A comprehensive model to study nonlinear behavior of multilayered micro beam switches

A novel model to study the pull-in behavior of nonlinear electromechanically coupled systems has been developed. The proposed model is based on the multilayered cantilever and fixed–fixed micro beam type MEMS switches. Due to the complexity of the nonlinear beam mechanics, exact analytical solutions are not generally available; therefore, the derived nonlinear equation has been numerically solved fully using the nonlinear finite difference method. Furthermore, the results obtained are summarized and compared with the other existing empirical and analytical models. These results can be useful in the optimization of MEMS switch designs or other actuators. In addition, the method developed in this paper has a good potential for analyzing other types of complex MEMS devices. An erratum to this article can be found at     

An investigation into the electrostatic force representation for electrically actuated microelectromechanical systems

The ever-increasing demand for microelectromechanical systems (MEMS) in modern electronics has reinforced the need for extremely accurate analytical and reduced-order models to aid in the design of MEMS devices. Many MEMS designs consist of cantilever beams with a tip mass attached at the free end to act as a courter electrode for electrical actuation. One critical modeling aspect of electrically actuated MEMS is the electrostatic force that drives these systems. The two most used representations in the literature approximate the electrostatic force between two electrodes as a point force. In this work, the effects of the representation of the electrostatic force for electrically actuated microelectromechanical systems are investigated. The system under investigation is composed of a beam with an electrode attached to its end. The distributed force, rigid body, and point mass electrostatic force representations are modeled, studied, and their output results are compared qualitatively. Static and frequency analyses are carried out to investigate the influences of the electrostatic force representation on the static pull-in, fundamental natural frequency, and mode shape of the system. A nonlinear distributed-parameter model is then developed in order to determine and characterize the response of electrically actuated systems when considering various representation of the electrostatic forces. The results show that the size of the electrode may strongly affect the natural frequencies and static pull-in when the point mass, rigid body, and plate representations are considered. From nonlinear analysis, it is also proven that the representation may affect the hardening behavior of the system and its dynamic pull-in. This modeling and analysis give guidelines about the usefulness of the electrostatic force representations and possible erroneous assumptions that can be made which may result in inaccurate design and optimal performance detection for electrostatically actuated systems.

     

Design and process considerations for fabricating RF MEMS switches on printed circuit boards

Design considerations and process development for fabricating radio frequency microelectromechanical systems (RF MEMS) switches on microwave laminate printed circuit boards (PCBs) are presented in details in this work. Two key processes, high-density inductively coupled plasma chemical vapor deposition (HDICP CVD) for low-temperature silicon nitride deposition, and compressive molding planarization (COMP) have been developed for fabricating RF MEMS switches on PCB. The effects of process conditions of HDICP CVD on low-temperature nitride film are fully characterized for its use in RF MEMS switches on PCB. Not only can COMP planarize the surface of the photoresist for lithographic patterning over topologically complex surfaces, but also simultaneously create a membrane relief pattern on the surface of a MEMS structure. Several membrane-type capacitive switches have been fabricated showing excellent RF performance and dynamic responses similar to those on semiconductor substrates. This technology promises the potential of enabling further monolithic integration of switches with other RF components, such as antennas, microwave monolithic integrated circuits (MMICs), phase shifters, tunable filters, and transmission lines on the same PCBs reducing the losses due to impedance mismatching from components/system assembly and simplifies the design of the whole RF system. [1416].     

基于共平面波导的可调低通滤波器的设计和制作

介绍了一种使用多触点MEMS开关实现的新型可调微波MEMS低通滤波器,应用MEMS制作工艺在石英衬底上实现滤波器结构.滤波器基于慢波共平面波导周期性结构,具有尺寸小、插损低、可与单片微波集成电路工艺兼容等优点.滤波器截止频率的大小取决于MEMS开关的状态.实验结果表明,当MEMS开关受到激励时,低通滤波器的3-dB截止频率从12.5GHz转换至6.1GHz,带内纹波小于0.5dB,带外抑制大于40dB,开关的驱动电压在25V左右.     

