Deep understanding of oxide defects for stochastic charging in nanoscale MOSFETs

In nanoscale devices, trapping and de-trapping of single carrier charge caused by few defects in ultrathin gate dielectrics can affect the drain current significantly [1-4]. The oxygen vacancy in gate oxides is mostly considered as the criminal defect [1]. Recently, the stochastic charge trapping or dynamic behaviors (charging and discharging) of defect and its frequency dependence have been paid much attention with experiments [1-6]. The concept of metastable states of defect has been proposed for explaining its complete dynamics [1,5-9]. However, the atomistic origin of the stochastic single-charge trapping behavior and the missing metastable states are still not clear. In this paper, the stochastic defect transitions in SiO₂ and HfO₂ gate dielectrics are investigated by using ab-initio simulation of atomistic defect model, and the possible metastable defect states are directly obtained from climbing nudged elastic band simulation.