A novel linearly tunable MEMS variable capacitor

The linearly tunable microelectromechanical systems (MEMS) capacitor with 608 comb fingers changing the overlap area is developed. Unlike the conventional micromachined capacitor using the gap between the parallel plates, the proposed capacitor adopts the overlap area as the tuning parameter. In addition, the tuning range of the proposed capacitor has large nominal capacitance C sub 0 , whereas the parallel plates have a range of C sub 0 /3 theoretically. The 6-mum-thick single-crystal silicon MEMS structure is bonded to the pyrex glass substrate using the glass-silicon anodic bonding technique and the chemical mechanical polish (CMP) to make the desired capacitor. Single-crystal silicon was chosen as a capacitor structure material because it has excellent mechanical properties greater than those of polysilicon and aluminium as the structure material, and the pyrex glass is used as a substrate instead of silicon to reduce the RF losses through the substrate over the high-frequency range. The measured capacitor shows a nominal capacitance of 1.4 pF, and 10% tuning range at 8V. The capacitor model is also developed to explain the parasitic effect over the high-frequency range and proved by using the Serenade software of the Ansoft Corporation.