Conventionally, semiconductor devices used in display industries are made of amorphous silicon or amorphous oxides. However, these materials lack flexibility and strain tolerance, making them unsuitable for applications requiring flexibility. While the addition of polymers to oxide semiconductors can enhance their flexibility, there has been a limit to the amount that could be added without compromising the performance of the semiconductor.
In a recent study published in Advanced Materials Technologies, the researchers at IISc have successfully fabricated a composite semiconductor material containing a significant amount of polymer. The material, which can comprise up to 40% of the composite's weight, was created using a solution-process technique known as inkjet printing. This is a notable improvement compared to previous studies that reported only 1-2% polymer addition. Remarkably, the semiconductor properties of the oxide semiconductor remained unaffected even with the addition of a large quantity of polymer, making the composite highly flexible and foldable without compromising performance.
The composite semiconductor is composed of two main materials: a water-insoluble polymer such as ethyl cellulose, which provides flexibility, and indium oxide, a semiconductor known for its excellent electronic transport properties. By strategically mixing the polymer with the oxide precursor, the researchers created interconnected oxide nanoparticle channels, enabling electrons to flow smoothly from one end of a transistor to the other. This ensures a steady current flow and allows the material to function effectively.
The researchers discovered that the choice of the appropriate water-insoluble polymer, which doesn't mix with the oxide lattice during fabrication, was crucial for the formation of these connected pathways. This unique "phase separation" and the formation of polymer-rich islands also contribute to the composite's super flexibility, as explained by Subho Dasgupta, Associate Professor in the Department of Materials Engineering and corresponding author of the study.
Typically, semiconductor materials are fabricated using deposition techniques such as sputtering. However, Dasgupta's team opted for inkjet printing to deposit their material onto various flexible substrates, including plastics and paper. In their current study, they used a polymer material called Kapton. Similar to the printing of words and images on paper, electronic components can be printed on any surface using functional inks containing electrically conducting, semiconducting, or insulating materials. Nevertheless, the process presents challenges.
Divya Mitta, the first author of the study and former PhD student at the Department of Materials Engineering, now a postdoc at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia, explains that achieving a continuous and homogeneous film can be difficult. To address this issue, the team optimized protocols, including preheating the printed semiconductor layer on the Kapton substrate before high-temperature annealing. Another challenge is ensuring the right environmental conditions for inkjet printing. As Subho Dasgupta highlights, if the humidity is too low, the ink dries up within the nozzle, preventing successful printing.
Dasgupta envisions a future where printed semiconductors can be utilized to manufacture fully printed and flexible television screens, wearables, and large electronic billboards, in addition to printed organic light-emitting diode (OLED) display front-ends. These printed semiconductors would offer a cost-effective and easily scalable solution that could potentially revolutionize the display industry. The team has already obtained a patent for their material and plans to conduct further tests to assess its shelf-life and quality control across different devices before scaling up for mass production. Additionally, they aim to explore other polymers that can contribute to the design of flexible semiconductors.
The development of these super flexible composite semiconductors brings us one step closer to a future where electronic devices seamlessly integrate into our daily lives, offering enhanced flexibility and functionality. With continued advancements in the field of printed electronics, we can expect to witness remarkable innovations in the near future.Research Report:Super Flexible and High Mobility Inorganic/Organic Composite Semiconductors for Printed Electronics on Polymer Substrates
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