New carbon "spintronics" could replace silicon transistors

7/24/2017 UT Dallas and Victoria Halewicz, ECE

Written by UT Dallas and Victoria Halewicz, ECE

ECE Professor Jean-Pierre Leburton is part of an interdisciplinary team working on an all-carbon spin logic proposal, a computing system that could be made smaller than silicon transistors, with increased performance. Their work was published last month in Nature Communications. Leburton is also affiliated with the Beckman Institute, Coordinated Science Lab, and MNTL at Illinois.

The lead author, Dr. Joseph S. Friedman, is an assistant professor of electrical and computer engineering with the Erik Jonsson School of Engineering and Computer Science at UT Dallas who conducted much of the research while he was a doctoral student at Northwestern University.

Today’s electronic devices are powered by transistors, which are tiny silicon structures that rely on negatively charged electrons moving through the silicon, forming an electric current. Transistors behave like switches, turning current on and off.

In addition, to carrying a charge, electrons have another property called spin, which relates to their magnetic properties. In recent years, engineers have been investigating ways to exploit the spin characteristics of electrons to create a new class of transistors and devices called "spintronics."

An illustration of the all-carbon spin logic gate from 'Cascaded spintronic logic with low-dimensional carbon' by Joseph S. Friedman, et al.
An illustration of the all-carbon spin logic gate from 'Cascaded spintronic logic with low-dimensional carbon' by Joseph S. Friedman, et al.

The team’s spintronic switch functions as a logic gate that relies on a basic tenet of electromagnetics: As an electric current moves through a wire, it creates a magnetic field that wraps around the wire. In addition, a magnetic field near a two-dimensional ribbon of carbon—called a graphene nanoribbon—affects the current flowing through the ribbon. In traditional, silicon-based computers, transistors cannot exploit this phenomenon. Instead, they are connected to one another by wires. The output from one transistor is connected by a wire to the input for the next transistor, and so on in a cascading fashion.

In the team’s spintronic circuit design, electrons moving through carbon nanotubes—essentially tiny wires composed of carbon—create a magnetic field that affects the flow of current in a nearby graphene nanoribbon, providing cascaded logic gates that are not physically connected.

Because the communication between each of the graphene nanoribbons takes place via an electromagnetic wave, instead of the physical movement of electrons, they expect that communication will be much faster, with the potential for terahertz clock speeds. In addition, these carbon materials can be made smaller than silicon-based transistors, which are nearing their size limit due to silicon’s limited material properties.

While the concept is still on the drawing board, Friedman said work toward a prototype of the all-carbon, cascaded spintronic computing system will continue in the interdisciplinary NanoSpinCompute research laboratory, which he directs at UT Dallas.

For more information about this research, read the original paper or view the release from UT Dallas on the Beckman Institute website.

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This story was published July 24, 2017.