In Situ Characterization of Induced Stiction in a MEMS

Stiction remains a limiting factor in the performance and lifetime of MEMS devices. We have developed experimental tools for inducing and quantifying changes in stiction on a large array of MEMS actuators. Thousands of elements were subjected to aggressive wear in order to produce shearing forces that contributed to the degradation of contacting surfaces. Custom electronics were developed to accomplish nonstandard actuation of the MEMS array. Optical techniques were used to characterize the induction of and progression of stiction. A model incorporating experimental and geometrical values was used to determine stiction force as a function of actuation duration and packaging. For a depackaged array, an increase in stiction force of ~230nN (per element) was induced through three days of high-speed actuation     

On the Use of Structural Vibrations to Release Stiction Failed MEMS

This paper identifies dynamic excitation parameters that promote decohesion of stiction-failed microcantilevers. The dynamic response of "s-shaped" adhered beams subjected to harmonic loading is described using modal analysis; this model is then used to predict the onset of debonding in the context of a critical interface energy. These theoretical results are used to rationalize preliminary experiments, which illustrate that dynamic excitation may be used to affect partial or complete repair of stiction-failed microcantilevers. The theoretical results provide fundamental insight regarding regimes where resonant effects trigger debonding and can serve as a potential mechanism for stiction repair. The models illustrate that driving a structure at resonance is usually beneficial with regards to debonding. However, this is not universally true; there is no benefit to driving a device at frequencies with unfavorable mode-shapes. Thus, these results provide a reasonable physical and mathematical explanation for the preliminary experimental results, while providing a roadmap for identifying parameters in future tests     

Characterization and modeling of electro-thermal MEMS structures

Thermal functional circuits are an interesting group of the MEMS elements with high a potential. A practical realisation is called Quadratic Transfer Characteristics (QTC) element of which driving principle is the Seebeck effect. Such devices can be applied e.g. as RMS meters. In this paper we are dealing with the analyses of a QTC element from different perspectives. A family of compact models is presented. These models are suitable to use in network simulation programs. To investigate the detailed behaviour of the device, we measured a few secondary properties of the structure, such as temperature dependence, cut-off frequency and non-quadratic error.

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控制回路中的阀门迟滞补偿方法

迟滞是阀门最常见的问题之一,它会引起控制回路的振荡,造成能量的损失和产品质量的下降.目前解决阀门迟滞问题的方法主要有Knocker迟滞补偿、减弱或去除控制器的积分作用等方式.但Knocker迟滞补偿方法会导致阀门的频繁动作,增加阀门的磨损;而减弱或去除控制器的积分作用方式会导致稳态误差.通过对这两种方法的优劣比较,提出了一种改进的迟滞补偿方法.该方法可有效减少阀门动作的次数,延长阀门的使用寿命.     

Fabrication and Characterization of a Wafer-Level MEMS Vacuum Package With Vertical Feedthroughs

This paper reports a MEMS vacuum package with vertical feedthroughs formed in a glass substrate all at the wafer level. This approach satisfies requirements for MEMS vacuum packages, including small size, vacuum/hermetic capability, sealed and low parasitic feedthroughs, wafer-level processing, compatibility with most MEMS processes, and low cost. It also enables flip-chip solder attachment to a PC board. The package has an integrated micro-Pirani gauge on a glass substrate for in situ monitoring, a silicon cap, and vertical feedthroughs through the glass. The integrated Pirani gauge has 0.6 milli-torr resolution at 0.1 torr and 0.2 torr resolution at 100 torr. Using the Pirani gauge, the fabricated vacuum package is characterized. The package has maintained ~33 torr base pressure with plusmn1.5 torr uncertainty for more than four months without a getter. The long-term measured pressure uncertainty is from the measurement setup and environment, and can be improved using a getter inside the package. [2007-0160]     

