| abstract |
Oxygen is likely to be released or an oxygen vacancy is likely to occur during a manufacturing process particularly at a side surface of an oxide semiconductor layer. When an oxygen vacancy occurs at the side surface of the oxide semiconductor layer, a problem arises in that the resistance of the side surface is reduced, the apparent threshold voltage of a transistor varies, and variation in the threshold voltage is increased. Further, the variation in the threshold voltage may cause unintentional current to flow between a source and a drain, which might lead to an increase in the off-state current of the transistor and deterioration in the electric characteristics of the transistor. A semiconductor device in which a multilayer film including an oxide semiconductor layer and an oxide layer surrounding the oxide semiconductor layer is used for a channel formation region is provided. |