Investigating the reliability of electrostatic comb-drive actuators used in microfluidic and space systems using finite element analysis

This study focuses on investigating the design parameters of lateral electrostatic comb-drive actuators, where the effect of these parameters on the actuation performance is explored using finite element analysis (FEA). This level of analysis is essential to the design process of system-on-a-chip microelectromechanical systems (MEMS) applications, where a comb drive can represent the main source of actuation within the chip system. Of particular interest to this study is the application of the electrostatic comb-drive motor as a fluidic pump in on-a-chip systems used for drug delivery or in cooling of microprocessors used in space vehicles. The commercial FE package ANSYS is utilized to construct a robust comb-drive model and solve its multiphysics interaction problem using the direct coupled-field analysis. In this model, the thickness, gap and overlap of the comb fingers are varied. The design of this model is also modulated to account for changes in the number of comb fingers and the applied driving voltage. The calculated comb displacement and generated electrostatic force are shown to be directly proportional to the number of comb fingers. Moreover, the generated electrostatic force is found to be inversely proportional to the gap between the comb fingers. As the thickness of these fingers increases, the displacement is found to increase for a given value of the driving voltage. The electrostatic force is also shown to be proportional to the offset (i.e., overlap) value between the fingers. To facilitate the use of the current study results in optimizing the design process of comb drives, an effort is made in the current work to condense these results into a compact nondimensional form that correlates the geometric and electrical parameters of the studied comb drive to the resulting displacement and force.