IISc. scientists develop composite semiconductor for next-gen foldable phones and wearable devices

Traditional semiconductor devices – such as transistors – are either made of amorphous silicon or amorphous oxides, both of which are not flexible and strain tolerant

Updated - July 11, 2023 02:19 pm IST

Published - July 11, 2023 01:15 pm IST - Bengaluru

The composite semiconductor-based transistor material on fully printed flexible display.

The composite semiconductor-based transistor material on fully printed flexible display.

Scientists in the Department of Materials Engineering 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 display and foldable phones, and in wearable electronics.

Traditional semiconductor devices – such as transistors, the building blocks of most electronic circuits – used in display units are either made of amorphous silicon or amorphous oxides, both of which are not flexible and strain tolerant.

According to IISc, 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.

In the current study, published in Advanced Materials Technologies, researchers have found a way to fabricate a composite containing a significant amount of polymer – up to 40% of the material weight – using a solution-process technique, specifically inkjet printing.

The super flexible, composite semiconductor material was developed by scientists in the Department of Materials Engineering at the Indian Institute of Science (IISc.), Bengaluru.

The super flexible, composite semiconductor material was developed by scientists in the Department of Materials Engineering at the Indian Institute of Science (IISc.), Bengaluru.

In contrast, previous studies have reported only up to 1-2% polymer addition. Interestingly, the approach enabled the semiconducting properties of the oxide semiconductor to remain unaltered with the polymer addition. The large quantity of polymer made the composite semiconductor highly flexible and foldable without deteriorating its performance.

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.

How researchers came up with the new material

To design the material, 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 flow of current. 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.

(Top) The composite semiconductor-based transistors on flexible Kapton substrate and (Below) envisioned fully printed flexible display.

(Top) The composite semiconductor-based transistors on flexible Kapton substrate and (Below) envisioned fully printed flexible display.

“This phase separation and the formation of polymer-rich islands helps in crack arrest, making it super flexible,” said 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, Prof. Dasgupta’s team uses inkjet printing to deposit their material onto various flexible substrates ranging from plastic to paper. In the present study, a polymer called Kapton was used.

Potential use scenarios

Prof. Dasgupta adds that, in the future, such printed semiconductors can be used to fabricate fully printed and flexible television screens, wearables, and large electronic billboards alongside printed organic light emitting diode (OLED) display front-ends. These printed semiconductors will be low cost and easy to manufacture, which could potentially revolutionise the display industry.

The team has obtained a patent for their material, and plans to test its shelf life and quality control from device to device before it can be scaled up for mass production.

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