Electrical Characteristics Of MoS₂ Negative Capacitor Field-effect Transistor Based On Hf_1-xZr_xO₂ Ferroelectric Thin Film

With the development of the silicon-based metal oxide semiconductor field effect transistors(MOSFETs),power consumption has become the main problem.For breaking through the the minimum subthreshold swing(SS)of MOSFET(60 m V/dec)at room temperature which is limited by Boltzmann limit,the negative-capacitance field effect transistor(NCFET)is becoming one of the ultra-low power candidate.By the addition of the ferroelectric layer in the stack gate dielectric,the optimal matching between the ferroelectric capacitor(C_FE)and the Matching layer capacitance(C_ox)is obtained to achieve a passive amplification of the voltage and a steep slope.On the other hand,because Si technology is close to its physical limit,some two-dimensional transition metal sulfide(TMDC)used to be the channel material are considered to be one of the development trends of CMOS devices in recent years because of their ultra-thin thickness of atomic level,suitable band gap width,high carrier mobility and good CMOS process compatibility.In this paper,the ferroelectric thin film material integrated with the two-dimensional semiconductor material has been used to fabricate back gated NCFET,in which Mo S₂ is used as the active channel and the Hf_1-xZr_xO₂(HZO)thin film is used as the ferroelectric layer.So far,there are relatively few theoretical and experimental studies in this area,especially Mo S₂ NCFET based on ultra-thin HZO(<10 nm).The specific work are as follows:In theory:The device model of NCFET is constructed by using the semiconductor technology and the device simulation software Silvaco.By comparing with the electrical characteristics of traditional MOSFET,it was found that the SS of NCFET was able to achieve lower than 60 m V/dec because of negative capacitance effect could break through the Boltzmann limit.Besides,capacitance match of negative capacitance and dielectric layer material is another important factor effecing the electrical properties of the device,including their thickness and erroelectric properties of HZO thin film.It is found that good device performance can be obtained by using 2 nm Al₂O₃ material as dielectric layer.At the same time,the ratio of the residual polarization intensity(P_r)/the residual field size(E_c)is increasing with decreasing the thickness of the HZO film,which is good for achieving better capacitance match.In Mo S2 NCFET,an excellent performance has been realized with a thickness of 3 nm HZO thin film and 2 nm Al₂O₃ dielectric layer:SS of 35.44 m V/dec,threshold voltage of 0.075 V and current switching ratio of 3.83×10¹¹.In experiments:(1)The HZO thin film was prepared by atomic layer deposition(ALD)technology,and the influence of the thickness of the HZO film and the annealing temperature on the ferroelectric property was analyzed.The experimental results show that P_r increases at first and then decreases when the annealing temperature of HZO thin films increasing from 350 to 750?,the maximum value is obtained near 650?;,the P_r and E_c are becoming smaller and ferroelectricity is decreasing when the thickness of HZO film is decreasing,but the ferroelectricity is still could be obtained when HZO thickness down to 3 nm.(2)on the basis of(1),the process of preparing two-dimensional Mo S₂ NCFET samples was carried out.Mo S₂NCFET with SS(49.33 m V/dec)below 60 m V/dec is obtained by adjusting the experimental parameters.The effect of annealing temperature and thickness on the performance of the device have been analyzed combining with the simulation results.It is found that Mo S₂ NCFET exhibits the best electrical characteristics when the thichkness of Al₂O₃ is 2 nm and HZO is 3 nm:SS is 20.66 m V/dec(output current on the order of 5 orders),switching ratio is 0.95×10⁶,and the maximum mobility is153.66 cm²/Vs.