A thin film transistor includes a gate, an insulating medium layer and a Schottky diode. The Schottky diode includes a first electrode, a second electrode and a semiconducting structure. The first electrode is located on the surface of the insulating medium layer and includes a first metal layer and a second metal layer. The second electrode is located on the surface of the insulating medium layer and includes a third metal layer and a fourth metal layer. The semiconductor structure includes a first end and a second end. The first end is sandwiched by the first metal layer and the second metal layer, the second end is sandwiched by the third metal layer and the fourth metal layer. The semiconductor structure includes a carbon nanotube structure.