Plastic Displays

Polyester may be the material of choice for future flat panel displays. Researchers in the U.S. have recently made breakthroughs in developing thin film transistor displays out of polyethylene terephthalate (PET) - a thin, flexible and rugged plastic that you can bend, roll up, fold, or bend into practically any shape you need.

How do you coax a seemingly inflexible, delicate display to perform such acrobatics? The answer is in the roll to roll technique, a process for manufacturing thin film transistors (TFTs). Conventional TFTs are manufactured onto a rigid glass substrate, but the new technique calls for making the transistors on flexible plastic. In fact plastic displays can be manufactured in much the same way that potato chip bags are produced, in which a giant sheet is spooled onto a machine that prints the packaging and cuts the material into individual chip bags.

In manufacturing displays, the plastic would be spooled through a machine, transistor circuit layers would be deposited onto the material, etching processes would produce patterns to form the pixels, and the display would then be cut to size.

Technical challenges still remain. This type of process of making semiconductors doesn't exist yet. The concept holds promise not only for a new generation of ultralight, flexible displays but also for cost savings. Since manufacturing plants will need to be retooled for the roll to roll process, startup costs will be substantial. But the potential for cost savings in the long run because of cheap plastic and mass production techniques is also significant.

The real technical challenge though, is a matter of heat. In conventional TFT production, temperatures reach up to 350 degrees Celsius, hotter than plastic can withstand without deforming. The Lawrence Livermore group, funded by DARPA's High Definition Systems Project recently built high performance transistors at or below 100 degrees Celsius by using a short burst of light lasting 35 nanoseconds to produce the polycrystalline silicon (polysilicon).

Meanwhile, Philips Semiconductors Lab in Red Hill, Surrey, England, is also making headway in developing plastic displays. Its recipe calls for making polysilicon transistors on plastic by baking the plastic first, so that the heat used in the transistor production process doesn't cause expansion.

Although mass production of plastic displays is five years away, they could be used in all sorts of ways. The applications could include notebook and desktop displays, video game machines, and hand held appliances, as well as displays that don't exist now, for example, wrap around simulators, roll up displays, wearable displays sewn into clothing, and paper thin electronic books and newspapers. E Ink, based in Boston, is currently developing an ultrathin electronic book based on plastic technology.