Subthreshold swing improvement in MoS 2 transistors by the negative-capacitance effect in a ferroelectric Al-doped-HfO 2 /HfO 2 gate dielectric stack.

Obtaining a subthreshold swing (SS) below the thermionic limit of 60 mV dec ^-1 by exploiting the negative-capacitance (NC) effect in ferroelectric (FE) materials is a novel effective technique to allow the reduction of the supply voltage and power consumption in field effect transistors (FETs). At the same time, two-dimensional layered semiconductors, such as molybdenum disulfide (MoS ₂ ), have been shown to be promising candidates to replace silicon MOSFETs in sub-5 nm-channel technology nodes. In this paper, we demonstrate NC MoS ₂ FETs by incorporating a ferroelectric Al-doped HfO ₂ (Al : HfO ₂ ), a technologically compatible material, in the FET gate stack. Al : HfO ₂ thin films were deposited on Si wafers by atomic layer deposition. Voltage amplification up to 1.25 times was observed in a FE bilayer stack of Al : HfO ₂ /HfO ₂ with a Ni metallic intermediate layer. The minimum SS (SS _min ) of the NC-MoS ₂ FET built on the FE bilayer improved to 57 mV dec ^-1 at room temperature, compared with SS _min = 67 mV dec ^-1 for the MoS ₂ FET with only HfO ₂ as a gate dielectric.