Pull-in characterization of doubly-clamped composite beams

An electrostatic pull-in beam has been widely used to measure material properties. There has been an increasing need for MEMS devices with composite films in recent years. This paper presents an approach to characterize the material properties of the composite films using the electrostatic pull-in test structure which is composed of the composite fixed-fixed beam. An analytical model for the pull-in voltage of the composite doubly-clamped beam is presented, which takes into account the influence of lateral residual stress along width direction of the composite beam. Based on this improved model, a test structure is designed to avoid the influence of lateral residual stress along the width of the composite beam. An in situ method for simultaneously extracting material properties (Young's modulus and residual stress) of each layer for the composite films is reported. And doubly-clamped surface micromachined beams with multi-cup style anchors were fabricated to support the model of pull-in voltage. The validation and accuracy of the extracting method have been confirmed by FEM simulation and experiments.