Semiconductor device

A semiconductor device comprising:

• an oxide semiconductor layer over a substrate;
• an electrode layer over and in contact with the oxide semiconductor layer, the electrode layer comprising titanium nitride;
• a gate insulating film over the oxide semiconductor layer and the electrode layer;
• and
• a gate electrode layer over the gate insulating film, the gate electrode layer overlapping the oxide semiconductor layer.

A semiconductor device comprising:

• an oxide semiconductor layer over a substrate;
• a first electrode layer over and in contact with the oxide semiconductor layer;
• a second electrode layer over the first electrode layer, the second electrode layer comprising titanium nitride;
• a gate insulating film over the oxide semiconductor layer and the second electrode layer;
• and
• a gate electrode layer over the gate insulating film, the gate electrode layer overlapping the oxide semiconductor layer,
• wherein the second electrode layer is in contact with a side surface of the first electrode layer and a top surface of the oxide semiconductor layer.

A semiconductor device comprising:

• an oxide insulating film over a substrate;
• an oxide semiconductor layer over the oxide insulating film;
• a first electrode layer over and in contact with the oxide semiconductor layer;
• a second electrode layer over the first electrode layer, the second electrode layer comprising titanium nitride;
• a gate insulating film over the oxide semiconductor layer and the second electrode layer;
• and
• a gate electrode layer over the gate insulating film, the gate electrode layer overlapping the oxide semiconductor layer,
• wherein the second electrode layer is in contact with a side surface of the first electrode layer, a top surface of the oxide semiconductor layer and a top surface of the oxide insulating film.