Memristors, electrical components that store information in their electrical resistance, could reduce AI’s energy needs by about a factor of 90 compared to today’s graphical processing units. Already, AI is projected to account for about half a percent of the world’s total electricity consumption in 2027, and that has the potential to balloon as more companies sell and use AI tools.

“Right now, there’s a lot of interest in AI, but to process bigger and more interesting data, the approach is to increase the network size. That’s not very efficient,” said Wei Lu, the James R. Mellor Professor of Engineering at U-M and co-corresponding author of the study with John Heron, U-M associate professor of materials science and engineering.

The problem is that GPUs operate very differently from the artificial neural networks that run the AI algorithms — the whole network and all its interactions must be sequentially loaded from the external memory, which consumes both time and energy. In contrast, memristors offer energy savings because they mimic key aspects of the way that both artificial and biological neural networks function without external memory. To an extent, the memristor network can embody the artificial neural network.

“We anticipate that our brand-new material system could improve the energy efficiency of AI chips six times over the state-of-the-art material without varying time constants,” said Sieun Chae, a recent U-M Ph.D. graduate in materials science and engineering and co-first-author of the study with Sangmin Yoo, a recent U-M PhD graduate in electrical and computer engineering.

In a biological neural network, timekeeping is achieved through relaxation. Each neuron receives electrical signals and sends them on, but it isn’t a guarantee that a signal will move forward. Some threshold of incoming signals must be reached before the neuron will send its own, and it has to be met in a certain amount of time. If too much time passes, the neuron is said to relax as the electrical energy seeps out of it. Having neurons with different relaxation times in our neural networks helps us understand sequences of events.

Memristors operate a little differently. Rather than the total presence or absence of a signal, what changes is how much of the electrical signal gets through. Exposure to a signal reduces the resistance of the memristor, allowing more of the next signal to pass. In memristors, relaxation means that the resistance rises again over time.

While Lu’s group had explored building relaxation time into memristors in the past, it was not something that could be systematically controlled. But now, Lu and Heron’s team have shown that variations on a base material can provide different relaxation times, enabling memristor networks to mimic this timekeeping mechanism.

The team built the materials on the superconductor YBCO, made of yttrium, barium, carbon and oxygen. It has no electrical resistance at temperatures below -292 Fahrenheit, but they wanted it for its crystal structure. It guided the organization of the magnesium, cobalt, nickel, copper and zinc oxides in the memristor material.

Heron calls this type of oxide, an entropy-stabilized oxide, the “kitchen sink of the atomic world” — the more elements they add, the more stable it becomes. By changing the ratios of these oxides, the team achieved time constants ranging from 159 to 278 nanoseconds, or trillionths of a second. The simple memristor network they built learned to recognize the sounds of the numbers zero to nine. Once trained, it could identify each number before the audio input was complete.

These memristors were made through an energy-intensive process because the team needed perfect crystals to precisely measure their properties, but they anticipate that a simpler process would work for mass manufacturing.

“So far, it’s a vision, but I think there are pathways to making these materials scalable and affordable,” Heron said. “These materials are earth-abundant, nontoxic, cheap and you can almost spray them on.”

The research was funded by the National Science Foundation. It was done in partnership with researchers at the University of Oklahoma, Cornell University and Pennsylvania State University.

The device was built in the Lurie Nanofabrication Facility and studied at the Michigan Center for Materials Characterization.

Lu is also a professor of electrical and computer engineering and materials science and engineering. Chae is now an assistant professor of electrical engineering and computer science at Oregon State University.

The revelations, based on data obtained by the James Webb Space Telescope, mark the first measurements of an exoplanet’s core mass and will likely underpin future studies of planetary atmospheres and interiors, a key aspect in the search for habitable worlds beyond our solar system.

