Display device

Abstract

At least two TFTs which are connected with a light emitting element are provided, crystallinities of semiconductor regions composing active layers of the respective TFTs are made different from each other. As the semiconductor region, a region obtained by crystallizing an amorphous semiconductor film by laser annealing is applied. In order to change the crystallinity, a method of changing a scan direction of a continuous oscillating laser beam so that crystal growth directions are made different from each other is applied. Alternatively, a method of changing a channel length direction of TFT between the respective semiconductor regions without changing the scan direction of the continuous oscillating laser beam so that a crystal growth direction and a current flowing direction are different from each other is applied.

What is claimed is:  
     
         1 . A display device comprising: 
 a pixel comprising a light emitting element over a substrate;    a first thin film transistor and a second thin film transistor over the substrate, each comprising a semiconductor region having at least a source region, a drain region and a channel region,    wherein channel length directions of the respective first thin film transistor and the second thin film transistor are arranged in a different direction with each other,    wherein each one of the source regions and the drain regions is connected with the light emitting element, and the other one of the source regions and the drain regions is connected with each other through a wiring so that a same potential is applied, and    wherein the first thin film transistor and the second thin film transistor has a common gate electrode.    
     
     
         2 . A display device according to  claim 1 , wherein an organic compound is provided as a phosphor in the light emitting element.  
     
     
         3 . A display device according to  claim 1 , wherein the display device is incorporated in at least one selected from the group consisting of a video camera, a personal digital assistant, a portable telephone, a digital camera, and an electronic book.  
     
     
         4 . A display device comprising: 
 a pixel comprising a light emitting element over a substrate;    a first thin film transistor and a second thin film transistor over the substrate, each comprising a semiconductor region having at least a source region, a drain region and a channel region,    wherein crystals in the channel region of the first thin film transistor are grown along a channel length direction and crystals in the channel region of the second thin film transistor are grown so as to intersect a channel length direction,    wherein each one of the source regions and the drain regions is connected with the light emitting element, and the other one of the source regions and the drain regions is connected with each other through a wiring so that a same potential is applied, and    wherein the first thin film transistor and the second thin film transistor has a common gate electrode.    
     
     
         5 . A display device according to  claim 4 , wherein an organic compound is provided as a phosphor in the light emitting element.  
     
     
         6 . A display device according to  claim 4 , wherein the display device is incorporated in at least one selected from the group consisting of a video camera, a personal digital assistant, a portable telephone, a digital camera, and an electronic book.  
     
     
         7 . A display device comprising: 
 a pixel comprising a light emitting element over a substrate;    a first thin film transistor and a second thin film transistor over the substrate, each comprising a semiconductor region having at least a source region, a drain region and a channel region,    wherein a crystal grain boundary in the channel region of the first thin film transistor extends along a channel length direction and a crystal grain boundary in the channel region of the second thin film transistor extends so as to intersect a channel length direction,    wherein each one of the source regions and the drain regions is connected with the light emitting element, and the other one of the source regions and the drain regions is connected with each other through a wiring so that a same potential is applied, and    wherein the first thin film transistor and the second thin film transistor has a common gate electrode.    
     
     
         8 . A display device according to  claim 7 , wherein an organic compound is provided as a phosphor in the light emitting element.  
     
     
         9 . A display device according to  claim 7 , wherein the display device is incorporated in at least one selected from the group consisting of a video camera, a personal digital assistant, a portable telephone, a digital camera, and an electronic book.  
     
     
         10 . A display device comprising: 
 a pixel comprising an electrode over a substrate;    a first thin film transistor and a second thin film transistor over the substrate, each comprising a semiconductor region having at least a source region, a drain region and a channel region,    wherein channel length directions of the respective first thin film transistor and the second thin film transistor are arranged in a different direction with each other,    wherein each one of the source regions and the drain regions is connected with the electrode, and the other one of the source regions and the drain regions is connected with each other through a wiring so that a same potential is applied, and    wherein the first thin film transistor and the second thin film transistor has a common gate electrode.    
     
     
         11 . A display device according to  claim 10 , wherein the display device is a liquid crystal display device.  
     
     
         12 . A display device according to  claim 10 , wherein the display device is incorporated in at least one selected from the group consisting of a video camera, a personal digital assistant, a portable telephone, a digital camera, and an electronic book.  
     
     
         13 . A display device comprising: 
 a pixel comprising an electrode over a substrate;    a first thin film transistor and a second thin film transistor over the substrate, each comprising a semiconductor region having at least a source region, a drain region and a channel region,    wherein crystals in the channel region of the first thin film transistor are grown along a channel length direction and crystals in the channel region of the second thin film transistor are grown so as to intersect a channel length direction,    wherein each one of the source regions and the drain regions is connected with the electrode, and the other one of the source regions and the drain regions is connected with each other through a wiring so that a same potential is applied, and    wherein the first thin film transistor and the second thin film transistor has a common gate electrode.    
     
     
         14 . A display device according to  claim 13 , wherein the display device is a liquid crystal display device.  
     
     
         15 . A display device according to  claim 13 , wherein the display device is incorporated in at least one selected from the group consisting of a video camera, a personal digital assistant, a portable telephone, a digital camera, and an electronic book.  
     
     
         16 . A display device comprising: 
 a pixel comprising an electrode over a substrate;    a first thin film transistor and a second thin film transistor over the substrate, each comprising a semiconductor region having at least a source region, a drain region and a channel region,    wherein a crystal grain boundary in the channel region of the first thin film transistor extends along a channel length direction and a crystal grain boundary in the channel region of the second thin film transistor extends so as to intersect a channel length direction,    wherein each one of the source regions and the drain regions is connected with the electrode, and the other one of the source regions and the drain regions is connected with each other through a wiring so that a same potential is applied, and    wherein the first thin film transistor and the second thin film transistor has a common gate electrode.    
     
     
         17 . A display device according to  claim 16 , wherein the display device is a liquid crystal display device.  
     
     
         18 . A display device according to  claim 16 , wherein the display device is incorporated in at least one selected from the group consisting of a video camera, a personal digital assistant, a portable telephone, a digital camera, and an electronic book.