Layers promise cheap circuits

Many research teams are working on making practical organic transistors because they can be used in flexible and transparent electronics like displays and because they are potentially very inexpensive. The challenge is making organic transistors that work well electronically.

Researchers from the University of California at Los Angeles have moved organic transistors forward with a device whose structure is vertical rather than horizontal like most transistors.

The structure makes for transistors with a working voltage of less than 5 volts and an electrical current output of 10 milliamps. Horizontal organic transistors have working voltages as high as 100 volts and current outputs measured in microamps, or millionths of an amp.

The prototype vertical organic field effect transistor consists of thin stacked layers, with a layer of carbon C60 molecules as the organic semiconductor channel that regulates the flow of electricity. The device's low voltage and high output are the result of its short channel length and large channel area, according to the researchers.

Organic transistors made this way could eventually be used in active matrix displays, and have the potential to enable large, inexpensive screens.

The researchers demonstrated the transistor driving an organic light-emitting diode. The transistor can be switched in less than a millisecond; smaller prototypes will be faster, according to the researchers.

The vertical transistors could be used in practical applications in two to five years, according to the researchers. The work appeared in the November 22, 2004 issue of Applied Physics Letters.