Channel-Select Micromechanical Filters Using High-K Dielectrically Transduced MEMS Resonators

This paper demonstrates electrically and mechanically coupled channel-select filters comprised of dielectrically transduced thickness shear mode resonators. The filters are fabricated on the 3.2 μm thick device layer of a heavily doped SOI wafer with a 30 nm thick hafnium dioxide film sandwiched between the polysilicon electrodes and the silicon device layer. An 809 MHz half-wave thickness shear resonator is demonstrated with a quality factor (Q) of 7,800 in air and a motional impedance (RX) of 59 Ω. An array of such resonators is coupled electrically and mechanically to form dielectrically transduced MEMS filters. Electrically coupled channel-select filters with 814 MHz center frequency, 600 kHz bandwidth, -4 dB insertion loss (IL) and < 1dB pass-band ripple are presented. In addition, a mechanically coupled 804 MHz center frequency filter is demonstrated exhibiting -34 dB stop-band rejection and a 20 dB shape factor of 1.28.