Display device

Abstract

A protective circuit includes a non-linear element, which 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 second oxide semiconductor layer and a conductive layer are stacked, and a first oxide semiconductor layer which overlaps with at least the gate electrode and which is in contact with the gate insulating layer, side face portions and part of top face portions of the conductive layer and side face portions of the second oxide semiconductor layer in the first wiring layer and the second wiring 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 . (canceled) 
     
     
         2 . A display device comprising:
 a protective circuit, the protective circuit comprising:
 a first transistor comprising a first oxide semiconductor layer, a first gate electrode, a first source electrode and a first drain electrode; 
 a second transistor comprising a second oxide semiconductor layer, a second gate electrode, a second source electrode and a second drain electrode; and 
 a third transistor comprising a third oxide semiconductor layer, a third gate electrode, a third source electrode and a third drain electrode; and 
   a pixel electrically connected to the protective circuit,   wherein one of the first source electrode and the first drain electrode is a first region of a first conductive layer and one of the second source electrode and the second drain electrode is a second region of the first conductive layer,   wherein one of the third source electrode and the third drain electrode is a first region of a second conductive layer and the other of the first source electrode and the first drain electrode is a second region of the second conductive layer,   wherein the other of the third source electrode and the third drain electrode is a first region of a third conductive layer and the other of the second source electrode and the second drain electrode is a second region of the third conductive layer,   wherein the first gate electrode is electrically connected to the second conductive layer,   wherein the second gate electrode is electrically connected to the third conductive layer,   wherein the third gate electrode is electrically connected to the first conductive layer, and   wherein the first gate electrode, the second gate electrode and the third gate electrode comprise copper.   
     
     
         3 . The display device according to  claim 2 ,
 wherein the pixel comprises a fourth transistor, and   wherein the fourth transistor comprises a fourth oxide semiconductor layer.   
     
     
         4 . The display device according to  claim 2 ,
 wherein the first oxide semiconductor layer, the second oxide semiconductor layer and the third oxide semiconductor layer comprise indium, gallium and zinc.   
     
     
         5 . The display device according to  claim 2 ,
 wherein the pixel comprises a liquid crystal element.   
     
     
         6 . The display device according to  claim 2 , further comprising:
 an insulating layer over the first gate electrode and the second conductive layer; and   a transparent electrode over the insulating layer,   wherein the transparent electrode is in contact with the first gate electrode through a first opening of the insulating layer, and   wherein the transparent electrode is in contact with the second conductive layer through a second opening of the insulating layer.   
     
     
         7 . A display device comprising:
 a protective circuit, the protective circuit comprising:
 a first transistor comprising a first oxide semiconductor layer, a first gate electrode, a first source electrode and a first drain electrode; 
 a second transistor comprising a second oxide semiconductor layer, a second gate electrode, a second source electrode and a second drain electrode; and 
 a third transistor comprising a third oxide semiconductor layer, a third gate electrode, a third source electrode and a third drain electrode; 
   a pixel electrically connected to the protective circuit; and   a terminal portion electrically connected to the protective circuit,   wherein one of the first source electrode and the first drain electrode is a first region of a first conductive layer and one of the second source electrode and the second drain electrode is a second region of the first conductive layer,   wherein one of the third source electrode and the third drain electrode is a first region of a second conductive layer and the other of the first source electrode and the first drain electrode is a second region of the second conductive layer,   wherein the other of the third source electrode and the third drain electrode is a first region of a third conductive layer and the other of the second source electrode and the second drain electrode is a second region of the third conductive layer,   wherein the first gate electrode is electrically connected to the second conductive layer,   wherein the second gate electrode is electrically connected to the third conductive layer,   wherein the third gate electrode is electrically connected to the first conductive layer, and   wherein the first oxide semiconductor layer, the second oxide semiconductor layer and the third oxide semiconductor layer are spaced from each other.   
     
     
         8 . The display device according to  claim 7 ,
 wherein the pixel comprises a fourth transistor, and   wherein the fourth transistor comprises a fourth oxide semiconductor layer.   
     
     
         9 . The display device according to  claim 7 ,
 wherein the first oxide semiconductor layer, the second oxide semiconductor layer and the third oxide semiconductor layer contain indium, gallium and zinc.   
     
     
         10 . The display device according to  claim 7 ,
 wherein the pixel comprises a liquid crystal element.   
     
     
         11 . The display device according to  claim 7 , further comprising:
 an insulating layer over the first gate electrode and the second conductive layer; and   a transparent electrode over the insulating layer,   wherein the transparent electrode is in contact with the first gate electrode through a first opening of the insulating layer, and   wherein the transparent electrode is in contact with the second conductive layer through a second opening of the insulating layer.   
     
     
         12 . A display device comprising:
 a protective circuit, the protective circuit comprising:
 a first non-linear element comprising a first oxide semiconductor layer, a first gate electrode, a first source electrode and a first drain electrode; 
 a second non-linear element comprising a second oxide semiconductor layer, a second gate electrode, a second source electrode and a second drain electrode; and 
 a third non-linear element comprising a third oxide semiconductor layer, a third gate electrode, a third source electrode and a third drain electrode; 
   a pixel electrically connected to the protective circuit; and   a terminal portion electrically connected to the protective circuit,   wherein one of the first source electrode and the first drain electrode is a first region of a first conductive layer and one of the second source electrode and the second drain electrode is a second region of the first conductive layer,   wherein one of the third source electrode and the third drain electrode is a first region of a second conductive layer and the other of the first source electrode and the first drain electrode is a second region of the second conductive layer,   wherein the other of the third source electrode and the third drain electrode is a first region of a third conductive layer and the other of the second source electrode and the second drain electrode is a second region of the third conductive layer,   wherein the first gate electrode is electrically connected to the second conductive layer,   wherein the second gate electrode is electrically connected to the third conductive layer,   wherein the third gate electrode is electrically connected to the first conductive layer, and   wherein the first oxide semiconductor layer, the second oxide semiconductor layer and the third oxide semiconductor layer are spaced from each other.   
     
     
         13 . A display device according to  claim 12 ,
 wherein the pixel comprises a transistor, and   wherein the transistor comprises a fourth oxide semiconductor layer.   
     
     
         14 . A display device according to  claim 12 ,
 wherein the first oxide semiconductor layer, the second oxide semiconductor layer and the third oxide semiconductor layer contain indium, gallium and zinc.   
     
     
         15 . A display device according to  claim 12 ,
 wherein the pixel comprises a liquid crystal element.   
     
     
         16 . A display device according to  claim 12 , further comprising:
 an insulating layer over the first gate electrode and the second conductive layer, and   a transparent electrode over the insulating layer,   wherein the transparent electrode is in contact with the first gate electrode through a first opening of the insulating layer, and   wherein the transparent electrode is in contact with the second conductive layer through a second opening of the insulating layer.