Thermally Self-Consistent Monte Carlo Device Simulations

We present details of a Monte Carlo simulation code which is coupled to a Heat Diffusion Equation (HDE) solver. Through an iterative procedure, which bypasses the differences in electronic and thermal timescales, this coupled code is capable of producing steady-state thermally self-consistent device characteristics. Electronically-generated thermal flux is calculated by monitoring the net rate of phonon emission, which may be resolved both spatially and by phonon type. The thermal solution is extracted through use of a novel analytical thermal resistance matrix technique which avoids calculation of temperatures beyond the electronically important device region while including the large-scale boundary conditions. On application to a GaAs MESFET the expected thermal droop behaviour is obtained in the I-V characteristics and we find a linear relationship between peak lattice temperature and applied source-drain bias. At moderate biases the contribution of intervalley phonons to the thermal power output surpasses that of optical phonons.     

Quantum Monte Carlo Device Simulation of Nano-Scaled SOI-MOSFETs

Quantum transport properties of nano-scaled SOI-MOSFETs are investigated based on a quantum Monte Carlo (MC) device simulation. The quantum mechanical effects are incorporated in terms of a quantum correction of potential in the well-developed particle MC computational techniques. The ellipsoidal multi-valleys of silicon conduction band are also considered in the simulation. First, the validity of the quantum MC technique is verified by comparing the simulated results with a self-consistent Schrödinger-Poisson solution at thermal equilibrium. Then, we apply the technique to non-equilibrium and quasi-ballistic quantum transport in nano-scaled SOI-MOSFETs.     

Comparison of Quantum Corrections for Monte Carlo Simulation

As semiconductor devices are scaled down to nanometer scale dimensions, quantum mechanical effects can become important. For many device simulations at normal temperatures, an efficient quantum correction approach within a semi-classical framework is expected to be a practical way applicable to multi-dimensional simulation of ultrasmall integrated devices. In this paper, we present a comparative study on the three quantum correction methods proposed to operate within the Monte Carlo framework, which are based on Wigner transport equation, path integrals, and Schrödinger equation. Quantitative comparisons for the strengths and weaknesses of these methods are discussed by applying them to size quantization and tunneling effects.     

The Effective Conduction Band Edge Method of Quantum Correction to the Monte Carlo Device Simulation

To include quantum effects, a quantum correction is made to the semi-classical Monte Carlo (MC) simulation by the effective conduction band edge (ECBE) method. The quantum corrected potential energy can be calculated from the classical potential energy by the ECBE equation and thus the quantum mechanical force in the simulation replaces the classical force. Under the non-equilibrium condition, carriers have a temperature different from the lattice. For the simulation of a double-gate MOSFET, we replace thermal energy in the ECBE equation with the average value of the stress tensor along each transverse line, to account for the variation of the electron “temperature” along the longitudinal direction. A 3 nm thick double gate nMOSFET is simulated. The result shows that electrons now see a higher barrier from the source to the drain if the carrier temperature is considered, resulting in a smaller drain current compared to that obtained from the previous ECBE method.     

A Wigner Function Based Ensemble Monte Carlo Approach for Accurate Incorporation of Quantum Effects in Device Simulation

We present results of both Gaussian wave-packet tunneling though a single barrier structure and RTD operation achieved from a particle-based Ensemble Monte Carlo (EMC) simulation that is based on the Wigner distribution function (WDF). Methods of including the Wigner potential into the EMC, to incorporate naturally quantum phenomena, via a particle property we call the affinity are discussed. Results showing tunneling and correlation build-up in both cases are presented.     

Band-to-Band Tunneling by Monte Carlo Simulation for Prediction of MOSFET Gate-Induced Drain Leakage Current

Gate induced drain leakage (GIDL) current caused by band-to-band tunneling is studied by Monte Carlo simulation with ballistic least-action trajectory integration. Together with weak inversion and early subthreshold simulation by drift-diffusion formalism, the entire range of the OFF-state drain current can be predicted for technology evaluation. The methodology is demonstrated by a case study for source/drain asymmetry super-halo design.     

