Display device having an oxide semiconductor transistor

Abstract

An object is to reduce parasitic capacitance of a signal line included in a liquid crystal display device. A transistor including an oxide semiconductor layer is used as a transistor provided in each pixel. Note that the oxide semiconductor layer is an oxide semiconductor layer which is highly purified by thoroughly removing impurities (hydrogen, water, or the like) which become electron suppliers (donors). Thus, the amount of leakage current (off-state current) can be reduced when the transistor is off. Therefore, a voltage applied to a liquid crystal element can be held without providing a capacitor in each pixel. In addition, a capacitor wiring extending to a pixel portion of the liquid crystal display device can be eliminated. Therefore, parasitic capacitance in a region where the signal line and the capacitor wiring intersect with each other can be eliminated.

1 . (canceled) 
     
     
         2 . A display device comprising:
 a scan line extending in a first direction;   a capacitor wiring extending in the first direction, wherein the scan line and the capacitor wiring comprise the same material;   a first insulating layer over the scan line and the capacitor wiring;   a semiconductor layer over the scan line with the first insulating layer interposed therebetween;   a first signal line over and electrically connected to the semiconductor layer;   a conductive layer over and electrically connected to the semiconductor layer;   a second insulating layer over the first signal line and the conductive layer;   a pixel electrode over the second insulating layer, the pixel electrode electrically connected to the conductive layer through a contact hole of the second insulating layer; and   a second signal line adjacent to the first signal line with the conductive layer therebetween,   wherein the capacitor wiring intersects with the first signal line and the second signal line,   wherein the capacitor wiring comprises a region extending in a second direction in which the first signal line extends,   wherein the capacitor wiring comprises a region overlapping with the contact hole of the second insulating layer,   wherein the conductive layer comprises a region overlapping with the capacitor wiring so that the region of the conductive layer functions as an electrode of a capacitor,   wherein a width of the capacitor wiring in a second region overlapping with the first signal line is smaller than a width of the capacitor wiring in a first region overlapping with the conductive layer,   wherein the pixel electrode does not overlap with the first signal line,   wherein the pixel electrode does not overlap with the second signal line, and   wherein the pixel electrode does not overlap with the semiconductor layer.   
     
     
         3 . The display device according to  claim 2 , wherein the first signal line branches from a region not overlapping with the scan line so as to extend in the first direction.