Methods for noise isolation in RFCMOS ICs

Different process techniques of suppressing the transmission of high-frequency noise induced by fast-switching MOS gates through silicon (Si) substrate have been examined. The isolated n/sup +/-pocket structure formed by a new process technique designed in this work has proven to be most effective in guarding vulnerable devices from remnant high-frequency noise roaming in the substrate among the structures we have used in the experiment: p/sup +/ guard ring, proton implant, and pocket structures. The noise suppressing efficiency is -75 dB at 1 GHz of n/sup +/-pocket structure in contrast to -38 dB at 1 GHz of unprotected devices. The protecting structures should become a decisive measure for future success of Si-based radio frequency integrated circuit (RFIC) applications.