In this work, a conductive atomic force microscope (C-AFM) is used to study the reliability (degradation and breakdown, BD) of SiO2 and high-k dielectrics. The effect of a current limit on the post-BD SiO2 electrical properties at the nanoscale is discussed. In particular, the impact of a current limit imposed during the stress on the post-BD oxide conductivity at the position where BD has been triggered, the area affected by the BD event and the structural damage induced in the broken down region will be investigated. A purposely developed C-AFM with enhanced electrical performance (ECAFM) is also presented, which has been used for the electrical characterization of HfO2/SiO2 gate stacks. The conduction of the fresh (without stress), electrically stressed and broken down stacks have been analyzed. © 2006 Elsevier B.V. All rights reserved.