Search

This paper reports the theoretical and experimental characterization of a new z-axis silicon resonant micro accelerometer fabricated by the THELMA © surface micromachining technique, characterized by differential sensing and very small dimensions. The working principle of this device is based on the variation of the electrostatic stiffness of two torsional resonators. This work is a prosecution of the research on resonant accelerometers published in [1,2] . [ABSTRACT FROM AUTHOR]

The proper estimate of capillary attraction is of great importance in many situations, for example the reliability assessment of Micro- Electro-Mechanical Systems (MEMS) with respect to spontaneous adhesion. In spite of many theoretical studies, there is a lack of general methods for obtaining the exact shape of the liquid meniscus between the asperities of rough surfaces. In this paper, a new analytical method is developed for the specific case of axysimmetric configurations. The outcomes of such a method are critically compared with the approximate solution which is usually proposed in the literature. Moreover, an improved simplified method is constructed and validated. Finally, a more general procedure (based on the Finite Element Method) is proposed, with possible application to non-symmetric geometries. [ABSTRACT FROM AUTHOR]

A new out-of-plane resonant micro-machined accelerometer has been designed, modelled and fabricated. The sensing principle is based on the variation of the electrostatic stiffness of two torsional resonators mechanically coupled with an inertial proof mass. The accelerometer, fabricated by the ThELMA ® surface micro-machining process of STMicroelectronics, constitutes a further step of a research focussing on the design of in-plane and out-of-plane resonant micro accelerometers. Preliminary electrostatic measures of the torsional resonators response have been compared with the theoretical predictions. [ABSTRACT FROM AUTHOR]

Adhesion phenomena in poly-silicon Micro-Electro-Mechanical Systems (MEMS) are here studied by means of experimental characterization and numerical simulation. In the experimental part, the adhesion energy is measured on-chip by means of on-purpose designed and fabricated devices; moreover, the surface roughness is characterized through the Atomic Force Microscope. For the numerical part, a specific method is developed to simulate the process of adhesion based on a numerical description of surface roughness, on simplified modeling of adhesion forces due to van der Waals and capillary attraction and on non-linear constitutive modeling for polysilicon surfaces. [ABSTRACT FROM AUTHOR]

Abstract: Coupled electro-mechanical problems are frequently encountered when dealing with micro electro-mechanical systems (MEMS) with capacitive actuation and/or readout systems; their numerical solution can be extremely time consuming, due to the nonlinearity of the coupling terms. Coupled electrostatic – structural dynamic simulations are carried out in this paper through an innovative numerical procedure, based on the combined use of a domain decomposition technique and of a proper orthogonal decomposition methodology. The approach is assessed through the analysis of the dynamic response of a doubly clamped beam and of a plane resonator subjected to an electrostatic actuation, showing computational gains up to 98%. [Copyright &y& Elsevier]

Abstract: An innovative approach for the numerical study of spontaneous adhesion (or stiction) phenomena in Micro-Electro-Mechanical Systems (MEMS) is proposed, based on the use of 3D Finite Element (FE) models. Stiction is a major reliability problem in MEMS which can completely destroy the normal mobility of parts which have the task e.g. to sense the external acceleration in micro-accelerometers or the rotation velocity in micro-gyroscopes. Capillary and van der Waals forces are first selected as the most important sources of stiction; subsequently, these forces are modelled in a simplified way in view of their introduction in a FE model. As a second important ingredient in the proposed modelling approach for spontaneous adhesion, rough surfaces are numerically generated by making use of suitably adapted algorithms originally developed for tribology studies. A complete 3D FE model for two rough surfaces which come at very short distances is thus built and various results showing the modelling capabilities are shown. A comparison with experimental results recently appeared in the literature is proposed. [Copyright &y& Elsevier]

SUMMARY A domain decomposition approach for the solution of the coupled electro-mechanical problem in dynamics is proposed. The finite element analysis of a coupled electro-mechanical system is frequently found, for example, in the modelling and design of microsystems and may lead to a burdensome nonlinear problem solution, particularly in the dynamic case. Two versions of the algorithm are proposed: the first one, called single-level decomposition, exploits the natural partition of the analysis domain given by the two physics to be solved; the second one, called two-level decomposition, adds a further subdivision of each physics into subdomains. The multilevel domain decomposition strategy here proposed is shown to accurately predict the response of microsystems subjected to electro-mechanical coupling and to allow for a significant reduction in the computational burden. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The main aim here is to present the application of the generalized stochastic perturbation technique to thermo-piezoelectric analysis of solid continua. The general nth order Taylor series representation for all random input parameters and the state functions is employed to formulate the coupled thermo-electro-elasticity equilibrium equations of the additional order; a determination of any probabilistic moments and characteristics is described; the discretization of the problem in terms of the Stochastic perturbation-based Finite Element Method is also provided. Since this expansion includes the lowest order partial derivatives, the structural sensitivity analysis using direct differentiation is performed at the same time with probabilistic modeling contrasted with the Monte-Carlo simulation results. The probabilistic approach is extended here towards an accounting for the stochastic ageing processes, which appear frequently in aggressive external environments and under dynamic excitation. The two parametric stochastic process with Gaussian initial value and ageing velocity is tested for this purpose. The entire procedure is tested on the example of the thermo-electro-elastic pulsation of the beam modeled analytically using the symbolic software MAPLE, where polynomial approximations, design sensitivities, probabilistic moments and their histories are computed and visualized. [ABSTRACT FROM AUTHOR]

novel design strategy to avoid pull-in occurrence in electrostatic micro electro mechanical systems is proposed. It combines charge control with ring electrodes, on a circular geometry. This idea is introduced here for the design of efficient and reliable high stroke electrostatic diaphragm micropumps, while it has a broad potential applicability. A minimal lumped one degree-of-freedom model is derived and used to introduce and demonstrate the proposed approach for a circular plate geometry. Finite element models are subsequently adopted for a more detailed device modelling. As expected, charge control exhibits a stabilizing effect with respect to voltage drive, but not sufficient to achieve a full-range stability for the considered geometry. When the electrode area is properly defined, stability range can be extended up to gap closure in the central part of the membrane. In this configuration, the increase in voltage required for full-range device drive would be relevant, while in charge control the penalty is considerably lower. Finally, loading conditions and geometrical parameters for an optimized actuation are suggested. [ABSTRACT FROM AUTHOR]