Radio-Frequency Silicon-based CMOS-Compatible MEMS Variable Solenoid Micro-Fluidic Inductor with Galinstan-Based Continuously-Adjustable Turn-Ratio Technique

Fatemeh Banitorfian,  Farshad Eshghabadi,  Asrulnizam Abd Manaf,  Norlaili Mohd Noh,  Mohd Tafir Mustaffa
Advanced Integrated System Device Group (AISDe), School of Electrical and Electronic Engineering, Universiti Sains Malaysia (USM), Nibong Tebal, Malaysia


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.