| 摘要 |
An object is to increase the on-state current of a thin film transistor. A solution is to provide a projection in a back-channel portion of the thin film transistor. The projection is provided so as to be off a tangent in the back-channel portion between a source or a drain and a channel formation region. With the projection, a portion where electric charge is trapped and a path of the on-state current can be apart from each other, so that the on-state current can be increased. The shape of a side surface of the back-channel portion may be curved, or may be represented as straight lines in a cross section. Further, a method for forming such a shape by performing one etching step is provided.
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