Patent ID: 7859055

Claim:
A thin film transistor, comprising: a semiconductor layer, a gate insulating film, a gate electrode on a substrate in this order, wherein a cross section of the semiconductor layer has a forward tapered shape, the gate insulating film covers a top surface and a side surface of the semiconductor layer such that a vertical thickness of the gate insulating film above the top surface of the semiconductor layer is thicker than a lateral thickness of the gate insulating film on the side surface of the semiconductor layer, the gate insulating film has a multilayer structure including a silicon oxide film on a semiconductor layer side and a film made of a material with a dielectric constant higher than a dielectric constant of silicon oxide on a gate electrode side, the gate insulating film satisfies 0.5≦B/A where a thickness of the gate insulating film on the top surface of the semiconductor layer is defined as A and a thickness of the gate insulating film on the side surface of the semiconductor layer is defined as B, and the thickness of the gate insulating film is 70 nm or less on a silicon oxide capacitance equivalence basis.