
New Metal-Air Transistor Replaces Semiconductors - joak
https://spectrum.ieee.org/nanoclast/semiconductors/devices/new-metalair-transistor-replaces-semiconductors
======
jl2718
This article explains it better:
[https://spectrum.ieee.org/semiconductors/devices/introducing...](https://spectrum.ieee.org/semiconductors/devices/introducing-
the-vacuum-transistor-a-device-made-of-nothing)

~~~
btown
Really intriguing! I found
[https://www.engineering.com/ElectronicsDesign/ElectronicsDes...](https://www.engineering.com/ElectronicsDesign/ElectronicsDesignArticles/ArticleID/16337/Vacuum-
Tubes-The-World-Before-Transistors.aspx) to be a useful companion to explain
more about how control grids work in traditional vacuum tubes.

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twic
A few random thoughts:

* Air presumably doesn't mean atmospheric air here, otherwise you're getting a random mix of gases and water vapour inside your nanoscale wizardry - so will these be nitrogen-filled, like binoculars etc?

* What does this mean for cooling, especially in the high-density 3D architectures mentioned? Can you use air flow _through the chip_ to cool it?

* "tungsten, gold, and platinum were evaluated as metals of choice" \- compare their resistivities of 5.60e-8, 2.44e-8, and 1.06e-7 ohm-metres respectively to silicon's of 6.4e+2 [1] (i thought tungsten was much higher than that, TIL). Does this mean that chips would have less resistive heating? Is resistive heating a significant part of the TDP of a modern chip?

* "replacing silicon with metal means these ACT devices can be fabricated on any dielectric surface, provided the underlying substrate allows effective modulation of emission current from source to drain with a bottom-gate field" \- is there is also a lattice-spacing constraint, where the substrate's spacing has to work with that of the conductor, as i believe there is with silicon chips?

* Is this basically the return of the thermionic valve after fifty years in the wilderness?

[1]
[https://en.wikipedia.org/wiki/Electrical_resistivity_and_con...](https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity#Resistivity_and_conductivity_of_various_materials)

~~~
T-A
> Air presumably doesn't mean atmospheric air here, otherwise you're getting a
> random mix of gases and water vapour inside your nanoscale wizardry

Doesn't matter, as explained in the second paragraph of the article: the air
gap (35 nm) is shorter than the mean free path [1] in air, so the electrons
are effectively moving in a vacuum.

> Is this basically the return of the thermionic valve after fifty years in
> the wilderness?

Yes. The paper's abstract starts out saying just that: "Scattering-free
transport in vacuum tubes has always been superior to solid-state transistors.
It is the advanced fabrication with mass production capability at low cost
which drove solid-state nanoelectronics. Here, we combine the best of vacuum
tubes with advanced nanofabrication technology." [2]

[1]
[https://en.wikipedia.org/wiki/Mean_free_path](https://en.wikipedia.org/wiki/Mean_free_path)

[2]
[https://pubs.acs.org/doi/10.1021/acs.nanolett.8b02849](https://pubs.acs.org/doi/10.1021/acs.nanolett.8b02849)

~~~
roywiggins
Nanoscale vacuum tubes sounds like something out of steampunk/dieselpunk. I
hope it happens for aesthetic considerations alone!

~~~
ggm
Ah yes.. the sweet sweet distortions of valve on my mp3 player!

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jpmattia
As you might expect, this is more of an engineering press release and not a
balanced technical discussion. Two things jump out at me:

> _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._

Electron transport without scattering is usually termed "ballistic transport",
and as gate sizes shrink in traditional MOS devices, a larger fraction of
channel electrons make it across the channel before scattering. So maybe air
gaps might speed up the arrival of mass-production ballistic transistors.

However, there is a new problem: To get an electron out of the metal, you need
to kick it up to the vacuum level (the electron work function of the
material). Giving energy to the electron to get it out of the metal was the
reason that tubes had heating elements back in the day. In more modern
research, it's the reason why people have been exploring diamond thin-film
emitters: It turns out that diamond has the interesting property that the
conduction band is above the vacuum level (!), which means that a conduction-
band electron will fall out of the material given the chance. (Surface physics
gets in the way, which is why diamond engagement rings aren't positively
charged rocks, but very cool nevertheless.)

Alternatively, you need to apply an electric field to have electrons tunnel
out, but usually that corresponds to a very large field where other bad things
start to happen (breakdown, electromigration, etc)

> _Because the electrons flow between the electrodes just as well in a vacuum
> (think vacuum tube) as in air, radiation will not modulate channel
> properties, making ACT devices suitable for use in extreme radiation
> environments and space._

When radiation from space goes through an MOS-type device, there are two big
problems:

1\. Ionizing radiation in the channel creates electron-hole pairs, which
creates excess current between source and drain temporarily,

2\. Ionizing radiation in the dielectric creates electron-hole pairs in the
gate, and often the hole gets trapped in the gate leading to a permanent
threshold shift. This eventually causes failure, and is usually the bigger
problem when designing a space-qualified process.

