氧化对SOI基SiGe薄膜残余应变弛豫的影响

研究了氧化对外延在SOI衬底上的SiGe薄膜的残余应变弛豫过程的影响.通过对SiGe薄膜采用不同工艺的氧化,从而了解不同氧化条件对SOI基SiGe薄膜的应变弛豫过程的影响.氧化将会促使SiGe薄膜中的Ge原子扩散到SOI材料的顶层硅中.而SiGe薄膜的残余应变弛豫过程将会与Ge原子的扩散过程同时进行,通过对SiGe薄膜和SOI顶层硅中位错分布的分析发现:在氧化过程中,SiGe薄膜和SOI衬底之间存在一个应力传递的过程.     

氧化对SOI基SiGe薄膜残余应变弛豫的影响

研究了氧化对外延在SOI衬底上的SiGe薄膜的残余应变弛豫过程的影响.通过对SiGe薄膜采用不同工艺的氧化,从而了解不同氧化条件对SOI基SiGe薄膜的应变弛豫过程的影响.氧化将会促使SiGe薄膜中的Ge原子扩散到SOI材料的顶层硅中.而SiGe薄膜的残余应变弛豫过程将会与Ge原子的扩散过程同时进行,通过对SiGe薄膜和SOI顶层硅中位错分布的分析发现:在氧化过程中,SiGe薄膜和SOI衬底之间存在一个应力传递的过程.     

柔性高温NiCr薄膜应变计研究

耐高温的NiCr薄膜应变计在航空、航天领域有广泛的需求。采用射频磁控溅射方法制备了NiCr薄膜,研究了溅射气压和衬底温度对NiCr薄膜电阻温度系数的影响规律,结果表明:当溅射气压为0.2 Pa,基片温度为400℃时,电阻温度系数最小为130.7×10^-6/℃。利用优化的工艺条件,在Hastelloy柔性合金衬底上制备了NiCr薄膜应变计,测试结果表明,所制备的NiCr薄膜应变计在各个温度下其电阻随着应变呈线性变化,其应变灵敏度(GF)因子随温度增加而增大,当温度超过200℃后,GF因子缓慢变化。温度为400℃时,GF因子达到3。实验得到的基于Hastelloy合金衬底的柔性薄膜应变计为高温应变测量提供了一种新的手段。     

Si基外延Ge薄膜中残余应变的检测与分析

研究了Si衬底上外延Ge薄膜中的应变。在超高真空化学气相沉积系统中生长Ge薄膜,采用高精度X射线衍射(XRD)和拉曼散射光谱检测薄膜的组份和应变。结果表明,外延薄膜的组份为纯Ge,没有Si的扩散;Ge薄膜中存在少量应变。Ge薄膜XRD峰位和拉曼散射峰位的偏移是由残余应变引起的。定量计算了热膨胀失配引入的张应变和晶格失配引入的压应变与Ge薄膜生长参数的关系,张应变随着生长温度的升高而近似线性增加,压应变随着生长厚度的增加按反比例减小,Ge薄膜最终应变状态由两者共同决定。理论计算值与实验结果吻合良好。     

MOCVD生长AlGaN/GaN/Si(111)异质结材料

利用MOCVD在Si(111)衬底上生长了无裂纹的GaN外延薄膜和AlGaN/GaN异质结构。通过优化Si衬底的浸润处理时间、AlN层厚度等参数获得了无裂纹的GaN外延薄膜,研究了SiN缓冲层和插入层厚度对AlGaN/GaN异质结电学性质的影响,2DEG的迁移率和面密度分别达到1410cm2/V.s和1.16×1013cm-2。     

聚焦离子束在外延生长氮化镓薄膜失配位错研究中的应用

氮化镓具有直接能量带隙(3.4eV)适合用作短波长发光器件,具有非常广泛的应用前景[1]。氮化镓薄膜(厚度约为μm量级)的制备一般均采用异质处延生长的方法。由于受到衬底材料的限制(常用的衬底为三氧化二铝,单晶硅,砷化镓等),使衬底材料与外延薄膜在晶体结构和物理性质方面有所差异,如晶胞参数的不同和热膨胀系数的差异。这些差异在外延生长的薄膜中引起失配应力和应变。当外延薄膜的厚度达到临界厚度时,外延薄膜中的失配应力和应变均达到极大值。继续外延生长超过临界厚度时,就会在外延薄膜中引入失配位错来释放失配应力,降低失配能量。失配…     

