IISc scientists develop super flexible composite semiconductors for next-gen printed displays

BENGALURU: Scientists at the Indian Institute of Science (IISc) have developed a super flexible, composite semiconductor material that can have possible applications in next-generation flexible or curved displays, foldable phones and wearable electronics.

Traditional semiconductor devices -- such as transistors that are used in display industries -- are either made of amorphous silicon or amorphous oxides, both of which are not flexible and strain tolerant at all. Adding polymers to the oxide semiconductors may increase their flexibility, but there is a limit to how much can be added without compromising the semiconductor's performance, the IISc noted.

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In the current study, published in journal 'Advanced Materials Technologies', the researchers of the premier institute's department of materials engineering have found a way to fabricate a composite containing a significant amount of polymer – up to 40 per cent of the material weight – using a solution-process technique, specifically inkjet printing. In contrast, previous studies have reported only up to one to two per cent polymer addition.

Interestingly, the approach enabled the semiconducting properties of the oxide semiconductor to remain unaltered with the polymer addition. The added large quantity of polymer also made the composite semiconductor highly flexible and foldable without deteriorating its performance, IISc said. The composite semiconductor is made up of two materials -- a water-insoluble polymer such as ethyl cellulose that provides flexibility, and indium oxide, a semiconductor which brings in excellent electronic transport properties.

To design the material, the researchers mixed the polymer with the oxide precursor in such a way that interconnected oxide nanoparticle channels are formed (around phase-separated polymer islands) through which electrons can move from one end of a transistor (source) to the other (drain), ensuring a steady current flow. The key to form these connected pathways, the researchers found, was the choice of the right kind of water-insoluble polymer that does not mix with the oxide lattice when the oxide semiconductor is being fabricated.

"This 'phase separation' and the formation of polymer-rich islands helps in crack arrest, making it super flexible," says Subho Dasgupta, Associate Professor in the Department of Materials Engineering, and corresponding author of the study. Semiconductor materials are usually fabricated using deposition techniques such as sputtering. Instead, Dasgupta's team uses inkjet printing to deposit their material onto various flexible substrates ranging from plastics to paper. In the present study, a polymer material called Kapton has been used.