新型的调节阀迟滞检测量化方法

振荡是控制回路中存在的普遍现象,而调节阀的迟滞是造成控制系统振荡的重要原因.诸如迟滞等非线性因素的存在,大大限制了控制回路的性能.所以迟滞检测和量化对查找控制回路振荡的原因,提高控制回路的准确性,稳定性具有着重要意义,无论在技术应用还是经济效益方面都是大有裨益的.借鉴成熟的波形拟合检测和聚类量化体系,结合大量的事例,提出一种基于波形分割拟合的检测方法以及一种基于改进的模糊C均值聚类技术的量化方法.运用该方法研究了系统参数对迟滞的影响,仿真表明可以有效地指导实际的流程工程生产.     

控制回路中迟滞建模及在线检测

控制阀门中非线性的存在,比如迟滞、死区等,限制了控制回路的性能;大约30%的控制回路振荡是由于阀门的问题,而迟滞是过程工业中所发现的最普遍的阀门问题;尽管已有很多对迟滞现象的理解和建模的尝试,但是仍然缺少一种简单、直观且能比较精确反映真实阀门特性的模型;着重研究阀门迟滞的机理并结合大量的事例,提出了迟滞的模型以及基于系统辨识的在线检测方法,仿真与实际工业应用表明了该方法的有效性与准确性。     

Characterization of selective polysilicon deposition for MEMS resonator tuning

Variations in micromachining processes cause submicron differences in the size of MEMS devices, which leads to frequency scatter in resonators. A new method of compensating for fabrication process variations is to add material to MEMS structures by the selective deposition of polysilicon. It is performed by electrically heating the MEMS in a 25/spl deg/C silane environment to activate the local decomposition of the gas. On a (1.0/spl times/1.5/spl times/100) /spl mu/m/sup 3/, clamped-clamped, polysilicon beam, at a power dissipation of 2.38 mW (peak temperature of 699/spl deg/C), a new layer of polysilicon (up to 1 /spl mu/m thick) was deposited in 10 min. The deposition rate was three times faster than conventional LPCVD rates for polysilicon. When selective polysilicon deposition (SPD) was applied to the frequency tuning of specially-designed, comb-drive resonators, a correlation was found between the change in resonant frequency and the length of the newly deposited material (the hotspot) on the resonator's suspension beams. A second correlation linked the length of the hotspot to the magnitude of the power fluctuation during the deposition trial. The mechanisms for changing resonant frequency by the SPD process include increasing mass and stiffness and altering residual stress. The effects of localized heating are presented. The experiments and simulations in this work yield guidelines for tuning resonators to a target frequency.     

MEMS高温温度传感器的研制与测量精度研究

航空发动机智能化及其他机械系统的智能化需要原位集成制造的传感器,为此研制了发动机涡轮叶片原位集成高温传感器.该高温传感器采用MEMS微制造工艺将厚度在微米量级的微小传感器原位集成在航空发动机涡轮叶片表面,利用微技术制造的传感器和标准的热电偶进行了一系列的高温测量试验和一系列细致的高温温度表征测量研究.该微制造工艺攻克了两项技术难关:曲表面的光刻技术和高温绝缘层的制作技术.涡轮叶片表面原位集成的微传感器不仅可以原位测量高达800℃的环境温度,并且具有很高的机械强度,可以承受高达40 g的振动和100 g的冲力.研究还表明,在高温测量环境下,高温测量精度和高温环境下的温度场(高温温度的空间分布与升温时间迟豫)密切相关.由于高温环境温度场的差异,可以产生高达10%的测量本征误差.     

Stiction issues and actuation of RF LIGA-MEMS variable capacitors

High aspect ratio variable capacitors have been fabricated using deep X-ray lithography and electroplating. Stiction phenomena applicable to high aspect ratio devices are presented, including the conditions for stiction to occur and the critical dimensions of structures. Actuation tests at 3 GHz are also presented and show a maximum capacitance of 0.86 pF with no actuation voltage and a minimum capacitance of 0.70 pF with an actuation voltage of 20 V just before pull-in, which gives a tuning range of 1.23:1. Corresponding Q-factor values are 49.3 and 70.8 respectively. After pull-in, the measured capacitance is 0.61 pF, corresponding to a tuning range of 1.41:1, with a maximum Q-factor of 102.9.     

