The electrical properties of atomic layer deposition (ALD) nitrogen-doped ZnO (ZnO:N) thin films were investigated as a function of incorporated nitrogen concentration. The nitrogen concentrations in the films were controlled by using different concentrations of NH4OH solution, which was used as a single source for the reactant and nitrogen doping for ALD ZnO:N. The carrier concentrations in ALD ZnO:N decreased down to 6.13x10(13)/cm(3) using 29% NH4OH solution. Thin film transistors (TFTs) were fabricated using ALD ZnO:N thin films with different N contents as active channel layers. The device properties were significantly changed by the amount of nitrogen incorporation due to the change in the electrical properties of ZnO:N films. Especially, threshold voltages were changed from 20.0 to 3.1 V by adjusting nitrogen doping. Additionally, dc bias stability was enhanced by the increment in nitrogen concentration, producing a robust TFT at high nitrogen incorporation. Finally, a high performance flexible TFT was fabricated using ALD ZnO:N as an active layer on poly(ethylene naphthalate) substrate.