Optimization Of Hf_1-xZr_xO₂/Al₂O₃ Gate Dielectric For MoS₂ Negative-Capacitance Field-Effect Transistor

With the improvement of chip integration and the continuous development of device miniaturization,there has been faced with urgent need for overcoming the power consumption problem.Due to the“Boltzmann tyranny”,the sub-threshold swing(SS)of conventional MOSFETs cannot be reduced to below 60 m V/dec.Negative-capacitance field-effect transistors(NCFETs)can break through this limit through the internal gate voltage amplication induced by the ferroelectric film inserted into gate stack.In addition,the two-dimensional layered MoS₂is regarded as an excellent material as the nano-scale transistor channel due to its high mobility,almost ideal switching characteristics and good CMOS process compatibility.In this paper,MoS₂is used as the channel,Hf_1-xZr_xO₂(HZO)is used as the ferroelectric layer,and Al₂O₃is used as the matching layer for fabricating the back-gated MoS₂NCFET.The relevant ferroelectricity and electrical performance also has been studied.In experiments:(1)Zr component in the HZO films has been optimized,resulting that the residual polarization(P_r)and P_r/E_c(E_cis the coercive field)first increases and then decreases with increasing Zr component.The device with 50%Zr content in HZO film reaching the results of the largest P_rvalue,and the smallest subthreshold swing(SS)about31.4 m V/dec.Whats'more,according to the"capacitance matching"theory,the smallest counterclockwise hysteresis caused by the negative capacitance effect of this content device has also been achieved;(2)Different thicknesses of HZO films has been studied,and there are negative differential resistance(NDR)effects and capacitance spikes in the relevant decives.And the P_rvalue increases slightly as increasing the thickness of HZO films.But,the ferroelectric capacitance|C_FE|and SS decrease with increasing thickness of HZO film.The SS are 31.4 m V/dec and 28.2 m V/dec,when the thickness of HZO is 6 nm and 9 nm respectively.However,according to the"capacitance matching"theory,the counterclockwise hysteresis caused by negative capacitance increases with increasing HZO thickness.Therefore,considering the trade-off between counterclockwise hysteresis and SS,6nm HZO is the most appropriate thickness;(3)The influence of Al₂O₃thickness on the ferroelectricity of the gate dielectric film and the relevant electrical properties of MoS₂NCFET has also been studied.The NDR effects and capacitance spikes have also been observed in the devices.Interestingly,the P_rvalue increases slightly with decreasing the thickness of Al₂O₃,so does the oxide layer capacitance C_ox.The MoS₂NCFET with 2nm Al₂O₃achieved the smallest SS of 31.4 m V/dec,the highest on/off ratio of 3.26×10⁶and the smallest total hysteresis of 29.6 m V.In theory:MoS₂HZO NCFET model was constructed using Sentaurus TCAD,and the voltage amplification phenomenon was observed by simulation.It has been found that the larger the P_r,the thicker the HZO and the thinner the Al₂O₃,the lower the SS of the device.In addition,when the thickness of HZO and Al₂O₃changes,the decrease of SS is accompanied by the increase of counterclockwise hysteresis caused by the negative capacitance effect,which is consistent with the experimental results in Chapter 4 and verifies the correctness of the experimental results.