Estimation of thin film stress in buckled MEMS bridge from pull-in voltage

A simple and easy method to estimate either compressive or tensile thin film stress that exists within the buckled MEMS bridge structure is presented. An array of tantalum MEMS bridge with buckle profile is fabricated at length 570 μm–1620 μm. The distance between the maximum vertical deflection of the fabricated buckled tantalum bridge to the substrate is measured. The analytical pull-in voltage for buckled tantalum bridge at different length is calculated, taking into account the influence of strain and bridge's curvature profile. The pull-in voltage of the fabricated buckled tantalum MEMS bridge is measured and compared to the analytical model. The stress is then estimated by fitting the experimental measurement results to the analytical model using the least mean square method. The presence of stress within the buckled tantalum MEMS bridge structures has been found to be compressive. The average tantalum thin film stress value has been estimated to be ∼0.24 MPa.