Thin-film transistor array substrate, method of manufacturing the same, and display device

A method of manufacturing a thin-film transistor (TFT) array substrate, the method comprising:

• forming a non-doping semiconductor layer on an entire surface of a substrate;
• forming a gate insulating layer on the non-doping semiconductor layer;
• forming a preliminary-gate electrode of a TFT and a lower electrode of a capacitor on the gate insulating layer;
• forming an interlayer insulating layer covering the lower electrode and having an opening exposing portions that are to become a channel region and a source-drain region of the TFT;
• performing a first doping process by forming the source-drain region in the non-doping semiconductor layer;
• forming a source electrode and a drain electrode, which are connected to the source-drain region, and an upper electrode overlapping the lower electrode;
• and
• performing a second doping process by forming the channel region on the non-doping semiconductor layer.