Fixed-fixed Beam Structure Research Articles

Improved Test Fixture for Collecting Microcontact Performance and Reliability Data.

Microelectromechanical systems (MEMS) ohmic contact switches are considered to be a promising candidate for wireless communication applications. The longevity of MEMS switches is directly related to the reliability and performance of microcontacts. In this work, an improved microcontact test fixture with high actuation rates (KHz) and highly precise position control (nm) and force (nN) control was developed. Here, we collected microcontact performance data from initial contact tests (ICT) and microcontact reliability data from cold switched tests (CST). To perform these tests with our test fixture, we fabricated MEMS microcontact test structures with relatively high Young's modulus electroplated Nickel (Ni)-based, fixed-fixed beam structure with Au/RuO2 bimetallic microcontacts. These structures were characterized for forces ranging from 200-1000 µN in ICT tests. In a CST test, the tested microcontact survived more than 200 million cycles at a 1 KHz cycle rate, with a stable contact resistance value ranging between 3.8-5.2 Ω. These experiments validate the potentiality of our microcontact test fixture, and will facilitate further investigation on advanced microcontacts to enhance the MEMS switch's reliability.

A two-stage approach to updating of mass, stiffness and damping matrices

Model updating techniques are used to update a dynamic FE model of a structure so as to obtain its accurate representation in terms of mass, stiffness and damping matrices. Some of the existing updating methods update all the three matrices simultaneously using either complex FRFs or modal data. These methods, however, are faced with numerical problems in practical implementation due to large difference in the magnitudes of the elements of the stiffness and mass matrices on one end and of the damping matrix on the other.This paper proposes a two-stage approach for updating mass, stiffness and damping matrices and performs numerical and experimental investigations to assess the effectiveness of such an approach. The first stage of updating is based on the concept of normal FRFs, which represent the FRFs of a structure if the structure were undamped, to update the mass and stiffness matrices. In the second stage, the damping matrix is updated based on the difference of complex and normal FRFs, which represents the effect of damping in the structure on its frequency response.The numerical example of a fixed-fixed beam structure is first considered that allows investigating the impact of first stage of updating on the second stage. This is followed by an experimental example of an F shape structure. A new method called ‘hybrid’ method to deal with data incompleteness in the context of two-stage updating is suggested. Effectiveness of the two-stage method when updating parameters cannot be chosen correctly is also investigated. The two stage approach presented and the results of the investigations carried out would be helpful in proper implementation and application of the proposed updating method in practice.

Design Considerations of in-Plane Nanoelectromechanical Switches with Corrugation Beams for Low Voltage Logic Applications

Design consideration of nanoelectromechanical switches with low actuation voltage is presented. For a fixed-fixed beam structure design, it has been found that the actuation voltage can be largely reduced by integrating corrugations onto the fixed beam. An actuation voltage less than 3 V can be achieved with a relaxed design rule.

Use of resonance and antiresonance frequencies for better matching of frequency response function

Most of the finite element model updating method uses resonance frequencies and mode shapes. The mode shapes are not very accurate as suggested by many researchers. Whereas, antiresonance frequencies can be identified accurately from measured frequency response functions (FRFs). In this paper, a new model updating method is proposed, which uses resonance and antiresonance frequencies for better FRF matching of updated FRF and experimental FRF. The effectiveness of the proposed finite element updating method is demonstrated by measured data of fixed-fixed beam structure. The updated results have shown that the use of resonance along with antiresonance frequencies for finite element model updating can be used to derive accurate model of the system. This is illustrated by matching of the FRFs obtained from the updated model with that of experimental data.

