A novel movable electrode for realizing deep sub-micrometer gap in SOI-based MEMS square resonator

A novel movable electrode is demonstrated to realize deep sub-micrometer resonator-to-electrode gap. This design is based on SOI progress for better reducing the motional impedance. The movable structure contains two main beams, which can be actuated by DC voltage to realize lock-up. After the lock-up process, the DC voltage could be released, so this lock-up progress only needs to be implemented once and can be accomplished before encapsulation. The DC bias voltage for the resonator is thus reduced for better application. In order to examine the improvement of motional impedance using this structure, a 70 MHz lame-mode square resonator is employed in this study. The resonator-to-electrode gap is reduced from 1.05 μm to 50 nm, thus brings about a 280 Ω motional impedance, which is 157,000× smaller than that before the actuation of the movable structure. In addition, the capability to be realized in conventional SOI progress facilitates the fabrication process as well as the realization of high yield.