At a time when the United Nations called for cutting fossil fuel production by 6% per year to avoid global warming, a joint research effort redefined coal’s role in electronic devices.

The University of Illinois Urbana-Champaign, the National Energy Technology Laboratory, Oak Ridge National Laboratory and the Taiwan Semiconductor Manufacturing Company reached a breakthrough in their joint research as the world makes an effort to reconsider coal’s economic role, according to a piece on varsity’s website.

“The processing techniques we’ve developed can transform coal into high-purity materials just a couple of atoms thick,” said Qing Cao, a U of I materials science & engineering professor.

Cao, who was also a co-lead of the collaboration, said: “Their unique atomic structures and properties are ideal for making some of the smallest possible electronics with performance superior to the state of the art.”

The NETL, a US national laboratory under the Department of Energy, has developed a process where coal char is converted into nanoscale carbon disks called “carbon dots” which as per the university’s research group could be connected to form atomically thin membranes for applications in both two-dimensional transistors and memristors—electronic components capable of both storing and operating on data to greatly enhance the implementation of AI technology.

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Use in 2D electronics

Researchers have aimed at making devices made with materials just one or two atoms thick. Smaller than this limit would be impossible for devices while the small scale consumes far less energy. Experts have called for atomically thin insulators to construct working electronic devices like transistors and memristors.

Researchers in the joint programme atomically thin layers of carbon can be formed from carbon dots derived from coal char as they can work as a very good insulator for constructing two-dimensional devices.

“It’s really quite exciting, because this is the first time that coal, something we normally see as low-tech, has been directly linked to the cutting edge of microelectronics,” Cao said.

Transistor dielectric

Moreover, the coal-derived carbon layers were used as the gate dielectric in two-dimensional transistors built on the semimetal graphene or semiconductor molybdenum disulfide to enable more than two times faster device operating speed with lower energy consumption.

Like other atomically thin materials, the coal-derived carbon layers do not possess “dangling bonds,” or electrons that are not associated with a chemical bond. These sites, which are abundant on the surface of conventional three-dimensional insulators, alter their electrical properties by effectively functioning as “traps,” slowing down the transport of mobile charges and thus the transistor switching speed.

Unlike other atomically thin materials, the new coal-derived carbon layers are amorphous. They therefore do not have boundaries between different crystalline regions that serve as conduction pathways leading to “leakage,” where undesired electrical currents flow through the insulator and cause substantial additional power consumption during device operations.

Memristor filament

Memristors store and represent data by modulating a conductive filament formed by electrochemical reactions between a pair of electrodes with the insulator sandwiched in between.

Researchers found that the adoption of ultrathin coal-derived carbon layers as the insulator allows the fast formation of such filament with low energy consumption to enable high device operating speed with low power.

From research to production

The new devices developed by the Cao group provide proof-of-principle for the use of coal-derived carbon layers in two-dimensional devices. But it is yet to be shown how such devices can be manufactured on large scales.

“The semiconductor industry, including our collaborators at Taiwan Semiconductor, is very interested in the capabilities of two-dimensional devices, and we’re trying to fulfill that promise,” Cao said, “over the next few years, the U of I will continue to collaborate with NETL to develop a fabrication process for coal-based carbon insulators that can be implemented in industrial settings.”