Improved Tradeoff Between Subthreshold Swing and Hysteresis for MoS2Negative-Capacitance FETs by Optimizing Gate-Stack of Hf1−xZrxO2/Al2O3

Abstract

MoS₂ negative-capacitance field-effect transistors (NCFETs) with a gate-stack of Hf₁₋ₓZrₓO₂/Al₂O₃ are fabricated, and the effects of the Zr content and the thickness of the stacked gate on electrical performance of the devices are investigated. It is found that a large improvement of device performance can be achieved by optimizing these parameters, e.g., using 6-nm Hf $_{0.5}$ Zr $_{0.5}$ O₂ (Zr content of 50%) as a ferroelectric layer and 2-nm Al₂O₃ as a matching layer, the relevant MoS₂ NCFET exhibits the excellent electrical characteristics: a low subthreshold swing (SS) of 31.4 mV/dec, a smaller counterclockwise hysteresis of ~75 mV, and a high on/off current ratio of 3.26 x 10⁶. The involved mechanisms lie in that: 1) an enhanced remnant polarization leads to low SS and 2) changing the thickness of the Hf₁₋ₓZrₓO₂ and Al₂O₃ can adjust the magnitude of ferroelectric capacitance and MOS capacitance to realize a reasonable match between both.