| Currently, the lifetime of electrostatically actuated RF Microelectromechanical system (MEMS) capacitive switches is limited mainly by dielectric charging effects. This dissertation modeled and characterized the surface and bulk charging under different fields, humidities and packaging practices. Research work on charge transport mechanism is also presented.;We have developed a novel and extremely useful technique to electrically separate surface charging and bulk charging by analyzing the recovery of the pull-in (actuation) voltage after stress. Since surface charging is more critical to switch performance and reliability than bulk charging, understanding the trade off of surface versus bulk charging can help minimize their undesirable effects.;By using this novel technique, we examined the surface and bulk charging of RF MEMS capacitive switches under different electric fields and humidity levels. It was found that bulk charging dominated in dry air, while surface charging increased linearly with increasing humidity. Next, this technique was used to evaluate the effectiveness of packaging in maintaining a dry ambient atmosphere for switches and in preventing the charging of the dielectric surface after prolonged operation. It was found that as-packaged switches exhibited different degrees of surface charging. However, after the switches were delidded and baked dry, all switches showed minimal surface charging. These results imply that the switches can have consistently long lifetimes by improving the yield of the packaging process.;The ambient humidity affects surface charging and discharging through enhanced surface conduction. By solving a two dimensional surface-bulk charge diffusion problem and by fitting the solution with measured discharging characteristics of a silicon-nitride dielectric, the surface and bulk diffusivities were determined to be on the order of 10-10 cm2/s and 10 -14 cm2/s, respectively. Since humidity can be harmful by enhancing charging but beneficial by enhancing discharging, it is critical to optimize the ambient humidity level and dielectric surface chemistry of the switches.;To prevent the switches' lifetime from being limited by bulk charging, by applying a unipolar waveform, reducing control voltage, dielectric area and operating duty cycle, we minimized the bulk dielectric charging and achieved 100 billion switching cycles without failure. Bipolar control-voltage waveforms have also been proposed to mitigate bulk dielectric charging in switches. In this work, dielectric charging under bipolar waveforms is modeled and characterized quantitatively. |
