电子元件参数漂移的MΦItoft统计模型

参数漂移模型描述了元件参数从额定值发生偏移的行为。随着可靠性朝无故障寿命或无需维修工作周期的方向发展,对产品的参数漂移进行研究越来越显重要。利用MφItoft统计模型描述了电子元件的参数漂移行为,通过元件的早期寿命测试来预测元件寿命,并给出了应用实例。     

可靠性工程与环境工程

0309231结构元件疲劳可靠性估算的剩余寿命模型[刊]/郭盛杰//南京航空航天大学学报.—2003,35(1).—25～29(E)从安全余量的定义出发,提出了一个估算结构元件疲劳可靠性的剩余寿命模型。基于常幅载荷下,疲劳寿命可用对数正态函数分布描述,本文分析了常幅和变幅载荷作用下材料的疲劳剩余寿命的分布形式,认为可用带位置参数的对数正态函数近似描述。在此基础上,系统阐述了元件在常幅和多级载荷下的疲劳     

基于直流无刷电机的雷达伺服系统设计

介绍了连续扫描工作的长寿命伺服系统设计与实现,选用无刷电机作为执行元件并选用无刷旋转变压器作为测角反馈元件来实现长寿命要求。文中描述了直流无刷电机的Matlab模型和基于无刷电机的雷达伺服系统仿真模型。伺服系统的校正运算通过PI调节器实现,参数通过系统仿真决定,简化了系统参数的设计。仿真模型中考虑了结构谐振,用以保证调节器的可实现性。功放电路由单路PWM经FP—GA分离出6路开关信号来控制,简单可靠。从系统的实际工作数据结果来看达到了较好的控制性能。     

光学元件质量与加工参数间关系的数学模型研究

光学元件质量与加工参数之间存在复杂的关系,当前模型无法准确描述两者之间的变化特征,使得光学元件加工质量较差。为了获得更优的光学元件加工质量,构建了光学元件质量与加工参数间关系的数学模型。分析光学元件质量的变化特点,根据元件加工流程,获取与光学元件质量相关的参数,并根据参数优化数学模型。仿真测试结果表明,模型可以高精度地描述光学元件质量与参数之间变化关系,减小了元件表面厚度刻蚀误差,使得光学元件加工粗糙度下降,表面形貌更为平整。     

金属化膜脉冲电容器剩余寿命预测方法研究

 金属化膜脉冲电容器是惯性约束聚变激光装置的重要元器件之一,其寿命预测是激光装置维护和备件决策制定的依据.在分析金属化膜脉冲电容器退化失效机理的基础上,采用Wiener过程描述其性能退化过程.进一步考虑到各电容器之间的差异,将Wiener过程的漂移参数和扩散参数看成随机变量,提出了随机效果Wiener过程模型,由同一批电容器的历史性能退化数据拟合其分布.在对单个电容器进行寿命预测时,采用Bayes方法融合电容器总体信息与该电容器自身的性能退化信息,得到其剩余寿命参数的验后估计,因而在电容器性能退化数据较少时采用该方法能提高剩余寿命预测精度.     

基于EM-EKF与隐含比例退化模型的机载电子设备剩余寿命自适应预测

针对现有机载电子设备剩余寿命自适应预测方法在新研小样本条件下,未能综合考虑设备隐含退化建模与漂移系数在线更新的问题,本文提出一种基于期望最大-扩展卡尔曼滤波(Expectation Maximization-Extended Kal-man Filter,EM-EKF)与隐含比例退化模型的机载电子设备剩余寿命自适应预测方法.首先,基于非线性Wiener过程构建带比例关系的设备隐含退化模型;其次,在引入漂移系数更新机制的基础上建立设备退化状态方程,并采用EKF算法同步更新设备退化状态与漂移系数;然后,采用EM-EKF算法实现对退化模型参数的自适应估计;最后,基于全概率公式,推导出设备剩余寿命的概率密度函数.通过对单台微机械陀螺仪实测数据进行分析,验证了本文所提方法具有更好的模型拟合性与预测准确性.     

