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Inkjet Printing Method for Thin Film Transistors Developed in Japan

Monday, December 12th, 2011

In a recent Nature publication, Japanese researchers from The National Institute of Advanced Industrial Science and Technology (AIST) in Tsukuba, have described an innovative technique they have been working on – printing thin film transistors with InkJet technology. This research has lead to a completely new product that works on flexible substrates. Typically, printers with large-footprints use silicon-based products. This increases the costs of production. Hence, with innovative methods such as using a room temperature process along with flexible displays, large sheets of sensors as well as electronic paper and solar cells, production costs are being lowered.

New Inkjet Printing Technique

The research team has introduced a technique to perform the anti-solvent crystallization with inkjet printing to produce organic semiconductor thin transistors. It was initially difficult to produce uniform semiconducting thin film due to movement of tiny particles in the solvent during evaporation, resulting in a coffee ring-like formation, or self-crystallization.

However, researchers have now introduced a two-step process to overcome the earlier performance levels of inkjets. With this new method, a single crisp and sharp crystal formation begins at a single point and consumes all the ink even as it adheres to the thin film.

This method uses two inks – first, anhydrous dimethylformamide, an insoluble ink with the semiconductor, is sprayed. The second ink with the organic semiconductor solvent is also sprayed over the first layer. As these two inks mix naturally, a thin film of C8BTBT is affixed to the substrate. The solvent evaporates slowly, resulting in the thin film formation. The mixture begins to form at a single point where a tiny crystal grows and consumes the entire pool of ink, resulting in a film which is 30-300nm thick. The research team used a piezoelectric inkjet printing machine, which had double printing heads that eject droplets of 60 pl at a frequency of 500 Hz.

High Performance Transistors

Researchers have developed a method of combining a technique of anti-solvent crystallization with inkjet printing to produce organic semiconducting thin films of high crystalline formation. The mixing of the anti-solvent and a solution of the semiconducting component on the amorphous substrate triggers the controlled formation of exceptionally uniform polycrystalline thin film that develops at the liquid air surface interfaces. The average carrier motilities of the thin film transistors is high, at 16.4 cm 2V-1s-1.

This technique establishes a considerable step towards the use of high-performance single-crystal semiconductor devices for flexible electronics applications. Single crystal interfaces show the highest performance with their nearly perfect transitional symmetry and immensely high chemical purity.

The Future of InkJet Spraying Technology

Researchers believe that this new technique is a stepping stone for their further development of transistors that are made entirely from InkJet spraying technology to produce all printed electronic products. This technology ensures faster and better quality of printing, higher symmetry of printing and is maintained by a very high chemical purity.

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