UHF Micromechanical Compound-(2,4) Mode Ring Resonators With Solid-Gap Transducers

UHF vibrating micromechanical ring resonators with solid-filled dielectric transducer gaps (as opposed to previous air gaps) operating in a compound-(2,4) mode have been demonstrated at 979.6 MHz with Q´s on the order of 3,100 and motional resistances effectively 4.7x smaller than air gap counterparts under identical bias conditions. Due to their higher dielectric constant, substitution of solid dielectric materials for air or vacuum in the electrode-to-resonator gap leads to increased electromechanical coupling in capacitively transduced micromechanical resonators, which in effect generates more output current, and thus, reduces motional resistance. The advantages of using solid dielectric material as the ´ gap´ are multifold, as it (1) eliminates the need for the final gap release etch in the MEMS fabrication process, thereby enhancing yield; (2) lowers device impedance versus air gap renditions, allowing easier matching to other components; (3) eliminates the possibility of particles getting into an electrode-to-resonator air gap, which would otherwise pose a potential reliability issue; and (4) consolidates the resonator structure, making it less susceptible to shock This work greatly extends the frequency of direct (as opposed to indirect) solid-gap transduced MEMS resonators, from the previous 60 MHz using a compound (2,1) mode, to now nearly 1 GHz, and in a range desired for RF front ends, using a compound (2,4) mode.