Influence of Post-Annealing on Electrical Characteristics of Thin-Film Transistors with Atomic-Layer-Deposited ZnO-Channel/Al$_{2}$O$_{3}$-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$_{2}$O$_{3}$-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$\times$10$^{8}$, and a high electron effective mobility of 22.1 cm$^{2}$/V$\cdot$s. 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.