A MEMS Resonator Tank for an RF VCO Application

This paper presents the design and study of a MEMS tapped-inductor LC resonator tank, proposed to evaluate the improved performance over that generally achieved in standard CMOS passive component integration. The resonator tank, consisting of a fixed-value inductor and a variable capacitor, was implemented in the MetalMUMPs process and was targeted for a VCO intended for telemetry applications. A geometrically optimized 1.25 nH horseshoe inductor was designed and results show that it exhibits a Q-factor of 63 at 7.3 GHz and a self-resonating frequency of 17.6 GHz. In addition, an improved pi-inductor model is proposed for design and simulation purposes. The variable capacitor was designed in a parallel-plate topology, using four serpentine springs. The capacitance can be varied from 0.183 pF to 0.245 pF with an actuation voltage in the range of 0 V-to-11.7 V. A Q-factor of 62 at 1.1 GHz and a self-resonating frequency above 10 GHz were achieved. The designed inductor and capacitor were configured in a resonator tank topology yielding an overall Q-factor of 22 at 4.9 GHz.