Thin film transistor substrate having two different types of thin film transistors on the same substrate and display using the same

A display device, comprising:

• a substrate;
• a first gate insulating layer over the substrate;
• a second gate insulating layer over the substrate;
• a first thin film transistor including:
• a first semiconductor layer having a polycrystalline semiconductor material over the substrate, and
• a first gate electrode overlapping a portion of the first semiconductor layer, with the first gate insulating layer between the first semiconductor layer and the first gate electrode;
• and
• a second thin film transistor including:
• a second semiconductor layer including an oxide semiconductor material over the substrate, and
• a second gate electrode overlapping a portion of the second semiconductor layer, with the second gate insulating layer between the second semiconductor layer and the second gate electrode,
• wherein both the first gate electrode and the second gate electrode are respectively disposed directly on two separate parts of the second gate insulating layer, and
• wherein the second gate insulating layer of the second thin film transistor is formed discontinuously from the second gate insulating layer of the first thin film transistor.