Ab initio study of dipole-induced threshold voltage shift in HfO2/Al2O3/(100)Si

The ab initio work quantitatively explains the physical mechanism of threshold voltage shifts in n-type and p-type metal-oxide-semiconductor field-effect transistors with HfO₂/Al₂O₃ gate stack. In the study, the θ phase alumina has been chosen for better lattice matching of the (100) HfO₂ and (100) Si substrate. Using dipole correction method, the dominant dipole moment responsible for the threshold voltage shift has been identified at the interface of HfO₂/Al₂O₃. Our HfO₂/Al₂O₃ atomic model shows the dipole moment decreases almost linearly as the alumina thickness decreases from four monolayers (13 Å) to one monolayer (3 Å). On account of the effects of capacitance and the dipole moment, our ab initio calculation quantitatively explains the trend and sensitivity of experimental threshold voltage shifts on n- and p-MOSFET´s.