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Improving transistors with nanomaterials
High-performance silicon transistors and thin-film transistors used in display technologies are fundamentally limited to miniaturization. Incorporating nanomaterials—such as carbon nanotubes, graphene, and related two-dimensional materials like molybdenum disulfide—into these devices as gate materials may circumvent some of these limitations. Franklin reviews the opportunities and challenges for incorporating nanomaterials into transistors to improve performance. Because high-performance transistors are distinct from thin-film transistors, incorporating them into flexible or transparent platforms raises new challenges.
Science, this issue 10.1126/science.aab2750
Transistors are one of the most enabling “hidden” technologies of all time and have facilitated the development of computers, the Internet, thin mobile displays, and much more. Silicon, which has been the material of choice for transistors in nearly every application for decades, is now reaching the fundamental limits to what it can offer for future transistor technologies. The newest display technologies are already turning to metal oxide materials, such as indium gallium zinc oxide (IGZO), for the improvements needed to drive organic light-emitting diodes. Ranging from applications such as display backplanes to high-performance microprocessors for servers, nanomaterials offer lasting advantages for the coming decades of transistor technologies. In this Review, the advantages of nanomaterials are discussed in the context of different transistor applications, along with the breakthroughs needed for nanomaterial transistors to enable the next generation of technological advancement.
About 15 years ago, nanomaterials began receiving focused attention for transistors. Carbon nanotubes—molecules consisting of a cylindrical single layer of carbon atoms arranged in a hexagonal lattice—were the first to be given serious consideration, and their benefits quickly became widely acclaimed. Given their ability to transport electrical current with near-zero resistance, even at room temperature, the explosion of interest in nanotubes for electronics was understandable. Graphene, a related allotrope of carbon, benefited from the expansive interest carbon nanotubes had created for nanomaterial electronics. Although graphene transistors eventually proved less viable for digital applications, owing to the absence of an energy band gap, the excitement over graphene ushered in a complete revolution of interest in similar two-dimensional materials. Now, transition metal dichalcogenides and the so-called X-ene family of nanomaterials (e.g., silicence, phosphorene) dominate the attention of the nanoelectronics community. Hardly a day goes by without a paper being published on some advancement related to the use of nanomaterials in transistors. Hence, this Review focuses on how to keep such progress in the proper context with respect to the target transistor application, as well as the consideration of nanomaterials for completely new application spaces.
The benefits and practicality differ for each nanomaterial, and varied amounts of progress have been made in considering each of them for transistors. In just a few short years, thousands of papers have been published on improving synthesis or demonstrating simple functions of the newer nanomaterials. However, reflection on whether their newness translates to actual superiority over other options is warranted. Clearly, all of the nanomaterial possibilities offer certain advantages for future transistor technologies, but some do so with fewer caveats than others. Future research will benefit from keeping scientific advancement of nanomaterial transistors in line with end-goal deliverables. Overall, considering that only 15 years have elapsed since the study of nanomaterials for transistors began in earnest, the toolbox of available options and the developments toward overcoming challenges are promising.
For more than 50 years, silicon transistors have been continuously shrunk to meet the projections of Moore’s law but are now reaching fundamental limits on speed and power use. With these limits at hand, nanomaterials offer great promise for improving transistor performance and adding new applications through the coming decades. With different transistors needed in everything from high-performance servers to thin-film display backplanes, it is important to understand the targeted application needs when considering new material options. Here the distinction between high-performance and thin-film transistors is reviewed, along with the benefits and challenges to using nanomaterials in such transistors. In particular, progress on carbon nanotubes, as well as graphene and related materials (including transition metal dichalcogenides and X-enes), outlines the advances and further research needed to enable their use in transistors for high-performance computing, thin films, or completely new technologies such as flexible and transparent devices.