A novel gate-overlapped LDD poly-Si thin-film transistor

We fabricate a new polycrystalline silicon thin-film transistor (poly-Si TFT), called a gate-overlapped lightly doped drain (GO-LDD) TFT, which reduces the leakage current without sacrificing the ON current. A new GO-LDD TFT, of which the electrical characteristics are tolerable to the change of LDD doping concentration, can be easily fabricated by employing the buffer oxide without any additional LDD implantation. The change of ON current due to the misalignment of the LDD region may be eliminated. Experimental results show that the leakage current of the proposed TFT's is reduced by two orders of magnitude, compared with that of conventional nonoffset TFT, while the ON current is not decreased. It is observed that the ON/OFF current ratio is not changed significantly with LDD doping concentration and LDD length.