Nanoscale vacuum transistors – way cool, but still not as pretty as a glowing 12AU6

The venerable 12AU6 vacuum tube, still in use by audiophiles today – I used many like this in my youth

From AAAS, news of a super tiny vacuum-tube transistor hybrid that can operate up to .46 TERAHertz (thats 460,000 megahertz or 460 gigahertz):

Return of the Vacuum Tube

by Jon Cartwright

Peer inside an antique radio and you’ll find what look like small light bulbs. They’re actually vacuum tubes—the predecessors of the silicon transistor. Vacuum tubes went the way of the dinosaurs in the 1960s, but researchers have now brought them back to life, creating a nano-sized version that’s faster and hardier than the transistor. It’s even able to survive the harsh radiation of outer space.

Developed early last century, vacuum tubes offered the first easy way to amplify electric signals. Like light bulbs, they are glass bulbs containing a heated filament. But above the filament are two additional electrodes: a metal grid and, at the top of the bulb, a positively charged plate. The heated filament emits a steady flow of electrons, which are attracted to the plate’s positive charge. The rate of electron flow can be controlled by the charge on the intervening grid, which means a small electric signal applied to the grid—say, the tiny output of a gramophone—is reproduced in the much stronger electron flow from filament to plate. As a result, the signal is amplified and can be sent to a loudspeaker.

Vacuum tubes suffered a slow death during the 1950s and ’60s thanks to the invention of the transistor—specifically, the ability to mass-produce transistors by chemically engraving, or etching, pieces of silicon. Transistors were smaller, cheaper, and longer lasting. They could also be packed into microchips to switch on and off according to different, complex inputs, paving the way for smaller, more powerful computers.

But transistors weren’t better in all respects. Electrons move more slowly in a solid than in a vacuum, which means transistors are generally slower than vacuum tubes; as a result, computing isn’t as quick as it could be. What’s more, semiconductors are susceptible to strong radiation, which can disrupt the atomic structure of the silicon such that the charges no longer move properly. That’s a big problem for the military and NASA, which need their technology to work in radiation-harsh environments such as outer space.

The new device is a cross between today’s transistors and the vacuum tubes of yesteryear. It’s small and easily manufactured, but also fast and radiation-proof. Meyyappan, who co-developed the “nano vacuum tube,” says it is created by etching a tiny cavity in phosphorous-doped silicon. The cavity is bordered by three electrodes: a source, a gate, and a drain. The source and drain are separated by just 150 nanometers, while the gate sits on top. Electrons are emitted from the source thanks to a voltage applied across it and the drain, while the gate controls the electron flow across the cavity. In their paper published online today in Applied Physics Letters,

Full story here at AAAS, here’s my concept pictorial image (may not be fully accurate – I don’t have access to their paper diagrams) of what it looks like compared to the traditional vacuum tube (triode) based on what I’ve been able to find on the design:

The paper from AIP:

Vacuum nanoelectronics: Back to the future?—Gate insulated nanoscale vacuum channel transistor

Jin-Woo Han1, Jae Sub Oh2, and M. Meyyappan1

1Center for Nanotechnology, NASA Ames Research Center, Moffett Field, California 94035, USA

2National Nanofab Center, 335 Gwahangno, Yuseong-gu, Daejeon 305-806, Korea

(Received 24 February 2012; accepted 22 April 2012; published online 23 May 2012)

  • A gate-insulated vacuum channel transistor was fabricated using standard silicon semiconductor processing. Advantages of the vacuum tube and transistor are combined here by nanofabrication. A photoresist ashing technique enabled the nanogap separation of the emitter and the collector, thus allowing operation at less than 10 V. A cut-off frequency fT of 0.46 THz has been obtained. The nanoscale vacuum tubes can provide high frequency/power output while satisfying the metrics of lightness, cost, lifetime, and stability at harsh conditions, and the operation voltage can be decreased comparable to the modern semiconductor devices.
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Bill Marsh

Wow, very interesting. AS I recall, those old tubes were resistant to EMP damage as well.

