Patent ID: 8228477

Claim:
A method of manufacturing a liquid crystal display device comprising: forming a gate wiring over an insulating surface by using a first mask; forming a common electrode over the insulating surface; forming an insulating film over the gate wiring; forming a first amorphous semiconductor film over the insulating film; forming a second amorphous semiconductor film containing an impurity element which imparts n-type conductivity, over the first amorphous semiconductor film; forming a conductive film over the second amorphous semiconductor film; patterning the first amorphous semiconductor film, the second amorphous semiconductor film and the conductive film together by using a second mask; and removing a portion of the first amorphous semiconductor film, a portion of the second amorphous semiconductor film and a portion of the conductive film to form a source region, a drain region, a source wiring after patterning the first amorphous semiconductor film, the second amorphous semiconductor film and the conductive film; forming a transparent electrode electrically connected to the conductive film; forming an alignment film over the transparent electrode and the common electrode; and forming a protecting circuit comprising a same material as the common electrode when the common electrode is formed, wherein the portion of the second amorphous semiconductor film is between the source region and the drain region, wherein the transparent electrode and the common electrode are disposed so that liquid crystal molecules are controlled by an electric field produced between the transparent electrode and the common electrode, wherein the gate wiring is separated from the common electrode, and wherein the transparent electrode and the common electrode are overlapped with each other.