Method of fabricating polysilicon, thin film transistor, method of fabricating the thin film transistor, and organic light emitting diode display device including the thin film transistor

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

• a substrate;
• a buffer layer formed on the substrate;
• a first semiconductor layer and a second semiconductor layer disposed on the buffer layer;
• a gate electrode disposed on the substrate and insulated from the first semiconductor layer and the second semiconductor layer;
• a gate insulating layer to insulate the gate electrode from the first semiconductor layer and the second semiconductor layer;
• source and drain electrodes insulated from the gate electrode and connected to the second semiconductor layer;
• an insulating layer disposed on the substrate to cover the source and drain electrodes;
• and
• a first electrode, an organic light emitting layer, and a second electrode disposed on the insulating layer, the first electrode being connected to one of the source and drain electrodes,
• wherein the second semiconductor layer comprises a channel region corresponding to the gate electrode, and
• wherein crystal grains in the channel region of the second semiconductor layer are larger than crystal grains in a region of the first semiconductor layer corresponding to the gate electrode.