Effects of growth temperature on performance and stability of zinc oxide thin film transistors fabricated by thermal atomic layer deposition

Zinc oxide (ZnO) thin films were deposited at different temperatures by thermal atomic layer deposition as channel layers of oxide thin-film-transistors (TFTs) with an inverted staggered bottom gate structure. Although the electrical properties (carrier concentration, electrical resistivity, and Hall mobility) of the as-grown films was strongly dependent on deposition temperature, post-annealing under oxygen ambience decreased the differences of electrical properties among the films and induced appropriate electrical properties as channel layers (the order of ∼ 10¹⁷ cm ^{- 3} for the carrier concentration). The effects of growth temperature for the performance and the stability of the ZnO TFTs were evaluated. With increasing growth temperature, the threshold voltage (V_Th) negatively shifted from 3.3 to - 4.2 V and the V_Th shift under positive bias stress decreased from 9 to 2.2 V. The field-effect mobility (μ_FE) was ∼ 7 cm²/V s for the ZnO TFTs grown at 150 and 200 °C. The high μ_FE and stability observed in the TFTs grown at high temperature were attributed to the increase in grain size and the reduction of carbon or hydrogen related non-ideal bonding due to sufficient chemical reaction energy.