This article appears courtesy of Mobile Computing and Communications magazine and Emap-Petersen.

Sharp Electronics Corp. of Mahwah, NJ, has introduced an LCD panel that uses plastic instead of glass. While the substitution may sound simple, chemical processes had to be radically changed to make the LCD panel possible. Expect plastic LCD panels to show up first in cellular phones and pagers; appearances in small notebooks might follow.

"The key is weight - and durability," said Joel Pollack, vice president of display products at Sharp Laboratories of America of Camus, WA. The use of plastic in place of glass provides a tenfold savings in weight, making it practical for use in cellular phones and personal digital assistants (PDAs) - which must be lightweight to sell.

But using plastic also makes active-matrix technology impractical, because the complex manufacturing process requires temperatures well above the melting point of plastic, Pollack notes.

In some ways, the construction of a plastic LCD screen is much like that of its TFT counterpart. A polarizing filter is bonded to a plastic layer, but the side that faces the liquid crystal must be treated with a passivation layer, which acts as a chemical shield and keeps the plastic and liquid crystal from contaminating each other.

Next comes a layer of indium tin oxide, which conducts electricity. This layer is etched to make columns and rows that act as the screen's electrodes. Passing a current through the indium tin oxide is what changes the alignment of the liquid crystal so it blocks outgoing light, thus creating the images on the screen.

The crucial component in this scheme is the passivation layer. Prototypes of the plastic LCD screen several years ago used a very expensive plastic. Once engineers found a less expensive alternative, the chemical used for the passivation layer had to be reformulated in order for it to work well with the cheaper plastic.

That problem was licked recently, Pollack says. Sharp began making its new plastic LCD panels late last year, and the company expects the products to make their way to the OEM market during the first quarter of this year.