The disclosed provides a thin film transistor, an array substrate, a display device and methods of manufacturing the thin film transistor and the array substrate. An active layer of the thin film transistor is formed of metallic oxide material, and a source electrode and a drain electrode of the thin film transistor both are formed of graphene or silver nanowire. The source electrode and the drain electrode are formed through an ink-jet printing process. Due to characteristics of graphene or silver nanowire, the manufacturing process of the thin film transistor may be simplified, the performance of the thin film transistor may be improved and the size of a channel region may be decreased. Further, an aperture ratio of the array substrate and the display device having such a thin film transistor may be increased.