Plastic mix promises big displays

By Eric Smalley, Technology Research News

Big city newcomers can be overwhelmed by a blur of shapes and colors as buses, trolleys and delivery trucks wrapped in photo-quality advertising images whiz by. Imagine how much more disorienting the experience would be if the vehicles sported giant video displays.

There's a long way to go from today's flatscreen technology to something that can be painted on a large surface, but researchers at Philips Research Laboratories and Eindhoven University of Technology in the Netherlands have taken a big step in that direction.

Liquid crystal displays (LCDs) are usually made by sandwiching liquid crystals between two carefully positioned sheets of glass. Liquid crystals are long, randomly arranged molecules that line up in crystal-like order in the presence of an electric field. The molecules reflect light differently when they are ordered and disordered, which allows them to form pixels in a display.

The researchers have come up with a method for layering liquid crystals on a single surface of glass, plastic or silicon.

Because there's only one substrate rather than a sandwich of two, the displays can be very thin. "The single-substrate technology reduces the thickness of the display [to] smaller than 0.5 millimeters," said Dirk Broer, a research fellow at Philips Research Laboratories and a professor of polymer chemistry at Eindhoven University of Technology.

The process could lead to displays that are larger, thinner and more flexible than today's screens, said Broer. "It opens ways to make portable equipment smaller, [lighter] and more robust," and to make displays large enough to cover walls, he said.

To make the single-substrate screen, the researchers spread a liquid blend of plastic and liquid crystals onto a surface containing a grid of electrodes. The electrodes produce the electric field necessary to power individual pixels. The researchers then used two types of ultraviolet light to harden the plastic in the blend, forming a covering to contain the liquid crystals.

The researchers formed plastic walls on the substrate by shining 400-nanometer wavelength light in a grid pattern. Then, to form a top coat of plastic, they shined 340-nanometer light on the whole assembly. The end result was a grid of 500- by 500- by 10-micron boxes that contained the liquid crystal. Five hundred microns is about the diameter of a period-size dot. The grid walls were 100 microns thick and the cover layer 10 microns thick.

The researchers' prototype display takes 5 to 40 thousandths of a second to switch a pixel on and off and produces images with a contrast ratio of 1 to 20, according to Broer. Typical commercial LCDs have comparable switching times that range from 10 to 200 milliseconds, but better contrast ratios of at least 1 to 200, which result in clearer images and more vibrant colors.

The researchers' next steps are to improve the contrast ratio and brightness of the display and develop pilot production lines, said Broer. They are also working on using substrates with thin film transistors in order to use active matrix addressing, he said. Active matrix addressing systems are faster, enabling displays to show video.

The process could be used to make simple displays in two to five years, said Broer. The LCD process might never come to market if an alternative technology, organic light emitting diodes (OLEDs), matures sooner, he said. OLEDs could lead to displays made entirely out of sheets of plastic.

Broer's research colleagues were Roel Penterman, Stephen I. Klink, Henk de Koning and Giovanni Nisato of Philips Research Laboratories. They published the research in the May 2, 2002 issue of the journal Nature. The research was funded by Royal Philips Electronics.

Timeline:   2-5 years
Funding:   Corporate
TRN Categories:   Materials Science and Engineering
Story Type:   News
Related Elements:  Technical paper, "Single-substrate liquid-crystal displays by photo-enforced stratification," Nature, May 2, 2002


May 15/22, 2002

Page One

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Laser bridges infrared-microwave gap

Plastic mix promises big displays

Laser patterns particles in 3D


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