Maskless selective electrochemically assisted wet etching of metal layers for 3D micromachined SOI RF MEMS devices

This paper presents a novel method for selective local removal of metal layers using maskless, electrochemically assisted wet etching. This method has been developed, investigated and successfully applied to the fabrication of three-dimensional micromachined silicon-on-insulator-based radio-frequency transmission lines with embedded laterally actuated microswitches, consisting of a silicon core covered by a gold metallization layer. The full-wafer sputtered metallization layer must be locally removed to guarantee a well defined, low-reflections and low-loss signal propagation in the transmission line. Gold areas to be etch are exposed to a 1.2 V potential difference to a saturated calomel reference electrode in a NaCl(aq) solution. Further, the selective removal of the metallization on the stoppers of laterally moving electrostatic actuators has been shown to drastically reduce the mechanical wear on the stopper tip.