Patent ID: 9214474
Filing Date: 2015-12-15
Classification: H01L

Abstract:
1. A semiconductor device comprising: an oxide semiconductor stack layer comprising a first oxide semiconductor layer, a second oxide semiconductor layer, and a third oxide semiconductor layer; a source electrode layer and a drain electrode layer over the oxide semiconductor stack layer; a gate insulating film over the source electrode layer and the drain electrode layer; and a gate electrode layer over the gate insulating film, the gate electrode layer overlapping with the oxide semiconductor stack layer, wherein the second oxide semiconductor layer is between the first oxide semiconductor layer and the third oxide semiconductor layer, wherein the second oxide semiconductor layer has a smaller energy gap than the first oxide semiconductor layer and the third oxide semiconductor layer, wherein a first mixed region whose composition is different from a composition of the first oxide semiconductor layer and a composition of the second oxide semiconductor layer is between the first oxide semiconductor layer and the second oxide semiconductor layer, wherein a second mixed region whose composition is different from the composition of the second oxide semiconductor layer and a composition of the third oxide semiconductor layer is between the second oxide semiconductor layer and the third oxide semiconductor layer, and wherein the third oxide semiconductor layer covers and is in contact with a side surface of the first oxide semiconductor layer and a top surface and a side surface of the second oxide semiconductor layer.