Amorphous Dielectric-Integrated Retina-Inspired HfS2 Devices with Enhanced Synaptic Plasticity for Neuromorphic Vision Assistance.

Realizing neuromorphic functionalities in field-effect transistors (FETs) requires precise modulation of multilevel conductance states with robust retention. Two-dimensional (2D) semiconductor FETs, however, often suffer from a limited synaptic weight dynamic range and short retention times because of inadequate charge dynamics in the channel. This results from the low-k dielectric nature of the channel, which provides limited and unstable carrier storage sites and insufficient capacitive coupling. This study expands the weight dynamic range by forming a weight-control dielectric through oxygen plasma treatment of HfS2, producing an HfOx/HfS2 heterostructure. This engineered interface strengthens gate coupling and enables charge trapping via tailored defect states that act as dynamic storage centers, thereby providing tunable conductance and improved retention. Electrical characterization of the HfOx/HfS2 FETs reveals a tenfold increase in the ON/OFF ratio and enhanced hysteresis. Under optical illumination, the devices exhibit high photoconductive gain and stable synaptic behavior, including a 67.38% larger dynamic range for long-term potentiation/depression driven by trap-mediated charge dynamics. This synaptic plasticity is leveraged to demonstrate optical encoding/decoding, in-memory OR logic, and pattern-recognition functionality, highlighting the potential of oxygen-plasma-engineered HfS2 FETs for neuromorphic processors and integrated logic-in-memory systems.