Graphene field-effect transistors for high frequency and flexible electronics
Typ
Examensarbete för masterexamen
Program
Publicerad
2019
Författare
Krivic, Marijana
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Graphene field-effect transistors (GFETs), owing to graphene’s intrinsically
high velocity of charge carriers in combination with flexibility, are considered as
key components for development of the new generation of advanced electronics for
applications in the areas of high data rate communication, high-resolution sensors,
imaging etc. It is well recognised now, that the development of GFETs, operating
in the amplifying mode, is challenging due to relatively high differential drain
conductance, resulting from the zero energy bandgap in the monolayer graphene,
which prevents the drain current saturation and, hence, limits the transistor power
gain. However, there is an additional possible effect of the high drain conductance in
GFETs – the correspondingly high dissipating power which can result in additional
degradation of the transistor high frequency performance due to Joule heating, i.e.
self-heating, which is particularly pronounced in GFETs on polymer flexible substrates
with inherently low thermal conductivity. This effect has been insufficiently
addressed so far. The objectives of this Master’s thesis are both theoretical and experimental
study of the GFET self-heating, its effect on the transistor high frequency
performance and optimisation of the transistor design with the aim to reduce the
self-heating.
In this work, GFETs on rigid (Si/SiO2) and flexible polymer (Kapton) substrates
have been designed, fabricated and characterised. The key issues of fabrication
of GFETs on flexible substrates, e.g. misalignment during e-beam lithography,
have been identified, discussed and addressed. A number of thermal resistance models
allowing for evaluation of the GFET channel temperature defined by the selfheating
have been considered. The models appropriate for certain GFET layouts
and layered structure, on both Si/SiO2 and Kapton substrates, have been selected
and applied. This allowed for considering GFET design optimisation for lower thermal
resistance with the aim to reduce the self-heating effect. The actual GFET
channel temperature has been measured by the means of infrared imaging and applying
method of the thermo-sensitive electrical parameters, i.e. gate and drain currents,
which showed a good agreement with the modelling. Finally, the effect of the
self-heating on the high frequency performance of the fabricated devices has been
analysed.
Beskrivning
Ämne/nyckelord
graphene field-effect transistors , Joule heating , self-heating , thermal resistance , high frequency electronics , flexible electronics , infrared imaging , thermo-sensitive electrical parameters