Patent ID: 7605786

Claim:
A liquid crystal display device comprising: a first thin film transistor and a second thin film transistor, both of them in a pixel; and third thin film transistors in a source driver and a gate driver; an optically compensated birefringence mode liquid crystal over the first thin film transistor and the second thin film transistor; wherein each of the first thin film transistor and the second thin film transistor comprises a first semiconductor layer, a first gate insulating film, and a first gate electrode; wherein the first semiconductor layer comprises a first channel formation region, a first impurity region and a second impurity region; wherein a concentration of impurity in the first impurity region is lower than a concentration of impurity in the second impurity region; wherein each of the third thin film transistors comprises a second semiconductor layer, a second gate insulating film and a second gate electrode; wherein the second semiconductor layer comprises a second channel formation region, a third impurity region and a fourth impurity region; wherein a concentration of impurity in the third impurity region is lower than a concentration of impurity in the fourth impurity region; wherein an overlap length of the third impurity region and the second gate electrode is larger than an overlap length of the first impurity region and the first gate electrode; wherein the liquid crystal display device has light emitting diodes used as a backlight; wherein the liquid crystal display device and the light emitting diodes are driven by a field sequential driving method, and wherein the first thin film transistor and the second thin film transistor are connected in series, between a pixel electrode and a source signal line.