This letter presents the fabrication and the modeling of a continuously tuned microfluidic capacitor. On one hand its electrodes are realized by classical electrodeposition techniques and on the other hand, the lamination of SU-8 films allows superposing some microfluidic channels. According to the experimental results, the capacitor value increases continuously following the deionized (DI) water penetration in microchannels. The capacitance variations are comprised between Cmin = 0.52 pF and Cmax = 18.5 pF, allowing a wide tuning range that reaches 3460% at 500 MHz. The quality factor decreases from Qmax = 69 when the capacitor is empty to Qmin = 5.3 when it is fully filled with DI water. We have also investigated the theoretical aspects of our device by modeling the electric field and the current distributions inside the channels: when they are entirely filled with the DI water, the electric field is cancelled.

We propose a new type of on-chip micro-variable inductor fabricated by using microelectronic technology and lamination process. The proposed inductor is a dual circular coil and has an inductance of few nH. The fundamental idea is to place a liquid droplet between the metal turns of a coil in order to modify the capacitive/resistive coupling between metal tracks and hence to change the stored magnetic energy. In this study salt water has been used to fill partly or totally the channels constituting these three-dimensional coils. The numerical modeling allows us to obtain inductance values according to the liquid position, which can rise from zero to 100% of the total length of channels. The SU-8 resin was used to realize the microfluidic channels and Au as metallic tracks. The measured electrical characteristics show that these devices can be used up to 1.6 GHz frequency. The relationship between the inductance and the liquid position indicates that the tuning range of the inductance is approximately 107% (from 5.4 to 2.6 nH at a frequency of 1.6 GHz). Without liquid, the peak quality factor is 12, and the self-resonance frequency is 4 GHz; when the channels are completely full, these parameters become respectively 6 and 4.3 GHz.

A planar miniaturized inductor has been designed in order to realize some transduction functions linked to the presence of fluids. Its electrical behavior has been studied for two liquids: Galinstan (an alloy of GALium INdium STANum) and salted water. Their presence between metallic armatures modifies the inductance value at a nominal frequency, chosen at 2GHz. By using a FEM software, the spatial distributions of magnetic field and surface current density in the entire device have been modelized for six arbitrary positions of these liquids in inductor microchannels. The geometrical aspects of the device have been studied and their influence examined for each liquid. We show that the inductor performances are influenced by the spiral width variations and the inter-turn distances of the coil. Considering the device as a sensor, we have evaluated the variations of two parameters: inductance and quality factors, which can respectively attain 664% (for Galinstan) and 175% (for salted water) from their nominal values.

In this work, RF MEMS continuous reversible variable inductor has been fabricated by using microelec-tronic technology and lamination process. We review, evaluate and compare this variable inductor with other work. The proposed inductor is a dual circular coil and has an inductance of few nH. The fundamental idea is to place a liquid droplet between the metal turns of a coil in order to modify the capacitive/resistive coupling between metal tracks and hence to change the stored magnetic energy. The SU-8 resin was used to realize the microfluidic channels and Au as metallic tracks. To prove the reversibility of the inductor, two cases were studied: filling and emptying of channels. The tuning range of the inductance is approxi-mately 107 % at 1.6 GHz, making these devices very suitable as building blocks in many RF applications.