Atomic Layer Deposition Based Fabrication And Electrical Transportation Measurements Of Graphene Devices

Graphene(Gr) has been widely studied by researchers of physical, chemical, material and electronical societies for its ultra high mobility, superior thermal conductivity, high mechanical strength, transparency and flexibility. Known as the thinnest material with very high mechanical and chemical stability, graphene has shown extensive potential applications in smart sensors. In this thesis, we systematically investigate the growth and doping methods for single layer graphene film, the atomic layer deposition(ALD) based fabrication technique of graphene devices and the electrical transportation properties of graphene in complex environments such as salt solution and high temperature.Chemical vapor deposition of monolayer graphene and doping effect firstly studied in this thesis. Graphene film was grown on Cu foil(25 μm) by chemical vapor deposition(CVD) method using methane as a carbon source, hydrogen as carrier gas in a tube furnace. The scanning electron microscope(SEM) characterizations show that the large area of single atomic layer graphene could be formed under appropriate conditions. The graphene layers are transferred onto other insulated substrates such as glass and silicon using PMMA coating and substrate etching methods. These graphene on different insulated substrates are then used to fabricate solution-gated field effect transistors(FET) to detect the doping effects. Changes of Dirac point show that the graphene can be modulated from the usual p-type doping into n-type doping via PEI solution.ALD technique is extensively used to fabricate graphene devices in our study. ALD is a layer-by-layer chemical reaction process that can control the thickness and uniformity of films atomically. Previous reports have shown that the ALD Al2O3 layer is very helpful for the enhancement of mobility and stability of graphene. However, the hydrophobicity of graphene surface makes it difficult to deposit highly uniform Al2O3 film on graphene. We test a series ALD conditions such as low/high temperature, ozone-assisted, to grow Al2O3 on graphene and then fabricate graphene FETs on different substrates. We demonstrate that these FET devices are not sensitive to different substrates but very sensitive to solution components.We also carefully study the performances of graphene devices under high temperature. We measure the resistance-temperature(R-T) curves of graphene both in the air and in vacuum, and the curves are quadratic-like: with the increasing of temperature, the resistance of graphene is decreasing at the first stage and then increasing. The joint effect of thermal activated carriers, lattice scattering and gradually failure of electrical contacts may cause this result. In addition, we deposit the hexagonal boron nitride(h-BN) and Al2O3/h-BN hybrid layers on graphene to protect graphene from oxidation. These atomically protection layers can notably enhance the high-temperature stability of graphene, but have only slight effect on electrodes and contacts. Thus, the contact failure induced resistance becomes the main factor for graphene devices under high temperature.