Credit: Christoph Hohmann, Nanosystems Initiative Munich (NIM)

In the field of inorganic semiconductors, dimensions below 100 nanometers are already standard. However, organic semiconductors have not been able to keep up. In addition, they have poorer performance for charge-carrier transport. 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.

Thomas Weitz, a professor in the Ludwig-Maximilians-Universität München (LMU) Faculty of Physics and a member of the Nanosystems Initiative Munich, and his team are working intensively on the optimization of organic transistors. They have described the fabrication of transistors with an unusual structure. By carefully tailoring a small set of parameters during the production process, they 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.

Their aim was to develop a transistor design that combines the ability to drive high currents typical of classical transistors with the low-voltage operation required for use as artificial synapses. With the successful assembly and characterization of vertical organic field-effect transistors with exactly selectable dimensions and 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. Of special interest is their possible use in so-called memristive elements. “Memristors can be thought of as artificial neurons, as they can be used to model the behavior of neurons when processing electrical signals,” explains 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 submitted a patent application for the device to enable them to develop the new transistor architecture for industrial use.