A comparison of the predictions of a finite element model and multiscale model for a rough MEMS electrical contact

Rough surface contact is difficult to model effectively due to multiple scales of detail that need to be considered. This work presents the results of a multiscale rough surface contact model in comparison to a finite element based deterministic model for the electrical contact of a MEMS microswitch. The real area of contact and electrical contact resistance are predicted and compared as a function of normal load. The results show good quantitative and qualitative correlation between the two methods. As expected, the contact area increases nominally linearly with load, while the contact resistance decreases with load. It is notable though that the contact pressure is up to 16% higher than the hardness (2.8 times yield strength), and could be even higher for other surfaces

Finite element based surface roughness study for ohmic contact of microswitches

Finite element method (FEM) is used to model ohmic contact in microswitches. A determinist approach is adopted, including atomic force microscope (AFM) scanning real contact surfaces and generating rough surfaces with three-dimensional mesh. FE frictionless models are set up with the elastoplastic material and the simulations are performed with a loading-unloading cycle. Two material properties, gold and ruthenium, are studied in the simulations. The effect of roughness is investigated by comparing the models with several smoothing intensities and asperity heights. The comparison is quantitatively analyzed with relations of force vs. displacement, force vs. contact area and force vs. electrical contact resistance (ECR); further the evolution of spots in contact during a loading-unloading cycle is studied

Modélisation par éléments finis du contact ohmique de microcommutateurs MEMS

Les microcommutateurs MEMS ohmiques comportent un contact électrique sous très faible force, très sensible à des paramètres difficiles à maîtriser. Ce contact a été l'objet d'une méthode de modélisation développée précédemment au LAAS-CNRS, dont le principe consiste à effectuer une simulation par éléments finis du contact mécanique avec les données AFM puis évaluer analytiquement la résistance électrique. Cette thèse a pour objectif d'évaluer les possibilités d'extension de cette méthode à des simulations multiphysiques.La thèse comporte une partie dédiée à la validation de la simulation mécanique par éléments finis par rapport à des résultats expérimentaux obtenus précédemment.Des simulations multiphysiques sont alors réalisées et les résultats en termes de résistance électrique sont comparés avec des résultats expérimentaux. On observe une très forte sous estimationde la résistance électrique, et donc des élévations de température. Ce constat est attribué à la présence de films isolants en surface d'une au moins des surfaces de contact.Enfin, des modèles qui incluent un film isolant sont développés avec une géométrie simplifiée d'aspérité. Les modèles les plus intéressants incluent des "nanospots": le film isolant est parsemé de zones conductrices, de très faibles dimensions. Les résultats permettent de cerner les caractéristiques typiques possibles de la géométrie dans cette configuration.MEMS ohmic microswitches include very low force electrical contacts. These are very sensitive to parameters which reveal difficult to control. A previously developed modelization method consists in computing mechanical contact using finite elements, then estimating electrical resistance using analytical expressions. Here we focus on the possibilities of multiphysical finite element computations instead.Validation of the contact mechanical computation is first attempted, based on experimental results of previous works. Multiphysical contact computations are carried out. Resulting electrical contact resistance isfound to be much lower than experimental results. The presence of insulating surface films is supposedly the cause for that. Eventually, a simplified geometry for asperities is used to build models with insulating films.The most relevant models feature nanospots : some very small conductive areas are scattered on the contact area. The results allow us to determine some possible geometry configurations that could lead to contact resistance values such as those measured on real devices.TOULOUSE-INSA-Bib. electronique (315559905) / SudocSudocFranceF

Validation of Finite Element Structural Simulation for Ohmic Microcontact

AbstractIn the current literature, there is no model able to accurately predict the electrical resistance value of rough micro- contacts. Such model requires a coupled thermo-electro-structural analysis that is very difficult to validate in a straightforward manner. In the present approach, atomic force microscopy (AFM) scanned data of contact surface with roughness are used to build finite element (FE) model. As a first step towards multiphysics analysis, the aim of this study is to validate results of structural simulation of a rough gold micro-contact.A setup with a nanoindenter and a real microswitch is used to extract force-displacement curves. These results are compared to FE simulations which allow evaluating the effects of the main parameters. It is shown that the accuracy of these structural simulations is acceptable for an accurate evaluation of the electrical contact resistance

Hybrid Regional Aircraft: A Comparative Review of New Potentials Enabled by Electric Power

This article assesses the benefits of hybridization within the regional aircraft scale using a conventional twin-turbo propeller aircraft as reference. For a fair comparison, this reference aircraft was designed assuming a 2035 technology level. The propulsion system of the reference aircraft is analyzed along the mission and the phases of flight with low efficiencies are highlighted. Then the potential benefits of new power management through the use of secondary power generation systems but also through the variation of the size of prime movers are presented and discussed. In particular, the effect of the gas turbine size on its efficiency is studied. Finally, the article focuses on aerodynamic improvements enabled by new propeller or fan integrations and the associated concepts such as differential thrust, blown wing and boundary layer ingestion. For each topic, simplified analyses provide estimated potential of energy saving. These results can be used as indicators for selecting the most promising hybrid architecture concepts for a regional aircraft

Hybrid Propulsion for Regional Aircraft: a Comparative Analysis based on Energy Efficiency

This article assesses the potential benefits of transient energy storage for a hybrid regional aircraft. The mission profile of a reference aircraft is analyzed according to energetic intermittence and the results are compared to typical figures for cars, trains, and ships. Also, the opportunity of recovering energy in descent and during landing is studied. This article shows that energy saving potential brought by transient energy storage is much smaller than for ground-based transportation. In addition, energy recovering does not bring benefit on a hybrid aircraft in normal operation. Nevertheless, the best energy management strategies in descent are highlighted and the use of a hybrid propulsion system in this phase shows significant potential energy savings. Finally, the article addresses other strategies enabled by hybrid propulsion to improve the aircraft energy efficiency