Study On Preparation And Properties Of Amorphous Indium Gallium Zinc Oxide Thin Film Transistor

At present,display technology develops rapidly.Large,flexible and transparent display has become an important research focus.The traditional amorphous silicon has low mobility and poor transparency,which can not meet the demand of display.Indium gallium zinc oxide(IGZO)thin films have received extensive attention owing to high mobility,good uniformity as well as high light transmittance in the visible light range.In this paper,amorphous indium gallium zinc oxide thin film transistor(a-IGZO TFT)has been prepared by using IGZO thin films as the active layer on Si substrate and quartz glass substrates with high light transmittance.The effect of preparation process on the performance of a-IGZO TFT has been studied,the main contents are as follows:A-IGZO thin films have been prepared by radio frequency magnetron sputtering.The crystal structure and composition of the prepared films have been analyzed by X-ray diffraction(XRD)and energy dispersive spectroscopy(EDS).It has been found that the IGZO thin films deposited at room temperature are still amorphous,when the annealing temperature reaches 500 ?.A-IGZO TFT on Si substrate has been prepared.The effects of oxygen argon ratio,active layer thickness and sputtering power on the properties of TFT have been studied.The results show that the optimal technology conditions of TFT are: oxygen argon ratio of 10 : 90,active layer thickness of 161 nm,and sputtering power of 100 W.The TFT device has switching ratio of 4.9×105,saturation mobility of 8.19 cm2/Vs,and threshold voltage of 3.0 V,subthreshold swing of 1.84 V/dec.When oxygen argon ratio is lower than or higher than 10 : 90,the mobility of the device will reduce and the threshold voltage will increase.When the active layer thickness is less than 161 nm,carrier number transported to channel layer is small due to the active layer is thin which will reduce the mobility of the device.When the active layer thickness is greater than 161 nm,transmission of the carriers will be affected by scattering effects of much charge and charged ions in active layer which reduce the mobility of device.In 100 W,with the increase of sputtering power,switch ratio and migration rate of the device will increase and threshold voltage and subthreshold swing will reduce.Transparent a-IGZO TFT device has been successfully fabricated on the substrate of quartz glass on which Si3N4 film has been deposited by PECVD.The deposition of Si3N4 thin films and the device annealing process have been optimized.The results show that the optimal technology conditions are: the deposition temperature of Si3N4 of 350 ? and device annealing temperature of 400 ?.The device has switch ratio of 6.5×104,saturation mobility of 7.46 cm2/Vs,threshold voltage of 4.1 V and subthreshold swing of 1.98 V/dec.In 350 ?,with the increase of deposition temperature,Si3N4 films have more better insulation.In 500 ?,transmittance of IGZO thin films in the visible range increases with increasing annealing temperature.A-IGZO TFT with double active layers has been prepared.The double active layers are made up of IGZO films of two layers with different oxygen content.Experiments show that this structure can reduce the off-state current,improve switch ratio and mobility obviously.When oxygen argon ratio equals to 7 : 93/35 : 65,TFT has the optimal performance with switch ratio of 2.6×107,saturation mobility of 18.39 cm2/Vs,threshold voltage of 1.6 V and subthreshold swing of 0.97 V/dec.In this paper,the impact of different annealing atmospheres(N2,Air,O2)on the transparent double active layer device electrical performance has been investigated.Experiments show that TFT annealed in N2 has the best performance whose saturation mobility is up to 22.73 cm2/Vs.The XPS results show that IGZO thin films annealed in N2 have oxygen vacancy of the optimal concentration and indium of the maximum concentration.In ions can introduce a large number of electrons to increase the carrier concentration,so the mobility of the device is improved.Finally,this paper has tested the stability of the TFT annealed in N2.The result shows that threshold voltage increases and the mobility decreases with the extension of time in air.