Strain-Assisted Large-Scale 1T-MoS2 Synthesis and its Optical Synaptic Flash Memory Application

Abstract

2D transition-metal dichalcogenides (TMDCs) have attracted attention as promising materials for next-generation devices owing to their versatile electronic and optical properties. The phase variety of TMDCs provides strategic opportunities for performance enhancement. Herein, a novel method is proposed to synthesize wafer-scale 1T phase MoS₂ and, simultaneously, induce a phase transition via a plasma-assisted metal-sulfidation process and spontaneous internal strain. With thicker MoS₂ layers, the strong internal strain during synthesis suppresses the undesirable phase transition from the metastable 1T phase to the 2H phase, ensuring stabilization of the 1T phase. Furthermore, as-synthesized 1T-MoS₂ shows remarkable electrical properties owing to the narrow bandgap (0.4 eV) of its semi-metallic state. As a result, the 1T-phase MoS₂ floating gate (1T-FG) flash memory demonstrates a wider memory window, a higher on/off ratio, and improved stability compared to the 2H-phase MoS₂ floating gate (2H-FG) flash memory. A 5 × 5 array structure is constructed to validate large-scale integration. Notably, under light irradiation, a single 1T-FG memory enables carrier trapping in the floating gate, even in the off state. This study introduces a facile phase control strategy and provides insights into advanced nonvolatile memory and optoelectronic synaptic functionalities.