Jer0me

Very interesting how we can make old stuff better rather than just replacing it.
I remember my old valve amp very well. I suspect my neighbors at the time still do too, and they lived about 500m away!

Hmmm I wonder how this will play out regarding maximum data rates for digital systems?
That is a huge achievement!
Larry

Way cool!

Steve in SC

Vacuum Tubes have always been superior to transistors at RF.
Check any TV or Radio station transmitter.

polistra

Tubes were naturally suited to analog uses because of their response curve. I wonder if this technology will finally make super-complex analog computers … i.e. true neural equivalents … more feasible?

Bill H

EMP resistive, Gama resistive, and need little shielding in space..
great achievement… and one that will push out telecommunications abilities to great lengths by reducing weight needed in space for them to operate…

Robert of Ottawa

460GHz, amazing, Bye-Bye travelling wave tubes. Not sure the diagram is quite accurate. Of course, first you need a vacuum and are able to keep it.

JinOH

As an avid ham radio operator – I collect 1950’s era tube transmitters and receivers. I have always loved the warm glow of vacuum tubes. I use a transceiver that has 3 vacuum tubes in it daily. Tubes are able to take abuse that solid state devices cannot – plus they have made a huge ‘comeback’ with audiophiles because they have a much better ‘sound’. Don’t get me wrong, I deal with digital devices on a daily basis & they are indeed wonderful, but if you want a device that can literally take some serious abuse and ‘keep on ticking’ – vacuum tubes win every time. Great stuff!

Robert of Ottawa

BTW I remember meddling with my valve radios and amplifiers.
BBTW There is a company in the UK named E2V which makes blazingly fast (and yes, they are also hot) analog-to-digital converters. They used to be The English Electric Valve Company. (Ed Note: The Brits call a vacuum tube a “valve”).
KT66 anyone?

Curious George

At the first glance, this appears to be a solution looking for a problem. The speed of integrated circuits is determined mostly by delays in “wires”, not by delays in individual transistors.It could become important in true 3-dimensional circuits; the vacuum should generate much less heat.

Wahior

12AU6s are OK, but you can’t beat an output stage of glowing KT88s.

Gary Hladik

This reminds me of a 1951 sci fi short story which included a future space fleet battle computer with “a million vacuum tubes”:
http://www.mayofamily.com/RLM/txt_Clarke_Superiority.html
Reading it decades later in the era of transistors and laptop computers, I smiled indulgently at the author’s lack of vision.
Oh, wait…

Robert of Ottawa

I think the structure may be more like a vacuum between source and drain and the metal gate physially on top of the vacuum space between the two, insulated by SO2.

a jones

The concept is not new, the basic idea was being bandied around physics depts here as early as the late 1960’s. The essential problems are current density, low, dissipation of waste heat, and of course engineering the blighters to close enough tolerances.to operate. I forget the order of voltage gradient you need for what were then called cold cathode valves, and I am not going to look up my notes, but I seem to remember it is really rather high which causes other engineering problems.
But of course the truth is at that time the transistor had become incredibly cheap, the integrated circuit was starting to appear and nobody was much interested. There was a revival in the mid eighties with much better field computation techniques but nothing came of it, the engineering was still too difficult.
Time will tell whether these new fabrication techniques work well enough to produce a commercially viable product.
Still I have a certain nostalgia for glass bottles with fires in, UK and US designations were not the same, but my particular favourite was the mighty KT 66.
Kindest Regards

Merovign

A NEW TOY! YAAAAAAAAY!
I suspect it will be a few years, but I look forward to seeing them in action.
One wonders if they will be able to replicate the more subjective differences in things like Amp output frequencies that cause people to keep building tube amps, and if they will actually be EMP-hard or if that is too dependent on everything *else* in a circuit.

eyesonu

I just never know what to expect on WUWT. It will surely be the cutting edge of science and/or technology.
Thanks Anthony.

