After it was introduced in the middle of the last century, the TV set remained basically unchanged for decades.

While there were minor design variations along the way, it wasn't until flat-panel plasma and LCD sets arrived that manufacturers finally gave us a new take on the tired old tube.

At first, sky-high prices made plasma TVs a symbol of wealth and status (no self-respecting rapper would let an MTV camera crew enter his crib unless there was one hanging on the wall), but costs for both plasma and LCD models have since come crashing down to real-world levels. And given their sleek, space-saving form factor, you'd be crazy not to consider one when shopping for a new TV.

It turns out that people are doing just that. About half the respondents to a recent Consumer Electronics Association survey said their next TV purchase will be a flat-panel display. Consumer confusion has actually helped the boom, since other surveys indicate that a lot of people believe that all HDTVs are flat-panels.

With interest in thin TVs surging, now's a good time to peer into the future and find out what technologies will be surfacing over the next few years to challenge plasma and LCD.

THE CONTENDERS

Since there's plenty of money to be made as Americans upgrade to high-def over the next decade, you'd think there'd be heaps of new flat-TV technologies on the way. But only two serious contenders are currently in development.

The first, Surface-conduction Electron-emitter Display (SED), was jointly developed by Canon and Toshiba and is intended for big-screen (50 inches and larger) TVs. To judge from demos at recent trade shows, SED's stunning picture quality will make it a formidable flat-panel competitor — if it ever makes it to market. Toshiba planned to release models earlier this year, but the rapid price erosion of plasma and LCD TVs sent developers back to the lab to figure out a more cost-effective way to manufacture SED sets. The latest word is that Toshiba plans to introduce SED to coincide with the 2008 Summer Olympics in Beijing.

The other flat technology in the queue, Organic Light-Emitting Diode (OLED), is being positioned as a successor to LCD. You can already find small OLED screens in digital cameras, camcorders, portable audio and video players, cellphones, and PDAs. But big-screen versions are also in the works: Sony recently exhibited a strikingly slim 13-inch computer monitor, while both Samsung and Epson have shown prototype 40-inch widescreen HDTVs. However, as with SED, the stiff competition from ever cheaper plasma and LCD sets might keep OLED out of the market for a while. There are also some technical hurdles to overcome, with the life expectancy of displays currently hovering well below that of the competing flat-panel technologies. Still, it's anticipated that bigscreen OLED HDTVs could arrive sometime around 2010.

SED :: Potential Plasma-killer
Toshiba and Canon's recipe for a new flat screen draws from both plasma and old-school cathode-ray tube (CRT) TVs. Light is produced by phosphor dots coating the inside of the screen. In an SED display, these are masked with red, green, or blue filters. (Each trio of colored subpixels forms a single pixel.) In a plasma set, phosphors are triggered by cells containing a gaseous mixture that discharges in reaction to a flow of electrical current; in a CRT screen, they're barraged by magnetically steered electron beams fired from "guns" in the tube's neck.

SED, in contrast, uses a grid of emitters, each of which fires electrons directly at a specific phosphor dot located on the panel's screen. Because the space between the emitter array and the screen is extremely narrow, an SED panel is only a few centimeters thick — kind of like tube technology without the tube.

SEDs have many of the same things going for them that plasmas do: They're thin, have a wide viewing angle, and display fast-moving images clearly. But they also have the capability of topping plasma (and LCD, DLP, and LCoS as well) when it comes to contrast ratio — something that's proven to be the Achilles' heel of the new generation of post-tube displays.

As with CRT — which still offers pictures with a reference-quality black level — the intensity of the light generated by a pixel in an SED display is modulated by the drive strength of its corresponding electron emitter. Pixels meant to display black exist in an "off" state, with no electrons reaching the phosphor dot. But the cells in plasma sets need to be "primed," with a low level of current constantly flowing through them — which serves to boost black levels toward dark gray.

