Surface conduction Electron emitter Display (SED)

Surface conduction Electron emitter Display (SED)
The SED technology has been developing since 1987. The flat panel display technology that employs surface conduction electron emitters for every individual display pixel can be referred to as the Surface-conduction Electron-emitter Display (SED). Though the technology differs, the basic theory that the emitted electrons can excite a phosphor coating on the display panel seems to be the bottom line for both the SED display technology and the traditional cathode ray tube (CRT) televisions.

When bombarded by moderate voltages (tens of volts), the electrons tunnel across a thin slit in the surface conduction electron emitter apparatus. Some of these electrons are then scattered at the receiving pole and are accelerated towards the display surface, between the display panel and the surface conduction electron emitter apparatus, by a large voltage gradient (tens of kV) as these electrons pass the electric poles across the thin slit. These emitted electrons can then excite the phosphor coating on the display panel and the image follows.

The main advantage of SED’s compared with LCD’s and CRT’s is that it can provide with a best mix of both the technologies. The SED can combine the slim form factor of LCD’s with the superior contrast ratios, exceptional response time and can give the better picture quality of the CRT’s. The SED’s also provides with more brightness, color performance, viewing angles and also consumes very less power. More over, the SED’s do not require a deflection system for the electron beam, which has in turn helped the manufacturer to create a display design, that is only few inches thick but still light enough to be hung from the wall. All the above properties has consequently helped the manufacturer to enlarge the size of the display panel just by increasing the number of electron emitters relative to the necessary number of pixels required. Canon and Toshiba are the two major companies working on SED’s. The technology is still developing and we can expect further breakthrough on the research.

A surface-conduction electron-emitter display (SED) is a flat panel display technology that uses surface conduction electron emitters for every individual display pixel. The surface conduction emitter emits electrons that excite a phosphor coating on the display panel, the same basic concept found in traditional cathode ray tube (CRT) televisions. This means that SEDs use tiny cathode ray tubes behind every single pixel (instead of one tube for the whole display) and can combine the slim form factor of LCDs and plasma displays with the superior viewing angles, contrast, black levels, color definition and pixel response time of CRTs. Canon also claims that SEDs consume less power than LCD displays

The surface conduction electron emitter apparatus consists of a thin slit across which electrons tunnel when excited by moderate voltages (tens of volts). When the electrons cross electric poles across the thin slit, some are scattered at the receiving pole and are accelerated toward the display surface by a large voltage gradient (tens of thousands of volts) between the display panel and the surface conduction electron emitter apparatus. Canon Inc. working with Toshiba uses inkjet printing technology to spray phosphors onto the glass. The technology has been in development since 1986.

How it Works
SED technology works much like a traditional CRT except instead of one large electron gun firing at all the screen phosphors that light up to create the image you see, SED has thousands of tiny electron guns known as "emitters" for each phosphor sub-pixel. Remember, a sub-pixel is just one of the three colors (red, green, blue) that make up a pixel. So it takes three emitters to create one pixel on the screen and over 6 million SED emitters to produce a true high definition (HDTV) image! It's sort of like an electron Gatling gun with a barrel for every target positioned at point-blank range. An army of electron guns, if you will.



This may bode well for video purists who feel that CRTs offer the best picture quality, bar none. One prototype has even attained a contrast ratio of 100,000:1. Its brightness of 400cd/m2 is a tad on the low side for an LCD TV and nowhere close to a plasma. This is expected to increase in the future, but still works out to about 116 ftL (foot Lamberts) or more than twice a regular TV. To put this in perspective, a movie theater shows a film at about 15 ftL.

Life Expectancy
It does look like SED TVs will last a good while as it has been reported that the electron emitters have been shown to only drop 10% after 60,000 hours, simulated by an "accelerated" test. This means that it is likely the unit will keep working as long as the phosphors continue to emit light. That can be a while. Maybe yours will even show up on the Antiques Roadshow in working condition in the far distant future. Time will tell but "accelerated" testing results should always be taken with a grain of salt as it only imitates wear and tear over time.

SED TV Compared to CRT
SED is flat. A traditional CRT has one electron gun that scans side to side and from top to bottom by being deflected by an electromagnet or "yoke". This has meant that the gun has had to be set back far enough to target the complete screen area and, well, it starts to get ridiculously large and heavy around 36". CRTs are typically as wide as they are deep. They need to be built like this or else the screen would need to be curved too severely for viewing. Not so with SED, where you supposedly get all the advantages of a CRT display but need only a few inches of thickness to do it in. Screen size can be made as large as the manufacturer dares. Also, CRTs can have image challenges around the far edges of the picture tube, which is a non-issue for SED.

SED TV Compared to Plasma TV
Compared to plasma the future looks black indeed. As in someone wearing a black suit and you actually being able to tell it's a black suit with all those tricky, close to black, gray levels actually showing up. This has been a major source of distraction for this writer for most display technologies other than CRT. Watching the all-pervasive low-key (dark) lighting in movies, it can be hard to tell what you're actually looking at without the shadow detail being viewable. Think Blade Runner or Alien. SED's black detail should be better, as plasma cells must be left partially on in order to reduce latency. This means they are actually dark gray – not black. Plasma has been getting better in this regard but still has a way to go to match a CRT. Hopefully, SED will solve this and it's likely to. Also, SED is expected to use only half the power that a plasma does at a given screen size although this will vary depending on screen content.

