A new cold electron emitter technology patented by NIST produces an electron flow comparable to a thermionic source but with many advantages.
According to co-inventor Fred Sharifi, the new field emitters have inherently fast response times compared with thermionic sources, and the absence of heat makes it easier to create arrays of sources. Moreover, the porous nanostructure of the emitters makes them very reliable. Even if the emitter surface wears away during use—a common problem—the newly exposed material continues to work just as well.
Could this usher in a new era of filament-less vacuum tube analogues? Tubes on a chip?
Electron field emitter technology to improve imaging, communications
According to co-inventor Fred Sharifi, the new field emitters have inherently fast response times compared with thermionic sources, and the absence of heat makes it easier to create arrays of sources. Moreover, the porous nanostructure of the emitters makes them very reliable. Even if the emitter surface wears away during use—a common problem—the newly exposed material continues to work just as well.
Could this usher in a new era of filament-less vacuum tube analogues? Tubes on a chip?
Electron field emitter technology to improve imaging, communications
The basic technology is available for licensing to anyone who wants to pay the fee and is interested in working this up into an amplifier "tube". Will it be the most lucrative potential application? Most likely not, but the concept of combining the emitter with a control grid and an anode to form a triode is feasible.
So now all we need is a tube sound-lover who happens to own a chip fabrication plant and wants to try it out...I'm not giving up my tubes just yet.
So now all we need is a tube sound-lover who happens to own a chip fabrication plant and wants to try it out...I'm not giving up my tubes just yet.
Yes, current capability is impressive, higher than in a regular hot cathode tube.
And at a very low "plate" voltage, they mention 7V.
What they don't say is whether that emission was into vacuum or some kind of gas, nor how could it be controlled (I mean beyond simple "plate voltage" variation).
So far they describe (not too clearly) something akin to a tube diode.
X-Ray tubes, by the way, are exactly that
And Magnetrons are close , if weird, cousins.
Clearly they see no future in triodes or tubes in general but in X-Rays, Phosphorescent displays, etc., and maybe "cold, low voltage fluorescent tubes".
And at a very low "plate" voltage, they mention 7V.
What they don't say is whether that emission was into vacuum or some kind of gas, nor how could it be controlled (I mean beyond simple "plate voltage" variation).
So far they describe (not too clearly) something akin to a tube diode.
X-Ray tubes, by the way, are exactly that
And Magnetrons are close , if weird, cousins.
Clearly they see no future in triodes or tubes in general but in X-Rays, Phosphorescent displays, etc., and maybe "cold, low voltage fluorescent tubes".
The researchers are from NIST and a university; their business is the research, to develop new enabling technologies and license them to other folks who can build on them and create commercial products. I'm sure the technologies they named were simply where they thought the market would be. If someone showed interest in licensing the technology to produce triodes, they'd add that to the application list.
The first vacuum tubes were also diodes, until Lee DeForest introduced a grid between the anode and cathode to create the Audion. It doesn't seem like a big stretch to do the same on a chip scale.
The first vacuum tubes were also diodes, until Lee DeForest introduced a grid between the anode and cathode to create the Audion. It doesn't seem like a big stretch to do the same on a chip scale.
Interesting read, Magz. Thanks!
The 6A/cm^2 current was produced using a 7V/um field - which implies a fairly high plate voltage. Not unexpected. The paper doesn't show the test setup schematic or diagram, but describes the test geometry as having the emitter and anode separated by 1mm in a vacuum.
The structure seems to have some thermal issues, which the author alludes to in the text. Looking at Fig. 4 it's pretty obvious - as the "off" pulse time decreases, the emissions during subsequent "on" times increase. For the 5sec "on" 200sec "off" the emissions are pretty stable, but the 5sec "on" 60sec "off" chart shows each pulse of current increasing both pulse-to-pulse and also during each pulse.
It's a very exciting idea, but seems to need a lot more work to make it useable as a product. Not quite ready for prime-time.
And putting a control grid in that 1mm gap is gonna be real fun!! (Pentode structure geometry, anybody??)
Having said that, there are a lot of SEMS devices being designed into high-end radio products that just a few years ago were a pipe-dream in a lab just like this. They are rapidly becoming mainstream components - so it's not impossible. But that is a topic for another forum
The 6A/cm^2 current was produced using a 7V/um field - which implies a fairly high plate voltage. Not unexpected. The paper doesn't show the test setup schematic or diagram, but describes the test geometry as having the emitter and anode separated by 1mm in a vacuum.
The structure seems to have some thermal issues, which the author alludes to in the text. Looking at Fig. 4 it's pretty obvious - as the "off" pulse time decreases, the emissions during subsequent "on" times increase. For the 5sec "on" 200sec "off" the emissions are pretty stable, but the 5sec "on" 60sec "off" chart shows each pulse of current increasing both pulse-to-pulse and also during each pulse.
It's a very exciting idea, but seems to need a lot more work to make it useable as a product. Not quite ready for prime-time.
And putting a control grid in that 1mm gap is gonna be real fun!!
(Pentode structure geometry, anybody??)Having said that, there are a lot of SEMS devices being designed into high-end radio products that just a few years ago were a pipe-dream in a lab just like this. They are rapidly becoming mainstream components - so it's not impossible. But that is a topic for another forum
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