Article - Return of the Vacuum Tube

[überfuzz]

I stumbled over this while surfing: Return of the Vacuum Tube

Some members might find it interesting.

Cheers!

[Steve Conner]

Return? In the audio field, it didn't really go away. There's never been a time when you couldn't go to a shop and buy a tube amplifier, except maybe when they were rationed in WW2.

[überfuzz]

I don't konw if you read it, but it's really about "nano tubes". And that wouldn't be a return either...

[J M Fahey]

Funny thing is they claim nanotubes have a "source" , "drain" , and "gate" (ring a bell?), are built into a block of crystalline doped silicon and ... hear this ... don't use vacuum.
Let alone that they don't use heated filaments either.
So, what part of it matches the label "vacuum tube"?

[überfuzz]

Funny thing is they claim nanotubes have a "source" , "drain" , and "gate" (ring a bell?), are built into a block of crystalline doped silicon and ... hear this ... don't use vacuum.
Let alone that they don't use heated filaments either.
So, what part of it matches the label "vacuum tube"?

I don't know, but I'm pretty sure they're well aware of the fact that vacuum tube is a stupid name. A bit like calling a mailbox, an air container. They're trying to or hoping to mimic some characteristics of a "vacuum tube" , and that I find very interesting. First time I heard about the idea of minimizing a "vacuum tube" was back in the nineties. Somewhere down the road a real solution might emerge...

[Steve Conner]

I think the crucial difference is that the electrons travel through an empty space inside the semiconductor, and the transistor action happens there. In regular transistors and ICs, everything happens inside the crystal lattice.

[Chuck H]

Also... Notice that there is an active voltage stated at 10V!!! I expect it's not hard to make a PN/NP type junction that moves through free air IF operating voltages aren't a consideration. So... To take advantage of the greater speed we only need to make Iphones and PC's that operate with a minimum of 10V on any gate!?! I'm going to need bigger pockets to put my phone in then. Maybe some kind of man purse thing. R and D or grant $$$ squandering.

[Mike Burgundy]

I distinctly remember someone at the TUDelft (Netherlands) getting an article in the University tech paper on him succeeding in making "tubes" on a wafer. Basically cathode layer etched to shape, insulator on top, grid layer, isolator, anode layer. The cathode was needle shaped and stuck through the "grid*(basically a hole in another conducting layer). Because the needle was incredibly sharp even at nano-scale, it naturally wanted to spray electrons. That spray was pulled to anode and controlled by the grid layer charge, all without heaters and at low voltage. Sounds very tube-like in principle. I thought it was so cool. I think the main aim was surviving EMP and radiation, just like stated in the OP article.
I'm sure they invented something new and better, but still, I read that bit *years* ago. Late 90's, very early 2000's I think.
Edit: I think it did need vacuum in the "grid chamber", so it will probably fall into that category of "previous attempts"

[J M Fahey]

I find it interesting but the part that worries me is that about "the distance is so short that the electrons hardly find an atom of air in their path"
Fact is, even in that (for us) short path, there must be at least thousands of "air" atoms.
Too late and sleepy now to google a nitrogen or oxygen atom size and compare it to that space, but tomorrow will.

EDIT: obviously got hooked and can't go to sleep with that doubt burning my brain:
They talk about 150 nanometers "jump".
Got only the Nitrogen atom size; it's enough to compare magnitudes: supposing it spherical it's 521 picometers diameter.
Since "nano" is 1000 times larger than "pico" , you can have 1000x150/521= 288 Nitrogen atoms in the path of that poor Electron, with the aggravation that each Nitrogen atom weighs 25500 times the weight of the poor Electron.

So NOW we know why vacuum is necessary, *plus* heating the cathode red hot so it "boils" electrons away, *plus* applying hundreds of volts to get the thing working.

In : http://www.nasatech.com/NEWS/Oct02/who_1002.htm
Dr Meyappan talks about making nano sized carbon tubes.
Tubes as in a pipe, a cylindrical hole surrounded by a wall.
He says "sometime in the Future" they "might" be built "either as an insulator or as a semiconductor"

[Chuck H]

Excellent analysis. Good thing for the developers you weren't on the review panel when they asked for more funding!!!

[überfuzz]

Fahey - Well, that's an... interesting analysis. If you ever feel like refining your analysis, consider a exponential decline over the distance the electrons travels in air. The energy of the travelling electrons is determine by the potential, I believe they were talking about a need of 10V to jump the 150 nm gap.

What I couldn't find in the article is information about efficiency decline when this little valve is pushed. Point being, in not going to play guitar in "the harsh radiation of outer space". I just want my amp to mojofy the tones I'm playing.

[soundmasterg]

One of Merlin's professors was working on the vacuum nanotubes mentioned above where the little triodes are grown on a substrate and the whole thing is in a vaccum. There weren't any heaters and each little triode was getting gains of over 800, but it was very expensive still...I think they were using diamond or something for the substrate!

This other one in this article isn't using vacuum so its a bit different...but both techniques look similar in that they are merging the triode and the FET. We'll see what happens I guess, but I don't think these will replace our thermionic valves in our amps any time soon!

Greg

[mooreamps]

I find it interesting but the part that worries me is that about "the distance is so short that the electrons hardly find an atom of air in their path"
Fact is, even in that (for us) short path, there must be at least thousands of "air" atoms.

There is no air ; in space..... :|

-g

[Steve Conner]

Since "nano" is 1000 times larger than "pico" , you can have 1000x150/521= 288 Nitrogen atoms in the path of that poor Electron, with the aggravation that each Nitrogen atom weighs 25500 times the weight of the poor Electron.

This would be reasonable if the space were filled with solid nitrogen, but in a gas the spaces between molecules are much larger than the dimensions of the molecules themselves.

Mean Free Path, Molecular Collisions

In an ideal gas at STP, the molecules have a mean spacing of about 3.3nm.

[Steve Conner]

Since "nano" is 1000 times larger than "pico" , you can have 1000x150/521= 288 Nitrogen atoms in the path of that poor Electron, with the aggravation that each Nitrogen atom weighs 25500 times the weight of the poor Electron.

This would be reasonable if the space were filled with solid nitrogen, but in a gas the spaces between molecules are much larger than the dimensions of the molecules themselves.

Mean Free Path, Molecular Collisions

In an ideal gas at STP, the molecules have a mean spacing of about 3.3nm.