硅纳米线拉伸与熔化行为的原子模拟

Molecular dynamics simulations with Stillinger-Weber potential are used to study the tensile and melting behavior of single-crystalline silicon nanowires（SiNWs）.The tensile tests show that the tensile behavior of the SiNWs is strongly dependent on the simulation temperature,the strain rate,and the diameter of the nanowires.For a given diameter,the critical load significantly decreases as the temperature increases and also as the strain rate decreases.Additionally,the critical load increases as the diameter increases.Moreover,the melting tests demonstrate that both melting temperature and melting heat of the SiNWs decrease with decreasing diameter and length,due to the increase in surface energy.The melting process of SiNWs with increasing temperature is also investigated.     

A non-contact real-time measurement of lamp dimension based on machine vision

The scintillation indices(SIs)of Gaussian beams and vortex beams propagating in turbulent atmosphere are investigated experimentally.It is shown that with the increase of propagation distance,the SI of Gaussian beam around optical axis increases gradually,but the SI of vortex beam with topological charge of 4 increases,achieves the maximum value at a fixed distance,and then decreases as the continued increase of propagation distance.The SI of vortex beam can be smaller than that of Gaussian beam under certain conditions.     

A novel approach for justification of box-triangular germanium profile in SiGe HBTs

This work presents a unique and robust approach for validation of using the box-triangular germanium profile in the base of SiGe heterojunction bipolar transistors, where the methodology considers the simultaneous optimization of the p-type base doping profile in conjunction with the germanium profile in the base. The study analyses the electron motion across the SiGe base in SiGe HBTs, owing to different accelerating electric fields. The analysis first presents a figure of merit, to achieve the minimum electron transit time across the base in conjunction with the increased current gain in n–p–n-SiGe HBTs, which shows a general trend vis-à-vis the advantage of a trapezoid germanium profile, but with additional accuracy as we considered simultaneously optimized p-type base doping. The effect of minority carrier velocity saturation is then included to make the study more detailed. The analysis then investigates the shifted germanium profile in the base to further minimize the base transit time. Finally,it is shown that a shifted germanium profile eventually evolves into a box-triangular Ge-profile in the SiGe base,which could simultaneously minimize the base transit time and reduce emitter delay by virtue of the high current gain. The analysis verifies that for an average Ge-dose of 7.5% Ge across the base, a box-triangular germanium profile in conjunction with an optimum base doping profile has an approximately identical base transit time and a 30% higher current gain, in comparison with an optimum base doping and triangular Ge-profile across the whole base.     

基于GaAs基大功率激光器的热分析

The thermal characteristics of 808 nm Al Ga As/Ga As laser diodes(LDs) are analyzed via electrical transient measurements and infrared thermography. The temperature rise and thermal resistance are measured at various input currents and powers. From the electrical transient measurements, it is found that there is a significant reduction in thermal resistance with increasing power because of the device power conversion efficiency. The component thermal resistance that was obtained from the structure function showed that the total thermal resistance is mainly composed of the thermal resistance of the sub-mount rather than that of the LD chip, and the thermal resistance of the sub-mount decreases with increasing current. The temperature rise values are also measured by infrared thermography and are calibrated based on a reference image, with results that are lower than those determined by electrical transient measurements. The difference in the results is caused by the limited spatial resolution of the measurements and by the signal being captured from the facet rather than from the junction of the laser diode.     

Effect of junction temperature on the large-signal properties of a 94 GHz silicon based double-drift region impact avalanche transit time device

The authors have developed a large-signal simulation technique extending an in-house small-signal simulation code for analyzing a 94 GHz double-drift region impact avalanche transit time device based on silicon with a non-sinusoidal voltage excitation and studied the effect of junction temperature between 300 and 550 K on the large-signal characteristics of the device for both continuous wave(CW) and pulsed modes of operation.Results show that the large-signal RF power output of the device in both CW and pulsed modes increases with the increase of voltage modulation factor up to 60%,but decreases sharply with further increase of voltage modulation factor for a particular junction temperature;while the same parameter increases with the increase of junction temperature for a particular voltage modulation factor.Heat sinks made of copper and type-IIA diamond are designed to carry out the steady-state and transient thermal analysis of the device operating in CW and pulsed modes respectively. Authors have adopted Olson’s method to carry out the transient analysis of the device,which clearly establishes the superiority of type-IIA diamond over copper as the heat sink material of the device from the standpoint of the undesirable effect of frequency chirping due to thermal transients in the pulsed mode.     

