

The Vacuum Transistor: A Device Made of Nothing - troydj
http://spectrum.ieee.org/semiconductors/devices/introducing-the-vacuum-transistor-a-device-made-of-nothing

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jpmattia
I'm surprised the IEEE editors allowed the word "Introducing" in the title.
Vacuum FETs are often a target of the diamond thin-film community. (Diamond
has a very interesting electronegativity: Very little energy is required to
get an electron out of diamond and into the "vacuum" (usually air.))

~~~
valarauca1
The problem is with carbon in general is it has a band gap 5x larger then
Silicon. Which overall (but not entirely) means if you want to build a
transistor with Diamond (or graphene) you need to put 5x as much voltage into
it.

The reason graphene is great for transistors is with its higher band energy
its 5x harder for it to soft set itself. So if we pretend todays 11nm
transistors have a 1% chance of electron tunneling, carbon would have a 0.2%.

The problem is that same switch would take 5x as much power to switch. Which
means a modern 220w cpu would now need 1100watts of power :x

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ars
You started by saying 5x voltage, switched to 5x power, and ended with 5x
energy.

Those are not the same thing. You can have 5x voltage without changing the
power or the energy.

~~~
marcosdumay
You can have 5x the voltage without changing the power consumption if you
reduce the capacitance. If you keep the transistors at the same size, a
computer working with 5x mode voltage will use 5x more power if operating at
the same frequency. (But you can probably make it run faster...)

That said, except for very few embedded applications, computers today operate
on a voltage that's much bigger than the silicon band gap. I'm not convinced
it'd be a problem.

~~~
cfallin
Actually, all else being constant, 5x voltage yields 25x power:

P = CV^2 * f (multiply by activity factor if pedantic; assuming all
transistors toggle every cycle here.)

~~~
marcosdumay
And, of course, you are right.

------
Kapura
I'm no scientographer, but it seems to me that a dependence on helium may be a
stumbling point for getting cheap vacuum transistors to the market. The
ongoing helium shortage[1] is driving the price of helium up which could make
helium-based vacuum transistors expensive, limiting widespread adoption. It
could be that high-speed helium vacuum transistors become a speciality product
for those projects that feel the need justifies the additional cost.

[1] [http://www.decodedscience.com/helium-shortage-situation-
upda...](http://www.decodedscience.com/helium-shortage-situation-update-one-
year-later/42314)

~~~
jerf
Well, let's see, a modern chips die size is on the order of 300mm^2. Let's be
generous (I think) and call it 5mm thick. A single helium canister can contain
around 300 cubic feet of helium [1]. Those are nasty units to work with by
hand, but
[https://www.google.com/search?q=%28300+cubic+feet%29+%2F+%28...](https://www.google.com/search?q=%28300+cubic+feet%29+%2F+%28300mm^2+*+5mm%29+)
suggests one such cylinder would be enough for 5.5 million new chips, assuming
the entire chip was just helium. You can probably safely add at least two more
entire factors of magnitude for the fact the chip will still mostly be silicon
(or something), my gut suggests 3 or 4 is probably even closer.

Oh, sure, there will be losses and such, but this is still a trivial expense
next to the billions of dollars of fab work that will be required. In these
quantities we literally use gold without hardly a second thought for price.

[1]:
[http://www.praxairdirect.com/Product2_10152_10051_14626_-1_1...](http://www.praxairdirect.com/Product2_10152_10051_14626_-1_11537___ProductDisplayErrorView)

~~~
Retric
300mm^2 * 5mm = 1.5 milliliters

24k Gold is 42$/gram, 1 gram is 0.052 milliliters.

So, 42 / .052 * 1.5 = 1,211$.

Note: The important parts are not 5mm thick etc, but gold is rather expensive
by volume.

~~~
jerf
Sorry, by "these quantities" I meant "at computer-chip quantities" in general;
gold we pretty much use by _area_ , and not much of that, either. The numbers
I gave were purposely quite generous for volume. After all, I did say they
were probably 3 or 4 orders of magnitude too generous. Per reitzensteinm's
post, looks like you can recover another 1.5 or so out of my chip-height
estimate, too.

------
pimlottc
Regarding the opening anecdote - some have suggested the Soviets used vacuum
tubes so that their planes would survive the electromagnetic pulse from a
nuclear explosion.

