Display device

Abstract

A protective circuit includes a non-linear element, which further includes a gate electrode, a gate insulating layer covering the gate electrode, a pair of first and second wiring layers whose end portions overlap with the gate electrode over the gate insulating layer and in which a conductive layer and a second oxide semiconductor layer are stacked, and a first oxide semiconductor layer which overlaps with at least the gate electrode and which is in contact with side face portions of the gate insulating layer and the conductive layer of the first wiring layer and the second wiring layer and a side face portion and a top face portion of the second oxide semiconductor layer. Over the gate insulating layer, oxide semiconductor layers with different properties are bonded to each other, whereby stable operation can be performed as compared with Schottky junction. Thus, the junction leakage can be decreased and the characteristics of the non-linear element can be improved.

1 . A display device comprising:
 a scan line and a signal line intersecting with each other over a substrate having an insulating surface;   a pixel portion including a pixel electrode and a thin film transistor, wherein the thin film transistor comprises:
 a gate electrode connected to the scan line; 
 a channel formation region including a first oxide semiconductor layer; 
 a first wiring layer connected to the signal line and the first oxide semiconductor layer; and 
 a second wiring layer connected to the pixel electrode and the first oxide semiconductor layer; 
   a non-linear element formed between the pixel portion and a signal input terminal disposed at a periphery of the substrate, wherein the non-linear element comprises:
 a gate electrode connected to the scan line or the signal line; 
 a gate insulating layer covering the gate electrode; 
 a pair of first and second wiring layers over the gate insulating layer and overlap the gate electrode, wherein each of the pair of first and second wiring layers includes a conductive layer and a second oxide semiconductor layer over the conductive layer; and 
 a first oxide semiconductor layer in contact with a top surface and a side surface of the second oxide semiconductor layer, and in contact with a side surface of the conductive layer, 
 wherein the first wiring layer or the second wiring layer of the non-linear element is connected to the gate electrode via a third wiring layer. 
   
     
     
         2 . A display device according to  claim 1 , wherein the first oxide semiconductor layer has higher oxygen concentration than the second oxide semiconductor layer. 
     
     
         3 . A display device according to  claim 1 , wherein the first oxide semiconductor layer has lower electrical conductivity than the second oxide semiconductor layer. 
     
     
         4 . A display device according to  claim 1 , wherein the first oxide semiconductor layer has an amorphous structure and the second oxide semiconductor layer includes a nanocrystal in an amorphous structure. 
     
     
         5 . A display device according to  claim 1 , wherein the first oxide semiconductor layer is oxygen-excess type and the second oxide semiconductor layer is oxygen-deficiency type. 
     
     
         6 . A display device according to  claim 1 , wherein the first oxide semiconductor layer and the second oxide semiconductor layer include indium, gallium, and zinc. 
     
     
         7 . A display device according to  claim 1 , wherein the third wiring layer is formed from the same material as the pixel electrode. 
     
     
         8 . A display device according to  claim 1 , wherein the display device is incorporated in one selected from the group consisting of a poster, an advertisement, an electronic book, a television device, a digital photo frame, a game machine and a phone. 
     
     
         9 . A display device comprising:
 a scan line and a signal line intersecting with each other over a substrate having an insulating surface;   a pixel portion including a pixel electrode and a thin film transistor, wherein the thin film transistor comprises:
 a gate electrode connected to the scan line; 
 a channel formation region including a first oxide semiconductor layer; 
 a first wiring layer connected to the signal line and the first oxide semiconductor layer; and 
 a second wiring layer connected to the pixel electrode and the first oxide semiconductor layer; 
   a protective circuit including a non-linear element formed over the substrate and outside the pixel portion, wherein the protective circuit connects the scan line and a common wiring to each other or connects the signal line and a common wiring to each other, and wherein the non-linear element comprises:
 a gate electrode; 
 a gate insulating layer covering the gate electrode; 
 a pair of first and second wiring layers over the gate insulating layer and overlap the gate electrode, wherein each of the pair of first and second wiring layers includes a conductive layer and a second oxide semiconductor layer over the conductive layer; and 
 a first oxide semiconductor layer in contact with a top surface and a side surface of the second oxide semiconductor layer, and in contact with a side surface of the conductive layer, 
 wherein the first wiring layer or the second wiring layer is connected to the gate electrode of the non-linear element via a third wiring layer. 
   
     
     
         10 . A display device according to  claim 9 , wherein the first oxide semiconductor layer has higher oxygen concentration than the second oxide semiconductor layer. 
     
     
         11 . A display device according to  claim 9 , wherein the first oxide semiconductor layer has lower electrical conductivity than the second oxide semiconductor layer. 
     
     
         12 . A display device according to  claim 9 , wherein the first oxide semiconductor layer has an amorphous structure and the second oxide semiconductor layer includes a nanocrystal in an amorphous structure. 
     
     
         13 . A display device according to  claim 9 , wherein the first oxide semiconductor layer is oxygen-excess type and the second oxide semiconductor layer is oxygen-deficiency type. 
     
     
         14 . A display device according to  claim 9 , wherein the first oxide semiconductor layer and the second oxide semiconductor layer include indium, gallium, and zinc. 
     
     
         15 . A display device according to  claim 9 , wherein the third wiring layer is formed from the same material as the pixel electrode. 
     
     
         16 . A display device according to  claim 9 , wherein the display device is incorporated in one selected from the group consisting of a poster, an advertisement, an electronic book, a television device, a digital photo frame, a game machine and a phone.