     Wearable electronics   Zhong, Zhaohui