A Study for the Effect of the PCB Motion on the Dynamics of MEMS Devices Under Mechanical Shock

We present a theoretical and experimental investigation into the effect of the motion of a printed circuit board (PCB) on the response of microelectromechanical systems (MEMS) devices to shock loading. For the theoretical part, a 2-DOF model is used, where the first degree of freedom accounts for the PCB. The second degree of freedom represents the motion of the MEMS microstructure. Low-g acceleration pulses are applied to the MEMS–PCB assembly base to simulate shock pulses generated from a drop-table test. Simulation data are presented to show the effects of the natural frequency of the PCB, the natural frequency of the microstructure, and the shock pulse duration. Universal 3-D spectra representing the effect of these parameters are presented. It is found that neglecting the PCB effect on the design of MEMS devices under shock loads can lead to undesirable motion of their microstructures. The effects of electrostatic force and squeeze film damping are investigated. It is found that the amplification of motion due to the PCB can cause early pull-in instability for MEMS devices implementing electrostatic forces. The effect of higher order modes of a microbeam is studied through a continuous beam model coupled with a lumped model of the PCB. The limitations of the 2-DOF model are discussed. An experimental investigation is conducted to verify the theoretical results using a capacitive accelerometer. Experimental data for the response of the accelerometer while it is mounted on two representative PCBs due to different low-g shock conditions are shown.$hfill$[2008-0026]      

LF55GN Photosensitive Flexopolymer: A New Material for Ultrathick and High-Aspect-Ratio MEMS Fabrication

A growing interest in the development of thick functional structures with high aspect ratio for microelectromechanical system (MEMS) applications has triggered the investigation of several polymer materials. This paper presents LF55GN flexopolymer material as a new negative-tone photoresist to fabricate ultrathick MEMS microstructures. Up to 4-mm-thick layers are obtained using a casting method in a single photolithography step. Standard UV illumination is used to polymerize such thick microstructures in less than 1 min and with an aspect ratio up to 27. We have fabricated microstructures on rigid, flexible, and stepped substrates. Using oblique UV exposure, tilted pillars are achieved with an angle of 25deg to the substrate normal. Due to the elastomeric nature of the LF55GN flexopolymer, the microstructures can be easily deformed without causing any stress-related problems.     

车载环境下MEMS微镜长期可靠性及控制方法

作为一种新型微光机电系统,MEMS微镜可完成微尺度下的光调控工作,在光电通信、医疗成像、民用投影、雷达探测等领域应用广泛.近年来,以微镜为核心部件的MEMS激光雷达因其体积小和功耗低等优势,有望成为更具竞争力的辅助驾驶传感器之一.然而,鉴于车载应用特殊性,MEMS微镜在温湿、电磁、振动和冲击等复杂多物理场耦合环境下的各类可靠性问题严重制约了MEMS激光雷达的工程应用.本文立足MEMS微镜可靠性研究领域,综述其在高频振动、温湿循环、电磁耦合等极端环境下的分层翘曲、结构断裂、静电吸合、短路烧毁等复杂失效形式及失效机制,总结了MEMS微镜常见动力学建模理论及控制方法,讨论并展望了MEMS激光雷达车规化面临的主要挑战和发展趋势.     

Sacrificial layer process with laser-driven release for batchassembly operations

A dry sacrificial layer process is presented in which microstructures fabricated on UV-transparent substrates are released by excimer laser ablation of a polymer sacrificial material using laser light incident from the reverse side of the substrate. We investigate the application of this technique to the batch assembly of hybrid microelectromechanical systems (MEMS) built from parts fabricated on different substrates. Preliminary measurements of initial velocity are presented for nickel test structures released from polyimide sacrificial layers using a KrF excimer laser. At fluences in the range 50-250 mJ/cm ² (i.e., close to the ablation threshold), structures with heights of 100 μm are shown to exhibit initial velocities in the range 15 ms^-1, allowing controlled transfer of parts between substrates. Application of the new assembly method to a MEMS device is demonstrated by assembling arrays of electrostatic wobble motors from component parts fabricated on separate substrates by UV-LIGA processing     

Study on fabrication of high aspect ratio MEMS microparts using a compact SR beamline