~~~
daveslash
DISCLAIMER: This is what I remember once _hearing_ in an ECE class. I was
hesitant to post this comment given that it might be garbage, but perhaps
someone can help confirm or disprove this.

I once heard that one of the reasons the Soviets continued to use analog
systems was that they were "faster, more compact, and more power efficient"
[than a digital computer]. This came at the cost of flexibility. For example,
an op-amp allegedly can do integration faster and with less power than a
digital computer, but the IC can't be reprogrammed. Digital computers have
huge benefits, but ones that come at a cost.

Thoughts/input anyone? As I said, I might be completely off base so please
nobody take that as anything more than "food for though".

~~~
pjc50
At 1980s levels of integration, then I'd agree that for many sorts of signal
processing it's easier to do it in analog than digital. Especially if all your
engineers are trained for analog. In 2014 the situation is the other way
round.

Robustness of power electronics is another consideration: tubes are
mechanically fragile but not vulnerable to ESD, whereas FETs are, especially
during assembly. If their factory process control was poor it would have been
easier to stick with the tubes.

------
danparsonson
How does one speed-test a device that switches significantly faster than the
available electronics?

~~~
DigitalJack
drive a periodic waveform and sample repeatedly. Assuming you don't somehow
sample the same point in the periodic waveform each time, you'll eventually
get the complete waveform.

~~~
jpmattia
> Assuming you don't somehow sample the same point in the periodic waveform
> each time, you'll eventually get the complete waveform.

To add an example of a real technique: You can use a short laser pulse and
change the time-of-flight (mirrored path on a stepper motor, for instance).
This technique will get you to the terahertz region, which is pretty much
state of the art for where electronic devices still have gain.

[http://en.wikipedia.org/wiki/Terahertz_time-
domain_spectrosc...](http://en.wikipedia.org/wiki/Terahertz_time-
domain_spectroscopy#Electro-optical_sampling)

------
ChuckMcM
Oh that is pretty cool. I wonder if they have considered them as power
switching devices. Something like that which had an effective Rds of nano-ohms
could make electric cars more efficient.

~~~
mikepurvis
Yeah, I'm skeptical about plans to build whole integrated circuits out of
them, but these high frequency, low-loss devices could be killer for a lot
power electronics applications— motor controllers, DCDCs, etc.

~~~
neltnerb
Not sure about high power, but the physical requirement for small size scale
combined with the engineering goal of high current is usually contradictory.

I do absolutely think this could be awesome for lower power ultra tiny DC-DC
converters though. For instance:

[http://hexus.net/tech/news/psu/64161-finsix-laptop-power-
sup...](http://hexus.net/tech/news/psu/64161-finsix-laptop-power-supply-
quarter-size-traditional-models/)

is pushing to high enough frequencies so as to not need an inductor at all.
Problem with high frequencies is that usually the efficiency drops, so there's
a tradeoff. But if you can avoid the switching losses by moving to a
transistor with higher operating frequencies, it might be quite good =)

Or the tiny size might work well for letting you do cool stuff like on-chip
DC-DC conversion where you don't need an inductor because it's all so fast...

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zwieback
Would a guitar amp built with these sound like a tube amp?

~~~
marcosdumay
I'd bet computers will be emulating the sound of vacuum tubes way before any
of those things get into market.

You can get the correct vacuum tube-like amplification from a computer today,
it's just that tubes are still cheaper. A/D converters and first stage linear
amplifiers are only getting cheaper (even at this, post Moore's law era), thus
it's only a matter of time before computers retire valves on yet another
application.

EDIT: Also, tunnel devices have a completely different behavior from
macroscopic valves. They are very non-linear, what makes them great at digital
applications, but horrible sound amplifiers.

~~~
xellisx
They already do. Check out Line6.com

~~~
spiritplumber
Won't prevent audiophiles from being audiophiles. I remember reading a screed
against double-blind testing on some magazine (would link to, but can't find
it)

~~~
marcosdumay
Audiophiles are funny.

I had a huge problem of making an D/A converter with enough precision for
instrumentation a while back, but designing some digital I/O with enough
bandwidth for it was a nightmare. Then I looked at the Internet and saw an
audiophile complaining that a soundcard[1] with 20dB less noise than my design
was crap.

1 - A PCI express card, of course. Didn't try that bus. I'd have a really bad
time manualy creating a board for it.

