MEMS惯性器件敏感电容结构相关温度漂移特性仿真（英文）

基于MEMS器件的微型惯导系统的精度和MEMS惯性器件的全温稳定性具有很高的相关性。MEMS结构相关的温度漂移主要来自材料之间的热失配应力,工艺引入的应力,以及封装应力等。而相关应力在MEMS结构中的分布以及所造成的应变又和MEMS结构具有一定相关性。通过ANSYS有限元分析软件建立了多种MEMS惯性器件常用梁-质量块结构的FEM模型,具体包括悬臂梁结构、双端固支梁结构、L形梁结构、对角支撑梁结构。通过热-力耦合仿真,研究了热失配应力在上述结构中的分布以及所产生的结构变形。对比分析了不同芯片粘胶形式,包括中心粘胶、三点粘胶、整片粘胶对上述MEMS结构引入的封装应力以及其全温(-40℃~60℃)温度漂移特性。此外,还分析研究了不同衬底厚度对MEMS结构封装应力的隔离效果。     

一种采用圆片级真空封装的全硅MEMS三明治电容式加速度计

全硅MEMS加速度计具有温度特性好、封装体积小、成本低的优点,从而成为小型化GNC(制导、导航与控制)系统的关键器件。给出了一种具有三层硅结构的MEMS三明治加速度计的设计、加工以及圆片级真空封装方法,其中,中间硅摆片的3D结构通过双面KOH湿法腐蚀制造,腐蚀过程中使用台阶化的SiO_2作为硬掩模。硅盖板的加工主要通过KOH各向异性腐蚀和电感耦合等离子体垂直刻蚀完成。最后,上、下硅盖板通过基于Au-Si共晶反应的全硅键合技术从两侧与硅中间摆片进行键合,并实现圆片级真空封装。三明治加速度计的腔体内封装了压力为200 Pa的高纯氮气。测试结果表明,所述加速度计的闭环输出灵敏度为0.575 V/g,零位误差为0.43 g。加速度计的-3dB带宽为278.14Hz。加速度计1 h的输出稳定性为2.23×10-4 g(1σ)。加速度计在全温范围(-40℃~60℃)内的输出漂移为45.78 mg,最大温度滞环为3.725 mg。     

高量程MEMS加速度计的热应力仿真与可靠性评估

硅压敏电阻阻值漂移过大导致输出失效是高量程MEMS加速度计在恶劣温度环境下工作的主要失效模式之一。通过模拟仿真加速度计悬臂梁、芯片结构和封装后整体模型的热应力分布情况,确定了压敏电阻所在结构梁区域是最容易失效的位置,且最大热应力分布在芯片梁与质量块倒角处,其值约为107 N/m2;通过设计的高温加速恒定应力试验验证了加速度计的温度敏感特性,根据试验数据的特征采用三种可靠度评估方法定量外推出高量程MEMS加速度计在规定应力条件下的可靠度指标。研究结果表明,加速性能退化试验和基于退化量的可靠性评估方法适用于高量程MEMS加速度计在温度环境中的可靠性研究,能够利用有限的试验数据获得可信度较高的评估结果。     

蝶翼式MEMS加速度计温度稳定性提升方法

环境温度变化造成的热应力是影响MEMS加速度计性能的关键因素。为了提升MEMS加速度计温度稳定性，以蝶翼式MEMS加速度计为研究对象，分别在敏感芯片上设计应力释放结构和敏感芯片与陶瓷基底之间设计应力隔离结构。利用有限元分析工具COMSOL对有无应力释放和隔离结构的情况进行了对比仿真，结果表明敏感单元上的敏感梁应用应力释放结构只有原结构最大应力水平的0.3%，封装时采用应力隔离结构间接连接比原直接连接方式最大应力下降一个数量级。采用微机械加工技术和微电子工艺技术结合的MEMS加工工艺实现含应力隔离结构的加速度计原理样机制作。对样机进行温度测试，试验结果表明有应力释放与隔离结构在-40?°C~60?°C区间的漂移量比无应力释放与隔离结构提升约3.5倍，验证了应力释放与隔离结构对温度稳定性提升的有效性，研究结果可以为加速度计在高性能、恶劣环境下的应用提供参考。     

