Investigation of Charge Relaxation in Silicon Nitride for the Reliability of Electrostatically Driven Capacitive MEMS Devices

Dielectric charging/discharging in the real-life electrostatic microelectromechanical system device is proposed to be evaluated by the capacitance-voltage response for an analogous metal-insulator-semiconductor (MIS) structure. An analytical model based on this approach has been established. In the experiment, the relaxation behaviors of trapped charges in silicon nitride of MIS structure have been systematically investigated. For both positive and negative dc bias polarities, fast and slow discharge stages were clearly observed in the early and late charge relaxation processes, respectively. The discharge ratio (DR) was found to depend on both the bias polarity and magnitude. It was shown that negative dc bias would cause a high hole injection level but low DR, whereas positive dc bias would lead to a low electron injection level but high DR. Moreover, the DR will increase with the dc bias voltage. It was further found that the hole relaxation reaches the steady state faster than the electron relaxation. To explain the experimental results, we pointed out that the traps close to the interface play an important role in dielectric charging and discharging process.