mems

Micro electro mechanical systems based radio frequency switches:

Micro electro mechanical systems based radio frequency switches By VENNALA

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MEMS Technology RF MEMS Switches RF Shunt Switch Fabrication Challenges Conclusion 1 2 4 5 7 Advantages and Applications 5 6 4 CONTENTS

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What is MEMS? Micro Electro Mechanical Systems Characteristics Miniaturization with no loss of functionality • Integration to form a monolithic system • Improved multiplicity, reliability and accuracy • Low insertion loss and good isolation • Fast actuation techniques • Improved selectivity and sensitivity

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Resonator RF MEMS filter Nanoguitars from Cornell. MEMS Devices MEMS Optical devices Accelerometer

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What is Micromachining? Micromachining is the TOOLBOX of MEMS fabrication Types Bulk Micromachining Surface Micromachining Micro molding

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Bulk micromachining Etched part Fig: Bulk Micromachining It defines structures by selectively etching inside a substrate Isotropic Etching (HNA etc.) Anisotropic Etching (KOH, EDP etc.) Accommodates sharp corners, small features and very smooth surfaces

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Surface micromachining is processing above the substrate. It mainly uses the substrate as a base to build upon as shown in Figure The substrate properties are not as important as in bulk micromachining The expensive silicon wafers can be replaced by cheaper substrates, such as glass or plastic Surface Micromachining 28-APRIL-2011

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Micro molding Molds to define the deposition of the structural layer. LIGA process-Lithographie, Galvanoformung, und Abformung (lithography, electroplating, and molding).

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RF Switches Switching and routing of RF signals between various modules is a routine and critical operation that determines the overall efficiency of the entire system. RF MEMS switches are of two configurations: RF series contact switch RF shunt capacitive switch 28-APRIL-2011

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RF Series Switches Fig: Circuit equivalent of RF MEMS series contact switch. Fig: Structure of MEMS dc series switch Operates by creating an open or short in the transmission line on application of DC bias Fig: Switch operation

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RF Shunt Switches The RF signal is shorted to ground by a variable capacitor Fig: Circuit equivalent of RF MEMS shunt switch

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Contd…….. Fig: Capacitive RF MEMS switch 11 28-APRIL-2011 A grounded beam is suspended over dielectric on the transmission line the beam in the up position - Switch ON the beam in the down position - Switch OFF

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Contd…….. Shunt configuration is more advantageous than series switches Better linearity Allows hot-switching Lower insertion loss Used only for RF signal frequencies (5-100 GHz)

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RF Shunt Capacitive Switch Fabrication Fig: Capacitive RF MEMS switch -cross-sectional view

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Contd…….. (f) Seed layer deposition dielectric layer deposition and patterning spacer coating and patterning transmission line electroplating Membrane deposition and patterning Membrane releasing

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Challenges Packaging stiction Lifetime and Reliability Dielectric Breakdown Power Handling Radiation and Other Effects

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Contd…. PARAMETER RF MEMS PIN-DIODE FET Voltage(v) 20-80 +/-3-5 3-5 Current(mA) 0 0-20 0 Power consumption 0.5-1 5-100 0.5-1 Isolation Very high High Medium Loss(dB) 0.05-0.1 0.3-2 0.4-3 Power handling <1 <10 <10 Rs(series)(ohms) 0.5-2 2-4 4-6 Cup(series)(fF) 1-6 40-80 70-140 Comparison of MEMS Switches with Solid State Switches

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APPLICATION AREA FREQUENCY RANGE UTILITY DEFENCE 5-94GHz PHASE SHIFTERS,RADARS AUTOMOTIVE 24,60,77GHz RADARS SATELLITE COMMUNICATION SYSTEMS 12-35MHz SWITCHING NETWORKS AND ANTENNA APPLICATIONS WIRELESS COMMUNICATION SYSTEMS 0.8-6GHz SWITCHED FILTER BANKS INSTRUMENTATION SYSTEMS 0.01-50GHz ATTENUATORS, PHASE SHIFTERS Application areas

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MEMS switches are attractive alternative to mechanical and solid state switches Virtually every MEMS switch configuration is available today The main question now is reliability and packaging Tomorrow, which is today, most MEMS switches will be developed for wireless applications and low-power applications Conclusion

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Bibliography [ 1] S.Majumdar, J.lampen, R.Morrison,and J.Maciel, MEMS SWITCHES,IEEE Instrumentation & measurement magazine, march 2003. [2] B.A. Cetiner,et al., Monolithic integration of RF MEMS switches with a diversity antenna on PCB substrate, IEEE Trans Microwave Theory Tech 51 (2003), 332-335. [3] G.M.Rebeiz, J.B.Muldavin, “RF MEMS switches and switch circuits”, IEEE Microwave magazine, pp. 59-71, Dec. 2001. [4] Electronics for You-magazine [5] www.ippbooks.com/store/microelectromechanicalsystems . [6] www.intellisense.com/papers/microelectromechanical.pdf [7] www.datasheetcatalog.com

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