Geometrical Effects on the Dynamical Behavior of MEMS structures

(2010, May 16)

The influence of geometrical dimensions on the dynamical behavior of polysilicon MEMS structures configurations is studied and presented in this paper. Electrostatically actuated MEMS components as ... [more ▼]

The influence of geometrical dimensions on the dynamical behavior of polysilicon MEMS structures configurations is studied and presented in this paper. Electrostatically actuated MEMS components as microbridges and microcantilevers are used to investigate the coupled electro-mechanic effect, frequency responses and the dynamic bending stress. The electrostatic principle is common in sensing and acting devices and there are many MEMS structures subjected to electrostatic forces. [less ▲]

Prediction of Stiction in Microswitch Systems

in EUROSIME 2010 (2010)

Stiction is a major failure mode of MEMS as microscopic structures tend to adhere to each other when their surfaces enter into contact. Although increasing the restoring forces of switch devices could ... [more ▼]

Stiction is a major failure mode of MEMS as microscopic structures tend to adhere to each other when their surfaces enter into contact. Although increasing the restoring forces of switch devices could overcome the stiction effect, this is not practical, as in turn, it also increases the actuation voltage. Therefore stiction prediction is important to be considered when designing micro- and nano- devices. In this paper, the numerical prediction of stiction for capacitive MEMS switches is considered. Toward this end, a micro-adhesive-contact law is derived from previous work and combined with a finite-element model. [less ▲]

Design of Microswitch Systems Avoiding Stiction due to Surface Contact

in SEM 2010 Annual Conference & Exposition on Experimental and Applied Mechanics (2010)

Stiction which results from contact between surfaces is a major failure mode in micro electro-mechanical systems (MEMS). Increasing restoring forces using high spring constant allows avoiding stiction but ... [more ▼]

Stiction which results from contact between surfaces is a major failure mode in micro electro-mechanical systems (MEMS). Increasing restoring forces using high spring constant allows avoiding stiction but leads to an increase of the actuation voltage so that the switch’s efficiency is threatened. A statistical rough surfaces interaction model, based on Maugis’ and Kim’s formulations is applied to estimate the adhesive forces in MEMS switches. Based on the knowledge of these forces, the proper design range of the equivalent spring constant, which is the main factor of restoring force in MEMS switches, can be determined. The upper limit of equivalent spring constant depends mainly on the expected actuator voltage and on the geometric parameters, such as initial gap size and ,thickness of dielectric layer. The lower limit is assessed on the value of adhesive forces between the two contacting rough surfaces. It mainly depends on the adhesive work of contact surfaces and on the surfaces’ roughness. In order to study more complicated structures, this framework will be used in a multiscale model: resulting unloading micro adhesive contact-distance curves of two rough surfaces will be used as contact forces in a finite-element model. In this paper the extraction of these curves for the particular case of gold to gold micro-switches is pursued. [less ▲]

Introduction to Electromechanical Coupling

in Computer and Experimental Simulations in Engineering and Science [=CESES] (2010), (7),

This paper is dedicated to the physical understanding of electrostatic forces with a one-dimensional reference problem. First a non-dimensional analysis prescribes the kind of assumptions to consider for ... [more ▼]

This paper is dedicated to the physical understanding of electrostatic forces with a one-dimensional reference problem. First a non-dimensional analysis prescribes the kind of assumptions to consider for the electric field model. An analytical study of electro-mechanical coupling is then performed to understand the type of non-linearity added by electrostatic forces, and static and dynamic analysis are used to define new characteristic parameters. To come closer to more realistic problems, cubic mechanical stiffness is added to account for the large displacement hypothesis prescribed for certain types of MEMS and damping effects are studied. [less ▲]

Dual approach for an accurate estimation of pull-in voltage

in Proceedings of the IVth European Conference on Computational Mechanics (ECCM 2010) (2010)

Influence of Adhesive Rough Surface Contact on Micro-Switches

in Journal of Applied Physics (2009), 106(11), 113502

Stiction is a major failure mode in micro electro-mechanical systems (MEMS). Undesirable stiction, which results from contact between surfaces, threatens the reliability of MEMS severely as it breaks the ... [more ▼]

