Transistor and manufacturing method thereof, display substrate and display device

A top gate metal oxide transistor, comprising:

• a base substrate;
• a light shielding layer on the base substrate, wherein an upper surface of the light shielding layer has a non-protruding region and a protruding region protruding from the non-protruding region;
• a first insulation layer with an uniform thickness on the light shielding layer;
• an active layer on the first insulation layer and covering both of the non-protruding region and the protruding region of the light shielding layer;
• a gate insulating layer on the active layer;
• and
• a gate electrode on the gate insulating layer,
• wherein the active layer comprises a channel portion, and a first conductorized portion and a second conductorized portion on both sides of the channel portion, and the first conductorized portion and the second conductorized portion are formed by performing a conductorization process on an oxide semiconductor material of the active layer,
• both of the first conductorized portion and the second conductorized portion are in the non-protruding region of the light shielding layer, the channel portion is in the protruding region of the light shielding layer, and lower surfaces of the first conductorized portion and the second conductorized portion are lower than a lower surface of the channel portion.