Subthreshold swing improvement in MoS₂ transistors by the negative-capacitance effect in a ferroelectric Al-doped-HfO₂/HfO₂ 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 (MoS₂), have been shown to be promising candidates to replace silicon MOSFETs in sub-5 nm-channel technology nodes. In this paper, we demonstrate NC MoS₂ FETs by incorporating a ferroelectric Al-doped HfO₂ (Al : HfO₂), a technologically compatible material, in the FET gate stack. Al : HfO₂ 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 : HfO₂/HfO₂ with a Ni metallic intermediate layer. The minimum SS (SS_min) of the NC-MoS₂ 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 MoS₂ FET with only HfO₂ as a gate dielectric.