https://arstechnica.com/science/2025/04/researchers-build-a-risc-v-processor-using-a-2d-semiconductor/ Skip to content Ars Technica home Sections Forum Subscribe * AI * Biz & IT * Cars * Culture * Gaming * Health * Policy * Science * Security * Space * Tech * Feature * Reviews * Store * AI * Biz & IT * Cars * Culture * Gaming * Health * Policy * Science * Security * Space * Tech Forum Subscribe Story text Size [Standard] Width * [Standard] Links [Standard] * Subscribers only Learn more Pin to story Theme * HyperLight * Day & Night * Dark * System Search dialog... Sign In Sign in dialog... Sign in Taking a risc A 32-bit processor made with an atomically thin semiconductor It's slow and inefficient, but the semiconductor is only one molecule thick. John Timmer - Apr 2, 2025 12:46 pm | 59 A circular wafer with a grid of individual processors on its surface. One of those is highlighted and zoomed in on the right of the image. A circular wafer with a grid of individual processors on its surface. One of those is highlighted and zoomed in on the right of the image. Credit: Ao, et. al. Credit: Ao, et. al. Text settings Story text Size [Standard] Width * [Standard] Links [Standard] * Subscribers only Learn more Minimize to nav On Wednesday, a team of researchers from China used a paper published in Nature to describe a 32-bit RISC-V processor built using molybdenum disulfide instead of silicon as the semiconductor. For those not up on their chemistry, molybdenum disulfide is a bit like graphene: a single molecule of MoS[2] is a sheet that is only a bit over a single atom thick, due to the angles between its chemical bonds. But unlike graphene, molybdenum disulfide is a semiconductor. The material has been used in a variety of demonstration electronics, including flash storage and image sensors. But we've recently figured out how to generate wafer-scale sheets of MoS[2] on a sapphire substrate, and the team took advantage of that to build the processor, which they call RV32-WUJI. It can only add single bits at a time and is limited to kilohertz clock speeds, but it is capable of executing the full RISC-V 32-bit instruction set thanks to nearly 6,000 individual transistors. Going flat We've identified a wide range of what are termed 2D materials. These all form repeated chemical bonds in more or less a single plane. In the case of graphene, which consists only of carbon, the bonds are all in the same plane, meaning the molecule is as thick as a carbon atom. Molybdenum disulfide is slightly different, as the angle of the chemical bonds is out of plane, resulting in a zig-zag pattern. This means the sheet is slightly thicker than its component atoms. [Molybdenite-3D-balls] Molybdenum disulfide consists of sulfur (yellow spheres) and molybdenum (blue spheres) in a staggered hexagonal structure. Credit: Ben Mills/Wikipedia In any case, the electronic properties of these materials are strictly a product of the orbital configurations of the molecule itself--there is no bulk material from which bulk properties can emerge. While graphene is an excellent conductor, MoS[2] is a semiconductor. Some of the demonstration devices built using MoS[2] have used graphene for the conductive material. But the team behind the new work focused on making the experimental hardware that was compatible with silicon manufacturing techniques. This would allow for easier production and could enable the integration of silicon support chips. Still, there were some distinct challenges involved with MoS[2]. In normal silicon, a transistor's threshold voltage can be adjusted by doping the silicon--implanting impurities that change the semiconductor's behavior. But there's no way to implant an impurity in a single molecule. All of the semiconductors of RV32-WUJI are n-type, and their performance can't be adjusted. So the researchers here used two different metals (aluminum and gold) for the wiring and adjusted each transistor's threshold voltages through the choice of wiring, as well as the material the wiring was embedded in. Making chips On the chip level, the researchers experimented with building many individual devices and then used machine learning to identify the optimal combination of wiring and materials that ensured each individual transistor would reside within the needed performance envelope. At the transistor level, the device uses what are called depletion-mode inverters. To build functional circuitry, the researchers built and tested a full suite of 25 logic gates and tested them. Eighteen were functional, and the researchers built the chip using those. They used the longest path through the chip to determine the delay they had to account for, which set an upper limit on clock speed in the kilohertz range. The overall yield when finally making the chip was over 99.9 percent, with a chip-level yield of 99.8 percent. That said, some of the circuitry proved considerably more challenging. The yield on eight-bit registers, for example, was only 71 percent, and that dropped to only 7 percent for a 64-bit register (which required 1,152 transistors). The resulting processor involves 5,900 individual transistors and is capable of implementing the full 32-bit version of the RISC-V instruction set, which necessarily means it includes sophisticated circuitry like the RISC-V instruction decoder. At the same time, some aspects are intentionally kept simple; while it can perform the addition of two 32-bit numbers, it does so by operating a single bit at a time, meaning it takes 32 clock cycles to perform the operation. This also required on-board buffers to store the intermediate results. Still, it works, and the authors argue that it's probably one of the most sophisticated bits of "beyond silicon" hardware yet implemented. That said, they don't expect this technology to replace silicon; instead, they view it as potentially filling some niche needs, like ultra-low-power processing for simple sensors. But if the technology continues to advance, the scope of its potential uses may expand beyond that. Nature, 2025. DOI: 10.1038/s41586-025-08759-9 (About DOIs). Photo of John Timmer John Timmer Senior Science Editor John Timmer Senior Science Editor John is Ars Technica's science editor. He has a Bachelor of Arts in Biochemistry from Columbia University, and a Ph.D. in Molecular and Cell Biology from the University of California, Berkeley. When physically separated from his keyboard, he tends to seek out a bicycle, or a scenic location for communing with his hiking boots. 59 Comments Comments Forum view Loading Loading comments... Prev story Next story Most Read 1. Listing image for first story in Most Read: Trump White House budget proposal eviscerates science funding at NASA 1. Trump White House budget proposal eviscerates science funding at NASA 2. 2. That groan you hear is users' reaction to Recall going back into Windows 3. 3. Apple silent as Trump promises "impossible" US-made iPhones 4. 4. Powerful programming: BBC-controlled electric meters are coming to an end 5. 5. AI isn't ready to replace human coders for debugging, researchers say Customize Ars Technica has been separating the signal from the noise for over 25 years. With our unique combination of technical savvy and wide-ranging interest in the technological arts and sciences, Ars is the trusted source in a sea of information. 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