 A compact beamline dedicated to hard x-ray deep lithography for fabrication of high aspect ratio MEMS microparts has been developed. The exposure stage was only 3 meters away from the synchrotron radiation (SR) source so that a relatively high photon flux could be achieved with a compact super-conducting SR source. The deep lithography using PMMA resist could be as deep as 1000 μm and the maximum aspect ratio achieved was about 50. The throughout for the 200 μm-deep lithography was found to be on the order of 5 cm²/h using the membrane-free mask under the routine SR conditions. Templates with the high aspect ratio microstructures have been made of the PMMA resist based on conducting substrates and applied further to electroforming to create metallic microstructures. In order to fabricate microparts for the MEMS applications, we have concentrated on development of masks for the hard x-ray deep lithography. The masks now can be made to have the 8 μm-thick gold absorber on the 2 μm-thick SiC membrane. Received: 25 August 1997/Accepted: 3 September 1997     

Numerical simulation of shock response of disk-suspension-slider air bearing systems in hard disk drives

 As non-traditional applications of hard disk drives emerge, their mechanical robustness during the operating state is of greater concern. A procedure for simulating the shock responses of a disk-suspension-slider air bearing system is proposed in this paper. A finite element model of the system is developed and modified, and it is used to obtain the dynamic normal load and moments applied to the air bearing slider. The dynamic load and moments are then used as input data for the air bearing dynamic simulator to calculate the dynamic flying attitudes. We obtain not only the responses of the structural components, but also the responses of the air bearing slider. The procedure is convenient for practical application, because it separates the work into two essentially uncoupled steps. It is used to simulate the shock response of a drive. The system modeled is linear if the load dimple of the suspension maintains contact with the slider, but it is non-linear if the dimple separates due to a strong shock. The air bearing has different responses for upward and downward shocks. Slider-asperity contacts occur when a strong shock is applied. Received: 5 July 2001 / Accepted: 11 December 2001     

MEMS惯性器件的主要失效模式和失效机理研究

针对微机电系统(MEMS)器件的可靠性问题,通过大量的历史资料调研和失效信息收集等方法,针对微机电系统(MEMS)器件的可靠性问题,对冲击、振动、湿度、温变、辐照和静电放电(ESD)等不同环境应力条件下的MEMS惯性器件典型失效模式及失效机理进行了深入分析和总结,研究结果有利于指导未来MEMS惯性器件的失效分析和可靠性设计.     

孔的形状和排列方式对厚孔板微结构压膜空气阻尼的影响分析

本文对微结构上孔的形状和排列方式对压膜空气阻尼的影响进行了理论和模拟分析.理论研究表明对于不同厚度、不同排列方式下的孔单元阵列,若孔的总面积和孔单元面积均为常数,当孔数增加到某一值时有最小阻尼力,并用FEM工具ANSYS证明了该结论的正确性.结果还表明孔数对恒定尺寸微结构空气阻尼的影响随着结构厚度和孔数的增加而变得更加明显.分析结果对比表明在同样的尺寸条件下,孔方形排列微结构的空气阻尼小于孔蜂窝式排列微结构的空气阻尼,该现象随着孔单元面积的增加变得越明显,但是随着孔单元接近微结构的边界,阻尼之间的差距减小.研究结果可以用在高精度MEMS器件如MEMS地震检波器、MEMS光开关和MEMS红外光传感器等的优化设计中去.     

一种MEMS微结构谐振频率的测试技术

MEMS技术的发展离不开相应的测试技术与装置,建立了一种简单的MEMS微结构动态特性的测试装置,以压电陶瓷为核心的基座激励装置实现对微结构的冲击,以微器件自身的输出作为被测信号.结合MEMS工艺中批量制作的特点,在同一测试装置的同一次测试中安装两种不同尺寸的被测微压电悬臂梁试件,采集两个梁的冲击响应信号及它们的联合输出信号,通过FFT频谱分析,比较三种情况下的频谱分析结果并提取出梁的固有频率,采用对比测试的方法获得压电微悬臂梁的谐振频率.试验结果与理论分析一致,该方法具有测试装置简单、实用性强等特点.     

Characterization of the influence of fabrication methods on microstructure failure

Single-crystal silicon microstructures, of identical design, exhibit different failure rates (following fabrication or mechanical shock testing) due to various processes. The microstructures fabricated with a boron diffusion and subsequent removal of the boron-diffused layer have a higher survival rate to the fabrication process and to mechanical shock. The survival rate (a survivor has an intact proof mass and beam) through the process is increased by 26.5%. At a 3680g shock, the boron-diffused devices have a 2.3% lower failure rate but the difference is not statistically significant. These results have been developed with wafer-level shock testing, which permits bulk testing of many samples in a cost-effective manner.     

