The researchers generated wafer-scale sheets of MoS2, which is just over one atom thick, on a sapphire substrate.
The processor, called RV32-WUJI, has 6000 transistors, operates at KHz speeds and can execute the full RISC-V 32-bit instruction set.
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.
Doping to alter performance is not possible with MoS2 because there’s no way to implant an impurity in a single molecule. All of RV32-WUJI ‘s transistors 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.
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 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.
The yield on eight-bit registers was only 71 percent, and that dropped to only 7 percent for a 64-bit register (which required 1,152 transistors).
