This week researchers from Lawrence Berkeley National Laboratory have reported a new method to create transistors and circuits that are only a few atoms thick. Their report, Large-scale chemical assembly of atomically thin transistors and circuits, published in Nature Nanotechnology, is another reminder that novel materials and approaches may indeed contribute to extending Moore’s law.
“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, in a report on the LBNL website.
Here is an excerpt from the paper’s abstract:
- “Next-generation electronics calls for new materials beyond silicon, aiming at increased functionality, performance and scaling in integrated circuits. In this respect, two-dimensional gapless graphene and semiconducting transition-metal dichalcogenides have emerged as promising candidates due to their atomic thickness and chemical stability. However, difficulties with precise spatial control during their assembly currently impede actual integration into devices.
- “Here, we report on the large-scale, spatially controlled synthesis of heterostructures made of single-layer semiconducting molybdenum disulfide contacting conductive graphene. Transmission electron microscopy studies reveal that the single-layer molybdenum disulfide nucleates at the graphene edges. We demonstrate that such chemically assembled atomic transistors exhibit high transconductance (10 µS), on–off ratio (∼106) and mobility (∼17 cm2 V−1 s−1). The precise site selectivity from atomically thin conducting and semiconducting crystals enables us to exploit these heterostructures to assemble two-dimensional logic circuits, such as an NMOS inverter with high voltage gain (up to 70).”
Researchers have for some time looked to two-dimensional crystals that are only one molecule thick as alternative materials to keep up with Moore’s law. “These crystals aren’t subject to the constraints of silicon,” an article on the LNBL website noted. “In this vein, the Berkeley Lab 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.”
Zhang is also quoted in an IEEE Spectrum account of the work, “We used the transistors to form an inverter and demonstrate that logic is possible with our devices. This is a platform for making more complex circuits, and therefore computers, using completely 2-D materials.”
The molybdenite channels are about 2 micrometers wide and Zhao cautions, “If this technology were truly be used as a silicon-replacement, we need extremely thin transistor channels,” adding it remains uncertain what molybdenite performance will be like when transistor channels get very narrow.”
Link to paper: http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2016.115.html
Link to LBNL article: http://newscenter.lbl.gov/2016/07/11/atomically-thin-transistors/
Link to IEEE article: http://spectrum.ieee.org/nanoclast/semiconductors/nanotechnology/atomically-thin-circuits-made-from-graphene-and-molybdenite
Image: Nature