Preparation And Performance Study Of N-doped In-Sn-Zn-O Thin Film Transistors

At present,with the advent of curved screens and large-size display panels on the market,the changes of display technology have put forward the new high requirement to the performance of thin film transistors(TFTs).Doped multi-oxide TFTs with special properties have attracted the researcher's attention.Indium tin zinc oxide(ITZO)material is an ideal candidate for preparing active layer of TFT.This kind of TFT has high transmittance in the visible range,high field effect mobility,high on/off ratio and low sub-threshold swing,which is expected to produce high-definition and high-contrast display panels.However,during the practical applications,ITZO TFT is unstable.Besides,the research based on ITZO is not sufficient.The fabrication and performance of ITZO materials still need further exploration.Therefore,in the current work,TFT was prepared by RF magnetron sputtering.The performance of TFT was optimized by nitrogen passivation of oxygen vacancies.The device performance was optimized by adjusting the parameters of active layer as well as the drain-source electrode materials.(1)ITZO TFTs were prepared at different nitrongen flow rate of 0,2,4,6,8 and 10 mL/min.the results reveal that all ITZO thin films are amorphous,the average transmittance of ITZO films is about 90%and the optical band gaps of films are 3.28-3.32 eV.The addition of nitrogen can improve the electrical performance and the stability of TFTs.But excessive nitrogen will cause device performance deterioration due to the increased N-induced defects.When nitrogen flow rate is 4 mL/min,ITZO TFT shows the best electrical properties and stability.(2)ITZO:N TFTs with active layer thickness of 15,25,35,45 and 55 nm were deposited by RF magnetron sputtering.As the active layer thickness increases,ITZO:N thin films become crystallized and present a crystal orientation along InN(002).When the active layer thickness is too thin,the film quality is poor,resulting in more defect states in the TFT.ITZO:N TFT shows enhanced electrical properties as the active layer thickness is 35 nm,its field effect mobility,on/off ratio and sub-threshold swing are 17.53 cm2/(V·s),106 and 0.36 V/dec.(3)Effects of sputtering power on ITZO:N TFT performance were studied.The results show that all ITZO:N thin films are amorphous and the average transmittance is about 90%.When the sputtering power is 60 W,ITZO:N active layer becomes dense and uniform,this TFT has good electrical properties.On the contrary,the defects of TFT increase as sputtering power increase,resulting in the performance degradation.(4)ITZO:N TFT with different drain-source electrodes were deposited at room temperature.The effect of drain-source electrode materials on electrical properties was studied.Compared with the ITO film,there are holes and large particles in the Al film,which will increase the defect states in the TFT.In addition,the interface between the Al and ITZO:N active layers is prone to interfacial reaction,forming a AlOx high-resistance layer.Blocking carrier migration and reducing the switching ratio of the TFT result in poor TFT performance.