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, two-resonator 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.

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