A novel approach to enhancing performance and endurance in GeS2 OTS devices using amorphous carbon doped W2N electrodes

Abstract

Three-dimensional (3D) cross-point (X-point) memory has gathered interest for its fast data processing and high density, achieved by stacking memory with a selector device to prevent misinterpretation. Ovonic threshold switching (OTS) is a promising selector due to its reversible switching behavior. Although, OTS devices typically employ transition metal nitrides (TMN) such as TiNx, TaNx, and WNx for electrodes owing to their good stability, high melting points, and low resistivity, TMNs can diffuse and degrade device performance by recrystallizing with chalcogenide alloys. Amorphous carbon (a-C) can be a good alternative electrode material due to its low roughness, cost-effectiveness, high work function (WF), and excellent thermal stability. However, the high resistivity of a-C (similar to 150 m Omega-cm) increases threshold voltage (V-th), causing high power consumption. Therefore, combining both a-C and TMN materials can effectively obtain their advantages. This study explores the effect of varying a-C content in W2N electrodes on GeS2-based OTS selectors. The (W2N)(1-x)C-x (0 <= x <= 0.25) electrodes were deposited using DC magnetron co-sputtering. The phase of (W2N)(1-x)C-x (0 <= x <= 0.25) films transformed from polycrystalline to amorphous with increasing x. Devices with (W2N)(1-x)C-x/GeS2/W2N structure showed decreased V-th and off current, improving from 4.8 to 3.8 V and 8.0-4.17 nA, respectively. The subthreshold slope, distance between traps, and interface trap density (N-it) were extracted using the Pool-Frenkel model. The reduced V-th may be attributed to a higher WF and lower N-it with increasing x. The device's lifetime improved up to 1.0 x 10(9) pulses for the highest a-C content in (W2N)(1-x)C-x (0 <= x <= 0.25) electrodes.