The influence of Hf-doping on the leakage currents and conduction mechanisms in Ta 2 O 5 stacks is investigated. The current conduction mechanisms as well as the traps participating in them are identified by temperature dependent current–voltage measurements. A strong dependence of the dominant conduction mechanism on the doping and the layer thickness is established. Hf-doping alters substantially the dominant mechanism of conductivity in pure Ta 2 O 5 . Conduction in Hf-doped Ta 2 O 5 is performed through shallower traps as compared to the pure Ta 2 O 5 , which results in a higher leakage current in the former stacks. A certain trap can assist in different conduction processes depending on the layer thickness and the applied field. It is found that Hf-doping passivates oxygen vacancies in Ta 2 O 5 and the deep traps level associated with this defect is not observed in Hf-doped samples. The origin of the detected traps is also commented.