Thin film transistor substrate, display device including a thin film transistor substrate, and method of forming a thin film transistor substrate

A method of forming a thin film transistor substrate, the method comprising:

• providing a first thin film transistor comprising:
• providing a polycrystalline semiconductor layer;
• providing a first gate electrode overlapping the polycrystalline semiconductor layer;
• providing a nitride layer on the first gate electrode;
• providing an oxide layer on the nitride layer;
• and
• providing a first source electrode and a first drain electrode on the oxide layer;
• and
• providing a second thin film transistor comprising:
• providing a second gate electrode on a same layer as the first gate electrode;
• providing a hydrogen collecting layer between the second gate electrode and the nitride layer;
• providing an oxide semiconductor layer on the oxide layer;
• providing a second source electrode contacting one side of the oxide semiconductor layer;
• and
• providing a second drain electrode contacting the other side of the oxide semiconductor layer,
• wherein the first thin film transistor and the second thin film transistor are disposed on a same substrate,
• wherein the providing the nitride layer comprises forming an opening exposing the hydrogen collecting layer of the second thin film transistor, and
• wherein the opening of the nitride layer overlaps the oxide semiconductor layer in a vertical direction.