Quantum Corrected Full-Band Cellular Monte Carlo Simulation of AlGaN/GaN HEMTs

A full-band Cellular Monte Carlo (CMC) approach is applied to the simulation of electron transport in AlGaN/GaN HEMTs with quantum corrections included via the effective potential method. The best fit Gaussian parameters of the effective potential method for different Al contents and gate biases are calculated from the equilibrium electron density. The extracted parameters are used for quantum corrections included in the full-band CMC device simulator. The charge set-back from the interface is clearly observed. However, the overall current of the device is close to the classical solution due to the dominance of polarization charge.     

基于蒙特卡洛仿真的航空用测控装置可靠性预计

文章研究了某型面向航空应用的高可靠性测控装置的可靠性预计问题。文章根据测控装置设计原理图建立了可靠性框图,基于GJB/Z299C手册和应力分析法得到了元器件可靠性数据,建立了基于蒙特卡洛仿真方法的系统可靠性预计数学模型,预计了测控装置的可靠性指标,并通过分析查找可靠性薄弱环节,改进了设计方案,提高了可靠性,最终达到设计要求。文章研究表明,蒙特卡洛仿真方法对于混连复杂电子系统的可靠性预计具有较好的实用性。     

Wigner Function-Based Simulation of Quantum Transport in Scaled DG-MOSFETs Using a Monte Carlo Method

Source-to-drain tunneling in deca-nanometer double-gate MOSFETs is studied using a Monte Carlo solver for the Wigner transport equation. This approach allows the effect of scattering to be included. The subband structure is calculated by means of post-processing results from the device simulator Minimos-NT, and the contribution of the lowest subband is determined by the quantum transport simulation. By separating the potential profile into a smooth classical component and a rapidly varying quantum component the numerical stability of the Monte Carlo method is improved. The results clearly show an increasing tunneling component of the drain current with decreasing gate length. For longer gate lengths the semi-classical result is approached.     

Monte Carlo simulation of double gate MOSFET including multi sub-band description

A new two-dimensional self-consistent Monte-Carlo simulator including the multi sub-band transport in a 2D electron gas is described and applied to an ultra-thin Double Gate MOSFET. This approach takes into account both out of equilibrium transport and quantization effects. This method improves significantly microscopic insight into the operation of deep sub-100 nm CMOS devices. We analyze the ballistic, quantization and roughness effects in a 12 nm-long DGMOS transistor. In particular, we focus on the link between non-stationary transport and the evolution of sub-band occupancy along the channel.     

Quantum Ensemble Monte Carlo simulation of silicon-based nanodevices

A Quantum Ensemble Monte Carlo (QEMC) simulator is used to calculate electrical characteristics and transient response of actual nanotransistors: both sub-50 nm CMOS N-MOSFETs and ultrathin double gate SOI transistors have been deeply studied. Doping profiles and oxide thickness have been selected to cope with the available specifications of the ITRS Roadmap. The Quantum corrected Ensemble Monte Carlo simulator (QEMC) has been used to self-consistently solve the Boltzmann Transport and Poisson equations in actual devices. Quantum effects are included through the Multi-Valley Effective Conduction Band Edge (MV-ECBE) technique, and adequate approaches for phonon and surface roughness scattering have been developed to include the effects of carrier quantization in pseudo-2DEG simulations.     

Quantum Corrected Monte Carlo Simulation of Semiconductor Devices Using the Effective Conduction-Band Edge Method

In recent years much effort has been devoted to the quantum mechanically corrected Monte Carlo simulation of nano-scale semiconductor devices. The effective potential and the Wigner or the Bohm quantum potential are usually chosen for making such quantum correction. In this study we propose another approach based on the Bohm potential by transforming the density gradient to an effective conduction-band edge gradient. Similar to the effective potential method, this method has the advantage of not being affected by density fluctuations. We have applied this method to the simulation of a double-gate nMOSFET. Results are compared to those obtained from the semi-classical Monte Carlo simulation without the quantum correction.     

Monte Carlo Simulation of Carbon Nanotube Devices

A self-consistent Monte Carlo simulator for carbon-nanotube, field-effect transistors (CNTFETs) is reported. Transport is simulated in zigzag (n, 0) nanotubes having a coaxial gating geometry, and key aspects of the Monte Carlo implementation are described. The simulator is used to extract the channel mean-free path (MFP) of CNTFETs. Although the mean-free path of acoustic phonons in metallic tubes is known to be very large (on the order of a micron), our results show that the channel MFP is much shorter and bias dependent in CNTFETs, and that CNTFETs therefore operate near the ballistic limit only at channel lengths that are considerably shorter than those required for near-ballistic transport in metallic tubes.     

