On Fabrication Processes And Properties Of A-IGZO TFTs

As the key component of the flat panel displays, the active matrix flat panel display are dependent on the control of the thin film transistor (TFT). With the development of the large size liquid crystal display and active matrix organic light emitting diode, the hydrogenated amorphous silicon TFT and polysilicon TFT cannot meet the requirements of the displays. In recent years, an amorphous oxide semiconductor TFT, especially transparent amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFT), have received extensive attention, since it has a high carrier mobility, stability, good uniformity and wide applications. In this paper, a-IGZO TFTs were fabricated, and the active layers prepared in different oxygen partial pressure, working pressure, RF power, and target distance were investigated.(1)The a-IGZO TFTs were prepared in different oxygen partial pressure by RF sputtering and shadow mask technology at room temperature, and the effect of oxygen partial pressure on the performance of the a-IGZO TFTs was investigated. As the oxygen partial pressure increased, the performance of the a-IGZO TFTs changed a lot as the carrier concentration of the active layer changed. When the active channel layer was deposited at the oxygen partial pressure of7.47%, the a-IGZO TFT exhibited good transfer and output characteristics with a field effect mobility of4.44cm2V-s-1, sub-threshold swing of2.1V/decade and Ion/Ioff ratio higher than105.(2)The effect of the working pressures on the performance of the a-IGZO TFTs was investigated. As the working pressure increased, the performance first turned good and then bad, which was caused by the collision between the argon ion and the target atom or molecule.(3)The a-IGZO TFTs were prepared at different RF sputtering powers of50W,60W、70W、80W, and influenced of the RF sputtering power on the performance of the devices was obvious. As the RF sputtering power increased, the deposition rate of the IGZO film increased, which leaded to the increase of the oxygen vacancies and improvement of the covalent bond. As the RF sputtering continued to increase, the deposition rate of the IGZO film increased too, there would be many clusters on the surface of the substrate, and then the performance of the device was worse. When the RF sputtering power was70W, the device showed the best performance.(4)The effect of the target distance on the performance of the a-IGZO TFT was investigated. The characteristic of the device first turned good and then turned bad as the target distance increased. When the target distance is short, the radiation of the secondary electron become strong, the substrate is damaged when they reach the substrate. But when the target distance is too long, the quality of the IGZO film is bad, which cause the device performance degradation. The appropriate target distance is4.5cm, and the device with the field-effect mobility of0.56cm2V-1s-1and Ion/Ioff ratio of7.92x106were fabricated in this condition.