Semiconductor device

摘要

A transistor in a display device is expected to have higher withstand voltage, and it is an object to improve the reliability of a transistor which is driven by high voltage or large current. A semiconductor device includes a transistor in which buffer layers are provided between a semiconductor layer forming a channel formation region and source and drain electrode layers. The buffer layers are provided between the semiconductor layer forming a channel formation region and the source and drain electrode layers in order to particularly relieve an electric field in the vicinity of a drain edge and improve the withstand voltage of the transistor.

主权项

1. A semiconductor device comprising:
a gate electrode layer over a substrate; a gate insulating layer over the gate electrode layer; an oxide semiconductor layer over the gate insulating layer; a first buffer layer having n-type conductivity on and in contact with the oxide semiconductor layer; a second buffer layer having n-type conductivity on and in contact with the oxide semiconductor layer; a source electrode layer on the first buffer layer, wherein the first buffer layer extends beyond an inner side edge of the source electrode layer; and a drain electrode layer on the second buffer layer, wherein the second buffer layer extends beyond an inner side edge of the drain electrode layer, wherein inner side edges of the first buffer layer and the second buffer layer are tapered, wherein the first buffer layer and the second buffer layer comprise an oxide of tin, and wherein the oxide semiconductor layer includes crystals whose c-axes are aligned in a direction perpendicular to one surface of the oxide semiconductor layer and whose a-b planes are not aligned with each other.