Lattice-gas approach to semiconductor device simulation

A new approach to semiconductor device simulation is presented which is based on a lattice-gas or cellular-automata model and is quite similar to methods recently explored in fluid dynamics. The approach obtains a stochastic solution to the diffusion-drift partial differential equations describing electron transport in semiconductors. The lattice-gas method appears to be fairly well-suited to electron transport simulation with its ability to handle complex geometry, its ease of programming and its stability being some key advantages. In addition, we show that the structure of the model itself—its Boolean character—leads to a partial inclusion of electron degeneracy effects. Finally, we make a preliminary assessment of the performance of the diffusion-drift lattice-gas model, finding it to be competitive with conventional approaches when its inherent parallelism is fully exploited.     

Monte-Carlo simulation of decananometric nMOSFETs: Multi-subband vs. 3D-electron gas with quantum corrections

In this paper two Monte-Carlo simulators implementing different models for the influence of carrier quantization on the electrostatics and transport are used to analyze sub-100 nm double-gate SOI devices. To this purpose a new stable and efficient scheme to implement the contacts in the simulation of double-gate SOI devices is introduced first. Then, results in terms of drain current and microscopic quantities are compared, providing new insight on the limitation of a well assessed semiclassical transport simulation approach and a more rigorous multi-subband model.     

Simulation of Silicon Nanowire Transistors Using Boltzmann Transport Equation Under Relaxation Time Approximation

An efficient approach for the simulation of electronic transport in nanoscale transistors is presented based on the multi-subband Boltzmann transport equation under the relaxation time approximation, which takes into account the effects of quantum confinement and quasi-ballistic transport. This approach is applied to the study of electronic transport in circular gate-all-around silicon nanowire transistors. Comparison with the nonequilibrium Green's function method shows that the new method gives reasonably accurate terminal characteristics. We study the influence of silicon body diameter and gate length on the terminal current and subthreshold slope (SS). We have found that the calculated ON current is inversely proportional to the gate length to the power 1/2, and that the silicon body diameter should be smaller than roughly 2/3 of the channel length in order to maintain the SS within 80 mV/dec.     

MC simulation of strained-Si MOSFET with full-band structure and quantum correction

A new two-dimensional full-band Monte Carlo simulator, "Monte Carlo University of Texas" (MCUT) is introduced and described in this paper. MCUT combines some of the best features of semiclassical MC device simulation including full-band structure and flexibility of scattering processes, with generality of material composition and the ability to address degeneracy breaking among energy valleys and the associated effects on scattering and transport due to quantum confinement and strain effects. The latter capability derives from extension of a prior crystal-momentum-independent self-consistent Poisson-Schro/spl uml/dinger-based quantum corrected potential, to a valley dependent quantum correction via, in part, a new modeling concept of "effective strain" within the full-band structure code. Low field mobility simulation results for large tensile strained-Si channel nMOSFETs and unstrained-Si channel nMOSFETs device are compared with other simulation methods and experimental data to demonstrate the effectiveness of the approach, and the abilities to simulate high-field transport and transport in devices of a few 10s of nanometer channel lengths are briefly demonstrated.     

基于SDN的链式快速转发网络模型研究

针对当前网络中降低数据包传输时延的机制复杂且在数据包的匹配过程中存在较高的处理时延,提出了基于软件定义网络(SDN)架构的虚拟链式快速通道路由模式(Chain-Like Hyperchannel Routing Mode,CHRN),在将不同优先级的数据流映射到不同的虚拟传输网络上的同时,时延敏感型数据将采用不查表的快速转发方式来降低数据包的处理时延.实验证明,这种方式在不影响普通数据包传输的条件下,有效提高了时延敏感型数据的传输效率.     

Physics-based modeling of submicron GaN permeable base transistors

We present the first physics-based nonstationary modeling of a submicron GaN permeable base transistor. Three different transport models are compared: drift-diffusion, energy balance, and ensemble Monte Carlo. Transport parameters and relaxation times used by the carrier transport equations are consistently derived from particle simulation. The current-voltage (I-V) characteristics predicted with the energy balance model are in good agreement with those obtained from direct Monte Carlo device simulation. On the other hand, the drift-diffusion approach appears to be inadequate for the device under study, even if improved high-field mobility models are adopted     

