Effects of annealing on top-gated MoS₂ transistors with HfO₂ dielectric

Transition metal dichalcogenides (TMDs) have attracted intensive attention due to their atomic layer-by-layer structure and moderate energy bandgap. However, top-gated transistors were only reported in a limited number of research works, especially transistors with a high-k gate dielectric that are thinner than 10 nm because high-k dielectrics are difficult to deposit on the inert surface of the sulfide-based TMDs. In this work, the authors fabricated and characterized top-gated, few-layer MoS₂ transistors with an 8 nm HfO₂ gate dielectric. The authors show that the cleaning effect of ultrahigh vacuum annealing before high-k deposition results in significantly reduced gate leakage current of HfO₂, and they show that N₂ or a forming gas anneal after device fabrication affects the threshold voltage, drive current, dielectric leakage, and C-V frequency dependence. This work demonstrates how the fabrication process can affect the yield and the electrical characterization of top-gated TMD transistors, which in effect can help researchers further enhance the performance of their devices.