Researchers at the University of Illinois Urbana-Champaign have developed a method using coal-derived carbon nanodots to build insulating layers on two-dimensional (2D) materials, a step that could help overcome a key bottleneck in making next-generation transistors. The work, reported in the journal Nature Communications, was highlighted by Chinese automotive news outlet First Electric Vehicle (d1ev.com).
Overcoming a long-standing challenge
2D materials—sheets just one atom thick—are seen as a promising alternative to silicon as conventional microelectronics approaches its physical limits. However, their lack of a three-dimensional chemical structure makes it difficult to grow the dielectric layers needed for transistors directly on their surface, a problem that has persisted for years.
Qing Cao, a professor of materials science and engineering at the Grainger College of Engineering, working with the U.S. Department of Energy's National Energy Technology Laboratory (NETL), discovered that carbon nanodots derived from bituminous coal can serve as an atomic-scale adhesive. These nanodots, which are 1 to 5 nanometers wide and just one atom thick, promote bonding with 2D materials such as graphene and molybdenum disulfide without hybridizing with the conductive channel, resulting in a clean interface that supports the growth of ultra-thin, thermally stable dielectric layers.
"Devices made from 2D materials are attractive because they can continue to scale down to dimensions where silicon begins to face serious performance challenges," Cao said. "However, the lack of three-dimensional chemical structure makes it difficult to grow the insulating dielectric layer needed for transistor operation directly on the surface of 2D materials. This is a long-standing bottleneck, and we found a solution from an unexpected source: carbon nanodots made from processed coal. They act as a base coating to grow high-quality thin dielectric layers on 2D materials while maintaining a clean interface, which is a critical step in making transistors."
The team reported that their dielectric layer outperforms industry targets set by the IEEE International Roadmap for Devices and Systems (IRDS), achieving an equivalent oxide thickness of 0.6 nanometers and a leakage current density below 0.1 milliamps per square centimeter.
Lower voltage, lower energy
Using this approach, the researchers demonstrated field-effect transistors and integrated logic gates that operate at about 0.5 volts—well below the 0.6 to 0.8 volts typically required by current advanced silicon technology—potentially reducing the energy needed for computation.
While the research is still at an early stage, it offers a new pathway for the semiconductor industry to continue improving performance and efficiency as silicon approaches its limits. The use of coal, an abundant and low-cost material, adds an interesting twist to the search for advanced electronic materials.
