EARLY-STAGE ANALYSIS FOR MEMS STRUCTURAL OPTIMIZATION II: ITS APPLICATION TO MICRORELAY RELIABILITY

摘要

This paper discusses a new structural optimization methodology for MEMS and its application to reliability evaluation of micro relays. Clarifying the relationship between system characteristics and design factors, our new design optimization method (called MESA) enables numerical evaluation of MEMS structures at the concept design stage. The relation is defined as sensitivity, which is calculated based on the system governing equations with an experimental method technique and a FEM analysis. The sensitivities show not only the effect of design parameters for the system performances but also the system tradeoffs. The MESA allows designers to obtain "rough" total system performance and create a new concept. The MESA is successfully applied to evaluate an electrostatic microrelay for DC/RF signal switching. With the aid of the MESA, we define existing problems of current cantilever-shape MEMS switches and propose new mechanical approaches in order to enhance the mechanical reliability. The MESA clearly shows us that there are tradeoffs in the switching phenomenon of cantilever microrelay. Based on the MESA information, a new switching concept, which has tri-state multi-finger lateral contacts, is established and the MEMS structure is designed and fabricated. The tri-state switching concept reduces the number of contacts and also disperses the impact energy, which aggravates adhesion. In addition, bi-electrostatic actuators increase the adverse force to prevent stiction without the increase of restoring force, which causes degradation or cracks of the contact surfaces. Furthermore, a new push-pull switching structure is designed as a second generation by means of the MESA. The MESA shows that the second concept will provide superior mechanical performance with keeping the high RF isolation.