Modeling Of ZnO Thin Film Transistor And Investigation Of Its Device Structure Improvement

Due to the high transparency, conductivity, low light sensitivity and preparationtempreture, ZnO TFT has been the most popular candidate of the next generation activematrix liquid crystal display(AMLCD). The channel of ZnO TFT is polycrystallinewhich limited the device characteristics and application. The theoretical investigationand analysis of improvement in the polycrstalline channel and electrical performanceis at the initial stage.A carrier transport and the subgap density of states model in a polycrystalline ZnOthin film transistor is proposed in the paper. The model considered exponentialdistribution band tail states and gaussian distribution deep level states in the grainboundary and we found it could reproduces well the characteristics of polycrystallineZnO TFT by fitting the simulation and experiment results. Furthermore, using thedeveloped model, we study the effects of defect parameters on the electricalperformances of the polycrystalline ZnO TFT.Based on our proposed model, we analyze the performance improvements and thecharacteristics of different operation mode of double gate ZnO TFT. The influence ofthe source and drain electrode contact on the device performance is analyzed bycomparing the potential and the current density distribution betwee n two operationmode. In the case of the double gate ZnO TFT proposed in the paper, the top contactwould increase the contact resistance while the bottom contact would change thepotential in the region near the electrode and limited the gate modulation of the channel.The above factors were considered and the improvement of the contact was proposedand simulated.On the basis of developed device structure, double gate double insulator ZnO TFTis proposed and analyzed by simulation, which has steeper subthreshold slope and betteron-state current compared with the convention TFT. At last we illustrated themechanism of the performance improvement in the double gate double insulator ZnOTFT considering the energy band and grain boundary potential in the channel, andanalyzed the effect of the permittivity and the thickness of the insulator on the deviceperformance.