压力下光学声子对应变纤锌矿AlN/GaN异质结中电子迁移率的影响

A variational method combined with solving the force balance equation is adopted to investigate the influence of strain and hydrostatic pressure on electronic mobility in a strained wurtzite AlN/GaN heterojunction by considering the scattering of optical-phonons in a temperature ranges from 250 to 600 K. The effects of conduction band bending and an interface barrier are also considered in our calculation. The results show that electronic mobility decreases with increasing hydrostatic pressure when the electronic density varies from 1.0 × 1012 to 6.5 × 1012 cm-2. The strain at the heterojunction interface also reduces the electronic mobility, whereas the pressure influence becomes weaker when strain is taken into account. The effect of strain and pressure becomes more obvious as temperature increases. The mobility first increases and then decreases significantly, whereas the strain and hydrostatic pressure reduce this trend as the electronic density increases at a given temperature （300 K）. The results also indicate that scattering from half space phonon modes in the channel side plays a dominant role in mobility.     

High-sensitivity temperature sensor based on long-period fiber grating

Temperature sensitivity is greatly improved by taking the following three measures： proper long-period fiber grating （LPFG） whose strain coefficient of the core is larger than that of the cladding is employed, the LPFG is coated with a thin film of the material whose refractive index decreases with the temperature, and the sensor is encapsulated by metal material whose thermal expansion coefficient is large. By computer simulation, a measured temperature coefficient of 0.2375 nm/℃ and a temperature resolution less than 0.1 ℃ are obtained.     

Influence of temperature and LO phonon on the effective mass of bipolarons in polar semiconductor quantum dots

The temperature and LO phonon effects of the bipolaron in polar semiconductor quantum dots(QDs)are studied by using the Tokuda modified linear-combination operator method and the Lee-Low-Pines variational method.The expressions for the mean number of LO phonons and the effective mass of the bipolaron are derived.Numerical results show that the mean number of LO phonons of the bipolaron decreases with increasing the temperature and the relative distance r between two electrons,but increases with increasing the electron-phonon coupling strengthα.The effective mass of the bipolaron M* increases rapidly with increasing the relative distance r between two electrons when r is smaller,and it reaches a maximum at r≈4.05r p,while after that,M*decreases slowly with increasing r.The effective mass of the bipolaron M*decreases with increasing the temperature.The electron-phonon coupling strengthαmarkedly influences the changes of mean number of LO phonons and the effective mass M*with the relative distance r and the temperature parameter γ.     

Influence of growth conditions of oxide on electrical properties of AlGaN/GaN metal–insulator–semiconductor transistors

AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors(MIS-HEMTs) on a silicon substrate were fabricated with silicon oxide as a gate dielectric by sputtering deposition and electron-beam(EB) evaporation. It was found that the oxide deposition method and conditions have great influences on the electrical properties of HEMTs. The low sputtering temperature or oxygen introduction at higher temperature results in a positive equivalent charge density at the oxide/AlGaN interface(Nequ), which induces a negative shift of threshold voltage and an increase in both sheet electron density(ns) and drain current density(ID). Contrarily, EB deposition makes a negative Nequ, resulting in reduced ns and ID. Besides, the maximum transconductance(gm-max) decreases and the off-state gate current density(I_G-off) increases for oxides at lower sputtering temperature compared with that at higher temperature, possibly due to a more serious sputter-induced damage and much larger Nequ at lower sputtering temperature. At high sputtering temperature, I_G-off decreases by two orders of magnitude compared to that without oxygen, which indicates that oxygen introduction and partial pressure depression of argon decreases the sputter-induced damage significantly. I_G-off for EB-evaporated samples is lower by orders of magnitude than that of sputtered ones, possibly attributed to the lower damage of EB evaporation to the barrier layer surface.     

HgCdTe长波红外n-on-p结线列的串音研究

Crosstalk of HgCdTe long-wavelength infrared （LWIR） n-on-p diode arrays was measured using scanning laser microscopy. During the measurement, HgCdTe diode arrays with different diode pitches were frontside illuminated by a He-Ne laser at liquid nitrogen temperature and room temperature. The experimental results show that crosstalk between the nearest neighboring diodes decreases exponentially as the diode pitch increases, and the factors that affect the obtained crosstalk are presented and analyzed. Crosstalk out of the nominal diode area （optically sensitive area） is also measured and discussed.     

