Study On The Characteristics Of Oxide Gypsum Base Field Effect Transistor

In recent years, rapid develop of various kinds of late-model smart mobile terminal make higher demands for integrated circuits (ICs), higher degree of integration, better running speed and lower power consumption become the most important indicators in the design and fabrication of ICs. However, silicon now as the foundation of IC industry, its physical characters deeply hinder the further advance of the integration and running speed. Graphene, which is a kind of one atom thick two dimensional carbon based material, possesses excellent electrical properties. Graphene based transistors have more reduced scale, lower cost, and smaller switching voltages, so graphene based ICs may meet the demands of lower power consumption and higher integration. A fly in the ointment is that graphene is a zero band-gap material and its superior electrical characters are degraded easily by exogenous impurities introduced during traditional fabrication process. So the preparation of graphene with tunable band-gap and application of advanced transistor fabrication technologies which minimize the degradation of graphene’s characters are the premise for massive application of graphene in IC. Here in our work, a kind of nano-tip based nanolithography is introduced and the obtained reduced graphene oxide (RGO) was used as the channel to fabricate back-gate transistors, the details are introduced as following:(1) Firstly, graphene oxide (GO) solution with homogeneous dispersion was prepared via the chemical reactions of graphite powder and a mixture of sulfuric acid and nitric acid. Then GO films were obtained by spinning-coating of GO solution on the substrates of300nm SiO2/Si and Si, respectively. Here silicon is highly-doped. Lorentz oscillator model is added in spectroscopic ellipsometry to character GO and GO in our experiment is estimated to be about7layers. Secondly, voltages are applied on the substrate and control the nano-tip to scan over the GO film in Contact Mode in cAFM. It’s observed that GO can be reduced only when negative voltages applied on substrate. In order to rule out the possibility of current leakage caused by mechanical damage introduced in Contact Mode, the topography measurements of GO film before and after the reduction process were performed in Tapping Mode and almost the same results mean that no mechanical damage occurred during the reduction process. And the Raman spectrums of same region in GO film before and after the reduction process indicates that there are more sp2clusters and less COOH-, OH-and C=O functional groups after the reduction process and GO becomes RGO in this region. The mechanism of this polarity dependence correlated to the electrochemical reduction involves into hydrogen ions on the GO surface. When a negative voltage is applied to GO, a high electrical field converges between the tip and GO surface, and electrons are injected from sample which induces the hydrogen ions. Thus electrochemical reduction of GO happens. Besides the field polarity, the electrochemical reduction also depends on the electrical field strength. The threshold voltage here for this7-layer-GO is about-6.5±0.5V and current achieves saturation when-9V is applied. Currents profile also shows that this nano-tip based nanolithography possesses accurate control of reduction position. GO with controlled reduction degree via other chemical methods show a tunable band-gap, so it’s believed that here the controlled electrochemical reduction of GO will also lead to RGO with tunable band-gap. Finally, a back-gate transistor with RGO nanoribbon acting as the channel material was fabricated successfully with outstanding characteristics and RGO nanoribbon was patterned as400nm long and10.5μm wide.(2) In addition to the reduction of GO, resistive memory effect was observed in GO films. Pristine GO is in high resist and turns into low resist after reduction by applying negative voltages. However, when positive voltages were applied again in the same region, the reduction currents disappeared which meant that RGO returned to GO in high resist. Measurements of the GO/Si structure in probe station show that the on/off ratio is extremely high and the retention characteristic is excellent. The processes of SET and RESET is also observed in cAFM measurements. Electrical field induced H+and OH-play important roles in this reversible reduction and oxidation of GO.