Thin film transistor, method of fabricating the same, and organic light emitting diode display device including the same

A method of fabricating a thin film transistor, comprising:

• preparing a substrate;
• forming a first amorphous silicon layer on the substrate;
• crystallizing the first amorphous silicon layer into a first polycrystalline silicon layer by using a crystallization inducing metal;
• forming a second amorphous silicon layer on the first polycrystalline silicon layer;
• implanting an impurity into the second amorphous silicon layer;
• annealing the first polycrystalline silicon layer and the second amorphous silicon layer, the crystallization inducing metal in the first polycrystalline silicon layer being transferred into the second amorphous silicon layer, the second amorphous silicon layer being crystallized into a second polycrystalline silicon layer;
• patterning the first polycrystalline silicon layer to form a first semiconductor layer;
• patterning the second polycrystalline silicon layer to form a second semiconductor layer, the second semiconductor layer having an opening to expose a predetermined portion of the first semiconductor layer;
• forming a source electrode and a drain electrode to be connected to the first semiconductor layer and the second semiconductor layer;
• forming a gate insulating layer to cover the source electrode, the drain electrode, and the exposed portion of the first semiconductor layer;
• and
• forming a gate electrode on the gate insulating layer above the exposed portion of the first semiconductor layer through the opening.

An organic light emitting diode display device (OLED display device), comprising:

• a substrate;
• a first semiconductor layer disposed on the substrate;
• a second semiconductor layer disposed on the first semiconductor layer, the second semiconductor layer having an opening to expose a predetermined portion of the first semiconductor;
• a source electrode and a drain electrode connected to the first semiconductor layer and the second semiconductor layer;
• a gate insulating layer disposed to cover the source electrode, the drain electrode, and the exposed portion of the first semiconductor layer;
• and
• a gate electrode disposed on the gate insulating layer above the exposed portion of the first semiconductor layer through the opening
• a first electrode connected to the source or drain electrode;
• a second electrode;
• and
• an organic layer disposed between the first electrode and the second electrode, the organic layer emitting light.