基于一维漂移布朗运动的SLD退化失效建模

超辐射发光二极管(SLD)集LD大输出功率和LED宽光谱优点于一体,是光纤陀螺仪中的关键元件与薄弱环节,其可靠性在很大程度上决定了光纤陀螺仪的可靠性。针对SLD寿命长、失效数据难于获取的特点,研究了基于性能退化数据的可靠性评估方法。在对SLD进行失效机理分析的基础上,提出用一维漂移布朗运动模型对产品在环境应力作用下的退化特性进行建模,基于所得模型,由SLD的性能退化信息估计模型中的参数进而评估得到SLD的可靠性指标。这克服了传统可靠性分析方法依赖寿命数据的缺点,能够在没有寿命数据的情况下评估得到SLD的可靠性指标,从而可节约大量的试验经费和试验时间,在工程应用上具有重要的价值。     

基于状态信息的退化失效型产品模糊可靠性评估

考虑到退化失效型产品性能下降主要表现为状态参数发生漂移,可靠性评估模型中随机参数具有模糊特性,提出一种利用状态信息评估模糊可靠性的方法.采用随机冲击累积失效模型描述退化过程,模糊化参数漂移的动态范围,引入模糊隶属函数,推导出产品模糊可靠度的分析模型.结合具体实例进行验证,对比分析了不同隶属函数下的模糊可靠性与常规可靠性...     

基于指数分布的加速寿命试验简论

讨论了4种用于描述加速寿命试验中失效分布参数和环境条件之间关系的失效物理模型。针对阿伦尼斯模型,探讨了加速寿命试验中的参数估计方法,构建了参数的极大似然估计(MLE)方程组,解得加速寿命试验中失效分布参数的MLE值,进而通过转化,借助于标准正态分布表获得其寿命指标的近似值,并通过一个实例介绍了其具体应用。     

基于Kalman滤波和Wiener过程的系统性能退化数据建模方法

目前寿命预测的建模过程中很少考虑漂移系数变化产生的影响,这并不合理且不符合实际情况,为解决这个问题,建立了基于Kalman滤波和Wiener过程的系统性能退化模型,在此基础上采用Kalman滤波和EM算法实现了模参数的估计和更新,最后通过某陀螺仪的寿命预测实例验证了方法的有效性。     

场引晶体管理论:Ⅻ.双极飘移扩散电流(薄及厚、纯及不纯基体,单及双MOS栅极)

上篇论文(Ⅺ)报告双极场引晶体管的电化电流理论,这篇论文(Ⅻ)报告飘移扩散理论.两篇都讨论了单栅双栅,纯基不纯基,薄基厚基的情形.两篇都用表面及内部电势作为参变量耦合电压方程和电流方程.在这飘移扩散理论中,有许多电流项,属飘移电流的用迁移率因子标识,属扩散电流的用扩散率因子标识.给出完备飘移扩散解析方程,用以计算四种常用MOS晶体管的直流电流电压特性.飘移电流有四项:一维体电荷漂移项,一维载子空间电荷漂移项,一维横向电场漂移项,二维漂移项.扩散电流有三项:一维体电荷扩散项,一维载子空间电荷扩散项,二维扩散项.现有的晶体管理论都没认识到一维横向电场漂移项.当基区几乎是纯基,这项贡献显著,约总电流的25%.二维项来自纵向电场的纵向梯度,它随德拜长度对沟道长度比率的平方按比例变化.当沟道长度为25nm,几乎纯基时,(LD/L)2=106,杂质浓度1018cm-3时,(LD/L)2=10-2.     

Investigations on the high current behavior of lateral diffused high-voltage transistors

This paper describes the high current behavior of a lateral, n-channel, high-voltage transistor. The starting points are TCAD experiments where the phenomenological behavior is analyzed. Based on these results a transistor high current model is derived, which is based on the vertical integrated free carrier concentration in the drift region. The important model parameter is the gate voltage, which defines the boundary condition for the free electron concentration at the beginning of the drift region. Because of the coupling of the carrier continuity equation and the Poisson equation (drift-diffusion model), this boundary condition plays a major role, and defines the carrier concentration inside the drift region. Together with an intrinsic low-voltage transistor model (intrinsic NMOS transistor), a series network is solved numerically. The network behavior reflects the TCAD experiments quite well and covers the different electrical regimes (the on-resistance regime, the quasi-saturation regime, and the saturation regime). The model output is compared with the TCAD experiments and the measured transistor data as well.     

