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This is just a curiosity question but I remember when 90nm seemed insane so I was wondering what the theoretical limit would be on process size before we couldn't go any smaller. Wiki tells me that there is FinFet down to 3nm, and that someone built a single atom transistor as small as 180 pm but using larger electrodes.

So my question is what's the smallest transistor size that could be made with a single atom, in theory.

Then that same wiki link tells me that to go further than that we'd have to build transistors using subatomic particles like electrons or protons as transistors. Is that theoretically possible? I understand how a transistor works well at least a larger FET say, but how would a transistor made out of electrons and protons even work. Has anyone done it or is that just the author saying maybe someday...

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    $\begingroup$ Since electronic conduction is possible across $\pi$-conjugated molecular bonds, one can certainly make molecular size circuits, which brings us into the 1nm range. I wouldn't call that an extension of process nodes, though... it's a totally different technology. Switching speeds can approach, at least, far to mid infrared frequencies i.e. they would be in the THz to hundred THz range. That's where molecules have their rotational spectra, so imagine pinning a molecule down at one of its chemical bonds around which it can rotate freely and then using two or three other bonds as a switch. $\endgroup$
    – CuriousOne
    Commented Jun 20, 2015 at 3:00
  • $\begingroup$ Although reading your Wiki link makes this clear, I think you need to emphasize in your text that your question is what the limit is regardless of technology: otherwise you may get people answering what limits today's technology are, i.e. optical diffraction limits (I had to read through the whole question and follow the link before inferring this: but that may simply be my background (optics)). @CuriousOne 's comment, as you note, would be a good partial answer. $\endgroup$
    – Selene Routley
    Commented Jun 20, 2015 at 3:57
  • $\begingroup$ @WetSavannaAnimalakaRodVance: I think it's hard to answer what future limits there may be. I can't imagine going beyond the molecular scale, which is why I picked the example, but I am still almost an order of magnitude above the atomic limit and in terms of switching frequency one could imagine that it's not capped by atomic physics until we reach at least a few times 1e15Hz... and now imagine what a tiny physicist living on a neutron star can do! $\endgroup$
    – CuriousOne
    Commented Jun 20, 2015 at 4:19
  • $\begingroup$ Everyone else over the last 50 years has pretty much been wrong, so I stopped worrying about it years ago... $\endgroup$
    – Jon Custer
    Commented Jun 26, 2015 at 19:02

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