Effects of high electric field and elevated-temperature bias stressing on radiation response in power VDMOSFETs

The effects of pre-irradiation high electric field and elevated-temperature bias stressing on radiation response of power VDMOSFETs have been investigated. Compared to unstressed devices, larger irradiation induced threshold voltage shift and mobility reduction in high electric field stressed devices have been observed, clearly demonstrating inapplicability of electrical stressing for radiation hardening of power MOSFETs. On the other hand, larger irradiation induced threshold voltage shift in elevated-temperature bias stressed, and more considerable mobility reduction in unstressed devices have been observed, confirming the necessity of performing the radiation qualification testing after the reliability screening of these devices. The underlying changes of gate oxide-trapped charge and interface trap densities have been calculated and analysed in terms of the mechanisms responsible for pre-irradiation stress effects.     

高热负荷激光介质热应力场的分析与优化研究

研究了高热负荷板状激光介质在抽运面采用常规冷却技术时,换热面积较小的上下侧面的换热强度对激光介质最高温度及最大应力的影响情况,并对热应力场进行了优化研究。结果表明,任意抽运功率下,介质的最高温度及最大应力均随侧面换热系数的变化而变化,并存在最优换热系数。与侧面采用常规冷却手段时相比,采用最优换热系数时介质的最大应力降幅高达36%。另外,对介质上下侧面进行温度控制,也可达到与控制换热系数相同的效果。     

Microstructure and electrical properties of high power laser thermal annealing on inkjet-printed Ag films

In this work, a high power continuous-wave (CW) Nd:YAG laser was used for thermal treatment of inkjet-printed Ag films - resulting in the elimination of organic additives (dispersant, binder, and organic solvent) in the Ag ink and annealing of Ag nano-particles. By optimizing laser parameters such as laser power and defocusing value, the laser energy can be totally converted into heat energy, which is used for thermal treatment of inkjet-printed Ag films. This results in the microstructure and the resistivity of the films to be controlled. We investigated the thermal diffusion mechanisms during laser annealing and the resulting microstructures. The impact of high power laser annealing on microstructures and electrical characteristics of inkjet-printed Ag films was compared to those of the films annealed by a conventional furnace annealing. Focused ion beam (FIB) channeling images show that the laser annealed Ag films have large columnar grains and a dense void-free structure, while furnace annealed films have much smaller grains and exhibit void formation. As a result, the laser annealed films have better electrical properties (low resistivity) compared to furnace annealed samples.     

Comparison between the effects of positive noncatastrophic HBM ESDstress in n-channel and p-channel power MOSFETs

The effect of noncatastrophic positive human body model (HBM) electrostatic discharge (ESD) stress on n-channel power MOSFETs is radically different from that on p-channel MOSFETs. In n-channel transistors, the stress causes negative shifts of the current-voltage characteristics indicative of positive charge trapping in the gate oxide. In p-channel transistors, the stress increases the drain-to-source leakage current, probably due to localized avalanche electron injection from the p-doped drain     

NBTI related degradation and lifetime estimation in p-channel power VDMOSFETs under the static and pulsed NBT stress conditions

The effects of static and pulsed NBT stressing on threshold voltage in p-channel power VDMOSFETs are analysed, and the results are compared in terms of the effects on device lifetime. The results obtained by both “1/V_G” and “1/T” models, which are used for extrapolation to normal operation voltages and temperatures, respectively, indicate the device lifetime could be much longer under the pulsed stress conditions than under the static ones. It is also shown that lifetime tends to increase with decreasing the duty cycle of pulsed stress voltage applied.     

大功率通信天线介质降损与末端电场的均化特性分析

为解决大功率通信天线因末端开口处电场畸变严重、局部场强过高导致介质损耗发热量过大进而使天线末端易发生断裂问题, 通过对天线损耗发热的理论分析和建立天线末端三维电准静态场计算模型对天线介质降损与末端电场的均化特性开展了研究.得到如下结论:天线末端介质发热量与电场强度的平方成正比关系; 天线外护套采用半导电材料、对天线末端承力金具进行倒角均可有效均化天线末端畸变电场; 在天线末端安装均压金具是解决天线损耗发热断裂最有效的方法.     