基于ARMA建模的MEMS陀螺随机误差补偿改进算法研究

基于MEMS技术生产的MEMS器件,具有体积小、重量轻、成本低、耐冲击性、高可靠性等特点,它被广泛应用于动态水平测量装置当中。但是由于外界环境的干扰,MEMS器件的测量精度一直难以达到实际应用水平。分析了在动态水平测量当中影响MEMS器件测量精度的各种因素之后,提出了一种基于ARMA模型的针对MEMS陀螺器件随机误差补偿的改进型算法。以某型号的陀螺的随机误差为研究对象进行实验验证,结果表明,MEMS陀螺的测量精度在滤波之后有了明显的提高。经过改进后的卡尔曼滤波器和引入自适应渐消因子的卡尔曼滤波器,在静态环境下,它们的误差标准差分别降为原始误差的3.75%和4.8%,动态环境下的滤波精度也得到有效提高。证明该方法是可行的和有效的,具有较大的工程实践意义。     

A Lagrangian approach for electrostatic analysis of deformableconductors

Deformable conductors are frequently encountered in microelectromechanical systems (MEMS). For example, in electrostatic MEMS, microstructures undergo deformations because of electrostatic forces caused by applied potentials. Computational analysis of electrostatic MEMS requires an electrostatic analysis to compute the electrostatic forces acting on micromechanical structures and a mechanical analysis to compute the deformation of micromechanical structures. Typically, the mechanical analysis is performed by a Lagrangian approach using the undeformed position of the structures. However, the electrostatic analysis is performed by using the deformed position of the conductors. In this paper, we introduce a Lagrangian approach for electrostatic analysis. In this approach, when the conductors undergo deformation or shape changes, the surface charge densities on the deformed conductors can be computed without updating the geometry of the conductors. The Lagrangian approach is a simple, but critical, idea that radically simplifies the analysis of electrostatic MEMS     

Ionic-Liquid Lubrication of Sliding MEMS Contacts: Comparison of AFM Liquid Cell and Device-Level Tests

Lubrication of microelectromechanical systems (MEMS) became very critical as the devices became complex and its reliability began to deteriorate. In this paper, ionic liquids (ILs) with low volatility and high environmental stability were investigated as lubricants for sliding MEMS devices. A method that is based on atomic force microscopy (AFM) with a liquid cell was developed to study friction and wear properties of surfaces lubricated with ILs, having a systematic variation in molecular geometry and chemistry. Six-member pyridinium and five-member imidazolium rings are compared as cations in ethyl methyl pyridinium and ethyl methyl imidazolium ethyl sulfate; influence of short and long alkyl chain lengths on lubrication is studied with butyl methyl pyrrolidinium and hexyl methyl pyrrolidinium bis(trifluro methyl sulfonyl) imide. Formation of a surface-screening cation layer was discovered and linked to low friction and wear of IL-lubricated hydrogenated-silicon (H-Si) substrates. Several promising IL lubricants were identified from the AFM study and were tested in real MEMS motor devices. The friction and wear data obtained for these tests showed good correlation with the failure life span of lubricated MEMS motors. This supports a conclusion that the AFM-liquid-cell technique can be used in screening IL lubricants for MEMS devices.     

Process yields for laser repair of aged, stiction-failed, MEMSdevices

Stiction, the adhesion of micromachined components to each other or the substrate, decreases production yields and operational lifetimes for MEMS devices. A recent study demonstrated the feasibility of using a Nd:YAG, 1063 nm laser to repair 2 μm thick polycrystalline silicon microcantilevers with lengths up to 1000 μm which had adhered to the substrate. This investigation examines the influence of sample age at the time of laser irradiation on the repair of stiction-failed MEMS structures. The operating conditions for the 1064 nm, Nd:YAG laser included a fluence of 70 mJ/cm², a repetition rate of 20 Hz, a pulse duration of 20 ns, and an exposure time of 60 s. For samples irradiated on the same day of release, repair yields were 100% for beams up to 500 μm in length. For 1000 μm long beams, the 10- and 30-μm-wide cantilevers had same-day repair yields of 56% and 71%, respectively. The experimental results show that increasing the amount of time the microstructures are adhered to the substrate before laser irradiation decreases the ability to repair stiction-failed devices with delays of longer than 1 month resulting in a decreased repair yield     

Polymer Microfabrication for Microarrays, Microreactors and Microfluidics

Polymer microfabrication methods are becoming increasingly important as low-cost alternatives to the silicon or glass-based MEMS technologies. Polymer hot embossing and injection molding are replication methods applicable to microreplication of a diversity of materials and microstructures.

Equipment with high precision control of pressure and temperature for hot embossing of polymer materials is now available commercially. These systems have made possible the replication of chips containing microchannels for capillary electrophoresis (CE) and microfluidics devices, microoptical components and microreactors. Stable and reproducible polymer microstructures have been demonstrated in several types of materials with structural and optical properties meeting other biocompatibility and detection requirements. The process involves few variable parameters and results in high structural accuracy suited for a wide range of microfabrication applications.

