THIN FILM TRANSISTOR SUBSTRATE, SHIFT REGISTER AND DISPLAY DEVICE

A thin film transistor substrate can include a buffer layer on a base substrate and having a first buffer layer and a second buffer layer; a semiconductor layer disposed on the buffer layer; a gate insulating film on the semiconductor layer; and a gate electrode spaced apart from the semiconductor layer, at least a part of the gate electrode overlapping with the semiconductor layer. The base substrate, the first buffer layer, the second buffer layer, the semiconductor layer, the gate insulating film and the gate electrode are sequentially stacked, and a surface oxygen concentration of the first buffer layer is higher than a surface oxygen concentration of the second buffer layer.