Experimental evidence for the flatband voltage shift of high-k metal-oxide-semiconductor devices due to the dipole formation at the high-k/SiO2 interface

We have examined an origin of the flatband voltage (V-FB) shift in metal-oxide-semiconductor capacitors by employing bilayer high-k gate dielectrics consisting of HfO2 and Al2O3 on the interfacial SiO2 layer. We found that the high-k/SiO2 interface affects the V-FB shift through an electrical dipole layer formation at its interface, regardless of the gate electrode materials. Furthermore, we demonstrated that the V-FB shift in the metal/high-k gate stack is determined only by the dipole at high-k/SiO2 interface, while for the Si-based gate it is determined by both gate/high-k and high-k/SiO2 interfaces.