The Silicon Valley in California is still the most important high-tech location in the world. Semiconductor manufacturers, electronics and computer companies as well as innovative start-ups have settled in the Santa Clara Valley not far from San Francisco since the 1970s. The name of the region is based on the basic material for classic microelectronics and every computer, the semiconductor silicon. But the classic semiconductors have grown up in competition in the past few years: organic molecules with semiconducting properties. These materials enable applications that are not possible for brittle and rigid silicon and related substances such as germanium and gallium arsenide: large and flexible screens and photovoltaic components, intelligent labels and textiles or sensors,that adapt to the skin.
Semiconducting plastics were first examined more closely when Silicon Valley was just picking up speed. They have long since left the laboratory stage and can be found in many applications. Organic light emitting diodes (OLEDs) and organic solar cells were the first commercial products. Like silicon, organic semiconductors, which are made up of several doped layers, can convert light into electrical energy or electrical energy into light. The mechanism is the same: photons generate electrons and positively charged holes in the material and vice versa. However, what the organic components have ahead of their inorganic counterparts: They can be applied quickly and cheaply as a thin layer on large surfaces. Glass, foil, paper and textiles come into question.This has made new applications possible, such as rollable light sources or transparent solar foils that can be stuck to window panes and thus used as power sources.
Fast organic electronics for new display technology
At the Technical University of Dresden, the properties of organic semiconductors and their possible applications have been intensively researched by, among others, the work group around Karl Leo.
The research activities have meanwhile made a number of spin-offs possible.
Karl Leo, who recently received the European Inventor Award from the European Patent Office for his life's work, likes to speak of "Organic Valley" when he means the Dresden Elbe Valley - with 17 research institutions and around 40 companies, the location is the largest cluster for organic electronics in Become Europe.
A research focus at the TU Dresden is currently on the central component of microelectronics, the transistor. Conventional computer chips made of silicon have an unmatched integration density: Billions of transistors are etched in the form of extremely fine structures in silicon wafers. The electrons move in vertical channels that are only a few nanometers wide. "This miniaturization makes little sense with plastic, since the strengths of the material lie in other areas, namely where flexibility is required, transparency or biodegradability," says Leo.
One of the decisive factors for the performance of each transistor is how quickly it can switch back and forth between two states. The classic components achieve switching rates of a few gigahertz. Leo and his colleagues have been able to increase this value enormously for organic transistors in recent years. This is thanks to a new concept based on a vertical structure. The components of the transistor - collector, base and emitter - are stacked one on top of the other, and the electrons flow vertically through the substrate. This architecture takes advantage of typical manufacturing processes - thin films of various organic substances are vapor-deposited or printed on. This leads to short vertical channels in which the charge carriers flow.In this way, the Dresden researchers recently succeeded in achieving very high switching frequencies of up to 100 megahertz and increasing the mobility of the charge carriers. As the researchers report in “Nature Communications”, they were able to link the transistors to form logic gates - the elementary circuits of every microprocessor.