面光源的蒙特卡洛模拟

本文从点光源出发,讨论了面光源的蒙特卡洛模拟的方法,提出了模拟的公式和原则.然后以圆柱面光源为例,给出了模拟光源、标准光源和实际的卤钨灯L7386A通过自由曲面反射器后获得的照度图,比较了它们的结果,并简要分析了原因.     

Quantum Monte Carlo simulation of dissipative transport using Bohmian trajectories

In this paper, a Monte Carlo method is proposed, which utilizes Bohmian trajectories to simulate dissipative transport in one-dimensional quantum devices. The proposed method, similar to the classical Monte Carlo method, is capable of simulating both elastic and inelastic scattering effects, with the distinction that quantum effects such as tunneling are also included. At first, the Bohmian trajectories for the wave packets injected from the right and the left contacts are obtained by solving the time-dependent Schrodinger equation, and then scattering effects are included via stochastic changes applied on the electron trajectories. We have shown that the results of the proposed model agree well with those of NEGF formalism.     

电力系统小扰动概率稳定性的蒙特卡罗仿真

计及发电方式、负荷水平及网络拓扑的不确定性,基于蒙特卡罗状态抽样方法,通过分析系统特征值、特征向量及参与因子等特征参数的概率特性和失稳概率研究电力系统小扰动概率稳定问题。分析中分别用离散分布随机变量和正态分布随机变量描述发输电元件状态及负荷水平的概率特性,并重点讨论了网络拓扑的不确定性对失稳概率指标的影响。一个两区域算例表明所提出的方法能够从概率统计意义上为小扰动稳定性分析及电力系统稳定器（PSS）的合理配置等提供更为丰富、全面的信息。     

A Monte Carlo Method Seamlessly Linking Quantum and Classical Transport Calculations

A Monte Carlo method for carrier transport is presented, which simultaneously takes into account quantum interference and dissipation effects. The method solves the space-dependent Wigner equation including semi-classical scattering through the Boltzmann collision operator. To this equation a particle model is assigned, which interprets the non-local potential operator as a generation term for numerical particles of positive and negative statistical weight. A numerical technique to control the avalanche of numerical particles is discussed. Since the Wigner equation simplifies to the Boltzmann equation in classical device regions, the solutions of the quantum kinetic equation and the classical one are linked in a natural way. This approach allows the simulation of a quantum region embedded in an extended classical region. Results of this approach are demonstrated for a resonant tunneling diode.     

基于蒙特卡洛模拟的电力客户满意度测评

采用科学的方法客观评价供电企业的服务质量,更精准地提高供电公司的客户满意度,更精准地定位各类顾客的需求,是十分重要的。在样本采集数量有限的前提下,用蒙特卡洛模拟大样本,得出符合市场情况的各个指标评分及该地区的综合评分。通过实例验证了蒙特卡洛模拟对于普通的加权平均法更具有随机性,能反映出每个指标细小的数据波动情况,可以精准地定位各类顾客的需求及其所反映的不满意项,为电力公司开展满意度测评工作提供参考依据。     

Towards Fully Quantum Mechanical 3D Device Simulations

We present a simulator for calculating, in a consistent manner, the realistic electronic structure of three-dimensional heterostructure quantum devices under bias and its current density close to equilibrium. The electronic structure is calculated fully quantum mechanically, whereas the current is determined by employing a semiclassical concept of local Fermi levels that are calculated self-consistently. We discuss the numerical techniques employed and present illustrative examples that are compared with quantum transport calculations. In addition, the simulator has been used successfully to study shape-dependent charge localization effects in self-assembled GaAs/InGaAs quantum dots.     

Smart Dust: Monte Carlo Simulation of Self-Organised Transport

Smart dust is envisaged as swarms of miniature communication/sensor devices useful for remote monitoring in space exploration. With diameters and densities comparable to sand particles the behaviour of passive dust will be identical to the movement of airborne sand. Here we examine algorithms for the adaptive shape change of smart dust modes that permits a change in drag coefficient depending on whether or not the random motion is in a favourable direction. Monte Carlo simulations are reported for swarms of smart dust devices transporting in the wind-dominated environment of the Martian landscape. It is concluded that relatively simple shape changing algorithms, activated through an electro-active polymer sheath, will permit self-organised transport over large distances.