Influence of Post-Annealing on Electrical Characteristics of Thin-Film Transistors with Atomic-Layer-Deposited ZnO-Channel/Al_2O_3-Dielectric

High-performance thin-film transistors (TFTs) with a low thermal budget are highly desired for flexible electronic applications. In this work, the TFTs with atomic layer deposited ZnO-channel/Al_2O_3-dielectric are fabricated under the maximum process temperature of 200^\circ\!C. First, we investigate the effect of post-annealing environment such as N_2, H_2-N_2 (4%) and O_2 on the device performance, revealing that O_2 annealing can greatly enhance the device performance. Further, we compare the influences of annealing temperature and time on the device performance. It is found that long annealing at 200^\circ\!C is equivalent to and even outperforms short annealing at 300^\circ\!C. Excellent electrical characteristics of the TFTs are demonstrated after O_2 annealing at 200^\circ\!C for 35 min, including a low off-current of 2.3\times10^-13 A, a small sub-threshold swing of 245 mV/dec, a large on/off current ratio of 7.6\times10^8, and a high electron effective mobility of 22.1 cm^2/V\cdots. Under negative gate bias stress at -10 V, the above devices show better electrical stabilities than those post-annealed at 300^\circ\!C. Thus the fabricated high-performance ZnO TFT with a low thermal budget is very promising for flexible electronic applications.