Oct 23, 2017

Plastic, not glass, to spawn new breed of thin, flexible displays

Published May 23, 2004

Eindhoven, Netherlands — There is a Jetsons-like world coming, not too far in the future, where digital displays line clothing, deliver robust content in mobile devices and even offer video cooking tips on the sides of soup cans. The enabler? Many think it's plastic.

Display R&D efforts at Royal Philips Electronics are "no longer on glass-based displays," which are breakable and expensive to manufacture, said Peter Wierenga, a senior vice president with Philips Research. Instead, the company is pursuing "plastic-based and cheap manufacturing technology," he said. Moreover, Philips is applying a range of video-processing techniques originally developed for TV to new types of displays, including screens designed for mobile systems. "By combining and reusing the existing technologies in a clever way, a lot of gain can be achieved," Wierenga said.

Plastic, not glass, to spawn new breed of thin, flexible displays-Body

Wierenga and several of his colleagues at Philips Research will offer a glimpse of these new technologies at the Society for Information Display conference in Seattle this week (see related story, page 22). Examples include a 13-inch PolyLED TV, a "paintable LCD" process, video-processing techniques such as adaptive color gamut mapping applied to displays, as well as a three-dimensional display that combines Philips' lenticular-lens technology with new real-time 3-D rendering software.

Flexible displays are one of the hottest trends in display technology, said Kimberly Allen, director of technology and strategic research at iSuppli/Stanford Resources, who especially singled out active-matrix organic-LED displays. They are "important because they can help people imagine new forms for displays," she said. "Rather than a display being a rigid, breakable, rectangular object, it might be circular or curved, or even flexible."

Moreover, "They also help manufacturers break out of the dreary cycle that LCDs are stuck in"larger and larger investments in huge factories that process ever-bigger pieces of glass. Most LCD makers secretly wish they could get off this endless escalator, even if they won't say so out loud," Allen said.

Indeed, techniques leveraged from the semiconductor industry"everything from substrate strategies to lithography"have forced large display vendors into a manufacturing arms race, throwing immense sums at costly fabs. The burden has forced some vendors, particularly in Japan, to consolidate and partner on R&D in their efforts to stay competitive with suppliers in Taiwan and South Korea.

Philips Research, for its part, is working on ever thinner displays using polymer technology on two fronts: emissive and reflective displays. Polymer Vision, an incubator company established by Philips Research, this year unveiled an ultrathin, flexible reflective display that can be rolled up inside a pen or mobile phone. Developed in collaboration with E Ink Corp., the 5-inch organics-based quarter-VGA active-matrix display has 80,000 thin-film transistors on a plastic substrate.

For the emissive displays, Philips Research is betting on polymer organic light-emitting diode (OLED) technology. Polymer OLEDs have active molecules suspended in a liquid like pigments in paint. Those molecules can be printed onto flexible substrates using inkjet printing.

The company last week demonstrated its first 13-inch PolyLED TV prototype. Philips started polymer OLED development in 1991 and has used earlier small-screen versions in shavers and mobile handsets. The new prototype shows full color with 576 x 324 resolution in a 13-inch display that is "carved out" of a wide-screen 30-inch display with WXGA (1,365 x 768) resolution.

Philips hopes its prototype will silence skepticism within the display industry over larger polymer OLEDs. With few inkjet products in the market and few demonstrated, Allen of iSuppli/Stanford Resources said, "People were beginning to wonder ifmer OLED was really going to make it."

Philips' prototype "shows the viability of inkjet printing on large-size panels," she said.

Philips' Wierenga stressed the company's early commitment to polymer rather than another technology, small-molecule-based OLEDs, "because we believe in solution processing" that allows the use of printing technology. Such a process could be critical for larger OLEDs, he added. Philips predicts that PolyLEDs will be fit for bigger-screen TV applications after 2006.

However, polymer technology is immature compared with small-molecule-based OLEDs, which are built by depositing molecules of the compound onto the display in vacuum chambers, in the same way that silicon circuits may be layered onto displays. There is no standardized manufacturing equipment, and panel and materials prices remain high. According to iSuppli, the 2003 worldwide OLED panel market amounted to $250 million, 98 percent of which went to small-molecule panels. The research firm expects the OLED market to reach $470 million this year and $4 billion in 2010.

Pioneer, Samsung SDI, RiTdisplay and SK Display (a Sanyo-Kodak joint venture) are among those selling small-molecule-based OLED displays in small sizes. But this technology has limitations when screens get bigger, Allen said, since the shadow mask used is vulnerable to thermal expansion and sagging.

On the other hand, the "polymer OLED offers good potential for the long term," said Allen, because inkjet printing may ultimately allow for larger panels than are possible with the small-molecule evaporation method.

And they make for great viewing, said Nijs van der Vaart, principal scientist at Philips Research. He cited the advantages of Philips' PolyLED TVs compared with today's LCD sets, including superior picture contrast (because a polymer OLED display is an emissive display); no need for a backlight; wide viewing angle with faster response; and exceptionally thin form factors. Although the new PolyLED TV prototype still uses two glass plates, Philips Research is working on a unit based on one glass plate, using a thin layer of silicon oxide and silicon nitride, van der Vaart said.

Philips Research has also developed an inkjet printing process using "the first high-resolution multihead printer equipped with 256 piezo-driven nozzles," he said. Collaborating with PolyLED materials suppliers and with print head manufacturer Spectra, Philips developed inks, print heads and substrate processes capable of recreating "homogeneous pictures" and printing large-screen OLED displays "up to 24 inches diagonal," van der Vaart said.

Philips believes that once OLEDs can be manufactured using so-called roll-to-roll techniques, they will be cost-effective enough to rival LCDs and plasma display panels (PDPs). "OLEDs will undergo a paradigm shift when roll-to- roll manufacturing takes over," said industry consultant Malcolm Thompson, president of MJT Inc. "At 15 inches, XGA-resolution OLED panels have a great cost advantage once volume production takes off." By all estimates, that will happen next year.

Roll-to-roll manufacturing is used in other industries"printing, for example"but its application in flexible displays "remains cloudy," said M. Robert Pinnel, chief technology officer of the U.S. Display Consortium. The process must be stable, process flow matching is tricky and volume demand must be high, Pinnel maintains.

"This scenario is certainly not a good fit to flexible-display manufacturing, at least at this point in technology development," he said in a recent USDC report. "But by no means should we yet give up the investigation and pursuit." Analyst Allen, however, cautioned that it's premature to count OLEDs as a "strong rival" to LCD or PDP televisions. "By the time OLED TVs of any large size reach the market in five years, LCDs and PDPs will be even more advanced," she said, as will digital light projectors and other projection systems. "OLED will be a competitor, and maybe a strong one, but it is not going to take over the market in the TV space."

One of Philips' big rivals in polymer OLEDs, Seiko Epson, has shown a tiled 40-inch panel built up from four 20-inch panels, said Allen. Philips' van der Vaart claimed, however, "We believe we developed better image quality by adopting a new 'scrolling-bar' video-addressing scheme, slightly different materials and a new method of printing."

The novel addressing scheme varies the duty cycle for each display line depending on image load. For example, in dark scenes, high local peak brightness is combined with the perfect black state of OLEDs, while in bright scenes the brightness is kept at an average value.

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