Contact behavior evolution induced by damage growth in radio-frequency microelectromechanical system switches

Abstract

This study provides a two-contact-event model to explain the evolution of the contact behavior of microelectromechanical system (MEMS) switches through their lifetime. The succession of two dynamic contact events is carefully considered during actuation inspired by experimental observations. The contact between the MEMS switch tip and the drain can be treated as an effective contact between an elastic hemisphere and a rigid plane. If the first contact event results in elastic deformation, the effective hemisphere will fully recover. Consequently, the subsequent contact event also produces elastic deformation. If, on the other hand, the first contact event induces elastoplastic or plastic deformation, a residual depth will be produced between the hemisphere and the rigid plane. The contact force of the subsequent contact event can be significantly reduced due to this additional residual depth. With the growth of residual depth during the switch cycling process, the modeling results show three possible situations of contact radius evolution: (1) The contact radius increases to a maximum value and then decreases to zero; (2) the contact radius increases to one local maximum value; then decreases to a local minimum value; subsequently increases again to another maximum value, and finally decreases to zero; and (3) the contact radius increases to one maximum value and then decreases to zero; after an intermittent response, the contact radius increases again to another maximum value and finally decreases to zero. Furthermore, the Maxwell spreading formula is applied to determine the contact resistance which is inversely proportional to the contact radius. Three situations of contact resistance evolution corresponding to the evolution of contact radius are obtained. All three situations are also observed and validated by the experimental results.