Control of Switching Modes and Conductance Quantization in Oxygen Engineered HfOx based Memristive Devices

Hafnium oxide (HfOx)‐based memristive devices have tremendous potential as nonvolatile resistive random access memory (RRAM) and in neuromorphic electronics. Despite its seemingly simple two‐terminal structure, a myriad of RRAM devices reported in the rapidly growing literature exhibit rather complex resistive switching behaviors. Using Pt/HfOx/TiN‐based metal–insulator–metal structures as model systems, it is shown that a well‐controlled oxygen stoichiometry governs the filament formation and the occurrence of multiple switching modes. The oxygen vacancy concentration is found to be the key factor in manipulating the balance between electric field and Joule heating during formation, rupture (reset), and reformation (set) of the conductive filaments in the dielectric. In addition, the engineering of oxygen vacancies stabilizes atomic size filament constrictions exhibiting integer and half‐integer conductance quantization at room temperature during set and reset. Identifying the materials conditions of different switching modes and conductance quantization contributes to a unified switching model correlating structural and functional properties of RRAM materials. The possibility to engineer the oxygen stoichiometry in HfOx will allow creating quantum point contacts with multiple conductance quanta as a first step toward multilevel memristive quantum devices. Oxygen stoichiometry engineering is intrinsically achieved in hafnium‐oxide‐based memristive devices via reactive molecular beam epitaxy in a Pt/HfOx/TiN device configuration. This allows for uncovering the nature of complex coexistence of multiple switching modes (unipolar, bipolar, complementary, threshold) and occurrence of quantum conductance states. The findings are relevant to the control of switching dynamics in all oxide‐based switching devices.