Influence of precursor purge time on the performance of ZnO TFTs fabricated by atomic layer deposition

In the present work, the impact of purge time on the performance of TFTs was systematically studied because both ZnO channel layers and Al2O3 insulators were deposited using deionized water (H2O) as oxidant at low temperature. Compared with the Al2O3 thin films (short purge time), the Al2O3 thin films (long purge time) exhibit larger dielectric constant and breakdown voltage. With the increase of purge time, the concentrations of oxygen vacancy and impurities in Al2O3 and ZnO thin films decrease, which is beneficial to improve device stability. A small hysteresis window of 0.39 V and better stability with a minor shift of Vth (0.09 V under positive bias stress) were achieved when the purge time reaches 20 s, which is comparable to the stability achieved by the purge time of 30 s. Besides that, all devices exhibit excellent performance, including a high mobility of 32.5 +/- 0.20 cm(2)V(-1)s(-1), a high I-on/T-off 10(8), and an excellent uniformity of electrical characteristics. Therefore, this study not only shows that the stability of oxide TFTs can be enhanced through prolong purge time but also the time cost of the low temperature TFTs can be reduced by setting appropriate purge time.