Threshold Voltage Variations Due to Oblique Single Grain Boundary in Sub-50-nm Polysilicon Channel

We investigate the effect of single grain boundary (SGB) with arbitrary angles on the threshold voltage (V_th) variation in sub-50-nm polysilicon (poly-Si) channel devices using 3-D simulation. An SGB in the poly-Si channel causes changes in potential barrier profile resulting in the variation of V_th. As the planar devices scale down to 20-nm, oblique SGB can significantly increase the whole potential barrier profile and cause large V_th variation. However, due to superior gate controllability, the gate-all-around devices show relatively small increase of the conduction energy band, and thus mitigate the V_th variation even in 20-nm poly-Si channel.