There was a flurry of excitement last week at SID when it seemed as though LG Display was announcing a roll-to-roll process for fabricating thin-film transistors for LCD backplanes. That initial excitement resulted, in part, because the title of a technical paper and the headline on a press release incorrectly labeled the technology as "roll-to-roll" printing. It isn’t, Eun Hee Jeong, Assistant Manager of LGD’s Product Planning Team, assured me, but it’s pretty exciting nonetheless.

Ken Werner
Senior Analyst and Editor

Rather than being roll-to-roll printing, this is printing with a roller onto a flat bed - or "roll" printing, which is how it was described in the technical paper and on posters in the booth. Five layers are used for the TFT.

Six-micron patterns are possible, and 85 ppi was demonstrated on a 15-inch prototype in LGD’s booth. This is a resist printing process, with the photoresist printed first, and the functional materials then deposited through printed windows in the resist, and the excess material removed. Conceptually, the process is similar to traditional photolithography, but with resist printing replacing photolithographic patterning, which is an attractive substitution by itself.

But things will get even more interesting in the next generation, when functional materials will be printed directly where they are wanted, and the resist will not be needed. The present version of the process delivers TFT performance that is the same as that produced by conventional TFT fabrication, Jeong said.

The LGD booth at SID contained a 15-inch XGA TN-LCD with TFTs made by the resist printing process (bottom of photo), along with a 15-inch XGA S-IPS LCD with traditional TFTs but with the CF made by the roll printing process (top of photo).

Novel ways of making LCD backplanes and color filters were a recurring them at SID. To learn more, see the June issues of Large Display Report and Mobile Display Report.