 What
OLED (organic light-emitting diode) displays use organic materials that, when properly charged, give off a bright glow—significantly brighter and sharper than LCDs. While glass has been the substrate of choice for most OLED displays, attention is shifting to plastic (particularly thin-film plastic manufactured in long rolls) as a means to facilitate flexible displays. Why
LCDs are at an inherent disadvantage because they rely on power-hungry backlights that are then shuttered by the liquid-crystal material and polarizing filters used in TFT monitors. Because OLED pixels are electroluminescent, meaning they give off their own light when charged, there's no need for a backlight or filter between the pixels and the viewer. This is why OLED displays are considerably brighter and sharper than conventional flat-panel displays.
Moreover, OLEDs conserve far more power. A glowing OLED pixel requires between 2 volts to 10 volts but only needs this power when active. A black OLED pixel requires no power. In contrast, TFT displays must power their backlights constantly and apply power to LCD cells to block that light from escaping.
OLED pixel-response rates are more than 100 times faster than LCD, according to Kodak (which holds many of the original OLED patents), thus making OLED a better fit for movies and gaming. Kodak claims its organic materials deliver a wider color range than LCD, far better luminance, and wider viewing angles (170 degrees) and can be implemented in screens a mere 1.5mm thick.
This image of a Philips 13-inch PolyLED TV prototype gives
you an idea of the image quality an OLED display is capable of.
Photo courtesy of Philips |
How
OLEDs use thin layers of organic material sandwiched between a transparent anode and a metallic cathode, all of which is usually built onto a glass or plastic substrate. With proper voltage, the organic materials produce light. The specific structuring of the layers, the materials in the anode and cathode, and the fluorescent molecules used to "dope" the electroluminescent layers all contribute to the efficiency and precision of OLED color output. The active-matrix addressing often used to control TFT pixel cells in today's screens also carries over to OLED displays.
There are two general types of organic materials in OLED displays: "small molecule" and "macro polymer." Most OLEDs thus far have used small molecule materials, but the technology encounters serious challenges as screen size increases, including thermal warping of the shadow mask.
Royal Philips Electronics is betting that polymer displays are the direction of the future, both in reflective and emissive varieties. Reflective-polymer technology is typified in Philips' collaboration with E Ink, the result being a pigment-based "epaper." (See April 2004's "Under Development," page 107 for more.) Emissive polymer OLEDs, though, have their electroluminescent molecules suspended in a paint-like liquid that can be literally printed through inkjet nozzles. When
OLED screens have already appeared in devices such as Kodak's EasyShare LS633 digital camera and MSI's MEGA Player 515. The first 15-inch (1,280 x 720) OLED prototype, designed by Kodak and Sanyo, went on display in October 2002. Three years earlier, state-of-the-art OLED prototypes had been 2.5-inch displays.
Some experts believe roll-to-roll OLED display manufacturing should quickly become less expensive than LCD technology once it starts volume production. Some believe this may happen in 2005, although this seems a bit optimistic. Chances
According to market analysis firm iSuppli, the 2003 global OLED panel market was just $250 million (17.3 million units). Many were small panels that went into cellular phones and other portable electronic devices. However, iSuppli expects the OLED market will reach $470 million this year (36.2 million units), up to $3 billion by 2007, and possibly exceed $4 billion in 2010 (more than 366 million units).
Small-molecule OLED technology has a head start, but manufacturing depends on a vacuum chamber and other costly elements. If makers can "print" polymer displays, particularly on flexible substrates, the market could change, with large displays being made relatively cheaply. |
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