Molybdenum Disulfide Field Effect Devices: Fabrications And Integrations

Monolayer molybdenum disulfide(MoS₂)transistors are promising candidates for constructing next-generation digital integrated circuits(ICs)due to its natural atomic layer thickness,optimal bandgap size,and mass production of wafers.This thesis focuses on 2D materials device fabrications,performance optimizations,functional device demonstrations as well as large-scale and vertical integrations applications.First,we develop a controllable and nondestructive oxygen doping technique of monolayer MoS₂ by CVD process.Oxygen concentrations up to 20?25%can be reliable achieved in these doped MoS2?_xO_x films.These oxygen dopants are in a form of substitutional Sulphur atoms in MoS₂ lattice and can reduce the bandgap of intrinsic MoS₂ without inducing in?gap states.Field effect transistors that are made of these MoS2?_xO_x films feature with superior electrical properties,such as enhanced film conductance as well as n-doping effect.This in situ oxygen doping technique for monolayer MoS₂ holds great potential on developing high performance and low power consumption 2D materials electronics.Second,we adapt three typical 2D materials as‘Lego'building blocks,i.e.,monolayer MoS₂,few layer h BN and graphene flakes,as semiconducting channel,dielectric layer,and contact/gate electrodes,respectively,for vertically integrated multilayer all-2D FETs via layer?by?layer assembling techniques.An individual FET layer unit shows outstanding device performances with ultrahigh I_on/I_off ratio,ideal subthreshold swing,and decent device mobilities,benefiting from enhanced gate controllability with gate-all-around geometry and high contact quality with graphene contact.Further,we demonstrate vertically integrated multifunctional devices,e.g.,memory,logic and sensor layers.This work provides a technological base for future high?performance vertically integrated device nano systems based on all-2D materials.Third,high?performance and reliable artificial synapse devices are critical indispensable for developing neuromorphic computing systems,which could break through the Von Neumann computing bottleneck.However,the reliability and variability issues such as nonlinear and asymmetric weight update behaviors are still major hurdles in neuromorphic computing applications.Here,we fabricated all?2D materials two terminal floating gate memory(2TFGM)as an artificial synapse,which exhibits excellent linear and symmetric synaptic weight updating characteristics with high reliability and tunability.These results demonstrate the potential of all?2D2TFGM for high?speed,high-precise and low?power consumption neuromorphic computing.Fourth,high performance and low power consumption monolayer MoS₂ thin film transistors are promising for ICs as well as flexible electronics,but are still restricted by high quality electronic-grade material innovation,ultra-thin high-?dielectric layer or metal-semiconductor contact fabrication technologies.To meet the industrial manufacturing requirements,the material's mass production,electronic device performance,yield and uniformity,as well as power consumption challenges must be solved.Herein we address these challenges by optimizing Hf O₂ dielectric layer with equivalent oxide thickness down to 1 nm,and fabricate high electronic performance MoS₂ FETs featured with sharp subthreshold slope,high current densities,negligible hysteresis,ultra-low leakage current,as well as ideal device uniformity based on high-quality 4 inch monolayer MoS₂ wafer with large domain sizes.Further,flexible logic integrated circuits could work reliably under sub-1 V supply voltages(lowering to 0.3 V)with a ultra-high voltage gain of 397.The high electronic quality 2D MoS₂transistors are highly desirable for energy-efficient ICs or systems.