Thin film transistor and display device

A thin film transistor, comprising:

• a gate electrode,
• an oxide semiconductor layer comprising at least a first and a second oxide semiconductor layer,
• an etch stopper layer,
• a source-drain electrode, and
• a gate insulator film,
• wherein
• the oxide semiconductor layer is configured to be a channel layer;
• the etch stopper layer is configured to protect a surface of the oxide semiconductor layer;
• the gate insulator film is interposed between the gate electrode and the channel layer;
• the first oxide semiconductor layer is in direct contact to the gate insulator film and satisfies the following expressions:
• 15≦[In]≦35, 50≦[Zn]≦60, 15≦[Sn]≦30
• where [In], [Zn], and [Sn] represent a content of each element in atomic % relative to a total content of all metal elements in the first oxide semiconductor layer;
• a hydrogen concentration in the gate insulator film in direct contact to the first oxide semiconductor layer is 4 atomic % or lower;
• and
• the second oxide semiconductor layer is in direct contact to the source-drain electrode and satisfies the following expressions:
• 10≦[In]≦20, 30≦[Zn]≦40, 5≦[Sn]≦15, and 35≦[Ga]≦50
• where [In], [Zn], [Sn], and [Ga] represent a content of each element in atomic % relative to a total content of all metal elements in the second oxide semiconductor layer.