SED

EASILY the biggest news coming out of any trade show this year was something called a Surface-conduction Electron-emitter Display (SED). The new display technology developed by Canon and Toshiba was unveiled at CES in January of this year and is already being regarded as the real next big thing from the top media organizations in attendance.

To have a new product leave such an impression on the naturally critical hardware correspondents is a pretty amazing feat to say the least. So what exactly is this “SED” and what makes it so damn good?

These days you would be extremely hard pressed to find anyone willing to agree that the image quality of a high-end CRT screen can be beat. A lot of these diehard CRT fans are in the arena of competitive gaming, where it is nearly impossible to find a professional gamer on an LCD screen by choice. The primary argument of most of these steadfast gamers is over a subject called “ghosting”. Ghosting occurs in LCD monitors due to something called response time. On an LCD, pixels have to switch from being active to inactive in order to display an image. The amount of time it takes them to do this is called response time. A common response time for gaming-grade LCD’s these days is about 8ms. 8ms is pretty quick, 8 thousandths of a second. However, in this amount of time, images can get “mixed together”, creating a blurred or fuzzy image that is disgustingly annoying to hardcore gamers that demand superb image quality and no “lag”. Although not really noticeable to a gamer that has been exclusively using LCD monitors for quite some time, ghosting is very apparent to a gamer trying to migrate from CRT to LCD. CRT displays do not exhibit ghosting because response times are virtually non-existent. It is this “image quality” characteristic that makes LCD monitors look undesirable in the eyes of gamers. To the rest of the world however, issues like limited viewing angles, very untrue black, and often times less-than-vibrant colors are more severe problems. Plasma screens on the other hand have great picture quality in contrast to LCD’s, but still not as good as a high quality CRT display. They use the same technology as fluorescent lights to produce a very bright picture and due to the nature of their construction, also have a very wide viewing angle. However, if you’ve recently checked the prices of Plasma screens, you probably noticed what would seem like an extra digit tacked on the end. That is because Plasma displays cost A LOT of money. Price, and the fact that they sure don’t save you anything on the electricity bill, makes Plasma screens a somewhat less than perfect option.

It seems like each of the three aforementioned mainstream technologies have their advantages and disadvantages. If only there were a way to combine the three into a “super-display” of sorts that could end up being the end-all TV or computer monitor. Well, that is exactly what SED is supposed to be.

SED works a lot like a CRT monitor. In a CRT monitor, an electron gun (made up of a cathode and some anodes) shoots electrons through a large glass tube (cathode ray tube) at a large flat surface (screen) that is coated in phosphor. When the negatively charged electrons collide with the phosphor-coated surface, they excite the material, causing electrons to drop valence rings, and give off visible light photons. If you’ve ever seen inside a monitor, you will have seen something glowing at the skinny end of the big glass tube. This is the cathode filament, which heats up the cathode and causes it to emit a bunch of electrons. Anodes then take these electrons and speed them up and focus them in a concentrated beam towards the phosphor-coated screen. In color monitors, three electron suns (Red, Green, and Blue) work together to produce the image you see. In an SED screen however, the electron gun is replaced by something called an electron emitter. The principle is the same here: generate electrons and make them hit a phosphor-coated screen. An electron emitter works by sending a small charge of about 10-20 Volts through a cathode (electrode) to create electrons. These electrons would move accordingly down the “path” and end up wherever they ended up. Instead, there are little “slits” or gaps in their path that cause some of the electrons to stray ever so slightly off the path and end up scattering out of this narrow gap (several nanometers wide) and into the void in between the two glass substrates. At this point, the electrons are hit with a much larger amount of voltage, somewhere in the neighborhood of 10,000 Volts, which causes them to accelerate straight in the direction of the phosphor-coated display screen. There are three of these little slits, or electron emitters, per pixel on the monitor. This means that if a monitor has a resolution of 1280x1024, there would be more than 3.9 million electron emitters producing the image. Because each pixel is generated by its own set of electron emitters, the need for the long cathode ray tube and beam deflector is eliminated, resulting in a very thin final product.

The process seems really complicated, and it kind of is, but the end result is simple: a screen capable of producing an image unlike any of the reporters at CES had ever seen. SED monitors that have been developed so far and displayed at trade shows provide contrast ratios of nearly 10,000:1 (displayed whites are ten thousand times brighter than displayed blacks). However, the technology is expected to reach its full contrast ratio capability of 100,000:1. That’s a big number; easily ten times greater than the next best thing. Here are specifications that are supposed to be achieved on the final product (approximate):

• Response Time: Less than 1ms
• Contrast Ratio: 100,000:1
• Viewing Angle: 180° in each direction (full hemisphere)
• Power Consumption: Less than LCDs, highly efficient
• SED is also expected to fully support all HDTV video modes (1080i, 720p, etc.)