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Comment by magnat | Hacker News Reader

> It uses two in-plane symmetric metal electrodes separated by an air gap of less than 35 nanometers

With air dielectric strength of 3kV/mm, why wouldn't such electrodes continously arc over when applied voltage is over 0.1V?

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In general, the dielectric strength of a gas varies with the gap length, so for small gaps it's not strictly correct to say that air has a dielectric strength of 3 kV/mm or any other single value. [0] But at this scale, the gap is so small that the idea of "dielectric strength" isn't really meaningful anyway. There are so few atoms between the electrodes that electrons can flow with negligible resistance at any reasonable field strength.

[0] https://en.wikipedia.org/wiki/Paschen%27s_law

The first ionization energies of oxygen, nitrogen etc are all > 10 eV [1]. If you accelerate an electron over 35 nm with a 1 V electric field, it picks up 35e-9 eV. So it can't ionize anything, even if it happens to collide with a molecule, which is unlikely [2].

[1] http://www-personal.umich.edu/~cowley/ionen.htm

[2] https://en.wikipedia.org/wiki/Mean_free_path

Correcting myself: if you accelerate an electron through a potential difference of 1 V, it picks up 1 eV and nothing else. While the conclusion stands (it can't ionize anything), I plead temporary insanity for the way I arrived at it.

I think that is the general idea, the field below regulates that arc.

edit - This design is so absurdly straight forward, I am genuinely impressed. The damn thing is even reversible. Is cool as hell that this works. I wonder what the pitfalls are?

edit2 for magnat as it is not letting me reply to the comment below - The way I understand it (given it is described as a FET), those two electrodes sit directly on top of a gate. If you flood the gate with electrons, then the gate's negative electric field will keep the electrons in the electrodes away from the gap, reducing or completely halting the flow of current.

You mean ions/electrons between electrodes are deflected by voltage applied at the gate, as in vacuum tube?

There is mention of one issue - melting of the tips. They are working on modifying the collector to reduce the stress on the emitter, which suggests that a practical device will not be reversible. (from a sufficiently abstract point of view, transistors appear to be reversible too, but in practice they are not.)

Oh, wow, this is basically a chip full of trigatrons isn't it? https://en.wikipedia.org/wiki/Trigatron

For anyone who doesn't feel like reading the wiki, these things are normally switches you use when all other types of switch would be destroyed by the amount of current you're trying to pass (the pictured device has a mesh cage to catch fragments if it blows up).

If you've ever seen one of those demos where someone 'shrinks' a quarter or crushes cans with magnetic fields, there's a good chance that's what they're using to switch the power on.

Seeing the same concept used in a cpu is bizarre, but really exciting if it works.

It does not seem to use arcs, so it does not use a trigger. It's more suitable to think about this as a triode valve or a FET where the the channel is made of vacuum instead of silicon. (And only comes on N variety, what is not great.)

> The nanoscale air gap is less than the mean-free path of electrons in air, hence electrons can travel through air under room temperature without scattering.

The device is so small that air needs to be thought of like ping-pong balls bouncing around inside a lottery machine, not a homogeneous bulk. Does that mean things like arc formation work differently? I honestly don't know!

I get the impression that the gas molecules are not being ionized, the electrons merely pass between them.

Thinking some more about this, does not dielectric breakdown in gases depend on electrons gaining sufficient energy to cause ionization in collisions with the molecules [1]? With the gap well below the mean free path, perhaps they cannot reach that speed at the voltages being used?

[1] https://en.wikipedia.org/wiki/Paschen's_law#Physical_mechani...

I'd also wonder at the thermal properties and with a gap of 35nm, these would make chips large again. However, I suspect they would need to do vertical placement to allow the gap to be large enough without stepping back in silicon real estate. However, the question then becomes more important about the thermal properties of such an approach.

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