Abstract: The physical origin of post soft breakdown (SBD) current saturation behavior of ultrathin gate oxides is discussed on the basis of electron velocity saturation concept.The post soft breakdown current-voltage (I-V) characteristic is studied with the proportional difference operator (PDO) method.It is shown that the proportional difference of the soft breakdown I-V curve is a peak function.Its peak position and height are related to the saturation velocity of electron in SBD path and the saturation current density through the SBD path,respectively.In addition a simple and useful method of defining and characterizing the SBD path cross-section in SiO2 based on the defect scattering mechanism is also presented.

Key words: ultrathin SiO2, soft breakdown, I-V saturation characteristics