A novel high tuning ratio MEMS cantilever variable capacitor
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TECHNICAL PAPER
A novel high tuning ratio MEMS cantilever variable capacitor Hedie Mahmoodnia • Bahram Azizollah Ganji
Received: 17 August 2012 / Accepted: 30 May 2013 Ó Springer-Verlag Berlin Heidelberg 2013
Abstract This paper presents a novel cantilever-type MEMS variable capacitor with high tuning ratio. In previous works, the cantilever is used as a switch but in our design, it is applied as a variable capacitor. For increasing the maximum achievable capacitance of the cantilever, the suspended capacitive plate should be moved as parallel with fixed plate. The parallel movement can be obtained using the novel structure which utilized two additional lateral beams. Also to overcome the pull-in phenomenon in new structure, the different membrane thickness technique is used. The novelty of our design is adding the lateral beams to make parallel movement of the suspended plate to increase the variable capacitor of the cantilever. The new device is designed on a thick silicon substrate with a thin poly silicon membrane. The results show the tuning range of tunable capacitor with initial capacitance of 560.1 fF can be improved from 6:1 for conventional cantilever to 22.5:1 for the new cantilever. In other words the capacitance tuning range increased three times.
1 Introduction In recent years, Microelectromechanical systems (MEMS) variable capacitors have been incorporated in different systems to attain more diverse functionalities. Their tuning range (the ratio of maximum changed capacitance to the minimum capacitance) is the key performance parameter when designing a wildly tunable device such as voltage controlled oscillator (VCO), phase locked loop (PLL) H. Mahmoodnia B. A. Ganji (&) Department of Electrical Engineering, Babol University of Technology, Babol, Mazandaran, Iran e-mail: [email protected]
circuits, phase shifters, wideband antenna and so on (Reinke et al. 2011; Sankaranarayanan et al. 2007; Innocent et al. 2003; Zvolensky et al. 2011). In RF applications, parallelplate MEMS variable capacitors have been wide studied for LC tanks. Due to the electrostatic actuation, the polarity of the actuation voltage is not important, which prevents any forward-biasing problems which can be a crucial issue in p-n junction varactors. Chang-Hoon et al. (2011) reported a parallel plate MEMS variable capacitor with superior linearity and large tuning ratio by moving the plate to an increasing-gap direction. In this structure, by adopting a levering structure, the common closing-gap motion of the electrostatic actuator was transformed into an increasinggap movement. So a capacitance tuning ratio of 0.34:1(34 %) was achieved. Bakri-Kassem et al. (2009) proposed a curl-up-plate MEMS varactor with almost linear response and high tuning capacitance ratio. This MEMS varactor exhibits a linear capacitance with tuning ratio of 4:1(400 %). Rijks et al. (2004) presented a continuous and reversible MEMS tunable capacitor with a tuning ratio up to 16:1(1,600 %), using a dual gap relay-type design. Nowadays, the researches o
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