STTR Phase I: Next-Gen Radiofrequency Transistors on Silicon via Aligned, Residue-Free Carbon Nanotubes

The broader/commercial impact of this Small Business Technology Transfer (STTR) Phase I project seeks to overcome the highest risks facing the commercialization of a novel semiconductor for wireless communications devices. As the demand for wireless communication increases (e.g., cell phones, WiFi, Internet of Things devices), wireless component suppliers and manufacturers must utilize new materials and integration methods to yield necessary increases in data bandwidth, energy efficiency, and functionality, while shrinking component footprint. Carbon nanotubes offer a solution to this problem. A carbon nanotube is comprised of an atomically thin layer of carbon rolled into a seamless tube. Carbon nanotubes act like tiny semiconducting wires that can significantly outperform current semiconductors such as silicon and gallium arsenide. When aligned into dense arrays, nanotubes offer superior wireless characteristics including high frequency and linearity, which are vital for next-gen communication technologies. Importantly, carbon nanotubes can be deposited onto existing semiconductors (such as silicon), enabling the previously unfeasible integration of multiple types of high-performance circuits on the same chip, allowing for more functionality in less space. By addressing problems related to wireless communication, this project will have widespread societal impact and underpin the wireless radiofrequency technologies of tomorrow, while bolstering American competitiveness in this important sector. The project will leverage recently developed carbon nanotube alignment technology that overcomes the materials and manufacturing challenges that have limited previous nanotube research and development. The room-temperature alignment technology is fast, cost-effective, and area-scalable – enabling seamless industry integration. The technical innovations of this project will be to: (1) develop approaches to remove organic processing residues that coat the surfaces and interfaces of nanotube arrays and decrease the performance of nanotube-based wireless communications transistors; and (2) fabricate and demonstrate wireless communications transistors based on aligned nanotubes that do not suffer from the effects of such impurities. Spectroscopic measurements of residues, electrical measurements sensitive to impurities, and additional high frequency transistor characterization will be used in a feedback loop to inform residue removal process development. Specific activities will focus on: (1) systematically studying the effect of different treatments to selectively remove residues; (2) determining how the treatments depend on array density; and (3) fabricating and testing wireless communications transistors. The project will provide a database of impurity removal rates for a library of treatments, a demonstration of transistors free of performance loss from residues; and a demonstration of nanotube-based transistors integrated on silicon. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.