MEMS optical switches and interconnects

This paper reviews several optical connecting devices that are based on microelectromechanical systems (MEMS) components. In this paper, we divide optical connecting devices into two categories. The first category includes MEMS-based optical switches developed for optical fiber communication, which perform optical switching, wavelength division multiplexing (WDM) routing, and/or optical cross connection. The other category consists of MEMS-based optical interconnects that have been constructed primarily for use in rack-to-rack, board-to-board, chip-to-chip, card-to-card and/or intra-chip interface connections. Working principles of these MEMS optical connecting devices will also be discussed in this paper.     

Command-Shaping Techniques for Electrostatic MEMS Actuation: Analysis and Simulation

Precision positioning of microelectromechanical systems (MEMS) structures using electrostatic actuation has been widely used for optical and radio-frequency MEMS. How to achieve fast switching without exciting excessive residual vibration or structural impact is an important issue for these applications. This paper presents the analysis and simulation of applying command-shaping techniques for controlling MEMS electrostatic actuation. According to the nature of application fields, electrostatic actuators are classified into three categories: 1) lateral linear actuation; 2) vertical nonlinear actuation; and 3) pull-in actuation. Their corresponding linear or nonlinear command-shaping schemes are developed and presented. Both lumped element and continuous models of typical MEMS electrostatic actuated structures are simulated using Simulink and the finite-element method, and results indicate that the shaped command would yield a much superior response than that by the unshaped commands. Essential sensitivity studies are also conducted to examine the robustness of these shaping schemes, and results shows that within a certain level of parameter variation, these shapers are robust enough to retain the performance.     

Towards improved reliability of RF-MEMS: mechanical aspects and experimental testing of a micro-switch design with embedded active self-recovery mechanism to counteract stiction

Microsystem Technologies - In this work, the operation of an active self-recovery mechanism embedded within microelectromechanical systems (MEMS) switches for Radio Frequency (RF) passives (i.e....     

Stiction-protected MEMS switch with low actuation voltage

Microsystem Technologies - Commercial success of microelectromechanical systems (MEMS) switches is limited by several issues. A high actuation voltage requires special circuitry solutions that...     

Robust design and model validation of nonlinear compliant micromechanisms

Although the use of compliance or elastic flexibility in microelectromechanical systems (MEMS) helps eliminate friction, wear, and backlash, compliant MEMS are known to be sensitive to variations in material properties and feature geometry, resulting in large uncertainties in performance. This paper proposes an approach for design stage uncertainty analysis, model validation, and robust optimization of nonlinear MEMS to account for critical process uncertainties including residual stress, layer thicknesses, edge bias, and material stiffness. A fully compliant bistable micromechanism (FCBM) is used as an example, demonstrating that the approach can be used to handle complex devices involving nonlinear finite element models. The general shape of the force-displacement curve is validated by comparing the uncertainty predictions to measurements obtained from in situ force gauges. A robust design is presented, where simulations show that the estimated force variation at the point of interest may be reduced from /spl plusmn/47 /spl mu/N to /spl plusmn/3 /spl mu/N. The reduced sensitivity to process variations is experimentally validated by measuring the second stable position at multiple locations on a wafer.     

RF MEMS Sequentially Reconfigurable Sierpinski Antenna on a Flexible Organic Substrate With Novel DC-Biasing Technique

Devices and systems that use RF microelectromechanical systems (RF MEMS) switching elements typically use one switch topology. The switch is designed to meet all of the performance criteria. However, this can be limiting for highly dynamic applications that require a great deal of reconfigurability. In this paper, three sets of RF MEMS switches with different actuation voltages are used to sequentially activate and deactivate parts of a multiband Sierpinski fractal antenna. The implementation of such a concept allows for direct actuation of the electrostatic MEMS switches through the RF signal feed, therefore eliminating the need for individual switch dc bias lines. This reconfigurable antenna was fabricated on liquid crystal polymer substrate and operates at several different frequencies between 2.4 and 18 GHz while maintaining its radiation characteristics. It is the first integrated RF MEMS reconfigurable antenna on a flexible organic polymer substrate for multiband antenna applications. Simulation and measurement results are presented in this paper to validate the proposed concept.[2007-0013]     

Analysis of Hybrid Electrothermomechanical Microactuators With Integrated Electrothermal and Electrostatic Actuation

