Design rule of indium bump in infrared focal plane array for longer cycling life

In light of the proposed equivalent method, a three-dimensional structural modeling of InSb infrared focal plane arrays (IRFPAs) is created, and the simulated strain distribution is identical to the deformation distribution on the top surface of InSb IRFPAs. After comparing the deformation features at different regions with the structural characteristics of IRFPAs, we infer that the flatness of InSb IRFPAs will be improved with a thinner indium bump array, and this inference is verified by subsequent simulation results. That is, when the diameter of indium bump is smaller than 20 μm, the simulated Z-components of strain on the whole top surface of InSb IRFPAs is uniform, and the deformation amplitude is small. When the diameter of indium bump is larger than 28 μm, the simulated Z-components of strain increases rapidly with the thicker indium bump, and the flatness of InSb IRFPAs is worsened rapidly. According to the changing trend of deformation amplitude with diameters of indium bump, and employing element pitches normalization method, a design rule of indium bump is proposed. That is, when the diameter of indium bump is shorter than 0.4 times the element pitch, the flatness of InSb IRFPAs is in an acceptable range. This design rule was supported by different IRFPAs with different formats delivered by several main research groups for achieving a longer cycling life.     

液氮冲击中锑化铟焦平面探测器形变研究

液氮冲击中锑化铟红外焦平面探测器(InSb IRFPAs)的形变研究对理解探测器结构设计可靠性、预测探测器耐冲击寿命具有重要意义.在系统分析液氮冲击结束时模拟得到的InSb IRFPAs形变分布与方向的基础上,提出了降温过程中累积热应变完全弛豫的设想,升至室温后的模拟结果重现了室温下拍摄的InSb IRFPAs典型形变分布特征.经分析认为室温下拍摄的InSb IRFPAs表面屈曲变形源于底充胶固化中引入的残余应力应变,变形幅度随降温过程逐步减弱,至77 K时完全消失,升温过程则依据弹性变形规律复现典型棋盘格屈曲模式.这为后续InSb IRFPAs结构设计、优化及耐冲击寿命预测提供了理论分析基础.     

Modeling and deformation analyzing of InSb focal plane arrays detector under thermal shock

A higher fracture probability appearing in indium antimonide (InSb) infrared focal plane arrays (IRFPAs) subjected to the thermal shock test, restricts its final yield. In light of the proposed equivalent method, where a 32 × 32 array is employed to replace the real 128 × 128 array, a three-dimensional modeling of InSb IRFPAs is developed to explore its deformation rules. To research the damage degree to the mechanical properties of InSb chip from the back surface thinning process, the elastic modulus of InSb chip along the normal direction is lessened. Simulation results show when the out-of-plane elastic modulus of InSb chip is set with 30% of its Young’s modulus, the simulated Z-components of strain distribution agrees well with the top surface deformation features in 128 × 128 InSb IRFPAs fracture photographs, especially with the crack origination sites, the crack distribution and the global square checkerboard buckling pattern. Thus the Z-components of strain are selected to explore the deformation rules in the layered structure of InSb IRFPAs. Analyzing results show the top surface deformation of InSb IRFPAs originates from the thermal mismatch between the silicon readout integrated circuits (ROIC) and the intermediate layer above, made up of the alternating indium bump array and the reticular underfill. After passing through both the intermediate layer and the InSb chip, the deformation amplitude is reduced firstly from 2.23 μm to 0.24 μm, finally to 0.09 μm. Finally, von Mises stress criterion is employed to explain the causes that cracks always appear in the InSb chip.     

