Since 2007, there are 11 inch TVs and mobile phones labeled organic EL on market. These use the principle of electroluminescence i.e. lighting by passing charge carriers through very thin films of organic dyes as semiconductive materials. Compared to liquid crystal displays (LCD) and plasma display panels (PDP), the screens are much thinner (the thinnest part is 3 mm thick), and the images are clearer (excellent color reproducibility and high contrast ratio of over one million fold), and sharp (fast response time of microseconds). Devices with these characteristics were possible with the use of organic material which is essentially the same as coloring pigments used in paintings and decorations.

There are some organic materials that allow the flow of electricity. These are materials that have been developed from the achievements of the research by which Hideki Shirakawa, professor emeritus at the University of Tsukuba, won the Nobel Prize in Chemistry in 2000. When these materials were first discovered, the electrical characteristics (charge carrier mobility) were as low as 10,000th to 1 millionth of that of inorganic semiconductors as silicon. Recently, however, materials such as single crystals of organic compounds of condensed benzene rings (as pentacene and rubrene) have been found which have the same level of mobility as polycrystalline silicon. Various conductive polymer materials whose molecular structure is optimized for appropriate self-assembly have been also developed, which show mobility as high as that of amorphous silicon. Compared to silicon, these new materials are soft and do not break when dropped, and in fabrication, unlike lithography that needs vacuum chamber and many time-consuming processes, they can be printed to form a film in one lot on a large surface, and there are high expectations for such organic devices.

Here are presented materials and processes to make such devices as organic thin film transistor (TFT) and memories by forming a film of dielectric polymers and organic semiconductors on plastic sheets.

With electronic devices as transistors, not only semiconductors but various materials are needed, such as wiring, electrodes, dielectric material for condenser (capacitor), and insulating material for layer insulation. These various members are made into ink, and are used to form a fine pattern by ink jet printing and screen printing methods. With conductive and insulating materials, it is necessary, however, to improve and stabilize the characteristics by sintering. To use flexible plastic sheets, the sintering temperature must be kept under 150 °C. We, at AIST, have succeeded in developing a special insulating ink that can be sintered at low temperatures, and also have successfully found a process to form wire patterns in low temperatures (Fig. 1).

Furthermore, there is a need to develop technologies to use these ink materials to form fine patterns in a large scale. First, patterns are formed on silicon wafer and glass surfaces using electron beam lithography. These master patterns are copied on silicone resin. Using this soft silicone rubber as a stamper, the patterns are printed in the various types of above-mentioned ink. This technology was made public as soft lithography or micro-contact printing by Whitesides et al. of Harvard University in 1991, and drew world-wide attention. However, although it made formation of fine patterns of several tens nm possible, it was not practical as the printable surface area was less than 1 inch square. We, at AIST, in collaboration with private companies, have improved this technology under the "Technological Development of Superflexible Display Components Project (2006-2009)" of New Energy and Industrial Technology Development Organization (NEDO). We were successful in printing thin lines (L/S: 2 µm) and words (AIST line width: 1 µm) all over a 6 inch square surface (Fig. 2).

With the fusion of these ink parts and nano-printing technology, there is an expectation for an organic device that can be made by printing (Fig. 3).