Silicon Beam Microelectromechanical Systems Resonator with a Sliding Electrode

Abstract

A silicon beam microelectromechanical systems (MEMS) resonator with a sliding driving electrode (DE) has been investigated. Although the narrow gap between a driving electrode and a resonant beam greatly improves the resonator performance, it has been difficult to fabricate the narrow gap owing to the process limitation. In this study, the gap is decreased by sliding the driving electrode after the resonator process is completed (postprocessed narrow gap formation). The effective gap length for a fabricated resonator was decreased to 0.84 µm after the pull-in, while the initial gap was 3.44 µm. After the pull-in, the fabricated resonator vibrated at the 899.5 kHz resonant frequency (the Q-factor of 6600). The resonant beam displacement amplitude increased 17.5 times compared with that for the as-fabricated (before the pull-in) resonator. In the electrical domain, the magnitude of the impedance largely decreased from ∼58 to 3.85 MΩ. The large phase transition, 50°, was also measured. From these results, largely improved resonator characteristics due to the narrow gap effect were confirmed. Moreover, the displacement amplitude ratio of the sliding DE to the resonant beam was found to be less than 4.5×10-5 for the resonator after the pull-in. This implies that the vibration of the sliding DE could affect negligibly the overall beam resonator vibration.