Hydrogen passivation on the grain boundary and intragranular defects in various polysilicon thin-film transistors

We investigated the hydrogenation effects on two types of trap states in poly-Si thin-film transistors (TFT:s), where the gate oxide thickness was varied from 1000 Angstrom to 4000 Angstrom and the active poly-Si layers were altered by different annealing methods. The decrease of threshold voltage, which is related to the density of deep states,has shown a similar tendency irrespective of device structures. However, the other device parameters, such as field-effect mobility and minimum leakage current, which are influenced by the tail states, are improved considerably in the poly-Si TFT's with a thick gate oxide or with postannealed active layers. It was verified by the comparison of trap state distributions that the tail states were decreased significantly in the above TFT's with the thick gate oxide and postannealed poly-Si layers.