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.