Gate-overlapped lightly doped drain poly-Si thin-film transistors for large area-AMLCD

We have fabricated a gate-overlapped lightly doped drain (GO-LDD) polycrystalline silicon thin-film transistor (poly-Si TFT) applicable for large area AMLCD by employing the uniform and low-temperature doping techniques, such as ion shower doping and in situ doping. Experimental results show that the leakage current of the proposed TFT´s is reduced by more than the magnitude of two orders, compared with that of conventional nonoffset TFT, while the ON current is scarcely decreased. It is verified by the device simulator that the electron concentration in the LDD region is increased under the ON state and decreased under the OFF state due to the field plate with gate potential over the LDD region. Furthermore, the vertical peak electric field in the LDD region is decreased significantly by the extended field plate potential during the OFF state. It is observed that the gate bias stress degrades significantly the subthreshold slope of the ion shower doped GO-LDD TFT´s at the low drain bias but does not degrade the device characteristics of those with in situ doping due to the high-quality TEOS SiO₂ interlayer