Characterisation of high-frequency noise in graphene FETs at different ambient temperatures
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Typ
Examensarbete för masterexamen
Program
Applied physics (MPAPP), MSc
Publicerad
2019
Författare
Li, Junjie
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Graphene is a promising channel material for high-frequency field-effect transistors,
owing to its intrinsically high carrier velocity and purely two-dimensional structure.
At high frequencies, the noise originated in device itself, especially the thermal
noise, becomes very crucial for the performance of transistors. The thermal noise
can be influenced by ambient temperature or self-heating due to high drain bias.
This motivates the study of the effect of temperature on the noise performance of
graphene field-effect transistors (GFETs).
In this thesis, the results on high-frequency noise characterisation and modelling
of the GFETs at different temperature and bias conditions are presented. The basic
idea and main procedures of high-frequency noise modelling are based on Pospieszalski’s
noise model. Two different high-frequency noise characterisation techniques,
i.e., the Y-factor and cold-source methods, and two calculation methods of highfrequency
noise parameters, i.e., the source-pull and 50
impedance termination
(F50) methods, have been analysed and discussed. The high-frequency noise of the
GFETs at an ambient temperature range from -60 C to 25 C is presented. The
minimum noise figure (Fmin) of the GFETs decreases with the drain bias and saturates
above approximately -1 V due to the carrier mobility saturation in the channel.
The noise performance shows a rather strong dependence on both temperature and
gate bias mainly due to the change of carrier density and the contact resistance. The
minimum noise figure (Fmin) is 1.2 dB at 6.5 GHz at room temperature, which is
comparable with that of the best metal-semiconductor field effect transistors. And
it decreases down to 0.3 dB at 8 GHz for an ambient temperature of -60 C. An
empirical noise model for the GFETs considering both temperature and gate voltage
has been proposed and verified by the experimental results.
In conclusion, a way to characterise the temperature dependence of noise performance
of the GFETs is discussed, which allows for further development of low-noise
GFETs for high-frequency applications.
Beskrivning
Ämne/nyckelord
graphene , GFET , noise characterisation , thermal experiments , minimum noise figure , F50 method , field effect transistors , microwave electronics