Thin film transistor and manufacturing method thereof, array substrate and display device

A method for manufacturing a thin film transistor, comprising:

• preparing a substrate;
• and
• forming an active layer on the substrate such that a surface of the active layer distal to the substrate is provided with at least one groove and a depth of the at least one groove penetrating through the active layer is larger than half of a thickness of the active layer in a direction perpendicular to the substrate, and the active layer comprises two contact parts respectively in contact with a first electrode and a second electrode of the thin film transistor, and a middle part positioned between the two contact parts, and the middle part is a channel region of the thin film transistor;
• orthographic projections of the two contact parts on the substrate are not overlapped with an orthographic projection of the middle part on the substrate;
• and
• the at least one groove is disposed in the middle part;
• and
• the method further comprises comprising forming a gate insulating layer on the active layer to conform to the active layer and form at least one groove on a surface of the gate insulating layer distal to the substrate such that the at least one groove comprises a plurality of grooves, which are arranged at intervals along a direction pointing from the first electrode to the second electrode;
• filling the at least one groove on the surface of the gate insulating layer with an organic insulating material, and planarizing the organic insulating material to form a planarized organic insulating material layer;
• forming a gate material layer on the planarized insulating material layer;
• processing the gate material layer by a nano-imprint lithography process to form a gate electrode, an orthographic projection of which on the substrate is not overlapped with an orthographic projection of the at least one groove on the substrate and expose the gate insulation layer in the at least one groove.