Electronic Design

OLEDs And CLCDs Each Seek Their Niche

OLEDs: Flat-panel displays made with the new organic light-emitting diode (OLED) technology consume roughly 75% less power than backlit LCDs. The OLED display is emissive, so it is sharp and highly viewable, even in bright sunlight. Perhaps more significantly, the OLED display lights up only the portion of the display that's required, keeping its power consumption low. Also, compared with conventional LCDs, OLED displays do not require backlighting and offer faster response time—it responds in microseconds.

For example, eMagin Corp. of Hopewell Junction, N.Y., implements millions of individual low-voltage light sources (the OLEDs) on low-cost silicon ICs to produce single-color, white, or full-color display arrays. Many computer and video system functions can be built directly into silicon under the display, yielding an ultra-compact system with low overall cost relative to alternative technologies. The company's OLED-on-silicon microdisplays have a wider viewing angle than conventional displays and appear equally bright at all angles (a).

CLCDs: The other new flat-panel display technology is based on cholesteric liquid crystals. This material is "bi-stable" because its two distinct states, transmissive and reflective, are stable. To be more precise, CLCs are "multistable" since the degree to which a pixel is transmissive or reflective is governed by applying electric fields of different intensities and durations. Once written, the CLCD retains its optical properties indefinitely after the electric field is removed. This nonvolatility is a revolutionary in displays.

The result is a reflective, full-color, nonvo-latile display. While the CLCD may eventually compete with electronic displays in the es-tablished markets, its unique properties make it a prime candidate for "electronic paper" today. Its reflectivity approaches that of a newspaper, which means it's quite legible over the complete range of "reading-level" ambient-light conditions. Since it draws no power to retain an image, a CLCD electronic book becomes viable. So, if you construct a CLCD sandwich on a plastic substrate, you achieve a degree of flexibility and robustness approaching that of a printed book, like the ebook made by Kent Displays Inc., Kent, Ohio (b).

TAGS: Components
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