Laterally driven tunable capacitors fabricated by a surface micromachining process for RF circuits

A laterally driven micro machined tunable capacitor is proposed. As an alternative to the traditional designs using two electrodes, three electrodes are used so that the series resistance could be reduced. This design also offers opportunities in the circuit design, since the DC-bias voltage is not applied on the two ports. To achieve the capacitance on the order of 0.4 pF, the electrodes are periodically arranged to form three groups of arrays. Thermal actuator arrays are employed to drive the movable electrodes. In order to simplify the design and fabrication, a structure using two layers to build the electrodes is provided, where the capacitance varies from 0.05 pF to 0.13 pF. This two-layer capacitor has been fabricated using a polysilicon surface micro machining process potentially compatible with CMOS process.