Comparison of analysis methods for package-induced stresses on moulded Hall sensors

Due to the piezoresistive and the piezo-Hall effect in semiconductor materials, Hall sensors show a strong temperature dependency and also a drift when subjected to temperature cycles Manic et al. (2000). Four factors mainly influence the mechanical stress in the sensitive layer. These are the geometry of the device, the differences of the coefficients of thermal expansion of the package materials, the temperature-dependent material properties and the time-dependent, viscous material properties. The objective of this investigation was to determine the mechanical stress in a moulded Hall sensor during the packaging process by finite-element simulation in comparison to experimental methods. It is shown that after each process-step the mechanical stress in the sensitive layer changes over time depending on the absolute value and the rate of the temperature change. Measurements of the inverse bending radius of glued and moulded chips show good agreement to the simulations.

     

The influence of package-induced stresses on moulded Hall sensors

The output signals of moulded Hall sensors show changes in offset and sensitivity when the devices are affected by changing temperatures. This behaviour is a result of the differences in the thermal expansion behaviour of the package materials and is also affected by their time-dependent, viscous material properties. The stresses affected to the sensor’s sensitive layer will become effective via the piezo-Hall-effect as well as via piezo-resistivity which both change the sensitivity and the offset of the sensor’s output voltage. For modelling the stress in the sensitive area correctly it is indispensable to consider the visco-elastic and the visco-plastic behaviour of the materials constituting the package. Especially for very accurate sensors or components operating in harsh environments these effects must be regarded. In this work we investigate the thermo-mechanical stresses, which are induced in the sensitive layer of a moulded Hall sensor during the assembly process, the investigations were based mainly on finite-elements-simulations.     

First principle study of electronic,mechanical, optical and thermoelectric properties of CsMO3 (M = Ta,Nb) compounds for optoelectronic devices

The electronic, mechanical, optical and thermoelectric properties of Cesium based perovskites CsMO₃ (M = Nb, Ta) in the cubic phase has been performed through PBEsol-mBJ scheme in the framework of DFT. The electronic band structures and density of states show the studied materials having a direct band gap in the visible range. The mechanical stability and ductile behavior have been analyzed from elastic constants. Moreover, the optical behavior of the studied materials has been analyzed in terms of dielectric functions, refractive index, extinction coefficient, absorption coefficient, optical conductivity, reflectivity and energy loss factor. Finally, the material response with temperature has been elaborated by electrical conductivity, thermal conductivity, Seebeck coefficient, power factor, heat capacity, Hall coefficient, susceptibility and electron density by using BoltzTraP code. This first principle calculation of optical and thermoelectric properties of the novel compounds provides a new route to the experimentalist for the potential application in energy renewable devices.     

SiC高温高量程MEMS加速度传感器的仿真与分析

加速度传感器材料的特性对传感器的性能影响很大,SiC作为新一代半导体材料具有优良的力学温度特性,适用于高温、高过载加速度传感器.基于SiC提出了一种可用于高温、高过载环境的加速度传感器设计方案.根据悬臂梁的相关力学理论知识,对传感器结构、尺寸进行了设计,并利用ANSYS有限元仿真软件对SiC材料传感器敏感结构进行模态分析、静力学分析、热分析.仿真结果表明,6H-SiC材料表现出了比Si材料更优异的抗高温、抗过载特性,为应用于高量程、高温环境下的加速度传感器研究提供了可靠的理论基础.     

Software for estimation of second order effective material properties of porous samples with geometrical and physical nonlinearity accounted for

A method and an algorithm for numerical estimation of effective mechanical properties of porous materials are presented. The effective properties are sought in the form of the nonlinear relation between the second Piola–Kirchhoff stress tensor and the Green strain tensor for anisotropic materials with second-order nonlinearities accounted for. The effective characteristics of test models are computed by means of a CAE Fidesys program module based on the proposed algorithm. The effective material properties as functions of porosity are examined. The finite element mesh that contained more than a million of elements was used while performing stress analysis of a specimen. To reduce computing time, assembly and solution of the global equation system was done in parallel using CUDA technology. The computations were carried out on NVIDIA Tesla C2050 graphics processors. Our results show that accounting for nonlinear effects is essential for correct estimation of effective properties of porous materials.     

