Patent ID: 7626205

Claim:
A semiconductor device comprising: a substrate; and a thin film transistor that uses a polycrystalline silicon film disposed over the substrate as an active layer thereof, wherein the polycrystalline silicon film is sandwiched between a first gate insulation layer and a second gate insulation layer, the thin film transistor has a first thin film transistor portion and a second thin film transistor portion, the first thin film transistor portion having a first channel region and a first front gate electrode, the first channel region being formed at the drain-side position of the polycrystalline silicon film, the first front gate electrode being opposed to the first channel region with the first gate insulation layer being sandwiched therebetween, the second thin film transistor portion having a second channel region and a second front gate electrode, the second channel region being formed at a source-side position adjacent indirectly to the drain-side first channel region with an impurity implantation region being interposed therebetween in the polycrystalline silicon film, the second front gate electrode being opposed to the second channel region with the first gate insulation layer being sandwiched therebetween, the first thin film transistor portion has the same conductivity type as that of the second thin film transistor portion, the first thin film transistor portion and the second thin film transistor portion being connected in series, the first front gate electrode and the second front gate electrode are electrically connected to each other, and a source-side back gate electrode is formed at a region that is opposed to the second channel region with the second gate insulation layer being sandwiched therebetween, a source potential being applied to the source-side back gate electrode.