Preparation And Electrical Properties Of AZTO Thin Film Transistor

Amorphous oxide thin film transistor（AOS-TFT）,such as indium gallium zinc oxide thin film transistor（IGZO-TFT）,has the advantages of high mobility,low turn-off leakage current and good film uniformity compared with the traditional silicon based thin film transistor,and has a broad prospect in the field of display technology.But because IGZO contains the rare elements indium and gallium,the cost is relatively high.Therefore,it is of great practical significance to develop thin film transistor without rare element oxide.Aluminum and tin are stored in large quantities on Earth,and they are abundant globally at low cost.In addition,neither element is toxic,making the manufacturing process more environmentally friendly and one of the low-cost viable alternatives to IGZO.In this thesis,an aluminum-zinc-tin oxide thin film transistor（AZTO-TFT）device was prepared by using the RF magnetron sputtering method and according to the carrier transmission mechanism,replacing in with Sn and Ga with Al,and the electrical properties of AZTO thin film and its thin film transistor were studied as follows:（1）The effects of elemental components on the electrical properties of AZTO films and AZTO-TFT were studied.AZTO films with different Sn O₂content were prepared on silicon substrate by magnetron sputtering method.The transmittance,crystallization characteristics and surface morphology of AZTO films were characterized by using AZTO target materials with different Sn O₂content.In the wavelength range of 300-800 nm,the average transmittance is 80%,and all of them are amorphous structures with relatively flat surfaces.Furthermore,AZTO thin film was used as channel layer to prepare AZTO-TFT devices.The results show that when the content of Sn O₂is 40%,the devices have the best electrical performance,the carrier mobility is 3.83 cm²/V·s,the current switching ratio is 1.12×10⁸,and the subthreshold swing is 0.09 V/decade.（2）The effects of argon-oxygen ratio on the electrical properties of AZTO thin film and AZTO-TFT were studied.By magnetron sputtering method,AZTO films were prepared on silicon substrate under different argon-oxygen ratios and characterized.XRD and AFM characterization results show that AZTO films with different argon-oxygen ratios are amorphous with relatively flat surfaces.When argon-oxygen ratio is 98:2,the transmittance of AZTO films can reach more than95%in the visible long-wave band.The roughness is the lowest.Furthermore,AZTO thin film was used as channel layer to prepare AZTO-TFT devices.The results show that the electrical performance of the devices is the best when the argon-oxygen ratio is 98:2,the mobility is 4.71 cm²/V·s,the current switching ratio is 1.83×10⁸,and the subthreshold swing is 0.37 V/decade.（3）The influence of channel thickness on the electrical properties of AZTO-TFT was studied.The effects of different channel thickness on the electrical properties of AZTO-TFT were studied by adjusting the thickness of AZTO film by changing the growth time.The experimental results show that AZTO film still has a good transmittance under different thickness conditions,and the amorphous structure remains unchanged.When the film thickness is 50 nm,the film roughness is the lowest,and the electrical properties of TFT devices are the best.The device mobility is 4.71 cm²/V·s,the threshold voltage is-5.25 V,the subthreshold swing is 0.37V/decade,and the current switching ratio is 1.83×10⁸.Too thin or too thick channel layer will lead to deterioration of device performance.（4）AZTO-TFT was prepared on a flexible substrate.Flexible AZTO-TFT devices were prepared on flexible polyimide（PI）substrate with AZTO prepared under optimal conditions as channel layer and Hf O₂and Ta₂O₅as insulating layers,respectively.Considering the long-term temperature resistance limit of flexible polyimide,AZTO-TFT was annealed at 300℃and Hf O₂as insulating layer,The device mobility is 0.43 cm²/V·s,threshold voltage is 0.66 V,subthreshold swing is1.34 V/decade,and current switching ratio is 3.67×10².When Ta₂O₅is used as the insulation layer,the device performance is improved to a certain degree.The mobility of the device increases to 1.58 cm²/V·s,the threshold voltage is-5.7 V,the subthreshold swing is 1.48 V/decade,and the current switching ratio increases to9.3×10³.By contrast,AZTO-TFT was prepared on silicon substrate with the same channel layer preparation conditions and annealing process,and the device switching ratio reached 10⁶.