Researchers at the Massachusetts Institute of Technology (MIT) use electron spin, a quantum property, to create low-power, high-performance computer memories and programmable computer chips. Luqiao Liu, Associate Professor in the Department of Electrical Engineering and Computer Science and a member of the Electronics Research Laboratory, is working with students and colleagues to advance the young field of spin electronics.
Spin electronics has been a largely unexplored field since it emerged in the 1980s. Therefore, researchers are now developing next-generation electronics that use significantly less power than conventional devices, using novel materials and nanoscale fabrication techniques.
“There are numerous obstacles that we must overcome in our work. There is still a gap between what could be done fundamentally and what has been done so far in spin electronics. There is still a lot to learn about getting better materials and discovering new mechanisms to achieve higher and higher performance,” says Liu.
He hopes to use antiferromagnetic materials in conjunction with existing technologies to create hybrid computing devices with even better computing performance. He intends to delve deeper into quantum technologies. Spin electronics, for example, could be used to control the flow of information in quantum circuits efficiently.
Spin electronics for better computing
Electrons are subatomic particles with the fundamental quantum property of spin. The spinning top, which circulates around itself and has angular momentum, creates mass, radius, and velocity. Although electrons do not rotate on an axis like a top, they have the same spin type. Their angular momentum can point either up or down. Engineers can use the binary nature of electron spin instead of positive and negative electric charges to represent binary information (1s and 0s) in electronic devices.
Changing the spin direction of electrons requires less energy, so researchers can use electron spin to switch transistors in electronic devices with much less power than traditional electronics. To regulate electrical signals, transistors, the basic building blocks of modern electronics, are used.
Their angular momentum causes electrons eventually behave like tiny magnets. These magnetic properties can be used by researchers to represent and store information in computer memory hardware. Liu and his colleagues hope to speed up the process by removing the speed bottlenecks that stymie lower-power, higher-performance computer memory devices. “We are constantly exploring and delving into many exciting and challenging new topics to improve computing memory or digital logic devices using spin electronics.”
Antiferromagnetic material
At MIT, Liu’s most recent work involves creating computer memories out of nanoscale antiferromagnetic materials. Finding better materials to use in computer memories to leverage electron spin can lead to devices that use less power, store more information, and retain that information for extended periods.
Antiferromagnetic materials, such as manganese, contain ions that, due to electron spin, act as tiny magnets. They arrange themselves so that the ions spinning “up” and those turning “down” are opposite one another, cancelling out the magnetism.
Antiferromagnetic materials can be packed closer together on a memory device because they do not generate magnetic fields, resulting in greater storage capacity. Because antiferromagnetic materials lack a magnetic field, the spin states can be switched between “up” and “down” very quickly, allowing them to change transistors much faster than traditional materials, according to Liu.
Liu builds and tests nanoscale devices using cutting-edge equipment at MIT.nano, a shared 214,000-square-foot nanoscale research facility. Having such advanced facilities at his disposal is a boon to his research. However, for Liu, human capital becomes the thing that drives the work.
