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-effect transistors subject to a stress gate voltage of 5.5 V, three distinct events are encountered in the time evolution of the gate current: stress-induced leakage current (SILC), soft breakdown (SBD), and hard breakdown (HBD). The localization of SBD and HBD paths, as well as their developments with the time, is determined electrically, showing random distribution in nature. At several stress times, we interrupt the stressing to measure the drain current low-frequency noise power S_id. As expected, S_id follows up the spontaneous 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 percolation paths, which can couple indirectly to drain via underlying channel in series, or directly to drain if the SBD path is formed close to drain extension. In particular, a fluctuation in S_id itself in the whole SBD duration 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 features a flat S_id, indicating the set-up of a complete conductive path prevailing over the trapping-detrapping processes.