What is the essence of v_FB shifts in high-k gate stack?

Several origins for V_FB shift have so far been discussed about metal/high-k/SiO₂/Si structures and we focus on three topics such as bottom interface dipole at the high-k/interfacial layer (IL)-SiO₂ interface, charge or dipole of bottom reaction layer in IL-SiO₂, and dipole due to oxygen vacancy (Vo) in high-k layer by separating each type of these dipoles. We employed bi-layer high-k dielectrics such as HfO ₂/Al₂O₃/SiO₂ and Al ₂O₃/HfO₂/SiO₂ and demonstrated that the bottom interface dipole plays a critical role in determining the V _FB shifts We also show that V_FB roll-off behavior in thinner EOT region can be associated with charge or dipole of the bottom reaction layer induced by re-oxidation at the IL-SiO₂/Si interface. Finally, we show that Vo in HfO₂ and Al₂O₃ dielectrics generated by Hf_xRu_1-x alloy gates induces dipole at the high-k/IL-SiO₂ bottom interface