The critical assumptions in the drift-diffusion model are the local force approximation
and the use of the Einstein relation under nonequilibrium conditions. The validity of
these two approximations is investigated by full-band Monte Carlo simulation for a
SiGe-HBT. It is found that neither the local force approximation nor the Einstein
relation holds. Even Einstein relations generalized with the local temperature fail under
quasiballistic transport conditions, indicating that the energy transport and hydrodynamic
approach are also problematic.

C. Jungemann

B. Neinhüs

B. Meinerzhagen

Investigation of the Local Force
Approximation in Numerical Device
Simulation by Full-band
Monte Carlo Simulation

Total energy calculations based on a density-functional tight-binding scheme have beenperformed on polymorphic modifications of various thiophene crystals. The investigatedstructures include sulphanyl-substituted quater-thiophene and methyl-substitutedsexithiophene, in the monoclinic and triclinic modifications. Attention has been focusedon the intermolecular interaction between the molecular units. Despite the similarities inthe backbone geometries, the strength and nature of intermolecular interaction differslargely in the various polymorphs. Sulphur atoms belonging to the thiophene rings arestrongly involved in the interaction. Sulphanyl substituents play an important role,while methyl groups do not contribute. The strength of intermolecular interaction is nota direct function of atom distance.

J.  Widany

G.  Daminelli

A.  Di Carlo

P.   Lugli

Density-functional Based Tight-bindingCalculations on Thiophene Polymorphism

In this paper we compare the well-known and widely used hydrodynamical model ofBlotekjaer-Baccarani-Worderman (BBW model) with a new hydrodynamical modelrecently proposed by Anile, Liotta and Mascali (ALM model). The benchmark utilizedis a standard two-dimensional MESFET already employed in computational studies.Suitable numerical methods for hyperbolic systems of balance laws have been used.

A. M. Anile

S. F. Liotta

G.  Mascali

S.  Rinaudo

Two Dimensional MESFET Simulationof Transients and Steady State with KineticBased Hydrodynamical Models

We present a proposal for an experiment to demonstrate QCA (Quantum Cellular
Automaton) functionality for a cell fabricated with silicon-on-insulator technology. The
fundamental feature of a working QCA cell consists in the anticorrelated transition of
electrons in the two pairs of dots forming the cell: we show how such a phenomenon can
be detected from the appearance of a “locking” effect between the Coulomb Blockade
current peaks relative to each pair. The proposed approach allows the detection of QCA
action without the need for additional noninvasive charge detectors probing each dot.
We have performed detailed numerical simulations on the basis of interdot capacitance
values obtained from experimental data and determined the range of parameters within
which the effect should be detectable.

M. Gattobigio

M. Macucci

G. Iannaccone

Detection of Quantum Cellular Automaton
Action in Silicon-on-insulator Cells

Fluctuation effects are becoming important in advanced VLSI devices because of theirincreasing impact on circuit performance and chip yields. Accurate modelling of theseeffects generally requires full 3D simulation, which is used here to analyse four of theprimary such effects. Polysilicon line edge roughness causes excess device leakage, whichcan be reduced at the cost of decreased performance. Phase-shift mask defects canreduce current drive and increase capacitance. Random dopant fluctuation, whichcauses variation in threshold voltage, is evaluated for three technology generations andit is shown that proper tip scaling can reduce these variations. Finally, a study of alphaparticle strikes evaluates the effectiveness of SOI in improving soft error reliability.

Thomas D. Linton

Shaofeng  Yu

Reaz  Shaheed

3D Modelling of Fluctuation Effects in HighlyScaled VLSI Devices

Issues associated with modeling of quantum devices within the framework of the
transient Wigner equation are addressed. Of particular importance is the structure of
the Wigner function, hysteresis, and device switching time, whose value is determined by
the large signal device properties.

H. L. Grubin

R. C. Buggeln

Wigner Function Methods in Modeling of Switching
in Resonant Tunneling Devices

We investigate the design of a Coulomb blockade device consisting of a rectangulararray of quantum dots or ultrasmall metallic islands with regard to its stability againstgeometric size disorder and offset charges. To simulate the device operation we performa statistical analysis of the Coulomb blockade voltage which results in practical designrules.

H.-O.  M&#252;ller

D. A. Williams

H.  Mizuta

Design Optimization of Coulomb Blockade Devices

We have studied quantum transport in both Si and GaAs interband tunneling diodes(ITD&#39;s). In the simulation, a non-equilibrium Green&#39;s function method based anempirical tight binding theory has been used to take into account evanescent-wavematching at interfaces and realistic band structures. Comparison has been madebetween the results of our multiband (MB) model and those of conventional two-band(2B) model. As a result, it is found that the current&#8211;voltage (I&#8211;V) characteristics of theSi ITD have considerably smaller peak current density than the conventional 2B model,since our MB model reflects correctly the indirect gap band structure. On the otherhand, in the GaAs ITD, there is small difference between the two models, becausetunneling occurs between the conduction band and the valence band at F point. It isalso found that the matching of evanescent electron modes is essentially necessary toinclude the valley-mixing effects at the tunneling interfaces.

Matsuto  Ogawa

Ryuichiro  Tominaga

Tanroku  Miyoshi

Tight Binding Simulation of Quantum Transportin Interband Tunneling Devices

We report on the 2D and 3D modeling of ultra-small MOS structures using a newly developed full-band device simulator. The simulation tool is based on a novel approach, featuring a hybrid Ensemble Monte Carlo (EMC)-Cellular Automata (CA) simulation engine. In this hybrid approach charge transport is simulated using the CA in regions of momentum space where most scattering events occur and the EMC elsewhere, thus optimizing the trade-off between the fast, but memory consuming CA method and the slower EMC method. To account for the spatial distribution of the electric field and charge concentration, the hybrid EMC/CA simulator is self-consistently coupled with a 2D and 3D multi-grid Poisson solver. The solver is then used to simulate the performance of a 40 nm gate length n-MOSFET structure.

S. J. Wigger

S. M. Goodnick

M. Saraniti

Hybrid Particle-based Full-band Analysis of Ultra-small MOS

We present a generalized transfer field method with the microscopic noise sources
directly connected with the velocity and energy change during single scattering events.
The advantages of this method are illustrated by hydrodynamic calculations of current
and voltage noise spectra in several two-terminal submicron structures.

P. Shiktorov

E. Starikov

V. Gruzinskis

T. GonzáLez

J. Mateos

D. Pardo

L. Reggiani

L. Varani

J. C. Vaissiére

Langevin Forces and Generalized Transfer Fields for
Noise Modelling in Deep Submicron Devices

About this journal

Journal profile

Meet the editorial board

Editor spotlight

Submit your proposal

Do you think there is an emerging area of research that really needs to be highlighted? Or an existing research area that has been overlooked or would benefit from deeper investigation? Raise the profile of a research area by leading a Special Issue.

Special Issues

title

https://images.hindawi.com/journals/vlsi/vlsi.banner.jpg

twitter:card

twitter:site

twitter:title

twitter:url

twitter:image

VLSI Design | Hindawi

VLSI Design

This Issue is now open for submissions.
Papers are published upon acceptance, regardless of the Special Issue publication date.

Call for papers

John Barker

Jeremy Watling