Modelling of field-effect transistors based on 2D materials targeting high-frequency applications /

Resumen

New technologies are necessary for the unprecedented expansion of connectivity and communications in the modern technological society. The specific needs of wireless communication systems in 5G and beyond, as well as devices for the future deployment of Internet of Things has caused that the International Technology Roadmap for Semiconductors, which is the strategic planning document of the semiconductor industry, considered since 2011, graphene and related materials (GRMs) as promising candidates for the future of electronics. Graphene, a one-atom-thick of carbon, is a promising material for high-frequency applications due to its intrinsic superior carrier mobility and very high saturation velocity. These exceptional carrier transport properties suggest that GRM-based field-effect transistors could potentially outperform other technologies. This thesis presents a body of work on the modelling, performance prediction and simulation of GRM-based field-effect transistors and circuits. The main goal of this work is to provide models and tools to ease the following issues: (i) gaining technological control of single layer and bilayer graphene devices and, more generally, devices based on 2D materials, (ii) assessment of radio-frequency (RF) performance and microwave stability, (iii) benchmarking against other existing technologies, (iv) providing guidance for device and circuit design, (v) simulation of circuits formed by GRM-based transistors. In doing so, a key contribution of this thesis is the development of a small-signal model suited to 2D material based field-effect transistors (2D-FETs) that guarantees charge conservation. It is also provided a parameter extraction methodology that includes both the contact and access resistances, which are of upmost importance when dealing with low-dimensional FETs. Taking it as a basis, an investigation of the GFET RF performance scalability is performed, together with an analysis of the device stability. The presented small-signal model is potentially useful for fast prototyping, which is of relevance when dealing with the first stages of any new technology. To complete the modelling task, an intrinsic physics-based large-signal compact model of graphene field-effect transistors (GFETs) has been developed, ready to be used in conventional electronic design automation tools. This is a necessary step towards the design of complex monolithic millimetre-wave integrated circuits (MMICs). Most of the demonstrated circuits based on GRMs so far are not integrated circuits (ICs), so requiring external circuitries for operation. At mm-wave frequencies, broadband circuits can practically only be realized in IC technology. The compact model presented in this thesis is the starting point towards the design of complex MMICs based on graphene. It has been benchmarked against high-performance and ambipolar electronics’ circuits such as high-frequency voltage amplifiers, high-performance frequency doublers, radio-frequency subharmonic mixers and multiplier phase detectors. The final part of the thesis is devoted to the bilayer graphene based FET. Bilayer graphene is a promising material for RF transistors because its energy bandgap might result in a better current saturation than the single layer graphene. Because the great deal of interest in this technology, especially for flexible applications, gaining control of it requires the formulation of appropriate models. A numerical large-signal model of bilayer graphene field-effect transistors has been realized, which allows: (i) understanding the electronic properties of bilayer graphene, in particular the tunable bandgap, (ii) evaluating the impact of the bandgap opening on the RF performance, (iii) benchmarking against other existing technologies, and (iv) providing guidance for device design. The model has been verified against measurement data reported.