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。     

多离子束反应共溅射制备TbTiO3铁电薄膜的微结构研究

本文利用多离子束反应共溅射装置，分别在Ｓｉ和ＭｇＯ衬底上原位制备了Ｐｂ－Ｔｉ氧化物薄膜。研究表明，利用多离子束反应共溅射技术，可以显著降低薄膜后续热处理的温度；薄膜中焦绿石结构的消失温度与薄膜中Ｐｂ的含量有关；较之Ｓｉ衬底，在ＭｇＯ衬底上的薄膜较易获得好的晶体结构和优良的薄膜表面形貌。对所观察到的形象，从衬底与薄膜相互作用的角度进行了讨论。     

多离子束反应共溅射制备PbTiO_3铁电薄膜的微结构研究

本文利用多离子束反应共溅射装置，分别在Ｓｉ和ＭｇＯ衬底上原位制备了ＰｂＴｉ氧化物薄膜。研究表明，利用多离子束反应共溅射技术，可以显著降低薄膜后续热处理的温度；薄膜中焦绿石结构的消失温度与薄膜中Ｐｂ的含量有关；较之Ｓｉ衬底，在ＭｇＯ衬底上的薄膜较易获得好的晶体结构和优良的薄膜表面形貌。对所观察到的现象，从衬底与薄膜相互作用的角度进行了讨论     

射频磁控溅射生长C轴择优取向AIN压电薄膜

采用射频磁控反应溅射工艺，在Si（400）衬底上制备了高c轴取向的AlN薄膜。用X射线衍射仪（XRD）分析了薄膜特征。研究了不同的Ar／N2比、衬底偏压、工作压强对AlN薄膜c轴择优取向的影响。研究了AlN薄膜在以氮终止的硅衬底和纯净硅衬底两种表面状态的生长机制，发现在以氮终止的硅衬底表面生长的AlN薄膜非常容易得到c轴择优取向的AlN薄膜。     

6H-SiC衬底上采用不同厚度AlN缓冲层对GaN外延层的影响

采用不同厚度AlN作为缓冲层在6H-SiC衬底上生长了GaN外延层,并利用X射线衍射,拉曼散射和透射电子显微镜等对GaN性质进行了研究。AlN缓冲层的应变状态对GaN的晶体质量和表面形貌有很大影响。较厚的AlN缓冲层会导致GaN表面出现裂纹,而太薄的AlN缓冲层会导致GaN层较高的位错密度,从而恶化器件性能。分析了GaN产生裂纹和高位错密度的机制,并采用较优厚度（100nm）的AlN缓冲层生长出高质量的GaN外延层。     

Characteristics of GaN grown on 6H-SiC with different AlN buffers

Characteristics of GaN grown on 6H-SiC (0001) substrates using different thicknesses of AlN buffers are studied. It is found that the surface morphology and crystal quality of GaN film closely depends on the strain state of the AlN buffer. For a thicker AlN buffer, there are cracks on GaN surface, which make the GaN films unsuitable for applications. While for a thinner AlN buffer, more dislocations are produced in the GaN film, which deteriorates the performance of GaN. Possible generation mechanisms of cracks and more dislocations are investigated and a ～100 nm AlN buffer is suggested to be a better choice for high quality GaN on SiC.     

Crack formation in metallized single crystal silicon substrates

Ball bonding of metallized silicon substrates has been simulated by microindentation, with a hemispherical diamond indentor, of (100) silicon wafers that contained aluminum film layers. The indentation loads varied up to 35N and the thickest aluminum film, composed of four layers, was 100 × 10^-6 m. The radial cracks in the silicon, beneath the aluminum film, were measured as a function of indentation load and aluminum film thickness, and compared to that of unmetallized silicon. The crack lengths have been used to determine the fracture toughness,K _c = 24.4 ± 4.9 MPam^0.5, which is twice the value obtained by Vickers indentation experiments. A model describing the relationship between the film thickness versus the radial crack length is presented.     

Kinetics of strain relaxation in semiconductor films grown on borosilicate glass-bonded substrates

Changes in the strain relaxation of semiconductor films due to growth on a thin epitaxial template bonded via a borosilicate glass to a mechanical handle wafer have been observed. Akinetic analysis of the mechanical decoupling between the film/template heterostructure and the handle wafer is developed in order to estimate and evaluate the contribution of glass viscous deformation to the observed strain relaxation. The thickness and elastic constants of the template and film, the thickness and viscosity of the bonding media, and the lateral dimension of the bonded structure are included in this model. Based on this model, the viscous flow of the glass is unlikely to have played a role in previous observations of changes in film strain relaxation due to growth on glass-bonded substrates. The calculations are used in conjunction with simple expressions for the temperature and composition dependence of borosilicate glass viscosity to result in design guidelines for substrate structures and annealing schedules in which the viscous flow of a borosilicate glass will contribute to the strain relaxation of a lattice-mismatched film.     

