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%.     

考虑表面效应的双层圆板的自由振动分析

考虑微生化传感器中谐振器的结构特点,基于Kirchhoff薄板理论与表面弹性理论推导了考虑表面效应的双层圆板的自由振动方程.使用伽辽金法得到了近似解.分析了硬化与软化表面效应与表面残余应力对双层圆板固有频率的影响.结果表明,与已有简化的单层圆板模型相比,现有考虑表面效应的双层板模型会得到与之不同的固有频率.随着板厚与上...     

The Potential of MEMS for Advancing Experiments and Modeling in Cell Mechanics

Response to mechanical stimuli largely dictates cellular form and function. A host of extraordinary yet unexplained responses have been identified within the hierarchical cell structure. As experimental and model-based investigations in cell mechanics advance, the underlying structure-function mechanisms dictating these responses emerge. Here we explore the potential of microelectromechanical systems (MEMS) for advancing understanding of cell mechanics. To motivate the discussion, existing experimental techniques are summarized. Interrelated model-based approaches, which aim to interpret or predict observed results, are also outlined. We then focus on a representative set of MEMS-based devices designed for investigations in cell mechanics and point to the fact that, while these devices have yet to maximize their functionality through higher levels of sensor/actuator integration, they are highly complementary to existing techniques. In closing, novel MEMS sensor and actuator schemes that have yet to materialize in this field are discussed to motivate the next generation of MEMS for investigations in cell mechanics.     

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.     

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。     

MEMS-Based Nanomechanics: Influence of MEMS Design on Test Temperature

Microelectromechanical system (MEMS) devices based on electro-thermal actuation have been used over the past few years to perform tensile tests on nanomaterials. However, previous MEMS designs only allowed small (e.g., <100 nm) total displacement range without a significant increase in temperature near the nanospecimens (<20°C), thereby limiting the design of the load sensor or the range of nanomaterials to test. Here we characterize the thermo-mechanical behavior of three MEMS devices, using optical displacement measurements, micro-Raman temperature measurements, and finite element modeling. We observe the increase in temperature near the nanospecimen gap per displacement of thermal actuator to linearly decrease with the distance between nanospecimen gap and thermal actuator. We also present a MEMS device that can provide up to 1.6 μm of total displacement with less than 10°C increase in temperature near the nanospecimens, more than one order of magnitude improvement with respect to previously published MEMS material testing setups. This MEMS device can be used for accurate, temperature-controlled tensile testing of nanocrystalline metallic nanobeams.     

A multibody-based dynamic simulation method for electrostatic actuators

A numerical simulation method is developed to analyze the dynamic responses of electrostatic actuators, which are electromechanically-coupled systems. The developed method can be used to determine the dynamic responses of cantilever-type switches, which are an example of typical MEMS (Micro-Electro-Mechanical System) devices driven by an electrostatic force. We propose the approach that adopts a point charge to deal with electric field effects between electrodes. This approach may be considered as a lumped parameter model for the electrostatic interactions. An advantage of this model may be the easy incorporation of the electrostatic effects between electrodes into a multibody dynamics analysis algorithm. The resulting equations contain the variables for position, velocity, and electric charge to describe the motion of the masses and the charges on the electrodes in a system. By solving these equations simultaneously, the dynamic response of an electrostatically-driven system can be correctly simulated. In order to realize this approach, we implement the procedures into RecurDyn, the multibody dynamics software developed by the authors. The developed numerical simulation tool was evaluated by applying it to cantilever-type electrostatic switches in many different driving conditions. The results suggest that the developed tool may be useful for predicting behaviors of electrostatic actuators in testing as well as in design.     

MEMS-based Universal Fatigue-Test Technique

We have developed a MEMS (micro electro mechanical systems)—based method for fatigue testing of micrometer— millimeter-sized specimens of any material (hence ‘universal’). The miniature, re-usable, stand-alone fatigue test frame is fabricated as a single MEMS chip. Specimens of any material can be manually mounted in the chip and fatigue-tested. We describe the design and construction of the MEMS device and specimens, the test protocol and data analysis procedure, and show stress versus number of cycles to failure (S-N) results for 25 μm thick Al 1145 H19 foil. The S-N results are in accord with expectations, and examination of the fracture surface by scanning electron microscopy shows distinct regions corresponding to slow and fast crack growth.     

