脉冲激光溅射沉积制备La0.67Ba0.33MnO3薄膜的应变效应研究

采用脉冲激光溅射沉积技术在LaAlO3(001)衬底上制备了一系列不同厚度(40～240 nm)的La0.67Ba0.33MnO3薄膜。通过控制薄膜的厚度，获得了不同应变态的La0.67Ba0.33MnO3薄膜。根据X射线衍射(XRD)数据详细分析了薄膜厚度变化对c轴晶格常数的影响。采用标准的直流四探针法和超导量子干涉仪分别测量了薄膜的电阻温度特性和磁化强度温度特性。研究发现，La0.67Ba0.33MnO3薄膜的居里温度和金属绝缘态转变温度随压缩应变的增大而减小，即压缩应变抑制了La0.67Ba0.33MnO3薄膜的铁磁性，降低了居里温度。这一结果与以往压缩应变增强铁磁性并提高居里温度的结论相异，不能利用Millis的应变理论模型进行定性解释。利用超巨磁电阻(CMR)薄膜材料的应变效应对eg轨道稳定性的影响对La0.67Ba0.33MnO3薄膜的异常磁电输运效应进行了解释。     

Bonding-Induced Strain Effects in InP DFB Components Soldered p-Side-Up on AlN Substrates

Bonding-induced strain is shown to have significant impact on the performance of distributed feedback (DFB) lasers mounted p-side up on AlN carriers using AuSn solder. Degree of polarization (DOP) of photoluminescence was used to estimate top-side longitudinal strain profiles in InP chips soldered to AlN carriers. Asymmetric strain profiles were revealed, the orientation of which are shown to be dependent on bonding tool coplanarity. Solder profiles measured on the same chips by scanning electron microscopy (SEM) were found to be nonuniform. Finite-element method (FEM) simulations were used to confirm that the asymmetric strain profiles resulted from solder nonuniformity caused by the bonding process. The FEM simulations were extended to analyze the effects of various bonding parameters on the top-side longitudinal strain profiles in InP chips, and suggestions are made for minimizing strain variations. The measured strains were included in a DFB laser model, and are shown to cause changes in slope efficiency and threshold current. These changes in slope efficiency and threshold current with bonding compare well with data collected from a large ensemble of DFB laser devices measured before and after the mounting process.      

Flexible strain sensor with high performance based on PANI/PDMS films

A high strain sensor composed of elastomer polydimethylsiloxane (PDMS) and polyaniline (PANI) was fabricated by electrodeposition method for PANI preparation and daubing method for PDMS preparation. This kind of sensor could subject to a large tensile strain (∼50%) and revealed a high gauge factor (54 at 50% strain), which was higher than other sensors reported previously. Also, the sensor displayed a current with a magnitude of mA when applied to 1 V, indicating it didn't need expensive and huge test equipment. Moreover, cyclic strain on the sensor obtained repeatable resistive responses. Its work mechanisms were discussed. The flexible sensor was proved to be useful in sensing strains and other various applications.     

<100>沟道方向对高迁移率双轴应变硅p-MOSFET的作用

双轴应变技术被证实是一种能同时提高电子和空穴迁移率的颇有前景的方法;<100>沟道方向能有效地提升空穴迁移率.研究了在双轴应变和<100>沟道方向的共同作用下的空穴迁移率.双轴应变通过外延生长弛豫SiGe缓冲层来引入,其中,弛豫SiGe缓冲层作为外延底板,对淀积在其上的硅帽层形成拉伸应力.沟道方向的改变通过在版图上45°旋转器件来实现.这种旋转使得沟道方向在(001)表面硅片上从<110>晶向变成了<100>晶向.对比同是<110>沟道的应变硅pMOS和体硅pMOS,迁移率增益达到了130%;此外,在相同的应变硅pMOS中,沟道方向从<110>到(100)的改变使空穴迁移率最大值提升了30%.讨论和分析了这种双轴应变和沟道方向改变的共同作用下迁移率增强的机理.     

