Coal is playing a vital role in next-generation electronics

Coal, an abundant resource in the United States, has historically been associated with environmental concerns due to its role as a fossil fuel. However, as energy production shifts towards alternative sources, the economic relevance of coal is being reconsidered. A collaborative research initiative, involving the University of Illinois Urbana-Champaign, the National Energy Technology Laboratory (NETL), Oak Ridge National Laboratory, and the Taiwan Semiconductor Manufacturing Company, has revealed coal's potential in advancing electronic device technology.

“Coal is usually thought of as something bulky and dirty, but the processing techniques we’ve developed can transform it into high-purity materials just a couple of atoms thick,” stated Qing Cao, a materials science and engineering professor at U. of I. and co-lead of the collaboration. “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.”

A process created by NETL transforms coal char into nanoscale carbon discs, termed ‘carbon dots’. The U. of I. research group demonstrated these dots can be assembled into atomically thin membranes. These membranes are pivotal for developing two-dimensional transistors and memristors, essential for constructing more advanced electronics.

In the quest for more compact, rapid, and energy-efficient electronics, the ultimate goal is devices comprised of materials only one or two atoms thick. At this scale, devices not only reach the minimum possible size but also operate faster and use less energy. While ultrathin semiconductors have received considerable attention, atomically thin insulators, which prevent electric currents, are equally vital for functional electronic devices like transistors and memristors.

The research team has discovered that carbon layers derived from coal char, with their disordered atomic structure, serve as excellent insulators for two-dimensional devices. Cao's group at U. of I. has developed two prototypes of such devices.

One application explored by Cao’s team involves using coal-derived carbon layers as the gate dielectric in two-dimensional transistors. This approach has enabled devices to operate over two times faster with reduced energy consumption. Unlike other atomically thin materials, these coal-derived carbon layers are amorphous and lack regular, crystalline structures, preventing the formation of conduction pathways that lead to leakage and increased power consumption in conventional devices.

Another potential use is in memristors, components critical for enhancing AI technology implementation. These devices store and process data by modulating a conductive filament between electrodes, with the insulator in between. The use of ultrathin coal-derived carbon layers as insulators allows for the rapid formation of these filaments, reducing energy consumption and enhancing device speed, data storage fidelity, and reliability.

The next step in this research is to scale up the manufacturing of these coal-based carbon insulators for industrial use.

“The semiconductor industry, including our collaborators at Taiwan Semiconductor, is very interested in the capabilities of two-dimensional devices, and we’re trying to fulfil that promise,” Cao remarked. The U. of I., in continued collaboration with NETL, aims to develop a fabrication process for these coal-based carbon insulators, paving the way for their industrial application and redefining the role of coal in the realm of advanced electronics.