oOrganic light-emitting diode (OLED) technology continues to buck the industry’s current economic struggles, carving out lucrative applications in numerous display and lighting applications. And indications show that active-matrix (AM) OLEDs rather than passive-matrix (PM) OLEDs will eventually dominate this space.
DisplaySearch forecasts that OLED display revenues will reach $6 billion by 2015, up from $591 million in 2008, with a compound annual growth rate (CAGR) of 40%. OLED TVs will become the largest segment by then, totaling $2.6 billion. Mobile phone displays, which are largely of the PM OLED variety today, will account for $1.9 billion (Fig. 1a).
The market research company also says that while PM OLED displays will grow in the number of unit shipments by 2015, their revenues will stay flat. Meanwhile, the number of AM OLED unit shipments will triple this year and surpass those of PM OLEDs in 2011 (Fig. 1b).
DisplaySearch states that there’s a significant oversupply of PM OLEDs. Further, many companies that set up large PM OLED production lines are finding that those lines are now underutilized due to a limited number of applications and competition from liquid-crystal displays (LCDs). Compared to LCDs, PM OLED displays are hampered by their inability to be produced cost-effectively in large panel sizes like LCDs.
“AM OLEDs are making up for the slowdown in PM OLEDs over the past year,” says Jennifer Colegrove, DisplaySearch’s director of display technologies. “Going forward, it will be important for OLEDs to find a niche market where it will be difficult for LCDs to compete, such as flexible or transparent displays or lighting. OLED developers should also look for opportunities to combine their technology with other hot technologies such as touchscreen.”
Production capacity for AM OLED displays, on the other hand, is ramping up for an expected large demand. Compared to LCDs, AM OLED displays offer a thinner form factor; a wider viewing angle; a faster response time; lower power dissipation; a better color gamut and reproduction; higher contrast ratios; and a wider operating-temperature range.
However, companies still must work out how to scale to larger panels and provide higher operating lifetimes. Also needed are more efficient and longer-life blue OLEDs. To address these issues, designers are turning to amorphous silicon, improved materials, thin-film transistor (TFT) and metal-oxide driver circuitry, and better processing methods that can provide higher yields for TFT backplanes.
An AM OLED pixel turns on and off more than three times faster than the speed of pixels in a conventional motion-picture film. AM OLEDs, which have faster response times and consume less power than PM OLEDs, are ideal for fluid, full-motion video and graphics. They’re better suited to large-screen monitors and TVs, electronic signs, and billboards.
“The power-efficiency benefits of AM OLEDs are much better than those of PM OLEDs,” says Janice Mahon, vice president for technology commercialization at Universal Display Corp. (UDC).
A SIMPLER STRUCTURE
A PM OLED is structurally simpler than an AM OLED and thus less expensive to produce. PM OLEDs can be patterned using conventional fabrication techniques. The entire panel fabrication process can easily adapt to large-area and high-throughput manufacturing. PM OLEDs are well suited for low-cost and low-information-content small display panels with diagonals of 1.6 to 4 in., like those found in mobile phones, MP3 players, and cameras.
Despite the PM OLED’s attributes, it’s AM OLEDs that are becoming the rage. Nearly all major OLED display manufacturers, including Sony, RiT Display Corp., Univision, Nippon Seiki, MicroEmissive Displays, Truly Semiconductor Ltd., Samsung SDI, Taiwan-based Chei Mei EL (CMEL), Pioneer, eMagin, Wintek, and LG Display, have or will adopt the technology.
AM OLEDs are finding homes in highend 3G and 4G mobile phones from Nokia, Sanyo, and Toshiba. Other landing spots include digital cameras, digital photo frames, and portable media players, as well as handheld and free-standing TVs.
Driving OLEDs, particularly AM OLEDs, can be challenging. That’s because unlike LCDs, OLEDs are current-driven. Thus, any variation in a thin-film-transistor (TFT) driving circuit’s performance affects the OLED display’s luminance.
Kodak developed its global mura correction (GMC) technology to deal with AM OLED driving performance variations. (“Mura” is the Japanese word for “error.”) GMC is incorporated in an external driver IC that detects and compensates for mura problems.
Ignis Innovations Inc., which develops and licenses complete backplane and driver technologies for AM OLEDs, offers two technology platforms: AdMo and MaxLife. Admo is aimed at handheld and ultra-mobile devices, while MaxLife targets monitors, desktops, and TVs. Both platforms come in amorphous and polysilicon versions to correct for image-sticking and mura artifacts. At this year’s International Consumer Electronics Show (CES), Ignis demonstrated a 2.2-in. QVGA OLED display driven by the company’s technology.
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