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Old 16th November 2007, 06:15 PM   #1
Nevod is offline Nevod  Russian Federation
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Default Future micro-tube technology

Recently, reading Wiki's article on vacuum tubes, i have noticed an update concerning an upcoming tecnology of so-called gated field emission triodes, a micro-scale tubes utilising field emission effect from a cold Spindt-type cathode, with proposals of creating, essentially, tube-based integrated circuits, for use in various RF applications.

After some search, I have managed to find limited info on them, mainly because articles describing research on these 'tubes' were not free, with only some information being free. Their advantages seem to be much increased robustness, especially mechanical, ease of manufacture, high scalability - a low-voltage, high-current IC can be produced, as well as high-voltage, low-current discrete element(just an example, instant readyness for operation, no heaters, better modulation - instead of deflecting electron flux, gate's field blocks emission at cathode itself, leading to very good HF operation.

The research on technology had started back in 1960s, with Spindt cathode being developed in 1969. Then, research seemingly faded away until recently, when FED/SED displays surfaced, as it's essentially the same technology. Recent articles tell about successful creation of integrated field-effect triode differential amplifier, but hardly of anything more.

Of course, there is little information to think about, but nevertheless, these devices do seemingly open some new possibilities. I'm intrested, if these devices will replace the current tubes, not only transistors in RF? Will they allow a OTL "tube" amp with essentially transistor schematics? Will they allow for easy direct-drive ESL amp? These devices, although at least few years from production, are quite interesting..
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Old 16th November 2007, 07:25 PM   #2
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I saw an article in New Scientist about these a few years back- thanks for reminding me.

I think the article mentioned that they would be more robust (static-wise) than standard semiconductor devices, and that they would allow maller, faster RF chips.

Interesting stuff- I too wondered about the Audio possibilities, but I suspect that they will sound different to both SS and Tubes.

james
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Old 16th November 2007, 07:41 PM   #3
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Is that the needle-cathode ones they've been promising since a 1984 issue of Radio-Electronics magazine that never materialized outside the lab?
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Old 16th November 2007, 11:55 PM   #4
Nevod is offline Nevod  Russian Federation
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jrevillug
Most likely yes, but still, i think their characteristics would be more sumilat to tubes, rather than ss.


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Most likely yes. Though, judging by last few years' articles, progress is quite good, and besides being backed by FED/SED displays' research.

Oh, and i have some newbie questions
When reading about field emission devices, i noted that some of them had a under-grid construction, with grid being under cathode, and others (more recently developed) had a integral anode configuration, with grid in same layer as anode, aside it. First type devices had positive cut-off voltage, second had negative cut-off. So I wondered: all tubes i knew of have negative cut off. What defines cut-off voltage? Seems to be geometry. Then, why no positive cut-off tubes have been made? Is it not possible, or just I don't know of examples, or was it not needed at all? What would positive cut-off tubes allow what negative cut-off couldn't, and vice versa?
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