考虑底充胶固化过程的InSb面阵探测器结构分析模型

液氮冲击中In Sb面阵探测器的易碎裂特性制约着探测器的成品率,建立适用于面阵探测器全工艺流程的结构模型是分析、优化探测器结构的有效手段.本文提出了用底充胶体积收缩率来描述底充胶在恒温固化中的体积收缩现象,同时忽略固化中底充胶弹性模量的变化来建立底充胶固化模型,给出了底充胶在恒温固化中生成的热应力/应变上限值.借鉴前期提出的等效建模思路,结合底充胶固化后的自然冷却过程和随后的液氮冲击实验,建立了适用于In Sb面阵探测器全工艺流程的结构分析模型.探测器历经底充胶固化、自然冷却至室温后的模拟结果与室温下拍摄的探测器形变分布照片高度符合.随后模拟液氮冲击实验,得到面阵探测器中累积的热应力/应变随温度的演变规律,热应力/应变值极值出现的温度区间与液氮冲击实验结果相符合.这表明所建模型适用于预测不同工艺阶段中面阵探测器的形变分布及演变规律.     

Study on thermal effects of InSb infrared focal plane arrays irradiated by pulsed laser

To learn thermal effects of InSb infrared focal plane arrays (IRFPAs) detector irradiated by pulsed laser, basing on ANSYS software, and considering temperature dependent thermal parameters of InSb, a three dimensional temperature field analysis model of InSb IRFPAs detector by 1064 nm Gauss laser irradiation is built. The characteristics of temperature rise and temperature distribution in InSb IRFPAs detector are studied. The results show that the maximum temperature always occurs in InSb chip, locating at the top layer of InSb IRFPAs detector, the temperature rises in each layer are different, and the temperature distribution in InSb IRFPAs detector is quite different from that in single-layer material. The temperature distribution of InSb chip in InSb IRFPAs reduces from center to outside, while it shows not a smooth decrease, but a concentric-ringed ripple decrease with non-consecutive high temperature extremum regions. The temperature distribution patterns in underfill, Si readout integrated circuits are similar to that in InSb chip, but the discontinuous high temperature areas in InSb chip, underfill locate at the regions between indium bumps, and the discontinuous high temperature areas in Si readout integrated circuits locate at the contact area with indium bumps. This different temperature distribution phenomenon in each material is mainly due to its multi-layer architecture and quite different thermal properties of the middle layer, which is an interlacing layout of underfill and indium bumps. Besides, the influences of indium bump structure size on the temperature rise are also discussed. All these results qualitatively reflect the disciplines of temperature rise in InSb IRFPAs detector, providing a theory support for thermal analysis of detectors irradiated by laser.     

Influences of electrode material and design on the reliability of IRFPAs detector under thermal shock

Under thermal shock, high fracture probability in indium antimonide (InSb) infrared focal plane arrays (IRFPAs) limits its applicability. Typical fracture photographs under thermal shock shows that the cracks originating from the area above public electrode are dominant. In order to learn the influences of electrode material parameter and design on the reliability in InSb IRFPAs detector, the proposed improved equivalent modeling method is employed to build three dimensional InSb IRFPAs structure analysis model. Simulated results show that different electrode materials greatly influence the maximal thermal stress appearing in InSb chip and public electrode, and among the electrode material parameters, the coefficient of thermal expansion is the main affecting factor on thermal stress. With the increasing electrode thickness, the maximum thermal stresses in InSb chip and public electrode both decrease, which means the smaller electrode thickness leads to larger thermal stress in InSb chip and electrode. Besides, it is also found that adjusting the electrode layout to avoid the overlap between indium bumps and the embedded part of electrode can effectively reduce the stress concentration in the area of InSb chip above public electrode. All these are beneficial to optimize the structure of InSb IRFPAs and reduce the fracture probability.     

Local delamination of InSb IRFPAs in liquid nitrogen shock tests

Both the local delamination and the local fracture, appearing in the InSb infrared focal plane arrays (IRFPAs) detectors in liquid nitrogen shock tests, restrict the final yield of the InSb IRFPAs detectors. To explore the mechanism of the local delamination appearing in the region of the negative electrode of the InSb IRFPAs detectors, basing on the created structural modeling of the InSb IRFPAs detectors, we obtain the distributions of the interfacial stresses in the different interfaces of the InSb IRFPAs detectors. After comparing the distributions of the simulated interfacial stresses with the measured local delamination region in the InSb IRFPAs detectors, we think that the local delamination originates from the interfacial shear stresses, and the crack extension is the typical sliding mode. Besides, the weakened gluing strength between the InSb chip and the underfill in the negative electrode region also causes this region to be prone to the local delamination. All these findings provide the theoretical references for both the structure design and the structure optimization of the InSb IRFPAs detectors assembly in the future.     

