Provided is a thin film transistor array substrate having at least one thin film transistor. The thin film transistor includes a semiconductor layer having a channel area with a first doping concentration on a substrate, a source-drain area disposed at opposite sides of the channel area and with a second doping concentration greater than the first doping concentration, and a substantially undoped area extending from the source-drain area. The substrate has a gate insulating layer on the semiconductor layer and a gate electrode disposed on the gate insulating layer and overlapping the channel area in at least some portions. The substrate has a source electrode and a drain electrode, each insulated from the gate electrode and electrically connected to the source-drain area. The gate electrode includes a first gate electrode layer and a second gate electrode layer, wherein the second gate electrode layer is thicker than the first gate electrode layer.