870,000 Q-Factor Capacitive Lamé Mode Resonator with Gap Closing Electrodes Enabling 4.4 kΩ Equivalent Resistance at 50 V.

This work presents a Lamé mode resonator featuring a novel gap closing mechanism which employs electrostatic force to reduce the capacitive transduction gaps to sub-micron values in order to overcome fabrication technology critical spacing limitations. This leads to significant resonator loss and motional resistance reduction while maintaining high Q-factor even in air. Prototypes were fabricated in two commercial siliconon- insulator processes. Upon the application of a DC voltage of 55 V between the resonator structure and the electrodes, the gaps sizes are reduced to as low as 200 nm. A resonance frequency of 18 MHz with Q-factors as high as 866,000 were observed under 1 mTorr vacuum and of 32,000 at atmospheric pressure. A loss of 33 dB was measured at 55 V, which corresponds to an equivalent resistance of 4.4 kΩ, more than 60 times lower than that of a similar design without a gap closing mechanism at the same voltage. This significantly reduces the complexity of the oscillation sustaining circuitry. The frequency tuning range is also increased significantly as a result of the gap reduction, which can be useful for overcoming ambient conditions and fabrication variations.