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Coal is an abundant resource in the United States that has, unfortunately, contributed to climate change through its use as a fossil fuel. As the country transitions to other means of energy production, it will be important to consider and reevaluate coal\u2019s economic role. A joint research effort from the University of Illinois Urbana-Champaign, the National Energy Technology Laboratory, Oak Ridge National Laboratory and the Taiwan Semiconductor Manufacturing Company has shown how coal can play a vital role in next-generation electronic devices.<\/p>\n

Credit: The Grainger College of Engineering at University of Illinois Urbana-Champaign<\/p>\n

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Coal is an abundant resource in the United States that has, unfortunately, contributed to climate change through its use as a fossil fuel. As the country transitions to other means of energy production, it will be important to consider and reevaluate coal\u2019s economic role. A joint research effort from the University of Illinois Urbana-Champaign, the National Energy Technology Laboratory, Oak Ridge National Laboratory and the Taiwan Semiconductor Manufacturing Company has shown how coal can play a vital role in next-generation electronic devices.<\/p>\n

\u201cCoal is usually thought of as something bulky and dirty, but the processing techniques we\u2019ve developed can transform it into high-purity materials just a couple of atoms thick,\u201d said Qing Cao, a U. of I. materials science & engineering professor and a co-lead of the collaboration. \u201cTheir unique atomic structures and properties are ideal for making some of the smallest possible electronics with performance superior to state-of-the art.\u201d<\/p>\n

A process developed by the NETL first converts coal char into nanoscale carbon disks called \u201ccarbon dots\u201d that the U. of I. research group demonstrated can be connected to form atomically thin membranes for applications in both two-dimensional transistors and memristors, technologies that will be critical to constructing more advanced electronics. These results are reported in the journal Communications Engineering.<\/p>\n

Perfect for 2D electronics<\/strong><\/p>\n

In the ongoing search for smaller, faster and more efficient electronics, the final step will be devices made with materials just one or two atoms thick. It is impossible for devices to be smaller than this limit, and their small scale often makes them operate much quicker and consume far less energy. While ultrathin semiconductors have been extensively studied, it is also necessary to have atomically thin insulators \u2013 materials that block electric currents \u2013 to construct working electronic devices like transistors and memristors.<\/p>\n

Atomically thin layers of carbon with disordered atomic structures can function as an excellent insulator for constructing two-dimensional devices. The researchers in the collaboration have shown that such carbon layers can be formed from carbon dots derived from coal char. To demonstrate their capabilities, the U. of I. group led by Cao developed two examples of two-dimensional devices.<\/p>\n

\u201cIt\u2019s 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,\u201d Cao said.<\/p>\n

Transistor dielectric<\/strong><\/p>\n

Cao\u2019s group used coal-derived carbon layers 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 \u201cdangling bonds,\u201d 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 \u201ctraps,\u201d slowing down the transport of mobile charges and thus the transistor switching speed.<\/p>\n

However, unlike other atomically thin materials, the new coal-derived carbon layers are amorphous, meaning that they do not possess a regular, crystalline structure. They therefore do not have boundaries between different crystalline regions that serve as conduction pathways leading to \u201cleakage,\u201d where undesired electrical currents flow through the insulator and cause substantial additional power consumption during device operations.<\/p>\n

Memristor filament<\/strong><\/p>\n

Another application Cao\u2019s group considered is memristors \u2013 electronic components capable of both storing and operating on data to greatly enhance the implementation of AI technology. These devices store and represent data by modulating a conductive filament formed by electrochemical reactions between a pair of electrodes with the insulator sandwiched in between.<\/p>\n

The 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.  Moreover, atomic size rings in these coal-derived carbon layers confine the filament to enhance the reproducible device operations for enhanced data storage fidelity and reliability.  <\/p>\n

From research to production<\/strong><\/p>\n

The new devices developed by the Cao group provide proof-of-principle for the use of coal-derived carbon layers in two-dimensional devices. What remains is to show that such devices can be manufactured on large scales.<\/p>\n

\u201cThe semiconductor industry, including our collaborators at Taiwan Semiconductor, is very interested in the capabilities of two-dimensional devices, and we\u2019re trying to fulfill that promise,\u201d Cao said. \u201cOver 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.\u201d<\/p>\n

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Journal<\/h4>\n

Communications Engineering<\/p>\n<\/div>\n

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DOI<\/h4>\n

10.1038\/s44172-023-00141-9 <\/i><\/p>\n<\/div>\n

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Article Title<\/h4>\n

Ultrathin Quasi-2D Amorphous Carbon Dielectric Prepared from Solution Precursor for Nanoelectronics<\/p>\n<\/div>\n

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Article Publication Date<\/h4>\n

20-Dec-2023<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n