Frequency-Selective MEMS for Miniaturized Communication Devices

With Q’s in the tens to hundreds of thousands, micromachined vibrating resonators are proposed as IC-compatible tanks for use in the low phase noise oscillators and highly selective filters of communications subsystems. To date, LF oscillators have been fully integrated using merged CMOS+microstructure technologies, and bandpass filters consisting of spring-coupled micromechanical resonators have been demonstrated in the HF range. In particular, tworesonator micromechanical bandpass filters have been demonstrated with frequencies up to 14.5 MHz, percent bandwidths on the order of 0.2%, and insertion losses less than 1 dB. Higher-order three-resonator filters with frequencies near 455 kHz have also been achieved, with equally impressive insertion losses for 0.09% bandwidths, and with more than 64 dB of passband rejection. Evidence suggests that the ultimate frequency range of this high-Q tank technology depends upon material limitations, as well as design constraints—in particular, to the degree of electromechanical coupling achievable in micro-scale resonators.