3,211 research outputs found
A Numerical Study of Scaling Issues for Schottky Barrier Carbon Nanotube Transistors
We performed a comprehensive scaling study of Schottky barrier carbon
nanotube transistors using self-consistent, atomistic scale simulations. We
restrict our attention to Schottky barrier carbon nanotube FETs whose metal
source/drain is attached to an intrinsic carbon nanotube channel. Ambipolar
conduction is found to be an important factor that must be carefully considered
in device design, especially when the gate oxide is thin. The channel length
scaling limit imposed by source-drain tunneling is found to be between 5nm and
10nm, depending on the off-current specification. Using a large diameter tube
increases the on-current, but it also increases the leakage current. Our study
of gate dielectric scaling shows that the charge on the nanotube can play an
important role above threshold.Comment: 26 pages, 8 figure
Monte Carlo study of coaxially gated CNTFETs: capacitive effects and dynamic performance
Carbon Nanotube (CNT) appears as a promising candidate to shrink field-effect
transistors (FET) to the nanometer scale. Extensive experimental works have
been performed recently to develop the appropriate technology and to explore DC
characteristics of carbon nanotube field effect transistor (CNTFET). In this
work, we present results of Monte Carlo simulation of a coaxially gated CNTFET
including electron-phonon scattering. Our purpose is to present the intrinsic
transport properties of such material through the evaluation of electron
mean-free-path. To highlight the potential of high performance level of CNTFET,
we then perform a study of DC characteristics and of the impact of capacitive
effects. Finally, we compare the performance of CNTFET with that of Si nanowire
MOSFET.Comment: 15 pages, 14 figures, final version to be published in C. R. Acad.
Sci. Pari
Shot noise suppression in quasi one-dimensional Field Effect Transistors
We present a novel method for the evaluation of shot noise in quasi
one-dimensional field-effect transistors, such as those based on carbon
nanotubes and silicon nanowires. The method is derived by using a statistical
approach within the second quantization formalism and allows to include both
the effects of Pauli exclusion and Coulomb repulsion among charge carriers. In
this way it extends Landauer-Buttiker approach by explicitly including the
effect of Coulomb repulsion on noise. We implement the method through the
self-consistent solution of the 3D Poisson and transport equations within the
NEGF framework and a Monte Carlo procedure for populating injected electron
states. We show that the combined effect of Pauli and Coulomb interactions
reduces shot noise in strong inversion down to 23 % of the full shot noise for
a gate overdrive of 0.4 V, and that neglecting the effect of Coulomb repulsion
would lead to an overestimation of noise up to 180 %.Comment: Changed content, 7 pages,5 figure
A Three-dimensional simulation study of the performance of Carbon Nanotube Field Effect Transistors with doped reservoirs and realistic geometry
In this work, we simulate the expected device performance and the scaling
perspectives of Carbon nanotube Field Effect Transistors (CNT-FETs), with doped
source and drain extensions. The simulations are based on the self-consistent
solution of the 3D Poisson-Schroedinger equation with open boundary conditions,
within the Non-Equilibrium Green's Function formalism, where arbitrary gate
geometry and device architecture can be considered. The investigation of short
channel effects for different gate configurations and geometry parameters shows
that double gate devices offer quasi ideal subthreshold slope and DIBL without
extremely thin gate dielectrics. Exploration of devices with parallel CNTs show
that On currents per unit width can be significantly larger than the silicon
counterpart, while high-frequency performance is very promising.Comment: Submitted to IEEE TE
Analytical model of 1D Carbon-based Schottky-Barrier Transistors
Nanotransistors typically operate in far-from-equilibrium (FFE) conditions,
that cannot be described neither by drift-diffusion, nor by purely ballistic
models. In carbonbased nanotransistors, source and drain contacts are often
characterized by the formation of Schottky Barriers (SBs), with strong
influence on transport. Here we present a model for onedimensional field-effect
transistors (FETs), taking into account on equal footing both SB contacts and
FFE transport regime. Intermediate transport is introduced within the Buttiker
probe approach to dissipative transport, in which a non-ballistic transistor is
seen as a suitable series of individually ballistic channels. Our model permits
the study of the interplay of SBs and ambipolar FFE transport, and in
particular of the transition between SB-limited and dissipation-limited
transport
Towards Multi-Scale Modeling of Carbon Nanotube Transistors
Multiscale simulation approaches are needed in order to address scientific
and technological questions in the rapidly developing field of carbon nanotube
electronics. In this paper, we describe an effort underway to develop a
comprehensive capability for multiscale simulation of carbon nanotube
electronics. We focus in this paper on one element of that hierarchy, the
simulation of ballistic CNTFETs by self-consistently solving the Poisson and
Schrodinger equations using the non-equilibrium Greens function (NEGF)
formalism. The NEGF transport equation is solved at two levels: i) a
semi-empirical atomistic level using the pz orbitals of carbon atoms as the
basis, and ii) an atomistic mode space approach, which only treats a few
subbands in the tube-circumferential direction while retaining an atomistic
grid along the carrier transport direction. Simulation examples show that these
approaches describe quantum transport effects in nanotube transistors. The
paper concludes with a brief discussion of how these semi-empirical device
level simulations can be connected to ab initio, continuum, and circuit level
simulations in the multi-scale hierarchy
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