Nanocrystalline Silicon Thin Film Transistors

We review performance characteristics of top- and bottom-gate nanocrystalline silicon (nc-Si) thin film transistors (TFTs). Top gate TFTs with nc-Si active layer of nearly 80% crystallinity along with a silicon oxide gate dielectric produce high electron mobilities; values two orders higher than the amorphous silicon counterpart. In contrast, bottom-gate TFTs with silicon nitride gate dielectric and nc-Si active layer of similar crystallinity yield a mobility that is only marginally better than amorphous silicon TFT. However, they are highly stable with no visible presence of defect state creation in the active layer. In contrast, top-gate TFTs suffer from severe charge trapping in the low quality oxide gate dielectric.