| 초록 |
Metal oxide semiconductors is promising alternative of a-Si:H and poly-Si thin-film-transistors (TFTs) due to their high mobility and uniformity. Especially, Zinc oxide (ZnO) based TFTs such as ZnO, IGZO, and ZTO exhibit high mobility, high uniformity, and high transparency. The ALD method supplies various advantages such as easy thickness and exact composition control, and high uniformity. Because it is chemical reaction process based on the thermal energy, the film growth by the ALD method is considerably affected by gowth temperature. ZnO thin films were fabricated at various temperatures (100, 125, 150 and 200℃) by thermal atomic layer deposition as channel layers of oxide thin-film-transistors (TFTs) with bottom-gate structure. Even though the electrical conductivity of the as-grown ZnO films was intensively dependent on growth temperature, the post-annealing at oxygen ambient caused appropriate electrical properties as channel layers (the carrier concentration of ~1017cm-3), regardless of growth temperature. The effects of growth temperature on the TFT performance and stability of the ZnO TFTs were evaluated. With increasing growth temperature, the threshold voltage is negatively shifted from 3.3 to -4.2 V and the VTh shift under positive bias stress decreased from 9 to 2.2 V. The field–effect mobility (µF) showed the value of ~7cm2/Vs for the ZnO TFTs grown at 150 and 200℃. The high µF and stability observed in the sample grown at high temperature were attributed to the increase of grain size. In addition, it was expected that the µF was improved by the reduction of carbon or hydrogen related non-ideal bonding. |
