Improving the Stability of High-Performance Multilayer MoS₂ Field-Effect Transistors

In this study, we propose a method for improving the stability of multilayer MoS₂ field-effect transistors (FETs) by O₂ plasma treatment and Al₂O₃ passivation while sustaining the high performance of bulk MoS₂ FET. The MoS₂ FETs were exposed to O₂ plasma for 30 s before Al₂O₃ encapsulation to achieve a relatively small hysteresis and high electrical performance. A MoO_x layer formed during the plasma treatment was found between MoS₂ and the top passivation layer. The MoO_x interlayer prevents the generation of excess electron carriers in the channel, owing to Al₂O₃ passivation, thereby minimizing the shift in the threshold voltage (V_th) and increase of the off-current leakage. However, prolonged exposure of the MoS₂ surface to O₂ plasma (90 and 120 s) was found to introduce excess oxygen into the MoO_x interlayer, leading to more pronounced hysteresis and a high off-current. The stable MoS₂ FETs were also subjected to gate-bias stress tests under different conditions. The MoS₂ transistors exhibited negligible decline in performance under positive bias stress, positive bias illumination stress, and negative bias stress, but large negative shifts in V_th were observed under negative bias illumination stress, which is attributed to the presence of sulfur vacancies. This simple approach can be applied to other transition metal dichalcogenide materials to understand their FET properties and reliability, and the resulting high-performance hysteresis-free MoS₂ transistors are expected to open up new opportunities for the development of sophisticated electronic applications.