Light-emitting device

Abstract

A-light-emitting device which realizes a high aperture ratio and in which the quality of image is little affected by the variation in the characteristics of TFTs. The channel length of the driving TFTs is selected to be very larger than the channel width of the driving TFTs to improve current characteristics in the saturated region, and a high V GS is applied to the driving TFTs to obtain a desired drain current. Therefore, the drain currents of the driving TFTs are little affected by the variation in the threshold voltage. In laying out the pixels, further, wiring is arranged under the partitioning wall and the driving TFTs are arranged under the wiring in order to avoid a decrease in the aperture ratio despite of an increase in the size of the driving TFT.

What is claimed is: 
     
         1 . A display device comprising:
 a transistor comprising a semiconductor layer and a gate electrode,   wherein the semiconductor layer comprises a first region and a second region,   wherein the first region extends in a first direction,   wherein the second region extends in a second direction perpendicular to the first direction,   wherein the first region comprises a first impurity region,   wherein the second region comprises a second impurity region,   wherein the first impurity region and the second impurity region have the same conductivity type, and   wherein the gate electrode overlaps with the first region and the second region.   
     
     
         2 . The display device according to  claim 1 , further comprising an insulating film over the transistor and a current supply line over the transistor and the insulating film. 
     
     
         3 . The display device according to  claim 2 , further comprising a source signal line,
 wherein the source signal line is electrically connected to the transistor and configured to supply voltage to the transistor.   
     
     
         4 . The display device according to  claim 2 , further comprising a light emitting element comprising a pixel electrode over the insulating film,
 wherein the first impurity region is electrically connected to the pixel electrode.   
     
     
         5 . The display device according to  claim 4 ,
 wherein the second impurity region is electrically connected to the current supply line.   
     
     
         6 . A module comprising:
 a display device comprising a transistor comprising a semiconductor layer and a gate electrode; and   a FPC electrically connected to the display device,   wherein the semiconductor layer comprises a first region and a second region,   wherein the first region extends in a first direction,   wherein the second region extends in a second direction perpendicular to the first direction,   wherein the first region comprises a first impurity region,   wherein the second region comprises a second impurity region,   wherein the first impurity region and the second impurity region have the same conductivity type, and   wherein the gate electrode overlaps with the first region and the second region.   
     
     
         7 . The module according to  claim 6 ,
 wherein the display device comprises:
 an insulating film over the transistor; and 
 a current supply line over the transistor and the insulating film. 
   
     
     
         8 . The module according to  claim 7 ,
 wherein the display device comprises a source signal line, and   wherein the source signal line is electrically connected to the transistor and configured to supply voltage to the transistor.   
     
     
         9 . The module according to  claim 7 ,
 wherein the display device comprises a light emitting element comprising a pixel electrode over the insulating film, and   wherein the first impurity region is electrically connected to the pixel electrode.   
     
     
         10 . The module according to  claim 9 ,
 wherein the second impurity region is electrically connected to the current supply line.   
     
     
         11 . A electrical equipment comprising:
 a display device comprising a transistor comprising a semiconductor layer and a gate electrode;   an antenna electrically connected to the display device; and   a battery electrically connected to the display device,   wherein the semiconductor layer comprises a first region and a second region,   wherein the first region extends in a first direction,   wherein the second region extends in a second direction perpendicular to the first direction,   wherein the first region comprises a first impurity region,   wherein the second region comprises a second impurity region,   wherein the first impurity region and the second impurity region have the same conductivity type, and   wherein the gate electrode overlaps with the first region and the second region.   
     
     
         12 . The electrical equipment according to  claim 11 ,
 wherein the display device comprises:
 an insulating film over the transistor; and 
 a current supply line over the transistor and the insulating film. 
   
     
     
         13 . The electrical equipment according to  claim 12 ,
 wherein the display device comprises a source signal line, and   wherein the source signal line is electrically connected to the transistor and configured to supply voltage to the transistor.   
     
     
         14 . The electrical equipment according to  claim 12 ,
 wherein the display device comprises a light emitting element comprising a pixel electrode over the insulating film, and   wherein the first impurity region is electrically connected to the pixel electrode.   
     
     
         15 . The electrical equipment according to  claim 14 ,
 wherein the second impurity region is electrically connected to the current supply line.