Electronics hot off the press
It is a customer's utopia: no more waiting in supermarket queues. Scientists want to make it a reality with the help of radio tags that are printed like a logo onto the merchandise, such as a yoghurt container. The vision is this: as the customer passes a product barrier, the articles in the shopping trolley are all registered and the total is automatically deducted from the customer’s debit card.
To translate this vision into reality, researchers need to find a way of putting electronic circuits onto paper or plastics, and are searching for conducting and semi-conducting chemicals that can be printed using traditional technologies such as ink-jet, relief, gravure or flexo printing.
They use a variety of different materials: conducting polymers, metallic nano particles, semiconductors made of organic or inorganic materials. Yet all these materials must live up to high standards, as they will be exposed to environmental stress and must retain their electric qualities. TU Darmstadt is actively working on the field of printed electronics. Together with Darmstadt-based chemical company Merck and BASF Ludwigshafen, TU Darmstadt researches various materials for printed electronics in the “Forum Organic Electronics” cluster of excellence, financed by the Federal Ministry of Education and Research. Jointly with Merck, TU also operates a research laboratory for printed electronics, the “MerckLab”.
At the MerckLab, researchers develop inorganic materials suitable for various uses in a printed electronic component, such as conductor paths, semi-conducting materials or insulating material.
To do this, they dissolve materials in liquids of low or high viscosity in order to test them in different printing procedures. Researchers use laboratory printers, hardly larger than a multi-function office appliance, to find out which printing technology works best. One benchmark is whether conductor paths can be printed very densely in high resolution, as this enhances the performance of the component.
Once they have chosen a technique, they test-print a single electronic component such as organic field effect transistors (FETs), which allow them to take initial electric measurements.
Learning from mistakes
Whether and how well an element with a printed component actually works is tested in the diagnostic lab. Researchers are not only interested in making printed components that function well; malfunctioning components are also of interest because they help optimise the printing process once a thorough analysis has revealed the underlying error. To do this, researchers at the various TU institutes and departments have a vast arsenal of analytical tools at their disposal, such as the electron microscopes in the Department of Materials Research.
Defects and structural errors are then analysed. Finding out, for example, that a printed surface is too rough provides MerckLab researchers with clues as to how they can further improve their materials.
If, after several optimisation cycles, a material proves suitable for printing electronic components, it will be tested under near-industrial conditions and on a larger scale on a Heidelberger Druckmaschinen production printer at the Institute of Printing Science and Technology. This machine, that is about 10 metres long, is capable of printing thousands of electronic components onto sheets of paper or plastic that come rolling off reels as in newspaper printing – a veritable mass printing technique.