A study on fabrication of threshold switching selector device for 3D cross-point memory applications

Abstract

As the growing interest in research on the high-density nonvolatile memory, research on resolving critical issues in memory devices also increases. Among various issues, the unexpected leakage current induces sensing errors that can limit the maximum array size of memory devices. In this paper, we fabricate the atomic switch-based threshold switch selector device that can reduce the leakage current of the memory device using CMOS compatible deposition process. In Chapter 1, we introduce the necessity of threshold switch selector device for the fabrication of high-density memory devices. We also introduce the types of threshold switch selector device. Especially, we introduce about the operation principle of atomic switch-based threshold switch selector device. In Chapter 2, we report Pt/Ag-doped ZnO/ZnO/Ag-doped ZnO/Pt structured threshold switch selector devices fabricated using CMOS compatible sputtering process. When voltage is applied to the selector device, Ag ions in the Ag-doped ZnO layer form volatile conducting filaments in the switching layer. By constructing multilayer structure with doping concentration gradient, the formation of volatile filaments at high on-current state can be modulated. The devices exhibit high selectivity of 1010 with high on-current density of 2 MA m-2. Also, when the fabricated selector device connected to the resistive switching memory device, the selector device effectively reduced the leakage current of the memory device. These results demonstrated the compatibility of the fabricated selector device to the memory device. In Chapter 3, we report the atomic switch-based selector device with SiO2 interlayer for wide range of tunable threshold voltage characteristics. Such a wide range of threshold voltage characteristics is required to solve the voltage matching issue of a memory device and a selector device. Because of the SiO2 interlayer was deposited using ALD, the interlayer has few defects that facilitate the migration of Ag ions. It can interfere the formation of conductive filaments when voltage is applied to the selector device. Therefore, by controlling the thickness of the SiO2 interlayer, the threshold voltage of the selected device could be adjusted from 0.6V to 2.2V. Also, when comparing the leakage current of the memory device by connecting the selector device with the SiO2 interlayer and the selector device without interlayer to the memory device, it was confirmed that the selector device with the SiO2 interlayer can effectively control the leakage current. This study suggests that insertion of interlayer provide tunable threshold voltage to the selector device for high-density cross-point array.