Science & Technology, India (Commonwealth Union) – Researchers from the Department of Materials Engineering at the Indian Institute of Science (IISc) have achieved a groundbreaking development in the field of semiconductor materials. They have successfully created a super flexible composite semiconductor material with promising applications in the next generation of flexible or curved displays, foldable phones, and wearable electronics.
Conventional semiconductor devices, like transistors commonly used in the display industry, are typically made of amorphous silicon or amorphous oxides. However, these materials lack flexibility and strain tolerance, making them unsuitable for flexible and foldable electronics. While the addition of polymers to oxide semiconductors can enhance flexibility, there has been a limitation on the amount that can be added without compromising the semiconductor’s performance.
In their latest study, published in Advanced Materials Technologies, the IISc scientists have managed to fabricate a composite semiconductor containing a significant amount of polymer, up to 40 percent of the material’s weight. This was achieved using a solution-process technique, specifically inkjet printing. Notably, previous attempts have reported only minimal polymer additions of 1-2 percent. The researchers discovered that their approach preserved the semiconducting properties of the oxide semiconductor despite the substantial polymer addition. This innovation resulted in a highly flexible as well as a foldable composite semiconductor without any compromise on its performance characteristics. The successful creation of this flexible semiconductor opens up exciting possibilities for the advancement of cutting-edge electronic devices that can be seamlessly integrated into various form factors to meet the demands of modern technology.
The composite semiconductor comprises two main components: a water-insoluble polymer, like ethyl cellulose, which imparts flexibility, and indium oxide, a semiconductor known for its excellent electronic transport properties. The researchers devised a method to create this material by combining the polymer with the oxide precursor. This unique approach resulted in the formation of interconnected oxide nanoparticle channels, situated around phase-separated polymer islands. These channels enable the smooth movement of electrons from one end of a transistor (source) to the other (drain), thereby ensuring a consistent flow of current. The crucial discovery made by the researchers was that the choice of the appropriate water-insoluble polymer is key to generating these connected pathways. Importantly, the selected polymer should not mix with the oxide lattice during the fabrication process of the oxide semiconductor.
Subho Dasgupta, Associate Professor in the Department of Materials Engineering, who is also the corresponding author for the study indicated that the ‘phase separation’ as well as the making of polymer-rich islands assists in crack arrest, allowing it be super flexible.
Typically, semiconductor materials are manufactured through deposition techniques like sputtering. However, Dasgupta’s team has adopted a different approach by utilizing inkjet printing to deposit their material on a variety of flexible substrates, including plastics and paper. For this study, they employed a polymer material named Kapton. Similar to how words and images are printed on paper, electronic components can be printed onto diverse surfaces using specialized functional inks containing electrically conducting, semiconducting, or insulating materials. Despite the promising potential of this technique, it also comes with certain obstacles.
“Sometimes it is very difficult to get a continuous and homogeneous film. Therefore, we had to optimise certain protocols, for example, preheating the printed semiconductor layer on the Kapton substrate prior to high temperature annealing,” said 1st author Mitta Divya, who was previously a PhD student at the Department of Materials Engineering as well as a postdoc at King Abdullah University of Science and Technology (KAUST), Saudi Arabia right now. Another obstacle according to researchers is guaranteeing the right atmospheric conditions under which it can be printed by the ink. “If the humidity is too low, you can’t print, because the ink dries up within the nozzle,” added Subho Dasgupta.
