Maneuvering the pull-in voltage of the electrostatic actuator by introducing a pre-charged electrode

Abstract

In this thesis, a new method to greatly reduce and control the pull-in voltage of an electrostatic actuator has been introduced, simply by introducing a pre-charged floating electrode. Since the first Microelectromechanical System(MEMS) actuator was proposed, the MEMS actuators have been broadly utilized in various applications : RF, display, memory, sensor, and so on. Specially, due to their simple actuation mechanism and low power consumption, the electrostatic actuators are fascinatedly used. However, there is the most obstacle to the commercialization : trade-off of pull-in voltage and resonant frequency (actuating speed). For low pull-in voltage by decrease the spring constant, the resonant frequency goes to low. In the other words, for high actuating speed, the pull-in voltage goes to high. Destruction of the trade-off of the pull-in voltage and the resonant frequency is one of the most important issues in MEMS research area. In this works, the innovative way to maneuver the pull-in voltage of electrostatic actuators without decline of the resonant frequency had been proposed and tried to solve the fore-mentioned problems. First, the modeling of the proposed actuation for standard structures, parallel plate and cantilever had been provided. Second, the proper fabrication process for the new structure had been suggested and performed. Third, the design and settings for measurements of pull-in voltage shift, retention time, resonant frequency, and memory effect had been offered. Finally, it was successfully showed that the original pull-in voltage of 48V and resonant frequency was reduced to 3V and 63.5%. Also, the retention time of pre-charges was 105 seconds verified by the measurement of pull-in voltage shift as times goes by. In stressed condition (40V applied) for 2$\times10^5$ seconds, there was no degradation of the pull-in voltage.