So while "radiation will not modulate channel properties" is maybe technically
right, the press release is ignoring that the radiation will still modulate
gate properties, which will in turn modulate channel properties.

~~~
neltnerb
This design also struck me as a non-tunneling version of a single electron
transistor. Stick a 10nm metal island in the middle, make the spacing bigger,
and it would look the same. Are the electric fields required really so big?

~~~
smaddox
Yes, the fields required are large. But because the distance is so small, the
voltage difference can be quite reasonable.

------
adrianratnapala
Can someone explain why the electrodes have to be sharp? Intuitively it feels
right, but what is the actual reason?

As far as I can see, the challenge is to get the E-fields (aka voltage
gradients) high enough that electrons can easily leave the metal. But for that
you need the electrodes close to one another, but they don't have to be sharp.

I suppose if you have too big an area of metal at near-contact, then you will
get unwanted capacitance. But is that the only reason?

~~~
murbard2
They do have to be sharp. As an exercise, consider a metallic cone with a
charge of 1 and look at the distribution of the charge that minimizes the
electrostatic energy. You will find that the charge collects near the tip of
the cone. In general, charges will collect where the curvature is high. It's
easier to push electrons out of a pointy tip (or inside of a pointy tip)
because they are denser there.

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magnat
> 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?

~~~
starbeast
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.

~~~
anon_cow1111
Oh, wow, this is basically a chip full of trigatrons isn't it?
[https://en.wikipedia.org/wiki/Trigatron](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.

~~~
marcosdumay
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.)

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tonmoy
I’m not clear where the transistor action is coming from? If it is indeed a
transistor then leakage and gain numbers would be good to see

~~~
tim333
There's a clearer diagram here
[https://imgur.com/a/h6INwsu](https://imgur.com/a/h6INwsu)

You put a voltage on the gate and the field it produces varies the current
between the two metal bits.

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ArtifTh
So, basically a nanoscale electron tube?

~~~
blattimwind
Except without a vacuum (because the plate distance is so small that air
doesn't get in the way)

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dogma1138
So basically back to vacuum tubes?

~~~
klyrs
Pretty much exactly that. Only... the environment is hot enough that (a) you
don't need a heater, and even more interesting, (b) 1 atmosphere is an
effective vacuum for features of that size.

Amusingly, it sounds like these devices will be susceptible to helium
poisoning.

This all makes me wanna stop playing with superconductors and start playing
with tubes again...

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PopeDotNinja
You know this is a pretty new idea when googling "metal-air transistors" links
to the posted article and this HN thread, and searching for the same term on
YouTube reveals no videos (that I could recognize as being about this topic).

Hey SciShow and/or Computerphile, we need videos to give us the TL;DR on
metal-air transistors!

~~~
MrEldritch
Here's an older article from IEEE reporting on an earlier version of the same
technology -
[https://spectrum.ieee.org/semiconductors/devices/introducing...](https://spectrum.ieee.org/semiconductors/devices/introducing-
the-vacuum-transistor-a-device-made-of-nothing)

This one goes into somewhat greater technical detail.

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liftbigweights
What happened to graphene? A couple of years ago, that's all anyone talked
about? I thought graphene was going to get us back on the exponential incline
that is moore's law?

I'm guessing the answer is no ( betteridge's law ) and we are going to stay in
the multi-core environment for a while. 128, 256, 512, 1024, ... cores. Though
I suspect that is going to run into problems very quickly.

~~~
amacbride
“The only thing graphene _can’t_ do is make it out of the lab.”

~~~
amacbride
(I took the Stanford nanoscale materials science class this summer, and we all
had a good laugh. Graphene is very interesting, but it’s subject to the hype
cycle.)

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mabbo
As a general rule, anytime an article is titled with a question I presume the
answer to be "No".

~~~
api
I find heuristics like this to be anti-intellectual. In news orgs the person
who picks the headline often isn't even the person who wrote the article.

~~~
rlpb
The person who picks a headline like this is generally trying to create the
most attention with it without making a false statement.

Instead of "Can New Metal-Air Transistors Replace Semiconductors and Continue
Moore's Law?", the headline writer would love to write "New Metal-Air
Transistors Replace Semiconductors and Continue Moore's Law". That would be
more effective. The fact that the headline writer could not say this tells us
something.

The same goes for weasel words like "may".

> I find heuristics like this to be anti-intellectual.

It is absolutely appropriate to detect what might have been said but was not,
consider the motivations of the speaker, and infer non-importance
appropriately.

~~~
joak
I did write the original headline. I did not write the article though.

In reading the article the question arises naturally but I wasn't able to
answer it because I am not an expert of the domain. I thought that maybe
others could be interested in the question so I posted it in hn. The
conversation ended up being knowledgeable and interesting.

And yes, I would love these guys (or at least this solution) to succeed in
continuing Moore's Law, why I wouldn't ?

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madengr
I wonder what happened to cold cathode display technology. It’s similar in
that electrons are coaxed off a sharp tip. This would have the benefit of a
controlling gate.

