Improvement of switching uniformity in HfOx-based resistive random access memory with a titanium film and effects of titanium on resistive switching behaviors

In this study, the effects of the Ti layer on resistive switching behaviors of HfO x -based resistive switching random access memory (ReRAM) were investigated. After introducing a thin Ti layer (∼10 nm) between the Ta and HfO x layers, both cycle-to-cycle uniformity within one cell and cell-to-cell uniformity were significantly improved. In addition, the higher ON/OFF ratio was obtained owing to the resistance increase in the high-resistance state, and a high device yield (>90%) also was achieved. The improvement of switching uniformity can be explained by the Ti doping effect, which is caused by the diffusion of Ti into the HfO x layer. In addition, the Ti layer had the effect of generating more oxygen vacancies in the HfO x layer, which led to the lowering of forming voltage (∼2.6 V). To confirm the change in the amount of oxygen vacancies, X-ray photoelectron spectroscopy analysis was performed. The formation of the TiO x layer and the Ti doping effect are considered to contribute to the generation of more oxygen vacancies in the HfO x layer.