Thin film transistor and manufacturing method thereof, display device and manufacturing method thereof, and electronic appliance

A thin film transistor comprising:

• a first wiring layer;
• a gate insulating layer that covers the first wiring layer;
• a pair of first impurity semiconductor layers over the gate insulating layer, the pair of first impurity semiconductor layers partly overlapping with the first wiring layer;
• a semiconductor layer between the pair of first impurity semiconductor layers, the semiconductor layer being in contact with the pair of first impurity semiconductor layers;
• a pair of second impurity semiconductor layers,
• wherein one of the pair of second impurity semiconductor layers is provided over one of the pair of first impurity semiconductor layers,
• wherein the other of the pair of second impurity semiconductor layers is provided over the other of the pair of first impurity semiconductor layers, and
• wherein the pair of second impurity semiconductor layers is spaced from the semiconductor layer;
• and
• a second wiring layer over the second impurity semiconductor layer.

A method for manufacturing a thin film transistor comprising:

• forming a first wiring layer;
• forming a gate insulating layer to cover the first wiring layer;
• forming a first impurity semiconductor layer over the gate insulating layer;
• forming a stack including a semiconductor film and an insulating film to cover the first impurity semiconductor layer;
• patterning the insulating film to form an insulating layer;
• patterning the semiconductor film to form a semiconductor layer by using the insulating layer as a mask so as to be in contact with the first impurity semiconductor layer;
• and
• forming a stack including a second impurity semiconductor layer and a second wiring layer to cover at least an end portion of the first impurity semiconductor layer.

A method for manufacturing a thin film transistor comprising:

• forming a first wiring layer;
• forming a gate insulating layer to cover the first wiring layer;
• forming a first impurity semiconductor layer over the gate insulating layer;
• forming a stack including a semiconductor film and an insulating film to cover the first impurity semiconductor layer;
• patterning the insulating film to form an insulating layer;
• patterning the semiconductor film to form a semiconductor layer by using the insulating layer as a mask so as to be in contact with the first impurity semiconductor layer;
• and
• forming a stack including a second impurity semiconductor layer and a second wiring layer over the first impurity semiconductor layer,
• wherein the first impurity semiconductor layer, the second impurity semiconductor layer, and the second wiring layer are formed using a same photomask.