Ultrathin conductor surpasses copper for more energy-efficient nanoelectronics

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As computer chips become increasingly smaller and more intricate, their tiny wires carrying electrical signals are proving to be a major bottleneck. The standard metal wires used in these devices lose their effectiveness as they are made thinner, ultimately limiting the size, efficiency, and performance of nanoscale electronics.

Scientists at Stanford found that niobium phosphide can carry an electric current more effectively than copper when formed into very thin layers. These ultra-thin layers can be produced and applied at relatively low temperatures, making them compatible with current electronics manufacturing techniques. This breakthrough has the potential to enhance the power and efficiency of future electronics.

"We're breaking a fundamental roadblock with traditional materials like copper," said Asir Intisar Khan, who earned his Ph.D. from Stanford and is now a visiting postdoctoral scholar and first author of the study.

Our niobium phosphide conductors indicate that it's feasible to transmit faster, more efficient signals through slender wires. This could enhance the energy efficiency of future integrated circuits, and even minor advancements can accumulate significantly when many integrated circuits are utilized, for instance in the substantial data centers that store and process information currently.

A new category of conductors, known as "membership programmable materials" has been developed.

In the scientific community, niobium phosphide is classified as a topological semimetal. This designation is given because it has the ability to conduct electricity throughout its entirety, but its outer layers are more adept at doing so than the area in the middle. As a niobium phosphide film is thinned, the area in the middle decreases, but the outer layers remain constant, allowing them to contribute to the flow of electricity to a greater extent, ultimately making the entire material a superior conductor. In contrast, traditional metals like copper, whose thickness drops below about 50 nanometers, deteriorate in their ability to conduct electricity.

Researchers discovered that niobium phosphide exhibited higher conductivity than copper at film thicknesses below 5 nanometers, even when operating at room temperature. At this size, copper wires experience difficulties in handling rapid electrical signals and significantly lose energy to heat.

Super-dense electronics demand extremely thin metal connections, and if these metals don't conduct properly, they're wasting a lot of power and energy," said Eric Pop, the Pease-Ye Professor in the School of Engineering, a professor of electrical engineering, and senior author on the paper. "Improved materials could help us conserve energy in small wires and make better use of it for actual computation.

Many researchers have been striving to discover better conductors for tiny electronics, though the top contenders have possessed extremely precise crystalline structures that require high temperatures to form. The niobium phosphide films created by Khan and his team are the first examples of noncrystalline materials that become more conductive as they grow thinner.

People thought that to take advantage of these topological surfaces, we need high-quality single-crystal films that are difficult to make," said Akash Ramdas, a doctoral student at Stanford and a co-author of the study. "Now, we have another category of materials, these topological semimetals, which could help reduce energy consumption in electronics.

Because the niobium phosphide films don't have to be single crystals, they can be produced at lower temperatures. The researchers deposited the films at 400°C, a temperature low enough to avoid damaging or ruining existing silicon computer chips.

It won't work for nanoelectronics if you have to create perfectly crystalline wires," said Yuri Suzuki, the Stanley G. Wojcicki Professor in the School of Humanities and Sciences, a professor of applied physics and co-author on the paper. "However, if you can create wires that are amorphous or slightly disordered yet still provide the desired properties, that could lead to various practical applications.

Enabling future nanoelectronics

Researchers say niobium phosphide films show a great deal of promise, but might not immediately replace copper in all computer chips, since copper still has the edge when it comes to thicker films and wiring connections. However, niobium phosphide could be well-suited for the tiniest circuit connections, and serves as a foundation for further investigation into conductors made from other topological semimetals.

For these novel materials to be used in future electronics, we need them to be even better conductors," said Xiangjin Wu, a doctoral student at Stanford and co-author of the study. "To achieve this goal, we are researching alternative topological semimetals.

Pop and his team are also working on converting their niobium phosphide films into narrow wires for further testing. They aim to assess the reliability and effectiveness of the material in practical applications.

We've applied some really interesting physics concepts to the field of electronics," Pop said. "This kind of breakthrough in non-crystalline materials could help solve power and energy problems in both current and future electronics.

DOI: 10.1126/science.adq7096

Provided by Stanford University

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