A variable inductor based on liquid tuning has been fabricated and characterised. The fabrication process used SU-8 channel obtained by spin coating and lamination. A 107% tuning range with high inductance from 5.4 to 2.6 nH is achieved. With no actuation, the peak quality factor is 12, and the self-resonance frequency is 4 GHz.

1. Introduction: The tuning of passive RF circuits is often a critical issue. In wireless communication equipment, such as cellular phones, wide range in tuning is necessary for channelling. Narrow range tuning is required for precise impedance matching or when the fabricated circuits are unable to meet the required performance owing to process parameters deviation. In both types of tuning, not only variable capacitors but also variable inductors can be used. The main requirement for these components is a high variation ratio with continuous states. Microelectromechanical system (MEMS) technology has already been used to fabricate variable capacitors and inductors [1–12], but most of them have drawbacks like low quality factor and/or low tuning range. Even if liquids are used recently in RF components [13–15], few studies are focused on liquid variable inductors. In this Letter, a liquid-based RF MEMS inductor is proposed, where salt water is used to modify the capacitive coupling between metal spires. The authors present here a novel RF MEMS tunable inductor based on fluidic actuation. High inductance values (2.6–5.4 nH) are achieved with a large tuning range of 107% and acceptable Q factor.