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

A method of fabricating a thin film transistor, comprising:

• forming a buffer layer on a substrate;
• forming a first semiconductor layer on the buffer layer;
• forming a second semiconductor layer on the first semiconductor layer, which has a larger surface area than the first semiconductor layer;
• forming a gate insulating layer on the second semiconductor layer;
• forming a gate electrode on the gate insulating layer;
• and
• forming source and drain electrodes on the gate insulating layer which are connected to the second semiconductor layer,
• wherein the first semiconductor layer and the second semiconductor layer are polysilicon layers that are crystallized by a metal catalyst contained in the first semiconductor layer.

A method of forming a thin film transistor, comprising:

• forming a buffer layer on a substrate;
• forming a gate electrode on the buffer layer;
• forming a gate insulating layer on the gate electrode and the buffer layer;
• forming a first semiconductor layer on the gate insulating layer, which faces the gate electrode;
• forming a second semiconductor layer on the first semiconductor layer, which has a larger surface area than the first semiconductor layer;
• and
• forming source and drain electrodes on opposing sides of the second semiconductor layer, which are connected to the second semiconductor layer,
• wherein the first semiconductor layer and the second semiconductor layer are polysilicon layers crystallized by a metal catalyst contained in the first semiconductor layer.