Synthesis Of High Mobility Zinc Oxynitride Films And TFT Fabrication

ZnON material has unique advantages including small electron effective mass,high mobility and limited persistent photoconductivity effect by raising valence band leading to deactivation of oxygen vacancies in conventional oxides,and thus it is promising as an althemative to replacing conventional amorphous oxides TFT as the main force of the display industries towards the application in next generation display technology.Despite rapid progress of ZnON-TFTs in emerging display technologies,it still has several challenges in bandgap engineering and electronic modulation.Futhermore,the fundamental physical properties of such materials are not fully understood.The chemical stability issue has not been solved effectively and the carrier transport and leakage mechanisms in ZnON TFTs are still in detabe.To this end,we performed the synthesis of ZnON high mobility thin films by radio frequency sputtering technique.The physical properties including bandgap engineering,electrical properties,chemical stability,and carrier transport have been investigated.A ZnON prototype TFT devices have been developed with reasonable performance.The main achievements are summarized as follows:(1)The ZnON thin films with high mobility were prepared by radio frequency sputtering.The influence of different oxygen flow rates on the properties of ZnON films has been studied and the aging effect was systematically investigated.It is found that the competition between ZnO and Zn3N2 leads to the formation of a highly anion-disordered nanocrystalline ZnON films.The results show that the mobility and stability for ZnON films can be significantly improved by annealing.The optimum range for annealing temperature is 300?-400? under N2 at atmospheric pressure for 30 minutes and the mobility is up to 112 cm2/Vs.It is contributed to the atomic local reconstruction and the formation of stable Ox-Zn-Ny bonds for ZnON films at low annealing temperature;high annealing temperature promotes the breakage of Zn-N bonds,and as a result,ZnON films are finally oxidized to be ZnO.Furthermore,a proper model has also been put forward,which can well explain the carrier transport properties of ZnON materials.(2)The sandwiched structure of O-rich ZnON/N-rich ZnON/SiO2 was prepared by radio frequency sputtering in situ and demonstrated high stable chemical and electrical properties.The aging studies show that the ZnON thin films with sandwiched structure have excellent chemical and electronic stability due to the protection of dense O-rich ZnON layer.The effect of thermal annealing on the crystal structure,electrical properties,composition and chemical states of ZnON has been also investigated.An optimal thermal treatment condition of 250?-400? in N2 and vacuum is found to effectively improve carrier mobility up to 74.8 cm2/Vs.The defect assisted kick-out mechanism has been put forword to explain the diffusion behavior of nitrogen within ZnON layer.(3)The fabrication processes of ZnON TFT has been developed and optimized inlcuding photolithography,dry etching and wet etching.Finally,a prototype of ZnON TFT has been fabricated field effect mobility of 12.5cm2/Vs and current on/off ratio of 107.