This schematic shows the chemical assembly of 2D crystals. Channels are etched into graphene and then molybdenum disulfide begins to nucleate around the edges and within the channel. At the edges, molybdenum disulfide slightly overlaps the top of the graphene, while further growth results in molybdenum disulfide completely filling the channels. Image: Berkeley Lab.In an advance that helps pave the way for next-generation electronics and computing technologies, scientists at the US Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a way to chemically assemble transistors and circuits that are only a few atoms thick.
What's more, their method yields functional structures at a scale large enough to begin thinking about commercial production. They report their research in a paper in Nature Nanotechnology.
The scientists were able to synthesize an atomically-thin transistor by etching narrow channels onto graphene and then seeding a semiconducting material known as a transition-metal dichalcogenide (TMDC) into the 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 process is able to cover an area a few centimeters long and a few millimeters 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," says Xiang Zhang, a senior scientist in Berkeley Lab's Materials Sciences Division who led the study.
Zhang also holds an endowed chair at the University of California (UC) Berkeley and is a member of the Kavli Energy NanoSciences Institute at UC Berkeley. Other scientists who contributed to the research include Mervin Zhao, Yu Ye, Yang Xia, Hanyu Zhu, Siqi Wang and Yuan Wang from UC Berkeley, as well as Yimo Han and David Muller from Cornell University.
Their work is part of a new wave of research aimed at keeping pace with Moore's Law, which holds that the number of transistors in an integrated circuit doubles approximately every two years. In order to keep this pace, scientists predict that integrated electronics will soon require transistors that measure less than 10nm in length.
Transistors are electronic switches, so they need to be able to turn on and off, which is a characteristic of semiconductors. At the nanometer scale, however, silicon transistors likely won't be a good option. This is because as transistors made from silicon become smaller and smaller, their switching performance becomes less and less reliable, which is a major roadblock for future electronics.
Researchers have looked to two-dimensional crystals that are only one molecule thick as alternative materials for keeping up with Moore's Law. These crystals aren't subject to the same constraints as silicon.
In this vein, the Berkeley Lab scientists developed a way to seed a single-layered semiconductor, in this case a TMDC called molybdenum disulfide (MoS2), into channels lithographically etched into a sheet of graphene. The two atomic sheets meet to form nanometer-scale junctions through which graphene can efficiently inject current into the MoS2. These junctions can thus act as 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," says Mervin Zhao, a lead author and PhD student in Zhang's group at Berkeley Lab and UC Berkeley.
The scientists used optical and electron microscopy, together with spectroscopic mapping, to confirm various aspects related to the successful formation and functionality of the two-dimensional transistors.
In addition, the scientists demonstrated the applicability of these two-dimensional transistors by assembling them into the logic circuitry of an inverter. This further underscores the technology's ability to lay the foundation for a chemically-assembled atomic computer, the scientists say.
"Both of these two-dimensional crystals have been synthesized in the wafer scale in a way that is compatible with current semiconductor manufacturing. By integrating our technique with other growth systems, it's possible that future computing can be done completely with atomically thin crystals," says Zhao.
This story is adapted from material from the Lawrence Berkeley National Laboratory, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.