The dielectric constant deduced from this thickness series corresponds to 8.74 close to the bulk value of 9.8. The best equivalent oxide thickness value observed for this series - grown under high oxygen pressure - corresponds to 1.2 nm for a current density measured at VFB 鈭?#xA0;1 V of 0.1 A/cm2. The films grown with atomic oxygen display a lower capacitance and lower leakage compared to the films grown using molecular oxygen. This is due to the appearance of a thin SiO2 interface layer which is also responsible for the high defect density observed in the capacitance-voltage measurements. Upon annealing both types of films in forming gas for 15 min at 450 掳C, the capacitance decreases further while the leakage increases. This change is assigned to the appearance of the lower bandgap (6.6 eV), lower dielectric constant (6.6) phase of silicate, MgSiO3. Furthermore a VFB shift of 鈭?#xA0;0.6 V is observed and is related to the appearance of oxygen vacancies as Mg diffuses into the SiO2 interface layer.