British Develop Blue LEP Display

-- Semiconductor International, 3/1/1999

Cambridge Display Technology (CDT, Cambridge, UK) has produced a blue light emitting polymer (LEP) suitable for displays. This LEP is said to have properties well within the color ranges of other display technologies. The blue color is not identical with the industry standard blue from a cathode ray tube but close to it. CDT has red, green and blue plastic displays, all using polymers with similar chemical structures.

The synthesis of the polymer for blue displays is more complex than for the other colors. The blue panels have a lifetime of only a few hundred hours. Work is in progress to extend this to try to match the many thousands of hours available from LEP emitters of the other colors.

Intel has invested in CDT, but CDT holds the patents on use of light-emitting conjugated polymers. CDT has licensed the technology to Hoechst, Philips and Uniax, while working with DuPont and Seiko Epson.

The company claims that a major advantage of its technology is the ease of display production. In collaboration with Seiko Epson, it is planning to perfect the ink jet printing process using three nozzles, one for each color, and to print straight through onto a thin-film transistor active matrix substrate.

CDT claims its displays are solid-state devices with a 180° viewing angle and can be driven by the very low voltages suitable for active matrix drivers. The blue LEP needs a slightly higher voltage, 3.5 V, than the polymers that emit light of other colors, but it can be driven from a 5 V source. LEP displays can be used in applications for which a flexible display is needed. Their rapid switching capability makes them ideal for video use. CDT hopes to demonstrate an LEP video display this year.