Dipole formation at direct-contact HfO2∕Si interface

Direct-contact HfO2∕Si interfaces, which have virtually no interfacial SiO2 layer, exhibit characteristic interface-charge distribution. The authors report that direct-contact interfaces demonstrate a negative flatband-voltage shift that is reduced by the insertion of a ∼0.5-nm-thick Si-oxide layer. The authors propose that the observed flatband-voltage shift is mainly caused by an electrostatic dipole (∼0.5V) formed at the HfO2∕Si interface rather than fixed charges. The effects of the dipole on leakage current are also discussed.