MEMS加速度计温度漂移仿真分析

温度漂移是影响高精度、高稳定性MEMS加速度计整体工作性能的关键参数。采用有限元方法,建立了三种不同材料组合的MEMS"三明治"加速度计三维结构模型,开展热-应力耦合场仿真分析,并通过提取加速度计差动电容变化量及其变化率对温度漂移进行量化表征。结果显示,以带有薄层玻璃的单晶硅圆片作为器件盖板及衬底,并以其薄玻璃层作为绝缘层是最优的加速度计材料组合。进一步分析表明,盖板及衬底厚度达到500μm,加速度计差动电容变化率曲线趋于稳定,继续增大盖板及衬底厚度对于优化温度漂移性能无显著作用,研究结果为高性能MEMS加速度计设计提供了技术支撑。     

多层薄膜热应力模拟

针对MEMS器件和光电器件的薄膜结构在高温下产生的应力与应变会严重影响器件结构与功能的问题,本文采用Suhir异质生长薄膜热应力计算理论分析了三层薄膜结构的热应力大小分布情况,得到了不同镀膜温度、膜厚、基底厚度等条件下的热应力变化趋势,解决了困扰有限元分析的奇异点问题。通过分析模型与有限元分析结果的比对,得到该计算模型的应力分布较为符合有限元分析的结果,最大剪切应力差距约为6.1%。列举了一个通过分析关系对材料进行优化的实例。这些研究结果对恶劣工作环境下的MEMS器件以及光电子器件的薄膜设计具有一定的借鉴意义。     

连续旋转的光纤陀螺全温失准角快速建模与补偿方法

在全温范围内应用的光纤陀螺,其输入轴失准角随温度的变化是影响光纤陀螺惯性系统性能的重要指标之一。特别是在大角速率或者高精度应用时,失准角的变化误差甚至超过零偏漂移误差和标度因数误差。采用温度补偿技术是一种提升光纤陀螺温度性能的有效方法,其中建立精确的温度模型是关键。提出了一种连续旋转的光纤陀螺全温失准角快速建模补偿方法。基于单轴速率转台的连续旋转,可以有效识别光纤陀螺失准角在全温范围内的变化拐点,提高建模和补偿的精度。试验结果表明,某型光纤陀螺全温输入轴失准角变化约14″,补偿后全温输入轴失准角变化小于1″,精度提高了一个数量级以上。在高精度光纤陀螺惯性系统中,该方法可用于指导光纤陀螺失准角的实时温度补偿技术研究及工程实现。     

低成本GPS/DR容错组合导航系统设计

GPS信号易受建筑物或树木遮蔽,而低成本的MEMS惯性元件随机漂移大,性能随温度急剧变化,采用一般的Kalman滤波器融合GPS和低成本MEMS惯性元件信号,构成GPS/DR组合导航系统很难满足导航系统的容错和精度要求。针对GPS和MEMS惯性元件构成的低成本GPS/DR组合导航系统,设计了容错UKF/KF联邦Kalman滤波算法,提高了组合导航系统的定位精度和抗干扰能力;针对MEMS惯性元件随机漂移大的缺点,采用零偏试探消减算法,抑制了MEMS惯性元件的随机零漂,提高了MEMS惯性元件的精度。仿真结果表明,基于该算法的GPS/DR组合导航系统的定位精度高,抗干扰能力强,在GPS信号中断的情况下导航系统仍可在短时间内保持较高的定位精度。     

低g值微惯性开关单向敏感性设计与分析

选用典型的"弹簧-质量"系统,基于平面矩形螺旋梁结构,研制了一种具有良好单向敏感性的低g值微惯性开关。采用ANSYS有限元软件,对惯性开关的单向敏感性进行了静力学仿真分析。分析结果表明,横向加速度对惯性开关闭合阈值的影响较小。采用MEMS体硅加工工艺和圆片级封装技术,包括KOH腐蚀、ICP刻蚀和喷涂工艺等关键工艺技术,完成了微惯性开关的制备。经离心试验测试,微惯性开关的闭合阈值约为12.26g,具有约±0.2g的闭合精度。当横向惯性加速度小于15g时,对其闭合阈值的影响小于0.5g。测试结果表明,微惯性开关具有较好的单向敏感性,多次测试重复性好,具有体积小、结构简单、加工容易实现、环境适应性好等特点。     

