Dynamic Analysis Of Contact Characteristics Between The Film/substrate And Micro-cantilever With A Rough Surface

RF MEMS switch is a kind of device that using the mechanical movement to control the transmission of radio frequency signals.After repeated use,it will produce many problems such as adhesion,film-delamination,film-rupture and so on.The film/substrate and micro-cantilever is an important part of the DC contact RF MEMS switch,and the surface between them is rough,so that their contact characteristics determine the working reliability of the micro mechanical switch.This article establishes a contact model between the film/substrate and the micro-cantilever,which both have a rough surface,considering the elastic-plastic deformation,micro cantilever elastic restoring force,adhesion force,interaction between asperities,to analysis contact force and contact area of the thin film surface,elastic-plastic deformation and damage analysis of the film,thin film/substrate’s von Mises equivalent stress and so on.The results show that there exist many obvious contact and separation phenomena between the film/substrate and micro-cantilever beam in a single loading and unloading process,with great impact force,which is bad for the stability of the system.In the process of contact with each asperity,the position of the maximum equivalent stress occurs at a certain depth under the surface;the different working process of its position will be change accordingly,but always within the film.Besides,the film takes much of the external load,and the equivalent stress value of equivalent stress value is larger than that of the substrate.Due to the existence of the film,the stress of the base is greatly reduced,which protects the base;because the strength of the interfacial layer is strong,the protective effect of the film to the substrate is enhanced.The contact between the micro-cantilever and the surface of the film is just the contact between some higher asperities,which makes the real contact area relatively smaller than the nominal area of contact,and this is the source of the impact force.Elastic-plastic deformation is one of the main deformations of film/substrate,which directly reflect the relationship of stress and strain.In a single loading and unloading process,the film/substrate system mainly produces elastic deformation,plastic deformation is small and concentrates at the top and around of the asperity.Elastic-plastic deformation is affected by the impact force,especially the influence of the first impact force in the process of loading.In other conditions unchanged,adhesive force model is applied,this article establishes the contact model between the micro-cantilever and film/substrate with adhesive force.Then,the impact of film and adhesive force to the contact characteristics of the system is analyzed.The results show that the existence of the thin film has protective effect to the substrate;the impact of the film on the model is due to the interface layer.In the transfer process of the stress,the interface layer has the characteristics of timeliness.Adhesion between asperities affects the contact area,contact force and elastic-plastic deformation;the specific performance is that the contact area is stepped,the stress and contact force decrease,the number of impact decreased.Because of the influence of adhesion,the micro-cantilever ends and film/substrate is not immediately separated during unloading process.This study will enrich the research of film/substrate system,improve the reliability of RF MEMS switch,and provide theoretical basis for its design.