Optimization of the Forming Process of HfOx-Based RRAM to Achieve Bidirectional Forming and Enhanced Switching Performance by Inserting an Oxygen-Vacancy-Rich Layer

With the continuous advancement of science and technology, the application of resistive random access memory (RRAM) based on binary transition-metal oxides in nonvolatile memory devices is expanding. In our studies, the RRAM cell structure was constructed by the hypoxic vacancy layer (HfO_y) sandwiched between two oxygen-vacancy-rich layers (HfO_x), and then the complete forming, reset, and set processes were carried out. Because a bidirectional formation of conductive filaments was realized during the forming process, the TiN/HfO_x/HfO_y/HfO_x/TiN structure exhibits lower forming, reset, and set operating voltages compared to the device TiN/HfO_x/HfO_y/TiN. In addition, the effect of the voltage ramp rate (V_RR) on the characteristics of the device was studied. The research results revealed that, with a faster V_RR, the operating voltages of the set and reset processes for HfO_x/HfO_y/HfO_x also become larger. In the meantime, the conduction mechanism was also analyzed from the current–voltage characteristic during the switching processes. It was discovered that space-charge-limiting conduction is the conduction mechanism in the high resistance state and the ohmic conduction mechanism in the low resistance state.