Thin film transistor and display device

A thin film transistor, comprising:

• a channel region, an LDD region, and a drain region formed with a polycrystalline silicon active layer;
• a gate electrode provided at least in the channel region via a gate insulating film;
• and
• an electrically floating light-shielding layer which overlaps at least with the channel region and the LDD region via an insulating layer, wherein:
• the thin film transistor is of a single-gate structure;
• film thickness of the insulating layer is equal to or more than 200 nm and equal to or less than 500 nm;
• and
• Sg/Sd is 17 or more, provided that an area where the light-shielding layer overlaps with the drain region is Sd and an area where the light-shielding layer overlaps with the gate electrode is Sg.

A thin film transistor, comprising:

• a channel region, an LDD region, and a drain region formed with a polycrystalline silicon active layer;
• gate electrodes provided at least in the channel region via a gate insulating film;
• and
• an electrically floating light-shielding layer which overlaps at least with the channel region and the LDD region via an insulating layer, wherein:
• the thin film transistor is of a multi-gate structure;
• and
• the light-shielding layer is divided into a plurality of light-shielding layers which are in an electrically floating state from each other.