Development of a triangular-plate MEMS tunable capacitor with linear capacitance–voltage response

This paper introduces a modified structure for parallel-plate-based MEMS tunable capacitors. The capacitor has triangular electrodes with geometric and structural asymmetry, which enhances its performance. The device structure is also equipped with a set of cantilever beams between capacitor’s electrodes, called middle beams. These beams provide extra stiffness as tuning voltage increases and delay the pull-in which results in a higher tunability. They also reduce the high sensitivity of the capacitance to the voltage change and linearize the C–V response. An analytical model is developed to optimize the capacitor’s dimensions for maximum linearity of the response. Numerical simulations demonstrate tunabilities over 150% where more than 2/3 of which is highly linear. Capacitors fabricated with PolyMUMPs verify that the design technique proposed in this paper can improve the linearity of the device and increase the maximum tunability. The proposed design has a simple geometry and is fabricated using three structural layers, and therefore, it can be easily integrated in tunable filters or other RF circuits.