MoS2 negative-capacitance transistors with steep slope and negligible hysteresis by using monolayer Al1-xZrxOy as gate dielectric plus NH3-plasma treatment

Abstract

Although ferroelectric material is highlighted for its negative capacitance (NC) effect integrated into MoS2 devices, it usually needs a dielectric layer to provide positive capacitance, which is not conducive to scaling down of transistors. In this work, a monolayer Al1-xZrxOy is used as the gate dielectric to fabricate back-gated MoS2 negative-capacitance FETs (NCFETs), in which host Al2O3 exhibits a positive capacitance and the embedded ZrO2 crystals formed through rapid thermal anneal at 550℃ exhibit a NC effect. By optimizing the Zr content in the Al1-xZrxOy thin film, an enhanced ferroelectricity and a reasonable match between the negative capacitance and the positive capacitance have been achieved for the Al0.93Zr0.07Oy thin film, resulting in excellent device performances: small subthreshold swing (SS) of 28 mV/dec and high on/off current ratio of 6.4 × 107. Moreover, after the Al0.93Zr0.07Oy thin film is suffered from a remote NH3-plasma treatment, its ferroelectricity and NC effect are further enhanced due to the reduction of oxygen vacancies and the improvement of interface quality, thus boosting the performance of the relevant NCFET: the SS is lowered to 18 mV/dec, where the sub-60 mV/dec SS spans almost three orders of Id (drain current) magnitude, the hysteresis is reduced to 25 mV and the driving current is 30% higher than that of the untreated sample. Therefore, the Al0.93Zr0.07Oy thin film with the NH3-plasma treatment as the gate dielectric of MoS2 NCFET has a great potential in achieving the steep-slope, free-hysteresis and low power-consumption performances.