静电悬浮式惯性仪表中的微位移检测技术

静电陀螺仪、空间静电加速度计等基于静电悬浮的惯性仪表在高精度的惯性导航和空间微重力测量领域得到广泛应用。近年来，对基于MEMS工艺的悬浮式微惯性传感器的研究引起了广泛的重视。介绍了静电悬浮式惯性仪表中采用的差动电容式微位移检测电路的原理，分别对静电陀螺、静电加速度计和MEMS微陀螺、微加速度计的电极配置方案和位移检测的接口电路进行了分析，并对不同的位移检测方案进行了比较.     

Micro Fork Hinge for MEMS Devices

0Introduction Hingesareafundamentalelementforbuildingmechanicaldevices,appearingwheneverarotation aroundapointisneeded.Differentkindsofhingescanworkwellformillionsofcyclesinthemacro world.Howeverinthemicro world,smallsizedrealhingesorbearingsdonotlastlong…     

Using Micro-Raman Spectroscopy to Assess MEMS Si/SiO2 Membranes Exhibiting Negative Spring Constant Behavior

We introduce a novel micro-mechanical structure that exhibits two regions of stable linear positive and negative stiffness. Springs, cantilevers, beams and any other geometry that display an increasing return force that is proportional to the displacement can be considered to have a “Hookean” positive spring constant, or stiffness. Less well known is the opposite characteristic of a reducing return force for a given deflection, or negative stiffness. Unfortunately many simple negative stiffness structures exhibit unstable buckling and require additional moving components during deflection to avoid deforming out of its useful shape. In Micro-Electro-Mechanical Systems (MEMS) devices, buckling caused by stress at the interface of silicon and thermally grown SiO₂ causes tensile and compressive forces that will warp structures if the silicon layer is thin enough. The 1 mm² membrane structures presented here utilizes this effect but overcome this limitation and empirically demonstrates linearity in both regions. The Si/SiO₂ membranes presented deflect ~17 μm from their pre-released position. The load deflection curves produced exhibit positive linear stiffness with an inflection point holding nearly constant with a slight negative stiffness. Depositing a 0.05 μm titanium and 0.3 μm layer of gold on top of the Si/SiO₂ membrane reduces the initial deflection to ~13.5 μm. However, the load deflection curve produced illustrates both a linear positive and negative spring constant with a fairly sharp inflection point. These results are potentially useful to selectively tune the spring constant of mechanical structures used in MEMS. The structures presented are manufactured using typical micromachining techniques and can be fabricated in-situ with other MEMS devices.     

The response of clamped-clamped microbeams under mechanical shock

We present modeling, simulation, and characterization for the dynamic response of clamped-clamped microbeams under mechanical shock. A Galerkin-based reduced-order model is utilized and its results are verified by comparing to finite-element results. The results indicate that the response of a microbeam to mechanical shock is inherently non-linear because of the dominating effect of mid-plane stretching. The effect of the shock pulse shape is investigated. It is concluded that the shape of the shock pulse can result in significant dynamic amplification in the response of the microbeam even in cases where the shock load is considered quasi-static.The combined effect of the electrostatic force and mechanical shock is investigated. The results show that this combined effect can lead to early instability in microelectromechanical systems (MEMS) devices through dynamic pull-in. This could explain some of the reported experimental evidences for the existence of strange modes of failure of MEMS devices under mechanical shock and impact. These failures are characterized by overlaps between moving microstructures and stationary electrodes, which cause electrical shorts. The shock-electrostatic interaction is shown to be promising to design smart MEMS switches triggered at predetermined level of shock and acceleration. Finally, the mechanical shock combined with the packaging effect of MEMS devices is analyzed. A single-degree-of-freedom model representing the motion of the package, which is mounted over a printed circuit board, coupled with the continuous beam model is utilized. Our results reveal that neglecting the effect of the package motion on the response of microbeams can overestimate or underestimate their response. It is concluded that a poor design of the package may result in severe amplification of the shock effect leading to a device failure.     

An investigation into the effect of electric field on the performance of Dielectric Barrier Discharge plasma actuators

The influence of the inter-electrode electric field of a single Dielectric Barrier Discharge (DBD) actuator on the performance of the device was investigated. The electric field of the actuator was manipulated through the variation of the angle between the electrodes of the actuators. Response forces generated by the plasma actuators were used as performance indicators for these devices. These forces were measured directly utilizing a highly sensitive balance scale. It was verified that depending on the orientation of the variation of the angle between the electrodes, the performance of the actuator may be decreased or increased when compared to a DBD on a flat dielectric plate more commonly investigated in literature. The manner in which the ionic wind flows over the actuators was also explored in the effort to elucidate the influence of the variation of the angle between the electrodes on the response force generated by the device. Results demonstrated that the response forces generated by the actuators may be improved by up to 50% compared to the actuator configuration on a flat dielectric plate commonly investigated. These results indicate the potential available to advance plasma technology by physically manipulating these devices to increase the performances of the actuators.     

