Carbon-based organic semiconductors have been a hot topic of research due to the promise they hold for high-performance electronics of the future. There have been several novel advancements related to carbon-based materials in recent years, including the development of small organic molecules with key electrical parameters almost as good as those of amorphous silicon.
Large-scale manufacturing has however been held back, since it is very difficult to deposit these small organic molecules in a stable, uniform film. Larger molecule polymer semiconductors, which are easier for making high-quality thin films, have limited semiconductor properties. This has created the need for a compromise between the two techniques.
One way of addressing the challenge is to blend the semiconductor molecules with the polymer. But typically, when this technique is employed, the bulk of the semiconductor molecules end up at the top of the film. Therefore, when field effect transistors are made with the blend, they work well only in the ‘top-gated’ structure, where the critical active part of the film is on the top, and the switching part or gate is layered atop that. This process is difficult to be carried out on a large scale with very high risk of destroying the fragile film.
Researchers from Seoul National University (SNU) and Maryland, US-based National Institute of Standards and Technology (NIST), have now developed a new technique that is said to address this challenge and finally open the door to large-scale manufacturing. The research team substituted a polymer with significantly higher molecular mass, which enabled the organic semiconductor’s small molecules to be distributed evenly at the top and bottom of the film.
This results in having an active region of the film on the bottom, which is critical for large-scale manufacturing. The technique enables the gate, source and drain to be laid down first, and allows the delicate film layer to be added afterward.
The researchers achieved the result by observing how the distribution of the small organic semiconductor molecules that are embedded in the polymer films changed with depth. As the films are less than 100 nanometres thick, the research team used a neutron imaging technique to observe the distribution with nanometre resolutions.
The results of this research could be significant because it allows for a new class of polymer-based semiconductors and for manufacturers to control the location and alignment of the components of the blend. According to the researchers, the optimised blend of polymer and organic semiconductors has better performance characteristics than the organic semiconductor alone.
The success of the researchers in moving the molecules from the top to the bottom would finally enable the design of practical large-scale manufacturing techniques for a wide range of futuristic applications. In particular, this would pave the way for the development of printable, flexible electronic displays such as a tabloid-sized ‘digital paper’ that can be folded into one’s pockets. Also, this work opens up the possibility of manufacturing huge sheets of photovoltaic cells using inkjet printing, which would render them very inexpensive.
For more information contact Patrick Cairns, Frost & Sullivan, +27 (0)21 680 3274, patrick.cairns@frost.com, www.frost.com
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