Comprehensive understanding of field-dependent conduction mechanisms of sub-4-nm-thick post-soft-breakdown SiO2 films

The experimentally determined conduction mechanisms of gate leakage current are examined for two different soft-breakdown events: analog-soft breakdown and digital-soft breakdown. It is strongly suggested that space-charge-limited conduction does not, by itself, represent the main conduction mechanism after analog-soft-breakdown events. In contrast, the analog-soft-breakdown current behaviors suggest that various variable-range-hopping conduction mechanisms play important roles in the transport process. On the other hand, it is found that the incremental gate current after digital-soft-breakdown events can be experimentally expressed in a simple closed form as functions of temperature and gate voltage; the empirical expression given herein indicates that the post-digital-soft-breakdown current is not ruled by a simple or single conduction mechanism. Features of the post-digital-soft-breakdown current are examined by the field-dependent lifetime model formulated by Schenk [Solid-State Electron. 35, 1585 (1992)] it is strongly suggested that Schenk's theory primarily supports the experimental results. It is also suggested that the space-charge-limited current plays an important role, a background leakage current, in the post-digital-soft breakdown current.