Experimental characterization of electrostatically actuated in-plane bending of microcantilevers

Abstract

Experimental validation of numerical models developed by the authors to predict the static behaviour of microelectrostatic actuators is described. Cantilever microbeams, currently used in connection with RF-MEMS and micro-scale material testing were analysed. A set of microcantilevers, bending in the plane of the wafer, i.e. in the same plane as the profiling system's target, was tested. This differs from the popular case of out-of-plane microbeams, usually studied in the literature. Geometry nonlinearity caused by large deflection of the microbeam was investigated and nonlinear coupled formulation of electromechanical equilibrium was performed. Coupledfield analysis was implemented using the Finite Element Method (FEM), to predict displacements and pull-in voltage measured by Fogale Zoomsurf 3D, subsequently plotting the displacement-versus-voltage curve to complete model validation. FEM nonlinear analysis, based on iterative approach with mesh morphing, and FEM nonincremental approach, including a special element proposed by the authors, are compared to the linear solution and to experimental results. Geometry nonlinearity appears relevant in microbeam modelling and requires a nonlinear solution of the coupled problem. Investigative work, which compared the results of 2D and 3D models to experimental data, revealed that some three dimensional effects are significant in model validation, but the 2D approach may be effective in predicting static behaviour provided that at least a microbeam thickness equivalent is adopted.

Role of the electro-thermo-mechanical multiple coupling on the operation of RF-microswitch

“…Provided that geometrical dimensions were precisely measured, this result could be related either to an existing axial loading, like in case of tensile residual stress, or to a imprecise measurement of elastic properties of gold, after microfabrication. Several microcantilevers microfabricated on the same wafer where microswitches were processed, allowed verifying and measuring the material elastic properties and detecting their first resonance frequency and pull-in voltage, as in (Espinosa et al 2006;Ballestra et al 2008). Actually resonance frequency and pull-in voltage are related to the elastic properties of material, therefore both those inputs leaded to verify the Young modulus of gold certified by the microfabricator, within a tolerance of few percents.…”

“…A sequence of thermal and electromechanical loading conditions was applied. Iterative and sequential approaches to solve the coupled problem were implemented according to Munteanu 2006a, 2006b;Ballestra et al 2008;Bettini et al 2008;Brusa et al 2010b;Somà et al 2010). Among several numerical results obtained only the most impressive results will be herein proposed.…”

“…Pull-in and pullout phenomena are very seldom easily predicted, because they are affected by several phenomena occurring during the microswitch actuation. Up to now the intrinsic nonlinearity of the electromechanical coupling in static and dynamic behaviors was already deeply investigated and modeled by several authors, including those of this paper (Jing 2003;Reid 2003;Brusa et al 2004;Ballestra et al 2008;Bettini et al 2008). Interaction between electromechanical actions and environmental fluid surrounding the MEMS was evenly analysed (Veijola et al 2009).…”

Experimental verification of an out-of-plane repulsive-force electrostatic actuator using a macroscopic mechanism

“…Conventional micro electrostatic actuators use the attractive force between two parallel electrodes to generate movement, i.e., the two electrodes move towards each other. Attractive force micro electrostatic actuators suffer from the ''pull-in'' collapse problem (Degani et al 1998;Ballestra et al 2008;Rezazadeh et al 2007) and thus have a limited stroke and low reliability.…”

Optimal Design of Capacitive Micro Cantilever Beam Accelerometer

“…Cantilever beams are widely used as the basic components in micro-sensors, micro-switches and RF-MEMS as well as in experimental micromechanics for evaluating mechanical properties and the strength of materials (Ballestra et al, 2008).…”