A Research Of IGZO Thin Film Transistors Based On Optical Alignment Layer

Metal oxide thin film transistor has many advantages such as simple preparation,good uniformity,high mobility and flexibility,and has great development and application potential in the field of large-scale flexible display.In this paper,the alignment layer is added between the insulation layer and channel layer of the conventional bottom gate top contact TFT structure.a-IGZO TFT based on photo-alignment is prepared,and the alignment processing technology is changed to optimize the performance of the device.The specific experimental contents are as follows:(1)Firstly,the functional films of a-IGZO TFT were studied.In the first step,PMMA and PVA films were prepared by spin coating method.It was found that the thickness of PMMA and PVA films could be reduced by increasing the spin coating speed.Compared with PMMA films,the surface flatness of PVA films was poor and the defects were more.The second step is to prepare the alignment layer film by spin coating method,and study its effect of alignment.It is found that the aligned alignment layer film shows anisotropy in the polarization UV visible light absorption spectrum,which proves that the irradiation of linear polarization ultraviolet light has an effect on the arrangement of the alignment layer materials.The third step is to study the influence of oxygen argon flow ratio and background pressure on the electrical properties of IGZO thin films in channel layer.It is found that the increase of oxygen argon flow ratio and background pressure will cause the increase of film resistivity,and the change of background pressure will have greater influence on the resistivity of the film.The resistivity of a-IGZO film prepared at the oxygen argon flow ratio of 0.02 and background pressure of 3 m Torr is 7.2×10²?·cm,which is the most suitable for the resistivity condition of channel layer as a-IGZO TFT device.(2)Then the influence of insulating material and preparation technology on the performance of a-IGZO TFT is studied.It is found that the performance of SiO₂ inorganic insulation is the best,the current switch ratio is 1.08×10⁵,and the carrier mobility is 5.62cm²/V·s.Among the organic insulation devices,PMMA insulation layer devices have better performance than those of PVA insulation layer.The current switching ratio is3.74×10²,and the carrier mobility is 3.61 cm²/V·s.(3)Then,a-IGZO TFT based on alignment method is prepared,the results show that the ratio of carrier mobility of the device with the direction of the non alignment or alignment to the channel direction is 1:1.34:0.24.The results show that the parallel or vertical alignment makes the alignment of the materials parallel or vertical to the channel,which leads to the alignment direction of IGZO molecules in the channel layer parallel or vertical to the channel direction,the difficulty of carrier migration is reduced or increased,which improves or reduces the carrier mobility of the device.(4)Finally,the influence of alignment time on the performance of the device is studied.It is found that the carrier mobility of the device which was aligned by 15 minutes is the highest,is 6.87 cm²/V·s.The results show that the optical product accumulated by the alignment layer can make the alignment order of the molecules reach the best state when the alignment time is 15 minutes.The IGZO molecules in the channel layer are arranged according to the channel direction of the device to the maximum extent,which makes the devices have the highest carrier mobility.Compared with the devices without align,the carrier mobility of the devices is improved by 125%.