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Atomically Thin Circuits Made From Graphene and Molybdenite
Image: Nature Nanotechnology.

Atomically thin transistors and circuits made of graphene and molybdenum disulfide (molybdenite) can now be chemically assembled on a large scale, researchers say. Previous attempts to build circutis from 2-D materials involved placing materials precisely instead of growing them where they’re needed.

Researchers hope such atomically-thin devices will allow Moore’s Law to continue once it becomes impossible to make further progress using silicon. "A big drive for nanotechnology has been the search for new materials to replace silicon to meet Moore's law," says study senior author Xiang Zhang, a materials scientist at the University of California Berkeley.

Research into next-generation electronics has recently explored atomically thin materials such as graphene or molybdenite. Graphene is an excellent conductor, making it ideal for use in wiring and interconnections. However, graphene lacks an electronic band gap, meaning that it cannot easily be used in transistors. In contrast, molybdenite, or molybdenum disulfide (MoS2), has an electronic band gap.​

imgImage: Nature Nanotechnology.

Manufacturing atomically thin electronics has proven challenging because assembling precise structures from both conductive and semiconducting materials has proven extremely difficult. Now scientists have created transistors and circuits each woven from both conductive graphene and semiconducting molybdenite.

Previous research sought to physically assemble atomically thin electronics by placing different materials together. Instead, this new work chemically grows these electronics on a large scale.

First the researchers transferred graphene onto silica and used plasma to etch patterns of channels onto it. They next used chemical vapor deposition to grow molybdenite around the edges of each channel until it completely filled the channels. The molybdenite strips overlapped about 100 to 200 nanometers on top of the graphene.

The resulting transistors had high electron mobilities comparable to those of similar devices assembled physically. The scientists also assembled an atomically thin logic circuit—specifically, an inverter, or NOT gate. This circuit demonstrated a voltage gain of up to 70, a key quality for inverters.

"We used the transistors to form an inverter and demonstrate that logic is possible with our devices," says study lead author Mervin Zhao, a materials scientist at the University of California Berkeley. "This is a platform for making more complex circuits, and therefore computers, using completely 2-D materials."

Zhao does caution that in this preliminary work, the molybdenite channels are about 2 micrometers wide. "If this technology were truly be used as a silicon-replacement, we need extremely thin transistor channels," Zhao says. It remains uncertain what molybdenite performance will be like when transistor channels get very narrow, he says.

The scientists detailed their findings online 11 July in the journal Nature Nanotechnology. "We have filed a provisional patent for this work," Zhao adds.

The Conversation (0)

3 Ways 3D Chip Tech Is Upending Computing

AMD, Graphcore, and Intel show why the industry’s leading edge is going vertical

8 min read
A stack of 3 images.  One of a chip, another is a group of chips and a single grey chip.
Intel; Graphcore; AMD

A crop of high-performance processors is showing that the new direction for continuing Moore’s Law is all about up. Each generation of processor needs to perform better than the last, and, at its most basic, that means integrating more logic onto the silicon. But there are two problems: One is that our ability to shrink transistors and the logic and memory blocks they make up is slowing down. The other is that chips have reached their size limits. Photolithography tools can pattern only an area of about 850 square millimeters, which is about the size of a top-of-the-line Nvidia GPU.

For a few years now, developers of systems-on-chips have begun to break up their ever-larger designs into smaller chiplets and link them together inside the same package to effectively increase the silicon area, among other advantages. In CPUs, these links have mostly been so-called 2.5D, where the chiplets are set beside each other and connected using short, dense interconnects. Momentum for this type of integration will likely only grow now that most of the major manufacturers have agreed on a 2.5D chiplet-to-chiplet communications standard.

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