It is shown in this work that the presence of an ultrathin (similar to 1.5 nm) SiO2 interfacial layer reactively formed in between a thick (similar to 20 nm) high-permittivity CeOx film and a metal NiSi2 bottom electrode in a metal-insulator-metal structure has remarkable consequences for the hysteretic current-voltage (I-V) characteristic of the device. Conductance values in the low resistance state (LRS) close to integer and half-integer values of the quantum conductance unit G(0) = 2e(2)/h, where e is the electron charge and h the Planck constant, reveal the formation of filamentary structures across the stack with bottlenecks of atomic dimensions. Even though the hysteretic behavior partially remains when the bottom electrode (Ti, TiN, or W) is changed, the LRS I-V no longer exhibits so well defined conductance levels as in the NiSi2 case. This distinctive behavior is attributed to the presence of the SiO2 switching layer. Supplementary post-breakdown I-V data obtained from Al/SiO2/Si capacitors supports this hypothesis. (c) 2012 Elsevier B.V. All rights reserved.