回旋行波管电子枪阴极热分析

使用有限元分析软件ANSYS对回旋行波管电子枪阴极进行了热分析和形变分析,得到了阴极模型的温度分布和热形变。为了保持阴极发射带表面温度的均匀性,增大了发射带下端与导热介质的接触面积,同时减小了发射带上端处的加热线圈个数,发现温度差由原来的18 ℃减小到了0.9 ℃。在热分析的基础上进行了热形变分析,将形变量结果带入EGUN软件验证,发现电子注的速度比增大,横向、纵向速度零散以及引导中心半径也都有所增加。     

Reflection absorption infrared spectroscopy analysis of the evolution of ErSb on InSb

We discuss an ex-situ monitoring technique based on glancing-angle infrared-absorption used to determine small amounts of erbium antimonide (ErSb) deposited on an indium antimonide (InSb) layer epitaxially grown on an InSb (100) substrate by low pressure metal organic chemical vapor deposition (MOCVD). Infrared absorption from the indium–hydrogen (InH) stretching mode at 1754.5 cm^? 1 associated with a top most surface of an epitaxial InSb layer was used to compare varying levels of surface coverage with ErSb. Among four samples of varying coverage of ErSb deposition (7.2 to 21.5 monolayers), detected infrared absorption peaks distinct to InH weakened as ErSb surface coverage increased. In the early stage of ErSb deposition, our study suggests that outermost indium atoms in the InSb buffer layer are replaced by Er resulting in increase in absorption associated with the InH mode. Using this simple ex-situ technique, we show that it is possible to calibrate the amount of ErSb deposited atop each individual InSb substrate for depositions of few to tens of monolayers.     

AlN晶体物理气相传输法生长坩埚的热场分析

采用物理气相传输法在钨制坩埚上制备AlN单晶.通过采用COMSOL软件中的固体传热和磁场模块,对AlN晶体生长的坩埚的热场进行仿真,同时针对不同的线圈直径以及不同的线圈位置对坩埚热场的影响进行模拟,提出了相应的处理方式.结果表明:当线圈直径增大,坩埚结晶区和升华区的温度在相同的加热时间下会增加,并且增加的温度存在峰值.当线圈的垂直位置发生变化的时候,结晶区和升华区的温度场也会发生变化,从上向下移动的过程中仍然存在温度的峰值,并且结晶区和升华区的温度关系会发生翻转,导致温度梯度阻碍晶体生长.在晶体生长过程中升华区和结晶区的温度关系依旧会发生翻转.但是通过线圈跟随籽晶表面生长层的变厚而同步移动,可以保持相对稳定的温度关系,维持晶体正常持续生长.     

128× 128 InSb探测器结构模型研究

热冲击下红外焦平面探测器的高碎裂概率制约着其成品率.为明晰碎裂机理, 基于等效设想, 利用小面阵等效大面阵解决了128×128面阵探测器三维结构建模所需单元数过多的问题, 同时综合考虑材料线膨胀系数的温度依赖性、材料强度的各向异性、表面加工损伤效应, 合理选取InSb材料性能参数, 建立起128×128面阵探测器结构有限元分析模型.模拟结果表明:热冲击下最大Von Mises 应力值出现在N电极区域, 其极值呈非连续分布, 这意味着热冲击下128×128面阵探测器的裂纹起源于N电极区域, 且不止一条.上述结论与碎裂统计分析报告中典型裂纹起源地及裂纹分布这两方面相符合, 这为后续面阵探测器碎裂诱因的研究及结构可靠性设计提供了切实可行的研究思路．     

