Application of coupled electro-thermal and physics-of-failure-based analysis to the design of accelerated life tests for power modules

In the reliability theme a central activity is to investigate, characterize and understand the contributory wear-out and overstress mechanisms to meet through-life reliability targets. For power modules, it is critical to understand the response of typical wear-out mechanisms, for example wire-bond lifting and solder degradation, to in-service environmental and load-induced thermal cycling. This paper presents the use of a reduced-order thermal model coupled with physics-of-failure-based life models to quantify the wear-out rates and life consumption for the dominant failure mechanisms under prospective in-service and qualification test conditions. When applied in the design of accelerated life and qualification tests it can be used to design tests that separate the failure mechanisms (e.g. wire-bond and substrate-solder) and provide predictions of conditions that yield a minimum elapsed test time. The combined approach provides a useful tool for reliability assessment and estimation of remaining useful life which can be used at the design stage or in-service. An example case study shows that it is possible to determine the actual power cycling frequency for which failure occurs in the shortest elapsed time. The results demonstrate that bond-wire degradation is the dominant failure mechanism for all power cycling conditions whereas substrate-solder failure dominates for externally applied (ambient or passive) thermal cycling.     

Gate oxide thickness dependence of high-field-induced interface state generation in thin thermal oxides

The oxide thickness dependence of the high-field-induced interface state generation Delta D/sub it/ in the nanometre-range thin (6-10 nm) gate oxides prepared by rapid thermal oxidation have been studied. It is shown that Delta D/sub it/ is a strong function of the oxide thickness. The thickness dependence of Delta D/sub it/ is found to be a function of stress time. Physical mechanisms are discussed to account for the experimental results.<>     

An accurate prediction model for computational overheads of security mechanisms in Wireless Sensor Networks

In Wireless Sensor Networks (WSNs), it is necessary to predict computational overheads of security mechanisms without final implementations to provide guidelines for system design. This paper presents an accurate and flexible model to predict overheads of these mechanisms. This model is based on overheads of basic operations frequently used in cryptography algorithms, which are essential elements of security mechanisms. Several popular cryptography algorithms and security mechanisms are evaluated using this model. According to simulation results, relative prediction errors are less than 7% for most cryptography algorithms and security mechanisms.     

表面化学反应中间生成物的检测

对催化反应的各种中间生成物实施检测以直接确定反应的基元步骤、路径和机理，是研究表面催化反应的有效手段。探索一种检测化学中间生成物的方法是一个意义重大的课题。本文提出了用激光脉冲成象原子探针（Ｐｕｌｓｅｄ－ＬａｓｅｒＩｍａｇｉｎｇＡｔｏｍ－Ｐｒｏｂｅ，ＰＬＩＡＰ）［１］研究表面催化反应的方法，并对运用ＰＬＩＡＰ检测表面催化反应中间生成物的实验条件和实验结果的真实性进行了概括和探讨。     

关于稀疏编码理论及其应用

稀疏编码的概念源于视神经网络的研究,是对只有一小部分神经元同时处于活跃状态的多维数据的神经网络的表示方法。稀疏编码理论在视神经细胞的响应特性和外部环境刺激的统计特性之间建立一种科学的数量联系,逐渐成为了一种有效理解人类神经系统信息加工机制的理论工具,在盲源信号分离、语音信号处理、图像特征提取、自然图像去噪、以及模式识别等方面取得了许多成果,具有重要的实用价值。     

Darwin: customizable resource management for value-added networkservices

The Internet is rapidly changing from a set of wires and switches that carry packets into a sophisticated infrastructure that delivers a set of complex value-added services to end users. Services can range from bit transport all the way up to distributed value-added services like video teleconferencing, virtual private networking, data mining, and distributed interactive simulations. Before such services can be supported in a general and dynamic manner, we have to develop appropriate resource management mechanisms. These resource management mechanisms must make it possible to identify and allocate resources that meet service or application requirements, support both isolation and controlled dynamic sharing of resources across services and applications sharing physical resources, and be customizable so services and applications can tailor resource usage to optimize their performance. The Darwin project has developed a set of customizable resource management mechanisms that support value-added services. We present and motivate these mechanisms, describe their implementation in a prototype system, and describe the results of a series of proof-of-concept experiments     

Dynamic trajectory planning study of planar two-dof redundantly actuated cable-suspended parallel robots

This paper analyzes a set of dynamic trajectories for planar two-dof redundantly actuated cable-suspended parallel mechanisms. In recent literature, the global dynamic trajectory planning problem of cable-suspended mechanisms was addressed and some of the characteristic properties of such robots were revealed. In this paper, actuation redundancy is introduced and the dynamic trajectory planning is addressed using a series of periodic trajectories (i.e. straight line and circular periodic trajectories) and the application of the antipodal theorem. The experimental results obtained show that introducing actuation redundancy increases the dynamic capabilities of the robots. Also, cable tensions acquired via tension sensors confirm that cables always remain taut during all experimental verifications at feasible frequencies and that they are consistent with the tension variations predicted by theory. Furthermore, special frequencies are specified that are similar to those encountered with non-redundant mechanisms. Additionally, an alternative architecture is proposed to deal with cable interferences and it is shown that the novel architecture leads to improved dynamic capabilities when compared to the original architecture.     

