Glow, Little Glowplate, Glimmer, Shimmer

Even though the 2.4-in. screens won't go into production until later this year, prototype displays using organic light-emitting diode (OLED) technology are knocking the socks off trade show audiences nationwide.

The self-luminous OLED technology from Eastman Kodak Co. in Rochester, N.Y., evokes visions of a clearer, brighter future for everything from cell phones and digital cameras to, eventually, laptop PC displays. Bear in mind, however, that this is technology whose performance is still being tested.

But David Mentley, vice president at research firm Stanford Resources Inc. in San Jose, says he see a promising future for the technology. What was a $3 million market in 1999 will grow to $717 million by 2005, according to a Stanford Resources report.

That may be pushing it, says Chuck McLaughlin, principal at McLaughlin Consulting Group in Menlo Park, Calif. "There's a lot of la-la-land hype, but development time is usually measured in years," he says.

During the next five years, OLEDs will begin to edge out 8-in. or smaller LCDs, "especially in products requiring color, wide viewing angle and low power consumption," says Kodak spokesman Joseph Runde.

Visible Differences

The contrast between two handheld TVs from Tokyo-based Casio Computer Co. illustrates the advantages of the new technology. One is standard issue, and the LCD-generated image is ghostly pale. In the other, retrofitted with an OLED display, Runde explains, the same image is clear and the colors are more saturated.

The self-luminous OLED displays need no backlighting, and without lamps, they're thinner than conventional LCDs. They're so thin and flexible that a display may someday be made that can be rolled up into a tube, Runde says.

Power savings accrue because only the pixels needed to produce an image are lit, unlike with an LCD, in which all thin-film transistors (TFT) remain lit as long as the unit is on.

Small screens are appearing in car audio equipment and cell phones. Pioneer Corp. in Tokyo holds an OLED license from Kodak and features passive-matrix OLED, which it calls organic electroluminescence (OEL) technology, in some of its car audio equipment. Unlike the active-matrix OLED, the passive version doesn't have a backplane with its own processing capability built into its glass substrate. It's a less-sophisticated technology, well suited to low-information-content applications such as alphanumeric displays, according to Kodak.

The Timeport P8767 cell phone from Schaumberg, Ill.-based Motorola Inc. uses a Pioneer OEL display.

But it's "the Ulvac deal that's going to be really important" in bringing full active-matrix OLED to the market, Mentley says. Under the terms of a deal Kodak has signed with Japan-based Sanyo Electric Co. and Ulvac Japan Ltd., the first prototypes will be ready next month, with mass production scheduled for next year, says Akihiko Oiwa, chief planner at Sanyo.

Sanyo provides the TFTs used in the active-matrix OLED displays. Kodak's OLED technology specifies organic materials, number and composition of layers, and the method for evaporating the materials onto the TFT substrate. Ulvac will build equipment to combine the two technologies to produce the final product.

"Initially, Sanyo is planning to use the OLED technology in [2.4-in. displays for] mobile phones and personal digital assistant devices," Oiwa says.

The 5.5-in. screens will be for portable DVD players, car navigators and any devices in which LCDs are currently used, Oiwa says.

By the end of this year, Kodak and Sanyo plan to demonstrate a 10-in. active-matrix OLED display, says Kodak spokesman Daniel Gisser, although laptop-size screens are years away.

When Newer Isn't Better

The technology is promising, says McLaughlin, but don't write off LCD and conventional LED technologies. For example, he says, it's doubtful that the OLED display can retain its brightness in full sun.

And it's significant that the technology is available in aftermarket car audio equipment but "no one in the automobile business will touch them with a barge pole," McLaughlin says. That's because automakers want a product that will last about 10 years, or as long as the car, he says.

"There will continue to be areas in which conventional LED technology will be the most suitable choice," Oiwa says. And there have been "difficulties in developing to the product level," he says, including establishing stable mass-production technology and resolving reliability and durability issues. But, Oiwa adds, Sanyo is working on these problems in preparation for mass production next year.

Power consumption by active-matrix OLED displays "will be 20% less than that of standard TFT LCDs," Oiwa predicts.

"[The] 2.4-in. and 5.5-in. active-matrix OLEDs use about a third to a half the power of comparable LCDs, respectively," says Runde. "But further improvements are coming."

OLEDs

1. Voltage is applied to the metallic cathode layer, producing electrons that pass through the

2. Electron transport layer, to the

3. Emissive layer.

4. The anode (hole-injection) layer produces positively charged "holes" that pass through the

5. Hole-injection layer and the

6. Hole-transport layer, then on to the

7. Emissive layer, where the two charges combine and generate light (electroluminescence). Kodak "dopes" this layer with a small amount of highly fluorescent molecules to boost the amount of light that's produced. This light continues as long as the charge is applied.

8. Each cell or stripe in the emissive layer has evaporated on it organic metalized dyes, in red, green and blue. When the cell is excited, its light is filtered by the dye and light passes through the

9. Transparent anode and the

10. Outer glass substrate, which contains

11. Thin-film transistors, one for each cell, to control whether that cell is excited.

12. Because OLEDs emit in all directions, the viewing angle is 160 degrees. Also, OLEDs respond quickly to changing signals, allowing for full-motion (30 frames per second) video.
LCDs
 

1. Lamps provide backlight, which passes through a

2. Polarizing filter to the

3. Glass substrate.

4. A positive or negative goes through transparent electrodes embedded in the substrate and turns on the

5. Thin-film transistors.

6. Light shining through the glass substrate strikes the LCD material and passes through to the

7. Color filter.

8. The positive or negative charge coming from the electrodes is received by the transparent anodes and passes through the

9. Outer glass substrate.

10. Light continues through a polarizing filter. The two sets of polarizers move more or less perpendicularly to one another to let in less or more light. It taakes more than 40 microseconds for the filters to respond to the LCD material.

11. Because of backlighting, viewing the screen from an angle of more than about 40 degrees causes color and light shift.

This story, "Glow, Little Glowplate, Glimmer, Shimmer" was originally published by Computerworld.

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