RF-MEMS switching LC-tank network for multiband VCO
R. Gaddi, A. Gnudi, M. Bellei, B. Margesin and F. Giacomozzi
ARCES - University of Bologna, IT
RF-MEMS, tunable, network, VCO, LC-tank
A recently developed RF-MEMS technology based on high resistivity Silicon substrate and suspended gold membrane is proposed for the design of a switching dual frequency LC-tank, for the implementation of a hybrid MEMS-CMOS dual-band voltage controlled oscillator (VCO) for reconfigurable wireless transceiver applications. A differential circuit topology was chosen with a symmetric MEMS LC-tank network topology, which provides both frequency selection and bias feed. The switching network is based on ohmic RF-MEMS switches, metal-insulator-metal (MIM) capacitors and suspended spiral inductors. Test structures for half of the symmetric network were fabricated and characterised on-wafer through s-parameters measurements, obtaining the two resonance frequencies of 1.375 (Q = 7.2) and 3.605 GHz (Q = 14.4) for the up-state and down-state respectively. This data is well predicted by simulations, after allowing for an increased value of the input capacitance, due mainly to an increase in the dielectric constant of the low-temperature oxide (LTO) used for the MIM capacitor. The main loss mechanisms responsible for the limited quality factor values are identified through an analysis based on the extracted equivalent circuit for the switch.
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Nanotech 2005 Conference Program Abstract