Japanese scientists have worked out how to make an inkjet printer produce high-performance transistors.
Credit: Veer Images
LONDON: Inkjet printing techniques have produced high-performance, single crystal, thin film transistors for use in printed electronics, according to a new study.
The field of printed electronics offers great hope for low-cost production and manufacture of large-area and flexible electronics. But current printing processes result in poor crystallinity and low performance, limiting electronic properties.
Now, scientists in Japan have come up with an inkjet-printing process that involves combining two solutions on top of a substrate to achieve semiconducting thin films that have exceptionally high and uniform crystallinity. They hope the technique will lead to improvements in the manufacture of flexible displays, flexible solar cells, e-paper and large-area sensor sheets.
"The method enables the controlled formation of exceptionally uniform single-crystal or polycrystalline thin films that grow at the liquid-air interfaces," said Tatsuo Hasegawa from the National Institute of Advanced Industrial Science and Technology, author of the paper published in Nature this week. "The film quality and thickness profiles are strikingly different from those obtained by the conventional printing methods."
Solving the disarray problem
The printing process involves layering electronic ink, made up of semi-conductor solutions, on top of one another to form thin film transistors (TFT's).
Most semi-conducting materials in current use form disarrayed patches of varied thickness during the inkjet printing process, resulting in products that lack uniformity and quality.
But scientists have now found a way to overcome this problem by combining a semi-conducting material in its solvent with a solution in which the semi-conductor cannot dissolve - an anti-solvent. When combined on top of a substrate these result in the controlled formation of single-crystal semi-conducting thin films.
Improved organic semiconductors
The semi-conductor and anti-solvent are used as separate inks printed arbitrarily on top of a substrate to then mix on top of the substrate sheet to form a uniform thin film.
The group used organic semiconductors which until now have been unable to compete in terms of performance with widely used inorganic materials such as silicon, which are not printed and are commonly used in LCD flat panel screens.
"Since Silicon TFT's are really cheap to make, it is not commercially competitive to fabricate printed electronics with a [worse] performance, unless [they are] for some niche applications," said photonics expert Daping Chu from the University of Cambridge.
Printing electronic metal wires
"This work is the first time people have applied anti-solvent crystallisation for printed semiconductor materials and the results obtained are excellent, especially for organic TFTs," said Chu. "I am sure there will be many research investigations to follow this work, and even development work for commercial applications."
The findings have a wide range of future applications in electronics, according to the researchers. "This printing technique constitutes a major step towards the use of high-performance single-crystal semiconductor devices for large-area, light-weight and flexible electronics applications such as flexible displays, flexible solar cells, e-paper and large-area sensor sheets," said Hasegawa.
"The next step is to integrate the technique for printed electric metal wires, and then produce all-printed electronic products".
