224 research outputs found
A Three-Dimensional Quantum Simulation of Silicon Nanowire Transistors with the Effective-Mass Approximation
The silicon nanowire transistor (SNWT) is a promising device structure for
future integrated circuits, and simulations will be important for understanding
its device physics and assessing its ultimate performance limits. In this work,
we present a three-dimensional quantum mechanical simulation approach to treat
various SNWTs within the effective-mass approximation. We begin by assuming
ballistic transport, which gives the upper performance limit of the devices.
The use of a mode space approach (either coupled or uncoupled) produces high
computational efficiency that makes our 3D quantum simulator practical for
extensive device simulation and design. Scattering in SNWTs is then treated by
a simple model that uses so-called Buttiker probes, which was previously used
in metal-oxide-semiconductor field effect transistor (MOSFET) simulations.
Using this simple approach, the effects of scattering on both internal device
characteristics and terminal currents can be examined, which enables our
simulator to be used for the exploration of realistic performance limits of
SNWTs.Comment: 38 pages, 11 figures, submitted to Journal of Applied Physic
Computational Study of Tunneling Transistor Based on Graphene Nanoribbon
Tunneling field-effect transistors (FETs) have been intensely explored
recently due to its potential to address power concerns in nanoelectronics. The
recently discovered graphene nanoribbon (GNR) is ideal for tunneling FETs due
to its symmetric bandstructure, light effective mass, and monolayer-thin body.
In this work, we examine the device physics of p-i-n GNR tunneling FETs using
atomistic quantum transport simulations. The important role of the edge bond
relaxation in the device characteristics is identified. The device, however,
has ambipolar I-V characteristics, which are not preferred for digital
electronics applications. We suggest that using either an asymmetric
source-drain doping or a properly designed gate underlap can effectively
suppress the ambipolar I-V. A subthreshold slope of 14mV/dec and a
significantly improved on-off ratio can be obtained by the p-i-n GNR tunneling
FETs
Switching Mechanism in Single-Layer Molybdenum Disulfide Transistors: an Insight into Current Flow across Schottky Barriers
In this article, we study the properties of metal contacts to single-layer
molybdenum disulfide (MoS2) crystals, revealing the nature of switching
mechanism in MoS2 transistors. On investigating transistor behavior as contact
length changes, we find that the contact resistivity for metal/MoS2 junctions
is defined by contact area instead of contact width. The minimum gate dependent
transfer length is ~0.63 {\mu}m in the on-state for metal (Ti) contacted
single-layer MoS2. These results reveal that MoS2 transistors are Schottky
barrier transistors, where the on/off states are switched by the tuning the
Schottky barriers at contacts. The effective barrier heights for source and
drain barriers are primarily controlled by gate and drain biases, respectively.
We discuss the drain induced barrier narrowing effect for short channel
devices, which may reduce the influence of large contact resistance for MoS2
Schottky barrier transistors at the channel length scaling limit.Comment: ACS Nano, ASAP (2013
ROCSAT-1 telecommunication experiments
This paper addresses a telecommunication payload project approved by the R.O.C. NSPO's ROCSAT-1 space program. This project will enable several innovative experiments via the low-earth-orbit satellite ROCSAT-1, including multipath fading channel characterization, ionospheric scintillation measurement, real-time voice communications, and CDMA data communications. A unified L/S-band transponder payload is proposed for conducting these experiments in an efficient way. The results of these experiments would provide the evolving mobile communication communities with fruitful information
A review of selected topics in physics based modeling for tunnel field-effect transistors
The research field on tunnel-FETs (TFETs) has been rapidly developing in the last ten years, driven by the quest for a new electronic switch operating at a supply voltage well below 1 V and thus delivering substantial improvements in the energy efficiency of integrated circuits. This paper reviews several aspects related to physics based modeling in TFETs, and shows how the description of these transistors implies a remarkable innovation and poses new challenges compared to conventional MOSFETs. A hierarchy of numerical models exist for TFETs covering a wide range of predictive capabilities and computational complexities. We start by reviewing seminal contributions on direct and indirect band-to-band tunneling (BTBT) modeling in semiconductors, from which most TCAD models have been actually derived. Then we move to the features and limitations of TCAD models themselves and to the discussion of what we define non-self-consistent quantum models, where BTBT is computed with rigorous quantum-mechanical models starting from frozen potential profiles and closed-boundary Schr\uf6dinger equation problems. We will then address models that solve the open-boundary Schr\uf6dinger equation problem, based either on the non-equilibrium Green's function NEGF or on the quantum-transmitting-boundary formalism, and show how the computational burden of these models may vary in a wide range depending on the Hamiltonian employed in the calculations. A specific section is devoted to TFETs based on 2D crystals and van der Waals hetero-structures. The main goal of this paper is to provide the reader with an introduction to the most important physics based models for TFETs, and with a possible guidance to the wide and rapidly developing literature in this exciting research field
Drain current multiplication in thin pillar vertical MOSFETs due to depletion isolation and charge coupling
Selective culture enrichment and sequencing of feces to enhance detection of antimicrobial resistance genes in third-generation cephalosporin resistant Enterobacteriaceae
Metagenomic sequencing of fecal DNA can usefully characterise an individual’s intestinal resistome but is limited by its inability to detect important pathogens that may be present at low abundance, such as carbapenemase or extended-spectrum beta-lactamase producing Enterobacteriaceae. Here we aimed to develop a hybrid protocol to improve detection of resistance genes in Enterobacteriaceae by using a short period of culture enrichment prior to sequencing of DNA extracted directly from the enriched sample. Volunteer feces were spiked with carbapenemase-producing Enterobacteriaceae and incubated in selective broth culture for 6 hours before sequencing. Different DNA extraction methods were compared, including a plasmid extraction protocol to increase the detection of plasmid-associated resistance genes. Although enrichment prior to sequencing increased the detection of carbapenemase genes, the differing growth characteristics of the spike organisms precluded accurate quantification of their concentration prior to culture. Plasmid extraction increased detection of resistance genes present on plasmids, but the effects were heterogeneous and dependent on plasmid size. Our results demonstrate methods of improving the limit of detection of selected resistance mechanisms in a fecal resistome assay, but they also highlight the difficulties in using these techniques for accurate quantification and should inform future efforts to achieve this goa
Characterization of oral and gut microbiome temporal variability in hospitalized cancer patients
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