Novel Linearly Tunable MEMS Capacitors With Flexible Moving Electrodes

Abstract

In conventional MEMS parallel-plate capacitor designs, the moving electrode is commonly modeled as a rigid plate with flexible boundary conditions provided by a set of supporting beams. Such a capacitor generates limited tuning ratio up to 1.5 and its capacitance-voltage response is nonlinear. This paper presents novel designs where the moving electrodes are fixed-edge flexible plates. The plate displacement is selectively limited by a set of rigid steps, located between two electrodes, to generate a smooth and linear response and high tunability. Three different step heights are considered in the design and the linearity of the C-V curve is maximized by modifying the geometry of the plate, and changing the location and order of steps. Since the analytical solution for coupled electrostatic-structural physics in this case does not exist, ANSYS® FEM simulation is performed to obtain the C-V curves and optimize the design. Two designs with different electrode shapes, rectangular and circular, are developed. For rectangular-plate capacitors, tunabilities ranging from 120% to 140% and high linearity are achieved. Circular-plate designs, on the other hand, generate lower tunabilities and an extremely linear region in C-V curves. Design methodology introduced in this research is not limited to proposed geometries and can be extended to different topologies to obtain a combination of high tunability and linearity.