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

Abstract

A thin film transistor (TFT) having improved characteristics, a method for fabricating the same, and an organic light emitting display device (OLED) including the same. The TFT is constructed with a substrate, a semiconductor layer disposed on the substrate and including a channel region, source and drain regions, a gate insulating layer disposed on the semiconductor layer, a gate electrode disposed on the gate insulating layer and corresponding to the channel region, an interlayer insulating layer disposed on the gate electrode, and source and drain electrodes electrically connected to the source and drain regions of the semiconductor layer. The channel region is made from polycrystalline silicon (poly-Si), and the source and drain regions are made from amorphous silicon (a-Si). The polycrystalline silicon of the channel region is formed by crystallizing amorphous silicon using Joule's heat generated by the gate electrode.

1 . A thin film transistor (TFT), comprising:
 a substrate;   a semiconductor layer including a channel region, a source region and a drain region, disposed on the substrate;   a gate insulating layer disposed on the semiconductor layer;   a gate electrode disposed on the gate insulating layer in geometrical correspondence with the channel region;   an interlayer insulating layer disposed on the gate electrode; and   source and drain electrodes electrically connected to the source and drain regions of the semiconductor layer, with the channel region being made from polycrystalline silicon (poly-Si), the source and drain regions being made from amorphous silicon (a-Si).   
     
     
         2 . The TFT according to  claim 1 , with the gate insulating layer having a thickness of about 800 Å to 1500 Å. 
     
     
         3 . The TFT according to  claim 1 , with the gate insulating layer being either a silicon oxide layer or a silicon nitride layer. 
     
     
         4 . The TFT according to  claim 1 , with the gate electrode being made from a material selected from the group consisting of aluminum (Al), silver (Ag), titanium (Ti), tungsten (W) molybdenum (Mo), and a combination thereof. 
     
     
         5 . The TFT according to  claim 1 , further comprising a buffer layer disposed on the substrate. 
     
     
         6 . A method for fabricating a thin film transistor (TFT), comprising:
 providing a substrate;   forming an amorphous silicon (a-Si) layer on the substrate;   forming a semiconductor layer by patterning the a-Si layer;   forming a gate insulating layer on the entire surface of the substrate;   forming a gate electrode on the gate insulating layer, with the gate electrode corresponding to a certain region of the semiconductor layer;   crystallizing the certain region of the semiconductor layer using Joule's heat of the gate electrode to form a crystallized region;   forming an interlayer insulating layer on the entire surface of the substrate; and   forming source and drain electrodes to be electrically connected to the semiconductor layer.   
     
     
         7 . The method according to  claim 6 , with the crystallized region of the semiconductor layer being used to form a channel region, and the remaining a-Si region of the semiconductor layer being used to form source and drain regions. 
     
     
         8 . The method according to  claim 6 , after crystallizing the certain region of the semiconductor layer, further comprising forming source and drain regions by implanting impurity ions into the remnants of the a-Si region of the semiconductor layer that has not been crystallized. 
     
     
         9 . The method according to  claim 6 , with crystallizing the semiconductor layer using the Joule's heat of the gate electrode comprising:
 electrically connecting a positive electrode and a negative electrode to respective end regions of the gate electrode; and   applying an electric power to the positive electrode and the negative electrode.   
     
     
         10 . The method according to  claim 9 , with the Joule's heat being linearly proportional to the applied electric power. 
     
     
         11 . The method according to  claim 6 , with the Joule's heat ranging from about 700° C. to about 900° C. 
     
     
         12 . The method according to  claim 6 , with the semiconductor layer being used for a driver circuit region. 
     
     
         13 . The method according to  claim 6 , further comprising forming a buffer layer before forming the a-Si layer. 
     
     
         14 . An organic light emitting display device (OLED) comprising:
 a substrate;   a semiconductor layer disposed on the substrate and comprising a channel region made from polycrystalline silicon (poly-Si) and source and drain regions made from amorphous silicon (a-Si);   a gate insulating layer disposed on the semiconductor layer;   a gate electrode disposed on the gate insulating layer and corresponding to the channel region;   an interlayer insulating layer disposed on the gate electrode;   source and drain electrodes electrically connected to the source and drain regions of the semiconductor layer;   a first electrode electrically connected to the source and drain electrodes; and   an organic layer and a second electrode sequentially disposed on the first electrode,   
     
     
         15 . The OLED according to  claim 14 , with the gate insulating layer having a thickness of about 800 Å to 1500 Å. 
     
     
         16 . The OLED according to  claim 14 , with the gate insulating layer being either a silicon oxide layer or a silicon nitride layer. 
     
     
         17 . The OLED according to  claim 14 , with the gate electrode being made from one selected from the group consisting of aluminum (Al), silver (Ag), titanium (Ti), tungsten (W), molybdenum (Mo), and a combination thereof. 
     
     
         18 . The OLED according to  claim 14 , further comprising a buffer layer disposed on the substrate.