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OLED-Displays
By Erich Strasser
WHAT IS OLED?
Short for organic light-emitting diode, a display device that sandwiches carbon-based films between two charged electrodes, one a metallic cathode and one a transparent anode, usually being glass.
The organic films consist of a hole-injection layer, a hole-transport layer, an emissive layer and an electron-transport layer. When voltage is applied to the OLED cell, the injected positive and negative charges recombine in the emissive layer and create electro luminescent light. Unlike LCDs, which require backlighting, OLED displays are emissive devices - they emit light rather than modulate transmitted or reflected light.
OLED technology was invented by Eastman Kodak in the early 1980s. It is beginning to replace LCD technology in handheld devices such as PDAs and cellular phones because the technology is brighter, thinner, faster and lighter than LCDs, use less power, offer higher contrast and are cheaper to manufacture. An important step in the evolutionary process began with the use of thin-film organic layers. The first EL thin-film device used a single organic layer sandwiched between two injecting electrodes.
What is AM OLED - Active Matrix?
Active matrix (AM) OLED displays stack cathode, organic, and anode layers on top of another layer - or substrate - that contains circuitry. The pixels are defined by the deposition of the organic material in a continuous, discrete "dot" pattern. Each pixel is activated directly: A corresponding circuit delivers voltage to the cathode and anode materials, stimulating the middle organic layer. AM OLED pixels turn on and off more than three times faster than the speed of conventional motion picture film - making these displays ideal for fluid, full-motion video. The substrate - low-temperature polysilicon (LTPS) technology - transmits electrical current extremely efficiently, and its integrated circuitry cuts down AM OLED displays' weight and cost, too.
What is PM OLED - Passive Matrix
Passive matrix (PM) OLED displays stack layers in a linear pattern, much like a grid, with "columns" of organic and cathode materials superimposed on "rows" of anode material. Each intersection or pixel contains all three substances. External circuitry controls electrical current passing through the anode "rows" and cathode "columns," stimulating the organic layer within each pixel. As pixels turn on and off in sequence, pictures form on the screen. PM OLED displays' function and configuration are well-suited for text and icon displays in dashboard and audio equipment. Comparable to semiconductors in design, PM OLED displays are easily, cost-effectively manufactured with today's production techniques.
OLEDs are the latest and most promising buzzwords in display technology.
To give you an idea of their potential, imagine a cardboard-thin TV screen.
Now imagine that you can roll up your TV, put it away or carry it wherever
you go.
Automatically, you start appreciating why millions, if not billions, of dollars are being poured into OLED research every year.
http://www.oled.at
http://www.oled-display.net
About the Author
Webmaster of OLED plattforms
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