Study On Preparation And Performance Of Indium Tin Zinc Oxide Thin Film Transistors

Metal oxide semiconductor is considered to be the great potential active layer material of thin-film transistors?TFTs?.It fully meets the requirements of TFT performance for large-size,high-resolution,flexible and transparent novel displays.The traditional In Ga Zn O thin-film transistor still has the disadvantage of low electrical performance.Indium tin zinc oxide?ITZO?thin-film transistor has become a hot research topic because of its high mobility,low sub-threshold swing and other advantages,but there still exits the issue of poor stability.It is a major difficulty to balance high electrical performance and good stability.In view of the above characteristics,in this thesis,the ITZO TFT with high electronic performance and stability were fabricated by adjusting the conditions in the process of magnetron sputtering ITZO,changing annealing conditions,and adopting the suitable material of passivation layer.The details are as follows:?1?In order to address the issue of the dissatisfied electronic performance of traditional In Ga Zn O thin-film transistor,the active layer ITZO thin film with high electronic properties were prepared by co-sputtering ITO and Zn O,and the influence of sputtering process parameters on the transfer characteristics of ITZO TFT was studied.The results showed that it had the best electronic performances,when ITO sputtering power is 100W,Ar/O₂=10sccm/6sccm,working pressure is 0.5Pa,and active layer thickness is 41nm approximately.Under the best condition,the optimum ratio of?In+Sn?/?In+Sn+Zn?were found by adjusting ITO sputtering power.Ar/O₂ can effectively compensate oxygen vacancy V_O,without generating excess oxygen simultaneously.The optimal sputtering pressure would provide the films with high density and low structural defects.The thickness of active layer can control reasonable carrier concentration and defect state density.Ultimately,the ITZO TFT has a mobility of 26.93cm²/V·s,subthreshold swing of 0.071V/dec,threshold voltage of-0.19V and on/off current ratio of 2.07×10⁸.?2?In order to address the issue of poor stability of ITZO TFT,the influence of annealing temperature and atmosphere on the transfer characteristics and positive gate bias stability?PBS?of ITZO TFT was studied.The results showed that the device annealed at 350?in air had the best electrical performance,but the effect on PBS performance was not significant.Due to the fact that the water/oxygen molecules in the air wound fully penetrate into the active layer during annealing,the bulk defect state density and the interface state density between the active layer and the insulating layer were reduced.However,the decrease of defect state density has little influence on PBS.?3?In order to further address the issue of poor stability of ITZO TFT,a passivation layer was deposited on the back channel surface of the device by pulse laser deposition.The effects of Al₂O₃,Sc₂O₃ or Ti O₂ passivation layer materials on the stability of ITZO TFT were studied separately.The results showed that the ITZO TFT with Sc₂O₃ passivation layer had the best stability.It was attributed to the lowest channel defect state density and the best isolation characteristics of ITZO TFT with Sc₂O₃ passivation layer,which could effectively inhibit the erosion of external water molecules and oxygen molecules on the back channel.