Investigation of Thermal Creep in Metal-Based MEMS Cantilevers

Cantilevers are widely used as actuators and sensors in microelectromechanical system (MEMS) devices. The creep behavior of cantilevers is an important factor in the lifetime of a MEMS device. This study examines the creep phenomenon in metal-based MEMS cantilever devices and deformations of the cantilever were investigated at different temperatures. A Generalized-Accumulated-Temperature (GAT) parameter is introduced into the MEMS field for characteristic prediction, particularly for high-temperature storage lifetime prediction. Simplified radio frequency (RF) MEMS devices were designed, fabricated, and measured to investigate thermal creep. The devices were fabricated by surface micromachining processes at room temperature, strictly without any extra thermal effect before testing. The devices were tested with nanometer accuracy using the in-situ co-test method with three-dimensional (3D) optical microscope and RF probe station. The test results of the device with a gold-alloy cantilever showed that the deformation rate increased with temperature raising, and the logarithm of the rate exhibited a linear relationship with the temperature. A mathematical relation between the GAT parameter and cantilever deformation was established by which the lifetime of the cantilever can be predicted at different temperatures. The performances of pure gold and gold alloy were compared, and the alloy shows better thermal stability. This study shows that the gold alloy is more suitable on lifetime than pure gold for use as cantilevers. The GAT parameter introduced in this paper can enable the realization of metal-cantilever-based MEMS devices. It can also be widely used in other MEMS devices as a generic time–temperature parameter. [2023-0054]