“Looking into the interior of a planet hundreds of light-years away sounds almost impossible, but when you know the mass, radius, atmospheric composition, and hotness of its interior, you’ve got all the pieces you need to get an idea of what’s inside and how heavy that core is,” said lead author David Sing, a Bloomberg Distinguished Professor of Earth and Planetary Sciences at Johns Hopkins University. “This is now something we can do for lots of different gas planets in various systems.”

Published today in Nature, the research shows the planet has a thousand times less methane than expected and a core 12 times more massive than Earth’s.

A giant planet wrapped by a scorching atmosphere as fluffy as cotton, WASP-107 b orbits a star about 200 light-years away. It is puffy because of its build: a Jupiter-sized world with only a tenth of that planet’s mass.

Even though it has methane — a building block of life on Earth — the planet is not considered habitable because of its proximity to its parent star and lack of a solid surface. But it could hold important clues about late-stage planetary evolution.

In a separate study published today in Nature, other scientists also spotted methane with the Webb telescope and provided similar insights about the planet’s size and density.

“We want to look at planets more similar to the gas giants in our own solar system, which have a lot of methane in their atmospheres,” Sing said. “This is where the story of WASP-107 b got really interesting, because we didn’t know why the methane levels were so low.”

The new methane measurements suggest the molecule transforms into other compounds as it flows upward from the planet’s interior, interacting with a concoction of other chemicals and starlight in the upper atmosphere. The team also measured sulfur dioxide, water vapor, carbon dioxide, and carbon monoxide — and found WASP-107 b has more heavy elements than Uranus and Neptune.

The profile of the planet’s chemistry is starting to reveal key pieces in the puzzle of how planetary atmospheres behave in extreme conditions, Sing said. His team will conduct similar observations over the next year on an additional 25 planets with the Webb telescope.

“We had never been able to study this mixing process in an exoplanet atmosphere in detail, so this will go a long way in understanding how these dynamic chemical reactions operate,” Sing said. “It’s something we definitely need as we start looking at rocky planets and biomarker signatures.”

Scientists had speculated that the planet’s overinflated radius resulted from a source of heat inside, said Zafar Rustamkulov, a Johns Hopkins doctoral student in planetary science who co-led the research. By combining atmospheric and interior physics models with Webb’s data of WASP-107 b, the team accounted for how the planet’s thermodynamics influences its observable atmosphere.

“The planet has a hot core, and that heat source is changing the chemistry of the gases deeper down, but it’s also driving this strong, convective mixing bubbling up from the interior,” Rustamkulov said. “We think this heat is causing the chemistry of the gases to change, specifically destroying methane and making elevated amounts of carbon dioxide and carbon monoxide.”

The new findings also represent the clearest connection scientists have been able to make about the interior of an exoplanet and the top of its atmosphere, Rustamkulov said. Last year the Webb telescope spotted sulfur dioxide about 700 light-years away in a different exoplanet called WASP-39, providing the first evidence of an atmospheric compound created by starlight-driven reactions.

The Johns Hopkins team is now focusing on what might be keeping the core hot, and expects forces might be in play similar to those causing high and low tides in Earth’s oceans. They plan to test whether the planet is being stretched and pulled by its star and how that might account for the core’s high heat.

Other study authors are Daniel P. Thorngren and Elena Manjavacas of Johns Hopkins University; Joanna K. Barstow of the Open University; Pascal Tremblin of Université Paris-Saclay; Catarina Alves de Oliveira, Stephan M. Birkmann, and Pierre Ferruit of the European Space Agency; Tracy L. Beck, Néstor Espinoza, Amélie Gressier, Marco Sirianni, and Jeff A. Valenti of the Space Telescope Science Institute; Ryan C. Challener of Cornell University; Nicolas Crouzet, Giovanna Giardino, and Nikole K. Lewis of Leiden University; Elspeth K. H. Lee; Roberto Maiolino of University of Cambridge; and Bernard J. Rauscher of NASA Goddard Space Flight Center.

This research is based on data obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy Inc., under NASA contract NAS 5-03127.