Amplitude control on hinged-hinged beam using piezoelectric absorber: Analytical and numerical explanation

This study deals with the problem of reducing the amplitude vibration of flexible structures. Piezoelectric ceramics have been chosen as actuators. After modelling, we derive the corresponding equations governing the dynamic behaviour of structures under control. An analytical approach has been developed to obtain accurate control parameters and tested numerically. A variety of voltage source conditions on control design have been explored. These have been tested numerically.     

Design and fabrication of a micro thermal actuator for cellular grasping

The development of a novel polymer-based micro robotic gripper that can be actuated in a fluidic medium is presented in this paper. Our current work is to explore new materials and designs for thermal actuators to achieve micromanipulation of live biological cells. We used parylene C to encapsulate a metal heater, resulting in effectively a tri-layered thermal actuator. Parylene C is a bio-compatible dielectric polymer that can serve as a barrier to various gases and chemicals. Therefore, it is suitable to serve as a thermal/electrical/chemical isolation material for protecting the metal heater from exposing to an aqueous environment. We have demonstrated parylene actuators(2 mm&#215;100/μm&#215;0.5μm) to operate in an aqueous environment using 10 to 80 mW input power. The temperature of these actuators at full deflection was estimated to be～ 60℃, which is much lower than the typical requirement of &gt; 100℃ to actuate other conventional MEMS actuators. Danio rerio follicles in fluidic medium were captured successfully using these actuators. Moreover, these actuators were found to be responsive to moderate rise in environmental temperature, and hence, we could vary the fluidic medium temperature to actuate trimorphs on a chip without any input of electrical energy, i.e., raising the fluidic temperature from 23℃ to 60℃ could actuate the trimorphs to grasp follicles of～1mm size in diameter. At 60℃, the embryos inside the follicles were observed to be alive, i.e., they were still moving in the biological fluid isolated by the follicle membrane. The smallest follicles grasped were～500μm in diameter using 800μm&#215;130μm&#215;0.6μm actuators. The fabrication process, modeling, and optimization of the trimorph actuators are presented. Based on the successful operation of these polymer-based actuators, we are currently developing multifinger thermal microgrippers for cellular grasping and manipulation, which can potentially be hybridly integrated with circuits for computer control.     

On the Development of a Mesoscale Friction Tester

MEMS and NEMS devices typically have a large surface area to volume ratio. As a result, a major concern in the development of such devices is friction. Contact radii in MEMS and NEMS devices are expected to range from 10⁻⁸<a<10⁻⁵ m. This regime, which generally lies between the limits of single asperity and macroscopic contact, has yet to be explored because the apparati used to characterize friction at these limits do not operate in the range of forces appropriate to these length scales. A Mesoscale Friction Tester (MFT) with smooth probe tip radii from 50 nm to 50 μm and capable of applying forces ranging from 10 nN to l mN over contact radii from 10 nm to 10 μm has been developed to address this need. With carefully planned experiments, this device has the potential to help answer unresolved questions regarding friction mechanisms in the mesoscale range.     

微电子机械系统和流体流动

出现于８０年代后期的微机械工艺技术可提供微米尺度的传感器和致动器．这些微型转换器与信号调节和处理电路集成后，组成了可执行分布式实时控制的微电子机械系统（ＭＥＭＳ）．这种性能为流动控制研究开辟了一个崭新的领域．另一方面，由于微米尺度结构中表面积与体积之比很大，在流体流经这些微小机械器件时，表面效应占据了主导地位．为此需要重新审视动量方程中的各类表面力项．由于它们非常小，气体流动具有很大的Ｋｎｕｄｓｅｎ数，所以边界条件也应加以修正．总之，微电子机械系统（ＭＥＭＳ）不但是一项实用技术，也为流动机理的基础研究提出了许多挑战．     

氧化铝多孔膜振动性能的实验研究

电化学氧化法制备的氧化铝多孔膜有六角规则密排的纳米孔,其优良的结构特点使其具有良好的用途,可应用于微粒物质分离,氧化剂的载体,微电子机械系统的组件和纳米器件等。在前期研究了这种氧化铝膜的力学性能如拉伸性能和弯曲性能的基础上,本文实验研究了这种氧化铝多孔膜的振动特性即共振频率特性和振动模态,估算了该氧化铝多孔膜的相当弹性模量,与其他方法测得的相当弹性模量基本一致。