THIN FILM TRANSISTOR, MANUFACTURING METHOD OF THIN FILM TRANSISTOR AND DISPLAY DEVICE

PROBLEM TO BE SOLVED: To provide a thin film transistor having a channel structure compatible with a large ON-state current and a small OFF-state current.SOLUTION: A thin film transistor (100) includes: a substrate (10); a gate electrode (12); a gate insulating layer (13); a first silicon layer (16) formed over the gate insulating layer (13) in a central area in a length direction of the gate above the gate electrode (12); a pair of second silicon layers (15) formed in both sides of the first silicon layer (16) over the gate insulating layer (13) above both sides of the gate electrode (12) in the length direction of the gate; and a pair of source and drain electrodes (19). The first silicon layer (16) is thicker than the second silicon layers (15). The first silicon layer (16) is constituted of crystalline silicon. The second silicon layers (15) are constituted of crystalline silicon or amorphous silicon, average grain size thereof is smaller than that in the first silicon layer (16).