Influence of the tangential velocity on the compressible Kelvin−Helmholtz instability with nonequilibrium effects

Kelvin−Helmholtz (KH) instability is a fundamental fluid instability that widely exists in nature and engineering. To better understand the dynamic process of the KH instability, the influence of the tangential velocity on the compressible KH instability is investigated by using the discrete Boltzmann method based on the nonequilibrium statistical physics. Both hydrodynamic and thermodynamic nonequilibrium (TNE) effects are probed and analyzed. It is found that, on the whole, the global density gradients, the TNE strength and area firstly increase and decrease afterwards. Both the global density gradient and heat flux intensity in the vertical direction are almost constant in the initial stage before a vortex forms. Moreover, with the increase of the tangential velocity, the KH instability evolves faster, hence the global density gradients, the TNE strength and area increase in the initial stage and achieve their peak earlier, and their maxima are higher for a larger tangential velocity. Physically, there are several competitive mechanisms in the evolution of the KH instability. (i) The physical gradients increase and the TNE effects are strengthened as the interface is elongated. The local physical gradients decrease and the local TNE intensity is weakened on account of the dissipation and/or diffusion. (ii) The global heat flux intensity is promoted when the physical gradients increase. As the contact area expands, the heat exchange is enhanced and the global heat flux intensity increases. (iii) The global TNE intensity reduces with the decreasing of physical gradients and increase with the increasing of TNE area. (iv) The nonequilibrium area increases as the fluid interface is elongated and is widened because of the dissipation and/or diffusion.     

强激光干扰下运动目标热损伤效应的有限元研究

为对空中飞行目标实施合理有效的强激光干扰,需要综合考虑采用的干扰方式、干扰效果以及考虑光斑偏移对干扰效果的影响。以热传导理论为基础,建立了激光辐照下移动目标温度场模型,采用伽辽金法建立了有限元分析模型,采用了等效比热容的方法处理材料的相变过程;并以Ansys软件为仿真平台,对目标在高斯分布的强激光作用下的温度场和热应力进行了综合仿真分析。结果表明,光斑与目标辐照区域的相对偏移对目标表面温度影响较大,对目标纵深破坏效应相对较小,应力变化主要发生在激光辐照区域,应力最大处也会随热源的移动而变化。     

一种成像雷达的通信一体化信号设计与分析

雷达与通信系统一体化可以最大限度地利用雷达设备, 使雷达的优良性能为通信服务.根据信号共享的原则, 在保持成像雷达和通信各自功能实现的前提下, 设计了一种基于随机频率步进调制的成像雷达通信一体化信号.该信号的设计方法是对发送的通信数据进行随机编码处理, 然后将其调制到雷达载波的频点上发送出去, 实现通信功能; 而引入压缩感知理论后, 采用这种信号仍能获得高分辨率的雷达图像, 在一定功能上实现了成像雷达和通信的一体化.     

Raman scattering of polycrystalline GaSb thin films grownby co-evapouration process

<正>This paper reports that GaSb thin films have been co-deposited on soda-lime glass substrates.The GaSb thin film structural properties are characterized by Raman spectroscopy.The Sb-A_1g/GaSb-TO ratio decreases rapidly with the increase of substrate temperature,which suggests a small amount of crystalline Sb in the GaSb thin film and suggests that Sb atoms in the thin film decrease.In Raman spectra,the transverse optical（TO） mode intensity is stronger than that of the longitudinal optical（LO） mode,which indicates that all the samples are disordered.The LO/TO intensity ratio increases with increasing substrate temperature which suggests the improved polycrystalline quality of the GaSb thin film.A downshift of the TO and LO frequencies of the polycrystalline GaSb thin film to single crystalline bulk GaSb Raman spectra is also observed.The uniaxial stress in GaSb thin film is calculated and the value is around 1.0 GPa.The uniaxial stress decreases with increasing substrate temperature.These results suggest that a higher substrate temperature is beneficial in relaxing the stress in GaSb thin film.     

一种最小电压应力的软开关无桥PFC技术研究

针对传统桥式整流升压功率因数校正(PFC)电路效率较低的缺点,提出了一种最小电压应力的软开关无桥PFC电路拓扑.在理论分析和仿真验证的基础上,研制了一台300 W的实验样机.结果表明,改进的无桥PFC电路拓扑具有通态损耗低、电流采样简单,能实现开关管零电压关断和零电流开通,同时实现整流二极管零电压导通和接近零电流软关断...     

