Simple sticking models and adhesion criterion to predict sticking effects of fixed-fixed beams in RF MEMS switch design

摘要

The fixed-fixed beam in RF switches fabricated by MEMS techniques of a sacrificial layer is inclined to stick to the substrate due to the significant capillary force during drying process. In this paper, sticking models of the fixed-fixed beam are investigated to analyze the sticking effect. Based on these models, an adhesion criterion hc for the fixed-fixed beam is derived to determine whether the beam sticks to the substrate or not. The deduced formula shows that hc is determined by the material property of the beam and its length L and thickness t. It is also found that the width of the beam has no effect on hc. The theoretical models and adhesion criterion are simulated and verified by Finite Element Analysis. The effects of residual stress are also discussed to meet the uncertainty of real fabrication processes.