Vibrating micromechanical resonators with solid dielectric capacitive transducer gaps

Abstract

VHF and UHF MEMS-based vibrating micro-mechanical resonators equipped with new solid dielectric (i.e., filled) capacitive transducer gaps to replace previously used air gaps have been demonstrated at 160 MHz, with Q's ∼20,200 on par with those of air-gap resonators, and motional resistances (R x's) more than 8× smaller at similar frequencies and bias conditions. This degree of motional resistance reduction comes about via not only the higher dielectric constant provided by a solid-filled electrode-to-resonator gap, but also by the ability to achieve smaller solid gaps than air gaps. These advantages with the right dielectric material may now allow capacitively-transduced resonators to match to the 50-377 Ω impedances expected by off-chip components (e.g., antennas) in many wireless applications without the need for high voltages. In addition to lower motional resistance, the use of filled-dielectric transducer gaps provides numerous other benefits over the air gap variety, since it (a) better stabilizes the resonator structure against shock and microphonics; (b) eliminates the possibility of particles getting into an electrode-to-resonator air gap, which poses a potential reliability issue; (c) greatly improves fabrication yield, by eliminating the difficult sacrificial release step needed for air gap devices; and (d) potentially allows larger micromechanical circuits (e.g., bandpass filters comprised of interlinked resonators) by stabilizing constituent resonators as the circuits they comprise grow in complexity. © 2005 IEEE.