Chemistry of resistivity changes in TiTe/AlO conductive-bridge memories.

We report the chemical phenomena involved in the reverse forming (negative bias on top electrode) and reset of a TaN/TiTe/AlO/Ta memory stack. Hard X-ray photoelectron spectroscopy was used to conduct a non-destructive investigation of the critical interfaces between the electrolyte (AlO) and the TiTe top and Ta bottom electrodes. During reverse forming, Te accumulates at the TiTe/AlO interface, the TiO layer between the electrolyte and the electrode is reduced and the TaO at the interface with AlO is oxidized. These interfacial redox processes are related to an oxygen drift toward the bottom electrode under applied bias, which may favour Te transport into the electrolyte. Thus, the forming processes is related to both Te release and also to the probable migration of oxygen vacancies inside the alumina layer. The opposite phenomena are observed during the reset. TiO is oxidized near AlO and TaO is reduced at the AlO/Ta interface, following the O drift towards the top electrode under positive bias while Te is driven back into the TiTe electrode.