A thin film transistor (10) may include a substrate (100); a buffer layer (300) on a surface of the substrate (100); an active layer (400) on a surface of the buffer layer (300) opposite from the substrate (100); a gate insulating layer (500) on a surface of the active layer (400) opposite from the substrate (100), and a gate (600) on a surface of the gate insulating layer (500) opposite from the substrate (100). A width of the active layer (400) may be smaller than a width of the gate (600), and an orthographic projection of the gate (600) on the substrate (100) may cover an orthographic projection of the active layer (400) on the substrate (100).