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In this work, it is shown that the differential loss between the TE- and TM-polarized fundamental modes in a highly birefringent photonic crystal fiber (PCF) can be enhanced by bending the fiber. As a result, a design approach for single-mode single-polarization operation has been developed and is discussed. A rigorous full-vectorial H-field-based finite element approach, which includes the conformal transformation and the perfectly matched layer, is used to determine the single-polarization properties of such a highly birefringent PCF by exploiting its differential bending losses.
A golden spiral photonic crystal fiber (GS-PCF) design is presented in which air holes are arranged in a spiral pattern governed by the golden ratio, where the design has been inspired by the optimal arrangement of seeds found in nature. The birefringence and polarization properties of this fiber are analyzed using a vectorial finite-element method. The fiber that is investigated shows a large modal birefringence peak value of 0.016 at an operating wavelength of 1.55 μm and exhibits highly tuneable dispersion with multiple zero dispersion wavelengths and also large normal dispersion. The GS-PCF design has identical circular air holes that potentially simplify fabrication. In light of its properties, the GS-PCF could have application as a highly birefringent fiber and in nonlinear optics, and moreover the 2D chiral nature of the pattern...
The perfectly matched layer (PML) boundary condition is generally employed to prevent spurious reflections from numerical boundaries in wave propagation methods. However, PML requires additional computational resources. We have examined the performance of the PML by changing the distribution of sampling points and the PML’s absorption profile with a view to optimizing the PML’s efficiency. We used the collocation method in our study. We found that equally spaced field sampling points give better absorption of beams under both optimal and nonoptimal conditions for low PML widths. At high PML widths, unequally spaced basis points may be equally efficient. The efficiency of various PML absorption profiles, including new ones, has been studied, and we conclude that for better numerical efficiency it is important to choose an appropriate pr...
Intrinsic parameter fluctuations introduced by discreteness of charge and matter will play an increasingly important role when semiconductor devices are scaled to decananometer and nanometer dimensions in next-generation integrated circuits and systems. In this paper, we review the analytical and the numerical simulation techniques used to study and predict such intrinsic parameters fluctuations. We consider random discrete dopants, trapped charges, atomic-scale interface roughness, and line edge roughness as sources of intrinsic parameter fluctuations. The presented theoretical approach based on Green's functions is restricted to the case of random discrete charges. The numerical simulation approaches based on the drift diffusion approximation with density gradient quantum corrections covers all of the listed sources of fluctuations. ...
In this paper, we investigate various aspects of the polysilicon gate influence on the random dopant induced threshold voltage fluctuations in sub-100 nm MOSFETs with ultrathin gate oxides. The study is done by using an efficient statistical three-dimensional (3D) “atomistic” simulation technique. MOSFETs with uniform channel doping and with low doped epitaxial channels have been investigated. The simulations reveal that even in devices with a single crystal gate the gate depletion and the random dopants in it are responsible for a substantial fraction of the threshold voltage fluctuations when the gate oxide is scaled to thickness in the range of 1-2 nm. Simulation experiments have been used in order to separate the enhancement in the threshold voltage fluctuations due to an effective increase in the oxide thickness associated with th...
A three-dimensional (3-D) 'atomistic' simulation study of random dopant induced threshold voltage lowering and fluctuations in sub-0.1 μm MOSFETs is presented. For the first time a systematic analysis of random dopant effects down to an individual dopant level was carried out in 3-D on a scale sufficient to provide quantitative statistical predictions. Efficient algorithms based on a single multigrid solution of the Poisson equation followed by the solution of a simplified current continuity equation are used in the simulations. The effects of various MOSFET design parameters, including the channel length and width, oxide thickness and channel doping, on the threshold voltage lowering and fluctuations are studied using typical samples of 200 atomistically different MOSFETs. The atomistic results for the threshold voltage fluctuations ...
A comprehensive RF analysis technique based on ensemble Monte Carlo (EMC) simulation of compound FET's with realistic device geometry is presented. Y-parameters are obtained through Fourier transformation of the EMC transients in response to small changes in the terminal voltages. The terminal currents are statistically enhanced and filtered to allow for reliable y-parameters extraction. Improved analytic procedure for extracting the intrinsic device small-signal circuit components is described. As a result, stable y-parameters and reliable circuit components can he extracted for the whole range of device operation voltages. Parasitic components like contact and gate resistances are included in the y-parameters at a post processing stage to facilitate the forecast of the performance figures of merit of real devices. The developed RF te...
This paper describes a new measurement technique, the forward gated-diode current characterized at low drain voltages to be applied in MOSFET's for investigating hot-carrier stress-induced defects at high spatial resolution. The generation/recombination current in the drain-to-substrate diode as a function of gate voltage, combined with two-dimensional numerical simulation, provides a sensitive tool for detecting the spatial distribution and density of interface defects. In the case of strong accumulation, additional information is obtained from interband tunneling processes occurring via interface defects. The various mechanisms for generating interface defects and fixed charges at variable stress conditions are discussed, showing that information complementary to that available from other methods is obtained
Based on the successful calibration on a 0.25 /spl mu/m strained Si/SiGe n-type MODFET, this paper presents a gate length scaling study of double-side doped Si/SiGe MODFETs. Our simulations show that gate length scaling improves device RF performance. However, the short channel effects (SCE) along with the parasitic delays limit the device performance improvements. We find that it is necessary to consider scaling (dimensions and doping) of both the lateral and vertical architecture in order to optimize the device design.
We have studied the performance potential of sub 100 nm compound MOSFETs with InGaAs channel and high-k gate insulator, using ensemble Monte Carlo simulations. The results show that such devices could deliver 200-300% increase in the drive current compared to conventional MOSFETs with analogous channel lengths and device structure. This improvement is much higher than the 20-30% drive current increase in similar devices with strained Si channels on virtual SiGe substrates. As a viable solutions to the constant drive current bottleneck anticipated in the International Roadmap for Semiconductors for the next generations of Si MOSFETs it advocates further research in respect of the manufacturability of compound MOSFETs.
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