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.

1 . A display device comprising:
 a first transistor;   a second transistor;   a capacitor comprising a first terminal and a second terminal; and   a light-emitting element comprising:
 a first electrode electrically connected to one of a source and a drain of the first transistor and one of a source and a drain of the second transistor; 
 an organic compound layer over the first electrode; and 
 a second electrode over the organic compound layer, 
   wherein a first crystalline semiconductor layer comprises a channel formation region of the first transistor, a channel formation region of the second transistor,   wherein a gate of the first transistor is electrically connected to the second terminal of the capacitor,   wherein a channel length direction of the first transistor is perpendicular to a channel length direction of the second transistor, and   wherein the first crystalline semiconductor layer is continuous.   
     
     
         2 . The display device according to  claim 1 , wherein a gate of the second transistor is electrically connected to the gate of the first transistor and the second terminal of the capacitor. 
     
     
         3 . The display device according to  claim 1 , wherein the other of the source and the drain of the first transistor is electrically connected to the other of the source and the drain of the second transistor and the first terminal of the capacitor. 
     
     
         4 . The display device according to  claim 1 , further comprising a third transistor comprising a first channel formation region and a second channel formation region,
 wherein a second crystalline semiconductor layer comprises the first channel formation region and the second channel formation region of the third transistor, and   wherein one of a source and a drain of the third transistor is electrically connected to the gate of the first transistor, the gate of the second transistor, and the second terminal of the capacitor.   
     
     
         5 . The display device according to  claim 1 , wherein the first electrode of the light-emitting element is a cathode. 
     
     
         6 . The display device according to  claim 1 , further comprising a power source line electrically connected to the other of the source and the drain of the first transistor, the other of the source and the drain of the second transistor, and the first terminal of the capacitor. 
     
     
         7 . The display device according to  claim 1 , wherein a crystal growth direction of the first crystalline semiconductor layer is parallel to the channel length direction of the first transistor and is perpendicular to the channel length direction of the second transistor. 
     
     
         8 . An electronic equipment comprising the display device according to  claim 1 , wherein the electronic equipment is one selected from the group consisting of a video camera, a personal digital assistant, a portable telephone device, a digital camera, and an electronic book device. 
     
     
         9 . A display device comprising:
 a first transistor;   a second transistor;   a capacitor comprising a first terminal and a second terminal; and   a light-emitting element comprising:
 a first electrode electrically connected to one of a source and a drain of the first transistor and one of a source and a drain of the second transistor; 
 an organic compound layer over the first electrode; and 
 a second electrode over the organic compound layer, 
   wherein a first crystalline semiconductor layer comprises a channel formation region of the first transistor, a channel formation region of the second transistor,   wherein a gate of the first transistor is electrically connected to the second terminal of the capacitor,   wherein a channel length direction of the first transistor is perpendicular to a channel length direction of the second transistor,   wherein a crystal growth direction of the first crystalline semiconductor layer is parallel to the channel length direction of the first transistor and is perpendicular to the channel length direction of the second transistor, and   wherein the first crystalline semiconductor layer is continuous.   
     
     
         10 . The display device according to  claim 9 , wherein a gate of the second transistor is electrically connected to the gate of the first transistor and the second terminal of the capacitor. 
     
     
         11 . The display device according to  claim 9 , wherein the other of the source and the drain of the first transistor is electrically connected to the other of the source and the drain of the second transistor and the first terminal of the capacitor. 
     
     
         12 . The display device according to  claim 9 , further comprising a third transistor comprising a first channel formation region and a second channel formation region,
 wherein a second crystalline semiconductor layer comprises the first channel formation region and the second channel formation region of the third transistor, and   wherein one of a source and a drain of the third transistor is electrically connected to the gate of the first transistor, the gate of the second transistor, and the second terminal of the capacitor.   
     
     
         13 . The display device according to  claim 9 , wherein the first electrode of the light-emitting element is a cathode. 
     
     
         14 . The display device according to  claim 9 , further comprising a power source line electrically connected to the other of the source and the drain of the first transistor, the other of the source and the drain of the second transistor, and the first terminal of the capacitor. 
     
     
         15 . An electronic equipment comprising the display device according to  claim 9 , wherein the electronic equipment is one selected from the group consisting of a video camera, a personal digital assistant, a portable telephone device, a digital camera, and an electronic book device. 
     
     
         16 . A display module comprising:
 a panel comprising:
 a first transistor; 
 a second transistor; 
 a capacitor comprising a first terminal and a second terminal; and 
 a light-emitting element comprising:
 a first electrode electrically connected to one of a source and a drain of the first transistor and one of a source and a drain of the second transistor; 
 an organic compound layer over the first electrode; and 
 a second electrode over the organic compound layer, 
 
   a printed substrate;   a controller provided in the printed substrate;   a power source circuit provided in the printed substrate;   wherein a first crystalline semiconductor layer comprises a channel formation region of the first transistor, a channel formation region of the second transistor,   wherein a gate of the first transistor is electrically connected to the second terminal of the capacitor,   wherein a channel length direction of the first transistor is perpendicular to a channel length direction of the second transistor,   wherein the printed substrate is incorporated in the panel through a flexible printed circuit, and   wherein the first crystalline semiconductor layer is continuous.   
     
     
         17 . The display module according to  claim 16 , wherein a gate of the second transistor is electrically connected to the gate of the first transistor and the second terminal of the capacitor. 
     
     
         18 . The display module according to  claim 16 , wherein the other of the source and the drain of the first transistor is electrically connected to the other of the source and the drain of the second transistor and the first terminal of the capacitor. 
     
     
         19 . The display module according to  claim 16 , further comprising a third transistor comprising a first channel formation region and a second channel formation region,
 wherein a second crystalline semiconductor layer comprises the first channel formation region and the second channel formation region of the third transistor, and   wherein one of a source and a drain of the third transistor is electrically connected to the gate of the first transistor, the gate of the second transistor, and the second terminal of the capacitor.   
     
     
         20 . The display module according to  claim 16 , wherein the first electrode of the light-emitting element is a cathode. 
     
     
         21 . The display module according to  claim 16 , further comprising a power source line electrically connected to the other of the source and the drain of the first transistor, the other of the source and the drain of the second transistor, and the first terminal of the capacitor. 
     
     
         22 . The display module according to  claim 16 , wherein a crystal growth direction of the first crystalline semiconductor layer is parallel to the channel length direction of the first transistor and is perpendicular to the channel length direction of the second transistor. 
     
     
         23 . The display module according to  claim 16 , wherein the power source circuit comprising a switching regulator and a series regulator. 
     
     
         24 . An electronic equipment comprising the display module according to  claim 16 , wherein the electronic equipment is one selected from the group consisting of a video camera, a personal digital assistant, a portable telephone device, a digital camera, and an electronic book device.