The Effect of Silicon Nitride Stoichiometry on Charging Mechanisms in RF-MEMS Capacitive Switches

This paper discusses the mechanisms responsible for charging of plasma enhanced chemical vapor deposition (PECVD) silicon nitride films used in the fabrication of RF microelectromechanical (MEMS) switches. Nitride films deposited at different temperatures are characterized in order to better understand the effect of deposition conditions on material stoichiometry and stress. Both RF MEMS switches and metal-semiconductor-metal capacitors with PECVD silicon nitride as the dielectric layer were fabricated and their charging mechanisms were examined. Measurements indicate that charging arises from the formation of a defect band where charge transport occurs through a Poole-Frenkel-like effect. The calculated activation energy exhibits direct relation to material stoichiometry, and therefore to the nitride bandgap. Finally, it is viewed that lower temperature nitride is less prone to dielectric charging.