Effects of Semiconductor Thickness on Poly-Crystalline Silicon Thin Film Transistors

The effects of semiconductor thickness on poly-crystalline silicon (poly-Si) thin film transistors (TFTs) are studied. The small value of the threshold voltage (V th) appearing in thin film can improve the electrical properties of the corresponding TFTs. However, thin poly-Si film generally consists of small grains and contains many defects. When the film is extremely thin, it contains voids and it is in a separate island-like state. As a result, the extremely thin film possesses very many traps, which prevent the V th value from further decreasing. The way that thickness affects film quality differs according to how that film was prepared. Therefore, different TFT fabrication methods make the optimum semiconductor thickness different.