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Fabrication And Characterization Of Graphene Field-effect Transistors

Posted on:2015-09-12Degree:DoctorType:Dissertation
Country:ChinaCandidate:T T FengFull Text:PDF
GTID:1228330452469376Subject:Electronic Science and Technology
Abstract/Summary:PDF Full Text Request
Since graphene has been first successfully exfoliated from the graphite crystal in2004, this two-dimensional crystalline material with only one atomic layer thickness hasdemonstrated a series of unprecedented and superior properties, including submicronballistic transport, ultrahigh carrier mobility, excellent mechanical properties andthermal conductance, superior optical property and good chemical stability. As thedevice dimension continues to scale down, graphene is expected to open the"post-silicon" era with carbon-based circuits. Graphene field-effect transistor (GFET) isthe basic device structure for the realization of graphene-based high-frequency devices,memory, sensors and integrated circuits. This dissertation focuses on the fabrication andthe electrical properties of GFET devices, as well as the influences of surfacemodification and temperature on the electrical characteristics of GFETs.Large area and uniform monolayer graphene film with good quality is obtained onthe copper foil by chemical vapor deposition and is successfully transferred onto theSiO2/Si substrate for the fabrication of GFET devices. The process parameters of thereactive ion etching are optimized to pattern the graphene channel and the preparationof GFETs with different device sizes is realized. Three different types ofconductivity-gate voltage (σ-Vg) curves are obtained by characterizing the electricalproperties of the GFETs: the conventional V-shaped, the monotonic and the W-shapedcurve. The interfaces of the graphene/substrate, graphene/metal contact and thegraphene/surface medium are employed to explain the formation mechanisms of theunique monotonic and the W-shaped curves. Specifically, the hole-doping effect of airon graphene causes a monotonically decreasing electrical characteristic, while thehole-doping effect of the metal contact on graphene leads to a graphene p-n junction andgive rises to the W-shaped curve with double conductance minima. Meanwhile, thehysteresis phenomena and mechanisms of the GFETs are also analyzed.The tunable electrical properties of the GFETs are realized by using thenanometer-thick AlOxfilm, polyethylene imine (PEI) and hydrazine (N2H4) solutions tomodify the graphene surface. By studying the changes of the electrical properties ofGFETs, the mechanisms of the surface modification on graphene are summarized as thecharge transfer and doping, dielectric screening and the charge traps. In addition, the dissertation also studies the effect of temperature and voltage on the electrical propertiesof GFETs. The variations of the charge neutral point and conductivity of graphene withthe elevation in temperature are discussed. The relationship between the magnitude ofthe hysteresis and temperature/voltage is quantitatively analyzed and explained by thetemperature-dependent mechanisms.
Keywords/Search Tags:graphene, field-effect transistor, chemical vapor deposition, electrical properties, surface modification
PDF Full Text Request
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