Transient simulation of heterojunction photodiodes-part I:computational methods

A novel approach is presented for incorporating the transient solution of one-dimensional semiconductor drift-diffusion equations within a general circuit simulation tool. This approach allows simple representation of localized carrier transport models of simulated devices through equivalent circuit elements such as voltage controlled current sources and capacitors. It also lends itself to mixed-mode transient simulation of devices and circuits. The utility of the new simulation approach in state-of-the-art device design is demonstrated by the transient response analysis of a GaAs heterojunction p-i-n photodiode, and by the time-domain analysis of an integrated photoreceiver circuit     

A Genetic Algorithm Approach for Intermodal Cooperation with High-Speed Rail: The Case of Thai Transportation System

The Thai government has a plan to start the first operation of the Thai High-Speed Rail (THSR) in 2021. However, ensuring the profit of THSR while limiting the project impacts on existing transport options is challenging. In this study, an approach for identifying the optimal travel frequency for impacted transportation services after the THSR operation is implemented. The genetic algorithm (GA) is introduced with specific value functions of various transport options, including rail, bus, and van, to reschedule each travelling option under the intermodal cooperation model. The constraint of GA is that the profit of the individual transport option in the next generation will have to be higher than the total profit of the previous generation. From the case study between Nakhon Ratchasima and Bangkok, the simulation results show that THSR and other transport options have overall gain higher profits after the start of THSR operation. Regarding social welfare theory, the simulation results show that the profit of each transport option is proven to be stable concerning travel schedule frequency after implementation of the THSR system.

     

Flexible and robust packet transport for digital HDTV

The packet-oriented transport approach used in the advanced digital television (ADTV) system for terrestrial HDTV broadcast is described. ADTV achieves robust HDTV delivery on terrestrial simulcast channels via MPEG video compression, prioritization of MPEG data, and `cell-relay' type packet transport in conjunction with a two-tier physical transmission scheme. General design issues relevant to the development of the proposed transport protocol are discussed. ADTV's prioritization algorithm for partitioning MPEG-encoded video into high-priority (HP) and standard-priority (SP) bit streams is outlined. The data transport format supporting these prioritized compressed video bit streams is described. The three principal sublayers of the ADTV transport protocol are discussed in terms of specific functions, impact of system performance, and hardware implementation factors. A proof-of-concept simulation model that incorporates transport encoding and decoding functionality is outlined, and performance evaluation results are given for illustrative transmission scenarios     

Towards treatment planning for the embolization of arteriovenous malformations of the brain: intranidal hemodynamics modeling

This paper presents a patient-derived model for the simulation of the hemodynamics of arteriovenous malformations of the brain (BAVM). This new approach is a step toward the simulation of the outcome of the embolization of the BAVM during treatment planning. More specifically, two aspects of the planning are pursued: simulation of the change of blood flow in the brain vasculature after the blocking of the malformation and simulation of the transport of the embolic liquid. The method we propose is tested on 3 BAVM cases of varying complexity. Twenty two out of 24 main BAVM flow paths have been identified well by simulation.     

Discretization schemes for high-frequency semiconductor devicemodels

This paper provides an overview on the numerical issues involved in the spatial and time-domain discretization of the coupled transport-electromagnetic models used in the simulation of high-frequency semiconductor devices. The physical transport models derived from the Boltzmann transport equation (BTE) are reviewed in order of decreasing complexity, from the full hydrodynamic model to the drift-diffusion approach. Spatial discretization is introduced starting from ad hoc approaches developed in the field of semiconductor modeling, like the Scharfetter-Gummel (1969) scheme; a critical comparison is then provided with the upwind finite-element schemes. Finally, time-domain discretization issues are reviewed, with particular stress on innovative developments in the area of hydrodynamic and of coupled transport-full-wave EM models     

A quantum correction based on Schrodinger equation applied to Monte Carlo device simulation

A full-band Monte Carlo model has been coupled to a Schrodinger equation solver to account for the size quantization effects that occur at heterojunctions, such as the oxide interface in MOS devices. The overall model retains the features of the well-developed semi-classical approach, by treating self-consistently the Schrodinger solution as a correction to the particle-based Monte Carlo. The simulator has been benchmarked by comparing results for MOS capacitors and double gate structures with a self-consistent quantum solution, showing that the proposed approach is efficient and accurate. This quantum correction methodology is extended to device simulation, by accounting for the interplay between confinement and transport through a parameter which we call "transverse" temperature. This approach appears to be valid even for nanometer-scale devices in which nonequilibrium ballistic transport is occurring. We present simulations of a 25-nm MOSFET and compare results obtained with and without the quantum correction.     