A little background (and more info) on “Vacuum Transistors”, as they have been tried before (processing technology has advanced a lot since then, however, perhaps making this practical now):
http://tikalon.com/blog/blog.php?article=2012/vacuum_transistor

In 1973, Charles Spindt and his colleagues at the Stanford Research Institute (Menlo Park, California) fabricated miniaturized vacuum tubes by a planar process. These vacuum tubes solved two vacuum tube problems. They worked at a lower voltage, and they didn’t need a heater for thermionic emission.
The “Spindt” cathodes generated electrons by field emission, the idea that electric fields are concentrated at sharp points. This idea was improved in a recent device that used diamond as the field emitter. Diamond works well in this application, since it has an extremely low work function, so it will produce field emission electron beams at low voltage.

A different vacuum transistor has been designed by an international team of scientists from NASA’s Ames Research Center (Moffett Field, CA), and the National Nanofab Center, Daejeon, Korea. This transistor, details of which are soon to be published in Applied Physics Letters, uses a vertical architecture like the geometry of a standard MOSFET to mitigate these problems (see figure). The device characteristics of this so-called “vacuum channel transistor” are similar to those of a field effect transistor transistor.

.

Marian

Cool.
That’ll open up more radio spectrum. When do we get to use 460GHz ham band? 🙂

BarryW

Bill Marsh says:
May 24, 2012 at 4:04 pm

Wow, very interesting. AS I recall, those old tubes were resistant to EMP damage as well.

Which made the Soviet systems much more survivable than US systems since they had mostly vacuum tube systems long after we had switched to transistors. Audiophiles that I knew also prized “Red” tubes since they had really refined their manufacturing techniques.

Billy Liar
Mike Smith

Marian says:
Cool.
No. Hot 😉

Steve in SC says May 24, 2012 at 4:27 pm
Vacuum Tubes have always been superior to transistors at RF.
Check any TV or Radio station transmitter.

Not so much anymore; all your AMs are now solid state (saves TONS on cost of electricity), and everything except the PA stage in your UHF TV transmitters are tube/thermionic-emission devices …
As an example, take a look at the AM broadcast transmitters in the 3DX Transmitter Family from Harris, all solid-state with output power levels of 25, 50 and 100 kW (Kilowatts) and HD (digital) capable out of the ‘box’:
Overview – http://www.broadcast.harris.com/media/3DXTransmitterFamily_25-20445.pdf
Datasheet – http://www.broadcast.harris.com/media/3DXAMTransmitterFamily_25-20959.pdf
Note that overall “AC” (input power conversion to RF) efficiencies are better than 85%.
.

AJB

Neat!
BTW, valve audio amps are still being produced in the UK: http://www.fat-man.co.uk

Doug Allen

Operation up to 460 GHz is mind boggling, but there will be the same (or greater) power limitations as with all solid state devices. They are only around 50 % efficient, so a lot of heat has to be conducted away with heat sinks. High power devices are therefore impractical. I use a homebrew pair of 4-400s for a KW PEP out on 3.8 MHz and some other bands. I use a pair of 3CX800A7’s for legal 1500 watts out on 144 MHz and 432 MHz. Tubes are a little more efficient, ~ 65%, and not going to be replaced any time soon for high power applications. With low power, even 5 watts, you can be heard all over the world. With high power you can do things that you can not do with low power- like hear your echoes off the moon! There is very little ham radio operation above 10 GHZ. With the described device we can, I suspect, investigate the frequency spectrum 142-149 GHz, 241- 250 GHz, and everything above 300 GHz, all of which has been allocated by the FCC to ham radio. We pioneered the exploration and use of much lower frequencies in the 20th century. Maybe we can again!

Bob Diaz

WOW, this is an interesting one, but it will need more research to see how best to use it. Like many other technologies, I’m sure this will do well in some areas and other technology will do well in other areas.

So now we have the possibility of large scale integration of analog circuits? I’m thinking, emergent properties. Uh oh. Skynet.

Kaboom

I remember rebuilding a 1950s radio designed around vacuum tubes in the early 1980s, the local electric still had spare ones in stock. The whole thing was bigger than a microwave oven and made out of wood.

BarryW says May 24, 2012 at 5:05 pm

Which made the Soviet systems much more survivable than US systems since they had mostly vacuum tube systems long after we had switched to transistors.