After demonstrating equivalent and, in cases, improved performance, the alternative use of plastic as the microdevice material addresses needs for rapid prototyping in product development and provides cost advantages in product commercialization. Thus an increasing number of devices have been reported recently in the literature, fabricated on a variety of polymer substrates and using different fabrication methods such as laser ablation, injection molding, silicone rubber casting or embossing for microfabrication.     

MEMS陀螺仪在恶劣高温环境下提供准确的惯性检测

越来越多的应用需要从处于高温环境中的传感器收集数据.相比同等的分立式传感器,MEMS通常更小巧,功耗和成本都更低.此外,它们还可以在同样大小的半导体封装内集成信号调理电路.除了可以提供高精度倾斜(倾角)测量,还需要更加灵活和自由,以准确测量系统在严苛环境应用下的移动,在这些环境下,最终产品可能遭受冲击、振动和剧烈移动....     

用于细胞固定的微纳SiO2基底研究

细胞阵列芯片在细胞生物学研究、药物筛选等生物医疗领域有着广阔的应用前景.针对芯片上细胞固定时需要化学修饰的限制,提出了仅通过表面结构实现细胞固定的方案.基于MEMS技术,采用DRlE在硅片上得到超疏水的微纳结构,通过简单的高温氧化工艺实现超亲水性的SiO2 结构表面;再通过控制BOE腐蚀时间得到不同形貌的基底表面.计算了基底表面上的循环肿瘤细胞的黏附效率,并在SEM下观察了细胞与基底的相互作用行为,探讨了粗糙表面影响细胞黏附的原因.实验结果表明:采用DRlE和高温氧化制备的微纳SiO2 基底表面能极大促进细胞黏附,可应用于细胞阵列芯片设计中.     

Partial release and detachment of microfabricated metal and polymer structures by anodic metal dissolution

The large majority of microelectromechanical systems (MEMS) are fabricated on silicon, glass or Pyrex substrates by manufacturing techniques, which originated from the semiconductors industry. However, their final application often requires removal of the fabrication substrate or at least a partial release of some section of the device. This paper describes a technique based on anodic dissolution of sacrificial metal layers for the complete or partial detachment of microstructures. As an example, a thin-film of sacrificial aluminum is selectively removed in a neutral sodium chloride solution by applying a small positive potential to the aluminum. The method is evaluated theoretically and experimentally in a defined geometry and compared to diffusion-limited, chemical etching. It is shown experimentally that the process is significantly faster than conventional wet chemical etching and the method has been used to release planar and nonplanar thin-film devices made from polymers and metals. The method is applicable for a wide range of metals as sacrificial materials and is very versatile with respect to electrolyte composition and applied voltages. Ease of sacrificial material deposition (sputtering or evaporation) and structuring and the possibility of high process temperature and the nondestructive chemical environment (also environmentally friendly) during detachment make the process technology an interesting alternative to conventional chemical etching.     

Glass reflow on 3-dimensional micro-apertures for electrophysiological measurements on-chip

We propose a new method to fabricate micro-apertures for on-chip electrophysiological measurements of living cells. Thermal reflow of phosphosilicate glass (PSG) is applied to funnel- or nozzle-type microstructures to generate very smooth surfaces on the finalized chip. Such 3-dimensional microstructures show close similarities to fire-polished glass pipette tips. Immobilized cells fit perfectly to these structures offering a large contact area for sealing between the cell membrane and the oxide surface. A tight cell/chip-aperture seal is an important requirement for the present application. We demonstrate the formation of stable gigaseals with Chinese hamster ovary (CHO) cells for both types of microstructures without the need of any post-fabrication surface treatment. By adjusting the PSG reflow parameters, the shape of the apertures can be modified and diameters down to the sub-micrometer range may be achieved. The application of PSG reflow to MEMS fabrication is an interesting new option to create unconventional microstructures.     

Self Assembly of Polymer Structures Induced by Electric Field

A method has been developed for fabricating polymer microstructures based on electric field induced self assembly and pattern formation. A dielectric fluid placed in between two conductive plates experience a force in an applied electric field gradient across the plates, which can induce a diffusive surface instability and self construction of the fluid surface. This process is exploited for the fabrication of self assembled polymer microstructures as well as replicated patterns through the use of pre-patterned plates or electrodes. FEM simulation is used to decide the minimum wavelength and electric gradient distribution of polymer structures. A variety of structures in the micron and nanometer scales including bio-fluidic MEMS, polymer optoelectronic devices can be fabricated using this method.