Fabrication Of MoS₂ Transistor By Exfoliation And CVD Methods And Device Simulation

As a typical 2D semiconductor material,MoS₂ is expected to play an important role in nanoelectronic devices as a substitute for traditional silicon materials due to its excellent electrical properties.However,due to the large interface state density between MoS₂ and gate dielectrics and the uncontrollable size and thickness of the film obtained by micromechanical exfoliation method,the electrical properties of the prepared MoS₂ field effect transistors are far from their theoretical values,resulting in a large gap in industrial applications.Therefore,this paper focuses on improving the electrical performance and film quality of MoS₂transistor from both theoretical and experimental aspects.In experiment,?1?Two kinds of back-gate MoS₂ transistors with gate dielectric structures?MoS₂/HfO₂ and MoS₂/Al₂O₃/HfO₂?were designed and fabricated.Two groups of gate dielectrics were selected for NH₃ plasma treatment before transfer the MoS₂ on substrate.By comparing the electrical properties of back-gate transistors with and without gate dielectrics treatment,it is found that the transistors fabricated with Al₂O₃/HfO₂ gate dielectrics exhibit the best electrical properties after NH3 plasma treatment(I_on=15.2?A/?m,I_on/I_off=1.53?10⁷,SS=145 mV/dec,Hysteresis=0.2 V,?=26.51 cm²/V.s).The improvement of transistor's performance is mainly attributed to the repairing of oxygen vacancies in gate dielectrics,the reduction of trap charges and the passivation of suspension bonds on gate dielectrics.Additionally,adding Al₂O₃ as buffer layer also reduces the interface state density between gate dielectrics and MoS₂.?2?Large area monolayer MoS₂ thin films and back-gate field effect transistors were prepared by chemical vapor deposition.The results show that the growth morphology of MoS₂ films is closely related to the temperature of Mo source and the growth time.When the temperature of Mo source is 760 C and the growth time is 10 minutes,the size of monolayer MoS₂ flakes can achieved more than 120 um and the back-gate transistors fabricated by the thin film grown at this temperature has the best electrical performance(I_off¹0^-12 A,I_on/I_off¹0⁶,?=1.92 cm²V^-1s^-1,SS=194.6 mV/dec).In theory,the channel current expression of MoS₂ transistor based on Kaustav-Banerjee compact current-voltage model is introduced firstly,and the factors affecting the channel current are obtained.Then,with the help of Silvaco TCAD software,the effects of different gate length,dielectric thickness and materials on the electrical characteristics of back-gate MoS₂ transistors are studied.The simulation results show that:?1?as the gate length decreases,the threshold voltage of the transistor shifts negatively and the source-drain current increases with the increase of electron concentration in the MoS₂ channel.?2?with the decrease of gate dielectric thickness,the regulation of gate to the electrons in the channel increases,leading to the threshold voltage of transistor decreases and the open-state current increases.?3?when high-k materials such as HfO₂ and Al₂O₃ are used as gate dielectrics,the gate has stronger regulation effect on the channel and the back-gate MoS₂ transistor has better electrical performance because of the equivalent oxide thickness of high-k gate dielectrics is thinner.The simulation results are close to the experimental values.