Cathodic corrosion of polycrystalline silicon MEMS

Microelectromechanical systems (MEMS) commonly operate under high electric fields. When combined with humidity from the environment, corrosion becomes a critical reliability issue. While corrosion at the anode has been previously observed, the cathode is typically unaffected. In this paper, we provide the unusual report of damage occurring at the cathode in polycrystalline silicon MEMS in addition to the more common corrosion damage due to anodic oxidation. Both types of damage are observed in less than 24 It for an electrode spacing of 2 mu m under relative humidity of >= 57% and actuation voltage of 100 V. Under cathodic polarization, dissolution of the electrode and formation of oxygen-rich deposits are observed along the perimeter and sidewall of the cathode. This abnormal phenomenon is determined to be electrochemical and chemical in nature. The mechanism and accelerating factors leading to cathodic dissolution are discussed. (C) 2007 Elsevier B.V. All rights reserved.