We developed a high mobility polycrystalline oxide semiconductor, IGO (Indium Gallium Oxide), which is the crystalline In2O3 based random orientation polycrystalline material. The polycrystalline IGO has two unique characteristics. One is the high mobility with a wide window for fabrication process and the property is much stable. The other is the wet etching tolerance which enables the merged photolithography process. In spite of the low temperature process below 300°C, the mobility of polycrystalline IGO TFT was over 20cm2/Vs with the standard deviation smaller than 1cm2/Vs and the shift of the threshold voltage after positive bias temperature stress (Vg=Vd=15V, 10, 000s) was smaller than 0.3V. These results imply that the interruption of carrier conductivity at the grain boundaries of polycrystalline structure can be neglected with respect to the TFT characteristics and the reliability. From these properties, we concluded that the polycrystalline IGO is one of the promising channel materials for the backplane TFT of future OLED displays.
