Enhancement of InGaZnO Thin-Film Transistors by Contact Barrier Modulation Using Oxygen Defects

We have studied the effect of barrier-controlled electrodes on characteristics of amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) using an interlayer with modulated oxygen defects. Interlayers of a-IGZO with different electrical resistivities were controlled with various oxygen ratios during the RF sputtering deposition. As the ratio of O 2 /(O 2 + Ar) was increased from 0 to 20%, the carrier concentration decreased from 2.84 × 10 18 to 1.56 × 10 14 cm –3 and the electrical resistivity increased from 0.12 to 9600 Ω·cm. Using this result, a-IGZO thin layers with different resistivities (low and high) to control the contact barriers were inserted between the a-IGZO TFT channel and both the source and drain electrodes. In the case of a-IGZO TFT with a low resistivity interlayer, the threshold voltage ( V th ) was shifted by −4.1 V compared to the reference device without an interlayer. In addition, on/off ratio, the subthreshold swing, and the mobility of the devices were also enhanced by achieving Ohmic contact. In contrast, the a-IGZO TFT with a high resistivity interlayer showed a positive V th shift of 1.5 V and also improved device performance, while maintaining a mobility of ∼84% of the reference device due to the energy barrier.