Tag Archives: Josephson junction

Less is more—a superconducting synapse

It seems the US National Institute of Standards and Technology (NIST) is more deeply invested into developing artificial brains than I had realized (See: April 17, 2018 posting). A January 26, 2018 NIST news release on EurekAlert describes the organization’s latest foray into the field,

Researchers at the National Institute of Standards and Technology (NIST) have built a superconducting switch that “learns” like a biological system and could connect processors and store memories in future computers operating like the human brain.

The NIST switch, described in Science Advances, is called a synapse, like its biological counterpart, and it supplies a missing piece for so-called neuromorphic computers. Envisioned as a new type of artificial intelligence, such computers could boost perception and decision-making for applications such as self-driving cars and cancer diagnosis.

A synapse is a connection or switch between two brain cells. NIST’s artificial synapse–a squat metallic cylinder 10 micrometers in diameter–is like the real thing because it can process incoming electrical spikes to customize spiking output signals. This processing is based on a flexible internal design that can be tuned by experience or its environment. The more firing between cells or processors, the stronger the connection. Both the real and artificial synapses can thus maintain old circuits and create new ones. Even better than the real thing, the NIST synapse can fire much faster than the human brain–1 billion times per second, compared to a brain cell’s 50 times per second–using just a whiff of energy, about one ten-thousandth as much as a human synapse. In technical terms, the spiking energy is less than 1 attojoule, lower than the background energy at room temperature and on a par with the chemical energy bonding two atoms in a molecule.

“The NIST synapse has lower energy needs than the human synapse, and we don’t know of any other artificial synapse that uses less energy,” NIST physicist Mike Schneider said.

The new synapse would be used in neuromorphic computers made of superconducting components, which can transmit electricity without resistance, and therefore, would be more efficient than other designs based on semiconductors or software. Data would be transmitted, processed and stored in units of magnetic flux. Superconducting devices mimicking brain cells and transmission lines have been developed, but until now, efficient synapses–a crucial piece–have been missing.

The brain is especially powerful for tasks like context recognition because it processes data both in sequence and simultaneously and stores memories in synapses all over the system. A conventional computer processes data only in sequence and stores memory in a separate unit.

The NIST synapse is a Josephson junction, long used in NIST voltage standards. These junctions are a sandwich of superconducting materials with an insulator as a filling. When an electrical current through the junction exceeds a level called the critical current, voltage spikes are produced. The synapse uses standard niobium electrodes but has a unique filling made of nanoscale clusters of manganese in a silicon matrix.

The nanoclusters–about 20,000 per square micrometer–act like tiny bar magnets with “spins” that can be oriented either randomly or in a coordinated manner.

“These are customized Josephson junctions,” Schneider said. “We can control the number of nanoclusters pointing in the same direction, which affects the superconducting properties of the junction.”

The synapse rests in a superconducting state, except when it’s activated by incoming current and starts producing voltage spikes. Researchers apply current pulses in a magnetic field to boost the magnetic ordering, that is, the number of nanoclusters pointing in the same direction. This magnetic effect progressively reduces the critical current level, making it easier to create a normal conductor and produce voltage spikes.

The critical current is the lowest when all the nanoclusters are aligned. The process is also reversible: Pulses are applied without a magnetic field to reduce the magnetic ordering and raise the critical current. This design, in which different inputs alter the spin alignment and resulting output signals, is similar to how the brain operates.

Synapse behavior can also be tuned by changing how the device is made and its operating temperature. By making the nanoclusters smaller, researchers can reduce the pulse energy needed to raise or lower the magnetic order of the device. Raising the operating temperature slightly from minus 271.15 degrees C (minus 456.07 degrees F) to minus 269.15 degrees C (minus 452.47 degrees F), for example, results in more and higher voltage spikes.

Crucially, the synapses can be stacked in three dimensions (3-D) to make large systems that could be used for computing. NIST researchers created a circuit model to simulate how such a system would operate.

The NIST synapse’s combination of small size, superfast spiking signals, low energy needs and 3-D stacking capability could provide the means for a far more complex neuromorphic system than has been demonstrated with other technologies, according to the paper.

