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Stiction is a major failure mode in microelectromechanical 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. [ABSTRACT FROM AUTHOR]

This paper presents a fast design strategy for MEMS capacitive pressure sensors with sealed cavities. Based on circular Kirchhoff-Love plate theory and the perfect gas law, the underlying analytical model allows for a rapid and accurate evaluation of the sensitivity of the sensors, crucial for improving their design in function of the reference pressure applied in the sealed cavities. The accuracy of the new model is demonstrated by comparing its predictions with more computationally expensive simulation techniques (high-order parametric element and three-dimensional finite element models) and with experimental measurements performed on a 300 µm diameter membrane fabricated using the Poly-SiGe platform developed at imec. [ABSTRACT FROM AUTHOR]

Abstract: In micro-electromechanical systems (MEMS), coupling of structures through electrostatic forces is a primordial phenomenon. Simulating the dynamics of MEMS and taking into account such strong coupling effects allows one to predict dynamical performance and stability, and is therefore an essential issue in the design of highly effective and reliable devices. Analysis techniques for such systems require special attention in order to provide to the designer accurate and fast tools. We propose a finite element approach (FEM) that properly handles the strong electromechanical coupling in MEMS. In the simulation example of a micro-bridge, we show that such simulation techniques can reveal complex dynamical behaviors of MEMS such as dynamic pull-in. [Copyright &y& Elsevier]