Mechanical Shock Behavior of Bulk Pure Sn Solder

With the increasing focus on developing environmentally benign electronic packages, Pb-free alloys have received a great deal of attention. Mishandling of packages during manufacture, assembly or by the user may cause failure of the solder joint. A fundamental understanding of the behavior of Pb-free solders under mechanical shock conditions is lacking. Reliable experimental stress–strain data over a range of strain rates needs to be obtained for reliability models. In this paper we report on the intermediate strain rate behavior of pure Sn solder. The first part of the paper discusses modeling and analysis of the specimen geometry to obtain a relatively uniform stress (and strain) distribution within the gage section. Analysis by the finite element method (FEM) showed that a modified specimen geometry, with 10 mm gage length, provided a homogeneous strain distribution, similar to the American Society for Testing and Materials (ASTM) E8 specimen geometry. The second part describes microstructural characterization and experimental results on pure Sn at intermediate strain rates (~10/s). Ultimate tensile strength and strain to failure in the 10 mm specimen were quite similar to those of the ASTM specimen. A double necking phenomenon was observed in the ASTM specimen, which was not observed in the 10 mm specimen. FEM modeling of the dynamic behavior of the solder correlated very well with the experimental observations.     

Effects of boron incorporation on the strain and photoluminescence properties of GaAsSb/GaAs quantum wells

Boron-containing GaAsSb/GaAs quantum wells (QWs) with different antimony (Sb) mole fractions were grown by low-pressure metal–organic chemical vapor deposition for the first time. The effects of boron incorporation on the performance of GaAsSb/GaAs QWs are discussed. For samples with low compressive strain, injection of triethylboron can enhance the Sb content and increase the compressive strain, although boron incorporation can lead to a reduction in strain. This effect was less for strained GaAsSb/GaAs QWs, so the compressive strain of these QWs did not vary. Room-temperature photoluminescence emission at 1116 nm with a full-width at half-maximum (FWHM) value of 56 meV was obtained for strained BGaAsSb/GaAs QWs.     

基于各项异性的组合式PVDF应变传感器

在应用压电薄膜测量结构表面应变时,薄膜上的感应电压是其面内两个正交方向应变的函数。要获得结构表面某处一个方向的应变,就必须在该处粘贴和检测两片以上的压电薄膜,这对应用于随机载荷作用下的结构应变测量非常不便。利用压电薄膜材料的各向异性开发了组合式压电薄膜应变传感器,这使检测的感应电压和结构表面单一方向的应变成正比关系。根据压电方程推导了组合式压电薄膜输出电压和被测单向应变间的关系,并通过对一个带有小孔平板试件的应变分布测量试验和有限元数值分析,验证了该组合式应变传感器的可行性及具有很高的测量精度。该法操作简单,对实际工程结构应变测量具有重要的实用价值。     

MWCNTs based flexible and stretchable strain sensors

Carbon nanotubes have potential applications in flexible and stretchable devices due to their remarkable electromechanical properties. Flexible and stretchable strain sensors of multi-walled carbon nanotubes (MWCNTs) with aligned or random structures were fabricated on poly-dimethylsiloxane (PDMS) substrate with different techniques. It was observed that the spraycoatedtechniquebased strain sensor fabricated on PDMS substrate showed higher sensitivity higher stretchability, better linearity and excellent longer time stability than the sensor fabricated with other methods presented in this work. The scanning electron microscopy images indicated the spray coating technique can produce a better uniform and compact CNT network, which is the important role affecting the performance of CNT-based flexible strain sensors.     

狂犬病病毒不同毒株的形态学研究

将狂犬病（Rabies vims）固定毒CTN株（中国济南株）、CVS株（国际标准攻击毒株）、ERA株（兽用疫苗弱毒株）分别在小鼠脑组织增殖及ERA毒株在BHK21传代细胞增殖,通过超薄切片和负染色制备样品,电镜观察.结果发现在鼠脑组织中,CTN株病毒粒子比较难查找,而较易发现CVS株和ERA株.另外,在不同毒株的脑组织和细胞培养物中还发现了大量的非典型粒子,诸如截断的粒子及锥形、柱形等形态,同时还发现了胞浆包涵体.研究揭示：（1）典型病毒粒子数量与免疫原性呈正相关;（2）在观察鼠脑组织的病毒时,发现有神经髓鞘部位难以找到病毒粒子;（3）狂犬病病毒粒子存在于宿主细胞的胞浆内.     

Role of shape-memory alloy reinforcements on strain evolution in lead-free solder joints

Microelectronic solder joints are exposed to aggressive thermomechanical cycling (TMC) during service, resulting in strain localization near solder/bond-pad interfaces, which eventually leads to low-cycle fatigue (LCF) failure of the joint. In order to mitigate these strain concentrations, a “smart solder” reinforced with a martensitic NiTi-based shape-memory alloy (SMA) has been proposed before. In the present work, the role of NiTi particles on strain evolution in composite solders was studied using a combination of experimental and numerical means. Finite element modeling showed that NiTi pariculate reinforcements can reduce inelastic strain levels in the solder via shape recovery associated with the B19′ → B2 transformation. In situ TMC studies in the scanning electron microscope (SEM), in conjunction with strain analysis via digital image correlation (DIC), showed evidence of reverse deformation in the solder commensurate with the NiTi phase transformation, demonstrating the conceptual viability of the smart solder approach. The SEM-DIC experiments also suggested that the presence of particulates mitigates shear localization, which is commonly observed in monolithic solder joints close to joint/bond-pad interfaces. Finally, TMC experiments on monolithic solder and NiTi/solder single-fiber composite joints highlighted the beneficial effect of shape-memory transformation in reducing inelastic strain range of solders.     

