| AVS 60th International Symposium and Exhibition | |
| Electronic Materials and Processing | Tuesday Sessions |
| Session EM+MI+NS+SS+TF-TuA |
| Session: | High-k Oxides for MOSFETs and Memory Devices II/Oxides and Dielectrics for Novel Devices and Ultra-dense Memory I |
| Presenter: | H.S. Hwang, POSTECH, Republic of Korea |
| Correspondent: | Click to Email |
ReRAM has been considered as a promising candidate to overcome scaling limits of the conventional FLASH memory due to its superior performance. To realize the high density memory, 3D cross-point array or Vertical ReRAM are necessary [1]. To integrate cross-point (4F2) ReRAM device array, we need to develop bi-directional selector device to suppress the sneak current path through the unselected devices. Although various candidates with selector properties were recently reported, several problems such as insufficient current density at set/reset operations for nano-scale devices, low selectivity, and poor endurance have been raised. In this talk, two different types of selector device for cross-point ReRAM are introduced.
A. Threshold switching device
Various reports on threshold switching device with oxides of V, Nb, and Ti have been reported. This threshold switching is attributed to formation of a metallic phase as a result of local Joule heating induced metal-insulator transition (MIT) of the corresponding suboxides such as VO2, NbO2, and Ti2O3. Among them, we investigated threshold switching characteristics of NbO2 [2]. Ultrathin NbO2 layer (< 10nm) exhibits excellent threshold switching characteristics. Especially, thermal stability of threshold switching was obtained at a high temperature. Threshold switching property remains stable up to 433K, which is much higher than VO2 material (only a 340K). Furthermore, we demonstrate hybrid memory characteristic, which exhibits both threshold and memory switching, by controlling the oxygen concentration of NbOx layer.
B. Multi-layered oxide based device
Highly non-linear property of Ta2O5/TaOx/TiO2 structure was reported [3]. By using multi-layered oxide stack, a high current density of 107A/cm2 and a high selectivity (~104) were achieved. To maximize the selector performance, we have performed extensive tunnel barrier engineering such as the adoption of various materials and control of oxidation conditions to optimize the oxide stoichiometry, film thickness, and electrode material. Furthermore, in order to confirm the feasibility for cross-point array application, selector device was vertically-integrated with ReRAM.
We have demonstrated excellent selector characteristics of threshold switching device and multi-layered tunneling oxide based device. Superior performances of selector devices show good promise for future high density ReRAM applications.
REFERENCES
1. D. Kau et al., IEDM, 27.1, pp. 617-620, 2009.
2. S. Kim et al., VLSI, T18-3, pp. 155-156, 2012.
3. W. Lee et al., VLSI, T5-2, pp. 37-38, 2012.