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.
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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.
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.
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.
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 …
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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.
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.
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
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* 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.
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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).
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!
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.
Will we be able to go to Thrifty Drug Stores and test them?
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:
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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!
hmm. It will be interesting to see what the transfer curves look like …. definitely a new toy!
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!
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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.
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.
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.
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 …
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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.
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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.
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!
KevinK
May 24, 2012 at 6:53 pm
Cheers, Kevin (MSEE, working in the space qualified electronics business)
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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 🙂