But never mind the reliability of a vacuum-tube based radio or control system in a high-vibration and dynamic environment like a jet fighter aircraft (where the BIG advantage in “solid-state” shows up) eh?
Full disclosure: Our project in the day would test our ‘black boxes’ for that environment (fighter aircraft platform); some of the testing included a repeated sharp impact force called ‘gunfire vibration’ (simulated the impact force that cannon fire produced on the ‘black boxes’ through the A/C frame) and of course, ‘sine vibe’ (vibration) over a wide frequency range …
.

George Steiner

The problem with vacuum tubes is vacuum. Glass envelopes can be pumped down to ten to the minus six mm of mercury, heated to outgass the glass than fire a small pelet of gettering material to keep absorbing any gas molecules. This works for quite a while. As anybody who has used vacuum tubes knows. I don’t hold out much hope that this device will maintain vacuum for any lenth of time.

George Steiner

I have just read the article. There is no vacuum . Just air. They are hoping that the small distance reduces the chance of an electron hitting an atom. It depend how many atoms there are.

Billy Liar says May 24, 2012 at 5:11 pm
I like these small atomic clocks too:

Nice; but you’ll have to drive it (with a 1PPS pulse) with something like this for use in anything except a free-standing* application:
http://www.semiconductorstore.com/cart/pc/viewPrd.asp?idproduct=41718#Description_sec
.
* An application not synchronized time-wise with a larger external network, e.g. in WiMAX or other TDD (Time Division Duplex) GPS 1PPS time-synchronized system.
.

DesertYote

The Vacuum Tube has never really died. I worked with niche communication equipment that was almost all VTs and relays (except one huge FET) during the final days of the cold war. VT technology has continued to advance under the radar (umm inside the radar). This is just the latest chapter in a very exciting story. I ought to dig up and dust off a paper I wrote in the mid 90’s on the history of the Vacuum Tube in relation to the Bi-polar Transistor and how it compared to the history of European bronze metallurgy in relation to iron metallurgy.

Oh, Anthony, you’ve done it again – stirring up all us old geezers. I had my father’s Hallicrafters shortwave radio. The power supply rectifier was a tube 80, all the others had the new naming convention, and tube 80 became 5U4 (5 volt filament, “U” model ID, 4 elements).

But transistors weren’t better in all respects. Electrons move more slowly in a solid than in a vacuum, which means transistors are generally slower than vacuum tubes; as a result, computing isn’t as quick as it could be.

Given today’s tech, with a billion transistors on a 1 cm^2 chip, signal delay in a model made from vacuum tube tech would be a major impediment. Not to mention the power required to heat the cathodes. At least tube tech would have shrunk, so maybe just 1 W per cathode, so a gigawatt for the CPU.
When I was 12 or so, I picked up an English language broadcast on Radio Moscow one day. I learned more about propaganda in 30 seconds than I did in any classroom lesson!

George Steiner

For an analog computer you don’t need vacuum tubes. Just operational amplifiers. Transistors can do that very well. In addition you can emulate an analog computer using a digital computer. No, the problem is scale and programming. Analog computers are programmed differently.

Jeff

Will we be able to go to Thrifty Drug Stores and test them?

George Steiner says May 24, 2012 at 5:42 pm
The problem with vacuum tubes is vacuum. Glass envelopes can be pumped down to ten to the minus six mm of mercury, heated to outgass the glass than fire a small pelet of gettering material to keep absorbing any gas molecules. This works for quite a while. As anybody who has used vacuum tubes knows. I don’t hold out much hope that this device will maintain vacuum for any lenth of time.

George, Dev Gualtieri, who has had an advance look at the paper (courtesy of one the upcoming paper’s authors) says at the referenced link above the following regarding the ‘vacuum’ aspect:

Not only that, but a vacuum is not required. The channel dimension is less than the mean free path of electrons in air, and the low operating voltages are below the ionization potential for molecules in air. High frequency operation is assured, since the velocity of electrons in vacuum is 3 x 10^10 cm/sec. The electron velocity in semiconductors is only as high as 5 x 10^7 cm/sec.