Comparative study of finite element model updating methods

The effects of vibrations present major hazards and operating limitations ranging from discomfort (including noise), malfunctioning, reduced performance, early breakdown and structural failure which, in the worst case can be catastrophic. Hence, accurate mathematical models are required to describe the vibration characteristics of structures, which subsequently can be used for design purposes to limit the negative effects of vibrations. Finite element (FE) predictions are often called into question when they are in conflict with test results. Inaccuracies in FE models and errors in results predicted by them can arise due to the use of incorrect modeling of boundary conditions, incorrect modeling of joints, and difficulties in modeling of damping. This has led to the development of model updating techniques, which aim at reducing the inaccuracies present in an analytical model in the light of measured dynamic test data. In this paper, a detailed comparison of two approaches of obtaining updated FE models are evaluated with the objective that the frequency response functions (FRFs) obtained from updated FE models are able to predict the measured FRFs accurately. In the first method, the updated FE model is obtained by a direct method, which uses modal data. In the second method, the updated model is obtained by an iterative method, which uses FRF data and is also a parameter-based method. The effectiveness of both methods is evaluated by numerical examples, as well as by actual experimental data. Firstly, a study is performed using a numerical simulation based on fixed-fixed beam structure. The numerical study is followed by a case involving actual measured data for the case of an F-shaped test structure. The updated results have shown that the iterative method gives 20% better matching of FRFs with the experimental data and also the predictions of the iterative method is better than the direct method beyond the considered frequency range. The updated results have shown that the FE model obtained using the response function method, an iterative method, can be used to derive accurate model of the system. Updated models obtained by both methods are subsequently evaluated for its application in dynamic design.

RF MEMS tunable filter using micro fixed–fixed beam

AbstractIn this article, a tunable bandpass filter using micro fixed‐fixed beam structure is designed, simulated, and fabricated. The filter is designed by micromachined capacitive bridges, with an original passive topology. The fabricated filter occupies a chip area of 12 × 3 mm2 and achieved an insertion loss of less than 2 dB and return loss of less than −15 dB throughout the operation band, thereby tuning the filter centre frequency by 11% between 8.76 and 9.8 GHz. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 592–597, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24981

Modeling and Characterization of ALD Grown ZnO Nanotubes and their Application to Sub-Micron Devices

Characteristic properties and dimensions of ZnO nanowires grown by ALD and template technology have been used to model a nanowire into a fixed-fixed beam structure using conventional microelectromechanical systems (MEMS) design techniques. The frequency response of the structure as a result of piezoelectric actuation has been studied. Percentage error between the simulation and theoretical model has been found to be 0.97%.

Reduced-Order Modeling of Weakly Nonlinear MEMS Devices With Taylor-Series Expansion and Arnoldi Approach

In this paper, we present a new technique by combining the Taylor series expansion with the Arnoldi method to automatically develop reduced-order models for coupled energy domain nonlinear microelectromechanical devices. An electrostatically actuated fixed-fixed beam structure with squeeze-film damping effect is examined to illustrate the model-order reduction method. Simulation results show that the reduced-order nonlinear models can accurately capture the device dynamic behavior over a much larger range of device deformation than the conventional linearized model. Compared with the fully meshed finite-difference method, the model reduction method provides accurate models using orders of magnitude less computation. The reduced MEMS device models are represented by a small number of differential and algebraic equations and thus can be conveniently inserted into a circuit simulator for fast and efficient system-level simulation.

A new in situ residual stress measurement method for a MEMS thin fixed-fixed beam structure

A new method is described to measure the in situ residual stress state in a thin fixed-fixed beam structure used in microelectromechanical systems (MEMS). The methodology can be applied to devices at the anticipated operational and environmental temperatures. The new technique makes use of differences in the thermal expansion coefficient between the thin beam and the substrate. The residual stress distribution is determined by matching the thermal deflections from a finite element model (FEM) to measured deflections of the beam. All previous residual stress measurement methods for MEMS suspended structures reported a uniformly distributed residual stress. Experimental data coupled with the new analytical method suggests that this may not be adequate for the case of a suspended thin structure with nonplanar surface topology. A stress gradient through the thickness must be included in the determination of the stress state of the beam. The new method indicates a spatially varying residual stress distribution and is capable of de-coupling the mean stress and the stress gradient through the thickness. It was found through an extensive literature review that the quantification of the stress gradient in a thin suspended structure has never been reported. The de-coupling makes the prediction of the stress state at different temperature points possible. Details of the new method are demonstrated and discussed by the use of a capacitive radio frequency (RF) MEMS switch.