Hf-doped Ta2O5 stacks under constant voltage stress

Abstract

The stress-induced leakage current in Hf-doped Ta2O5 layers (7; 10nm) under constant voltage stress at gate injection was investigated in order to assess the mechanisms of conduction, the traps involved and the effect of Hf doping. The amount of Hf is found to affect the conduction mechanisms, the temperature dependence of the leakage current and the current response to the stress. A significant leakage current increase is observed only when the stress voltage and/or stress time exceed the corresponding threshold values, where the charge trapping at the pre-existing traps dominates below and defect generation above these threshold values. The energy levels of the traps responsible for the current transport are estimated. The stress effect on dominant conduction mechanisms appears quite weak, and the nature of the traps controlling the current transport before and after the stress seems to be nearly identical. The results indicate that the constant voltage stress affects the pre-existing traps in Hf-doped Ta2O5 and modifies their parameters, but there is no evidence for stress-induced generation of traps with completely new nature different from oxygen-vacancy related defects.