Thin film transistor

Claim 1

In a thin-film transistor comprising an insulating substrate, a gate electrode formed on the substrate, a gate insulating layer covering the gate electrode, a first semiconductor layer formed on the gate insulating layer, and source and drain electrodes electrically connected to the first semiconductor layer, the improvement comprising: a protective layer formed on the first semiconductor layer above the gate electrode; an insulating layer interposed between the source and drain electrodes and the first semiconductor layer, said insulating layer having a portion which overlies said gate electrode and said protective layer, and said insulating layer being provided with a pair of openings through which the source and drain electrodes are electrically connected to the first semiconductor layer; and source and drain electrical connection members disposed between said insulating layer and the first semiconductor layer, for electrically connecting the source and drain electrodes to the first semiconductor layer; wherein each said electrical connection member comprises a second semiconductor layer containing p-type or n-type impurity atoms and formed on the first semiconductor layer, and a diffusion preventive layer disposed between said second semiconductor layer and both said source and drain electrodes and said insulating layer for preventing metal constituting the source and drain electrodes from diffusing into said second semiconductor layer; said second semiconductor layer and said diffusion preventive layer partially overlap said protective layer; said insulating layer partially overlaps said second semiconductor layer and said diffusion preventive layer; and said source and drain electrodes overlie said insulating layer.