Design and fabrication of a continuously tuned capacitor by microfluidic actuation

International audienceThis paper presents the design and the fabrication of a continuously tunable RF MEMS capacitor using micro fluidics as a tuning parameter. The impedance variation principle is based on the modification of the capacitor gap permittivity produced by the presence of deionized water and its displacements in a channel inserted between electrodes. In addition, the electric field distribution changes in equiponderant way according to the DI water positions in the channel. This change modifies the capacitive coupling, the stored energy and consequently the self-resonant frequency. The fabrication process is based on two parts: metallic paths having a spiral form, and obtained by electroplating a 7 µm thick gold layer to constitute electrodes; and fluidic channels, realized by super imposing two SU-8 films. The measurements show a non-linear variation of the capacitor value according to the water positions. The tuning range is very large, reaching up to 4650% for the capacitance, and 335% for the resonant frequency. However, the quality factor reaches Qmax = 79 at 550 MHz if the capacitor is empty and decreases with the fluid displacements to Qmin = 3.13