惯性器件的热设计

本文从热干扰对惯性器件性能精度的影响出发,阐明热设计的重要意义,分析惯性器件热设计的特点,并介绍热设计通常采用的措施,设计时常用的计算方法、测试温度分布的手段。     

Stress Monitoring of Post-processed MEMS Silicon Microbridge Structures Using Raman Spectroscopy

Inherent residual stresses during material deposition can have profound effects on the functionality and reliability of fabricated Micro-Electro-Mechanical Systems (MEMS) devices. Residual stress often causes device failure due to curling, buckling, or fracture. Typically, the material properties of thin films used in surface micromachining are not well controlled during deposition. The residual stress; for example, tends to vary significantly for different deposition methods. Currently, few nondestructive techniques are available to measure residual stress in MEMS devices prior to the final release etch. In this research, micro-Raman spectroscopy is used to measure the residual stresses in polysilicon MEMS microbridge devices. This measurement technique was selected since it is nondestructive, fast, and provides the potential for in-situ stress monitoring. Raman spectroscopy residual stress profiles on unreleased and released MEMS microbridge beams are compared to analytical and FEM models to assess the viability of micro-Raman spectroscopy as an in-situ stress measurement technique. Raman spectroscopy was used during post-processing phosphorus ion implants on unreleased MEMS devices to investigate and monitor residual stress levels at key points during the post-processing sequences. As observed through Raman stress profiles and verified using on-chip test structures, the post-processing implants and accompanying anneals resulted in residual stress relaxation of over 90%.     

Characterization and Control of Residual Stress and Curvature in Anodically Bonded Devices and Substrates with Etched Features

While anodic bonding is commonly used in a variety of microelectromechanical systems (MEMS) applications, devices and substrates that incorporate this processing technique are often subjected to significant residual stress and curvature that create post-processing and reliability issues. Here, using an anisothermal anodic bonding procedure, residual stresses and the resulting wafer curvature in these structures are controlled by varying the initial bond temperatures of the silicon and Pyrex wafers independently. Residual stresses are quantified by measuring bulk wafer curvature and, locally, stress concentrations are measured using infrared photoelasticity accompanied by 3-D thermomechanical finite element analysis. Based on the good agreement between numerical predictions and experimental results, this process can be used to determine the bulk post-bond wafer curvature and to reduce the likelihood of structural failure at these sites, by changing the residual stresses from tensile in nature, which may drive initiation and growth of cracks, to compressive, which can suppress such failures.     

切削加工过程数值模拟的研究进展

近年来,有限元方法在切削加工模拟中得到了越来越广泛的应用,在研究切削工艺参数及切屑成形机理方面有着不可替代的作用。本文介绍了国外切削加工过程有限元数值模拟的研究进展,阐述了切削过程有限元模拟的关键技术,包括切屑形成、切削加工中的热力耦合、工件与刀具接触和摩擦、切屑分离和断裂准则以及工件残余应力、残余应变的模拟等技术;最后,还对切削工艺有限元数值模拟的发展方向作了探讨。      

Analytical solutions of thermal stress distribution in plastic encapsulated integrated circuit packages

IntroductionElectronicpackagesarecomplexcompositestructure.Theyhavemyriadcornersandinterfacesthatcanactaspotentialfailuresitesduringfieldoperation .Atpresenttime ,plasticencapsulatedintegratedcircuits (ICs)arewidelyusedinengineering .AplasticencapsulatedICpackageconsistsofasilicondie,dieattachment,passivation ,wireinterconnects,aleadframe ,andplasticmoldingcompound .Thermalexcursionduringpackagequalificationfromthermalcycling thermalshock ,orpowercyclingduringnormaloperationcansetupthermomec…     

圆柱外表面受热冲击问题的广义热弹性分析

基于 L-S 广义热弹性理论, 针对实心圆柱体在外表面受均匀热冲击作用下的一维广义热弹性问题进行研究分析. 利用热冲击的瞬时特征, 借助于 Laplace 正、反变换技术及柱函数的渐近性质, 推导了热冲击作用周期内温度场、位移场和应力场的渐近表达式. 通过计算, 得到了热冲击条件下各物理场的分布规律以及延迟效应和耦合效应对热弹性响应的影响规律. 结果表明: 当考虑延迟效应和耦合效应时, 热扰动将以两组速度不同的波的形式向前传播, 延迟效应和耦合效应对各物理场的建立时间, 阶跃间隔和阶跃峰值均产生影响, 且延迟效应和耦合效应均在一定程度上削弱了热冲击的作用效果.      

