See-through circuits speed up

December 15/22, 2004

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 electronics, however.

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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