THIN-FILM TRANSISTOR, THIN-FILM TRANSISTOR SUBSTRATE, LIQUID CRYSTAL DISPLAY DEVICE, AND METHOD FOR MANUFACTURING THIN-FILM TRANSISTOR

The present invention relates to a thin-film transistor (TFT) in which a channel region is formed by an oxide semiconductor, and which improves reliability by suppressing threshold voltage shifts caused by holes optically excited in the vicinity of a source electrode and a drain electrode. A lower semiconductor layer (140) is partially provided between an oxide semiconductor layer (130) and a gateinsulating film (120). The lower semiconductor layer (140) is present in a source overlapping region (171) where the oxide semiconductor layer (130) overlaps a source electrode (151) and/or a drain overlapping region (172) where the oxide semiconductor layer (130) overlaps a drain electrode (152). On the other hand, a region where the lower semiconductor layer (140) is not present is provided between the source overlapping region (171) and the drain overlapping region (172). 关于沟道区域由氧化物半导体构成的TFT，抑制在源电极以及漏电极的附近光激励的空穴所引起的阈值电压偏移，提高可靠性。在氧化物半导体层(130)与栅极绝缘膜(120)之间，部分性地设置下层半导体层(140)。下层半导体层(140)存在于氧化物半导体层(130)与源电极(151)重叠的源极重叠