Oxide Thin Film Transistors Fabricated by Sol-Gel Method
|Keywords||Thin film transistors sol-gel method GZO IZO IGZO|
Transparent oxide materials play a critical role in many current and emerging opto-electronicdevices due to their high transparency in the visible region and unique good electrical properties.During the past two decades, amorphous Indium-Zinc-oxide （a-IZO）, amorphousIndium-Gallium-Zinc oxide （a-IGZO） materials had drawn much attention. These materials canhave comparable electrical and optical properties, can be fabricated at low temperature and canobtain smooth surface. Compared with the traditional vacuum method, the sol-gel technology hasmore advantages: low energy, simple equipment, the compositions can be accurately controlled.Sol-gel technology is a promising fabrication method. Thin film transistors （TFTs）, as the coreswitch element of active array driver display device, have been the focus of researchers. For theflexible substrate, how to lower the TFTs’ annealing temperature is the core issue.In this study, oxide thin films were fabricated by sol-gel technology, including GZO, IZO,and a-IGZO. IZO TFT and IGZO TFT were fabricated by sol-gel technology and the deviceproperties were investigated respectively.The works of this paper are as follows:1. Different viscosity sols were fabricated and the effects of viscosity on the films’ propertieswere studied in this paper. It is found that viscosity play a core role on the films properties. Therelationship between the viscosity and the thickness is linear. When the viscosity is higher than3.0cps, the surface of the films’ roughness went worse, which deteriorated the electrical properties.2. IZO films with different In concentration were fabricated by sol-gel technology. Thetheory of the film’s formation was investigated in this study. All the IZO films have a goodtransparent property （90%） in the visible range. When the In concentration is higher than60%,the films’ structure began to crystallize. The effects of Ga concentration on the films were alsostudied. All the IGZO thin films had very smooth surface （measured root mean square Rms<0.4nm） and a transparent property of>80%.3. IZO TFTs and IGZO TFTs were successfully fabricated by sol-gel technology. The effectsof In concentration on the properties of the device were investigated in the study. The best IZOTFT device properties were obtained when the In concentration is60%: the saturation mobility is0.13cmV-1s-1, Ion/Ioffis6×106, threshold voltage is3V. The result shows that with the In increase,the saturation mobility of the IZO TFTs increased. But, when the In concentration is higher than75%, the IZO TFT Ion/Ioffbecome worse. Using the In:Zn ratio of3:2, different Ga concentrationIGZO TFTs were successfully fabricated at a lower temperature （300°C）. When the Gaconcentration is10.7%, the best device properties were obtain with the saturation mobility of0.03cmV-1s-1, Ion/Ioffof5.5×104, the threshold voltage is1.9V.In summary, the best In concentration for the IZO TFT is60%, and the best Ga concentrationis10.7%.