HRF estimation in fMRI data with an unknown drift matrix by iterative minimization of the Kullback-Leibler divergence

Hemodynamic response function (HRF) estimation in noisy functional magnetic resonance imaging (fMRI) plays an important role when investigating the temporal dynamic of a brain region response during activations. Nonparametric methods which allow more flexibility in the estimation by inferring the HRF at each time sample have provided improved performance in comparison to the parametric methods. In this paper, the mixed-effects model is used to derive a new algorithm for nonparametric maximum likelihood HRF estimation. In this model, the random effect is used to better account for the variability of the drift. Contrary to the usual approaches, the proposed algorithm has the benefit of considering an unknown and therefore flexible drift matrix. This allows the effective representation of a broader class of drift signals and therefore the reduction of the error in approximating the drift component. Estimates of the HRF and the hyperparameters are derived by iterative minimization of the Kullback-Leibler divergence between a model family of probability distributions defined using the mixed-effects model and a desired family of probability distributions constrained to be concentrated on the observed data. The performance of proposed method is demonstrated on simulated and real fMRI data, the latter originating from both event-related and block design fMRI experiments.     

Effect of charged dislocation walls on mobility in GaN epitaxial layers

A theoretical model in the context of a conventional representation on traditional notion concerning Read cylinders for interpretation of mobility collapse as a function of the concentration of free carriers in GaN-based films is suggested. Along with phonon and impurity scattering mechanisms, electron scattering due to charged dislocations embedded into the walls is taken into account in the model. An expression is obtained for the height of the drift barrier depending on the concentration of free carriers. Based on the derived equations, the dependence of the location of the mobility minimum on the dislocation structure is interpreted.     

Cramer-Rao bound on the estimation accuracy of complex-valuedhomogeneous Gaussian random fields

This paper considers the problem of the achievable accuracy in jointly estimating the parameters of a complex-valued two-dimensional (2-D) Gaussian and homogeneous random field from a single observed realization of it. Based on the 2-D Wold decomposition, the field is modeled as a sum of purely indeterministic, evanescent, and harmonic components. Using this parametric model, we first solve a key problem common to many open problems in parametric estimation of homogeneous random fields: that of expressing the field mean and covariance functions in terms of the model parameters. Employing the parametric representation of the observed field mean and covariance, we derive a closed-form expression for the Fisher information matrix (FIM) of complex-valued homogeneous Gaussian random fields with mixed spectral distribution. Consequently, the Cramer-Rao lower bound on the error variance in jointly estimating the model parameters is evaluated     

Field dependence of ionisation rates of electrons in silicon

A theoretical model for the ionisation coefficient of electrons in silicon has been developed based on the solution of the Boltzmann transport equation. Analytic expressions are obtained for the ionisation coefficient and the drift velocity. Modifications in the deformation potential constants have been suggested for obtaining a fit to the experimentally observed results for the drift velocity and ionisation coefficient. The mean free path for ionisation calculated with the help of this model fits well with the earlier predictions.     

Ion/electron-beam parametric amplifiers

Recent experiments with positive-ion beams suggest that an ion?electron beam, consisting of an electron beam superimposed on an ion beam, such that the two beams have different drift velocities, is realisable. A five-frequency parametric amplifier using an ion?electron beam is proposed.     

Theoretical model of magnetic effect on Gunn diode

A simplified theoretical model to explain a magnetic effect on a Gunn diode is presented. When a dc magnetic field is applied transversely to a Gunn diode, the oscillation frequency decreases. This phenomenon is explained using a concept of successive collisions of drift electrons with lattice with constant free path.     

Electron transport and ionization in silicon at high fields

The saturated drift velocity measured for electrons at high fields is inconsistent with Shockley's model for impact ionization in silicon. It is explained in terms of a field-dependent mean free path for high energy phonon creation in the electric field direction, electrons creating a high energy phonon as soon as they have acquired sufficient energy from the field. Assuming that the electron wavepacket travels at the saturated drift velocity without dispersion, it can be shown that the increased scattering rate at high fields must result in a large spread in the carrier energy. If a drifted Maxwellian distribution is assumed, a unique expression can be obtained for the carrier temperature T^* which is in good agreement with the measured field dependence of the ionization coefficient. In this model, a cylindrical hot carrier distribution must be assumed with the hot carrier energy in a plane perpendicular to the applied field. Exact calculations of the magneto-resistance of such a distribution can be made verifying that the drift velocity is indeed saturated.