Multilevel resistive switching behaviors of N₂-plasma-treated stacked GdO _x /SiN _x RRAMs

The resistive switching (RS) characteristics of N₂-plasma-treated SiN _x and stacked GdO _x /SiN _x resistance random access memories (RRAMs) have been investigated. With the N₂ plasma treatment on SiN _x films, the operation voltages and resistance ratio of SiN _x RRAMs are significantly improved by increasing the concentration of nitrogen vacancies, leading to a reduction in the Schottky barrier height at the Ir/SiN _x interface. The device reliabilities of N₂-plasma-treated SiN _x RRAMs such as a data retention of more than 10⁴ s and an endurance of 100 cycles for a resistance ratio of more than two orders of magnitude are also obtained. Further, the stacked GdO _x /SiN _x RRAMs present multilevel RS behaviors with an unbalanced formation and rupture of the conductive filaments, resulting from the differences in dielectric permittivity and Gibbs free energy of the stacked RS materials. A resistance ratio of more than one order of magnitude between each resistance state is achieved with a stable cycling endurance and data retention testing. The Schottky emission and space-change-limited-conduction are responsible for the carrier transport mechanism of the stacked GdO _x /SiN _x RRAMs at a high resistance state and middle resistance state, respectively. Stacked GdO _x /SiN _x RRAMs with N₂ plasma treatment have the potential to be adopted in future high-density nonvolatile memories.