Optical microscopy image of printed organic thin film transistors etched in gold. Image: 2020 Kitahara et al.
Optical microscopy image of printed organic thin film transistors etched in gold. Image: 2020 Kitahara et al.

For around the past 10 years, the screens of smartphones and computers have been based on a display technology composed of so-called thin film transistors. These are inorganic transistors that require very little power and so have found widespread use. But they do have some limits that researchers have been busy trying to overcome.

"We explore new ways to improve upon thin film transistors, such as new designs or new methods of manufacture," said Gyo Kitahara, a PhD student in the Department of Applied Physics at the University of Tokyo in Japan. "Organic thin film transistors, for example, have a bright future in LCD screen devices. Compared to the inorganic kind currently used, we expect the organic kind to be useful in low-cost, large-area, lightweight and wearable electronic products, especially by using printing-based production technologies."

The concept of organic thin film transistors is not new, but the ability to print such devices, which would allow for a design revolution, has eluded industry and academics – until now. Kitahara and his colleagues have come up with a way to print organic semiconductor films, the basis of these transistors, on a special surface that is highly solution-repellent, or lyophobic. They report this novel method in a paper in Science Advances.

Ordinarily, lyophobic surfaces would repel the materials used to print the structure of the transistor, which raises the question of why such surfaces would be useful at all. But lyophobic surfaces can help create transistor structures that are finely tuned for high performance. So how did the researchers overcome their repellent nature?

"We made use of a fluidic property you probably see every time you wash your hands with soap," explained Kitahara. "Soap bubbles can hold a shape by lowering the surface tension of liquid. We presume that the soap-film mechanism should be effective for formation of a thin liquid layer on lyophobic surfaces in spite of the repellent forces. Solid semiconductor films can be formed and grown via the formation of thin liquid layers during the printing processes."

With the hurdle of how to print organic transistors now overcome, other researchers can build on the team's findings and find ways to scale this method up. With a proliferation of large, flexible or wearable devices, Hasegawa's team envisages a convergence between the real world and the virtual world in ways never seen before.

"After having experimented by trial and error, we eventually found that the use of a special U-shaped metal-film pattern seems to be effective for uniform film growth thanks to the way it creates a thin liquid layer on lyophobic surfaces," said Kitahara. "We anticipated the results beforehand to some extent, but the success of these findings was finally demonstrated and obtained after overcoming several difficulties, which brought great pleasure and happiness to me."

This story is adapted from material from the University of Tokyo, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.