Digitally-tunable mems filter using mechanically-coupled resonator array

This paper reports on the design of a bandwidth-tunable RF MEMS filter using a series-coupled array of dielectrically-transduced square-extensional mode resonators. The proposed digital tuning scheme provides channel-agility and bandwidth granularity for analog spectral processors and RF spectrum analyzers. The resonators and filters are fabricated on the 3 mum thick device layer of a heavily doped SOI wafer with a 100 nm thick silicon nitride film sandwiched between the polysilicon electrodes and the silicon device layer. A 511 MHz overtone square-extensional mode resonator is demonstrated with a quality factor (Q) of 1,800 in air and motional impedance (R_X) of 1.1 kOmega. An array of four such resonators is coupled mechanically to form a channel-select filter with 1.4 MHz bandwidth at 509 MHz center frequency. By switching the DC-biasing scheme, the filter is split into narrower high and low sub-bands, each 700 kHz wide.