Influence of low temperature on the surface deformation of deformable mirrors

The two factors which influence the low temperature performance of deformable mirrors(DMs) are the piezoelectric stroke of the actuators and the thermally induced surface deformation of the DM. A new theory was proposed to explain the thermally induced surface deformation of the DM: because the thermal strain between the actuators and the base leads to an additional moment according to the theory of plates, the base will be bent and the bowing base will result in an obvious surface deformation of the facesheet. The finite element method(FEM) was used to prove the theory. The results showed that the thermally induced surface deformation is mainly caused by the base deformation which is induced by the coefficient of thermal expansion(CTE) mismatching; when the facesheet has similar CTE with the actuators, the surface deformation of the DM would be smoother. Then an optimized DM design was adopted to reduce the surface deformation of the DMs at low temperature. The low temperature tests of two 61-element discrete PZT actuator sample deformable mirrors and the corresponding optimized DMs were conducted to verify the simulated results. The results showed that the optimized DMs perform well.     

减小薄板玻璃工件研磨变形的研究

针对薄板玻璃刚度差，在研磨中易产生变形这一特点，探讨了减小其变形的不同方法。我们用传统的上盘法粘结固定工件进行加工，工件在下盘前面形精度较好，能满足要求（在２５ｍｍ×２５ｍｍ面积上的平面度为０．０５μｍ），但在下盘后产生的变形使其面形精度下降，在２５ｍｍ×２５ｍｍ面积上的平面度为０．２μｍ，已不能满足要求。采用真空吸附法国固定工件，消除了工件在粘结过程中由于温度变化产生的变形，而且在研磨过程中又设法减小对工件施加的压力，从而减小了工件在研磨过程中产生的变形，使加工后的工件面形与加工过程中的面形接近，这就保证了工件的面形精度。     

THz波段亚波长半导体球形阵列光学特性的数值模拟

利用T-matrix方法对太赫兹波段亚波长半导体球形阵列进行了数值模拟并在数值模拟结果的基础上讨论了其光学特性。在太赫兹波段可以通过掺杂等手段调节半导体的表面等离子体特性。以半导体InSb为例并采用Drude模型,对单个亚波长球及两个或多个亚波长球组成的阵列进行了数值模拟,主要以归一化消光截面为参数,讨论了不同阵元半径、不同球形单元间距、不同单元数目及入射波不同极化方向对阵列特性的影响。     

缓冲层对InSb/GaAs薄膜质量的影响

InSb是制作3~5μm红外探测器的重要材料。在GaAs衬底上外延生长InSb,存在的主要问题在于两种材料间14.6%的晶格失配度,会引入较大的表面粗糙度以及位错密度,使外延材料的结构和电学性能均会受到不同程度的影响。通过系列实验,研究了在生长过程中缓冲层对薄膜质量的影响。利用高能电子衍射仪(RHHEED)得到了合适的生长速率和Ⅴ/Ⅲ比,研究了异质外延InSb薄膜生长中低温InSb缓冲层对材料生长质量以及不同外延厚度对材料电学性质的影响。采用原子力显微镜(AFM)、透射电子显微镜(TEM)、X射线双晶衍射(DCXRD)等方法研究了InSb/GaAs薄膜的表面形貌、界面特性以及结晶质量。通过生长合适厚度的缓冲层,获得了室温下DCXRD半高峰宽为172″,77 K下迁移率为64300 cm²·V^-1·s^-1的InSb外延层。     

Numerical simulation of stress field for laser thermal loading on piston

To investigate the laser thermal loading on diesel engine piston, the employed Gaussian laser beam was transformed into concentric multi-circular patterns of specific intensity distributions with the aid of diffractive optical elements (DOEs), the time duration of laser thermal loading was controlled by computer with air cooling on the top surface of piston, and water cooling of oil tunnel and bottom surface of piston. Numerical simulation model of stress field of laser thermal action was established with the consideration of experimental conditions and the temperature dependent of thermal physical properties of the piston materials. Results show that the stress fluctuation rate at the concave pit site of top surface of piston is larger than that of laser irradiated region due to concave pit region near oil tunnel. Meanwhile, the regions of concave pit, oil tunnel and inner chamber near the top surface of piston are most vulnerable sites to form thermal cracks due to their direct contact with the cooling medium. Results of experimental and numerical simulation have good agreement, which validates the numerical simulation mode.     

