NIST invents fundamental component for 'spintronic' computing

April 27, 2017, National Institute of Standards and Technology

NIST has been granted a patent for technology that may hasten the advent of a long-awaited new generation of high-performance, low-energy computers.

Conventional microelectronic devices, for the most part, work by manipulating and storing electrical charges in semiconductor transistors and capacitors. Doing so requires a lot of energy and generates a lot of heat, especially as process engineers keep finding ways to pack more and smaller features into integrated circuits. Power consumption has become one of the principal obstacles to much higher performance.

One highly promising alternative approach, called "spintronics," utilizes the of the electron to hold information in addition to the charge. The two different spin orientations (typically designated "up" and "down") are analogous to positive and negative electrical charges in conventional electronics. Because changing an electron's spin requires very little energy and can happen very fast, spintronics offers the possibility of significant energy reduction.

"Our invention," says co-inventor Curt Richter of NIST's Engineering Physics Division, "is designed to provide one key component in spintronic systems. It's a very simple, fundamental building block that can be used in a variety of different ways. It can serve as an on-off switch for , as an interconnect between different spintronic components, and as an interface between magnetic and electronic features to realize multifunctional devices."

Spin is what makes magnetic things magnetic: Every electron behaves somewhat like a bar magnet, with two opposite poles. Materials in which most of the electron spins are aligned in the same direction (polarized) produce a magnetic field with the same orientation. Electrons with the same spin alignment as the material pass easily through it; electrons with the opposite alignment are blocked.

This property has been exploited to make microscopic "spin valves"—typically a channel with a magnetic layer at each end. The relative polarity of the two magnets turns the valve on or off: If both magnets have the same alignment, the spin-polarized current passes through the channel. If the magnets have opposite alignments, current cannot flow.

The device is "switched" by reversing one magnet's polarity, which is done by applying a sufficient current of electrons with the opposite spin. However, flipping the magnet's polarity takes more energy than researchers would prefer.

"Typically with spin valves," Richter says. "You have to flow a significant amount of spin current to flip the component. Larger currents mean you're using more energy and generating more heat. Our invention dramatically reduces both."

At first, the researchers had no intention of making a device or obtaining a patent. They weren't even working directly on spin transport. They were studying the behavior of a different class of devices commonly referred to as "memristors" (memory resistors), a technology that is barely a decade old but is widely heralded as a potential high-speed, low-energy basic element for future computers.

Memristors are layered microstructure sandwiches with an electrode at the top and bottom, between which are a layer of metal (for example copper) which is a good electrical conductor and a layer of material (such as certain oxides) which is a poor conductor. This configuration is also the most common structure used in a new type of memory called resistive random-access memory (RRAM or ReRAM). When a voltage is applied to the electrodes in one direction, current can flow. Reversing the voltage shuts down the current.

Scientists believe that the reason for this phenomenon is that when a bias voltage is applied in one direction, it causes atoms of the metal conductor to diffuse into and interact with the oxide, forming tiny metal filaments that act as low-resistance channels penetrating through the insulating layer. If the voltage is applied in the opposite direction, the oxide layer is depleted of metal atoms, and resistance increases.

Either way, when the bias voltage is removed, the oxide's resistance state is frozen. Because that state was formed by a specific bias applied in a specific direction, the device "remembers" its last resistance. That characteristic makes memristors attractive for use in "non-volatile" computer memory in which the stored information does not disappear when the power is turned off.

"So when we got started, there were spin valves and there were memristors," Richter says. "But nobody had thought to put them together. Being measurement guys at NIST, we didn't originally think about putting them together to invent a new device. We put them together so that we could make measurements to better understand how memristors work.

"We wanted to investigate how this voltage switch turns on and off. We thought that if we added spin to the analysis, we could get more insights into how a normal memristor works. In the process of doing that, we made this device and said 'Hey, this thing by itself has very interesting technological ramifications.' It combines the non-volatile memory in memristors with the technology of a to create a that allows you to turn on and off a spin channel."

"What makes it unique is that you can open or close a spin channel using an electric control," says co-inventor Hyuk-Jae Jang. "And so with a small amount of voltage, we can turn spin current on and off in sub-nanosecond time without having to flip the polarity of a spin valve's ferromagnetic electrode. This high speed and low power consumption operation is essential for building future spintronics-based logic technology to replace the current CMOS-based electronics technology used to fabricate nearly all integrated circuits today."

The NIST patent covers devices made with a variety of materials. The primary combination used in the inventors' experiments was, from the bottom up, a magnetic base layer made of cobalt that serves to spin-polarize the electrons, an insulating layer made of tantalum oxide, a layer of copper, and an alloy top electrode.

In the "on" configuration, the copper atoms are drawn into the oxide and their filaments extend all the way to the base cobalt layer. Reversing the voltage causes the copper to recede, and "there's an empty region in the oxide layer," Richter says. "As soon as that happens, the current stops. It could be only a few atoms' worth away, because of the exponential drop-off with distance. That makes it a very low-energy switch."

John Kramar, Acting Chief of NIST's Engineering Physics Division, calls the work "a very exciting invention that provides a great solution for the switching-energy problem for valves. It removes a significant technological barrier for spintronics to become a strong contender for beyond-CMOS microelectronics."

Explore further: Study reveals switching mechanism in promising computer memory device

Related Stories

Spinning better electronic devices

March 2, 2016

A team of researchers, led by a group at the University of California, Riverside, have demonstrated for the first time the transmission of electrical signals through insulators in a sandwich-like structure, a development ...

Recommended for you

Taking MRI technology down to micrometer scales

March 19, 2018

Millions of magnetic resonance imaging (MRI) scans are performed each year to diagnose health conditions and perform biomedical research. The different tissues in our bodies react to magnetic fields in varied ways, allowing ...


Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Apr 27, 2017
"At first, the researchers had no intention of making a device or obtaining a patent."

The purpose of a patent is to protect the investment of the inventor from being copied by a competitor who invest only in copying and commercializing it, so has an advantage. Protecting inventors from disadvantage by mere copiers is justified by the Constitution's codifying a government monopoly on the invention, "to promote progress in science and the useful arts".

This invention did not use that business model. It faced no disadvantage from competitors, its inventors were promoting progress in science and the useful arts without needing a monopoly on the invention. Their monopoly only slows the application of their invention, obstructs progress.

Besides, NIST is a US government institution; the investment is by the American people. Why should Americans have to pay twice to use this invention? What is the value in restricting it with a patent?
5 / 5 (1) Apr 27, 2017
The good thing about a government holding a patent on a basic process, rather than a private corporation, is that the government can ensure that the technology or process is used for the benefit of citizens, rather than the primary benefit of the shareholders of a corporation. This patent can speed the dissemination of the technology or process, because no private corporation can restrict the grant of licenses.

Taxpayers are not paying twice to use the invention. They are paying less than once to use the invention, which was developed at cost, without profit, by the government.

Government can use the licensing fees from the patent the government holds to pay for more public research, and to reduce the burden of paying for public research on taxpayers. The US Government holds many patents, and licensing such patents is a standard practice.
not rated yet Apr 27, 2017
Taxpayers are certainly paying at least once for the invention: US government activity is paid for by taxpayers. Then when a taxpayer pays to license it they're paying again.

Is there any evidence that the US government ensures any patent licenses are used to benefit its citizens, rather than just to get revenue?

Taxpayers are not paying twice to use the invention.

not rated yet May 01, 2017
I would like to compliment the writer of this article on a job well done :)

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.