Semiconducting materials are the primary building blocks for electronic devices. As new coating techniques influence the development of flexible and transparent electronics, researchers look to semiconductor materials to innovate these devices further.
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Flexible and Transparent Electronics: Current Market
A market survey for transparent electronics reported by IDTechEx predicts market growth of twenty billion dollars by 2041. According to the report, thin film transistors (TFTs), display devices, photovoltaics, smart windows are a few of the transparent electronics likely to be the highest in demand.
Another report by IDTechEX showcases the importance of flexible electronics and predicts the roadmap of such technologies. Various applications such as flexible displays, textile electronics, electronic skin patches need semiconductors that cover large areas over the flexible substrates.
Many multinational companies are involved in the flexible and transparent electronics industry. For example, KODAK reportedly offers a state-of-the-art facility for the fabrication of flexible and transparent devices to researchers for the manufacture of prototypes.
Samsung Electronics Co. Ltd., LG Electronics, 3M Co., E Ink Holding Inc. are other examples of flexible and transparent electronics manufacturers.
Semiconductors for Flexible and Transparent Electronics
Generally speaking, the materials mainly studied for transparent and flexible electronics are amorphous semiconductors, semiconducting transparent oxides, metal chalcogenides, and nanowires.
A journal article published in Advanced Materials by Sun et al. summarizes work exploring the application of inorganic semiconducting materials as a coating for plastic substrates.
Amorphous silicon (a-Si) is one of the dominant materials in semiconductor industry after the single crystalline Si. As for flexible devices, single-crystal Si is not suitable for flexible electronics because of its brittle nature. Hence, a-Si is preferred over single-crystal silicon for various applications.
Amorphous semiconductors are more commonly used for flexible devices due to the possibility of large-scale uniform deposition of these materials having low-temperature processibility.
One publication in Nature demonstrated the fabrication of transparent thin film transistors (TFT) using transparent amorphous oxide semiconductors (amorphous-In-Ga-Zn-O, referred as, a-IGZO). High charge mobility, room temperature processing and stable performance under bending conditions were found to be the material's advantages.
2D Semiconductors for Flexible and Transparent Electronics
Semiconducting transition metal dichalcogenides (TMDs) have attracted much attention from researchers due to their structural behavior. These materials are reported to have a layered structure, with properties relating to the number of layers. Such tunability of their properties makes it a favorable material for flexible and transparent electronics.
Two-dimensional materials are the most suitable materials for flexible and transparent electronics. Heterostructures of such 2D materials are reported to have excellent flexibility, transparency and charge transport properties. Other 2D semiconducting materials reported include transition metal oxides and metal chalcogenides.
In work published by Das et al., demonstrated the fabrication of transparent TFT composed of entirely 2D materials. The TFTs had a monolayer of graphene as the metal electrodes, hexagonal boron nitride (h-BN) as a dielectric material and tungsten diselenide (WSe2) as a semiconducting material.
The carrier mobility in the transistor was recorded ~100 times more than that recorded by a-Si-based TFTs. The device showed good temperature stability, along with several other parameters ideal for enhancing TFTs.
In another work by Yu et al., large-scale deposition of two-dimensional graphene and molybdenum disulfide (MoS2) heterostructure was achieved through chemical vapor deposition. The work reports of high-performing devices and circuits fabricated with the heterostructure, the performances of which were compared with the traditional MoS2-metal contact.
Future Scope and Commercial Viability
Much research is towards the direction of developing alternate materials and coating techniques with the goal of decreasing the device cost and increasing the performance.
Various substrates are explored that can be applied to blendable and stretchable electronics. Substrates such as metallic foils, plastic sheets and paper were explored as substrates for flexible devices.
Building devices over flexible and transparent substrates have few constraints, such as processing temperature. Plastic substrates are much more suitable for such applications but require a processing temperature below the glass transition temperature, after which the plastic will degrade.
Research interest in this area extends to devices that could have the properties of stretchability. Developing such devices is reported to be possible by employing elastomeric substrates with strong molecular interactions.
Investigations into flexible and transparent materials and substrates for device fabrication could open up a wide range of exciting applications such as flexible lighting, wearable charging devices, implantable bioelectronics, wearable sensors that could monitor the health of patients, novel display architecture for consumer electronics and many more.
Flexible and transparent electronics have a long way to go before being available for consumer use. With increased interest in the applications of semiconductor materials in this field, we are likely to see the field grow in the future.
References and Further Reading
IDTechEx. Available at: https://www.idtechex.com/en/research-report/transparent-electronics-materials-markets-2021-2041/795.
IDTechEX. Available at: https://www.idtechex.com/en/research-article/what-does-2023-hold-for-printed-flexible-electronics/28172
Website for more information: https://www.kodak.com/en/advanced-materials/page/flexible-printed-electronics
Sun, Y. and Rogers, J.A., (2007). Inorganic semiconductors for flexible electronics. Advanced Materials, 19(15), pp.1897-1916. doi.org/10.1002/adma.200602223.
Nomura, K., Ohta, H., Takagi, A., Kamiya, T., Hirano, M. and Hosono, H., (2004). Room-temperature fabrication of transparent flexible thin-film transistors using amorphous oxide semiconductors. Nature, 432(7016), pp.488-492. doi.org/10.1038/nature03090
Das, S., Gulotty, R., Sumant, A.V. and Roelofs, A., (2014). All two-dimensional, flexible, transparent, and thinnest thin film transistor. Nano Letters, 14(5), pp.2861-2866. doi.org/10.1021/nl5009037.
Yu, L., Lee, Y.H., Ling, X., Santos, E.J., Shin, Y.C., Lin, Y., Dubey, M., Kaxiras, E., Kong, J., Wang, H. and Palacios, T., (2014). Graphene/MoS2 hybrid technology for large-scale two-dimensional electronics. Nano Letters, 14(6), pp.3055-3063. doi.org/10.1021/nl404795z.
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