NSTI Nanotech 2009

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

M. Shavezipur, P. Nieva, A. Khajepour, S.M. Hashemi
University of Waterloo, CA

Keywords: parellel-plate capacitor, linear capacitor, pull-in free


Conventional designs for MEMS parallel-plate tunable capacitor suggest rectangular electrodes and linear structural stiffness which offer high Q-factor and quick responses; however, they have low tunability of 50% and nonlinear capacitance-voltage responses. This paper presents a novel fishbone-shape parallel-plate capacitor with high tunability and linear C-V response. The electrodes consist of a set of lateral cantilever beams of different lengths, attached to a longitudinal fixed-fixed beam resembling a fishbone. 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 the length and location of each beam, a local pull-in for that beam occurs at a different voltage and an insulator prevents contact between the electrodes leading to a controlled C-V response. Using ANSYSŪ FEM simulations, a design optimization is performed to enhance the C-V response for higher tunability and linearity. The simulation results exhibit tunability over 200%, 160% of which is highly linear. The design methodology, a combination of flexible structure and controlled displacements, presented in this paper is not limited to fishbone-shape electrodes and can be extended to different geometries to obtain higher tunability and linearity.
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