460GHz Vacuum Transistor

On a sunny day (Fri, 3 Nov 2017 16:58:22 -0500) it happened "Tim Williams" wrote in :

Some time ago there was some commotion about companies giving up on field emission display tech, selling of patents to other companies. I do not see many of those displays for sale, none AFAIK. At high field strength (due to small sizes) you are asking for trouble, things will be ripped of the surface.

And 460 GHz is not realy that fast, just a quick search with Bing: Silicon-germanium (SiGe) transistor at 798 gigahertz (GHz) fMAX:

NASA, they also have a prototype warp drive... sigh

Fun. I knew John Cressler at IBM Watson--I took a BJT design course from him back in about 1988, when IBM was still building mainframes out of ECL.

Re: field emitters

Just in order to get an output power level above the Johnson noise of 50 ohms in a 460 GHz bandwidth, you need

Pout > -204 dBW + 10 log(460 GHz) = -87 dBW (2 nW).

The RMS current in 50 ohms is I = sqrt(50* 2nW) = 300 uA.

With a transconductance of 20 nS/um (quoted by the Pittsburgh guys in Nature,

you'd need a device with gate width

W > 300 uA/(20 nA/um) = 15000 um (15 mm).

IOW it's the size of a 12AX7A except flatter--just to get out of the Johnson noise.

Not what you'd call a super practical device.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

Never mind. Note to self: don't post before having coffee.

Should be sqrt(2 nW/50) = 6 uA.

W > 6 uA/(20 nA/V/um) = 300 um, assuming 1V worth of grid drive. Of course that's with 1V of grid swing, so the voltage gain is about 0.0003 (50 ohms times 6 uA / 1V).

To get actual voltage gain, it would have to be much, much bigger. To reach a voltage gain of 1.0 (20 mA plate current @ 1V grid drive) it would need to be

W > 20 mA / (20 nA/um/V * 1 V) = 1,000,000 um = 1 meter wide, which is about 1500 wavelengths at 460 GHz.

And that's not counting the capacitance, which for something that size would be in the tens of picofarads.

So just getting a voltage gain of 1.0 in 50 ohms at 460 GHz would require quite the distributed amplifier structure, assuming you could keep the losses low enough even to get near there.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

That would be cool, a row of emitter tips squirting electrons onto a strip anode, a field-emitter distributed amplifier or, in a circle, an oscillator.

I think someone patented a distributed thermionic triode, but I don't know that it was ever used. There were CRTs with distributed deflection plates. It's a neat concept.

A field emitter in a cavity might oscillate. Too bad they degrade so fast.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

It could very well be that no one has tried to run the numbers, whether it's solving the condensed matter structure (known to be a hard problem, no matter how you cut it), or doing the experiments.

Could also be that it's a negative result and so no one published their findings.

Either way, do report your findings, somewhere!

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
Website: https://www.seventransistorlabs.com/

I see you are all po-poing the Idea then say it is not really that fast, on the other hand with only ONE built, not much optimizing has happened. But then, I thought LENR was going somewhere, all it became is an $89 million lawsuit. Hmm, looks like it was settled. "No details of the settlement are available because Rossi and Industrial Heat have apparently signed a non-disclosure agreement (NDA)."

I'm not pooh-poohing anything.

I spent six years of my life bringing a niche research device (the metal-insulator-metal tunnel junction) from a free-space curiosity at

0.01% quantum efficiency at a useless wavelength (10.7 um) to technologically interesting efficiencies (7% quantum efficiency) coupled to waveguides at telecom wavelengths (1.6 um), so I'm generally in sympathy with that sort of effort.

What I'm not in sympathy with is the hype machine. They claim 460 GHz, forsooth, when the gizmo can't drive its own plate capacitance at even

1% of that rate.

My point is that it's pretty silly to start talking about applications of a device when the current best is so very far off practicality, or to talk about speed when it's essentially impossible to use the present best version even to reach a gain of 1.0.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com