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Xerox prints transistors for use in LCDs

Posted: 16 Dec 2003 ?? ?Print Version ?Bookmark and Share

Keywords:= tft? lcd? poe? printed organic electronics? mems?

Xerox Corp. is looking to lower the cost of LCD panels by printing TFTs, rather than etching them with photolithographic techniques. The process, which uses an ink jet printer to implant semiconductive polymers on a flexible substrate, could replace the TFT backplanes currently used to turn on pixels on a color LCD.

The printed organic electronics (POE) process could lower the cost of LCD panels by two orders of magnitude, said Robert Street, a senior fellow at Xerox's Palo Alto Research Center.

POE makes plastic ICs at a fraction of the cost of amorphous silicon, and could pave the way for roll-up TVs or 8x11-inch electronic paper, Xerox said. The discussion of printed transistors - part of a recent corporate-wide technology showcase - also included rollouts of MEMS and graphics controllers, as well as elaborations on electronic paper and the JPEG-2000 image-processing standard.

The printed transistors are made with 2G liquid-crystal material that contains polarizing metals. The material can be provided as a powder or colloidal suspension, Street said. While their line widths - upward of 100?m - cannot approximate those of transistors etched in amorphous silicon, the plastic transistors can be constructed in minimal clean-room environments with less than Class 100 processing capability. Their large size, moreover, does not detract from the transistors' utility in display applications, the company said.

The devices themselves have characteristics suitable for LCD or organic LED drivers, as well as smart cards or RFID tags, according to the company. The ratio between current on-and-off settings is in the million-to-one range. Charge mobility is on the order of 0.12 cm2 per V-s, Street said.

Xerox's MEMS development includes both micromirrors for optical signal switching and "fluidic" devices for ink jet deposition. The optical switching devices - useful for DWDM - were developed initially for laser printers, said Joel Kubby, technical manager for MEMS research at Xerox's Wilson Research Center. The optical MEMS device, which Kubby called an "add-drop mux," is said to have enough resolution to serve as a color switch in optical communications.

- Stephan Ohr

EE Times

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