228 research outputs found
Modeling and Simulation of Negative Capacitance MOSFETs
The current and voltage characteristics of a MOSFET device are maily characterized by the source
to channel barrier which is controlled by the gate voltage. The Boltazmann statistics which govern
the number of carriers that are able to cross the barrier indicates that to increase the current by a
decade, atleast 60 mV of rise in gate voltage is required. As a result of this limitation, the threshold
voltage of modern MOSFETs cannot be less than about 0.3 V for an ION to IOFF ratio of 5 decades.
This has put a fundamental bottleneck in voltage downscaling increasing the power consumption in
modern IC based chips with billions of transistors.
Sayeef Salahuddin and Supriyo Dutta proposed the idea of including ferroelectric in MOSFET
gate stack which allows an internal voltage ampli�cation at the MOSFET channel which can be used
to achieve a smaller subthreshold swing which would further reduce the power consumption of the
devices. In this thesis we have undertaken a simulation based study of such devices to study how
the inclusion of negative capacitance ferroelectrics leads changes in various device characteristics.
Initially we have taken a compact modeling based approach to study device characteristics in
latest industry standard FinFET devices. For this purpose we have used the BSIM-CMG Verilog A
model and modi�ed the model appropriately to include the e�ect of negative capacitance ferroelectric
in the gate stack. This simulation allowed us to observe that negative capacitance (NC) devices can
indeed give a subthreshold swing lesser than 60 mV/dec. Further other interesting properties like
negative output resistance and drain induced barrier rising are observed.
Using the compact models developed above, we have analyzed some simple circuits with NC
devices. Initially an inverter shows a hysteresis in the transfer characteristics. This can be attributed
to negative di�erential resistance. Ring oscillator analysis shows that RO frequency for NC devices
is lesser than that of regular devices due to enhanced gate capacitance and slower response of
ferroelectrics.
Scaling analysis has been performed to see the performance of NC devices in future technologies.
For this we used TCAD analysis coupled with Landau Khalatnikov equation. This analysis shows
that NC devices are more e�ective in suppressing short channel e�ects like DIBL and can hence be
used for further downscaling of the devices.
Finally we develop models to take into account the multidomain Landau equations for ferroelec-
tric into account. We have performed such an analysis for a ferroelectric resistor series network. A
similar analysis is performed for short channel double gate MOSFET without inter layer metal be-
tween ferroelectric and the internal MOS device. This analysis showed that coupling factor between
ferroelectric domains plays an important role in the device characteristics
Electron-nucleus scalar-pseudoscalar interaction in PbF: Z-vector study in the relativistic coupled-cluster framework
The scalar-pseudoscalar interaction constant of PbF in its ground state
electronic configuration is calculated using the Z-vector method in the
relativistic coupled-cluster framework. The precise calculated value is very
important to set upper bound limit on P,T-odd scalar-pseudoscalar interaction
constant, k_s, from the experimentally observed P,T-odd frequency shift.
Further, the ratio of the effective electric field to the scalar-pseudoscalar
interaction constant is also calculated which is required to get an independent
upper bound limit of electric dipole moment of electron, d_e, and k_s and how
these (d_e and k_s) are interrelated is also presented here.Comment: 6 pages, 1 figure
Computing Adequately Permissive Assumptions for Synthesis
We solve the problem of automatically computing a new class of environment
assumptions in two-player turn-based finite graph games which characterize an
``adequate cooperation'' needed from the environment to allow the system player
to win. Given an -regular winning condition for the system
player, we compute an -regular assumption for the environment
player, such that (i) every environment strategy compliant with allows
the system to fulfill (sufficiency), (ii) can be fulfilled by the
environment for every strategy of the system (implementability), and (iii)
does not prevent any cooperative strategy choice (permissiveness).
