Researchers have transformed coal into high-purity materials for use in next-generation electronic devices, marking a major shift in coal's economic and technological applications. Coal is an abundant resource in the United States, but unfortunately, its use as a fossil fuel exacerbates climate change. As the United States transitions to other forms of energy production, it will be important to consider and reassess the economic role of coal.
Two samples are shown here of memristor-containing wafers made from high-quality 2D carbon processed from sapphire bituminous coal mined in southeastern Kentucky. Source: Grainger School of Engineering, University of Illinois at Urbana-Champaign
Coal could play an important role in the next generation of electronic devices, according to a joint study by the University of Illinois at Urbana-Champaign, the National Energy Technology Laboratory, Oak Ridge National Laboratory and the Taiwan Semiconductor Manufacturing Company (TSMC).
"People often think of coal as dumb and dirty, but the processing technology we developed can transform coal into high-purity materials that are only a few atoms thick," said Qing Cao, a professor in the Department of Materials Science and Engineering at the University of Illinois and co-leader of the collaboration. "Their unique atomic structure and properties are ideal for making some of the smallest electronic devices that outperform the state-of-the-art technology."
A process developed by NETL first converts coal into nanoscale carbon disks called "carbon dots," which the I.U. team demonstrated can be linked together to form atomically thin films for applications in two-dimensional transistors and memristors, technologies critical to building more advanced electronic devices. The results were published in the journal Communications Engineering.
Perfect 2D electronics
In the ongoing quest for smaller, faster and more efficient electronic devices, the final step will be to create devices using materials that are only one or two atoms thick. The size of the device cannot be smaller than this limit, and small size often makes it run faster and consume less energy. While ultrathin semiconductors have been extensively studied, building working electronic devices such as transistors and memristors also requires atomically thin insulators -- materials that block the flow of electricity.
Thin layers of atomically scale carbon with a disordered atomic structure can serve as excellent insulators for building two-dimensional devices. Collaborating researchers have shown that this carbon layer can be formed from carbon dots extracted from coal. To demonstrate their capabilities, the University of Illinois team led by Cao developed two two-dimensional devices.
"This is really exciting because it's the first time that something like coal, which we usually think of as low-tech, is directly linked to cutting-edge technology in microelectronics," Cao said.
transistor dielectric
The research team used a coal-derived carbon layer as the gate dielectric in two-dimensional transistors based on semimetallic graphene or the semiconductor molybdenum disulfide, allowing the device to run more than twice as fast while consuming less energy. Like other atomically thin materials, coal-derived carbon layers have no "dangling bonds," or electrons that are not associated with chemical bonds. There are a large number of these sites on the surface of traditional three-dimensional insulators. They change the electrical properties of the insulator by effectively functioning as "traps", slowing down the transmission speed of mobile charges, thereby reducing the switching speed of the transistor.
However, unlike other atomically thin materials, the new coal layers are amorphous, meaning they do not have a regular crystal structure. As a result, there are no boundaries between different crystalline regions, and these boundaries are conduction paths that lead to "leakage," where undesired current flows through the insulator and causes significant additional power consumption during device operation.
transistor filament
Another application considered by the team is memristor - an electronic component that can both store and manipulate data, which could greatly facilitate the implementation of artificial intelligence technology. These devices store and represent data by modulating an electrochemical reaction between a pair of electrodes to form a conductive filament, with an insulator sandwiched between them.
The researchers found that using an ultra-thin layer of coal-derived carbon as an insulator could quickly form such low-energy conductive filaments, allowing the device to operate at higher speeds with lower power. Additionally, the atomic-sized rings in these coal-derived carbon layers confine the filaments, thereby improving the repeatability of device operations, thereby enhancing the fidelity and reliability of data storage.
From research to production
The newly developed device provides proof-of-principle for the use of coal-derived carbon layers in two-dimensional devices. All that remains is to prove that the device can be manufactured at scale.
"The semiconductor industry, including our collaborators at Taiwan Semiconductor Corporation, is very interested in the capabilities of 2D devices, and we are working hard to deliver on this promise," Cao said. "I.I. University will continue to work with NETL in the coming years to develop a coal-based carbon insulator manufacturing process that can be implemented in an industrial setting."
Compiled source: ScitechDaily