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Prof. Bruce Wessels, Northwestern University
151 Everitt Lab
Prof. Jean-Pierre Leburton
The ability to switch a logic gate through control of electron spin is the fundamental concept underlying spintronic logic circuits. By using electron spin along with charge, new avenues for manipulating signal flow become available. It is therefore possible to develop logic devices with additional capabilities that are more efficient, leading to logic circuits with improved characteristics. We present novel logic families exploiting newly developed devices that can be used as spintronic switches. The power dissipation of circuits made from this logic family would be nearly independent of frequency, providing and advantage over CMOS for high-speed applications. As an example we have used magnetically sensitive transistors (spin transistors) to combine switching and amplification. One approach for realization of these devices is to use narrow gap III-V semiconductors. By alloying these semiconductors with manganese, dilute magnetic semiconductors result. These alloys are both semiconducting and magnetic. Giant magnetoresistance has been observed in narrow gap magnetic semiconductor p-n heterojunctions. The giant magnetoresistance which is positive is attributed to spin selective carrier scattering in the magnetic semiconductor. For InMnAs/InAs heterojunction diodes a giant magnetoresistance of 2680 % is observed at room temperature. This work indicates that highly spin-polarized magnetic semiconductor heterojunction switches can be realized that operate at room temperature. Devices based on the giant magnetoresistance include spin diodes and bipolar magnetic junction transistors. We utilize the diode magnetoresistance states to create a binary spin logic family based on high and low current. While our work centers on narrow band gap semiconductor devices, graphene can be potentially used as the active device material since it has been shown to exhibit a large negative magnetoresistance.
Bruce Wessels is the W.P. Murphy Professor of Materials Science and Engineering, and Electrical Engineering and Computer Science at Northwestern University. He received his undergraduate degree from U. of Pennsylvania and Ph.D degree in Materials Science from MIT. He is a fellow of APS and ASMI. He is author/co-author of 340 articles on electronic , magnetic and optical properties materials and devices. He is the holder of 15 U.S. patents. He is a former president of TMS.