The goal of this paper is to integrate electrothermal and electrostatic actuations in microelectromechanical systems (MEMS). We look at cases where these two types of actuation are intimately coupled and argue that such integrated electrothermomechanical (ETM) microactuators have more advantages than pure electrothermal or electrostatic devices. We further propose a framework to model hybrid ETM actuation to get a consistent solution for the coupled mechanical, thermal, and electrical fields in the steady state. Employing a Lagrangian approach, the inhomogeneous current conduction equation is used to describe the electric potential, while the thermal and displacement fields are obtained by solving the nonlinear heat conduction equation and by performing a large deformation mechanical analysis, respectively. To preserve numerical accuracy and reduce computational time, we also incorporate a boundary integral formulation to describe the electric potential in the medium surrounding the actuator. We show through the example of a hybrid double-beam actuator that ETM actuation results in low-voltage low-power operation that could be used for switching applications in MEMS. We also extend the same device toward bidirectional actuation and demonstrate how it may be used to overcome common problems like stiction that occur in MEMS switches.     

Accurate Assessment of Packaging Stress Effects on MEMS Sensors by Measurement and Sensor–Package Interaction Simulations

In this paper, packaging-induced stress effects are assessed for microelectromechanical systems (MEMS) sensors. A packaged MEMS sensor may experience output signal shift (offset) due to the thermomechanical stresses induced by the plastic packaging assembly processes and external loads applied during subsequent use in the field. Modeling and simulation to minimize the stress-induced offset shift are essential for high-precision accelerometers, gyroscopes, and many other MEMS devices. Improvement of plastic package modeling accuracy is accomplished by correlating finite-element analysis package models using measured material properties and package warpage. Using a refined reduced-order MEMS sensor and package interaction model, device offset is simulated, optimized, and compared with data collected from a unique three-axis accelerometer, which uses a single mass for all three axes sensing. As a result, this accelerometer has achieved very low offset in all axes over device operation temperature range of to . Device offset performance was improved by at least five times after the MEMS design optimization as compared with the one prior to the optimization.     

Fabrication and dynamic analysis of the electrostatically actuated MEMS variable capacitor

Future microwave networks require miniature high-performance tunable elements such as switches, inductors, and capacitors. In this paper, high performance variable capacitor was fabricated by simple microelectromechanical systems (MEMS) technology. The capacitance and quality (Q) factor at 1 GHz are 0.792 pF and 51.6. The pull-in voltage is 13.5 V and the tuning ratio of the capacitor is more than 1.31:1. A reduced-order model for the dynamic characteristics of the capacitor is established based on the equilibrium among the plate flexibility.     

Inductively‐loaded RF MEMS reconfigurable filters

This article presents an inductively loaded radio frequency (RF) microelectromechanical systems (MEMS) reconfigurable filter with spurious suppression implemented using packaged metal‐contact switches. Both simulation and measurement results show a two‐state, two‐pole 5% filter with a tuning range of 17% from 1.06 GHz to 1.23 GHz, an insertion loss of 1.56–2.28 dB and return loss better than 13 dB over the tuning range. The spurious passband response in both states is suppressed below ?20 dB. The unloaded Q of the filter changes from 127 to 75 as the filter is tuned from 1.06 GHz to 1.23 GHz. The design and full‐wave simulation of a two‐bit RF MEMS tunable filter with inductively loaded resonators and monolithic metal‐contact MEMS switches is also presented to prove the capability of applying the inductive‐loading technique to multibit reconfigurable filters. The simulation results for a two‐bit reconfigurable filter show 2.5 times improvement in the tuning range compared with the two‐state reconfigurable filter due to lower parasitics associated with monolithic metal‐contact MEMS switches in the filter structure. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

高灵敏压力传感器过载保护结构设计

采用微机电系统(MEMS)牺牲层技术制作的压力传感器具有芯片尺寸小,灵敏度高的优势,但同时也带来了提高过载能力的难题.为此,利用有限元法,对牺牲层结构压阻式压力传感器弹性膜片的应力分布进行了静态线性分析和非线性接触分析.通过这两种分析方法的结合,准确的模拟出过载状态下传感器的应力分布.在此基础上给出了压力传感器的一种结...     

