Subthreshold swing improvement in MoS₂ transistors by the negative-capacitance effect in a ferroelectric Al-doped-HfO₂/HfO₂ gate dielectric stack

Abstract

Obtaining a subthreshold swing (SS) below the thermionic limit of 60 mV dec 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), 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 FETs by incorporating a ferroelectric Al-doped HfO (Al : HfO), a technologically compatible material, in the FET gate stack. Al : HfO 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/HfO with a Ni metallic intermediate layer. The minimum SS (SS) of the NC-MoS FET built on the FE bilayer improved to 57 mV dec at room temperature, compared with SS = 67 mV dec for the MoS FET with only HfO as a gate dielectric.

Differential voltage amplification from ferroelectric negative capacitance

“…The fact that the ferroelectric material can exhibit such a state of negative capacitance has already been demonstrated. 3,4,[6][7][8][9][10][11][12][13][14][15][16][17][18] Therefore, if another dielectric capacitor is placed in series with the ferroelectric [as shown schematically in Fig. 1(b)], a voltage amplification is expected across the dielectric capacitor.…”

Energy Band Alignment of a Monolayer MoS2 with SiO2 and Al2O3 Insulators from Internal Photoemission

“…Atomically thin layers of two dimensional (2D) semiconductors are considered as highly promising materials for field‐effect transistor (FET) channels because the van der Waals character of bonding allows fabrication of mismatch‐free heterojunction stacks . Furthermore, the expected reduced density of mismatch‐induced coordination defects and suppression of short channel effects potentially enable efficient device downscaling additionally profiting from bandgap engineering by simple adjustment of the 2D channel thickness . However, the few‐monolayer (ML) thick channel mandates tight control of the electric field at the surface of the 2D semiconductor, particularly if targeting devices with steep sub‐threshold slope for low‐power applications such as tunnel FETs .…”

Monolayer–Trilayer Lateral Heterostructure Based Antimonene Field Effect Transistor: Better Contact and High On/Off Ratios

“…Howerver, states at the monolayer/trilayer interface is not negligible, which are detrimental to the on/off ratio. SS can be reduced by fabricating an FET with a thin high‐κ dielectric film or changing a passive gate insulator to an active one, use an electrochemical gate or exploiting the negative‐capacitance effect in ferroelectric (FE) materials …”

“…SS can be reduced by fabricating an FET with a thin high-κ dielectric film or changing a passive gate insulator to an active one, [26] use an electrochemical gate [27] or exploiting the negative-capacitance effect in ferroelectric (FE) materials. [28] Finally we discuss the on-state current which is often a problem for 2D FET due to the thin atomic monolayer of the channel. The computed on-current of hydrogenpassivated structure is 611.8 μA μm À1 , which has a remar kable increase comparing with 102 μA μm À1 for unpassivated condition.…”