Abstract
A gap with variable geometry is presented for both cantilever beam and fixed-fixed beam actuators as a method to reduce the pull-in voltage while maintaining a required displacement. The method is applicable to beams oriented either in a plane parallel to or perpendicular to a substrate, but is most suitable for vertically oriented (lateral) beams fabricated with a high aspect ratio process where variable gap geometry can be implemented directly in the layout. Finite element simulations are used to determine the pull-in voltages of these modified structures. The simulator is verified against theoretical pull-in voltage equations as well as previously published finite element simulations. By simply varying the gap in a linear fashion the pull-in voltage can be reduced by 37.2% in the cantilever beam case and 29.6% in the fixed-fixed beam case over a structure with a constant gap. This can be reduced a further 4.8% by using a polynomial gap shape (n = 4/3) for the cantilever beam and 1.2% for the fixed-fixed beam by flattening the bottom of the linearly varying gap.
Highlights
Electrostatic actuation as a method to obtain movement in microelectromechanical systems (MEMS) devices is extremely popular since this actuation method provides simplicity, fast actuation rates, very low, if not zero power consumption, and no special material requirements
The beam and stationary electrode are surrounded by an air box which is meshed with 0.25 μm rectangular electrostatic elements of type 121
Significant reductions in the pull-in voltage of both cantilever beam structures and fixed-fixed beam structures have been made by varying the geometry of the air gap while still achieving a required actuator displacement
Summary
Electrostatic actuation as a method to obtain movement in microelectromechanical systems (MEMS) devices is extremely popular since this actuation method provides simplicity, fast actuation rates, very low, if not zero power consumption, and no special material requirements. The shape of the gap between the beam and the attracting electrode is controlled in order to find suitable geometries that significantly reduce the pull-in voltage, while maintaining the required displacement before pull-in. This electrostatic-structural interaction is modeled using finite element simulation and verified using theoretical equations for pull-in voltage as well as previously published pull-in voltage results from an independent simulator
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