NIST has prepared an animation illustrating the research,

Caption: This is an animation of how NIST’s artificial synapse works. Credit: Sean Kelley/NIST

Here’s a link to and a citation for the paper,

Ultralow power artificial synapses using nanotextured magnetic Josephson junctions by Michael L. Schneider, Christine A. Donnelly, Stephen E. Russek, Burm Baek, Matthew R. Pufall, Peter F. Hopkins, Paul D. Dresselhaus, Samuel P. Benz, and William H. Rippard. Science Advances 26 Jan 2018: Vol. 4, no. 1, e1701329 DOI: 10.1126/sciadv.1701329

This paper is open access.

Samuel K. Moore in a January 26, 2018 posting on the Nanoclast blog (on the IEEE [Institute for Electrical and Electronics Engineers] website) describes the research and adds a few technical explanations such as this about the Josephson junction,

In a magnetic Josephson junction, that “weak link” is magnetic. The higher the magnetic field, the lower the critical current needed to produce voltage spikes. In the device Schneider and his colleagues designed, the magnetic field is caused by 20,000 or so nanometer-scale clusters of manganese embedded in silicon. …

Moore also provides some additional links including this one to his November 29, 2017 posting where he describes four new approaches to computing including quantum computing and neuromorphic (brain-like) computing.

Detecting dangerous liquids in airline luggage with a Josephson junction; NANOvember in Albany, New York; nano haiku for November

To be free of those clear plastic bags which hold all your bottles of liquids when you go through airport security with your luggage! That is a very worthwhile nanotechnology promise. From the news item on Nanowerk,

Restrictions on liquids in carry-on bags on commercial airliners could become a thing of the past thanks to a revolutionary nano-electric device which detects potentially hazardous liquids in luggage in a fraction of a second, according to a team of German scientists. Writing in the journal Superconductor Science and Technology, the researchers at the Forschungszentrum Juelich in western Germany claim that they have been able to do this using an optical approach that detects all existing and future harmful liquids within one fifth of a second.

Since the paper has been published, the researchers have been approached by industrial partners about producing a prototype. (sigh) Most likely this means they hope it will be about five years before we see the devices in airports. The device itself is known as a Josephson junction and you can read more about it on the Azonano site too.

I am happy to see that the College of Nanoscale Science and Engineering (CNSE) at the University of Albany (New York, US) has held a remarkably successful nano event, Community Day, during NANOvember  attracting about 1000 people.  From the news item on Nanowerk,

NANOvember is part of “NEXSTEP,” or “Nanotechnology Explorations for Science, Training and Education Promotion,” a partnership between CNSE and KeyBank. Spearheaded by CNSE’s Nanoeconomics Constellation, the initiative features a variety of educational programs designed to promote greater understanding of the changing economic and business environment in the Capital Region and New York State being driven by nanotechnology. “As nanotechnology increasingly shapes the educational and economic landscapes of the Capital Region, NANOvember offers a platform through which the community can better understand the impact and opportunities driven by this emerging science,” said Jeffrey Stone, president, Capital Region, KeyBank N.A.

I’m impressed they attracted that large a crowd in a city with a population of about 100,000 (Albany county has a population of about 300,000) according the 2000 census statistics. By contrast, the city of Vancouver (Canada) has a population of about 600,000 with a regional population of approximately 2 million (from the City of Vancouver website on November 9, 2009) and I’m hard pressed to recall either of our local universities claiming a similar success for one of their community days.

One other point about Albany and nanotechnology, in a July 2008 posting I noted a $1.5B investment for a research centre  in Albany, NY, being made by IBM. So this nanotechnology communication/education event seems to dovetail very nicely with past occurrences and suggests an overall strategy is at work.

Some haiku from NISEnet’s (Nanoscale Informal Science Education Network) newsletter,

After you read this
Your finger nail will have grown
a nanometer
by Troy Dassler

We struggle to show
The size of a molecule.
Kids wait patiently.

by Mike Falvo

You can check out the organization’s The Nano Bite blog here.