1,889 research outputs found
Extending ballistic graphene FET lumped element models to diffusive devices
In this work, a modified, lumped element graphene field effect device model
is presented. The model is based on the "Top-of-the-barrier" approach which is
usually valid only for ballistic graphene nanotransistors. Proper modifications
are introduced to extend the model's validity so that it accurately describes
both ballistic and diffusive graphene devices. The model is compared to data
already presented in the literature. It is shown that a good agreement is
obtained for both nano-sized and large area graphene based channels. Accurate
prediction of drain current and transconductance for both cases is obtained
Modeling spin transport in electrostatically-gated lateral-channel silicon devices: role of interfacial spin relaxation
Using a two-dimensional finite-differences scheme to model spin transport in
silicon devices with lateral geometry, we simulate the effects of spin
relaxation at interfacial boundaries, i.e. the exposed top surface and at an
electrostatically-controlled backgate with SiO_2 dielectric. These
gate-voltage-dependent simulations are compared to previous experimental
results and show that strong spin relaxation due to extrinsic effects yield an
Si/SiO_2 interfacial spin lifetime of ~ 1ns, orders of magnitude lower than
lifetimes in the bulk Si, whereas relaxation at the top surface plays no
substantial role. Hall effect measurements on ballistically injected electrons
gated in the transport channel yield the carrier mobility directly and suggest
that this reduction in spin lifetime is only partially due to enhanced
interfacial momentum scattering which induces random spin flips as in the
Elliott effect. Therefore, other extrinsic mechanisms such as those caused by
paramagnetic defects should also be considered in order to explain the dramatic
enhancement in spin relaxation at the gate interface over bulk values
Time-domain simulation of the full hydrodynamic model
A simple upwind discretization of the highly coupled non-linear differential
equations which define the hydrodynamic model for semiconductors is given in
full detail. The hydrodynamic model is able to describe inertia effects which
play an increasing role in different fields of opto- and microelectronics. A
silicon - structure is simulated, using the energy-balance
model and the full hydrodynamic model. Results for stationary cases are then
compared, and it is pointed out where the energy-balance model, which is
implemented in most of today's commercial semiconductor device simulators,
fails to describe accurately the electron dynamics. Additionally, a GaAs -structure is simulated in time-domain in order to illustrate the
importance of inertia effects at high frequencies in modern submicron devices.Comment: 15 pages, 8 figures, prepared using jnmauth.cl
Ballistic nanofriction
Sliding parts in nanosystems such as Nano ElectroMechanical Systems (NEMS)
and nanomotors, increasingly involve large speeds, and rotations as well as
translations of the moving surfaces; yet, the physics of high speed nanoscale
friction is so far unexplored. Here, by simulating the motion of drifting and
of kicked Au clusters on graphite - a workhorse system of experimental
relevance -- we demonstrate and characterize a novel "ballistic" friction
regime at high speed, separate from drift at low speed. The temperature
dependence of the cluster slip distance and time, measuring friction, is
opposite in these two regimes, consistent with theory. Crucial to both regimes
is the interplay of rotations and translations, shown to be correlated in slow
drift but anticorrelated in fast sliding. Despite these differences, we find
the velocity dependence of ballistic friction to be, like drift, viscous
ANALYTICAL MODELS AND ELECTRICAL CHARACTERISATION OF ADVANCED MOSFETS IN THE QUASI BALLISTIC REGIME
International audienceThe quasi-ballistic nature of transport in end of the roadmap MOSFETs device is expected to lead to significant on state current enhancement. The current understanding of such mechanism of transport is carefully reviewed in this chapter, underlining the derivation and limits of corresponding analytical models. In a second part, different strategies to compare these models to experiments are discussed, trying to estimate the "degree of ballisticity" achieved in advanced technologies
Two Dimensional Quantum Mechanical Modeling of Nanotransistors
Quantization in the inversion layer and phase coherent transport are
anticipated to have significant impact on device performance in 'ballistic'
nanoscale transistors. While the role of some quantum effects have been
analyzed qualitatively using simple one dimensional ballistic models, two
dimensional (2D) quantum mechanical simulation is important for quantitative
results. In this paper, we present a framework for 2D quantum mechanical
simulation of a nanotransistor / Metal Oxide Field Effect Transistor (MOSFET).
This framework consists of the non equilibrium Green's function equations
solved self-consistently with Poisson's equation. Solution of this set of
equations is computationally intensive. An efficient algorithm to calculate the
quantum mechanical 2D electron density has been developed. The method presented
is comprehensive in that treatment includes the three open boundary conditions,
where the narrow channel region opens into physically broad source, drain and
gate regions. Results are presented for (i) drain current versus drain and gate
voltages, (ii) comparison to results from Medici, and (iii) gate tunneling
current, using 2D potential profiles. Methods to reduce the gate leakage
current are also discussed based on simulation results.Comment: 12 figures. Journal of Applied Physics (to appear
Compact Models and the Physics of Nanoscale FETs
The device physics of nanoscale MOSFETs is reviewed and related to traditional compact models. Beginning with the Virtual Source model, a model for nanoscale MOSFETs expressed in traditional form, we show how a Landauer approach gives a clear, physical interpretation to the parameters in the model. The analysis shows that transport in the channel is limited by diffusion near the virtual source both below and above threshold, that current saturation is determined by velocity saturation near the source, not by the maximum velocity in the channel, and that the channel resistance approaches a finite value as the channel length approaches zero. These results help explain why traditional models continue to work well at the nanoscale, even though carrier transport is distinctly different from that at the microscale, and they identify the essential physics that physics-based compact models for nanoscale MOSFETs should comprehend
Emission-Diffusion Theory of the MOSFET
An emission-diffusion theory that describes MOSFETS from the ballistic to diffusive limits is developed. The approach extends the Crowell-Sze treatment of metalsemiconductor junctions to MOSFETs and is equivalent to the scattering/transmission model of the MOSFET. The paper demonstrates that the results of the transmission model can be obtained from a traditional, drift-diffusion analysis when the boundary conditions are properly specified, which suggests that traditional drift-diffusion MOSFET models can also be extended to comprehend ballistic limits
Full 3D Quantum Transport Simulation of Atomistic Interface Roughness in Silicon Nanowire FETs
The influence of interface roughness scattering (IRS) on the performances of
silicon nanowire field-effect transistors (NWFETs) is numerically investigated
using a full 3D quantum transport simulator based on the atomistic sp3d5s*
tight-binding model. The interface between the silicon and the silicon dioxide
layers is generated in a real-space atomistic representation using an
experimentally derived autocovariance function (ACVF). The oxide layer is
modeled in the virtual crystal approximation (VCA) using fictitious SiO2 atoms.
-oriented nanowires with different diameters and randomly generated
surface configurations are studied. The experimentally observed ON-current and
the threshold voltage is quantitatively captured by the simulation model. The
mobility reduction due to IRS is studied through a qualitative comparison of
the simulation results with the experimental results
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