Graphene Membrane Preparation, Building Field Effect Transistor And Its Performance Study

Graphene is a new type of carbon materials discovered in2004with a two-dimensional honey-comb lattice of carbon atoms. Due to its very high carrier mobility, excellent thermal conductivity, high transparency and good mechanical properties, graphene has attracted much attention. In this thesis, the graphene film was firstly grown by CVD, and the it was characterized by optical micorscopy, and Raman Spectroscopy; then, the microfabrication process of graphene field-effect transistor (Gr-FET) was investigated; finally, the transport properties of Gr-FET was investigated. The main conclusions are summarized as follows.(1) The graphene film was prepared on Cu foils by CVD methods using CH4as carbon source and H2as carrier gas. The graphene film was then transferred onto SiO2/Si substrate. The Raman Intensity of IG/I2D of the transferred graphene film is about0.295, indicating that the graphene film is monolayer; in adition, the full width at half maximum (FWHM) of the G and2D peaks are24.8cm-1,and43.8cm-1, which suggests that the graphene film has high crystal quality.(2) The field effect transistor with graphene as channel and SiO2as the back gate dielectric was made. The micorfabrication processes such as photolithography, develop, dry etching, and metal electrode evaporation process are investigated and optimized. The results show that the Gr-FET device has a typical bipolar transfer characteristics, showing p-type. The reason why could not find the Dirac point is mainly due to the residual PMMA on the graphene film and the adsorption of H2O, O2and other molecules on the surface of graphene or at the interface between the graphene and SiO2.(3) The effects of resistance heating, and the adsorption of ammonia, and the top gate Al2O3film on the transport properties of graphene were investigated. The main results are as follows,(ⅰ) The Joule heating of graphene film can lead to the desorption of the adsorpted molecules on the graphene film, and the results show that the resistance of graphene will increase30%after14DC volts connected to the two terminators of graphene film. With the volate increasing, the desorption trend of of molecules on graphene increases, which leads to the decrease in the doping concentration of graphene and the increase in the resistance of graphene.(ii) The graphene can be doped to N-type by using the ammonia. The results show that the Dirac point of graphene can move to-40V just after taken from ammonia, indicating a strong N doping. After the graphene sample exposed in the air, with the time elapsed, the adsorption of H2O and O2molecules increases, and the Dirac point of graphene film gradually moves to positive, showing p-type doping effect,(iii) In order to improve the performance of the grapheen device, Al2O3was used as the top gate dielectric. The results show that the top-gate structure can improve the performance of the Gr-FET device; however, the defects formation during the the process of Al2O3preparation leads to the decrease in the mobility of graphene film.