Downscaling challenges in IGZO transistors: A study on threshold voltage roll-up and roll-off effects

Abstract Besides the common short-channel effect (SCE) of threshold voltage ( V th ) roll-off during the channel length ( L ) downscaling of InGaZnO (IGZO) thin-film transistors (TFTs), an opposite V th roll-up was reported in this work. Both roll-off and roll-up effects of V th were comparatively investigated on IGZO transistors with varied gate insulator (GI), source/drain (S/D), and device architecture. For IGZO transistors with thinner GI, the SCE was attenuated due to the enhanced gate controllability over the variation of channel carrier concentration, while the V th roll-up became more noteworthy. The latter was found to depend on the relative ratio of S/D series resistance ( R SD ) over channel resistance ( R CH ), as verified on transistors with different S/D. Thus, an ideal S/D engineering with small R SD but weak dopant diffusion is highly expected during the downscaling of L and GI in IGZO transistors.