Patent ID: 7589383

Claim:
A thin film semiconductor device comprising: an insulating substrate; a low-voltage thin film transistor formed on said insulating substrate and having a first semiconductor film, a first gate electrode and a first gate insulating film, wherein said first semiconductor film is formed on said first semiconductor film through said first gate insulating film; and a high-voltage thin film transistor formed on said insulating substrate and having a second semiconductor film, a second gate electrode and a second gate insulating film, wherein said second semiconductor film is formed on said insulating substrate and said second gate electrode is formed on said second semiconductor film through said second gate insulating film, wherein said second gate insulating film comprises a combination of said first gate insulating film and at least another gate insulating film formed on said first gate insulating film, and said another gate insulating film is formed to cover said first gate electrode, and wherein when p-type dopant concentration is represented by positive values and n-type dopant concentration is represented by negative values, an impurity doping state with respect to a channel region of said high-voltage thin film transistor is adjusted to be in more negative side as compared with an impurity doping state with respect to a channel region of said low-voltage thin film transistor of the same conductivity type.