Active matrix liquid crystal display device having reduced leak current and switching element used therein

An active matrix liquid crystal display device comprising:

• a thin-film-transistor array substrate having thin film transistors formed on one surface of a substrate and a polarizer formed on the other surface of said substrate, each of said thin film transistors including a semiconductor region formed on an insulating film covering a gate electrode formed on said substrate, and a source electrode and a drain electrode formed apart from each other on both end portions of said semiconductor region so as to partly overlap said semiconductor region and extending on said insulating film, said source electrode and said drain electrode being formed in such a manner that widths of said source electrode and said drain electrode in a channel width direction are included in a width of said semiconductor region in said channel width direction, while both a planar source-side overlap area constructed by said gate electrode, said source electrode and said semiconductor region and a planar drain-side overlap area constructed by said gate electrode, said drain electrode and said semiconductor region axe provided such that an optimal overlap length of one of said source-side and said drain-side overlap areas in a channel length direction is determined for a light incident on a channel portion of each of said thin film transistors to have a light intensity of below or equal to 0.2% of a light intensity of a backlight incident on said substrate;
• an opposing substrate disposed to face said thin-film-transistor array substrate;
• and
• a liquid crystal sandwiched between said thin-film-transistor ray substrate and said opposing substrate.