Enhanced Current-voltage Nonlinearity by Controlling Oxygen Concentration of TiO_x Buffer Layer for RRAM Passive Crossbar Array

As a next-generation memory, resistive random access memory (RRAM) is attracting attention for its fast speed and non-volatility. Nevertheless, an additional selecting element is required to solve the sneak path problem. However, nonlinear devices such as transistors and selectors not only degrade density of the RRAM array, but also increase difficulty of 3D integration. Therefore, in this study, we propose a method for improving the current-voltage (I-V) nonlinearity of an Pt/Al₂O₃/ TiO_x/Ti/Pt RRAM. Oxygen concentration was controlled based on electrical flexibility of TiO_x encompassing metallic and semiconducting properties; and three devices with different TiO_x were fabricated. As the O/Ti atomic ratio increases from 1.31 to 1.74, the enhanced I-V nonlinearity was confirmed, which was also quantitatively verified through fitting with a hyperbolic sine function. Reflecting the measured nonlinearity, RRAM passive array was constructed and its read margin was investigated by SPICE simulation. As a result, it is demonstrated that the read margin was improved by increasing the nonlinearity. For TiO_1.74 sample which exhibits the highest nonlinearity, a read margin of 22.97% was achieved in 2⁷ × 2⁷ array size. By increasing the nonlinearity of RRAM devices, it is expected that RRAM passive array can be utilized for future high-density storage class memory.