Thin film transistors for liquid crystal displays

Abstract

The amorphous silicon layer overlaps the gate electrode and the edges of the amorphous silicon layer are substantially encompassed by the edges of the gate electrode. The distance between the edges is at least 2 microns. Accordingly, both the light obliquely incident on the amorphous silicon layer from the outside once the light normally incident on the amorphous silicon layer is blocked by the gate electrode. Insulation layers, which are separated from the amorphous silicon layer and made of an amorphous silicon, are interposed between the edges of the source/drain electrodes and the gate electrode to reinforce the insulation between the gate electrode and the source/drain electrodes and also to absorb the light reflected by the source/drain electrodes and the gate electrode. The source electrode may partially surround the drain electrode in annular shape, to reduce the parasitic capacitance generated between the gate electrode and the drain electrode. The amorphous silicon layer may protrude out the gate electrode near the edges of the gate electrode which encompasses a source electrode and the source/drain electrodes. The amorphous silicon layer covers the edges of the gate electrode which encompasses the source electrode. The source electrode may be curved to prolong the distance between the drain electrode and the portion of the amorphous silicon layer.

1. A thin film transistor for a liquid crystal display comprising:
 a gate electrode;  
 an insulator covering the gate electrode;  
 an amorphous silicon layer formed on the insulator, wherein edges of the amorphous silicon layer are substantially encompassed by edges of the gate electrode and the edges of the amorphous silicon layer are spaced apart from the edges of the gate electrode by at least 2 microns;  
 a source electrode which is formed on the amorphous silicon layer and overlaps the gate electrode; and  
 a drain electrode which is formed on the amorphous silicon layer and opposite and separated from the source electrode, and overlaps the gate electrode; 
 wherein the source electrode has an annular shape and wherein the source electrode at least partially surrounds the drain electrode.  
 
 
     
     
       2. The thin film transistor as claimed in  claim 1 , wherein the distance between the edge lines of the gate electrode and the amorphous silicon layer is at least 3.5 microns. 
     
     
       3. The thin film transistor as claimed in  claim 1 , further comprising a first insulation layer which is separated from the amorphous silicon layer and disposed between the source electrode and edges of the gate electrode. 
     
     
       4. The thin film transistor as claimed in  claim 3 , further comprising a second insulating layer which is separated from the amorphous silicon layer and disposed between the drain electrode and the edges of the gate electrode. 
     
     
       5. The thin film transistor as claimed in  claim 4 , wherein the first and the second insulation layers comprise a material which absorbs incident light. 
     
     
       6. The thin film transistor as claimed in  claim 5 , wherein the first and the second insulation layers are made of amorphous silicon. 
     
     
       7. A thin film transistor for a liquid crystal display, comprising:
 a gate electrode;  
 an insulator covering said gate electrode;  
 an amorphous silicon layer formed on said insulator;  
 a drain electrode which is formed on said amorphous silicon layer and overlaps said gate electrode; and  
 a source electrode which is formed on said amorphous silicon layer and opposite and separated from said drain electrode, and overlaps said gate electrode; 
 wherein said amorphous silicon layer covers an edge of said gate electrode that extends opposite said source electrode;  
 wherein said source electrode has an annular shape and at least partially surrounds said drain electrode; and  
 wherein said amorphous silicon layer covers an edge of said gate electrode which extends opposite said drain electrode.  
 
 
     
     
       8. The thin film transistor as claimed in  claim 7 , wherein edges of the source electrode which are encompassed by edges of the gate electrode are enclosed by edges of the amorphous silicon layer. 
     
     
       9. A thin film transistor for a liquid crystal display, comprising:
 a gate electrode;  
 an insulator covering said gate electrode;  
 an amorphous silicon layer formed on said insulator;  
 a drain electrode which is formed on said amorphous silicon layer and overlaps said gate electrode; and  
 a source electrode which is formed on said amorphous silicon layer and opposite and separated from said drain electrode, and overlaps said gate electrode; 
 wherein said amorphous silicon layer covers an edge of said gate electrode that extends opposite said source electrode and extends along said drain electrode;  
 wherein said source electrode has an annular shape and at least partially surrounds said drain electrode; and  
 wherein said amorphous silicon layer that extends along said drain electrode lies within a boundary of said drain electrode.  
 
