Ultrathin Carbon Interlayer-Enabled Enhancement of Threshold-Voltage Window and Switching Reliability in Ge2Se3Te5 Selector-Only Memory Devices

Abstract

Selector-only memory (SOM) has attracted attention as a promising memory technology because it enables programmable threshold-voltage state separation using a single ovonic threshold switch (OTS) device. In SOM devices, the electrode–chalcogenide interface strongly affects the threshold-voltage difference (ΔV_th) and switching reliability, as repetitive switching induces interfacial reactions and elemental diffusion. In this study, the electrode-dependent SOM characteristics of Ge₂Se₃Te₅ (GST) devices were investigated using W, TiN, and W with an ultrathin (∼6 nm) carbon interlayer (W/C) as top electrodes. The W/C device exhibited the largest ΔV_th (∼1.0 V) and the widest read window margin (∼0.9 V), and maintained a ΔV_th exceeding 0.7 V over repeated switching cycles, exhibiting the most stable characteristics. Conduction mechanism analysis based on the Poole–Frenkel emission model, Arrhenius analysis, and the thermally assisted hopping model revealed that the enhanced ΔV_th originates from increased trap-state separation and trap-density difference between programmed states. Transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy (TEM-EDS) and line-EDS analyses confirmed that the carbon interlayer effectively suppressed Te diffusion and interfacial phase formation at the W/GST interface during repetitive switching. These results demonstrate that ultrathin carbon interfacial engineering is an effective strategy for improving ΔV_th and switching reliability in GST SOM devices.