Evaluation of Creep in RF MEMS Devices

RF MEMS are capacitive switches consisting of a suspended aluminum beam that can be pulled down by electrostatic force. At elevated temperatures and high mechanical stresses the aluminum beam can exhibit creep phenomena that result in shifting of device parameters as a function of time. Experimental and numerical methodologies are presented for measuring and predicting the effect of creep on the RF MEMS device performance. A constitutive creep model is implemented in a Finite Element code where the parameters of this constitutive model for creep in thin aluminum layers are determined by wafer curvature experiments. In order to distinguish creep effect from charging effects, special test structures are designed. Simulations on the test with different geometries indicate the effect of creep and can result in design rules for the RF MEMS switches. The numerical predictions and the measured degradation on the RF MEMS switches are compared and conclusions are drawn with respect to the methodology.