For parity games, which are canonical representations of -regular
games, we present a polynomial-time algorithm for the symbolic computation of
adequately permissive assumptions and show that our algorithm runs faster and
produces better assumptions than existing approaches -- both theoretically and
empirically. To the best of our knowledge, for -regular games, we
provide the first algorithm to compute sufficient and implementable environment
assumptions that are also permissive.Comment: TACAS 202
Carrier Transport in High Mobility InAs Nanowire Junctionless Transistors
Ability to understand and model the performance limits of nanowire
transistors is the key to design of next generation devices. Here, we report
studies on high-mobility junction-less gate-all-around nanowire field effect
transistor with carrier mobility reaching 2000 cm2/V.s at room temperature.
Temperature-dependent transport measurements reveal activated transport at low
temperatures due to surface donors, while at room temperature the transport
shows a diffusive behavior. From the conductivity data, the extracted value of
sound velocity in InAs nanowires is found to be an order less than the bulk.
This low sound velocity is attributed to the extended crystal defects that
ubiquitously appear in these nanowires. Analyzing the temperature-dependent
mobility data, we identify the key scattering mechanisms limiting the carrier
transport in these nanowires. Finally, using these scattering models, we
perform drift-diffusion based transport simulations of a nanowire field-effect
transistor and compare the device performances with experimental measurements.
Our device modeling provides insight into performance limits of InAs nanowire
transistors and can be used as a predictive methodology for nanowire-based
integrated circuits.Comment: 22 pages, 5 Figures, Nano Letter
Enhancement of the optical gain in GaAs nanocylinders for nanophotonic applications
Semiconductor nanolasers based on micro disks, photonic crystal cavities, and
metallo-dielectric nanocavities have been studied during the last decade for
on-chip light source applications. However, practical realization of low
threshold, room temperature operation of semiconductor nanolasers is still a
challenge due to the large surface-to-volume ratio of the nanostructures, which
results in low optical gain and hence higher lasing threshold. Also, the gain
in nanostructures is an important parameter for designing all-dielectric
metamaterial-based active applications. Here, we investigate the impact of
p-type doping, compressive strain, and surface recombination on the gain
spectrum and the spatial distribution of carriers in GaAs nanocylinders. Our
analysis reveals that the lasing threshold can be lowered by choosing the right
doping concentration in the active III-V material combined with compressive
strain. This combination of strain and p-type doping shows 100x improvement in
gain and ~5 times increase in modulation bandwidth for high-speed operation.Comment: 19 pages, 6 figure
Analysis of the Molecular Networks in Androgen Dependent and Independent Prostate Cancer Revealed Fragile and Robust Subsystems
Androgen ablation therapy is currently the primary treatment for metastatic prostate cancer. Unfortunately, in nearly all cases, androgen ablation fails to permanently arrest cancer progression. As androgens like testosterone are withdrawn, prostate cancer cells lose their androgen sensitivity and begin to proliferate without hormone growth factors. In this study, we constructed and analyzed a mathematical model of the integration between hormone growth factor signaling, androgen receptor activation, and the expression of cyclin D and Prostate-Specific Antigen in human LNCaP prostate adenocarcinoma cells. The objective of the study was to investigate which signaling systems were important in the loss of androgen dependence. The model was formulated as a set of ordinary differential equations which described 212 species and 384 interactions, including both the mRNA and protein levels for key species. An ensemble approach was chosen to constrain model parameters and to estimate the impact of parametric uncertainty on model predictions. Model parameters were identified using 14 steady-state and dynamic LNCaP data sets taken from literature sources. Alterations in the rate of Prostatic Acid Phosphatase expression was sufficient to capture varying levels of androgen dependence. Analysis of the model provided insight into the importance of network components as a function of androgen dependence. The importance of androgen receptor availability and the MAPK/Akt signaling axes was independent of androgen status. Interestingly, androgen receptor availability was important even in androgen-independent LNCaP cells. Translation became progressively more important in androgen-independent LNCaP cells. Further analysis suggested a positive synergy between the MAPK and Akt signaling axes and the translation of key proliferative markers like cyclin D in androgen-independent cells. Taken together, the results support the targeting of both the Akt and MAPK pathways. Moreover, the analysis suggested that direct targeting of the translational machinery, specifically eIF4E, could be efficacious in androgen-independent prostate cancers
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