FEM Modeling of Squeeze Film Damping Effect in RF-MEMS Switches

A very important aspect in the design of RF- MEMS switches, is to obtain low switching time. The switching time not only depends on the device geometric parameters but also on the operating conditions. This paper presents the squeeze film damping effect on the dynamic response of the RF-MEMS switches. The squeeze film damping effect, with and without perforations, on the switching time is analyzed using finite element method (FEM) simulations. The effect of temperature and humidity on the squeeze film damping and switching time is also investigated

Design optimization of RF-MEMS switch considering thermally induced residual stress and process uncertainties

This paper presents the Design of Experiments (DOE) based parametric design optimization of the Symmetric Toggle RF-MEMS Switch (STS) for minimizing the actuation voltage considering the fabrication process uncertainties and thermally induced residual stress. Initially, three-dimensional (3D) non-linear Finite Element Method (FEM) models are developed and the formation of residual stress during the plasma etching step of the microfabrication process is explained using the Bauschinger effect. The pull-in voltage values and the switch profiles obtained after the thermal loading-unloading cycle in the FEM models are compared with the experimental values and optical profile measurements which showed a close agreement. A DOE based Dual Response Surface Methodology (DRSM) is implemented to identify the significant design parameters affecting the STS switch pull-in voltage in the presence of thermally induced residual stress. Two separate response surface empirical models are developed; one for the mean pull-in voltage and other for variation in the pull-in voltage due to microfabrication process tolerances. The developed response surface models are optimized simultaneously using the desirability function approach. The optimal levels of the design parameters that result in minimum pull-in voltage with increased insensitivity to process uncertainties are obtained using the direct search algorithm

Modeling and experimental verification of thermally induced residual stress in RF-MEMS

Electrostatically actuated radio frequency microelectromechanical systems (RF-MEMS) generally consist of microcantilevers and clamped-clamped microbeams. The presence of residual stress in these microstructures affects the static and dynamic behavior of the device. In this study, nonlinear finite element method (FEM) modeling and the experimental validation of residual stress induced in the clamped-clamped microbeams and the symmetric toggle RF-MEMS switch (STS) is presented. The formation of residual stress due to plastic deformation during the thermal loading-unloading cycle in the plasma etching step of the microfabrication process is explained and modeled using the Bauschinger effect. The difference between the designed and the measured natural frequency and pull-in voltage values for the clamped-clamped microbeams is explained by the presence of the nonhomogenous tensile residual stress. For the STS switch specimens, three-dimensional (3D) FEM models are developed and the initial deflection at zero bias voltage, observed during the optical profile measurements, is explained by the residual stress developed during the plasma etching step. The simulated residual stress due to the plastic deformation is included in the STS models to obtain the switch pull-in voltage. At the end of the simulation process, a good correspondence is obtained between the FEM model results and the experimental measurements for both the clamped-clamped microbeams and the STS switch specimens

A Dual-Mass Resonant MEMS Gyroscope Design with Electrostatic Tuning for Frequency Mismatch Compensation

The micro-electro-mechanical systems (MEMS)-based sensor technologies are considered to be the enabling factor for the future development of smart sensing applications, mainly due to their small size, low power consumption and relatively low cost. This paper presents a new structurally and thermally stable design of a resonant mode-matched electrostatic z-axis MEMS gyroscope considering the foundry constraints of relatively low cost and commercially available silicon-on-insulator multi-user MEMS processes (SOIMUMPs) microfabrication process. The novelty of the proposed MEMS gyroscope design lies in the implementation of two separate masses for the drive and sense axis using a unique mechanical spring configuration that allows minimizing the cross-axis coupling between the drive and sense modes. For frequency mismatch compensation between the drive and sense modes due to foundry process uncertainties and gyroscope operating temperature variations, a comb-drive-based electrostatic tuning is implemented in the proposed design. The performance of the MEMS gyroscope design is verified through a detailed coupled-field electric-structural-thermal finite element method (FEM)-based analysis

Experimental investigations of creep in gold RF-MEMS microstructuresSmart Sensors, Actuators, and MEMS VII; and Cyber Physical Systems

Lifetime prediction and reliability evaluation of micro-electro-mechanical systems (MEMS) are influenced by permanent deformations caused by plastic strain induced by creep. Creep in microstructures becomes critical in those applications where permanent loads persist for long times and thermal heating induces temperature increasing respect to the ambient. Main goal of this paper is to investigate the creep mechanism in RF-MEMS microstructures by means of experiments. This is done firstly through the detection of permanent deformation of specimens and, then, by measuring the variation of electro-mechanical parameters (resonance frequency, pull-in voltage) that provide indirect evaluation of mechanical stiffness alteration from creep. To prevent the errors caused be cumulative heating of samples and dimensional tolerances, three specimens with the same nominal geometry have been tested per each combination of actuation voltage and temperature. Results demonstrated the presence of plastic deformation due to creep, combined with a component of reversible strain linked to the viscoelastic behavior of the material

Creep in MEMS

The study of creep in MEMS is crucial for their lifetime prediction and reliability evaluation. The experimental approaches used in macromechanics can be extended to the microscale if their effectiveness is proved by dedicated experiments. This goal may provide more general validity of creep effects prediction in MEMS, instead of spotted experiments on single devices like those ones reported in most of the work presented in literature. The demonstration of the validity of some established creep models and experimental methodologies also in the micromechanics is the goal of this paper

Effect of creep in RF MEMS static and dynamic behavior

This paper presents the experimental characterization of the creep effect in electrostatically actuated gold microstructures. The tested specimens follow the typical configuration of the microbridge based radio frequency microelectromechanical systems switches and varactors. Initially, the plastic creep strain accumulation with time is measured for the specimens with different geometric dimensions and at different actuation voltages and temperatures. To avoid the size and cumulative heating effects, three specimens with the same geometric dimensions, actuation voltages and constant temperatures are tested. The test results allowed decoupling the permanent plastic strains due to the creep effect and reversible anelastic strains due to the viscoelastic behavior. The pull-in voltage and natural frequency values measured before and after the creep tests are compared, revealing the mechanical stiffness decrease caused by creep