2010 IEEE MTT-S International Microwave Symposium Technical Program

Session: TH1B	RF-MEMS Circuits
Chair:	Joachim Oberhammer, Royal Institute of Technology
Co-Chair:	Jing Wang, University of South Florida
Abstract:	This session presents recent results on RF MEMS tuneable circuits, ranging from high power handling highly linear varactor topologies, tuneable filters for WDCDMA receivers, to feedback mechanisms for sensing varactor states and circuit implications of viscoelastic behavior of microelectromechanical tuning components.

TH1B-1	A High Power-Handling RF MEMS Tunable Capacitor Using Quadruple Series Capacitor Structure
8:00 AM-8:20 AM	H. Yamazaki¹, T. Ikehashi¹, T. Saito¹, E. Ogawa¹, T. Masunaga², T. Ohguro¹, Y. Sugizaki¹, H. Shibata¹, ¹Toshiba Corporation, Yokohama, Japan, ²Toshiba Corporation, Yokohama, Japan
(1422)	This paper presents an RF MEMS tunable capacitor that achieves excellent power-handling property with relatively low actuation voltage. The tunable capacitor consists of two fixed MIM (Metal-Insulator-Metal) capacitors and two MEMS capacitor elements, all connected in series. This quadruple series capacitor (QSC) structure enables to reduce the actuation voltage without sacrificing the power-handling capability, since the MIM capacitor reduces the RF voltage amplitude applied to the MEMS capacitors. Measured result demonstrates +36dBm hot-switching at 85C with 21V pull-in voltage.

TH1B-2	Anti-Biased RF MEMS Varactor Topology for 20-25 dB Linearity Enhancement
8:20 AM-8:40 AM	K. Chen, A. Kovacs, D. Peroulis, Purdue Univerisity, West Lafayette, United States
(1831)	A new topology for significantly improving the linearity of RF MEMS varactors is reported in this paper. A single MEMS varactor subject to a low frequency noise and/or modulating signal is the main structure under consideration. The key idea is to separate the single varactor into two varactors in parallel which are anti-biased. This leads to the opposing vibration of two beams under the influence of the low-frequency signal, which eventually leads to a nearly constant capacitance of the entire topology. The effectiveness of this method is demonstrated by both measured results from fabricated RF MEMS varactors and simulated results using a large-signal model of MEMS varactor in ADS. Both experimental and simulated results indicate an improvement of 20-25 dB compared to the conventional designs. This underlines the potential of the proposed topology in high-power RF MEMS circuits.

TH1B-3	A Tunable Asymmetric Notch Filter using RFMEMS
8:40 AM-9:00 AM	J. R. De Luis², A. S. Morris III¹, Q. Gu¹, F. De Flaviis², ¹Wispry Inc, Irvine, United States, ²University of California Irvine, Irvine, United States
(1582)	In this paper, a single pole single zero asymmetric notch filter using RF micro electromechanical tunable capacitors is presented. The high Q value of the tunable capacitors enables this filter to achieve 25.5dB rejection with less than 1.2dB insertion loss over a 5MHz signal bandwidth. This tunable filter is designed to suppress transmission leakage in the IMT Band I (1.92-1.98GHz) band for handset WCDMA receivers. It also can serve as a component in handset tunable duplexers.

TH1B-4	An Experimental Investigation on Viscoelastic Behavior in Tunable Planar RF-MEMS Resonators
9:00 AM-9:20 AM	H. Hsu, D. Peroulis, Purdue University, West Lafayette, United States
(1746)	In this paper, the viscoelastic behavior of a tunable RF-MEMS resonator and its impacts are studied by means of direct RF measurements for the first time. This tunable resonator consists of one lambda/2 coplanar waveguide (CPW) Resonator and two nanocrystalline-Ni RF-MEMS varactors. S-parameters of this tunable resonator have been measured for 80 hours under a bi-state bias condition of 0 and 40 V. It is demonstrated that the resonant frequency is shifted by 90 MHz and the varactor deformed by 0.12 ¹m over the 80 hour period. The gap of the loaded varactor is extracted from the measured S-parameters using finite-element analysis (FEA) tools. A generalized Voigt-Kelvin model is employed to verify the viscoelastic behavior of the resonator. The creep compliance extracted from the RF measurements is in excellent agreement with results in literature.

TH1B-5	A MEMS Variable Capacitor with Piezoresistive Position Sensing Fabricated in a Standard 0.35um CMOS Process
9:20 AM-9:40 AM	N. Zahirovic¹, R. R. Mansour¹, M. Yu², ¹University of Waterloo, Waterloo, Canada, ²COM DEV International, Cambridge, Canada
(1688)	A variable MEMS capacitor with piezoresistive feedback is presented. The capacitor is fabricated in a commercial 0.35um CMOS process with MEMS post-processing. The work presented demonstrates a piezoresistive sensing scheme capable of controlling hysteresis effects in a CMOS-MEMS variable capacitor. Potential applications of the sensing scheme include closed-loop control of variable capacitors and detection of dielectic charging.

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