Reducing Stress Concentration in RF MEMS Switch by Optimizing Serpentine Spring Design

In this paper we present a method of reducing stress concentrations in serpentine beam structures to improve the fatigue life of RF MEMS switches. It was found that slight design modifications to the turning corners of serpentine springs can greatly improve the uniformity of stresses through the structure with minimal negative impact on the original spring constant. Before RF MEMS switches are widely adopted, they must achieve a low actuating voltage and working lives of greater than 10 billion cycles. The sharp turning corners of serpentine springs results in stress concentration creating an area prone to fatigue failure. In this paper, fillets of increasing radius were added to the inner and outer edges of a serpentine spring and the structure analyzed to determine their effect on global maximum stress and effective spring constant of the structure. It was found that adding fillets reduces maximum stress in the structure while redistributing the stress throughout the length of the meander. This results in a more uniform structure without significantly increasing the overall spring constant of the structure.