Direct Observation of Conduction Mechanism in Te-Based Selector-Only Memory via Low-Frequency Noise Characterization

Selector-only memory (SOM) based on ovonic threshold switches is a promising candidate for dense cross-point memory by integrating selector and memory functions in a single two-terminal device. However, the physical origins of off-state conduction and threshold voltage (V_th) modulation remain unclear. Here, we investigate these mechanisms in a Te-rich Ge-Sb-Se-Te:Sn SOM by correlating DC transport, low-frequency noise (LFN), and materials analyses. DC I-V characteristics analyzed using Poole-Frenkel (PF) emission and trap-assisted tunneling (TAT) models reveal identical trap energy levels across prefirst firing, low-V_th, and high-V_th states, indicating a common trap species with state-dependent spatial redistribution. LFN measurements distinguish PF- and TAT-dominated regimes and show consistent state-dependent noise behavior. Cross-sectional energy-dispersive X-ray spectroscopy reveals electric-field-polarity-dependent Te redistribution near the top electrode, while ab initio calculations identify Te-Te dimer defects as acceptor-like deep traps governing off-state conduction. These results provide a unified mechanism for V_th modulation in Te-based SOM devices.