Electrical and environmental reliability characterization of surface micromachined MEMS polysilicon test structures

While considerable press has been given to characterization of mechanical properties of MicroElectroMechanical Systems (MEMS) as related to reliability, environmental robustness, and lifetimes studies, characterization of electrical properties of MEMS have not been widely published. In this paper we present an examination of electrical properties (surface and substrate leakage currents, sheet resistance, substrate contact resistance and interlayer contact resistances) of polysilicon thin films used in surface micromachined MEMS test structures. Environmental and electrical overstress conditions that affect leakage current have been studied. Two test structures have been used to independently study surface and substrate leakage currents at different levels of humidity (0% to 80% RH) and applied voltage (100 to 150 volts). Both static and lifetime studies have been conducted. Significant differences in surface and substrate leakage lifetime characteristics are observed, suggesting different failure mechanisms for these two important electrical phenomena in MEMS reliability.