Carrier dynamics studies through free-carrier absorption: a MonteCarlo study for silicon

Monte Carlo based computer simulations normally used for transport studies in semiconductors are extended and used to study free-carrier absorption of subbandgap radiation in semiconductors. The approach is applied to n-type silicon where we find very good agreement with experimental results and calculations based on quantum electrodynamics. The computer simulation method also allows us to study free-carrier absorption in semiconductors with a dc bias. We solve the classical transport equation to show that the absorption coefficient in the presence of a dc bias can be used to obtain information on the carrier temperature, momentum relaxation time, as well as energy relaxation time. Monte Carlo studies show this to be the case. Thus, we show that important carrier dynamics properties can be obtained from long-wavelength free-carrier absorption studies done on samples with a dc bias     

Calculation of channeling effects during ion implantation using the Boltzmann transport equation

The Boltzmann transport equation approach for ion implantation simulation has been enhanced to allow the calculation of channeling effects. Simple models are used for scattering into channeling directions and for motion along channels in order to obtain useful results without requiring excessive amounts of computation time. Comparison with experimental profiles show good agreement for boron implantation into and silicon based on experimental values for electronic stopping powers. Where stopping data is not available, parameters can be adjusted to fit the experimental profiles.     

Full-wave electromagnetic simulation of millimeter-wave active devices and circuits

This paper discusses the most recent progress in developing effective physics-based models for devices operating at millimeter-wave frequencies. The model is based on coupling dynamic electromagnetic wave solutions with carrier transport models. The potentials of this modeling approach for both device simulation and the global simulation of millimeter-wave circuits are demonstrated. Results comparing the full-wave model developed with conventional electrostatic models are provided through the simulation of different microwave transistors. The ability of the model to detect traveling wave effects, such as phase mismatch between the input and output electrodes of a conventional transistor, and their effects on the device gain are also provided. Results from the simulation of an air-bridged gateMesfet, designed to reduce traveling wave effects in high frequency transistors and solve the problem associated with high gate resistance, are illustrated and discussed. Finally, results showing the ability of this technique to model the nonlinearity and the harmonic distortion are provided through the simulation of an amplifier circuit.     

A simplified impact ionization model based on the average energy ofhot-electron subpopulation

A previously developed nonlocal impact ionization model based on the average energy of hot-electron subpopulation has been further simplified. The system of hydrodynamic transport equations consisting of three equations for these high-energy electrons has been reduced to a single equation. The simulation results for n⁺-n-n⁺ structures are in good agreement with Monte Carlo (MC) calculations. The model is easily applicable to two-dimensional (2-D) problems by exploiting the current flow line approach     

Multi-layer loss recovery in TCP over optical burst-switched networks

It is well-known that the bufferless nature of optical burst-switching (OBS) networks cause random burst loss even at low traffic loads. When TCP is used over OBS, these random losses make the TCP sender decrease its congestion window even though the network may not be congested. This results in significant TCP throughput degradation. In this paper, we propose a multi-layer loss-recovery approach with automatic retransmission request (ARQ) and Snoop for OBS networks given that TCP is used at the transport layer. We evaluate the performance of Snoop and ARQ at the lower layer over a hybrid IP-OBS network. Based on the simulation results, the proposed multi-layer hybrid ARQ + Snoop approach outperforms all other approaches even at high loss probability. We developed an analytical model for end-to-end TCP throughput and verified the model with simulation results.     

An accurate charge control approach for modeling excess phase shiftin the base region of bipolar transistors

The conventional charge control approach is extended to enable the accurate determination of excess phase shift in the ac common-emitter current gain of bipolar transistors arising from distributed stored minority carrier charge in the neutral base. Generalized expressions, valid for transistors with arbitrary impurity profiles and position-dependent transport parameters, are presented from which the excess phase shift can be determined solely from device structure and process data. The ac model parameters which result from the extended charge control approach are used in an existing high-frequency compact nonquasi-static bipolar model which is suitable for SPICE simulation     

Quasi-two-dimensional modeling of GaAs MESFET's

A numerical simulation of GaAs MESFET structures is presented. The approach taken in this paper combines an analytical solution with a full simulation. Poisson's equation, the current continuity equation, and an electron-temperature equation are formulated in terms of a geometry factor that defines the shape of the conducting channel in the MESFET. The transport equations are then solved in one dimension and the channel geometry factor is found analytically. This method was found to be considerably faster than full two-dimensional simulations. The model has been compared to full two-dimensional drift-diffusion and energy-momentum results to determine its validity.