一种新型无源电容式温度传感器的制备与测试

为了实现高温、机械旋转和密闭空间等恶劣环境中的原位温度测量,以高居里点的铁电陶瓷为温度敏感介质材料,在传统低温共烧陶瓷(LTCC)工艺的基础上,采用牺牲层填充技术,保证了制备过程的工艺兼容性,成功制备出了一种基于LTCC衬底的新型无源电容式温度传感器。通过外部读取天线与传感器线圈的互感耦合,实现了从常温至700℃的传感器温度特性测试,测试结果表明:这种电容式温度传感器具有良好的温度敏感特性,其平均灵敏度为-7.33 kHz/℃。     

Optimal design of compliant mechanisms using functionally graded materials

This research applies topology optimization to create feasible functionally graded compliant mechanism designs with the aim of improving structural performance compared to traditional homogeneous compliant mechanism designs. Converged functionally graded designs will also be compared with two-material compliant mechanism designs. Structural performance is assessed with respect to mechanical/geometric advantage and stress distributions. Two design problems are presented – a gripper and a mechanical inverter. A novel modified solid isotropic material with penalization (SIMP) method is introduced for representing local element material properties in functionally graded structures. The method of moving asymptotes (MMA) is used in conjunction with adjoint sensitivity analysis to find the optimal distribution of material properties. Geometric non-linear analysis is used to solve the mechanics problem based on the Neo-Hookean model for hyperelastic materials. Functionally graded materials (FGMs) have material properties that vary based on spatial position. Here, FGMs are implemented using two different resource constraints – one on the mechanism’s volume and the other on the integral of the Young’s modulus distribution throughout the design domain. Tensile tests are performed to obtain the material properties used in the analysis. Results suggest that FGMs can achieve the desired improvements in mechanical/geometric advantage when compared to both homogeneous and two-material mechanisms.     

热释电探测器敏感层材料关键性能参数测试

热释电材料铌酸锂(LN)晶片可作为热释电探测器敏感层材料。介电常数和介电损耗是判断热释电材料性能的2个重要参数。为解决在测试参数时,测试数据量大,测试精度要求高、测试时间较长等问题,提出了一种自动采集、自动记录及处理的测试系统,并测试出减薄前后LN晶片的介电常数和介电损耗随温度的变化曲线。经过数据分析得出,LN晶片的相对介电常数随着温度的升高呈增大趋势,减薄前后其相对介电常数变化不是很大,减薄后略减小;而LN晶片的介电损耗随着温度的升高呈增大趋势,160℃以下增长缓慢,但在160℃以上迅速增大;LN晶片的介电常数和介电损耗随温度的变化情况基本符合低温条件下德拜模型偶极子弛豫。     

Study on demolding temperature in thermal imprint lithography via finite element analysis

Demolding in thermal imprint lithography is a process to overcome chemical and mechanical interactions of all levels between stamp and substrate formed by the process history, stamp geometries, and materials used, accounting for most of imprint failure. Undesired deformation in resist may occur depending on the stress generated in the resist with respect to the yield stress. In thermal imprint lithography, temperature is one of the most important parameters not only for the flow of resist during the molding process, but also for the demolding because the thermal stress, the friction and adhesion forces, and the mechanical strength of resist are all dependent on temperature even at below the glass transition temperature of the resist. In this paper, we have developed a method via a numerical simulation of the demolding process to determine an optimal demolding temperature that leads to the least resist deformation. Considering the viscoelasticity of the resist and the temperature dependence of friction coefficients at the resist/stamp interface, an optimal temperature was extracted via normalization of the local Von Mises stress in the resist by its yield stress. For a simple two-dimensional model system with Si stamp and PMMA as a resist layer, the optimal demolding temperature was found to be ～70°C.     

