Radio-frequency silicon-based CMOS-compatible MEMS variable solenoid micro-fluidic inductor with Galinstan-based continuously-adjustable turn-ratio technique

This paper proposes a continuously-variable MEMS solenoid inductor with resonating frequency of over 8 GHz. This inductor allows high-tuning capability for resonance adjustment purpose in reconfigurable radio-frequency circuit devices. To achieve this goal, a channel is contrived to bypass the turns of the coil through the injection of a conductive liquid (here, Galinstan). Once the number of turns decreases, the inductance value falls according to the injection level. The proposed solenoid inductor is simulated using a full-wave three-dimensional electromagnetic analysis tool, HFSS, for silicon substrate with copper metallic coil for different level of conductive liquid injection. Beside the cost-effective and easy manufacturing process, the simulation results demonstrate the 150% tuning range. The EM simulation results show a maximum quality factor of 85 at 3 GHz for proposed inductor. The minimum and maximum inductance values are 1.5 and 4 nH at 4 GHz for low-resistivity Silicon. This tunable inductor can be applied into reconfigurable radio-frequency circuits and matching networks to tune the operating frequency of the system.