See-through displays and electronic paper
require semiconductor devices that are transparent and flexible. Today's
transparent semiconductors are not nearly as fast and durable as traditional
Researchers from the Tokyo Institute of Technology have moved
transparent semiconductors forward with an indium gallium zinc oxide mixture
that can be deposited on plastic, is transparent, and potentially performs
one to three orders of magnitude better than today's plastic transistors.
The material is also easy to manufacture, making it potentially
inexpensive and appropriate for large-area electronics like large displays.
It can be applied in a very thin coating to a sheet of plastic at room
temperature. The manufacturing process is also environmentally friendly,
according to the researchers.
The semiconductor could eventually be used in many types of flexible,
lightweight, shock resistant electronics, including flexible displays,
electronic paper, and wearable computers, according to the researchers.
The researchers produced an amorphous indium gallium zinc oxide
compound. Amorphous materials have randomly arranged atoms, while crystalline
materials have ordered atoms and polycrystalline materials consist of
microscopic grains of crystalline material. Amorphous semiconductors are
easier to use in electronics, but do not perform as well as crystalline
and polycrystalline semiconductors.
The researchers' semiconductor has a carrier mobility of 10 square
centimeters per volt second. Carrier mobility is a measure of how readily
electricity moves through a material. Plastic semiconductors have carrier
mobilities as high as 1 square centimeter per volt second, amorphous silicon
has a carrier mobility of 1 and, crystalline silicon -- the stuff of computer
chips -- has a carrier mobility of 1,500.
The transparent semiconductor could be used practically in two
to four years, according to the researchers. The work appeared in the
November 25, 2004 issue of Nature.
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