A novel self-aligned bottom gate poly-Si TFT with in-situ LDD

A lithography independent self-aligned bottom gate thin film transistor (SABG-TFT) technology is proposed and experimentally demonstrated. The unique feature of the technology is the formation of self-aligned and symmetrical lightly doped source/drain (LDD) structure without any additional photolithographic or implantation steps. Thus, the number of masks used in the technology is the same as that in a conventional top gate TFT technology. Moreover, devices formed by the proposed method have thick source/drain and a thin channel region for providing low source/drain resistance and improved IV characteristics. P-channel TFT devices are fabricated using a simple low temperature (≤600 °C) process. The fabricated SABG-TFT exhibits symmetrical transfer characteristics when the polarity of source/drain bias is reversed. The effective mobility and on-off current ratio of the devices are about 35 cm²/V-s and 6 × 10⁶ respectively.