Microstructural and mechanical analysis of Cu and Au interconnect on various bond pads

Effects of High Temperature Storage (HTS) and bonding toward microstructure change of intermetallic compound (IMC) at the wire bonding interface of 3 types of bond pad (Al, AlSiCu and NiPdAu) were presented in this paper. Optical and electron microscope analyses revealed that the IMC growth rate of samples under 175 and 200 °C HTS increased in the order of Al > AlSiCu > NiPdAu. Besides, higher HTS and bonding temperatures also promoted higher IMC thickness. The compositional study showed that higher HTS and bonding temperature developed rapid interdiffusion in bonding interface. In the mechanical ball shear test, a decrease of the shear force of Al and AlSiCu bond pads after 500 h HTS was believed due to poorly developed IMC at bonding interface. On the other hand, shear force degradation at 1000 h was due to excessive growth of IMC that in turn causes the formation of defects. For NiPdAu bond pad, increasing trend of shear force with HTS duration at 175 °C implied a good reliability of the Cu wire bonding. The rapid microscopic inspection on Cu wired Al bond pad under HTS 175 °C showed the IMC development from the periphery to the center of the ball bond. However, after 500 h voids started to develop until the crack was observed at 1000 h.     

室温下Cu/Sn3.5Ag焊点/Cu体系中电迁移引发裂纹的形成

Electromigration （EM） behavior of Cu/Sn3.5Ag/Cu solder reaction couple was investigated with a high current density of 5 × 10^3 A/cm^2 at room temperature. One dimensional structure, copper wire/solder ball/copper wire SRC was designed and fabricated to dissipate the Joule heating induced by the current flow. In addition, thermomigration effect was excluded due to the symmetrical structure of the SRC. The experimental results indicated that micro-cracks initially appeared near the cathode interface between solder matrix and copper substrate after 474 h current stressing. With current stressing time increased, the cracks propagated and extended along the cathode interface. It should be noted that the continuous Cu6Sn5 intermetallic compounds （IMCs） layer both at the anode and at the cathode remained their sizes. Interestingly, tiny cracks appeared at the root of some long columntype Cu6Sn5 at the cathode interface due to the thermal stress.     

Comparison of PVD, PECVD & PEALD Ru(-C) films as Cu diffusion barriers by means of bias temperature stress measurements

The diffusion barrier properties of PVD Ru and PECVD / PEALD Ru-C films, deposited by RuEtcp₂ precursor and N₂/H₂ plasma, were compared on the basis of bias temperature stress measurements. An MIS test structure was used to distinguish between thermal diffusion induced by annealing and a Cu field drift due to applied electric fields. BTS-CV, TZDB and TDDB measurements revealed that the barrier performance is significantly better for PEALD and PECVD Ru-C films. This improvement is associated with carbon impurities in the Ru films with a concentration in the order of several percent according to ToF-SIMS and ERDA. The TDDB mean time to failure at 250 °C, +5 MV/cm was 7 s for PVD Ru samples, ≈500 s for PECVD Ru-C, ≈800 s for PEALD Ru-C and >3600 s for PVD TaN. Triangular voltage sweep measurements at 300 °C, 0.1 V/s confirmed the presence of Cu ions inside the SiO₂ for degraded dots, in contrast to the Al reference sample and to PVD TaN, which performed best among all the Cu barriers under test. XRD data suggests that PEALD and PECVD Ru-C films are only weakly crystalline.     

From defects creation to circuit reliability - A bottom-up approach (invited)

This paper presents a theoretical framework about interface states creation rate from Si-H bonds at the Si/SiO₂ interface. It includes three mains ways of bond breaking. In the first case, the bond can be broken thanks to the bond ground state rising with an electrical field. In the two others cases, incident carriers will play the main role either if there are very energetic or very numerous but less energetic. This concept allows us physically modeling the reliability of MOSFET transistors, and particularly NBTI permanent part, and Channel Hot Carrier (CHC) to Cold Carrier (CCC) damage. Finally, the translation of these physical models into reliability spice models is discussed. These models pave the way to Design-in Reliability (DiR) approach which seeks to provide a quantitative assessment of reliability - CMOS device reliability in this case - at design stage thereby enabling judicious margins to be taken beforehand.     

基于回归分析和遗传算法的BGA焊点功率载荷热应力分析与优化

建立了球栅阵列BGA（Ball Grid Array）焊点有限元分析模型,选取焊点高度、焊点最大径向尺寸、上焊盘直径和下焊盘直径作为设计变量,以焊点应力作为目标值,采用响应曲面法设计了29组不同水平组合的焊点模型并建模进行仿真计算,建立了焊点应力与结构参数的回归方程,基于回归方程结合遗传算法对焊点结构参数进行了优化,获得了焊点应力最小的结构参数最优水平组合.结果表明：对于无铅焊料SAC387,焊点应力随焊点的高度增加而减小,随最大径向尺寸的减小而减小;应力最小的焊点水平组合为：焊点高度0.38mm、最大径向尺寸0.42mm、上焊盘直径0.34mm和下焊盘直径0.35mm;对最优水平组合仿真验证表明优化后焊点最大应力下降了4.66MPa,实现了BGA焊点的结构优化.