Putting a new spin on computer hardware | MIT News

Luqiao Liu was the kind of kid who would rather take his toys apart to see how they worked than play with them as they were intended.

Curiosity has been a driving force throughout his life, and it led him to MIT, where Liu is a newly appointed associate professor in the Department of Electrical Engineering and Computer Science and a member of the Electronics Research Laboratory.

Rather than taking things apart, he is now using new materials and nanoscale manufacturing techniques to build next-generation electronics that use dramatically less power than conventional devices. Curiosity still comes in handy, he says, especially as he and his collaborators work in the largely unknown area of ​​spin electronics—a field that only emerged in the 1980s.

“There are many challenges we have to overcome in our work. In spin electronics, there is still a gap between what can be fundamentally done and what has been done so far. There’s still a lot to study in terms of getting better materials and finding new mechanisms so we can achieve higher and higher performance,” said Liu, who is also a member of the MIT-IBM Watson AI Lab.

Electrons are subatomic particles that have a fundamental quantum property known as spin. One way to visualize this is to think of a spinning top that circulates around itself, giving the top angular momentum. That angular momentum, a product of the spin’s mass, radius, and velocity, is known as its spin.

Although electrons technically do not spin around an axis like a top, they have the same kind of spin. Their angular momentum can point “up” or “down”. Instead of using positive and negative electrical charges to represent binary information (1s and 0s) in electronic devices, engineers can use the binary nature of electron spin.

Because it takes less energy to change the spin direction of electrons, electron spin can be used to convert transistors into electronic devices that use much less power than traditional electronics. Transistors, the basic building blocks of modern electronics, are used to regulate electrical signals.

Because of their angular momentum, electrons also behave like tiny magnets. Researchers can use these magnetic properties to represent and store information in computer memory hardware. Liu and his collaborators aim to speed up the process and remove the speed bottlenecks that hold back lower-power, higher-performance computer memory devices.

Attracted to magnetism

Liu’s path to studying computer memory hardware and spin electronics began with refrigerator magnets. As a young child, he wondered why a magnet would stick to the fridge.

That early curiosity helped spark his interest in science and math. As he delved into those subjects in high school and college, learning more about physics, chemistry and electronics, his curiosity about magnetism and its use in computers deepened.

When he had the opportunity to pursue a PhD at Cornell University and join a research group studying magnetic materials, Liu found the perfect match.

“I spent the next five or six years looking for new and more efficient ways to generate electron spin current and use it to write information into magnetic computer memories,” he says.

While fascinated by the world of research, Liu wanted to try his hand at an industry career, so he joined IBM’s TJ Watson Research Center after graduate school. There, his work focused on developing more efficient magnetic random access memory hardware for computers.

“To finally make something work in a commercially available format is quite important, but I didn’t find myself fully involved in that kind of fine-tuning. I wanted to show the viability of a lot of new work – to prove that some new concept is possible,” says Liu. He joined MIT in 2015 as an assistant professor.

Material matters

Some of Liu’s most recent work at MIT involves building computer memories using nanoscale, antiferromagnetic materials. Antiferromagnetic materials, such as manganese, contain ions that act as small magnets due to electron spin. They arrange themselves so that ions spinning “up” and those spinning “down” are opposite each other, so the magnetism cancels out.

Because they do not produce magnetic fields, antiferromagnetic materials can be packed closer together on a memory device, resulting in higher storage capacity. And their lack of a magnetic field means that the spin states can be switched between “on” and “off” very quickly, so antiferromagnetic materials can switch transistors much faster than traditional materials, Liu explains.

“In the scientific community it has been under debate whether you can electrically change the spin orientation in these antiferromagnetic materials. Using experiments we have shown that you can,” he says.

In his experiments, Liu often uses new materials that were created only a few years ago, so all their properties are not yet well understood. But he enjoys the challenge of integrating them into devices and testing their functionality. Finding better materials to harness electron spin in computer memory could lead to devices that use less power, store more information, and retain that information for a longer period of time.

Liu uses state-of-the-art equipment inside MIT.nano, a shared 214,000-square-foot nanoscale research center, to build and test nanoscale devices. Having such modern facilities at his fingertips is a boon for his research, he says.

But for Liu, it’s the human capital that really fuels his work.

“The colleagues and students are the most precious part of MIT. To be able to discuss questions and talk to people who are the smartest in the world, it’s the most enjoyable experience doing this job,” he says.

He, his students and colleagues are pushing forward the young field of spin electronics.

In the future, he envisions using antiferromagnetic materials in tandem with existing technologies to create hybrid computing devices that achieve even better performance. He also plans to dive deeper into the world of quantum technology. For example, spin electronics can be used to efficiently control the flow of information in quantum circuits, he says.

In quantum computing, signal isolation is critical – the information must flow in only one direction from the quantum circuit to the external circuit. He is investigating the use of a phenomenon known as a spin wave, which is the generation of electron spin within magnetic materials, to ensure that the signal only travels in one direction.

Whether he’s investigating quantum computing or investigating the properties of new materials, one thing is true – Liu is still driven by an insatiable curiosity.

“We are constantly investigating, delving into many exciting and challenging new topics with the goal of making better computer memory or digital logic devices using spin electronics,” he says.