Stiction is a major failure mode in micro electro-mechanical systems (MEMS). Undesirable stiction, which results from contact between surfaces, threatens the reliability of MEMS severely as it breaks the actuation function of MEMS switches for example. Although it may be possible to avoid stiction by increasing restoring forces using high spring constants, it follows that the actuation voltage has also to be increased significantly, which reduces the efficiency. In our research, an electrostatic-structural analysis is performed to estimate the proper design range of the equivalent spring constant which is the main factor of restoring force in MEMS switches. The upper limit of equivalent spring constant is evaluated based on the initial gap width, the dielectric thickness, and the expected actuation voltage. The lower limit is assessed on the value of adhesive forces between the two contacting rough surfaces. The MEMS devices studied here are assumed to work in a dry environment. In these operating conditions only the Van der Waals forces have to be considered for adhesion. A statistical model is used to simulate the rough surface, and the Maugis’s model is combined with Kim’s expansion to calculate adhesive forces. In the resulting model, the critical value of the spring stiffness depends on the material and surface properties, such as the elastic modulus, surface energy and surface roughness. The aim of this research is to propose simple rules for design purposes. [less ▲]

Influence of Adhesive Rough Surface Contact on Micro-Switches

Scientific conference (2009)

Dual Approach for Electromechanical Coupling in MEMS

(2009)

In this paper we present an approach for the computation of coupled electromechanical problems in micro-electromechanical systems based on a vector potential formulation of the electrostatic problem. This ... [more ▼]

In this paper we present an approach for the computation of coupled electromechanical problems in micro-electromechanical systems based on a vector potential formulation of the electrostatic problem. This formulation is the dual of the scalar potential approach commonly used in the literature. We present an analytic derivation of the force computed using this dual method based on the virtual work principle, and compare the primal and dual approaches on the finite element solution of simple twodimensional test-cases. [less ▲]

High Vibration Sensors: Modelling, Design and Integration

in Proceedings of Thermal, Mechanical and Multiphysics Simulation and Experiments in Micro-Electronics and Micro-systems EuroSime (2009)

Since many years, the University of Liège is involved in micro-electronics and microelectromechanical systems modelling, design and integration. Recently, the University of Liege had received the ... [more ▼]

Since many years, the University of Liège is involved in micro-electronics and microelectromechanical systems modelling, design and integration. Recently, the University of Liege had received the opportunity to build a brand new infrastructure (clean rooms – ISO 7) with specific equipments for packaging and MEMS characterisation. This new facility (clean rooms and equipments) enables the University to be very well positioned in the nano/micro-electronics modelling, analysis and packaging world and is now able to answer specific research and related industrial needs. In this paper we consider the design of a vibration sensor in its significantly vibrating surroundings and investigate in its dynamical behaviour. Environmental vibrations affect the sensor part of the MEMS device and influence the choice of the “best” packaging methods for the application. Within the framework of packaging, we consider a simple test application ensuring best interconnection technology. Dynamical investigations include a preliminary analysis of the packaging and a separate finite-element analysis of the MEMS device (inside the package), testing the device under the condition of a harsh environment (high vibration spectral level). Computations are proposed in combination with experimental observations. [less ▲]

Multiphysic topology optimization of electromechanical microdevices considering pull-in voltage using an electrostatic force filter

in Proceeding of the 8th World Congress on Structural and Multidisciplinary Optimization (2009)

Electrostatic actuation is often used in microsystems as it is relatively easy to implement and provides a short response time. However, because of the non-linearity of electrostatic forces, these devices ... [more ▼]

Electrostatic actuation is often used in microsystems as it is relatively easy to implement and provides a short response time. However, because of the non-linearity of electrostatic forces, these devices may suffer from an unstable behavior called pull-in effect. Previous work of the authors intended to delay pull-in effect by maximizing pull-in voltage studying a simplified problem where the optimization domain was purely mechanical. The present paper generalizes the approach by considering a multiphysic optimization domain. However, the generalization of the optimization problem is not straightforward as local pull-in modes appear after a few optimization iterations. Therefore, the paper investigates several solutions to prevent the appearance of local pull-in modes. [less ▲]