Patent ID: 8766255

Claim:
A semiconductor device comprising: a first insulating layer; a first trench and a second trench in the first insulating layer; an oxide semiconductor layer over the first insulating layer; a gate insulating layer over the oxide semiconductor layer; a gate electrode adjacent to the oxide semiconductor layer with the gate insulating layer interposed therebetween; a first sidewall insulating layer and a second sidewall insulating layer in contact with the gate electrode; a source electrode over the first sidewall insulating layer; and a drain electrode over the second sidewall insulating layer, wherein at least part of the oxide semiconductor layer is formed in the first trench, wherein at least part of the gate insulating layer is formed in the first trench, wherein at least part of the gate electrode is formed in the first trench, wherein the source electrode and the drain electrode are in electrical contact with the oxide semiconductor layer, and wherein a depth of the second trench is deeper than a depth of the first trench.