.

R. Shearer

Remember how long it took the radio or TV to warm up and function? How about the circuit breaker on the back of the set and horizontal and vertical adjustments?
I’m still waiting for a good solid state replacement for photomultiplier tubes.

I enjoy the plasma burst from the quartet of 6L6’s in my Fender Twin Reverb…as I flip the standby switch. The smell of phenol in the evening…..mmmmmmmm! Moments later, the fuzzing and fritzing of the preamp-stage 12AX7’s, slightly microphonic. Yep!

sophocles

hmm. It will be interesting to see what the transfer curves look like …. definitely a new toy!

Doug Allen says May 24, 2012 at 5:34 pm
..
I use a pair of 3CX800A7′s for legal 1500 watts out on 144 MHz and 432 MHz. Tubes are a little more efficient, ~ 65%, and not going to be replaced any time soon for high power applications

You guys keep saying that, and yet commercial products put out by the likes such as Harris continue to supersede that oft-repeated “Solid-State Power Amplifiers are Limited” saw.
Okay, maybe for ‘ham’ apps for awhile, but in the commercial world they have entered the 21st century already. An example: Harris 16 kW SS Analog VHF TV transmitter. The liquid cooling they refer to is for the solid-state PAs (and not a PA tube with an external anode!) The 16 kW transmitter in conjunction with a modest 10 dB gain transmit antenna array yields a quite respectable 160 kW ERP signal!
.

Mariss Freimanis

12AU6’s are so… ’60s.
Real vacuum tubes had a shapely envelope outlines and Bakelite bases, the filament WAS the cathode and they had a really cool electrode caps at the top of the tube. Real vacuum tubes had 3 or less characters for a part number like ’30’ or ‘1A6’ or 6Y5.

DirkH

Alec Rawls says:
May 24, 2012 at 5:40 pm
“So now we have the possibility of large scale integration of analog circuits? I’m thinking, emergent properties. Uh oh. Skynet.”
There’s not really a qualitative difference between analog and digital computing. Think genetic programming in digital computers; if you want your computer to come up with some surprises, use that.
You might get a qualitative difference if quantum entanglement works the way it’s always advertised. There’s allegedly already a quantum system simulator with 320 qubits. Works with entangled spins.
http://www.nature.com/nature/journal/v484/n7395/full/nature10981.html
And Prof. Gerlich has managed to entangle a whole 340 atom hydrocarbon molecule.
http://www.slideshare.net/lewisglarsen/lattice-energy-llcnickelseed-lenr-networksapril-20-2011
What you would get with working quantum computing systems is an Oracle; a system that can solve an NP-complete problem in deterministic time – in other words, in a fixed number of steps deliver the optimal solution for a problem that has an exponentially exploding number of possible solutions. At the moment, the best algorithms can only approximate the solution even when running for a long time.

KevinK

Steve in SC wrote;
“Vacuum Tubes have always been superior to transistors at RF.
Check any TV or Radio station transmitter.”
Careful there, the term ”superior” needs to be carefully applied in this case. A transistor can do everything a vacuum tube can do, and just as well. The simple fact that vacuum tubes are still prevalent in high power Radio Transmitters is more a market force effect than a technology effect. The number of “really high” power radio transmitters (10’s-100’s of kiloWatts) is relatively small (100’s-1000’s). Thus, semiconductor manufacturers have never bothered to go after that market. The tube manufacturers have the processes and plants inplace to make the few (100’s) of replacement tubes necessary each year.
On the other hand, the market size for high power switching semiconductors (SCR’s, TRIACS, etc.) is very large (10,000s-millions) everything from light dimmers, variable speed motor drives, CFL lamp ballasts all the way up to railroad locomotives are just chock full of “high” power (1000’s-100000’s of kilowatts) semiconductor switches.
And at the lower power levels, (1-100mW) we have every cell phone (100’s of millions) which have lots of cheap transistors operating everyday in the GigaHertz range.
While this is an “interesting” development, the transistors in use today are on the 1 nanometer scale, this hybrid semiconductor vacuum tube is still in the 100 nanometer scale, a factor of 100x larger. So at this point in time they are not faster or smaller, although they might be in the future.
Regarding radiation “hardness”, that’s more of a “how small is the device” concern. If they shrink the contacts (implemented in semiconductor materials) to make the total device smaller, then the risk that radiation will “blow out” the device may be the same. So we have a device that is larger overall and may be “harder” from a radiation standpoint versus a smaller device. BUT you can just put some more radiation shielding around the smaller device. It maybe a total wash. You can just put a smaller device inside a thicker steel “can” and get the same level of radiation “hardness” in the same volume.
Cheers, Kevin (MSEE, working in the space qualified electronics business)