 
     
     
       10. A thin film transistor for a liquid crystal display comprising:
 a gate electrode;  
 an insulator covering the gate electrode;  
 an amorphous silicon layer formed on the insulator, wherein edges of the amorphous silicon layer are substantially encompassed by edges of the gate electrode and the edges of the amorphous silicon layer are spaced apart from the edges of the gate electrode by at least 2 microns;  
 a source electrode which is formed on the amorphous silicon layer and overlaps the gate electrode; and  
 a drain electrode which is formed on the amorphous silicon layer and opposite and separated from the source electrode, and overlaps the gate electrode; 
 wherein the source electrode has at least one portion that at least partially surrounds the drain electrode.  
 
 
     
     
       11. The thin film transistor as claimed in  claim 10 , wherein the at least one portion comprises at least one elongated portion. 
     
     
       12. The thin film transistor as claimed in  claim 10 , wherein the source electrode has more than one elongated portion that at least partially surrounds the drain electrode. 
     
     
       13. A liquid crystal display device, comprising:
 a transparent substrate having a surface thereon; and  
 a thin-film transistor on said transparent substrate, said transistor comprising: 
 a gate electrode that extends on the surface,  
 drain and source electrodes that cross over first and second edges of said gate electrode, respectively, when viewed in a first direction normal to the surface; and  
 an amorphous silicon active layer that is electrically coupled to said source and drain electrodes, said amorphous silicon active layer having a plurality of edges that extend within a perimeter of said gate electrode when viewed in the first direction and at least one edge that crosses the first edge of said gate electrode so that a first tab portion of said amorphous silicon active layer has a width greater than a width of said drain electrode and is spaced between said drain electrode and the first edge of said gate electrode.  
 
 
     
     
       14. The device of  claim 13 , wherein said source electrode has a shape that at least partially surrounds said drain electrode. 
     
     
       15. The device of  claim 14 , wherein a second tab portion of said amorphous silicon active layer has a width greater than a width of said source electrode and is spaced between said source electrode and the second edge of said gate electrode. 
     
     
       16. The device of  claim 14 , wherein a second portion of said amorphous silicon active layer is spaced between said source electrode and the second edge of said gate electrode. 
     
     
       17. A liquid crystal display device, comprising:
 a transparent substrate having a surface thereon; and  
 a thin-film transistor on said transparent substrate, said transistor comprising: 
 a gate electrode that extends on the surface;  
 drain and source electrodes that cross over first and second edges of the gate electrode, respectively, when viewed in a first direction normal to the surface;  
 an amorphous silicon active layer that is electrically coupled to said source and drain electrodes, said amorphous silicon active layer having a plurality of edges that extend within a perimeter of said gate electrode when viewed in the first direction;  
 a first amorphous silicon spacer that is disposed between the first edge of said gate electrode and said drain electrode and is electrically isolated from said amorphous silicon active layer; and  
 a second amorphous silicon spacer that is disposed between the second edge of said gate electrode and said source electrode and is electrically isolated from said amorphous silicon active layer.  
 
 
     
     
       18. A thin film transistor for a liquid crystal display comprising:
 a gate electrode;  
 an insulator covering the gate electrode;  
 an amorphous silicon layer formed on the insulator;  
 a source electrode which is formed on the amorphous silicon layer and overlaps at least a portion of the gate electrode; and  
 a drain electrode which is formed on the amorphous silicon layer and opposite and separated from the source electrode, and overlaps at least a portion of the gate electrode, 
 wherein,  at least a width of the amorphous silicon layer under the drain electrode is narrower than a width of the drain electrode at an edge of the gate electrode; and  
 wherein the source electrode has an annular shape and wherein the source electrode at least partially surrounds the drain electrode.  
 
 
     
     
       19. The thin film transistor as claimed in  claim 18 , wherein the gate electrode has a bending portion. 
     
     
       20. A thin film transistor for a liquid crystal display comprising:
   a gate electrode having first and second edges;        an insulator on the gate electrode;        a semiconductor layer formed on the insulator;        a first electrode formed on the semiconductor layer;        a second electrode formed on the semiconductor layer, the second electrode separated from the first electrode and overlapping the first edge of the gate electrode;        a first insulation layer laterally separated from the semiconductor layer and interposed between the second electrode and the first edge of the gate electrode; and        a second insulation layer separated from the semiconductor layer and interposed between the first electrode and the second edge of the gate electrode.     
     
