用透射光谱和模拟退火算法确定薄膜光学常数

提出了用透射光谱曲线和模拟退火算法同时确定薄膜材料折射率n、消光系数k及薄膜厚度d的方法,并给出了严格的理论公式和计算程序框架图。为了验证此方法的准确性和可行性,先进行了计算模拟,然后对SiNx薄膜进行了测量。模拟结果与理论值非常接近,根据实验结果恢复出来的曲线与原始实验曲线吻合得很好。此方法具有非破坏性、测量简单、操作方便、稳定性好和计算收敛速度快、精度高等特点。     

Chemical natures and distributions of metal impurities in multicrystalline silicon materials

We present a comprehensive summary of our observations of metal‐rich particles in multicrystalline silicon (mc‐Si) solar cell materials from multiple vendors, including directionally‐solidified ingot‐grown, sheet, and ribbon, as well as multicrystalline float zone materials contaminated during growth. In each material, the elemental nature, chemical states, and distributions of metal‐rich particles are assessed by synchrotron‐based analytical x‐ray microprobe techniques. Certain universal physical principles appear to govern the behavior of metals in nearly all materials: (a) Two types of metal‐rich particles can be observed (metal silicide nanoprecipitates and metal‐rich inclusions up to tens of microns in size, frequently oxidized), (b) spatial distributions of individual elements strongly depend on their solubility and diffusivity, and (c) strong interactions exist between metals and certain types of structural defects. Differences in the distribution and elemental nature of metal contamination between different mc‐Si materials can largely be explained by variations in crystal growth parameters, structural defect types, and contamination sources. Copyright © 2006 John Wiley & Sons, Ltd.     

Modeling node mobility for reliable packet delivery in mobile ip networks

In this paper, we analyze node mobility for reliable packet delivery in mobile IP networks. In mobile IP, packets destined to roaming nodes are intercepted by their home agents and delivered via tunneling to their care of addresses (CoA). A mobile node may roam across multiple subnets. At each boundary crossing, a handoff is initiated such that the CoA is updated and a new tunnel is established. We consider both basic mobile IP handoff and smooth handoff. We find that reliable packet delivery in mobile IP networks can be modeled as a renewal process, because the retransmission over a new tunnel after each boundary crossing is independent of the previous history. We then derive the probability distribution of boundary crossings for each successful packet, based on which the packet reliable delivery time can be obtained. Our analytical model is derived based on a general distribution of residence time in a subnet and a general distribution of successful retransmission attempts in each subnet. The results can be readily applied to any distributions for both items. We also provide numerical examples to calculate the probability distribution of boundary crossings, and conduct simulations to validate our analytical results     

Comprehensive Study of Emitter-Ledge Thickness of InGaP/GaAs HBTs

A comprehensive study of emitter-ledge thickness of InGaP/GaAs heterojunction bipolar transistors (HBTs) has been undertaken. It is shown that the recombination rate and electron densities are drastically increased near the exposed base surface between the base contact and the emitter ledge. In contrast, the corresponding hole densities are decreased. If the emitter ledge is too thick, current will flow through the undepleted ledge, which increases the emitter-size effect. In contrast, if the emitter ledge is too thin, it may not effectively passivate the surface. Therefore, the thickness of the emitter ledge is a crucial issue and should be carefully considered. It is shown that, from simulated and experimental results, the optimum emitter-ledge thickness of InGaP/GaAs HBT is 100-200 Aring     

An investigation into the effects of probing and wire bonding stress on the reliability of BOAC

This work describes two types of low stress bonding over active circuit (BOAC) structures applying a finite element analysis. The advantage of improving the chip area utility of the BOAC design is approximately 150–180 μm for each dimension. A 0.13 μm 2 Mb high-speed SRAM with fluorinated silicate glass (FSG) low-k dielectric was combined with these two BOAC structures as the test vehicles to evaluate the impact of the probing and wire bonding stress on the reliability. Initially, a cantilevered probe card was applied to probe the BOAC pads using the typical and the worse probing conditions. Before and after the circuits probing (CP1 and CP2) the experimental results were compared, including the 2 Mb high-speed SRAM yield and wafer bit map data. The difference between the CP1 and CP2 results were negligible for all probing split cells. Next, the cross-section of the BOAC pad under the probing area was investigated following the worst probing condition. In addition, the BOAC pads evaluate the bondability, including the use of ball shear, wire pull and cratering tests. Moreover, all BOAC packaging samples underwent reliability tests, including HTOL, TCT, TST, and HTST. All the bondability and reliability tests passed the criteria for both proposed BOAC structures. Finally, the immunity level of both proposed BOAC pads, for ESD-HBM (human body mode) and ESD-MM (machine mode), differed slightly from the normal pads. No performance degradation was detected. Accordingly, this work shows that both proposed BOAC structures can be used to improve the active chip area utility or save the chip area.     

