Semiconductor device and method for manufacturing the same

A semiconductor device comprising:

• a pixel over a substrate;
• and
• a driver circuit over the substrate, the driver circuit electrically connected to the pixel through a scan line,
• wherein the pixel comprises a first transistor and a light-emitting element electrically connected to the first transistor,
• wherein the driver circuit comprises a second transistor,
• wherein each of the first transistor and the second transistor comprises:
• a source electrode and a drain electrode over the substrate;
• an oxide semiconductor layer over the source electrode and the drain electrode;
• a first gate electrode overlapping the oxide semiconductor layer;
• and
• a gate insulating layer between the oxide semiconductor layer and the first gate electrode,
• wherein the first transistor has a single-gate structure,
• wherein the second transistor further comprises a second gate electrode overlapping the oxide semiconductor layer of the second transistor,
• wherein the oxide semiconductor layer of the second transistor is positioned between the first gate electrode of the second transistor and the second gate electrode of the second transistor,
• wherein the first gate electrode of the second transistor and the second gate electrode of the second transistor are at the same potential, and
• wherein the first gate electrode comprises a first titanium layer, an aluminum layer over the first titanium layer, and a second titanium layer over the aluminum layer.