Fabrication of a micromachined tunable capacitor using the complementary metal-oxide-semiconductor post-process of etching metal layers

In this study, we investigate the fabrication of a micromechanical tunable capacitor using the commercial complementary metal-oxide-semiconductor (CMOS) process and the post-process of maskless wet etching metal layers. The post-process has merits of easy execution and low cost. The post-process uses two etchants to etch the metal layers to release the suspended structures of the tunable capacitor. The comb-drive actuator is employed to change the position of the movable plate in the parallel capacitor, such that the overlap area between the two plates in the parallel capacitor is changed. The experimental results show a capacitance of 3.5 pF and a tuning range of 3.5:1 at 20 V.