DOI: 10.25549/usctheses-c127-658267
title: Application of carbon nanotubes and graphene for digital and analog electronics

description: Carbon nanomaterials, one-dimensional (1D) carbon nanotubes and two-dimensional (2D) graphene, exhibit the highest electron mobility (~100,000 cm²/V/s at room temperature) among all conductors, and huge current carrying capacity of more than 10⁹ A/cm². Additionally, single-atomic thickness provides ideal electrostatic geometry for field effect devices. These properties make carbon nanomaterials to be strong candidates to replace or supplement conventional semiconductors. Theoretical and experimental studies on individual nanotubes and graphene flakes demonstrated superior performance of carbon based field-effect transistors (FETs). However, in order to realize this potential in electronic applications, scalable synthesis and assembly of carbon nanomaterials, as well as further devices design and fabrication, still remain to be a significant challenge. ❧ In this thesis, I present our developments in order to overcome some of the critical problems in practical implementation of carbon based electronics. In our approaches, we address issues starting from the scalable controllable synthesis of carbon nanomaterials and their assembly, including design of electronic devices and material methods for their fabrication, and, finally, integration of these devices into functional circuits. This broad range of issues is tightly and often inseparably inter-connected with each other, as can be seen from an example of very large scale integrated (VLSI) silicon electronics, therefore, ultimately presenting one major goal of developing carbon based electronics. ❧ The structure of the thesis is as follows. Chapter 1 gives introduction to nano-scale carbon materials, their electronic properties and problems towards realization of carbon-based electronics. Chapter 2 presents chemical vapor deposition (CVD) methods for synthesis of carbon nanotubes and graphene. CVD synthesis methods proved to be highly promising for large scale synthesis of high quality carbon nanomaterials. The presented CVD methods for scalable fabrication of aligned carbon nanotubes and large-area single layer graphene serve as a material basis for all the following chapters. Chapter 3 presents the development of carbon nanotubes for digital electronics application. Here, we use dense parallel arrays of carbon nanotubes at wafer-scale, as an effective thin film to achieve wafer-scale registration free fabrication of large number of nanotube transistors, as well as integrated circuits such as inverters, NAND and NOR logic gates. Chapter 4 presents the results in application of carbon nanotube transistors for radio frequency (RF) electronics. In particular, I report RF and linearity performance of transistors based on high-purity separated semiconducting nanotubes. Here, we conclude that semiconducting nanotube FETs exhibit high potential for highly linear RF electronics. In Chapter 5, I present our development of scalable self-aligned fabrication of graphene transistors. Here, we developed novel highly scalable and reliable fabrication of graphene transistors with improved RF device design. Finally, Chapter 6 concludes the thesis and proposes future research directions that build on our developments. These results present important steps towards practical realization of carbon based electronics.