Characterization of Polycrystalline Silicon-Germanium Film Deposition for Modularly Integrated MEMS Applications

The deposition of in situ boron-doped polycrystalline silicon-germanium (poly-SiGe) films in a conventional low-pressure chemical-vapor deposition reactor has been characterized using the design of experiments method. The dependencies of deposition rate, resistivity, average residual stress, strain gradient, and wet etch rate in hydrogen peroxide solution are presented. Structural layer requirements for general microelectromechanical system applications can be met within the process temperature constraint imposed by complementary metal-oxide-semiconductor (CMOS) electronics. However, residual stress and strain gradient requirements for inertial sensor applications will be difficult to meet with a single homogeneous layer of poly-SiGe that is about 2 mum thick. By correlating stress depth profile measurements with cross-sectional transmission electron microscopy images, we conclude that the large strain gradient is due to highly compressive stress in the lower (initially deposited) region of the film. For films deposited at very low temperature (near the range of amorphous film deposition), in situ boron doping enhances film crystallinity and reduces the strain gradient     

Characterization and optimization to improve uneven surface on MEMS bridge fabrication

This paper presents an optimized fabrication method for developing a freestanding bridge for RF MEMS switches. In this method, the sacrificial layer is patterned and hard baked a 220 °C for 3 min, after filling the gap between the slots of the coplanar waveguide. Measurement results by AFM and SEM demonstrate that this technique significantly improves the planarity of the sacrificial layer, reducing the uneven surface to less than 20 nm, and the homogeneity of the Aluminum thickness across the bridge. Moreover, a mixture of O₂, Ar and CF₄ was used and optimized for dry releasing of the bridge. A large membrane (200 × 100 μm²) was released without any surface bending. Therefore, this method not only simplifies the fabrication process, but also improves the surface flatness and edge smoothness of the bridge. This fabrication method is fully compatible with standard silicon IC technology.     

MEMS高温温度传感器的研制和测量精度研究

智能航空发动机及其他机械系统的智能化需要原位集成制造的传感器,为此制作了发动机涡轮叶片原位集成高温温度传感器,该高温温度传感器采用MEMS微制造工艺将厚度在微米量级的微小传感器原位集成在航空发动机涡轮叶片表面,利用微技术制造的传感器和标准的热电偶进行了一系列的高温温度试验和一系列细致的高温温度表征测量研究。该微制造工艺攻克了两项技术难关：曲面表面的光刻技术和高温绝缘层的制作技术。涡轮叶片表面原位集成的微传感器不仅可以原位测量高达800C的环境温度,并且具有很高的机械强度,可以承受高达40g的振动和100g的冲力。研究还表明,在高温测量的环境下,高温温度的测量精度和高温环境的温度场（高温温度的空间分布与升温时间迟豫）密切相关。由于高温环境温度场的差异,可以产生高达10%的测量本征误差。     

RF MEMS引线键合的射频性能和等效电路研究

针对一种用键合线连接的简单封装模型进行射频性能的模拟.用HFSS软件对不同长度、不同高度、不同直径以及不同间距的键合线进行模拟,总结出这些参数对键合线射频性能的影响.提出了由顶盖、CPW和键合线组成的简单封装结构的等效电路,并提取参数值.用Mcrowave Office软件对等效电路进行模拟,其S11在6～8 GHz内与HFSS模拟的模型的S11相差2 dB以内,其S21在1～10 GHz内与模型的S21相差0.1 dB以内.     