SED TV Compared to LCD
LCDs have had a couple of challenges in creating great pictures but they are getting better. Firstly, latency has been a problem with television pictures with an actual 16ms speed needed in order to keep up with a 60Hz screen update. That needs to happen all the way through the grayscale, not just where the manufacturers decide to test. Also, due to LCD's highly directional light, it has a limited angle of view and tends to become too dim to view off axis, which can limit seating arrangements. This will not be an issue for SED's self illuminated phosphors. However, LCD does have the advantage of not being susceptible to burn-in which any device using phosphors will, including SED. SED is likely to use about two-thirds the power of a similarly sized LCD. Finally, LCD generally suffers from the same black level issues and solarization, otherwise known as false contouring, that plasma does. SED does not.

SED TV Compared to RPTV
SED is flat and RPTVs aren't. RPTV also has limitations as to where it can be viewed from, particularly being vertically challenged with regard to viewing angles. A particular RPTV's image quality is driven by its imaging technology such as DLP, LCoS, 3LCD or, more rarely recently, CRT. With the exception of CRT, these units need to have their lamps changed at various times but usually at around 6,000 hours, costing an average of $250.

Pricing
The cost of flat panels is largely dependent on production yields of saleable product. Nobody really knows for sure what this will be until real production starts, but new technology is always expensive in early production. If it works, the use of inkjet technology to make SED displays rather than the more expensive photolithography process used in LCD panels should help cost management. The first product release will be a 55" version at full HD resolution (1920x1080) priced comparably to today's plasma display panel (PDP) of similar size. That could be a big dollar difference by early 2007, as the price of plasma displays is expected to continue to drop.

Taking a look at the current crop of display technologies, one reality is hard to escape; we haven’t drastically improved on the nearly antique Cathode Ray Tube (CRT) televisions of years past. Sure we now have flat panels that can display resolutions of up to 1920×1080 pixels or higher in rare instances, but the often shunned CRT technology is capable of resolutions of 2560×1920 and higher, well within the future-proof 1080p spec.

Ok so flat panels don’t beat CRT’s on resolution, and to be honest they don’t really look better, with comparable resolutions. In addition both Plasma and LCD displays often fall short of CRT black levels, so why all the fuss? The flat screen of course, specifically screens less than 3 inches in depth.

What if a new display technology could combine the best attributes of both CRT’s and flat panel displays? Well I haven’t written this far to say wouldn’t that be nice, enter SED (Surface-Conduction Electron-Emitter Display). Spearheaded by Canon and Toshiba back in the mid eighties, SED appears to offer an excellent balance between cost, resolution and screen depth.

The inner workings of SED borrow from both LCD and Plasma technologies; a glass plate is embedded with electron emitters, one for each pixel on the display. The emitters on this plate face a fluorescent coating on a second plate. Between the two plates is a vacuum, and an ultra-fine particle film that forms a slit several nanometers wide. By applying voltage to this slit, the sets can produce a tunneling effect that generates electron emission. The panel emits light as the voltage accelerates some of the electrons toward the fluorescent coating.

SED displays offer brightness, color performance, and viewing angles on par with CRTs. However, they do not require a deflection system for the electron beam. Engineers as a result can create a display that is just a few inches thick; while still light enough for wall-hanging designs. The manufacturer can enlarge the panel merely by increasing the number of electron emitters relative to the necessary number of pixels. Canon and Toshiba believe their SED’s will be cost-competitive with other flat panel displays.
Technology Overview & Description

SED, or Surface-conduction Electron-emitter Displays are a new, emerging technology co-developed by Canon and Toshiba Corporation. The hope for this technology is a display which reproduces vivid color, deep blacks, fast response times and almost limitless contrast. In fact, if you take all of the claims made by the backers of SED you would think that there should be no reason to buy any other type of display. A long life filled with bitter disappointments and lengthy product-to-market times have increased my skepticism and lowered my tendency to act as a cheerleader until products start to hit the market. As far as the specs go, this is one hot technology.

An SED display is very similar to a CRT (and now we come full circle) in that it utilizes an electronemitter which activates phosphors on a screen. The electron emission element is made from an ultra-thin electron emission film that is just a few nanometers thick. Unlike a CRT, which has a single electron emitter that is steered, SEDs utilize a separate emitter for each color phosphor (3 per pixel, or 1 per sub-pixel) and therefore do not require an electron beam deflector (which also makes screen sizes of over 42" possible). Just for clarity that means a 1920 x 1080 panel has 6.2 million electron "guns". The emitter takes roughly 10V to fire and is accelerated by 10kV before it hits the phosphor lined glass panel. Sound like a lot of power? It's all relative as a typical SED display is expected to use about 2/3 the power of a typical plasma panel (and less than CRTs and LCD displays).

OK, here's the real interesting news. SED display electron emitters are supposed to be printable using inkjet printing technology from Canon while the matrix wiring can be created with a special screen printing method. The obvious result is the potential for extremely low production costs at high volumes once the technology is perfected.
What's Next?

Canon debuted an SED display prototype at the la Defense in Paris in October 2005. The specs referenced a <>
SED Display Advantages
CRT-matching black levels
Excellent color and contrast potential
Relatively inexpensive production cost
Wide viewing angle
SED Display Disadvantages
Unknown (though optimistic) life expectancy
Potential for screen burn-in
Currently prototype only