On the cyclic threshold voltage shift of dynamic negative-bias temperature instability

Based on new experimental evidence for the cyclical threshold voltage shift (ΔVt) under dynamic NBTI and a recent ab-initio study on the oxygen vacancy defects (hole traps) in the SiO2, an improved physical hole-trapping model for dynamic NBTI involving the Eδ∲ center is proposed. This model stipulates that the hole-trap precursor (i.e. the Si-Si dimer) responsible for the cyclic ΔVt only undergoes marginal structural relaxation under typical NBTI stress condition, such that the Si-Si bond is completely re-formed when the stress is terminated. This framework is subtly different from an existing one based on the earlier HDL model. The latter assumes that the switching hole traps are oxygen vacancy defects that have undergone significant structural relaxation and that the switching behavior is due to the repetitive transitions between the positively charged state and the charge-compensated state. Experimental results obtained from higher oxide-field stressing in fact do not support this proposition.