激光扫描测量信号边界检出方法研究

信号边界检出是激光扫描测量系统实现稳定和高精度测量的关键技术之一.本文对标准电平切割法和二次微分法等边界检出方法的特点进行了分析和比较.基于光电共轭原理,设计了一种可实现光电共轭信号边界检出的新型电路,并使用仿真软件Multisim对该电路进行了动态仿真,表明该电路采用测量信号的自共轭函数作为参考基准,通过确定两共轭交点可稳定实现信号的边界检出.实验验证了该甄别电路,具有灵敏度高、自适应特性好的优点.     

Low‐Threshold Distributed‐Feedback Lasers Based on Pyrene‐Cored Starburst Molecules with 1,3,6,8‐Attached Oligo(9,9‐Dialkylfluorene) Arms

Here, a detailed characterization of the optical gain properties of sky‐blue‐light‐emitting pyrene‐cored 9,9‐dialkylfluorene starbursts is reported; it is shown that these materials possess encouragingly low laser thresholds and relatively high thermal and environmental stability. The materials exhibit high solid‐state photoluminescence (PL) quantum efficiencies (>90%) and near‐single‐exponential PL decay transients with excited state lifetimes of ～1.4 ns. The thin‐film slab waveguide amplified spontaneous emission (ASE)‐measured net gain reaches 75–78 cm^?1. The ASE threshold energy is found to remain unaffected by heating at temperatures up to 130 °C, 40 to 50 °C above T_g. The ASE remained observable for annealing temperatures up to 170 or 200 °C. 1D distributed feedback lasers with 75% fill factor and 320 nm period show optical pumping thresholds down to 38–65 Wcm^?2, laser slope efficiencies up to 3.9%, and wavelength tuning ranges of ～40 nm around 471–512 nm. In addition, these lasers have relatively long operational lifetimes, with N_1/2 ≥ 1.1 × 10⁵ pulses for unencapsulated devices operated at ten times threshold in air.     

Nanoparticles of the Lead-free Solder Alloy Sn-3.0Ag-0.5Cu with Large Melting Temperature Depression

Due to the toxicity of lead (Pb), Pb-containing solder alloys are being phased out from the electronics industry. This has lead to the development and implementation of lead-free solders. Being an environmentally compatible material, the lead-free Sn-3.0Ag-0.5Cu (wt.%) solder alloy is considered to be one of the most promising alternatives to replace the traditionally used Sn-Pb solders. This alloy composition possesses, however, some weaknesses, mainly as a result of its higher melting temperature compared with the Sn-Pb solders. A possible way to decrease the melting temperature of a solder alloy is to decrease the alloy particle size down to the nanometer range. The melting temperature of Sn-3.0Ag-0.5Cu lead-free solder alloy, both as bulk and nanoparticles, was investigated. The nanoparticles were manufactured using the self-developed consumable-electrode direct current arc (CDCA) technique. The melting temperature of the nanoparticles, with an average size of 30 nm, was found to be 213.9°C, which is approximately 10°C lower than that of the bulk alloy. The developed CDCA technique is therefore a promising method to manufacture nanometer-sized solder alloy particles with lower melting temperature compared with the bulk alloy.     

UHV/CVD法生长硅基低位错密度厚锗外延层

采用超高真空化学气相淀积系统,以高纯Si2 H6和GeH4作为生长气源,用低温缓冲层技术在Si(001)衬底上成功生长出厚的纯Ge外延层.对Si衬底上外延的纯Ge层用反射式高能电子衍射仪、原子力显微镜、X射线双晶衍射曲线和Ra-man谱进行了表征.结果表明在Si基上生长的约550nm厚的Ge外延层,表面粗糙度小于1nm,XRD双晶衍射曲线和Ra-man谱Ge-Ge模半高宽分别为530'和5.5cm-1,具有良好的结晶质量.位错腐蚀结果显示线位错密度小于5×105cm-2可用于制备Si基长波长集成光电探测器和Si基高速电子器件.     

太赫兹Si/SiGe量子级联激光器波导模拟

波导层结构设计是制备太赫兹(THz)量子级联激光器的关键问题之一.本文基于德鲁得(Drude)模型,利用时域有限差分(FDTD)法,对Si/SiGe量子级联激光器的波导层进行优化设计,从理论上对传统的递变折射率波导、单面金属波导、双面金属波导以及金属/金属硅化物波导横磁模(TM模)的模式损耗和光场限制因子进行了对比分析.结果表明,金属/金属硅化物波导不但可以减小波导损耗,而且有很高的光学限制因子,同时其工艺也比双面金属波导容易实现,为Si/SiGe太赫兹量子级联激光器波导层的设计提供了一定的理论指导.