Photo: (From left) Supriyo Bandyopadhyay, Ph.D., Commonwealth Professor in the Department of Electrical and Computer Engineering, and Jayasimha Atulasimha, Ph.D., Qimonda Professor in the Department of Mechanical and Nuclear Engineering
Two researchers in the VCU School of Engineering are harnessing the spin properties of electrons to design more efficient technologies. With funding from the National Science Foundation, Supriyo Bandyopadhyay, Ph.D., Commonwealth Professor in the Department of Electrical and Computer Engineering, and Jayasimha Atulasimha, Ph.D., Qimonda Professor in the Department of Mechanical and Nuclear Engineering, are creating novel systems that exploit electron spin to improve device functionality, a process called spintronics.
Electronics relies on the charge of electrons to store, process and communicate information. Spintronics, by contrast, uses the “up” or “down” direction of electron spin — not electron charge — to store or transmit bits of information in ones or zeros. Spintronic devices can process exponentially more data using significantly less energy than conventional electronics, and, unlike most conventional electronics, they can store data without requiring any external energy supply.
Atulasimha and Bandyopadhyay are leveraging spintronics for applications that include optical devices and cyber security. One of their inventions is a spintronic infrared photodetector. Photodetectors, which convert light into an electrical signal, are used in technologies including night vision devices, car collision avoidance systems, mine detectors, missile defense and systems to measure global warming. The team’s spintronic device addresses a persistent challenge in infrared photodetector design: their tendency to misread normal thermal vibrations as the presence of infrared light. That is why these photodetectors have to be cooled well below room temperature in order to work. The VCU team has developed a spintronic photodetector technology that uses magnetic contacts and a semiconductor nanowire and is immune to the effect of thermal vibrations. “The nanowire should ideally have nearly infinite electrical resistance in the dark and a much lower resistance under infrared illumination even at room temperature. That makes it work as an infrared photodetector at room temperature,” Bandyopadhyay said.
They are also using nanoscale magnets that store information and are connected by semiconductor nanowires to develop a novel magnetic/spintronic version of bit comparators, an essential component of electronic circuits and cyber security keys. Bit comparators analyze extremely complex strings of data, one bit at a time, and render a yes/no decision as to whether each bit matches a corresponding stored bit. Magnetic bit comparators offer a key advantage over their electronic counterparts. “If you build [a bit comparator] in a typical transistor device, when you switch off the power, the information is lost. In a nanomagnet, the comparator’s inputs and decision stay there forever — In fact, it could stay there for centuries. We call such a device non-volatile,” Atulasimha said.
The two VCU researchers are collaborating with Arunkumar Subramanian, Ph.D., associate professor in the Department of Mechanical and Industrial Engineering at the University of Illinois at Chicago. He is a co-investigator on the NSF grant and uses dielectrophoresis (DEP) to assemble semiconductor nanowires between magnetic contacts.