The present disclosure discloses a thin film transistor, an array substrate and their manufacturing methods, and a display apparatus. The method for manufacturing the thin film transistor of the present disclosure comprises a step of forming an insulation layer, wherein the step of forming the insulation layer further comprises forming a siloxane material layer, oxidizing the siloxane material layer such that an inorganic silicon film is formed on a surface of the siloxane material layer, and curing the oxidized siloxane material layer to obtain the insulation layer. In this disclosure, the outer layer of the insulation layer is an inorganic silicon film which is a commonly-used material for making the insulation layer in prior art, and the inner layer of the insulation layer is made of the siloxane material having a low dielectric constant and high chemical stability.