Widely Tunable 20-NM-Gap Ruthenium Metal Square-Plate Resonator

A capacitive-gap transduced flexural-mode square-plate resonator constructed in rapid-thermal-annealed (RTA'ed) ruthenium metal posts quality factors ( Q's) exceeding 5000 and an impressive transducer strength Cx/Co (equivalent to kt
²
) of up to 71% intrinsic and 36% with 55fF of bond capacitance loading, which in turn permits more than 46% voltage-controlled resonance frequency tuning (from 18.005 to 9.713MHz) with a voltage excursion from 0.5 to 2.8V. The 36% Cx/Co is 75 times larger than the 0.48% of published AlN piezoelectric material in this HF frequency range [1]. With processing temperatures potentially below 350°C (with localized annealing), this metal resonator is amenable to integration directly over even advanced node CMOS [2], making this technology attractive for single-chip widely tunable filter and oscillator applications, e.g., for wireless communications [3].