Electrochemically prepared oxides for resistive switching devices

Redox-based resistive switching memories (ReRAM) based on metal oxides are considered as the next generation non-volatile memories and building units for neuromorphic computing. Using different deposition techniques results however in different structural and electric properties, modulating the device performance. In this study HfO₂ and Nb₂O₅ were prepared electrochemically by anodizing sputtering-deposited Hf and Nb in borate buffer solution. Photoelectrochemical measurements were used to study the solid state properties of the anodic oxides, such as band gap and flat band potential. In the case of anodic HfO₂, detected photocurrent is ascribed to optical transitions between localized (generated by the presence of oxygen vacancies into the oxide) and extended states. Impedance measurements disclosed the formation of n-type Nb₂O₅ and insulating HfO₂. Pt top electrode was deposited onto the metal/anodic oxide junctions to fabricate ReRAM cells. Whereas switching behaviour of Nb/anodic Nb₂O₅/Pt cells was not reliable, good endurance and retention performances were proved in the case of Hf/anodic HfO₂/Pt cells, showing that electrochemical growth of the oxides can be a reliable way to fabricate solid electrolytes for resistive switching memories.