强THz场下GaAs和InSb中瞬态谷间散射和碰撞电离

运用系宗蒙特卡罗法计算了强THz场作用下, n型掺杂的GaAs和InSb中随时间变化的散射机制以及载流子非线性动力学演变, 获取了电子散射至卫星谷并弛豫回原能谷的时间信息, 并追踪描绘了载流子瞬态增加的过程, 结果同时显示了强场作用下谷间散射是GaAs中的主要散射机制, 而碰撞电离则是InSb中的关键因素.此外进一步讨论了这两种机制对于相关物理量: 平均动能、平均速度、材料的电导率的影响, 结果说明这两种机制导致了非线性效应并在两种材料中起到相反的作用, InSb中碰撞电离的响应时间比GaAs中谷间散射的响应时间更长.该研究结果在THz调制领域有一定的指导意义.     

The applicability of logarithmic extreme value distributions in electomigration induced failures of Al/Cu thin-film interconnects

In electromigration failure studies it is in general assumed that electromigration induced failures may be adequately modelled by a log normal distribution. Further to this it has been argued that a log normal distribution of failure times is indicative of electromigration mechanisms. We have combined post processing of existing life-data from Al/Cu+TiW bilayer interconnects with our own results from Al/Cu interconnects to show that the Log Extreme Value distribution is an equally good statistical model for electromigration failures, even in cases where grain size exceeds the line width. The significance of such a modelling is particularly apparent in electromigration failure rate prediction.     

Subspace methods for identification of human ankle joint stiffness

Joint stiffness, the dynamic relationship between the angular position of a joint and the torque acting about it, describes the dynamic, mechanical behavior of a joint during posture and movement. Joint stiffness arises from both intrinsic and reflex mechanisms, but the torques due to these mechanisms cannot be measured separately experimentally, since they appear and change together. Therefore, the direct estimation of the intrinsic and reflex stiffnesses is difficult. In this paper, we present a new, two-step procedure to estimate the intrinsic and reflex components of ankle stiffness. In the first step, a discrete-time, subspace-based method is used to estimate a state-space model for overall stiffness from the measured overall torque and then predict the intrinsic and reflex torques. In the second step, continuous-time models for the intrinsic and reflex stiffnesses are estimated from the predicted intrinsic and reflex torques. Simulations and experimental results demonstrate that the algorithm estimates the intrinsic and reflex stiffnesses accurately. The new subspace-based algorithm has three advantages over previous algorithms: 1) It does not require iteration, and therefore, will always converge to an optimal solution; 2) it provides better estimates for data with high noise or short sample lengths; and 3) it provides much more accurate results for data acquired under the closed-loop conditions, that prevail when subjects interact with compliant loads.     

Threshold voltage characteristics of depletion-mode MOSFET's

This paper presents the results of a study of the characteristics of the depletion-mode MOSFET. In particular, it is shown that the threshold voltage of this device is a function of its mode of operation (linear or saturated) due to a change in dominant conduction mechanisms caused by the finite depth of donor impurities in the channel. The effect of these impurities on the short channel behavior of the devices also is examined.     

General study of jitter mechanisms for metric-based wireless routing protocols

To ameliorate high collision, a nefarious side effect of route discovery stage of reactive routing protocols in wireless networks, jitter mechanisms are proposed which enforce wireless nodes to postpone their transmission for a random amount of time so as to reduce probability of simultaneous transmission. Although it has been shown that jitter mechanisms can dramatically improve reactive routing protocols, it was not until recently that jitter mechanisms have been subjected to study. In this paper, different random distributions are proposed for jittering mechanisms and also shaping function, with the aim of which a simple routing protocol like AODV becomes sensitive to any arbitrary metric, is defined. Comprehensive simulation of routing metrics and jitter mechanisms have revealed that simple modification of a jitter mechanism, which can be even implemented independent of a routing protocol, greatly improves routes discovered by any routing protocol.     

Theory of the two-photon absorption-fluorescence method of pulsewidth measurement

A three-level model of a two-photon absorber is set up, and the response of the system to a pulsed excitation is calculated, including the effects of homogeneous and inhomogeneous broadening. The results are applied to the two-photon absorption-fluorescence (TPF) mesurement technique and it is shown that the larger of the two broadening mechanisms sets an upper limit to the spectral width of pulses, for which an unambiguous interpretation of the TPF display can be made. Effects that occur when this condition is violated are discussed.     

