Low-frequency noise in n-channel metal-oxide-semiconductor field-effect transistors undergoing soft breakdown

For 3.3-nm thick gate oxide n-channel metal-oxide-semiconductor field-effec t transistors subject to a stress gate voltage of 5.5 V, three distinct eve nts are encountered in the time evolution of the gate current: stress-induc ed leakage current (SILC), soft breakdown (SBD), and hard breakdown (HBD). The localization of SBD and HBD paths, as well as their developments with t he time, is determined electrically, showing random distribution in nature. At several stress times, we interrupt the stressing to measure the drain c urrent low-frequency noise power S-id. As expected, S-id follows up the spo ntaneous changes at the onset of SBD and HBD. The S-id spectra measured in fresh and SILC mode are reproduced by a literature model accounting for the carrier number and surface mobility fluctuations in the channel, and, as a result, both preexisting and newly generated trap densities are assessed. The post-SBD S-id does originate from current fluctuations in the SBD perco lation paths, which can couple indirectly to drain via underlying channel i n series, or directly to drain if the SBD path is formed close to drain ext ension. In particular, a fluctuation in S-id itself in the whole SBD durati on is observed. This phenomenon is very striking since it indeed evidences the dynamic percolation origin concerning the trapping-detrapping processes in and around the SBD paths. The subsequent HBD duration remarkably featur es a flat S-id, indicating the set-up of a complete conductive path prevail ing over the trapping-detrapping processes. (C) 2001 American Institute of Physics.