Walls and curtains
could sport liquid-crystal digital displays. 2 May 2002
One layer LCDs could
lead to smaller, cheaper, lighter gadgets.
Homes of the future could change their wallpaper
from cream to cornflower blue at the touch of a button, says Dirk Broer. His
team has developed paint-on liquid crystal displays (LCDs) that offer the
technology.
Liquid crystals are peculiar liquids: their
molecules spontaneously line up, rather than being randomly orientated as in a
normal liquid. Passing a voltage across the molecules switches their alignment,
blocking the transmission of light so a display changes from light to dark.
Current LCDs on digital watches, mobile phones
and laptops sandwich the crystal between heavy glass plates. The complicated
production process is time-consuming, expensive and restricts the size of
screens to just 1 metre square.
Broer and his colleagues have devised a new
open-sandwich technique that instead deposits a layer of liquid crystal onto a
single underlying sheet. Working at Eindhoven University of Technology and
Philips Research Laboratories in the Netherlands, Broer's team has already
produced prototypes on glass and plastic; fabric could be next.
The technique could create giant TV screens,
digital billboards and walls that change colour. Slim, plastic LCDs sewn into
fabric could display e-mail or text messages on your sleeve. "It depends
what future societies want," says Broer.
The technique should feed people's thirst for
smaller, cheaper gadgets. Conventional glass LCDs now make up an increasing part
of a laptop's weight - plastic versions could change that, says Peter Raynes,
who studies LCD technology at the University of Oxford, UK.
Crystal glazing
Broer's team made the LCD paint by mixing liquid
crystal with molecules that link together into a rigid polymer when exposed to
ultraviolet. In a two-stage process they effectively build tiny boxes holding
the liquid1.
Don't expect to buy a watch featuring one of the new
displays in the next six months
Peter Raynes, University
of Oxford, UK
They coat a glass or plastic base with a thin
layer of the LCD paint and mask out squares so that a blast of ultraviolet forms
a grid of walls. When they remove the mask, a second exposure - at a wavelength
that does not penetrate the whole liquid layer - seals over the boxes with a
lid.
Standard LCDs, which are divided up into pixels,
turn dark when a voltage crosses between electrodes on the two glass plates. The
new displays instead pass voltage between two points on the same plate. Colour
LCDs fit each pixel with red, green and blue colour filters.
"Don't expect to buy a watch featuring one
of the new displays in the next six months," warns Raynes, however. He
cautions that the technique needs work: compared with glass, the thin outer
layer may be more easily penetrated by oxygen or water that degrade the crystal.
