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 in Nature.

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.

Researchers are looking at InkJet sprayed transistor technologies in the hope that it could lead to a whole host of products that are based on bendable substrates, such as flexible displays, solar cells, large sheets of sensors, or true ePaper, and because it would offer a lowered cost of production compared to traditional silicon based products.

The authors say their new method offers exceptionally uniform creation of the crystals, a development that could lead InkJet sprayed technology out of the lab and into real world products. The team next plans to look into whether their new technique could also be used to create metal wires which would allow for a transistor to be made entirely from InkJet spraying technology.

Source: PhysOrg