An analytical method of evaluating variation of the threshold voltage shift caused by the negative-bias temperature stress in poly-Si TFTs

The variation of the threshold voltage shift (V/sub th/ shift) caused by negative-bias temperature stress (-BT stress) in poly-crystalline silicon thin-film transistors (poly-Si TFTs) was investigated. Based on the chemical reaction caused by -BT stress at the poly-Si/SiO/sub 2/ interface and the poly-Si grain boundary, an analytical method of evaluating the variation of both the V/sub th/ shift and the initial V/sub th/ was proposed. It was shown from this analysis that the enlargement of the poly-Si grain, using Si/sub 2/H/sub 6/ gas could be a solution for efficient reduction of the easily hydrogenated dangling bonds which resulted in the V/sub th/ shift and suppression of the V/sub th/ shift and its variation. Moreover, it was suggested that there are two kinds of the dangling bonds; one is hydrogenated by hydrogenation and can be dehydrogenated by -BT stress; the other is not hydrogenated and the variation of its density is much smaller than the former.