Organic transistors reach nanometer dimension, switch high currents

March 22, 2019 //By Christoph Hammerschmidt
Organic transistors
Semiconductor devices made of organic materials (aka printed electronics) today have some disadvantages: Because their structures are very large, it is not possible to implement complex circuits in a small space. And they cannot switch any significant currents. A team of scientists from the Ludwig Maximilian University in Munich (LMU) has now developed an organic transistor that no longer has either of these disadvantages.

Conventional electronic components made of silicon have standard structure sizes far below 100 nanometers; the most modern circuits today have structures of 7 nm. Organic semiconductors are not yet able to keep up with this because their performance in terms of charge transport is significantly lower. At present, their strengths lie in a different area: organic semiconductor components can be printed on a large scale, material costs are low and they can be applied transparently to flexible surfaces such as films. A working group led by Professor Thomas Weitz of the Ludwig Maximilian University Munich (LMU), which is dedicated to the optimization of organic transistors, has now presented transistors that are in contrast to typical organic transistors, very small, powerful and adaptable due to their design. For example, a few parameters can be used in manufacturing to control whether the semiconductor should be optimized for high or low current densities. The special feature is an atypical geometry, which also makes it possible to produce the nanoscopically small transistors more easily. While the channel length of typical organic transistors today is greater than 1 micrometer, Weitz succeeded in reducing this characteristic parameter to 40 nanometers.

But Feature Size is not an end in itself. The scientists' goal was to develop components that combined two tasks: On the one hand, the ability to function as classical transistors at high currents and, on the other hand, to operate at low currents. The new organic transistors achieve current densities of up to 3 mA/cm2. "Similar current densities are also achieved in highly integrated commercial Si transistors," explains Weitz. "What is new here is that the very high current densities can now also be driven with organic transistors and in 40 nm short channels for the first time," says the scientist.

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