The Fabrication of Indium–Gallium–Zinc Oxide Sputtering Targets with Various Gallium Contents and Their Applications to Top-Gate Thin-Film Transistors

We prepared amorphous indium–gallium–zinc oxide (a-IGZO) thin films with various Ga content ratios and investigated their feasibility as the active channel layers of top-gate thin-film transistors (TFT). First, the 2-inch IGZO sputtering targets with stoichiometric ratios of InGaZn2O5, InGaZnO4, and InGa2ZnO5.5 were fabricated using In2O3, Ga2O3, and ZnO oxide powders as raw materials via sintering treatments at temperatures ranging from 900 °C to 1300 °C for 6 h or 8 h. X-ray diffraction analysis indicated that the InGaZn2O5 and InGaZnO4 targets are single-phase structures whereas the InGa2ZnO5.5 target is a two-phase structure. Hall effect measurement indicated that the a-InGaZn2O5 and a-InGaZnO4 layers possess a carrier concentration (N) of about 1019 cm−3 and a resistivity (ρ) of about 10−2 Ω·cm; however, the N of the a-InGa2ZnO5.5 layer is only 1017 cm−3, and the ρ is about 1 to 4 Ω·cm. Moreover, the a-InGaZn2O5 layer exhibited the highest Hall-effect mobility (μHall) of 21.17 cm2·V−1·sec−1. This indicated that the impedance of Ga3+ ions to carrier migration is the main factor affecting the electrical properties of a-IGZO layers. Ga content in the a-IGZO channel similarly affects the performance of the TFT devices prepared in this study. The annealing at 300 °C for 1 h in an ambient atmosphere was found to significantly improve the electrical properties of the TFT devices. The best performance was observed in the a-InGaZnO4 TFT sample subjected to post-annealing at 300 °C with Vth = −0.85 V, μFE = 8.46 cm2, V−1·sec−1, SS = 2.31, V·decade−1, and Ion/Ioff = 2.9 × 104.