Direct observation of local strain field for ULSI devices

The in-depth profile of strain distribution from the silicon surface is one of the most important pieces of information for optimizing the device performance. The convergent-beam electron diffraction(CBED) method has been applied to analyze the local strain filed of the active regions for both test structure with the shallow trench isolation(STI) and the conventional LOCOS on a cross-sectional surface. As a result, strain distribution was observed successfully. It was found that the compressive stress exist all over the survey regions. The active region close to the bottom corner of the STI shows a larger stress than that of the conventional LOCOS. It is demonstrated that the CBED technique is very effective for the determination oflocal strain field in a small area of semiconductors and the optimizing of the STI structure andfabrication process.     

Three-Dimensional Finite Element Analysis of Multiple-Grained Lead-Free Solder Interconnects

A combination of various experimental techniques was coupled with three-dimensional numerical simulation to study the strain distribution in anisotropic, heterogeneous lead (Pb)-free solder ball grid array interconnects used in electronic packages. An in situ full-field deformation map on the cross section of the joint showed a nonuniform strain distribution when the package was subjected to thermal loading. This nonuniformity was correlated with the locations of various grains on the cross section as obtained by orientation imaging microscopy (OIM) and optical microscopy. The solder interconnect was progressively sectioned and imaged under cross polarizers to discern the␣three-dimensional shapes of various grains in the solder interconnect. A methodology to replicate the three-dimensional shapes and orientations of the various grains and grain boundaries in a microstructure-based finite element model was developed. The numerical results were compared with the displacement and strain distributions obtained experimentally. The demonstrated strain localization along the grain boundaries in the case of multigrain joints and along the pad-solder interfaces in the case of the single-grain joints matched very well with the locations of plastic damage accumulation when the same interconnect was subjected to several thermal cycles.     

平面应变压缩过程中初始取向对AZ31镁合金变形行为的影响

在室温和150℃下对AZ31镁合金进行平面应变压缩试验,应变速率为0.01 s-1,形变量为0.1.试样(切割于强织构的热轧板)的压缩轴c与其基面法向成不同的角度,从而研究初始织构对AZ31镁合金塑性变形行为的影响.利用电子背散射衍射花样(EBSD)采集变形试样的微观结构和织构信息,分析孪生和滑移行为.实验发现AZ31镁合金塑性变形由{10(-12)}<(-10)11>拉伸孪生和基面滑移共同控制,并确定了各种变形模式比例与晶体初始取向的关系,其中拉伸孪生在压缩轴垂直于c轴方向时占主导作用.     

基于高阶模干涉的光纤应变传感器

介绍一种利用光纤内的高阶模干涉原理实现对应变测量的新型光纤应变传感器.在采用相同光纤的条件下,该应变传感器具有与光纤布拉格光栅(FBG)相反符号的应变系数,其温度灵敏度与FBG传感器相同,而应变灵敏度约为FBG传感器的2倍,非常适合与FBG结合实现应变与温度的同时测量,并具有结构简单、制作方便和成本低等特点.     

in-situ electromigration study on Sn−Ag−Cu solder joint by digital image speckle analysis

The phenomenon of electromigration in Pb-free Sn−Ag−Cu solder joint specimens subject to high current density was characterized. Digital image speckle analysis (DISA) was used to measure the in-situ microdeformation and strain of cross-sectioned solder joints, which are subject to electromigration with a current density of 5 × 10³ A/cm² under an ambient temperature of 150°C. After a 120 h electromigration test, a higher strain near large voids was detected near preexisting voids in the solder joints. The current-crowding effect on strain formation was characterized, as it was found that the strain is high near the interface, while in the middle of the solder bump, the strain is low and could be neglected. Nanoindentation markers were used to form dummy voids to study the effect of preexisting voids. The Sn atomic flux and its effect on formation of electromigration strain are discussed.     

