Fabrication method of thin film transistor, fabrication method of array substrate, display panel, and display device

A fabrication method of an array substrate, comprising:

• forming a gate electrode and a gate line, a gate insulating layer and an oxide active layer on a base substrate, the gate insulating layer being located between the gate electrode and the oxide active layer;
• forming an inverted trapezoidal dissolution layer whose cross section is inverted trapezoidal on the oxide active layer, the inverted trapezoidal dissolution layer being soluble in an organic solvent, and the inverted trapezoidal dissolution layer only covering a first portion, which is directly opposite the gate electrode, of the oxide active layer but portions of the oxide active layer other than the first portion of the oxide active layer are not covered by anything;
• forming a source/drain layer on the oxide active layer, the gate insulating layer and the inverted trapezoidal dissolution layer, a thickness of the inverted trapezoidal dissolution layer being greater than a thickness of the source/drain layer;
• dissolving and removing the inverted trapezoidal dissolution layer with the organic solvent and removing the source/drain layer on the inverted trapezoidal dissolution layer, to form a source electrode, a data line and a drain electrode;
• forming a passivation layer on the source electrode, the oxide active layer and the drain electrode;
• and
• forming a pixel electrode on the passivation layer.