Design and analysis of micro-electrostatic actuator with trapezoidal-shaped comb fingers and folded beams

• Trapezoidal- and rectangular-shaped comb fingers are compared. • TECA and RECA are investigated to optimize the actuation performance. • Displacement of TECA can be enhanced 5 times compared to that of RECA. • Low mechanical stiffness and poor resistance from the pull-in effect are discussed. We present a design of electrostatic comb actuator (ECA), which consists of two sets of interdigitated comb microstructures with an intersection angle. The inner combs are fixed to form the fish-bone microstructures with the movable outer combs connected to folded beams. By replacing the traditional rectangular-shaped comb finger with the trapezoidal-shaped comb finger in three trapezium modes, the displacement of the ECA can be enhanced five times, due to its additional electrostatic force from the tilt gaps. Moreover, the impacts of the intersection angle of the folded beam on its mechanical stiffness and resistance from the pull-in effect are investigated with the simulated mechanical stiffness fitting well with its theoretical prediction. It is found that a larger intersection angle of folded angle leads to low mechanical stiffness as well as poor resistance from the pull-in effect which should be considered with a trade-off in real-life applications, especially for ECA with trapezoidal-shaped comb finger. This work provides more discussion and a full analysis model for the trapezoidal-shaped comb finger and innovatively proposed folded beam with its mechanical stiffness and resistance from pull-in effect investigated and predicted, which paves the way for the application of ECA in the fields of gyroscope, motion sensor, accelerometers, inkjet print head, tunable optical device, and so on.