Fabrication and properties of self-aligned double-gate poly-Si TFT

In this paper a novel selfaligned double-gate (SADG) TFT technology is proposed and experimentally demonstrated for the first time. The self-alignment between the top- and bottom-gate is realized by a non-critical chemical-mechanical polishing (CMP) step. An ultra-thin channel and a thick source/drain that allow better device performance and lower source/drain resistance, are also automatically achieved. N-channel polysilicon TFTs are fabricated with maximum fabrication temperature below 600°C. The fabricated SABG-TFT exhibits symmetrical bi-directional transfer characteristics when the polarity of source/drain bias is interchanged. Moreover, the on-current under double-gate operation is more than 4 times that under single-gate operation and more than 2 times the sum of that under top-gate and bottom-gate operation respectively. Furthermore, the effective mobility is also increased from 53 cm^-2/V-s of single-gate mode to 87 cm^-2/V-s of double-gate mode.