Patent ID: 8124972

Claim:
A thin film transistor comprising: a gate electrode over a substrate having an insulating surface; a gate insulating layer over the substrate, the gate insulating layer covering the gate electrode; a first semiconductor layer over and in contact with the gate insulating layer, the first semiconductor layer including a plurality of crystal regions included in an amorphous structure; at least two second semiconductor layers for forming a source region and a drain region, the at least two second semiconductor layers including an impurity element imparting one conductivity type; and a buffer layer formed using an amorphous semiconductor between the first semiconductor layer and the at least two second semiconductor layers, wherein the plurality of the crystal regions includes an inverted conical or inverted pyramidal crystal grain which grows substantially radially in a direction in which the first semiconductor layer is deposited, from a position away from an interface between the gate insulating layer and the first semiconductor layer, and wherein the first semiconductor layer includes a crystal grain with a size of greater than or equal to 1 nm and less than or equal to 5 nm.