Modeling and Simulation of Graphene-Based Devices for RF Applications

The first experimental preparation and characterization of a monolayer graphene in 2004 has triggered the interest of the scientific community because of the peculiar graphene properties (e.g. structural, electrical). The two-dimensional (2D) structure with monoatomic thickness and the incredible high carrier mobility of graphene have created widespread expectations that it could be the perfect material for future nanoelectronic devices. Graphene-Field-Effect-Transistors (GFETs) have been extensively investigated, but the absence of an energy bandgap in monolayer graphene (which heavily hampers its use in digital electronics which requires high Ion/Ioff ratios) leads to non-saturated output characteristics, hence in poor intrinsic voltage gains. For this reason, vertical graphene-based architectures, as the Graphene-Base-Transistor (GBT), have been proposed as alternative solution for THz RF electronics. Unluckily, the technological difficulties related to the fabrication processes have slowed-down the improvement of these transistor concepts. Because of the early stage of the technology, the modeling and simulations play a major role, in order to understand the physical mechanisms involved in the graphene-based device operation and to provide useful guidelines to support the design of optimized devices. This thesis is positioned in this framework, and it is focused on the development of physics-based models and simulators for GFETs and GBTs, with the aim to support the design of fast transistors and to reliably predict the device performance limits. Concerning GFETs, in this work we mostly focused on the drawbacks related to the series resistances associated to the metal/graphene contact, both from modeling and experimental perspectives. For GBTs, instead, we developed an electrical model and a single-particle Monte Carlo simulator able to predict the RF performance and the impact of electron scattering on the device operation, respectively. The developed simulators represent an important set of tools to support future investigations on the use in electronic devices of graphene and other 2D materials, e.g. semiconducting transition metal dichalcogenides, which show properties that can overcome the limits of graphene.