电子设备热设计、热评估实施要求

介绍了对电子设备进行热设计、热评估的必要性，指出对电子设备进行可靠性热设计，实施有效的热控制是提高设备工作可靠性的关键措施；同时简明阐述了热设计的概念和热设计的主要内容和实施要求，并介绍了热评估的必要性和对保障电子设备可靠性的实用意义。     

远程荧光LED球泡灯热仿真分析

采用FloEFD流体分析软件分析了改变LED散热器翅片数和基板厚度对LED球泡灯热量的影响。首先对LED芯片进行仿真,然后用蓝宝石替换LED芯片其他部分简化后仿真,将两者进行了对比。接着对远程荧光LED集成封装光源进行了热模拟,发现将大功率芯片集成在铝基板上,工作时产生的热量非常大,模拟时芯片的结温在159.9℃,超过了LED正常工作结温,所以仅仅依靠铝基板难以达到散热要求。最后对LED球泡灯散热器不同翅片数和不同基板厚度分别进行了热仿真,得出当翅片数为16,基板厚度为2mm时,LED球泡灯的整体散热良好,模拟结果显示LED芯片的温度只有83.8℃,完全满足散热要求。     

电子设备热评估及实施流程

明确了对电子设备实施热评估的目的，详细地叙述了热评估的主要内容和具体的实施流程，并介绍了工程上实用的热测量方法对电子设备进行热评估的技术方案和主要设备。     

智能移动终端产品热设计研究

为了解决智能移动终端局部过热的问题,从平面热布局面积入手,采用热传导技术,抓住多模智能移动终端热源器件布局的关键,给出一个考虑散热的布局最小面积;根据热流密度来计算结构的整机高度。通过热仿真来进行布局和结构设计的模拟,给出结构设计的参考意见,最后通过测试去验证和完善热设计。经过实际产品的发热红外图谱分布试验,获得智能移动产品实际的温度分布平面图,得到了与仿真一致的结论。     

电子封装的简化热模型研究

集成电路的飞速发展使得从封装到电子设备的单位体积功耗和发热量不断增加。电子系统散热问题需要在设计阶段就通过热仿真予以充分考虑和预测。电子封装作为电子系统的最小组成部分,其简化模型的优劣直接影响电子系统热分析的速度和准确性。本文主要讨论单芯片封装稳态简化热模型的建立。先后介绍了从最简单的单热阻模型到目前广为关注的边界条件独立的DELPHI简化模型的结构。其中着重分析了两热阻模型和DELPHI模型的建模方法及过程。     

光轴竖直大口径长焦距平行光管热设计

工作在真空罐内的平行光管的工作环境特点决定了其与空间光学遥感器相同的热设计原则,光管的结构形式对工作温度提出了严格要求。首先,确定光管结构表面的热控涂层和多层隔热材料的包覆方式;其次,光管热设计的关键是加热区设计,设计了两种加热方案,从可实施性和加热功耗大小对两种方案进行了比较;最后,对最终的热设计方案进行仿真分析。结果表明:平行光管光机结构的温度水平可控在19.3~20.8℃,主镜温度为19.5℃,满足设计要求,验证了热设计方案的可行性,可对其他同类型的地面光机结构的热设计提供借鉴。     

基于TASPCB的PCB热分析、热设计技术探讨

简要地介绍了电子产品热分析、热设计的重要性及其方法的发展。重点介绍基于TASPCB环境下的电子元器件热模型的建立方法和电子元器件热功耗评估技术,并给出典型PCB热设计的实例,提出电子产品PCB设计的热设计优化措施。     

LD侧面泵浦Nd:YAG激光器的热效应研究

对激光二极管侧面泵浦Nd:YAG激光器的热效应进行了分析。由热传导方程得出YAG晶体内的温度分布，分析了激光介质中的热效应力热应力双折射，并得到YAG的热焦距及激光束腰和远场发散角随泵浦功率的变化图形。     

室外光纤转接机箱的温度分析、仿真与测试

散热控制是通信产品可靠性设计中的一个重要组成部分,结合公司室外转接机箱BNU05,本文具体讨论了研发过程中通信产品的温度控制、估算分析、软件仿真与试验测试,希望借此来提高系统的可靠性,从而提高产品的质量.     

热探测器温度对非制冷红外热像仪测温的影响

根据红外辐射理论和热像仪测温原理，给出了热探测器非制冷红外热像仪的温度计算公式；针对热探测器热像仪，分析了探头温度对热像仪测量结果的影响。