Investigating the electrical properties of (TaN)_1-xC_x thin films and their crystal phase evolution for enhanced performance in OTS selector devices

Three–dimensional (3D) cross–point memories have attracted significant interest owing to their fast processing and high densities, achieved by stacking memories with selector devices. Ovonic threshold switching (OTS) is a promising selector for memory arrays because of its reversible electrical switching behavior. Although transition metal nitrides (TMNs) such as TiN_x, TaN_x, WN_x are commonly used as electrodes in OTS devices owing to their superior thermal stability with low resistivity, the metal ions in TMNs can diffuse and recrystallize with chalcogenide alloys, thereby degrading device performance. Amorphous carbon (a–C) can be a promising alternative electrode material, offering advantages such as low surface roughness, cost–effectiveness, high work function (WF), and excellent thermal stability. However, its high resistivity (∼ 150 mΩ–cm) increases threshold voltage (V_th) of the device, resulting in higher power consumption. Therefore, combining a–C with TMNs can leverage their strengths. In this study, we explored C content in (TaN)_1-xC_x (0 ≤ x ≤ 0.20) electrodes and its effect on GeS₂–based OTS selector devices. The resistivity ranged from 0.850 to 1.203 mΩ–cm with increasing x (0 ≤ x ≤ 0.20). In device characteristics, both V_th and I_off decreased from 5.10 to 4.10 V and 12.80–6.00 nA with increasing x, respectively, indicating that power consumption can be effectively reduced. The decrease in V_th and I_off induced from incorporating C can be attributed to the increased WF and decreased interface–trap density (N_it) of (TaN)_1-xC_x electrodes; while, an excellent device lifetime (6.0 × 10⁹ pulses) was obtained due to higher bonding strength and thermal stability. The higher subthreshold swing of (TaN)_1-xC_x (x = 0.20)/GeS₂ (OTS selector)/TaN device allows to reduce N_it, minimizing charge trapping effect, in turns, reducing V_th.