A precision linear actuator using piezoelectrically driven friction force

A friction drive-type precision actuator which is capable of high positioning accuracy was developed by using piezoelectric elements. To anticipate dynamic behavior, system modeling was performed by using stick-slip friction models such as classical, Karnopp, and reset integrator. Dynamic characteristics over various types of driving input signals and driving conditions were investigated by simulation and experiment. By varying phase angle difference and amplitude of driving inputs, it was found that it is possible to control the moving direction and distance of the slider. From simulation and experimental results, it was observed that the dynamic behavior of the simulation predictions agreed well with that of experimental results. This indicates that the model developed in this study is applicable to many other precision mechanisms in which driving friction force is generated by ellipsoidal motion.     

一种改进的遗传算法的实现及性能研究

在Visual C 环境下,用C语言实现了一种改进的遗传算法,该算法通过实数编码、改进的遗传操作算子,并引入精英保留策略,可克服常规算法中收敛速度慢、早熟及局部收敛等缺陷。经GA测试函数验证该算法是有效的。与MATLAB遗传算法优化工具箱和SGA的系统仿真结果进行了比较,结果显示该算法不仅显著提高了全局搜索能力,加快了收敛速度,而且也改善了求解的质量及其优化结果的可靠性,是求解复杂函数优化问题的一种有潜力的算法,结合自行研发的微波管CAD软件,可望用于微波管性能优化,提高微波管设计能力。     

无线传感器网络链路层组确认机制的研究与实现

实验测量发现WSNs的底层通信链路存在着丢失、非对称等特性;该文针对传统链路层可靠机制运用于无线传感器网络中存在着路径效率低,能量开销大的缺点,提出了一种面向效率的链路层组确认机制,并就路径效率、缓存需求、时间开销等指标进行了理论分析;最后,与传统链路层可靠传输机制在MicaZ平台上分别加以实现.测试结果表明该文提出的组确认机制的路径效率高、缓存需求固定,特别适合于高可靠,低实时要求的一类应用.     

Radar reflections from explosion and gas wake of operating engines

The mechanisms of radar reflections from the explosion area and gas wake of operating engines are analyzed; it is shown that the reflections caused by radiowave backscattering from a turbulent gas-like explosion and combustion products can be observed for rather a long time. The results of the investigations into local spatial-temporal characteristics of the disturbed area and radar observations, carried out at wavelengths 10, 3, 0.8, and 0.4 cm are presented     

Natural balancing of three-level neutral-point-clamped PWM inverters

This paper explores the natural balancing mechanisms of the three-level neutral-point-clamped (NPC) multilevel inverter. An equivalent circuit of the three-level NPC inverter is derived that facilitates an understanding of the balancing mechanisms. This is followed by a detailed analysis of the balancing mechanisms. The theory is applied to a three-level NPC inverter under vector control. It is shown that this inverter possesses natural balancing mechanisms in which the load impedance and spectra of the switching functions play an important role. Finally, it is illustrated how the natural balancing can be enhanced by using a passive balancing circuit which provides a low impedance at the sampling frequency.     

A New Recovery Scheme Against Short-to-Long Duration Transient Faults in Combinational Logic

This paper presents a new recovery scheme for dealing with short-to-long duration transient faults in combinational logic. The new scheme takes earlier into account results of concurrent error detection (CED) mechanisms, and then it is able to perform shorter recovery latencies than existing similar strategy. The proposed scheme also requires less memory resources to save input contexts of combinational logic blocks. In addition, this work also proposes a taxonomy of CED techniques. It allows pointing out which are the necessary recovery resources as well as identifying which are the types of CED mechanisms that can be used with the new recovery scheme of this paper. The effectiveness of the proposed scheme was evaluated through electrical-level simulations. For all short-to-long duration transient-fault injections, it was never slower than state-of-art similar strategy, and indeed its recovery latency was faster for 34 % of the simulated faulty scenarios.     

ESD与EMP对微波晶体管损伤机理研究

主要论述了电子装备中易受静电放电(ESD)和电磁脉冲(EMP)损伤的微波半导体器件的失效模式和失效机理.实验与理论分析结果表明,电流放大系数hFE是ESD、EMP损伤的敏感参数;在ESD、EMP的作用下,器件进入雪崩击穿状态(反偏注入),从而诱发热电子注入效应,使hFE逐渐退化;BC结反偏时的失效能量低于EB结反偏时的失效能量,BC结是EMP损伤的较易损端口;改进器件的结构设计、提高器件抗ESD、EMP能量,可有效提高电子装备抗电磁脉冲的可靠性水平.