Theory, Modelling and Implementation of Graphene Field-Effect Transistor
Abstract
Two-dimensional materials with atomic thickness have attracted a lot of attention from
researchers worldwide due to their excellent electronic and optical properties. As the
silicon technology is approaching its limit, graphene with ultrahigh carrier mobility and
ultralow resistivity shows the potential as channel material for novel high speed transistor
beyond silicon.
This thesis summarises my Ph.D. work including the theory and modelling of graphene
field-effect transistors (GFETs) as well as their potential RF applications. The introduction
and review of existing graphene transistors are presented. Multiscale modelling
approaches for graphene devices are also introduced. A novel analytical GFET model
based on the drift-diffusion transport theory is then developed for RF/microwave circuit
analysis. Since the electrons and holes have different mobility variations against the
channel potential in graphene, the ambipolar GFET cannot be modelled with constant
carrier mobility. A new carrier mobility function, which enables the accurate modelling
of the ambipolar property of GFET, is hence developed for this purpose. The new model
takes into account the carrier mobility variation against the bias voltage as well as the
mobility difference between electrons and holes. It is proved to be more accurate for the
DC current calculation. The model has been written in Verilog-A language and can be
import into commercial software such as Keysight ADS for circuit simulation.
In addition, based on the proposed model two GFET non-Foster circuits (NFCs) are
conducted. As a negative impedance element, NFCs find their applications in impedance
matching of electrically small antennas and bandwidth improvement of metasurfaces.
One of the NFCs studied in this thesis is based on the Linvill's technique in which a pair
of identical GFETs is used while the other circuit utilises the negative resistance of a
single GFET. The stability analysis of NFCs is also presented. Finally, a high impedance
surface loaded with proposed NFCs is also studied, demonstrating significant bandwidth
enhancement.
Authors
Tian, JingCollections
- Theses [4125]