IN THE movie Superman, the Man of Steel discovers why he was
jettisoned from the doomed planet Krypton by watching a video message stored on
a transparent crystal. Now, more than 20 years on, Japanese scientists are
working on a revolutionary new semiconductor that might one day be turned into
just this kind of gadget.
Computer displays made of the material will have all the image processing and
memory circuits invisibly buried in the screen itself, making them cheaper and
less power hungry than today鈥檚 displays.
A team led by Yuji Matsumoto of the Tokyo Institute of Technology (Titech) in
Yokohama were looking for a material that was both a semiconductor and a
permanent magnet, or 鈥渇erromagnet鈥�. They succeeded鈥攁nd were amazed to find
that the material is transparent as well.
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Best of all, the new material works at room temperature. 鈥淭his is a very
important step,鈥� says Hideo Ohno, a semiconductor physicist at Tohoku University
in Sendai. 鈥淚f it didn鈥檛 work at room temperature it would be no good for use in
everyday applications.鈥� Ohno and his colleagues have created a ferromagnetic
semiconductor of their own by mixing manganese into gallium arsenide. But their
material is opaque, and only works at a frigid 110 kelvin.
To produce magnetic semiconductors that can stand the heat, the Titech team
with colleagues from the National Institute for Research in Inorganic Materials
in Tsukuba turned to a technique called combinatorial chemistry. They carried
out thousands of tiny chemical reactions simultaneously in a vacuum, each with
slightly different ingredients. They then screened the products of the different
reactions en masse to see which had the best properties.
Matsumoto and his colleagues will soon report in Science that one of
the reactions produced a thin film of titanium dioxide doped with just under 8
per cent cobalt. This transparent material turned out to be both semiconducting
and permanently magnetic at room temperature. Using magnetic microscopy the
researchers found areas in the material where electron spins line up
spontaneously to produce magnetism.
The Titech researchers say they don鈥檛 know why the cobalt has this effect.
鈥淲e need to accumulate more data,鈥� says team member Hideomi Koinuma.
Ohno says the discovery is important in the emerging field of 鈥渟pintronics鈥�,
in which engineers hope to harness both the charge-carrying aspects of electrons
and their spin, which is the root of magnetism. Because the material is magnetic
parts of it could store data in much the same way as a computer hard drive. And
as a semiconductor, other parts could process information like the transistors
in a microchip.
Ohno says the material will most likely be turned into flat-panel displays
which have all their processing and storage circuits invisibly built-in.
鈥淐urrently, transistors in laptop displays absorb a quarter of the brightness of
the backlight. Transparent transistors could solve this.鈥�
