Numerical Investigation of Shot Noise between the Ballistic and the Diffusive Regime

We investigate shot noise suppression in several mesoscopic structures by means of a numerical approach based on the computation of the transmission matrix with the recursive Green's function method. We retrieve the universal values of the suppression factor obtained with random matrix theory for chaotic cavities and diffusive conductors. We then extend the investigation to more complex structures, such as multiple cascaded cavities and partially diffusive systems, and discuss the consequences on the shot noise suppression factor. Finally, we analyze the behavior of shot noise in an electron waveguide containing a large number of scatterers as the spatial position of the scatterers is changed from a regular array to a random distribution.     

Numerical Analysis of Coaxial Double Gate Schottky Barrier Carbon Nanotube Field Effect Transistors

Carbon nanotube field-effect transistors (CNTFETs) have been studied in recent years as a potential alternative to CMOS devices, because of the capability of ballistic transport. The ambipolar behavior of Schottky barrier CNTFETs limits the performance of these devices. A double gate design is proposed to suppress this behavior. In this structure the first gate located near the source contact controls carrier injection and the second gate located near the drain contact suppresses parasitic carrier injection. To avoid the ambipolar behavior it is necessary that the voltage of the second gate is higher or at least equal to the drain voltage. The behavior of these devices has been studied by solving the coupled Schrödinger-Poisson equation system. We investigated the effect of the second gate voltage on the performance of the device and finally the advantages and disadvantages of these options are discussed.     

Influence of Ballistic Effects in Ultra-Small MOSFETs

Single Gate (SG) and Double Gate (DG) MOSFETs with strained and unstrained Si channel are studied using semi-classical Monte Carlo simulation to investigate the influence of ballistic electrons. We analyze how the intrinsic ballisticity B_int, directly deduced from accurate counting of scattering events undergone by carriers in the channel, depends on channel length, channel doping, strain, MOS architectures and bias. Besides, we show that the intrinsic ballisticity B_int seems to be a relevant parameter to explain the performance of small devices. It is highlighted that in undoped channels shorter than 50 nm, quasi-ballistic effects are responsible for a significant improvement in the on-current. However, for channel length smaller than about 30 nm (B_int > 20%) the current tends to the ballistic limit and the increase in intrinsic ballisticity has a decreasing impact on the current.     

Code for the 3D Simulation of Nanoscale Semiconductor Devices, Including Drift-Diffusion and Ballistic Transport in 1D and 2D Subbands, and 3D Tunneling

We present a three-dimensional device simulator, suitable for the study of a wide range of nanoscale devices, in which quantum confinement and carrier transport are taken into account. In particular, depending on the confinement, the 1D, 2D or 3D Schrödinger equation with density functional theory in the local density approximation is coupled with the Poisson equation in the three-dimensional domain. Continuity equation in the ballistic and in the drift-diffusion regime are also solved assuming separation of the subbands.     

Study of Noise Properties in Nanoscale Electronic Devices Using Quantum Trajectories

Noise properties in nanoscale devices are studied extending, via quantum trajectories, the classical particle Monte Carlo techniques to devices in which quantum non-local effects are important. This approach can be used to study noise in a wide range of frequencies and can also be easily coupled to a Poisson solver to study long range Coulomb effects in noise characteristics. As a numerical example, we have studied noise in a tunneling barrier showing that the results obtained within our approach exactly reproduce those of the standard Landauer-Buttiker formalism in the zero frequency limit.     

A Computational Exploration of Lateral Channel Engineering to Enhance MOSFET Performance

Techniques to engineer a MOSFET's channel in the lateral direction have been proposed to enhance the device performance. In this paper, we present a thorough simulation study to evaluate the feasibility of such lateral engineering techniques. Each of three types of transport equations, the ballistic Boltzmann, drift-diffusion and non-equilibrium Green's function with scattering, is solved self-consistently with 2-D Poisson equation to simulate device performance under both the ballistic and dissipative transport conditions. The results indicate that even if highly idealized device structures are assumed, only limited improvements over the conventional MOSFETs can be achieved by the channel engineering techniques. These results don't conflict with reports of large on-current improvements using the lateral channel engineering, because those comparisons with the conventional MOSFETs were done without specifying a common off-current.     

现场低压电力线噪声对载波通信的影响分析

噪声特性作为电力线信道的1个重要特性,对低压电力线载波通信有着较强的影响作用.我国低压电网环境复杂,电力线上存在着各种强时变性的噪声干扰.结合现场某一典型台区的电能采集情况以及采集到的噪声数据,分析得出电力线噪声在频域与时域2个方面对低压电力线载波通信的影响规律.     

电力变压器噪声研究与控制

为了降低变压器噪声给人们工作和生活带来的影响,笔者较全面地阐述了变压器噪声控制的重要意义和这些年来国内外的研究成果,说明了振动是产生变压器本体噪声和冷却装置噪声的原因.归纳了变压器噪声的研究方法:变压器远场辐射噪声可以通过实测数据统计和建立计算模型两类方法进行分析,变压器辐射噪声的测量用声强法比传统的声压法更加接近真实情况.详细介绍了变压器的噪声控制方法,在噪声源控制上选用优质高取向硅钢片,在设计、工艺和安装等诸多方面采取有效措施降低噪声;在噪声传播过程中采用缓冲装置、消声法、设置隔音层、隔音室等方法增大噪声在传播过程中的衰减以降低噪声.最后,对变压器噪声控制的发展趋势提出了一些看法.     

Effect of elastic processes and ballistic recovery in silicon nanowire transistors

Scaling of silicon devices is fast approaching the limit where a single gate may fail to retain effective control over the channel region. Of the alternative device structures under focus, silicon nanowire transistors (SNWT) show great promise in terms of scalability, performance, and ease of fabrication. Here we present the results of self-consistent, fully 3D quantum mechanical simulations of SNWTs to show the role of surface roughness (SR) and ionized dopant scattering on the transport of carriers. We find that the addition of SR, in conjunction with impurity scattering, causes additional quantum interference which increases the variation of the operational parameters of the SNWT. However, we also find that quantum interference and elastic processes can be overcome to obtain nearly ballistic behavior in devices with preferential dopant configurations.     

变压器噪声产生的原因及降低噪声的措施

分析了变压器运行中噪声产生的原因,介绍了在制造过程中采取的降低变压器噪声的措施,利用实例阐述了将变压器置于室内降低环境噪声的效果。     

形态学一小波综合滤波器抑制局放现场干扰

提出了一种用于电力变压器局部放电在线检测中滤除周期性干扰 (利用形态开、闭组合形态滤波器 )和白噪声干扰 (利用小波模极大值法 )的形态学 小波综合滤波新方法。仿真结果表明该方法对干扰的噪声抑制比 (NNR) >80dB ,而现场实测的NNR >30dB。     

牵引电机整机气动噪声特性的数值模拟研究

一般牵引电机噪声由冷却风扇噪声、电磁振动噪声和机械噪声组成,其中冷却风扇引起的气动噪声是重要构成部分。建立牵引电机整机计算流体动力学(CFD)计算模型,利用DES-SST湍流模型计算牵引电机内流场,通过回转面、子午面上流线和旋涡强度分布发现风扇流道内流动分离现象十分显著,风扇进风口及叶尖处存在高强度的旋涡运动。建立牵引电机整机气动噪声有限元计算模型,以非定常流场计算结果为声源预测牵引电机辐射噪声。计算结果表明,噪声监测点上仿真计算值与试验值的总声压级最小相差0.1 dB(A),多点平均声压级相差1.8 dB(A),计算结果较准确。牵引电机气动噪声由离散噪声和宽频噪声组成,其中离散噪声的最高峰值来自于冷却风扇的偶极子噪声,且风扇叶片不等间距排列导致叶片通过频率的基频由369 Hz偏移至221 Hz。同时该频率下噪声的辐射指向性呈现典型的偶极子特征,并主要从牵引电机进出风口向外传播。试验结果可为牵引电机降噪优化工作提供参考。     

Silicon-Germanium Structure in Surrounding-Gate Strained Silicon Nanowire Field Effect Transistors