Thermal stability and morphological variation of carbon nanorings of different radii during the temperature elevating process: a molecular dynamics simulation study

We study the thermal stability and morphological variations of nanorings with different radii during the temperature elevation using the molecular dynamics (MD) simulation method. Five metastable nanorings were generated using the different initial C–C bond length of armchair carbon nanotubes. The stable structures of the two smallest nanorings have several kinked regions around the nanorings, with the deformations of the inner and outer walls occurring at the same temperature. For the largest three cases, the morphologies of nanorings from the top view display circular shapes at 0 K. For the nanoring with a radius of 146 Å(350 units), the thermal deformation process is very similar to the smallest two cases, but the temperature at which the thermal deformation begins is higher. For the nanoring with nanoring radii of 165 Å (400 units) and 185 Å (450 units), thermal deformation will take place at the inner wall of the nanoring, and then will induce deformation of the outer wall at a higher temperature. Variations of local structures at the kinked regions at different temperatures are also drawn.     

Effect of different heating methods on deformation of metal plate under upsetting mechanism in laser forming

In a laser forming process, different forming mechanisms have different deformation behaviors. The aim of laser forming is to acquire plane strain under an upsetting mechanism, while a plate undergoes a small bending deformation. In some industrial applications, the bending strain should not occur. To achieve high-precision forming, the deformation behaviors of a metal plate when an upsetting mechanism plays a dominant role are studied in the paper. Several heating methods are proposed to reduce the plane strain difference along the thickness direction and little bending deformation resulting from a small temperature difference between the top and bottom surfaces of the plate. The results show that negligible bending deformation and a uniform plastic plane strain field can be obtained by simultaneously heating the top and bottom surfaces with the same process parameters. A conventional scanning method needs a larger spot diameter and slower scanning speed under the upsetting mechanism, but a smaller spot diameter and quicker scanning speed may be selected using the simultaneous heating method, which can greatly widen the potential scope of process parameters.     

Thermal deformation of a solid surface under laser irradiation

A calculation is presented for the deformation of a solid surface when subjected to laser irradiation. The elastic response of the target is given in terms of the stress and displacement field due to thermal expansion, thus allowing an explicit evaluation of the shape of the deformed target surface. Quantitative results are obtained for the height and shape of the induced bump as a function of the laser pulse and target properties. The thermal load threshold is specified for the onset of plastic yield.     

A method for determining the yield of indium bump contacts for integration in hybrid focal plane arrays at room temperature

A simple electrical method for determining the yield of indium bump integration between the infrared photosensing chip and the silicon readout chip in hybrid focal plane arrays (FPAs) is proposed. In our case, the IR photosensing chip consists of a 16 × 16 HgCdTe (MCT) photovoltaic (PV) array and the readout chip is a 16 × 16 silicon-CCD multiplexer (MUX). However, the method can be used for even larger array sizes. The method allows one to determine the yield of integration at room temperature. In addition, it does not necessitate the vacuum sealing of hybrid FPA in the dewar and subsequent testing at 77 K for determining this yield. The proposed method essentially verifies the electrical connectivity between the MCT PV diodes and their corresponding input diffusions in the CCD MUX on pixel-to-pixel basis. A simple examination of the readout of the whole array on the oscilloscope at room temperature, initiated at the detector and through CCD MUX is used for determining exactly how many MCT PV diodes have been joined successfully to their corresponding CCD MUX pixels after indium bump integration.