Soft breakdown as a cause of current drop in an MOS tunnel structure

Abstract

The effect of electric stress on current-voltage characteristics of Al/SiO2/p +-Si MOS diodes with a tunnel-thin (2.5–3.0 nm) insulator was studied at constant current and constant voltage. Under constant-voltage stress, the current increase related to soft breakdown was followed in several cases by an abrupt drop in current. Typically, the drop occurs at a high bias, and it may be a specific manifestation of a soft breakdown. At strong nonuniformity of the SiO2 thickness, the effect can be significant even if the breakdown is localized within a rather small area.