An organic transistor for all purposes

Friday, 29 March, 2019

An organic transistor for all purposes

Transistors are everywhere — from mobile phones to fridges and planes — but they often operate only within a restricted current range. Now, physicists at Ludwig-Maximilians-Universität München (LMU) have developed an organic transistor that functions perfectly under both low and high currents.

Transistors are semiconductor devices that control voltage and currents in electrical circuits. To reduce economic and environmental costs, electronic devices must become smaller and more effective. This applies above all to transistors.

In the field of inorganic semiconductors, dimensions below 100 nm are already standard, but organic semiconductors have not been able to keep up — and their performance when it comes to charge-carrier transport becomes considerably worse. But organic structures offer other advantages: they can easily be printed on an industrial scale, the material costs are lower, and they can be transparently applied to flexible surfaces.

LMU’s Professor Thomas Weitz, a member of the Nanosystems Initiative Munich, and his team are now working intensively on the optimisation of organic transistors. Writing in the journal Nature Nanotechnology, they describe the fabrication of transistors with an unusual structure, which are tiny, powerful and above all versatile.

By carefully tailoring a small set of parameters during the production process, the researchers have been able to design nanoscale devices for high- or low-current densities. The primary innovation lies in the use of an atypical geometry, which also facilitates assembly of the nanoscopic transistors.

“Our aim was to develop a transistor design which combines the ability to drive high currents that is typical of classical transistors with the low-voltage operation required for use as artificial synapses,” said Prof Weitz. With the successful assembly and characterisation of vertical organic field-effect transistors with exactly selectable dimensions and an ionic gating, this goal has now been achieved.

Potential areas of application for the new devices include OLEDs and sensors where low voltages, high ON-state current densities or large transconductances are required. The researchers are particularly interested in possibly deploying the transistors in so-called memristive elements.

“Memristors can be thought of as artificial neurons, as they can be used to model the behaviour of neurons when processing electrical signals,” said Prof Weitz. “By fine-tuning the geometry of a memristive device, it could be applied in a variety of contexts, such as learning processes in artificial synapses.”

The researchers have already submitted a patent application for the device to enable them to develop the new transistor architecture for industrial use.

Image credit: Christoph Hohmann, Nanosystems Initiative Munich (NIM).

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