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MEMS: From Micro Devices to Wireless Systems

Vol. 7, Special Issue, October 2009, pp.15-24





A Parallel-Plate-Based Fishbone-Shape MEMS Tunable Capacitor with Linear Capacitance-Voltage Response


*,1Mohammad Shavezipur, *,2Patricia Nieva, Seyed **Mohammad Hashemi and *,3Amir Khajepour

*Department of Mechanical and Mechatronics Engineering, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, N2L 3G1, Canada

Tel.: (001) 519-888-4567

**Department of Aerospace Engineering, Ryerson University, 350 Victoria Street, Toronto, Ontario, M5B 2K3, Canada

Tel.: (001) 416-979-5000

E-mail: 1mshavezi@engmail.uwaterloo.ca, 2pnieva@uwaterloo.ca, 3akhajepour@uwaterloo.ca, smhashem@ryerson.ca



Received: 28 August 2009 /Accepted: 28 September 2009 /Published: 12 October 2009


Abstract: Conventional designs for MEMS parallel-plate tunable capacitors suggest the use of rectangular electrodes and linear structural stiffness which have two drawbacks; low tunability (up to 50 %) and nonlinear capacitance-voltage (C-V) response. This paper presents a novel fishbone-shape parallel-plate capacitor with high tunability and linear C-V response. The moving electrode consists of a set of lateral cantilever beams of different lengths, attached to a longitudinal fixed-free beam which resembles the spinal column of a fishbone. When a DC voltage is applied, the beams undergo out-of-plane deformations, the gap between the fixed and moving electrode reduces and the capacitance increases. As the bias voltage is increased and depending on the length and location of the beams, local pull-in occurs on every beam at different voltages. In addition, an insulation layer prevents direct contact between the electrodes leading to a controlled C-V response. Using ANSYS® FEM simulations, a design optimization has been performed to enhance the C-V response for higher tunability and linearity. Simulation results exhibit tunabilities over 200 %, 4/5 of which is highly linear. The experimental data obtained from capacitors fabricated using PolyMUMPs display similar trends with reasonable deviation caused mainly by fabrication uncertainties. The design methodology introduced in this paper could be easily extended to other design geometries.


Keywords: MEMS tunable capacitor, Fishbone-shape electrode, Linear response, Structural nonlinearity


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