Free-Form Simulation of Sequential Etching and Surface Characterization for 3-D MEMS Fabrication

A new diffusion-based simulation model of isotropic wet etching and free-form surface characterization method for 3-D free-form microelectromechanical systems (MEMS) fabrication is presented in this paper. To simulate the etching process, a diffusion-based model solved by the finite-element method (FEM) has been developed, allowing extraction of more accurate etch-front data at discrete time steps. In the developed method, free-form MEMS objects are modeled as B-spline functions with material concentration. Finite elements are generated by discretization in the parametric domain of the free-form object and mapping back to the Euclidean space. Points on the etch front are extracted using a Z-map method. The extracted point data are characterized to obtain a B-spline representation of the etch-front surface. Examples from the isotropic etching simulation of 2-D and 3-D objects with both regular and free-form geometry are presented. The developed method allows the simulation of 3-D objects with free-form input and free-form mask opening and facilitates the simulation of sequential etching of free-form objects with irregular mask openings. This paper also discusses applications of the developed method in MEMS process planning that can be realized by taking advantage of the better control of geometry that it provides in MEMS fabrication.     

Optical actuation of a bistable MEMS

This paper presents an optical actuation scheme for MEMS devices based on the well-established fact that light possesses momentum, and hence, imparts a force equal to 2 W/c when reflected by a surface. Here, W is the total power of the reflected light, and c is the speed of light. Radiation pressure, as it is known, is nearly insignificant for most macroscale applications, but it can be quite significant for MEMS devices. In addition, light actuation offers a new paradigm. First, intersecting light beams do not interfere, in contrast to electrical conductors, which short when they come into contact. Second, light can operate in high temperature and high radiation environments far outside the capability of solid state electronic components. This actuation method is demonstrated, both in air and in vacuum, by switching the state of a bistable MEMS device. The associated heat transfer model is also presented.     

一种Z轴微机械陀螺的自解耦方法研究

在分析了微机械陀螺机械耦合误差产生原因的基础上,提出了一种解耦梁方案,可以从结构上消除振动式微机械陀螺敏感模态对驱动模态的耦合影响;基于该解耦梁方案设计了一种新型的Z轴微机械陀螺结构.分析表明,该陀螺结构消除了敏感模态对驱动模态的耦合影响,实现了解耦设计的目的.     

一种新型的电热驱动MEMS微继电器的研制

设计和制备了一种新型的电热驱动微电子机械(MEMS)继电器,并进行了性能测试.整个工艺采用非硅MEMS工艺,利用Cu作为牺牲层材料,Ni作为微继电器的结构材料.微继电器是基于杠杆放大原理设计的,因此能够获得较大的行程;驱动臂采用"U"型梁设计,能够在不增加功耗的条件下,获得较大的驱动力.并采用Ansys10.0有限元软件对微继电器进行了模拟分析.测试结果表明,这种微型继电器具有体积小、驱动电压低、切换速度快等优点.     

平面S型与平面W型MEMS弹簧性能比较研究

S型与W型是平面MEMS弹簧中两种典型的结构形式,各自结构特点导致了它们具有不同的力学性能。通过理论分析、仿真计算和实验验证方法对平面镍质S型与平面W型MEMS弹簧性能进行了比较研究,得出了在同样的外廓尺寸及相同的线宽、厚度和梁间距情况下,平面S型微弹簧的刚度大于平面W型微弹簧的刚度的结论,为MEMS弹簧的进一步优化设计提供理论参考。     

一种新型MEMS微驱动器的设计与仿真分析

提出并设计了具有双稳态功能的新型电磁型MEMS微驱动器结构形式。微驱动器由导磁的两端固支的扭梁、两端可自由摆动的悬臂梁,以及永磁体、下磁路和平面线圈组成。永磁体的使用,实现了器件的双稳态功能,从而可以得到低功耗的磁驱动器。通电线圈用来实现器件的姿态转换。对设计的器件进行了电磁仿真分析,验证了器件的双稳态机制,分析表明:铁芯的存在对器件功能有决定性的影响。