
Return of the Vacuum Tube (2012) - curtis
http://news.sciencemag.org/physics/2012/05/return-vacuum-tube
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Animats
This paper was published in 2012. The abstract uses the term "nano" three
times, and it appears twice in the title. Bad sign. They made a small
transistor gate in a standard semiconductor wafer fab. The gate has an air
gap, but charges make it across the gap. This is called a vacuum-channel
transistor, and they've been known for years. It's more like a MOSFET than a
triode. Speeds are currently up to 0.5THz.

There are better articles.[1]

It's a low-power device, so it's not going to power terahertz radars. Fast
logic, maybe, but that's a ways off.

[1]
[http://spectrum.ieee.org/semiconductors/devices/introducing-...](http://spectrum.ieee.org/semiconductors/devices/introducing-
the-vacuum-transistor-a-device-made-of-nothing)

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privong
I didn't notice it until after I'd read it, but this is from 2012. Does anyone
know of an update on this particular technology or approach? Has it yielded
any progress after nearly three years?

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sjtrny
[http://www.korg.com/us/news/2015/012212/](http://www.korg.com/us/news/2015/012212/)

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duskwuff
What KORG's got there is a lot more like a traditional vacuum tube than what's
being described in the 2012 article. It's primarily intended for audio
equipment that'd traditionally have used a tube anyway.

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stox
Don't get your hopes up. There has been discussion of variants of this setup
for almost 40 years now. None has made it to market, as far as I am aware.

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sjtrny
> Electrons move more slowly in a solid than in a vacuum

My understanding is that electrons wouldn't move at all in a vacuum because
they require a conductor.

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privong
> My understanding is that electrons wouldn't move at all in a vacuum because
> they require a conductor.

Electrons can propagae in the absense of a medium, in addition to within a
conductor. You might thinking of their motion through conductors relative to
insulators; but in that comparison, electrons don't (readily) move through
insulators because they are impeded.

In the particular case of a vacuum tube, the electrons are freed from the
surface of the filament, where they travel through the vacuum in a tube and
are attracted via electrostatic forces, to the positively charged plate at the
top of the tube.

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sjtrny
Could the absence of a medium also be considered an insulator? The description
of Thermionic emission on Wikipedia
([http://en.m.wikipedia.org/wiki/Thermionic_emission](http://en.m.wikipedia.org/wiki/Thermionic_emission))
seems general enough that things like rubber and vacuums are both insulators
in some sense.

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tjradcliffe
"Insulator" usually means "made of insulating material", and a vacuum is not
made of material. :-)

Language is ambiguous, so it's important when asking questions like this to be
really clear about what you mean by terms.

In particular: "insulator" is a term of convenience that groups together
materials of sufficiently low conductivity under fairly normal conditions.
What constitutes "sufficiently low" and "fairly normal" are both highly
context dependent. Heat anything up enough and it'll become a conductor (it'll
also become a plasma). If you use a term like "insulator" without keeping all
this in mind it'll produce some pretty weird results.

So you can answer this question all kinds of ways. In normal high-voltage
parlance, vacuums are considered insulators. But unlike insulating materials,
which are full of electrons that can't move, vacuums are insulators purely
because they don't contain any electrons.

If you inject electrons, the vacuum becomes a conductor... or at least the
electrons do. After all, a vacuum is an absence of matter, and where there is
an electron there is matter, so where there is an electron there is not a
vacuum...

