16-bit RISC-V processor made with carbon nanotubes

[messe]

For those of us wondering what they meant by 16-bit RISC-V (as there isn't a 16-bit RISC-V ISA), it's just 32-bit RISC-V instructions operating on 16-bit data and addresses.

[squarefoot]

Sort of what the MC68008 was ages ago: 32 bit internal architecture but reduced external data and address buses so the chip could be used to build simpler/cheaper systems.

[limsup]

No, there is a 16-bit version https://content.riscv.org/wp-content/uploads/2017/05/riscv-s... See chapter 12, “C” Standard Extension for Compressed Instructions

> This chapter describes the current draft proposal for the RISC-V standard compressed instruction set extension, named “C”, which reduces static and dynamic code size by adding short 16-bit instruction encodings for common operations.

[noneeeed]

Can someone ELI5 what the advantage a CNT based chip would be? Is it more energy efficient, or can they operate at a higher frequency?

[gnode]

We want to make transistors ever smaller to increase their energy efficiency and fit more of them on a chip. Scaling down transistors made of materials like silicon hits limits, as the distances become so small that electrons can leak through the materials.

In a field effect transistor (FET), you have a channel and a gate. The channel is a bit like a bridge which can be raised and lowered as ships travel underneath. Ideally, electrons shouldn't be able to flow between the channel and the gate (falling off the bridge), and depending on the voltage at the gate (position of the ship), the channel should range in resistance between zero (completely open; transistor is on) and infinity (completely closed; transistor is off).

In a CNTFET, the channel is replaced with a carbon nanotube. The nanotube channel is very good at keeping the current carriers (electrons) inside, and so leakage is small. Additionally, nanotubes are very good at carrying current. To use the bridge analogy, the CNTFET has a bridge that is very wide, and so allows lots of people across, and has high walls such that the people don't fall in the water or onto the ship.

[Symmetry]

They have much better carrier mobility than silicon has. We can keep reducing power/operation by shrinking transistors but it looks like if we're every going to increase processor frequencies against we'll need to do a substrate switch like this. And we can't keep shrinking silicon transistors forever, anyways.

[philjohn]

Apparently faster and lower power, so a boon for mobile devices, data centres etc - plus a net positive if all computation is performed on them in energy consumption globally.

It doesn't appear that they would be any more environmentally friendly to create in the first place as silicon though.

[f00zz]

Not quite the rod logic [0] processor I expected from the headline, but pretty cool!

[0] https://youtu.be/ORjyXcLDd9M?t=1536

[lachlan-sneff]

Rod logic is super cool! Wish more people were looking into it!

[peter_d_sherman]

Awesome link! Thanks!

[Symmetry]

A creative way of getting around the low transistor yield that nanotubes are currently stuck with.

[Taniwha]

This is a stunt - but it's a pretty cool stunt

[rwmj]

A link to the paper would be nice. Unfortunately nature.com is paywalled. Does anyone know what open source design they modified? I'm guessing PicoRV32.

[3SunSyzygy]

sci-hub.se/10.1038/s41586-019-1493-8

[hcarvalhoalves]

A processor made out of tiny resistors?

[gnode]

That's one way of looking at field-effect transistors. A chip is a collection of channels with resistances controlled by each other.

[Koshkin]

Don't CNTs have some semiconductor properties?