CMU MEMS Laboratory Publication Abstract


in Proceedings of SRC Techcon (SRC Techcon), August 25-27, 2003, Dallas, Texas.
Frequency-hopping circuits based on reconfigurable MEMS capacitors
A. Oz, V. K. Saraf, D. Ramachandran, G. Fedder and T. Mukherjee
Post-foundry micromachining enables integration of RF electronics with RF MEMS suspended inductors and reconfigurable capacitors for single chip frequency-hopping (FH) radios. Spiral inductors are formed in the thickest metal layer of the BEOL foundry interconnect stack. Post-CMOS etching removes the oxide between the turns to increase self-resonance frequency and removes the silicon under the spiral to increase Q. RF MEMS capacitors are formed using interdigitated beams fabricated from the BEOL foundry interconnect. The capacitance can be varied by changing the gap between interdigitated beams using an electrothermal actuator that is heated using embedded polysilicon resistors. A Q of 52, 1.5 GHz, capacitor with tuning range from 42 fF to 148 fF (3.52:1) within a 12 V control voltage and 34 mW power has been designed, fabricated and characterized in a 0.35 µm CMOS process. Reconfigurable capacitors with higher Q (>200) and zero standby power (using mechanical latch stops) have been designed. They have been integrated with the suspended inductor to form a RF filter that hops between 1.2 and 2.1 GHz. The p-network filter uses two reconfigurable capacitors: 170 fF/400 fF for dc blocking and 140 fF/800 fF for the tank capacitor. The relative insertion loss difference between the two frequencies is simulated to be 2.8 dB. Integration of the RF MEMS passive inductor and capacitor devices with 47 GHz SiGe HBT, enables the design of a negative-Gm FH oscillator that can also switch between 1.2 and 2.1 GHz. The oscillator is based on a MEMS capacitor that can reconfigure between 360 fF and 1.2 pF. Simulations indicate that phase noise exceeds -110 dBc/Hz for this 4.1 mW oscillator. These FH circuits are being fabricated.
© 2003 Semiconductor Research Corporation. All rights reserved
Full paper not available from outside CMU

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