Patent ID: 8492760

Claim:
A semiconductor device including a thin film transistor, the thin film transistor comprising: a gate electrode layer; a gate insulating layer over the gate electrode layer, the gate insulating layer comprising a first region, a second region, and a third region; a source electrode layer and a drain electrode layer over the gate insulating layer; a first conductive layer having n-type conductivity over the source electrode layer, the first conductive layer comprising a fourth region between the source electrode layer and the drain electrode layer; a second conductive layer having n-type conductivity over the drain electrode layer, the second conductive layer comprising a fifth region between the source electrode layer and the drain electrode layer; and an oxide semiconductor layer over the first conductive layer and the second conductive layer, the oxide semiconductor layer comprising a sixth region between the source electrode layer and the drain electrode layer, wherein: the sixth region overlaps with the gate electrode layer; the sixth region is over and in contact with the third region; a carrier concentration of the first conductive layer and the second conductive layer is higher than a carrier concentration of the oxide semiconductor layer; the oxide semiconductor layer and the source electrode layer are electrically connected to each other with the first conductive layer interposed therebetween; the oxide semiconductor layer and the drain electrode layer are electrically connected to each other with the second conductive layer interposed therebetween; the first region is in contact with the fourth region; and the second region is in contact with the fifth region.