A zipper-action differential micro-mechanical tunable capacitor

We present a differential multi-fingered micro-electro-mechanical tunable capacitor. This device is intended to be used in RF IC applications such as filters and VCOs. The device is based on the zipper actuation principle, which allows for potentially wide tuning range. Differential structure is used to improve the quality factor. This capacitor was fabricated in MUMPs polysilicon surface micromachining process and achieves 46% tuning range with tuning voltage of 35 V. A CMOS VCO with this capacitor exhibited tuning range of 4.8% with the center frequency of 1.5 GHz. The phase noise was -131 dBc/Hz at 600 kHz offset from carrier with the output power of 1.6 dBm.