Modulation of the Conductive Filament Growth During the Electroforming Process in Metal Oxide-Based RRAM

Metal oxide-based Resistive Random-Access Memories (RRAM) exhibit multiple intermediate resistive states, due to the formation/rupture of a conductive filament (CF) inside a switching layer. While there have been extensive studies on the resistive switching behavior caused by a pre-existing CF, the initial stage of the formation and growth of a CF, i.e., the electroforming process has been less understood. In this work, we developed a physical model to fundamentally understand the formation and growth behavior of a CF in a metal oxide layer constrained by the top/bottom electrodes. It is revealed that the CF formation is assisted by the supply of oxygen vacancies at the anode and the oxygen vacancies transport in the oxide layer. The effects of the external conditions (the oxygen exchange rate j 0 and the applied voltage) and the physical properties of the oxides (the electrical σ and thermal conductivity k th ) on the CF morphology evolution, current density evolution, and local temperature and electrical potential distribution have been systematically explored. It is found that larger oxygen vacancy exchange rate and relatively small voltage sweep rate result in a more uniform CF. Furthermore, by choosing oxides with lower Lorenz number (ratio of k th and σ ), CF with more homogeneous morphology can be realized. This work provides a fundamental understanding of the kinetic behaviors of the CF formation and growth during the electroforming process, and could potentially guide the oxide and electrode materials selection, synthesis and working conditions for switching to achieve improved RRAM stability and functionality.