柔性太阳翼叠层电池弯曲适应性仿真与设计

航天器在轨进、出地影时，基于复合结构柔性基板的柔性太阳翼叠层电池在高、低温交变作用下会产生热弯曲变形。针对这一问题，采用有限元建模仿真，分析由太阳电池、盖片胶和抗辐照玻璃盖片组成的叠层电池的弯曲适应性，计算不同结构尺寸、不同叠层材料参数的叠层电池在跨中弯曲载荷下的最大应力。借助响应面技术研究设计变量与复合结构性能之间的关系，采用目标驱动优化分析，获得理想的结构尺寸参数。结果表明：叠层电池的宏观力学性能取决于微观不同叠层材料的组合方式；等效弹性模量不是定值，而是与叠层材料的参数有关；弯曲工况的失效模式取决于电池单体的最大拉应力，而不是宏观表征的整体弯曲强度。     

微电热驱动器中偏置层的分析

设计了一种电热微驱动器,根据几何关系、泰勒公式和材料力学求得偏置层结构末端的位移公式,并验证了采用镍作为偏置层材料的合理性.通过Coventorware软件中的有限元模块进行仿真分析,得出施加驱动电压为5 V,响应时间为5 ms,驱动器的初始温度为300 K时,得出偏置层宽度W1与驱动器位移d的曲线关系.通过验证驱动器的最大应力为235 MPa,小于镍的许用应力,确定驱动器在W1=20μm可以进行可靠的工作.分析偏置层厚度和宽度的加工误差对驱动器末端位移的影响,可得在对偏置层进行加工时要严格控制偏置层厚度H1的加工误差.     

Bending stress analysis of flexible touch panel

Flexible touch panel is required to undertake extensive bending operations during service; thus, bending testing of flexible touch panel for mechanical behaviors and even reliability is crucial for realizing the technology. This study aims at exploring the bending behaviors of a flexible touch panel under a four-point bending test using finite element analysis. The touch panel is a laminated structure composed of seven thin film layers, namely a polyester layer, an adhesive layer, a polyimide layer, two organic layers and two indium tin oxide conductive layers. Because the touch panel structure is symmetry, only a quarter of the flexible touch panel is established in the analysis model. The mechanical properties of the materials are first obtained using both nanoindentation and uniaxial tensile/compressive testing. Furthermore, a modeling technique based on global and local finite element analysis is applied to evaluate the bending stress at a specified radius of curvature. Special emphasis of the calculation is put on the critical region with respect to stress, which is identified as the most susceptible cracking site.     

纳米孔Al2 O3修饰Si基氨气传感器设计

针对Si基微结构气体传感器中Si基与敏感材料之间附着性较差的问题,提出在Si基与敏感材料之间引入纳米孔Al2 O3膜形成新型Si基微结构传感器,利用ANSYS分析软件对微结构进行热分析。采用薄膜工艺、光刻工艺、电化学阳极氧化工艺在Si衬底上制成Si基微结构,采用超声波的方法使聚苯胺敏感材料渗入纳米孔Al2 O3膜中制成气体传感器,并在室温下测试了传感器对氨气的检测特性。结果表明：将纳米孔Al2 O3膜移植到Si基上增加了敏感材料的附着性;传感器对响应时间约为40 s,恢复时间约为960 s,灵敏度随着氨气浓度的增加而增大,并且呈现出良好的线性关系。     

Mechanical material characterization of photosensitive polymers

In addition to the development of materials and technologies for smart HARMST applications the analysis of the thermo-mechanical material properties seems to be necessary to describe the photosensitive polymers applied. To do this, a microtensile analysis system has been developed to determine stress–strain curves, Young’s modulus and Poisson’s ratio. The results are compared with those of dynamical mechanical thermal analysis and discussed.     

