A Parallel-plate-based Fishbone-Shape MEMS Tunable Capacitor with Linear Capacitance-Voltage Response

A novel fishbone-shape parallel-plate-based capacitor with high tunability and linear C-V response is presented. The electrodes consist of a set of lateral cantilever beams of different lengths, attached to a longitudinal fixed-fixed beam. An insulating layer prevents contact between the electrodes. When a DC voltage is applied, the longitudinal and lateral beams undergo out-of-plane deformations changing the gap between two electrodes and the capacitance. As bias voltage increases, depending on their length and location, local pull-in for beams occurs at different voltages leading to a controlled C-V response. Using ANSYS FEM simulations, a design optimization is performed to enhance the response for higher tunability and linearity. The simulation results of capacitors designed for PolyMUMPs exhibit tunability over 200%, 160% of which is highly linear. The presented design methodology, a combination of flexible structure and controlled displacements, is not limited to fishbone-shape electrodes and can be extended to different geometries to obtain higher tunability and linearity.