流体MEMSキャパシタの高周波等価回路モデルの検討

概要

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There exists a growing demand on high performance variable filters for multi-function, multi-band wireless systems used in wide variety of applications. A variable capacitor with high capacitance ratio (CR) is one of the key devices to realize such controllable/reconfigurable filters. This paper reports the device structure, fabrication process, and the performance of a very high CR variable capacitor using pure water as dielectric material. The device holds two reservoir cells and was fabricated by microelectromechanical systems (MEMS) technology. It exhibited three digitally-stepped capacitances; varied from 0.93 pF to 32.9 pF (CR=35), then to 74.4 pF (CR=80) at 1 MHz by filling each of the cells with pure water. In order to confirm the electrical behavior for such a fluid MEMS capacitor, its microwave performance was evaluated. An equivalent RF circuit model with 9 elements has been introduced and the device performance was successfully simulated up to 4 GHz. It is also confirmed that the 3 step capacitance values stay effective in the same frequency range.