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MEMS enable brighter, cheaper displays

Posted: 20 Oct 2009     Print Version  Bookmark and Share

Keywords:MEMS  display  LCD 

Uni-Pixel Inc. claims that a possible successor to the CRT, LCD and even the organic LED is scheduled to hit the market next year.

The company recently announced volume deliveries of its MEMS films dubbed "Opcuity" that are used in time-multiplexed optical shutter (TMOS) displays and are 10x brighter and 60 per cent cheaper to manufacture than LCDs. The films also can be fabricated on the same manufacturing lines as LCDs.

Earlier this year, Samsung Electronics revealed that it had a joint development agreement with Uni-Pixel for its TMOS display technology.

"One of the beauties of our manufacturing process is that it subtracts from existing LCD lines—you just need to remove some equipment that is no longer needed," said Uni-Pixel's CFO James Tassone. "Since we use no red, green and blue sub-pixels, our process is less demanding, requiring only one-third as many thin-film transistors.

"In fact, we can use LCD manufacturing lines that are ageing and due to be retired; instead of scraping an ageing LCD line, you can retrofit it to make our advanced TMOS displays," Tassone claimed.

TMOS displays use only a single layer of MEMS film between the bottom ("mother") glass and the top glass sheet in an existing LCD structure. By contrast, LCDs have five different layers between the bottom and top glass, including polarisers and colour filters that reduce light emissions. As a consequence, the single layer used with TMOS produces displays that are much brighter than LCDs produced on the same line.

Instead of using sub-pixels for red, blue and green, each pixel in Uni-Pixel's MEMS film is uniform, deriving its colour by time-mutiplexing the red, green and blue light from side-mounted LEDs that inject light into the bottom glass layer. The scheme acts as a light guide.

Instead of a white backlight to illuminate RGB subpixels, Uni-Pixel's approach routes light from side-mounted LEDs onto the same pixel, with the Opcuity film acting as an optical shutter.

Applying a voltage to a TFT causes the Opcuity film to deform downward, coming into contact with the bottom glass, routing light from LEDs up to a particular pixel. By time-multiplexing in synchronisation with the blinking red, blue and green side-mounted LEDs, any colour can be mixed at any pixel location, Uni-Pixel claims.

The films, which are microfabricated on inexpensive roll-to-roll manufacturing lines, use MEMS-patterned structures to deflect light from guides to pixels with sub-10 micron micromirrors that are said to react 1,000x faster than liquid crystals (TMOS displays update pixels in microseconds compared to milliseconds for LCDs).

Uni-Pixel and Samsung are perfecting the TMOS process for 4-inch displays. Since TMOS displays are transparent from the backside, they are also suited for larger displays. By sandwiching Opcuity films between window panes side-lit with LEDs, large displays will be possible on store windows that are only visible from the outside, the company said.

- R. Colin Johnson
EE Times





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