Design of ReRAM cell structure by metal buffer and contact engineering via first-principles transport calculations

We performed first principles calculations of Resistive Random Access Memory (ReRAM) cell, which consists of HfO₂ resistive layer and TiN electrodes, by using nonequilibrium Green´s function theory combined with density functional theory (NEGF-DFT). To analyze the transport mechanism of low/high resistive (ON/OFF) states, we examined several models of the HfO_x wire (filament) structures and the oxidized interfaces. We found that concentration of vacancies in a only thin filament provides sufficiently low resistance than that of the thick filament. Furthermore, the oxidized interface by scavenged oxygen ions plays an important role to distinct ON/OFF ratio in low bias voltage. In order to argue the contact effect directly, we evaluated the complex site energies based on the effective Hamiltonian formalism. Then we proposed insertion of thin metal buffer layer to control the contact effects.