Display device

1. A display device comprising:

an insulative substrate;

a semiconductor layer located above the insulative substrate and formed of polysilicon, the semiconductor layer including a first channel region, a second channel region, a source region, a drain region, a first region located between the source region and the first channel region and having an impurity concentration which is lower than an impurity concentration of the source region and is higher than an impurity concentration of the first channel region, a second region formed between the first channel region and the second channel region and having an impurity concentration which is equal to the impurity concentration of the first region, and a third region located between the drain region and the second channel region and having an impurity concentration which is lower than an impurity concentration of the drain region and is higher than an impurity concentration of the second channel region;

an insulation film covering the semiconductor layer;

a first gate electrode formed on the insulation film and located above the first channel region,

a second gate electrode which is electrically connected to the first gate electrode, is formed on the insulation film, and is located above the second channel region;

a source electrode put in contact with the source region;

a drain electrode put in contact with the drain region;

a source line electrically connected to the source electrode and supplied with a video signal; and

a pixel electrode which is electrically connected to the drain electrode and in which a pixel potential corresponding to the video signal is written,

wherein the impurity concentration of the third region is equal to the impurity concentration of the first region,

a length of each of the first region and the third region is 3 μm or less, and

the second region has a length of 5 μm or more, which is greater than the length of each of the first region and the third region.

2. The display device of claim 1 , wherein

the first gate electrode and the second gate electrode are formed directly on the insulation film,

the first gate electrode and the second gate electrode are separate from each other at a position facing the semiconductor layer, and are connected to each other at a position not facing the semiconductor layer.

3. A display device comprising:

an insulative substrate;

a semiconductor layer located above the insulative substrate and formed of polysilicon, the semiconductor layer including a first channel region, a second channel region, a source region, a drain region, a first region located between the source region and the first channel region and having an impurity concentration which is lower than an impurity concentration of the source region and is higher than an impurity concentration of the first channel region, a second region formed between the first channel region and the second channel region and having an impurity concentration which is equal to the impurity concentration of the first region, and a third region located between the drain region and the second channel region and having an impurity concentration which is lower than an impurity concentration of the drain region and is higher than an impurity concentration of the second channel region;

an insulation film covering the semiconductor layer;

a first gate electrode formed on the insulation film and located above the first channel region,

a second gate electrode which is electrically connected to the first gate electrode, is formed on the insulation film, and is located above the second channel region;

a source electrode put in contact with the source region;

a drain electrode put in contact with the drain region;

a source line electrically connected to the source electrode and supplied with a video signal; and

a pixel electrode which is electrically connected to the drain electrode and in which a pixel potential corresponding to the video signal is written,

wherein the second region has a higher resistance than each of the first region and the third region,

the impurity concentration of the third region is equal to the impurity concentration of the first region,

the first channel region, the second region and the second channel region are arranged in a first direction,

the first channel region, the second region and the second channel region have a first width, a second width and a third width, respectively, in a second direction intersecting with the first direction, and

the second width is less than the first width and the third width.

4. The display device of claim 3 , wherein a length of the second region is greater than a length of each of the first region and the third region.

5. The display device of claim 4 , wherein the second region has a length of 5 μm or more.

6. The display device of claim 4 , wherein the length of each of the first region and the third region is 3 μm or less.

7. The display device of claim 3 , wherein

the first gate electrode and the second gate electrode are formed directly on the insulation film,

the first gate electrode and the second gate electrode are separate from each other at a position facing the semiconductor layer, and are connected to each other at a position not facing the semiconductor layer.