Improvement of the Bias Stress Stability in 2D MoS₂ and WS₂ Transistors with a TiO₂ Interfacial Layer

The fermi-level pinning phenomenon, which occurs at the metal-semiconductor interface, not only obstructs the achievement of high-performance field effect transistors (FETs) but also results in poor long-term stability. This paper reports on the improvement in gate-bias stress stability in two-dimensional (2D) transition metal dichalcogenide (TMD) FETs with a titanium dioxide (TiO₂) interfacial layer inserted between the 2D TMDs (MoS₂ or WS₂) and metal electrodes. Compared to the control MoS₂, the device without the TiO₂ layer, the TiO₂ interfacial layer deposited on 2D TMDs could lead to more effective carrier modulation by simply changing the contact metal, thereby improving the performance of the Schottky-barrier-modulated FET device. The TiO₂ layer could also suppress the Fermi-level pinning phenomenon usually fixed to the metal-semiconductor interface, resulting in an improvement in transistor performance. Especially, the introduction of the TiO₂ layer contributed to achieving stable device performance. Threshold voltage variation of MoS₂ and WS₂ FETs with the TiO₂ interfacial layer was ~2 V and ~3.6 V, respectively. The theoretical result of the density function theory validated that mid-gap energy states created within the bandgap of 2D MoS₂ can cause a doping effect. The simple approach of introducing a thin interfacial oxide layer offers a promising way toward the implementation of high-performance 2D TMD-based logic circuits.