A Hybrid Experimental/Numerical Investigation of the Response of Multilayered MEMS Devices to Dynamic Loading

In order to probe the mechanical response of microelectromechanical systems (MEMS) subjected to dynamic loading, a modified split Hopkinson pressure bar was used to load MEMS devices at accelerations ranging from 10³–10⁵  g. Multilayer beams consisting of a PZT film sandwiched between two metal electrodes atop an elastic layer of silicon dioxide were studied because of their relevance to active MEMS devices. Experiments were conducted using the modified split Hopkinson pressure bar to quantify the effects of dynamic loading amplitude, duration, and temporal profile on the failure of the multilayered cantilever beams. Companion finite element simulations of these beams, informed by experimental measurements, were conducted to shed light into the deformation of the multilayered beams. Results of the numerical simulations were then coupled with independent experimental measurements of failure stress in order to predict the material layer at which failure initiation occurred, and the associated time to failure. High-speed imaging was also used to capture the first real-time images of MEMS structures responding to dynamic loading and successfully compare the recorded failure event with those predicted numerically.     

难加工材料切削机理研究的新进展

航空发动机重要零件如机匣、压气机风扇叶片等广泛采用钛、镍基合金等先进结构材料.钛、镍基合金材料切削加工性较差,主要表现在材料热硬度和热强度很高,所需切削力很大,工件、刀具容易产生较大变形;材料热扩散率低;刀具切削深度线位置缺口现象严重,以及形成锯齿状切屑等几个方面.深入研究此类难加工材料的切削机理,对于实现薄壁件高效精密数控加工技术至关重要.本文重点介绍了关于高硬度金属材料锯齿状切屑的形成机制;非连续切屑形成过程的有限元数值模拟关键技术,包括自适应网格细化、切屑与工件之间的分离准则,以及用以描述单元网格中裂纹形核与扩展的断裂准则和算法;切削区域高温、高应变率条件下材料屈服流动行为的准确描述,系统考虑应变、应变率和温度三者之间的相互影响作用;切削温度场、工件表层残余应力场的分布规律,以期消除残余扭曲变形对航空工业中普遍使用的薄壁结构件加工精度的显著影响.      

Mechanics of energy transfer and failure of ductile microscale beams subjected to dynamic loading

The mechanical response of microelectromechanical systems (MEMS) under impulse loading conditions has not been thoroughly studied to date, partially because of the lack of means to provide such extreme loading rates to miniature devices. However, the increasing use of MEMS-based sensors and actuators in adverse environments, which include extreme strain rate loading, has motivated the investigation of the response of MEMS components under these conditions. In this work, basic and mostly commonly employed Au MEMS components were subjected to impulse loads of 40 ns in duration, which were generated by a high power pulsed laser in order to achieve acceleration levels on the order of 10⁹g. This allowed for the microdevice mechanical/structural response to be investigated at time scales that were of the order of wave transit times in the substrate and the devices. Basic microscale structures, such as cantilevers and fixed-fixed beams of uniform cross-section, were employed to facilitate comparisons with companion finite element simulations in order to gain insight into the mechanisms responsible for impulsive deformation at the microscale. The simulations investigated the effect of loading rate, boundary conditions, beam length, material constitutive response, and damping on the final deformed shapes of the beams. It was found that contact and momentum transfer mechanisms were responsible for the large permanent beam deflections which were measured postmortem. Additionally, the effects of both damping and material property rate dependence were found to be dominant in determining the final deformed shape of the beams. In fact, our observations suggest that the contributions of material rate dependence and damping are not simply additive, but rather involve a coupling between them that affects the final structure response.     

Investigation of the plane stress state of a multilayer structure under heat variations

Now that composite materials are used in various fields of technology, their resistance to heat variations, which cause additional stresses because of noncoinciding layer thermal expansion coefficients, becomes increasingly topical. Apparently, the first study in this field was performed in [1], where the stress state in beam-like thermostats was determined. In [2], it was shown that delamination moments arise at the ends of two-layer beams, and the possibility of their influence on the process of delamination of two-layer composites was considered. In [3], in a similar setting, delamination stresses in multilayer structures were considered. In [4–7], the stresses at the edges of two-layer beams were calculated. We note that in all these papers the main assumptions of beam theory were used, which were confirmed experimentally for the analysis of beams.