Failure and stress analysis of through-aluminum-nitride-via substrates during thermal reliability tests for high power LED applications

The objective of this study is to evaluate the reliability of through-aluminum-nitride-via (TAV) substrate by comparing those experimental results with the finite element simulation associated with measurements of aluminum nitride (AlN) strength and the thermal deformation of Cu/AlN bi-material plate. Two reliability tests for high-power LED (Light emitting diode) applications are used in this study: one is a thermal shock test from − 40 °C to 125 °C, the other is a pressure cook test. Also, the strength of AlN material is measured by using three-point bending test and point load test. The reliability results show that TAV substrates with thicker Cu films have delamination and cracks after the thermal shock test, but there are no failure being found after the pressure cook test. The determined strengths of AlN material are 350 MPa and 650 MPa from three-point bending test and point load test, respectively. The measurement of thermal deformation shows that the bi-material plate has residual-stress change after the solder reflow process, also indicating that a linear finite element model with the stress-free temperature at 80 °C can reasonably represent the stress state of the thermal shock test from − 40 °C to 125 °C without considering Cu nonlinear effect. The further results of the finite element simulation associated with strength data of AlN material have successfully described those of the reliability test.     

电场对负性向列相液晶薄盒影响的研究

基于Landau-de Gennes理论,利用松弛迭代法,研究了电场对垂直排列(VA)液晶薄盒和反扭曲向列相(ITN)液晶薄盒的影响。两系统在相同条件下的倾角变化相同,且系统双轴性与本征值的变化只取决于倾角的变化。研究表明,当盒厚大于一定临界值时,液晶系统一直处于正序参数态,此时ITN薄盒的扭曲角由线性排列逐渐变化到呈45°角排列;当小于此临界盒厚时,在一定电压下会出现负序参数单轴态,此时ITN薄盒的扭曲角会偏离线性变化出现回滞。     

高功率激光辐照CFRP的温度场和应力场的数值分析

为了研究高功率激光致碳纤维/环氧树脂复合材料的热损伤规律,采用COMSOL软件对多层结构的碳纤维/环氧树脂复合材料的热应力进行模拟计算,取得了不同功率密度激光辐照复合材料的瞬态温度场与应力场的时空分布及变化规律.测量得到不同功率密度的激光作用碳纤维/环氧树脂后的损伤面积和损伤形貌,与数值模拟结果的趋势吻合.结果表明,靶...     

Effect of radiation shield angle on temperature and stress profilesduring rapid thermal annealing

The effects of radiation shield angle and oven-temperature ramping rates on the temperature and thermal stress profiles in a gallium arsenide wafer undergoing rapid thermal annealing are studied. The numerical model of the heat transfer in a cylindrical oven considers conduction in the wafer radiative heat transfer from all oven and shield surfaces to the wafer. All simulations show that at some location in the wafer the induced thermal stress exceeds the critical stress. These results indicate that at high temperatures (T>750°C) it is very difficult to maintain a sufficiently flat temperature profile such that the induced thermal stress is maintained below the critical stress throughout the wafer. Possible ways to minimize the induced thermal stress during the annealing process using a radiation shield and specific oven-temperature ramping rates are discussed     

激光辐照CCD温度场与热应力场的研究

为了研究了激光与CCD传感器的作用过程及损伤机理,采用有限元分析的方法,对波长1.06μm的连续激光辐照行间转移型面阵CCD进行了理论分析和仿真研究。以基底Si表面激光辐照区域为热源建立热力耦合模型,模拟得出了CCD的温度分布和热应力分布。通过对比分析其组成材料的温度损伤和应力损伤所发生的时间,发现应力损伤先于温度损伤。结果表明,作为固定边界和自由边界的交汇处,基底Si下表面边缘处热应力于激光作用0.1s时最先超过破坏阈值120MPa,发生应力破坏; Si材料产生由下表面边缘向中心的滑移,基底逐步脱离固定; 激光作用0.3s时,遮光Al膜与SiO₂膜层也因热应力超过两种材料的附着力100MPa,而产生沿径向由内向外的Al膜层剥落的应力破坏行为,这种行为将加快基底Si材料的滑移,最终致使整个CCD因脱离工作位置而失效。该研究成果为CCD传感器的激光损伤及防护提供了理论依据。     

