Patent ID: 7317209

Claim:
A substrate for a thin film transistor, comprising: a plurality of bus lines formed on a substrate such that they intersect each other with an insulation film interposed; pixel regions provided in the form of a matrix in a display area on the substrate; and a thin film transistor device formed at a peripheral circuit provided around the display area; wherein the thin film transistor device includes: a first thin film transistor of a first conductivity type including a semiconductor layer formed on the substrate, a first gate insulation film formed on the semiconductor layer, a second gate insulation film formed on the first gate insulation film, and a first gate electrode formed on the second gate insulation film, a low density impurity region being formed between source and drain regions and a channel region of the semiconductor layer; and a second thin film transistor including the semiconductor layer, the first gate insulation film, a second gate electrode formed on the first gate insulation film, and an insulation film formed on the second gate electrode and being of the same material as the second gate insulation film.