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Cold CRT Guns for Thinner CRTs
Fly writes: "According to EETimes, an Austin startup company is close to producing CRTs with cold-emission electron guns. They claim this will reduce the parts needed for electron guns as well as allow for greater control and deflection of the electron beams leading to thinner CRTs. Their technology uses older chip-manufacturing techniquest to deposit diamond tips for the guns on silicon wafers. They hope to enter the CRT market next year."
CRT monitors no matter how small are still big, clunky, and waist energy. They also contain lead, which is banned from landfills. LCD and TFT monitors will take over the market simply because they are better for the sellers as for the buyers, Smaller size cheaper to store, cheaper to ship. IMHO this company has a few merits but is beating a dead horse.
Just Limin' Mon
You guys mean that i will be actually able to carry that 21in monitor all by myself - hoorray no more asking the school bully :)
Extreme Devices received what Kalar called "a godsend" when LG Electronics decided to close the former Zenith CRT manufacturing facility in Melrose Park, Ill., in October 1998, the same time that Extreme Devices was staffing up.
We can expect displays that will be encased in a big wood console.
A cold electron gun has some other benefits as well. Historically, the biggest problem with making monitor screens truly flat (no warping at the corners) was that the front material needs to be incredibly strong. Screens were rounded slightly to keep them from breaking due to the forces of the vacuum behind them. As screens grew larger and the depth of the monitor increased (in order to let the electron gun get the necessary width) screens had to be stronger. The premium for flat screens is still a couple hundred dollars more than their conventional counterparts.
By having a cold electron gun that allows wider dispersion angles, you can reduce the depth of the monitor, and thereby reduce the strength required from the front screen material.
Folks,
While the new LCD flat-panel displays are dropping in price, you still have to deal with three issues: 1) screen blurring on very fast motion (though this has gotten way better in the last year or so), 2) LCD's are optimized for one display resolution and 3) they're still fairly expensive (especially now with 19" CRT monitors now under US$200 in price).
Given the CRT monitors maintain their sharpness from 640x680 all the way up to 1600x1200 and beyond (depending on the dot pitch of the monitor) and can run at 85 Hz vertical refresh rate for true flicker-free viewing, I think they're still preferred for serious imaging processing work. The new very-low profile CRT's using this new technology will allow 17" to 21" monitors have less physical depth than even the old 14" monitors from way back, which means more room saved on your desk.
I think this company may license the technology to Samsung or LG Electronics, both of which now make excellent monitors at reasonable prices. Samsung could have a huge winner right here with high-resolution CRT monitors that have half the depth of their predecessors.
I think you may have two articles conflated.
This one seems to be talking about using a diamond "forest" of cold emitters to replace the heated-cathode in a conventional electron gun, then deflecting the beam in the standard fashion, leading to an ordinary rectangular-cone CRT (but with no heater and instant-on).
You seem to be referring to another approach that was to use cold-emitters (which would also benefit from this breakthrough.):
The display consisted of a (glass) honeycomb of short individual "tubes".
Each "tube" had a single emitter "spike" (substitute "small forest") at the base.
A control electrode near the emitter (maybe substitute one per emitter in the "forest") switched it on/off and modulated the beam intensity. The voltage is near the cathode's and the voltage swing is just a couple volts, so you can use conventional transistor electronics.
(You can actually use two or more electrodes to do a matrix address and beam modulation, with the voltage gradient at the emitter tip or a space charge near it performing the computation so you don't need a separate switch per-pixel.)
The beam was accellerated along the narrow channel - the front portion of which contained an accelleration electrode with a constant high voltage - similar to a normal CRT. Difference: The beam could be bounced repeatedly between the channel walls, picking up additional electrodes by secondary emission.
The beam strikes a single phosphor dot at the end of the channel.
So you end up with something that can be fabricated (except for the cathode spike and maybe the modulation electrodes) by glass molding, vapor deposition of electrode metal, and micropipette phosphor-solution placement, and driven by essentially the same chips that run an LCD plus a single, unmodulated, high-voltage supply. The tubes are very short and the honeycomb of glass separating the individual tubes also supports the front screen, so you don't need thick heavy glass to fight 15 PSI of atmospheric pressure across more than a foot of unsupported span. Pixel placement is controlled by fabrication, so there's no sensitivity to local magnetic fields, no geometry adjustment. Of course in addition to no need to heat the cathodes there's no need to power and rapidly modulate an enormous magnetic deflection field.
And this new article tells you why we don't yet have either the cold-emission conventional CRT or the honeycomb flat-panel CRT: Positive ions from any impurities in the vacuum or kicked off the target or the sides of the channel are accellerated back toward the gun, slamming into the tip(s) and rapidly eroding it. RCA had a patent on field emission vacuum tubes but didn't feel like pursuing the technology with materials research. So the whole filed languished.
One of the biggest problems in the development of these things is that there isn't that much room between the electron emiter and the phosphorus, because of that they couldn't speedup the electron to the same speeds they get in a normal CRT and need to find new low-energy phosphoruses.
Huh? Space shouldn't be an issue. The final velocity of the electron only depends on the accelleration voltage, not the length of the path. The path only needs to be long enough to prevent arc-over along the surface of the glass (or in any residual gas in the "vacuum"), and that's a fraction of an inch.
With a conventional tube the voltage gradient also has to be low enough that the electrodes don't bend out of place. But that limit would be MUCH higher with the electrodes plated onto a glass surface or supported by the walls of a pixel-wide glass honeycomb cell, rather than by mica spacers and thin copper wire.
I expect the conventional-CRT style to come out first. It's only being held back by the RCA patent that just expired. The flat-panel might take longer, due to other patents, the need to build a "wafer" the size of the screen rather than the size of an electron-gun cathode, and possibly worse problems with tip erosion due to the limited number of tips per pixel.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way