A 32-bit RISC-V processor made using molybdenum disulfide instead of silicon

A team of engineers at Fudan University has successfully designed, built and run a 32-bit RISC-V microprocessor that uses molybdenum disulfide instead of silicon as its semiconductor component. Their paper is published in the journal Nature.

Most microprocessors are made using the semiconductor silicon, which has worked out well for several decades. But as researchers attempt to make processors ever smaller, they have run into a dead end with silicon—they cannot make it any thinner. Instead, many researchers have turned to 2D materials such as graphene, but this is challenging because it is a conductor, not a semiconductor.

In this new study, the research team used a nearly 2D semiconducting material, single-molecule sheets of molybdenum disulfide. These sheets are not truly 2D because they bond at an angle, resulting in a slightly zigzag surface. To make a processor out of them, they put them on a sapphire substrate.

Because the molybdenum disulfide sheets were so thin, the researchers had to wire the transistors together rather than use simple doping as is done with silicon; they then used the wires to adjust voltage thresholds. Next, the team added logic gates to make depletion-mode inverters.

They then used the longest path distance between transistors to determine the chip's maximum processing delay, resulting in a clock speed in the kilohertz range. The average overall yield was measured at approximately 99.9%, with a chip-level yield of 99.8%.

The final test processor the team built was made using 5,900 transistors and was fully capable of running the full 32-bit version of the RISC-V instruction set. They proved it worked by adding together two 32-bit numbers.

The team suggests that their chip is likely the most sophisticated non-silicon microprocessor ever made. They also acknowledge that their chip is not yet ready for use in a real-world application, though they suggest with some tweaks it might be made useful for rudimentary niche applications, such as situations that require extremely low voltage.