OLED displays gain on LCDs

By:

Ruth DeJule

Technical editor, WaferNews

An organic light emitting diode (OLED) display technology has been developed that exhibits up to 16 million colors. Based on Kodak patents, the full-color active matrix OLED developed by eMagin Corp., Hopewell Junction, NY, contains more than 1.5 million individually addressable picture elements.

For objects to look “real,” a display must be able to render a wide range of colors and shades. With a limited color gamut, for example, images may look slightly washed out, appearing more pastel than vibrant. EMagin displays have a balanced full-color spectrum which adjusts the red, green, and blue relative intensities to create an acceptable looking white, stated Webster Howard, eMagin’s VP of technology. Optimal white balance may vary with individual preference but the overall effect is fuller, deeper colors, exceeding that of current notebook-type LCDs.

While LCDs dominate the flat panel display (FPD) market, there is room for improvement, such as better color range and dynamic response for fast-action videos like sports broadcasts. For TV applications, improvement in viewing angle is needed but often conflicts with the response time. And from a cost perspective, they are 2 to 3 times more expensive than cathode ray tubes (CRT). Most R&D laboratories still use CRT displays and miniature CRTs are frequently used in camcorders and other viewfinder applications. CRTs have better temperature and pressure ranges than LCDs; however, size, weight, high-voltage requirements, color resolution limitations, and cost make them a less attractive microdisplay solution, unless extreme operating conditions are required, such as being in the outdoors in the wintertime.

With the advent of laptops, FPDs have offered low power, high luminance, lighter weight, and easy integration with optics. Recently, they have benefited from the capability for integration on silicon ICs to provide system-on-a-chip. High resolution images make them suitable for mobile information products such as portable computers, wireless Internet viewers, portable DVD players, gaming platforms, and wearable computers. Most direct-view color OLEDs use three independent emitting materials to obtain red, green, and blue primaries. In microdisplays, the color subpixels are only a few micrometers wide. Filters are patterned at these dimensions and OLED pixels are made correspondingly small. To enhance color quality, eMagin modifies the color filter structures using a propriety process, said Howard.

eMagin’s 0.62-inch (diagonal) active screen has over 1.5 million potential color subpixel elements (600 X 3 X 852 pixels) and 52 more imaging columns than standard SVGA displays, making it possible for the display to run either 600 X 800 pixels in order to interface to the analog output of portable computers or 852 X 480 pixels in a 16:9 wide screen entertainment format. All the color and luminance value information at each of the pixel elements are stored in the display array to decrease flicker or color breakup.

In the next few years, the industry can expect improvements in life, efficiency, and cost, allowing penetration of OLEDs into market segments currently dominated by LCDs, noted Howard. Large screen OLEDs will take more than a few years.

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