Study On Preparation Of High Performance Indium Gallium Tin Oxide Thin Film Transistor At Low Temperature

In recent years,thin film transistor（TFT）has been widely studied as the core driving element of flat panel displays.Among them,the oxide semiconductor is a strong competitor to replace traditional silicon-based TFT with their advantages of medium mobility,simple process,extensive area deposition,and good uniformity.Commercialized In Ga Zn O TFT is one of the representatives of oxide semiconductor TFT.Its mobility is mostly 10 cm²/Vs.The lower mobility and high temperature thermal annealing process do not meet the requirements of the next generation display industry for flexibility,large area and ultra-high definition.Considering that the overlap of the 5s spherical electron cloud at the outermost layer of In and Sn can form a more effective electron transport path to improve the electrical performance of TFT,this paper selects indium tin oxide material as the active layer for research,and uses the full sputtering method,aiming to develop a high-performance oxide TFT with high mobility and more economic benefits at a lower process temperature by optimizing the preparation process.（1）In this paper,the magnetron sputtering method and the in-situ argon plasma process were designed in the chamber.The effects of argon plasma surface treatment on the physical and chemical properties of IGTO thin films and the electrical properties of IGTO TFT were studied,which reduced the thermal budget.After 5 minutes of argon plasma surface treatment,the electrical performance of the device is superior to that of 300℃thermal annealing for 70minutes.The entire process temperature is controlled below 150℃,achieving a high field effect mobility of 30.83 cm²/Vs,a sub threshold swing as low as 0.32 V/decade,a threshold voltage of-0.54 V,and a current switching ratio of 3.28×10⁷.By controlling the etching time and plasma energy,the interface defect density of the channel and gate insulation layer was passivated,ranging from 2.1×10¹² cm^?2e V^?1reduced to 9.4×10¹¹ cm^?2e V^?1,the surface roughness of IGTO film was reduced by 50%.The reduction of defect states,the enhancement of metal oxygen binding and the improvement of film quality are the main reasons for the good electrical properties of IGTO TFTs at low temperatures.This study has opened up a new path for the low-temperature preparation and flexible electronic applications of TFT.（2）To further improve the electrical properties of TFT,In Sn O（ITO）material with higher electron concentration was also used as the active layer,and the amorphous ITO TFT with high mobility and low thermal budget was finally prepared.The effect of post-treatment temperature on the properties of ITO TFT was systematically studied.The device annealed at 150℃only has a field effect mobility of 70.53 cm²/Vs,and a current switching ratio of more than 10⁸.The analysis of the crystallization,surface morphology,internal chemical states,and energy band relationship of ITO thin films shows that as the annealing temperature increases,the conduction band shift gradually decreases from 1.61 e V at room temperature to 1.1 e V at 300℃annealing,and a large number of free electrons are activated by thermal annealing.The increase of ITO TFT mobility and current switching ratio after annealing is attributed to the increase of donor-like oxygen vacancy and the stacking of electron transmission paths.Annealing at 150℃can reduce the roughness of the thin film to 0.403 nm and the interface defect state to 6.9×10¹¹cm^?2e V^?1.Moderate temperature annealing can optimize device performance,but excessive annealing temperature can cause the device to lose its gate control ability.This study is beneficial for the application and development of high electron concentration oxide TFTs in the next generation display.（3）IGTO TFT with high mobility（>50 cm²/Vs）was prepared by a simple co-sputtering process at the low temperature of 150℃.In the co-sputtering process of ITO and Ga₂O₃,the composition of IGTO thin films can be reasonably controlled by adjusting the sputtering power in the RF plasma,which significantly affects the performance and stability of IGTO TFTs.Through reasonable regulation of Ga composition in polyoxides,the oxygen vacancy and hydroxy defects in the channel are reduced to 19%and 20%,and the interfacial defect state density is reduced from 7×10¹¹ cm^?2e V^?1 to 5×10¹¹ cm^?2e V^?1,and a dense metal-oxygen-metal network is formed which is favorable for electron transport.Finally,IGTO TFT with mobility up to 58.73 cm²/Vs,threshold voltage of-1.33 V and subthreshold swing of 0.21 V/decade were prepared.The stability under positive and negative bias stress is also significantly improved.A simple co-sputtering process is entirely feasible for realizing high-mobility oxide TFT.The control of the process temperature below 150℃also extends its application in flexible electronic devices.In short,we have successfully prepared high-performance TFT devices at 150℃by exploring and optimizing the processing technology and material selection.The amorphous indium tin oxide（IGTO,ITO）and the process strategy（plasma treatment,annealing treatment and co-sputtering doping technology）studied in this paper effectively reduce the thermal budget of TFT preparation,ensure the high performance of the device at low temperature,and fully display its application prospects in flexible electronic and wearable devices.