Influence Of Ambient Gases On Stability Of Amorphous Indium-Gallium-Zinc-Oxide Thin Flim Transistors

Amorphous Indium-Gallium-Zinc-Oxide(a-IGZO)thin film transistors(TFTs)have been considered as one of the most promising candidates to drive next-generation displays including active-matrix liquid crystal displays(AMLCDs)and active-matrix organic light-emitting diodes(AMOLEDs)due to their higher field-effect mobility than the traditional hydrogenated amorphous silicon(p-Si)TFTs.However,from the practical application points of view,some critical issues such as the instability of a-IGZO TFTs still need to be solved.Especially,the instability if a-IGZO TFTs caused by the prolonged storage,high temperature and illumination are very important for the display products addressed by these novel semiconductor devices.In this work,we focused our attention on the storage stability,thermal stability and light stability from the perspective of ambient gases,trying to find out the exact ambient gas factor for the instability.In addition,we have put more efforts on the logical deduction and simulation to explore the physical mechanisms,in order to provide theoretical support for the practical production,which have suffered from the instability of a-IGZO TFTs.Firstly,we prepared the TFTs without passivation layer by RF magnetron sputtering deposition technology and established a set of experiment equipment which could test the electrical properties of devices,manage various ambient gases,control the temperature of devices and control the light illumination on the devices.Then,we investigated the ambient effects on the storage stability of a-IGZO TFTs.The results indicated that argon,nitrogen and oxygen could hardly affect the electrical properties of stored devices,whereas moisture was the main origin of the ambient degradation effects in natural ambient air conditions.Furthermore,the higher moisture content was,the larger the voltage threshold shift became.Secondly,we investigated the ambient effects on the thermal stability of a-IGZO TFTs.The results indicated that argon,nitrogen could hardly affect the electrical properties of heated a-IGZO TFTs and moisture had little effect on the heated a-IGZO TFTs either.However,with the increase of oxygen content,the stability of heated a-IGZO TFTs became better.Furtherly,we found that the higher ambient oxygen content could induce more combinations between the oxygen vacancies and adsorbed oxygen ions,result in the larger defect formation energy,and thus lead to the smaller variation of the threshold voltage for the corresponding TFT devices.Finally,we investigated the ambient effects on the light stability of a-IGZO TFTs.The results demonstrated that argon,nitrogen could hardly affect the electrical properties of heated a-IGZO TFTs.However,both moisture and oxygen could improve the stability of a-IGZO TFTs.The aforementioned results were also verified by the C-V tests of a-IGZO TFTs.In addition,we divided the active channel into the overlap region and exposure region,and clarified the mechanism concerning the stability respectively.