Nonlinear bidirectional selector without rare materials for stackable cross-bar bipolar memory applications

The advantage of a nonlinear bidirectional selector is its high access ratio with multiple transport mechanisms in a wide bias range. The multilayer structure of TiN/Al₂O₃/TiO₂/Al ₂O₃/Ti with a nonlinear varistor characteristic is proposed. The features of the structure include its low-temperature process (~250°C) for stackable applications, non-requirement of rare materials such as Pt, and its high access ratio (~3200). The varistor characteristic of the nonlinear selector is discussed and attributed to carrier tunneling and thermionic emission for small biases (OFF state) and large biases (ON state), respectively. The selector shows scaling feasibility owing to its property of inertness to SiO₂ encapsulation and is compatible with the current IC and memory industry.