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03 Jun 2004
Large displays based on organic light-emitting diode technology make Society for Information Display debut.
Large displays based on organic light-emitting diode (OLED) technology were all the rage at this year’s Society for Information Display (SID) symposium, which has just taken place in Seattle, US. Seiko Epson, Philips and Samsung took the opportunity to unveil their latest successes in scaling their manufacturing technology during the 23–28 May event.
Having already developed small OLED screens for digital cameras, shavers, mobile phones and other electronic items, the world’s leading display makers are now in a race to develop larger versions for televisions and computer screens.
The attraction is easy to understand. Unlike competing LCD technology, OLED displays are made from luminescent organic semiconductors and combine wide viewing angles with high contrast and short response times. However, until now it was not clear if the fabrication process could be scaled up to suit large displays.
Those fears can now be put to rest thanks to the news that Epson has made the world’s first 40 inch full-colour OLED TV, Samsung a 17 inch monitor and Philips a 13 inch demonstrator.
Seiko Epson’s massive 40 inch prototype boasts a resolution of 1280 x 768 pixels (WXGA) and 260 000 colors. The company is planning to commercialize the technology by 2007.
In contrast, Samsung’s 17 inch OLED monitor is smaller but has a higher resolution of 1600 x 1200 (UXGA). The Korean electronics specialist is now setting up a production line to make active-matrix OLED displays.
Philips was also keen to promote its OLED advances. The Dutch electronics firm was showing a color 13 inch “PolyLED” TV prototype with a resolution of 576 x 324 pixels which it says shows the feasibility of scaling up to large displays. A polymer-OLED TV could be a reality within five years and the application it has in mind is widescreen 30 inch TVs with a resolution of 1365 x 768 (WXGA).
Both Philips and Epson fabricate their displays by using specially developed inkjet printing processes that deposit light-emitting inks (soluble polymer OLED materials) onto a pixellated backplane. In effect the screen is printed onto a substrate that contains the display’s drive electronics.
The Philips process uses a printer with four print-heads and a total of 256 piezo-driven nozzles. Red, green and blue sub-pixels are simply made by ink droplets fired from different nozzles. Working with the print-head manufacturer Spectra, Philips says that it has developed a system to print displays up to 24 inches. Seiko-Epson uses a similar scheme to create its 40 inch OLED display.
Samsung has taken a different approach. Instead of working with polymer OLED materials it is using small-molecule OLED materials. The pixels of this type of display are traditionally made by spraying the OLED material through a patterned shadow mask. To date, the performance of the mask has limited display size to just a few inches. Samsung has got round the problem by developing a new patterning process which scans a laser across a film of the organic material to create individual pixels.
Author
Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.
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