Computer-aided generation of nonlinear reduced-order dynamicmacromodels. I. Non-stress-stiffened case

Reduced-order dynamic macromodels are an effective way to capture device behavior for rapid circuit and system simulation. In this paper, we report the successful implementation of a methodology for automatically generating reduced-order nonlinear dynamic macromodels from three-dimensional (3-D) physical simulations for the conservative-energy-domain behavior of electrostatically actuated microelectromechanical systems (MEMS) devices. These models are created with a syntax that is directly usable in circuit- and system-level simulators for complete MEMS system design. This method has been applied to several examples of electrostatically actuated microstructures: a suspended clamped beam, with and without residual stress, using both symmetric and asymmetric positions of the actuation electrode, and an elastically supported plate with an eccentric electrode and unequal springs, producing tilting when actuated. When compared to 3-D simulations, this method proves to be accurate for non-stress-stiffened motions, displacements for which the gradient of the strain energy due to bending is much larger than the corresponding gradient of the strain energy due to stretching of the neutral surface. In typical MEMS structures, this corresponds to displacements less than the element thickness, At larger displacements, the method must be modified to account for stress stiffening, which is the subject of part two of this paper     

Comparison of Au and Au–Ni Alloys as Contact Materials for MEMS Switches

This paper reports on a comparison of gold and gold-nickel alloys as contact materials for microelectromechanical systems (MEMS) switches. Pure gold is commonly used as the contact material in low-force metal-contact MEMS switches. The top two failure mechanisms of these switches are wear and stiction, which may be related to the material softness and the relatively high surface adhesion, respectively. Alloying gold with another metal introduces new processing options to strengthen the material against wear and reduce surface adhesion. In this paper, the properties of Au-Ni alloys were investigated as the lower contact electrode was controlled by adjusting the nickel content and thermal processing conditions. A unique and efficient switching degradation test was conducted on the alloy samples, using pure gold upper microcontacts. Solid-solution Au-Ni samples showed reduced wear rate but increased contact resistance, while two-phase Au-Ni (20 at.% Ni) showed a substantial improvement of switching reliability with only a small increase of contact resistance. Discussion of the effects of phase separation, surface topography, hardness, and electrical resistivity on contact resistance and switch degradation is also included.     

Contact dynamics between the rotor and bearing hub in an electrostatic micromotor

The most widely known nonlinear phenomena in microelectromechanical systems are probably the contact instabilities. Here, a mathematical model of the contact between the rotor and bearing hub of an electrostatic micromotor, which actuates MEMS, is constructed for the purpose of investigating the contact dynamics. The contact problem of the contact stress and strain equations is presented under the scaling effects of micro-scale. The parameters, geometries of the micromotor, electrostatic force, and applied gap voltages, which are related to the contact, are discussed in detail. The discriminations between unchanged gap and maximum changed gap are studied under different applied voltages. The model is studied by using a combination of numerical and finite element analytical techniques. Some results of the contact width, the contact stress, the contact strain, are compared with finite element model (FEM) solutions of an equivalent problem. The 1^st principal stress and strain and whole contact stress are shown for expressing the distributions.The authors are grateful to Dr. Wei KX for his valuable discussions. This project is supported by National Outstanding Youth Foundation of Peoples Republic of China under Grant no 10325209.     

Redundancy RF MEMS Multiport Switches and Switch Matrices

The objective of this paper is to investigate novel configurations of planar multiport radio-frequency (RF) microelectromechanical systems (MEMS) C-type and R-type switches and redundancy switch matrices for satellite communications. An in-house monolithic fabrication process dedicated to electrostatic multiport RF MEMS switches and switch matrices is developed and fine tuned. The proposed C-type switch is a four-port device with two operational states. This switch exhibits an insertion loss of less than 0.3 dB and isolation of about 25 dB at satellite C-band frequency range. The novel R-type switch is also a four-port device with an additional operational state. The measured results show an insertion loss of better than 0.4 dB and an isolation of better than 25 dB at C-band. This is the first time that an R-type RF MEMS switch is ever reported. Several of these switches are integrated in the form of redundancy switch matrices, and two novel monolithic five to seven redundancy switch matrices are developed, fabricated, and tested. It is shown that the additional operating state of the R-type switch not only decreases the number of elements by 50% but also reduces the size drastically