Bonding stress and reliability of high power GaAs-based lasers

GaAs-based lasers were bonded to oxygen-free high-conductivity (OFHC) copper heat sinks using a eutectic PbSn solder or a silver-filled conductive epoxy, and life tested. Epoxy-bonded devices were observed to have a larger failure rate on life test than solder-bonded devices. Bonding stress, as measured by the degree of polarization (DOP) of photoluminescence, was found to be the largest in epoxy-bonded devices. As well, the type of heat sink and bonding adhesive affected the stress in the laser material, with bonding stress increasing when there was a larger mismatch of coefficients of thermal expansion between the laser material, adhesive, and heat sink. Results suggested that heat sink material and bonding adhesive contribute to stress within the laser material and the resulting performance of the device     

电力营销电能计量现场作业危险点及预控措施研究

人们生产生活中电力需求的不断上升,促使电力企业的市场竞争也变得越来越激烈。电力企业想要在激烈的竞争环境中取得良好的发展成果,提升自身的竞争实力,就需要加强自身的电力营销工作。针对电力营销电能计量现场作业中存在的危险点,只有对其进行全面有效的分析,采用积极的预控措施,才能够起到有效的防护作用,提升现场作业的安全性和可靠性。文章主要从电力营销电能计量现场作业的基本情况入手,针对电力营销电能计量现场作业中的危险点,提出了一些有效的预控措施。     

Spectrum of an electron in a quantum well in high inclined magnetic field and high transverse electric field

The energy and wave functions of localized electron states in a quantum well in a high magnetic field arbitrarily oriented with respect to the layers of the structure, and a high transverse electric field are studied. The situation where the quantum-confined energy and the Landau energy are close to each other is considered. The evolution of the spectrum with varying orientation of the magnetic field over the entire angle range is studied.     

基于BOTDA的电力特种光缆应力应变研究

为解决光缆机械特性监测盲区,防止因机械性能劣化而产生的故障隐患,对光缆中光纤余长理论和BOTDA(布里渊光时域分析仪)、OTDR(光时域反射仪)监测原理进行研究。采用BOTDA监测技术,对光缆中光纤的应变进行了监测实验。结合理论分析,得出光纤应变随光缆的应力应变及机械特性变化的关系,能够对光缆机械性能劣化起到预警作用,防患于未然。     

The optimal design of the thermal spreading on high power LEDs

New energy and energy saving are the two basic energy issues. This study proposes an innovative optimal method to design LEDs with high thermal spreading holder. The optimization uses the FEM combined with the simplified conjugated gradient method (SCGM). The minimal temperature of the MCPCB backside of the LEDs is obtained throughout this design. The simulations have been proofed by the experiment of IR and thermal couple measurement. The optimal temperature decreases at about 4 °C compared with the original temperature without any active cooling device. This design can prolong the LEDs? life to benefit the energy saving obviously. In addition, this design combined with the active cooling device will achieve better heat dissipation on cooling of the electronic component.     

长脉冲高能激光与半导体材料的热作用分析

在入射激光光斑半径远远大于材料热扩散长度的条件下,应用固体热传导理论,使用有限元方法建立了相关模型.对长脉冲(脉宽1 ms)强激光与半导体材料si和Ge的热作用进行了分析,定量地描绘出了材料的温度分布,得到了不同能量激光辐照下靶材前、后表面中心点温度历史,以及不同能量激光辐照下的靶材后表面的温度分布情况.所得结果为高能量激光的应用提供了依据.     

Microwave conductivity of polar semiconductors in the presence of a high electric field

Theoretical results are presented for the small-signal microwave conductivity of nInSb at TL = 77°K in the presence of a high d.c. field directed parallel or perpendicular to the microwave field. Reasonable agreement with experiments by Richter and Bonek is demonstrated. At frequencies below 50GHz, the parallel microwave conductivity is smaller than the perpendicular one, whereas the opposite is true at 70GHz.