Printed electronics is predicted to be a $300billion market within two decades. Printing is a versatile enabling technology for electronic products that cannot be made with Si microelectronics technology. Single-crystal Si microelectronics must be constructed on rigid Si wafer and are restricted to small areas. Polycrystalline and amorphous Si (poly-Si and a-Si) can make large-area products but have low carrier mobility and are typically restricted to a rigid substrate. Further, the multiple lithographic steps and high-vacuum processes in a clean room environment make the cost of (single-crystal, poly- and a-) Si microelectronics products relatively high. Printing of semiconductor and metals, on the other hand, permits creation of large area electronics on flexible substrates, and enables high volume scale economies. The applications of printed electronics are diverse and pervasive, including electronics products (e.g. large active display pixel drivers and solar panels), conformal electronics for implantable medical sensors, wearable or textile electronics, biosensors, single-use electronics, low-cost sensors, and Radio Frequency Identification tags. Printed electronics will also lead to completely new products such as sophisticated diagnostic tools and smart packaging and inventory labels. It is believed that printed electronics will revolutionize our lifestyle within the next two decades just as Si microelectronics has done in past decades.
The largest segment of the total printed electronics industry will be printed transistors and memory. Organic semiconducting molecules are the dominant semiconductor materials used for printed thin-film transistors (TFTs). However, organic materials (such as polythiophene and pentacene) typically have low mobilities, so that the use of TFTs is restricted to applications involving only low-frequency and light-duty computation, control and communication. Further, organic transistors generally have low long-term stability. In recent years, various one-dimensional nanowires with much higher carrier mobilities and stabilities have emerged as alternative candidates for printable transistors. Single walled carbon nanotubes (SWNTs), which can be thought of as rolled-up cylinders of graphite monolayer with ~1 nm diameter and tens of nanometers to several centimeters length, are widely regarded to be an excellent candidate due to their unique properties. Due to their nearly one-dimensional and defect-free electronic structure, electronic transport in SWNTs is ballistic, allowing them to carry high current with essentially no heating. SWNTs have excellent thermal, mechanical and chemical stability, bendability and unique optical properties. Also of great importance, the “organic” SWNTs can be easily printed as their density is close to those of water and organic solvents and are easily functionalized, making low-cost roll-to-roll manufacturing possible. Hence, SWNTs are believed to be an ideal semiconducting material candidate for printed- electronics. Using SWNTs as transistor building blocks, a new-generation of much-higher performance printed plastic electronics shall be realizable.
The overall objective of this proposed research programme is to develop aligned SWNTnet-based field-effect transistors with high mobility, on/off ratio and yield and demonstrate their use in high-performance logic circuits and a prototype device. The project, approved in Singapore in the frame of the „Competitive Research Program“, is a collaborative effort lead by Nanyang Technological University of Singapore together with TUM, University of Illinois (Urbana-Champaign), MIT, Dayton University and one industry partner, ST Microelectronics. TUM will be involved together with NTU and STMicroelectronics in the final realization of a prototype device. The TUM Fellowships are sponsored by the TUM Institute of Advanced Studies.