Characteristics of self-aligned Si/Ge T-gate poly-si thin-film transistors with high on/off current ratio

In this paper, we have successfully developed and fabricated self-aligned Si/Ge T-gate poly-Si thin-film transistors (Si/Ge T-gate TFTs) with a thick gate oxide at the gate edges near the source and drain for the first time. The Si/Ge T-gate was formed by selective wet etching of Ge gate layer. The thick gate oxide layer at the gate edges and passivation oxide layer were deposited simultaneously in passivation process. The thick gate oxide at the gate edges effectively reduces the drain vertical and lateral electric fields without additional mask, lightly doped drain, spacer, or subgate bias. The Si/Ge T-gate TFTs not only reduce the off-state leakage current but also maintain a high on-state current. Experimental results show that the Si/Ge T-gate TFTs have low off-state leakage currents, improved on/off current ratio, and more saturated output characteristics compared with conventional TFTs.