     
       21. The thin film transistor of  claim 20 , wherein at least a width of the first insulation layer is greater than a width of the second electrode at the first edge of the gate electrode. 
     
     
       22. The thin film transistor of  claim 20 , wherein the first insulation layer extends along the second electrode. 
     
     
       23. The thin film transistor of  claim 22 , wherein the first insulation layer that extends along the second electrode lies within a boundary of the second electrode. 
     
     
       24. The thin film transistor of  claim 20 , wherein the first insulation layer comprises a material which absorbs incident light. 
     
     
       25. The thin film transistor of  claim 20 , wherein the semiconductor layer and the first insulation layer comprises an amorphous silicon layer. 
     
     
       26. The thin film transistor of  claim 25 , further comprising a doped amorphous silicon layer containing impurity on the amorphous silicon layer. 
     
     
       27. The thin film transistor of  claim 25 , wherein the semiconductor layer comprises amorphous silicon. 
     
     
       28. The thin film transistor of  claim 20 , wherein the first electrode overlaps the second edge of the gate electrode. 
     
     
       29. The thin film transistor of  claim 28 , wherein the first and the second insulation layers comprise a material which absorbs incident light. 
     
     
       30. The thin film transistor of  claim 28 , wherein the first and the second insulation layers are made of amorphous silicon. 
     
     
       31. The thin film transistor of  claim 30 , wherein the semiconductor layer comprises amorphous silicon. 
     
     
       32. The thin film transistor of  claim 20 , wherein the first electrode has an annular shape and at least partially surrounds the second electrode. 
     
     
       33. The thin film transistor of  claim 20 , wherein the semiconductor layer covers an edge of the gate electrode overlapping the first electrode. 
     
     
       34. The thin film transistor of  claim 32 , wherein the semiconductor layer extends along the first electrode. 
     
     
       35. The thin film transistor of  claim 34 , wherein the semiconductor layer that extends along the first electrode lies within a boundary of the first electrode. 
     
     
       36. The thin film transistor of  claim 20 , wherein edges of the semiconductor layer are substantially encompassed by edges of the gate electrode. 
     
     
       37. The thin film transistor of  claim 20 , wherein the first and the second electrodes are source and drain electrodes, respectively. 
     
     
       38. The thin film transistor of  claim 20 , wherein the first and the second electrodes are drain and source electrodes, respectively. 
     
     
       39. A thin film transistor for a liquid crystal display comprising;
   a gate electrode;        an insulator on the gate electrode;        a first semiconductor layer formed on the insulator;        a source electrode formed on the first semiconductor layer and overlapping a first edge of the gate electrode;        a drain electrode formed on the first semiconductor layer and separate from the source electrode, and overlapping a second edge of the gate electrode;        a second semiconductor layer laterally separated from the first semiconductor layer and interposed between the drain electrode and the second edge of the gate electrode; and        a third semiconductor layer laterally separated from the first semiconductor layer and interposed between the source electrode and the first edge of the gate electrode.     
     
     
       40. The thin film transistor of  claim 39 , wherein at least a width of the second semiconductor layer is greater than a width of the drain electrode at the second edge of the gate electrode. 
     
     
       41. The thin film transistor of  claim 39 , wherein the second semiconductor layer extends along the drain electrode. 
     
     
       42. The thin film transistor of  claim 41 , wherein the second semiconductor layer that extends along the drain electrode lies within a boundary of the drain electrode. 
     
     
       43. The thin film transistor of  claim 39 , wherein the first and the second semiconductor layers comprise amorphous silicon. 
     
     
       44. The thin film transistor of  claim 43 , further comprising a doped amorphous silicon layer containing impurity on the first and the second semiconductor layers. 
     
     
       45. The thin film transistor of  claim 39 , wherein the source electrode has an annular shape and at least partially surrounds the drain electrode. 
     
     
       46. The thin film transistor of  claim 39 , wherein edges of the first semiconductor layer are substantially encompassed by edges of the gate electrode.