Analysis of electrically conductive silver ink on stretchable substrates under tensile load

Electrical conductors were printed by the screen printing method on stretchable PVC substrates and on fabrics. Polymer thick film silver ink was used as the conductive medium. The electrical performance and the structure of the ink film were investigated in unloaded conditions and under strain. In addition, the ink film morphology was examined. The goal of this study was to provide information for developing a strain sensor for large strain levels using the materials under investigation. An additional aim was to assist the integration of electronics into other structures. The results showed that strain sensitive structures can be made using the materials selected for this study and these materials provide an opportunity to develop strain sensors. The structures also tolerated large strain levels and thus they can be integrated into other materials which are exposed to strain.     

InAs/InGaSb photodetectors grown on GaAs bonded substrates

The results of wafer fusion between GaAs and InP followed by transfer of an InGaAs film from the InP to GaAs substrate are presented in this paper. This technique of film transfer allowed the subsequent growth of epitaxial materials with approximately 7% lattice mismatch. Type-II InAs/GaInSb superlattices photodetectors of different designs have been grown by molecular beam epitaxy (MBE) on the alternative InGaAs/GaAs substrate and on standard GaSb substrates. Comparison between photodetectors grown on the two different substrates with nearly identical superlattice periods showed a shift in the cut-off wavelength. The superlattices grown on the alternative substrates were found to have uniform layers, with broader x-ray linewidths than superlattices grown on GaSb substrates.     

Design of Strain‐Limiting Substrate Materials for Stretchable and Flexible Electronics

Recently developed classes of electronics for biomedical applications exploit substrates that offer low elastic modulus and high stretchability, to allow intimate, mechanically biocompatible integration with soft biological tissues. A challenge is that such substrates do not generally offer protection of the electronics from high peak strains that can occur upon large‐scale deformation, thereby creating a potential for device failure. The results presented here establish a simple route to compliant substrates with strain‐limiting mechanics based on approaches that complement those of recently described alternatives. Here, a thin film or mesh of a high modulus material transferred onto a prestrained compliant substrate transforms into wrinkled geometry upon release of the prestrain. The structure formed by this process offers a low elastic modulus at small strain due to the small effective stiffness of the wrinkled film or mesh; it has a high tangent modulus (e.g., >1000 times the elastic modulus) at large strain, as the wrinkles disappear and the film/mesh returns to a flat geometry. This bilinear stress–strain behavior has an extremely sharp transition point, defined by the magnitude of the prestrain. A theoretical model yields analytical expressions for the elastic and tangent moduli and the transition strain of the bilinear stress–strain relation, with quantitative correspondence to finite element analysis and experiments.     

Estimation of warpage and thermal stress of IVHs in flip–chip ball grid arrays package by FEM

Flip–chip substrates have been developed to meet the recent technical trend. They have a small IVH (Inner Via Hole) diameter to improve electrical packaging performance. However, under thermal loading conditions, substrate warpage increases as substrate thickness decreases. Performance of FCBGA may be severely limited by substrate warpage. Furthermore, large thermal deformation induces cracks and delaminations in an IVH. It is important to understand substrate thermal deformation to improve FCBGA reliability.Thermal deformation of the FCBGA (Flip–Chip Ball Grid Array) with assembly conditions has been calculated globally by finite element analysis. And residual plastic strain of an IVH has been estimated microscopically to understand thermal stress of the IVH. Finite element method considering non-linear material model is verified with experiment on warpage to improve simulation accuracy. Also, the Taguchi method is applied to optimize FCBGA substrate design.Based on the computed results by the Taguchi method, we know core thickness in FCBGA substrate is the most determining factor for thermal deformation. The second most significant factor is the core material properties. Even though the plugging material in the IVH has little thermal deformation macroscopically with respect to the entire FCBGA substrate, the plugging material lowers the reliability of the IVH alone microscopically. In some cases depending on the plugging material, the IVH may develop some cracks.     

制备工艺对氧化钒薄膜微观结构的影响

为了研究制备工艺对氧化钒薄膜微观结构的影响,采用X射线衍射和扫描电镜,对用sol-gel法制作的、不同热处理条件下的硅基氧化钒薄膜之结构及形貌进行了分析。结果表明,470℃下制作出的有种子层薄膜无裂纹、致密性好、晶粒尺寸分布均匀,在此温度下热处理4 h得到的有种子层氧化钒薄膜V2O5相最纯,衍射峰最强,而提高热处理温度会导致晶向杂乱,V2O5相的衍射峰强度降低,使得VO2相增多。