Scalable T-Gate Aligned Gr–WS₂–Gr Radio-Frequency Field-Effect Transistors

Gigahertz field-effect transistors (FETs) have been the imperative need for the development of nanoelectronics based on atomically thin transition metal dichalcogenides (TMDs). Yet, WS2 FETs working in the gigahertz regime remain unexplored to date. Efforts to make high-frequency FETs from TMD materials have also been hampered by the lack of a scalable growth and fabrication scheme that meets the requirement of high-quality channels with low resistivity at contacts. Here, we report radio-frequency WS2 FETs with the channel grown by a devised chemical vapor deposition. The growth proceeds in a diffusion-controlled mode, allowing for site-selective synthesis of monolayer WS2 at the predefined graphene windows for low contact resistivity. The resulting WS2 FET exhibits an effective mobility of 112 cm2/V s at room temperature, with contact resistivity as low as 0.8 kΩ·μm. An Al/AlOx T-gate is made on top of the active channel for self-aligned deposition of drain and source contacts to achieve an appreciable reduction of parasitic resistance and increase of device transconductance, thereby yielding a high intrinsic cutoff frequency of 3.5 GHz and a maximum oscillation frequency of 3.2 GHz in a long gate length of 1 μm.