Migration of adhesive material in electrostatically actuated MEMS switch

Abstract

Microelectromechanical systems (MEMS) switches are attractive for many applications including radio frequency and microwave systems, logic devices, acceleration sensing and electric protection. However, low reliability limits the introduction of these devices into the commercial use. For two decades of research, many reliability issues have been successfully overcome, but some aspects have received little attention. The paper describes a failure mechanism of electrostatically actuated MEMS switch related to the migration of adhesive material in a dielectric substrate. The phenomenon is demonstrated for the device with Au and Pt electrodes deposited on Cr adhesion layer. After 102–105 working cycles, nanoscale structures consisting of Cr and C appear at the gate. The structures grow and coalesce into micron-sized formations that touch the beam during actuation and cause stiction or short circuiting. The material transfer takes place not only in the gap between the electrodes, but also around the gate and its connecting line, where Cr and C agglomerate into spots and droplets. In addition, the adhesive material migrates under the Au and Pt films, causing the delamination of electrodes from the substrate. A possible explanation of the described effect is the drift of Cr at the SiO2 surface under electric field. Chromium is widely used in microtechnology, but the field-induced migration was not reported previously. To all appearance, it became possible due to the features of the fabrication process. The conditions for the migration must be clarified in order to avoid this reliability issue for MEMS switches of various types and other microfabricated devices.