Japanese researchers develop method for printing single crystal thin-film transistors

Physorg.com

July 20, 2011

Researchers working out of the National Institute of Advanced Industrial Science and Technology (AIST) in Tsukuba, Japan have developed a means for printing thin film transistors using InkJet technology. The team describes the process in their paper published inNature.

To get around the problem of self-crystallization, inherent in other InkJet/transistor making processes, which result in spreading effects that make it difficult to print uniformly, the team instead chose to use a two step process, whereby one type of ink is sprayed first onto a substrate and is then followed by another immediately afterwards, directly on top of the first; the two then mix, creating an environment whereby one single crisp and sharp crystal grows and adheres to the material it is printed on.

The first ink applied is a liquid (anhydrous dimethylformamide) that holds a semiconductor but is not soluble. The second is comprised of an organic semiconductor in a solvent. After the first is sprayed onto the substrate, followed by a shot of the second, the two then mix naturally, and then, from a single point in the mixture a tiny crystal begins to grow, and keeps on growing until the entire pool of ink is consumed, resulting in a thin film (30-200nm thick) of C8BTBT affixed to the substrate. After printing a complete pattern with their new process onto a substrate, other components were added to complete the transistor.
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Additional Information:

• Position Control of a Transistor Source–Drain Junction with Sub-nanometer Accuracy

• Inkjet printing of single-crystal films