Improved Subthreshold Swing of MoS₂ Negative-Capacitance Transistor by Using HfZrAlO as Ferroelectric Layer of Gate-Stack

In this work, a hafnium–zirconium–aluminum–oxide (HZAO) is proposed and atomic layer deposition (ALD), and its ferroelectricity is shown to be stronger than hafnium–zirconium–oxide (HZO) by measuring polarization versus electric field ( ${P} - {E}$ ) loop. Also, a large sharp peak of capacitance–voltage ( ${C} - {V}$ ) curve is observed in ${C} - {V}$ measurement to confirm the strong negative-capacitance (NC) effect. The fabricated MoS2 NCFET using HZAO as a ferroelectric layer of gate-stack exhibits a significantly reduced subthreshold swing (SS) (17 mV/dec almost over four orders of drain current magnitude, with a minimal SS of 12.8 mV/dec) as compared to its counterpart with the HZO ferroelectric layer (a minimal SS of 38.5 mV/dec). The involved mechanisms lie in that incorporation of Al atoms into the HZO film can form the additional hafnium–aluminum–oxide (HAO) and zirconium–aluminum–oxide with ferroelectricity, and as a result, the formed composite HZAO film can convert more monoclinic phases to orthorhombic phase than the HZO film, leading to stronger ferroelectricity for the former than the latter and, thus, smaller SS for its relevant NCFET.