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OLED Technology (also AM OLED, PM OLED, SM OLED, PLED & LEP)

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Technology Overview & Description

KodakOLEDstructure.gif Organic Light-emitting Diode displays (OLEDs) represent, like SED displays, a very promising format for use in home theater. The contemporary technology was developed by Eastman-Kodak and works via electroluminescence whereby a bright light is emitted whenever current is applied to conductors surrounding organic thin films. These displays do not require backlighting and can be manufactured in very thin, compact designs. Viewing angles are expected to be at least 160 degrees in all directions and operation occurs with just 2-10 volts. There is a lot of confusion within OLED technology however, as there are multiple manufacturing methods and technology approaches. As such, we're waiting a bit for the industry to shake itself out and see which technologies will take off for each application type.

AM (Active Matrix) OLEDs seem to be the technology of choice when it comes to the types of displays that will make it into the home theater environment. In an AM OLED, the OLED pixels are placed onto a TFT (thin film transistor) array backplane which functions as a series of switches to control the current flowing to each of the pixels. Typically there are two TFTs at each pixel, which results in a the ability to have a constant current flow and eliminating the need for power-hungry current spikes as in passive OLED technologies.

A potentially more exciting form of the technology (though likely not home theater-related) is more commonly referred to as PLED (Polymer Light-emitting Diodes) or LEP (Light-emitting Polymers) whose emissive materials can be applied using techniques derived from commercial inkjet printing (thanks to Seiko Epson and a 30 micron printing process). This technology was developed by Cambridge Display Technologies (CDT). The end result is that these displays can be made in a very flexible (literally) and cost-effective manner. LEPs are very closely related to LEDs however instead of using a semiconductor material to produce light, LEPs use a 2-layer polymer.

What's Next

AM OLEDs and LEPs are both positioned to take over LCD displays - though the fruition of this endeavor remains to be seen. Both OLED technologies promise several advantages including: elimination of backlighting, requiring a single layer of plastic as opposed to two sheets of glass, lower power consumption, and the possibility for physically flexible displays. They also face significant challenges in the area of life expectancy and color consistency over the life of the display. Samsung demonstrated a 21" (1920 x 1080) prototype AM OLED display in January 2005 as well as a 40" (1280 x 800) prototype AM OLED display in May 2005. The 40" unit boasted 600cd/m^2 brightness, 5000:1 contrast ratio, 80% NTSC color gamut, and a panel depth of just 3cm. At CES 2007 they were nowhere to be found (on-site anyway). With LCD and plasma prices dropping and technology advancing, OLED has its work cut out for it.

OLED Display Advantages

  • Excellent brightness
  • Great color and contrast potential
  • Relatively inexpensive to manufacture
  • Thin, lightweight & durable
  • Fast response time
  • Eventually have capability of being physically flexible or rollable (LEPs)

OLED Display Disadvantages

  • Short life expectancy (especially blue)
  • Differing life expectancies for each color resulting for potential of color shift over time (needs to be controlled via electronics)
  • Currently prototype-only for larger screen sizes - most OLED displays are for portable devices

samsungOLED40_th.jpg
Samsung Prototype 40-inch OLED display

 

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