Washington | Scientists have developed a way to create transistors and circuits that are only a few atoms thick, an advance that may pave the way for next-generation, paper-thin gadgets. The method yields functional structures at a scale large enough to begin thinking about real-world applications and commercial scalability.
The scientists controlled the synthesis of a transistor in which narrow channels were etched onto conducting graphene, and a semiconducting material called a transition-metal dichalcogenide (TMDC) was seeded in the blank channels. Both of these materials are single-layered crystals and atomically thin, so the two-part assembly yielded electronic structures that are essentially two-dimensional. In addition, the synthesis is able to cover an area a few centimetres long and a few millimetres wide.
This is a big step toward a scalable and repeatable way to build atomically thin electronics or pack more computing power in a smaller area, said Xiang Zhang, a senior scientist at US Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), who led the study. Transistors are electronic switches, so they need to be able to turn on and off, which is a characteristic of semiconductors.
However, at the nanometre scale, silicon transistors likely are not a good option. That is because silicon is a bulk material, and as electronics made from silicon become smaller and smaller, their performance as switches dramatically decreases, which is a major roadblock for future electronics. Researchers have looked to two-dimensional crystals that are only one molecule thick. These crystals are not subject to the constraints of silicon.
Scientists developed a way to seed a single-layered semiconductor, in this case the TMDC molybdenum disulfide (MoS2), into channels lithographically etched within a sheet of conducting graphene. The two atomic sheets meet to form nanometre-scale junctions that enable graphene to efficiently inject current into the MoS2.
These junctions make atomically thin transistors. This approach allows for the chemical assembly of electronic circuits, using two-dimensional materials, which show improved performance compared to using traditional metals to inject current into TMDCs, said Mervin Zhao, a PhD student in Zhang’s group at Berkeley Lab.
Optical and electron microscopy images, and spectroscopic mapping, confirmed various aspects related to the successful formation and functionality of the two-dimensional transistors. The scientists showed the applicability of the structure by assembling it into the logic circuitry of an inverter. This further underscores the technology’s ability to lay the foundation for a chemically assembled atomic computer.
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