A study on the development of transmission-type extrinsicFabry-Perot interferometric optical fiber sensor

The conventional reflection-type extrinsic Fabry-Perot interferometric (EFPI) optical fiber sensor has good sensitivity and resolution compared with other types of optical fiber sensors. However, they have the disadvantage that the distinction of strain direction of EFPI is difficult because of measurement method by only fringe counting. This paper presents the newly developed transmission-type EFPI (TEFPI) optical fiber sensor, which has been improved by additional functions, and whose measuring system differs from that of the reflection-type EFPI optical fiber sensors using a single-mode fiber (SMF) and multimode (MMF) fibers as light guides and reflectors, respectively. The output signal of the TEFPI optical fiber sensor was analyzed with the uniform plane wave-based model, the SMF power distribution-based model and the splice loss-based model; the analyzed signals were then verified experimentally. Based on the results of analysis, the TEFPI optical fiber sensor was fabricated using two single-mode fibers connected to the light source and optical receiver; this was then used in strain measurement. The strain measured by the TEFPI optical fiber sensor was compared with that measured by the electric strain gauge     

Epitaxial layer morphology of highly strained GaInAs/InP multiple quantum well structures grown by CBE

We present a study of changes in the layer morphology of tensilely strained GalnAs/InP multiple quantum well (MQW) structures in dependence on strain and substrate off-orientation. Growth was performed by chemical beam epitaxy (CBE). For high tensile strain (x_Ga=0.77) lateral thickness fluctuations evolving into facets of the (411)A type are observed in cross-sectional transmission electron microscopy (TEM). These undulations are parallel to [01 ] and present for samples grown on both exactly oriented and off-oriented (100) InP substrates. For off oriented substrates the strain induced generation of macrosteps parallel to the surface steps is detected for x_Ga = 0.65 and x_Ga=0.77. The distance and height of the macrosteps directly correspond to the substrate off orientation angle. While the macrostep generation is a direct consequence of surface steps in combination with strain, the occurrence of the undulations might be connected with the (2 × 4) surface reconstruction during CBE growth. Both mechanisms are discussed with respect to experimental and theoretical literature data.     

Properties of the Mo Back Contact for the Formation of a Thin-Film Photovoltaic Absorber

A Taguchi experimental design was used to find which deposition parameter has the most dominant effect on the electrical resistivity of molybdenum (Mo) films. Based on the most important parameter, the Mo films were further characterized by structural, electrical, and adhesive methods. Then, a copper indium gallium selenide (CIGS) thin film was fabricated by a two-stage process on the obtained Mo layer. The results show that working pressure had a dominant effect on electrical resistivity. The Mo films deposited at 1 mTorr and 2 mTorr exhibited compressive strain and dense polycrystalline microstructure, whereas those deposited at 3 mTorr and 4 mTorr exhibited tensile strain and an elongated grain with open boundaries. A Mo film with open porous structure, tensile strain, and lower resistivity was suitable for the formation of CIGS films. After selenization at 560°C, a single-phase chalcopyrite CIGS film with a layer of MoSe₂ at the Mo/CIGS interface was obtained.     

Strain analysis of the GaN epitaxial layers grown on nitridated Si(111) substrate by metal organic chemical vapor deposition

The strain analysis of GaN film on nitridated Si(111) substrate with different growth times between 0 and 660 s via metal organic chemical vapor deposition (MOCVD) was conducted based on the precise measurement of the lattice parameters by using high-resolution X-ray diffraction (HR-XRD). The nitridation time (NT) was changed at a fixed growth condition. The a- and c-lattice parameters were measured, followed by the in-plane and out-of-plane strains. Then, the biaxial and hydrostatic components were extracted from the total strain values obtained, and were then discussed in the present study as functions of the NT. The biaxial strain and stress are also strongly affected by the non-uniformity of the SiN_x buffer layer thickness.     

Modeling and experiments on epitaxially grown multilayers with implications to critical thickness

In this study, using the equations for static equilibrium and Hooke’s law for isotropic materials under a plane stress condition, the elastic fields associated with each layer have been calculated. A model has been developed to calculate the elastic fields in multilayers grown epitaxially on a planar substrate. The strain partitioning in this model reduces to the limiting case of a two-layer structure that is available in the literature. We have chosen a particular system (SiGe) and calculated strain energy density for any number (N) of layers of graded Ge (Si_xGe_1−x) on silicon. The model was compared with experiment for graded SiGe grown over a planar silicon substrate. The results revealed qualitative agreement between the calculated strain energy density and the experimentally observed dislocation density in the layers. The effect of the choice of a strain partitioning model on the calculation of a film/epilayer critical thickness is demonstrated.