May 2003

LEDs vs. the Lightbulb

Continued from page 3

By David Talbot

Plastic Light

There's a dark horse in the white-light race: the organic light-emitting diode, or OLED. Whereas an ordinary LED makes a bright point of light, the organic variety resembles a patch of softly glowing plastic. Mass production of these products could be as simple as ink-jet printing because there is no need for the costly chip-fabrication facilities that make LEDs so expensive. Someday this technology might lead to flexible lighting fixtures that hang on walls, ceilings, and even furniture.

The main impetus for OLED development is coming from companies that seek backlighting for cheaper, brighter displays. But the technology is improving rapidly, approaching the point where it could be practical for illumination. Barely 18 months ago, GE researchers proudly touted a 2.5- by 2.5-centimeter white-light OLED that produced only 3.8 lumens per watt. Today, says Anil Duggal, manager of the light energy conversion program at GE Global Research, the company can show off a 15- by 15-centimeter prototype-about the size of a compact-disc case-with double the efficiency of the earlier OLED.

And just as Nakamura is adding nanostructures to LEDs, Duggal is adding particles to the OLED substrate to provide more chances for the light to zip from the surface of the device, rather than being absorbed internally. Employing such tricks could make OLED-based white lights competitive with fluorescent tubes within a decade, Duggal says. "There is no problem getting to high brightness, but lifetimes are still an issue, and efficiencies are an issue," he says.

To speed development, Ewing, NJ-based Universal Display is working with a new class of OLED materials. Invented in 1999 in collaboration with the University of Southern California and Princeton University, these materials incorporate atoms of heavy metals such as platinum, surrounded by carbon-based molecules that amount to "organic shrubbery," says Janice Mahon, vice president of technology commercialization at Universal Display. Last year the company and its academic partners used this material to build a white-light OLED prototype that achieved 11 lumens of light per watt of electricity. That device was made with a single OLED material that can emit a broad spectrum of colors. But the company is also pursuing a white- light source that relies on a combination of different materials, some emitting red, some blue, and others green. Universal Display expects to build a prototype this spring, Mahon says.

A more far-out vision for OLEDs embeds glowing specks of inorganic crystals into the lighting device. Each of these "quantum dots" is a cluster of cadmium selenide atoms one to five nanometers across. At that scale, the strange rules of quantum physics take over, and the wavelength of the emitted light depends purely on the size of the cluster. Late last year two MIT researchers-chemist Moungi Bawendi and electrical engineer Vladimir Bulovic-showed that a sprinkling of quantum dots could brighten an OLED significantly. But right now, Bulovic says, the quantum dot white OLED is only "a good proposal-it's far away from being a proved fact."

Regardless of whether quantum dots get their moment to shine, the future of illumination appears solid-solid-state, that is. The pitched competition across corporate and academic labs promises to upend the century-old lighting industry. In addition to Lumileds and GELCore in the United States, the leading players include Nichia and Toyoda Gosei in Japan and Osram Opto Semiconductors in Germany. "Those would be the five who have advanced the art the most," says Steele of Strategies Unlimited.

While for the next few years these and other companies are chasing big markets in backlighting for cell phone displays and automotive instrument panels, LED developers will increasingly find paradise beyond the dashboard lights. By 2007 the LED illumination business will top $500 million, according to Strategies Unlimited-of which $135 million will be for white-light LEDs.

And that's just a taste of what's to come: the field is still wide open for technology breakthroughs. "It is always possible that someone from left field is going to come in and do something dramatic," Steele says. Indeed, he and other industry observers agree, the great number of players pursuing solid-state lighting technology-and the great theoretical potential of LEDs-makes major advances in white-light LED illumination inevitable. It's only a question of who will make that next breakthrough.

In the test room at Nakamura's Santa Barbara laboratory, grad student John Kaeding describes the researchers' efforts by citing the adage about 10,000 monkeys pounding on 10,000 typewriters and eventually producing a work of Shakespeare. That old saw is new to Nakamura, but when the light pioneer absorbs the point, he nods vigorously: "Yes, yes," he says. With so many labs attacking the technology from so many angles, he believes that someday, somewhere, a researcher will open an oven and pull out a material that can emit a blue glow of unmatched brilliance-radically advancing the way we light our world.

No wonder the shades are drawn on Nakamura's windows.

Lighting the Way
COMPANY	TECHNOLOGICAL DISTINCTION
Cree Durham, NC	Bright blue light-emitting diodes (LEDs); silicon carbide substrate
Nichia Tokushima, Japan	First blue LEDs
Lumileds Lighting San Jose, CA	Bright white LEDs; unique heat-sink package
Osram Opto Semiconductors Regensburg, Germany	Chip faceting for bright white LEDs
GELcore Valley View, OH	Phosphor that promotes better-quality white light
General Electric Global Research Center Niskayuna, NY	White organic LEDs (OLEDs)
Universal Display Ewing, NJ	White OLEDs