Metals speed clear circuits

Electronic devices that are fast, flexible, transparent and sturdy require transistors that share these traits. Today's computer chips contain millions of transistors arranged to form the logic gates that carry out computing.

Researchers from Oregon State University and Hewlett-Packard Company have improved the performance of a new type of transparent transistor. The zinc tin oxide thin-film transistor is transparent, difficult to scratch, and conducts electricity an order of magnitude faster than previous efforts using the same class of material.

The thin-film transistors could eventually be used in electronics that are low-cost, transparent, and/or cover a large area, including giant screens, transparent switches, smart windows and solar cells, according to the researchers.

The researchers' transistors have carrier mobilities of 5 to 50 square centimeters per volt second. Carrier mobility is key measure of how well a transistor conducts electricity. The relatively inexpensive amorphous silicon and more expensive polycrystalline silicon thin film transistors commonly used in displays have carrier mobilities of 1.5 to 2, and 100 to 200 square centimeters per volt second, respectively.

The researchers' material is one of a class of materials that could be used in similar applications, according to the researchers. Amorphous metal oxides are inexpensive, can be processed at low temperatures, and the resulting film has a very smooth surface.

The researchers' prototype was processed at a relatively low 300 degrees Celsius. Recent experiments show that it may be possible to fabricate devices at 50 degrees Celsius, according to the researchers. Low temperature processing enables more types of surfaces to be coated with the material, and the smooth surface makes it much easier to coat with other layers of materials.

The transistors could be ready for commercial use in two to five years, according to the researchers. The work appeared in the January 3, 2005 issue of Applied Physics Letters.