Accelerated life test calculations using the method of maximum likelihood: an improvement over least squares

Reliability calculations from failure time data are often performed using least squares regression of the log of the mean time to failure (MTTF) vs. inverse temperature. It is demonstrated that this method produces estimates of relevant parameters like E_a and MTTF with confidence limits that are larger and more variable than necessary. In comparison, the method of maximum likelihood makes more efficient use of the data and as a result, does not suffer from the above difficulties. A previously published dataset is used to compare the two techniques and the maximum likelihood approach is shown to be superior.     

CAVITATION MODELING WITH A CFD APPROACH

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Effect of 0.1 at.% zirconium on the cyclic oxidation resistance ofβ-NiAl

The effect of 0.1 at.% Zr (0.2 wt.% Zr) on the cyclic oxidation of hipped -NiAl was studied. Oxidation testing was performed in static air at 1100–1200 °C, using 1-hr exposure cycles for test times up to 3000 hr. The weight change versus time data were modeled with the COSP computer program to analyze and predict cyclic-oxidation behavior. Zr additions significantly change the nature of the scale-spalling process during cooling so that the oxide spalls near the oxide-air interface at a relatively low depth within the scale. Without Zr, the predominantly -Al₂O₃ scale tends to spall randomly to bare metal at relatively high effective-scale-loss rates, particularly at 1150°C and 1200°C. This leads to higher rates of Al consumption for the Zr-free aluminide and much earlier depletion of Al, leading to eventual breakaway (i.e., failure).     

平顶光束激光冲击2024铝合金诱导残余应力场的模拟与实验

对平顶光束激光冲击2024铝合金诱导的残余应力情况进行了有限元模拟与实验研究。改进了平顶光束诱导冲击波的压力分布模型,并将该模型用于残余应力场的有限元模拟。在实验室环境下获得了适合用于激光冲击的高质量平顶光束,并使用该光束进行激光冲击2024铝合金的实验,实验结果和模拟结果基本一致。研究发现平顶光束冲击2024铝合金有如下特点:存在一个阈值,当激光冲击波压力小于该阈值时,影响区内残余应力场近似均匀分布;当冲击波压力大于该阈值时会引起"残余应力洞",但该"残余应力洞"内部近似均匀分布。在深度方向上,塑性影响深度和最大残余应力深度随激光冲击波压力的增加而增加。     

边缘接入智能化

MMAP(多功能、多业务接入平台)集成了光纤传输和接入技术,使接入网和城域网(MAN)融合在一起。     

High‐Performance Air‐Processed Polymer–Fullerene Bulk Heterojunction Solar Cells

High photovoltaic device performance is demonstrated in ambient‐air‐processed bulk heterojunction solar cells having an active blend layer of organic poly(3‐hexylthiophene) (P3HT): [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM), with power conversion efficiencies as high as 4.1%, which is comparable to state‐of‐the‐art bulk heterojunction devices fabricated in air‐free environments. High‐resolution transmission electron microscopy is combined with detailed analysis of electronic carrier transport in order to quantitatively understand the effects of oxygen exposure and different thermal treatments on electronic conduction through the highly nanostructured active blend network. Improvement in photovoltaic device performance by suitable post‐fabrication thermal processing results from the reduced oxygen charge trap density in the active blend layer and is consistent with a corresponding slight increase in thickness of an ～4 nm aluminum oxide hole‐blocking layer present at the electron‐collecting contact interface.     

用输入滤波器防止仪表放大器射频整流误差

仪表放大器用于需要从大共模噪声或干扰中提取微弱差分信号的各种设备.但是,设计师常常会忽视仪表放大器内存在的潜在射频整流问题.放大器的共模抑制通常能大大减小仪表放大器输入端的共模噪声.但遗憾的是,射频整流仍然会发生,这是因为即使最好的仪表放大器在频率高于20kHz时实际上也不能抑制共模噪声.放大器的输入级可能会对强信号进行整流,然后以直流偏移误差的形式出现.     

Methodology for predicting off-state reliability in GaN power transistors

Results of a lifetest across temperature and drain voltage on off-state high power GaN FET test structures are presented. The times to failure (t_f) are fitted to a combination of the Arrhenius model (ln(t_f) ∼ inverse temperature) and the linear field model (ln(t_f) ∼ drain voltage). The estimated activation energy (E_a) is 2.1 eV and the estimated linear field parameter (γ) is 0.03 V⁻¹. Reliability parameters estimated from the test structure data are used to predict the FIT rate for a product level FET using linear scaling of the gate width. Further, the effect of a burn-in and a transient voltage under a duty cycle on the FIT rate are modeled. The FIT rate of the product level FET is larger than that of the test structure. The burn-in and transient voltage similarly reduce the reliability. Contour plots are given that allow trade-offs between these factors in order to meet reliability requirements.     

OMVPE growth of P-type GaN using solution Cp2Mg

Bis(cyclopentadienyl)magnesium (Cp₂Mg) is a common source for p-type doping in GaN and AlInGaP materials. It is a white crystalline solid with very low vapor pressure, leading to transport problems similar to solid trimethyindium (TMI). Some of these problems can be alleviated by a newly developed source-solution magnesocene, Cp₂Mg, dissolved in a solvent that is essentially nonvolatile. In this paper, we report the growth and comparative results of Mg-doped GaN grown by OMVPE using solid and solution Cp₂Mg. Using both sources, we optimized parameters to obtain high-quality GaN growth with hole concentrations up to 1 10¹⁸/cm³.