Processes and Effects of Oxygen and Moisture in Resistively Switching TaO x and HfO x

Foreign components such as dopants and impurities in molecular or ionic form may significantly influence forming/switching processes in redox‐based memories. This work presents a systematic study and discussion on effects of oxygen and moisture in Ta 2 O 5 and HfO 2 thin films, being two of the most used materials for redox‐based resistively switching random access memories. Whereas oxygen is found to not affect the device behavior, the presence of moisture profoundly influences it. It plays a crucial role for the counter electrode reaction, providing additional charged species and enabling the formation of oxygen vacancies, thus determining the forming voltage and the kinetics of this process. Here, methods for incorporation of moisture within the oxide films and its defect chemistry are discussed. Based on the standard electrode potentials and analysis of the electrochemical processes at both electrodes, it is possible to predict their sequence during switching. The difference using symmetric cells with inert electrodes Pt/MeO x /Pt and asymmetric devices with ohmic electrodes Me/MeO x /Pt is explained by the electrochemical reaction sequence and ability of the ohmic electrode to undergo redox reactions. Upon oxidation the Me electrode can either exchange O 2− with the oxide or can be a source for cations within the MeO x , keeping the balance between oxygen rich/deficient matrix.