In this paper we numerically examine the electrical characteristics of surrounding-gate strained silicon nanowire field effect transistors (FETs) by changing the radius (R_SiGe) of silicon-germanium (SiGe) wire. Due to the higher electron mobility, the n-type FETs with strained silicon channel films do enhance driving capability (∼8% increment on the drain current) in comparison with the pure Si one. The leakage current and transfer characteristics, the threshold-voltage (V_t), the drain induced barrier height lowering (DIBL), and the gate capacitance (C_G) are estimated with respect to different gate length (L_G), gate bias (V_G), and R_SiGe. For short channel effects, such as V_t roll-off and DIBL, the surrounding-gate strained silicon nanowire FET sustains similar characteristics with the pure Si one.     

Thirty Years of Monte Carlo Simulations of Electronic Transport in Semiconductors: Their Relevance to Science and Mainstream VLSI Technology

We review briefly some aspects of the history of Monte Carlo simulations of electronic transport in semiconductors. In the early days their heavy computational cost rendered them suitable only to study problems of pure physics, as simpler models provided the answers necessary to design ‘electrostatically good’ devices. Now that scaling has taken another meaning (i.e., looking for alternative materials, crystal orientations, device geometries, etc.), Monte Carlo simulations may gain popularity once more, since they allow an efficient and reliable evaluation of speculative ideas. We show examples of both aspects of the results of Monte Carlo work.     

响洪甸抽水蓄能变极同步发电/电动机谐波磁场引起的铁心振动与电磁噪声分析计算

由于变极同步电机气隙磁场中将存在较大的谐波，这些磁场谐波对电机运行性能将产生一些影响。本文介绍了单绕组变极同步电机谐波磁场引起的铁心振动和噪声及其计算方法，并给出了响洪甸抽水蓄能变极同步发电／电动机的计算结果。     

变频空调外机噪声源分析及降噪措施

针对某变频空调外机试制出现的噪声进行分析,并采取相应的措施降噪,实验证明降噪措施是有效的。     

750 kV变电站噪声预测及防治

分析了750 kV变电站中的主要噪声源发声原理和传播途径,根据噪声发声体的声功率级,利用SoundPLAN软件对站内外不同位置进行噪声分析,得到直观的噪声分布图,制定出满足站内和厂界及敏感点的噪声控制措施。     

风机噪声的分析及控制

本文阐述了风机噪声产生的原因及各个噪声成分的特性,通过实验检测风机运转时噪音的大小及分布情况,明确风机噪声中的主要成分及类型,确定了相应的减噪措施,设计合理有效的消音装置,并通过实验验证该消音装置的有效性,达到降噪的效果。     

Analysis of Strained-Si Device including Quantum Effect

In this paper, we describe the analysis of strained-Si device including quantum effect. We linked the first principle band calculation program to the FUJITSU ensemble full band Monte Carlo simulator FALCON directly, which enables to take in arbitrary biaxial strained-Si band structure easily. And also the quantum effect was implemented by Bohm potential method. We show that the strain effect decreases with scaling to 10 nm gate length regime. However, in the domain which ballistic particle is majority, the effect of strain becomes useful again by the increase of the velocity by strain at the source region. This becomes more remarkable when quantum effect is taken into account.     

高压变电站噪声分离算法及其应用

为测量分析高压变电站同时存在的线路电晕噪声、电器(变压器、电抗器等)本体噪声和周边环境准平稳噪声,根据变电站噪声源的时频特性,提出一种基于梳状滤波器与小波变换相结合的高压变电站噪声分离算法。首先根据本体噪声的线谱特性,利用通带梳状滤波器滤波实现本体噪声的估计;其次利用高频小波系数构造电晕噪声检测信号实现电晕噪声与准平稳态噪声的分离。实验结果表明:噪声分离算法能有效估计出电晕噪声、本体噪声以及准平稳态噪声,噪声声压级以及A计权声压级估计误差1 d B;不同区域的噪声组成差别较大,靠近电抗区区域电晕噪声、本体噪声、准平稳态噪声是变电站噪声的主要来源,而在变电器附近主要为本体噪声与准平稳态噪声,电晕噪声衰减较大。