I still run several tube radios from the 30’s and 40’s on a regular basis including a 1935 Hellicrafter’s Super Skyrider receiver. The sound or static, as the case may be, from the old tube receivers was and still is special.

You know, if you tune your tinnitus just right, it gives you that “warm tube” sound in everything you hear.

KevinK says on May 24, 2012 at 6:53 pm
… The simple fact that vacuum tubes are still prevalent in high power Radio Transmitters is more a market force …

As detailed above, Kevin, not so much these days in contemporary broadcast ‘products’ today; one finds some prevalence of high-powered tubes in use in the cheaper shortwave operations though (by some of the ‘religious broadcasters’ e.g. WWCR with facilities for hire; one can literally buy airtime and air one’s own program for a reasonable two-figure fee per hour for instance) since the acquisition cost of a used/surplussed 200 kW transmitter was low and the cost for electricity is paid for in the per-hour airtime fees that are charged …
.

Tsk Tsk

KevinK says:
May 24, 2012 at 6:53 pm
Steve in SC wrote;
Regarding radiation “hardness”, that’s more of a “how small is the device” concern. If they shrink the contacts (implemented in semiconductor materials) to make the total device smaller, then the risk that radiation will “blow out” the device may be the same. So we have a device that is larger overall and may be “harder” from a radiation standpoint versus a smaller device. BUT you can just put some more radiation shielding around the smaller device. It maybe a total wash. You can just put a smaller device inside a thicker steel “can” and get the same level of radiation “hardness” in the same volume.
————————————-
Aside from the mechanical robustness problems of tubes they are superior from both a overvoltage and a radiation perspective. Lots of old time plasma physicists try to keep around old tube powered scopes because that accidental 10kV zap is probably survivable with that old scope whereas that nice new 30GHz Lecroy scope just became a pricey boat anchor. Can you protect these devices? Sure, but the tube devices are inherently more robust. Short of melting an electrode or sputtering material away there’s no channel to be permanently damaged as it’s a vacuum.
Similarly, tubes are intrinsically rad hard compared to any semiconductor. They’re not really susceptible to upset due to energetic particles passing through which is going to be the practical problem you have to deal with. Again, you can shield semiconductors to provide rad hard and you can play games like SOI and oversizing channels and such to make them more robust, but a tube is generally immune to such problems not counting truly massive energy bursts capable of melting components.

DJ

I’m running matched 12ax7’s and 6550’s in my Bud Wyatt (of Sheffield Lab fame) modified Mac 60’s. They’re big, and fat, and warm… and soothing to listen to, with shimmering highs and in-your-face mids. Love ’em.
…..Mariss…. pm fizzissist at CNC, I’ll tell ya more!

DesertYote

KevinK
May 24, 2012 at 6:53 pm
Cheers, Kevin (MSEE, working in the space qualified electronics business)
###
Cool, I also worked in the field also, starting as an engineering tech working up to a software architect. On top of that, after the blood letting of the late 80’s early 90’s I ended up working for a division of my company that was designing those revolutionary semiconductor devices that are now used in the high-powered applications you mentioned.
What many don’t realize is that semiconductor devices for space and defense applications use an array of techniques that yield them rather immune to the effects of radiation and to EMP. Testing showed that the semiconductors we were producing were just as hard as those Soviet VT’s that other posters mentioned.
Regardless, I still think Vacuum Tubes are cool 🙂