Analytical and numerical modelling of AlGaN/GaN/AlN heterostructure based cantilevers for mechanical sensing in harsh environments

Some industrial areas as oil, automotive and aerospace industries, require electromechanical systems working in harsh environments. An elegant solution is to use III-V materials alloys having semiconductor, piezoelectric and pyroelectric properties. These materials, particularly nitrides such as GaN or AlN, enable design of advanced devices suitable for harsh environment. A cantilever structure based on AlGaN/GaN/AlN heterostructures coupled with a High Electron Mobility Transistor (HEMT) can act as an electromechanical device suited for sensing applications. In this article, we present the mechanical modelling of such a structure. An analytical and a numerical model have been developed to obtain the electrical charge distribution in the structure in response to mechanical stress. A theoretical electromechanical sensitivity of 3.5 μC m⁻² was achieved for the cantilever free end displacement of several hundreds of nanometres. Both models show good agreement, presenting less than 5% deviation in almost the whole structure. The differences between the two models that are pronounced near the clamped area can be explained by particular boundary conditions of the numerical model. The topological characterization and numerical modelling allowed the estimation of the equivalent intrinsic residual stress in the structure and the stress distribution within each layer. Finally, the dynamic mechanical characterization of fabricated cantilevers using laser interferometry is presented and compared to numerical modal analysis with less than 10% deviation between theoretical and experimental resonant frequencies. The obtained results enable the use of the analytical model for further study of the electromechanical coupling with the HEMT structure.     

温度对硅-蓝宝石压力传感器影响研究

针对硅-蓝宝石压力传感器在高温环境下测量精度较差的问题,以双层敏感膜片结构为基础,研究了温度对传感器的影响;通过对温度场及热应力的理论分析,证明了材料热膨胀系数不一致所产生的额外热应力,将引起测量误差;相应的ANSYS有限元仿真及实验也表明,温度效应对压力传感器的测试精度会产生较大的影响,且压力传感器的输出与温度值之间存在一定的规律。     

CO2传感器的制作及特性

采用高温固相反应法制备了Na超离子导体（NASICON）的固体电解质材料，用IR技术分析了不同合成温度下制备的NASICON材料的基本性质。用所制得的NASICON材料制作了具有较高灵敏度和选择性的CO2气体传感器。     

Germanium as a versatile material for low-temperaturemicromachining

Though germanium (Ge) shares many similar physical properties with silicon (Si), it also possesses unique characteristics that are complementary to those of Si. The advantages of Ge include its compatibility with Si microfabrication, its excellent gas and liquid phase etch selectivity to other materials commonly used in Si micromachining, and its low deposition temperature (<350°C) that potentially allows Ge to be used after the completion of a standard CMOS run. Wider applications of Ge as a structural, sacrificial, and sensor material require a more systematic investigation of its processing and properties. The results of such an undertaking are presently reported. The topics covered are the formation of Ge thin films and novel application of the selective deposition of Ge to etch hole filling, characterization of the effects of thermal treatment on the evolution of the residual stress in Ge thin films, etch selectivity for etch mask and sacrificial layer applications, and gas phase release technique for stiction elimination     

铅黏弹性阻尼墙力学性能分析研究

为提高黏弹性阻尼墙耗能能力,改善其耗能方式,本文提出一种复合型铅黏弹性阻尼墙,介绍了铅黏弹性阻尼墙的构造与原理.对4种不同硬度天然橡胶进行材性试验及本构参数拟合,设计24组不同参数铅黏弹性阻尼墙,采用ABAQUS有限元软件进行模拟分析,研究了不同黏弹性材料、黏弹性层面积、铅芯直径、铅芯布置方式、复合黏弹性层厚度和单层薄钢板与黏弹性层厚度比对阻尼墙滞回性能及力学性能的影响,并给出了设计建议值.