SED's ability to provide power only to where it's needed moment-by-moment holds the promise of lower power consumption. In theory at least, the process is more efficient than both plasma's priming technique and the permanently switched-on fluorescent backlight that drives an LCD display — which also reduces picture contrast. (Samsung has demonstrated LCD panels using energy-efficient light-emitting diodes, or LEDs, instead of a fluorescent backlight, and Sony briefly offered a 46-inch model as part of its now-defunct Qualia line.) With home energy bills rising in tandem with the skyrocketing price of crude oil, any relief a new TV could provide on electricity consumption would be welcome.

OLED :: LCD's Eventual Successor
While its entry into the big-screen TV arena is farther off than SED's, OLED has the potential to be the bigger player. That's because of the flexibility of OLED displays: thin (a TV can be 3 centimeters or less deep) and lightweight, they can be manufactured in multiple sizes and resolutions, or even mounted on flexible substrates that can be used to create things like electronic paper and "wearable" displays. (Imagine a digital watch permanently embedded in your shirt cuff!) Also being developed are transparent OLEDs that can create a window-like effect by letting you see through the video screen when it's not displaying images.

The version of OLED destined to make its way into your living room is called Active-Matrix Organic Light-Emitting Diode (AMOLED). In an AMOLED, a stack of organic polymers including both emissive and conductive layers is deposited on a substrate containing a thin-film transistor (TFT) array. Different techniques can be used to apply the organic material, including an ink-jet method that "prints" a pixel matrix directly on the TFT. An electrical charge passing between the bottom electrodes and an additional transparent layer on the surface of the display stimulates the emissive organic layer, which in turn creates light. Color OLED displays can be created by depositing red-, green-, and blue-dyed pixel triads via the ink-jet technique or by color-filtering an array of white-light-emitting pixels. Either way, the shade of an individual pixel varies according to the amount of current traveling through it.

Since OLED displays create their own luminosity rather than relying on a backlight, they have a very wide viewing angle — on par with both plasma and SED. And the speedy refresh rate of active-matrix displays promises to prevent the picture-smearing effects typical of LCDs when showing fast-motion video. Also, the self-luminosity of OLED's organic material, along with its efficient emissive properties, is said to keep power use well below that of LCD or plasma. (Low power consumption has already made OLED attractive for use in portable electronics.)

But display longevity could be a stumbling block. People expect any set they buy to last 10 years or longer, and right now that's a serious stretch for OLED. To fix this, developers have been working on the differential aging of the pixels. In layman's terms, that means the life span of the blue-colored pixels, which drops off in brightness at a faster rate than that of red and green pixels, needs to be extended. (I've heard of prototype OLED screens that required replacement several times in the course of one trade show because of color shifts resulting from differential aging!)

One solution in the works is for manufacturers to modify TFT panels to compensate for brightness decreases in the display by selectively boosting pixel drive strength over time. But it would obviously be better to develop organic materials that can deliver bright pictures for as long as the competing technologies — 30,000 hours at least. At present, the small OLEDs used for cellphone displays have a life span of around 10,000 hours.

The Forecast
If you're looking to buy a flat-panel HDTV in the near future, your best bet is still going to be plasma or LCD. If Canon and Toshiba manage to bring the price of the technology down to where it can compete with current flat-panels, we'll see SED HDTVs in stores before OLED models. But even if SED remains expensive, its picture-quality potential will still generate interest from the high end of the video market.

While still lagging well behind SED on big-screen development, OLED is destined to be the more ubiquitous technology. But the really cool aspect of OLED is the futuristic stuff: flexible electronic paper you scroll out to read on the subway, TV screens that become windows at the press of a button, T-shirts with designs you update on your computer. If we someday get big-screen OLED HDTVs, that will be icing on the cake. But from what I can see, OLED is going to be way more than just a means of watching movies at home.

HDTV Info Center
Display Technology Smackdowns
Back to Homepage
What's New on S&V