The passivation of the Ge interface is a key issue in the fabrication of Ge MOSFETs. Recently, the poor reliability of Ge/GeO2/Al2O3 MOSFETs was attributed to the border traps in Al2O3. We here propose a Ge/GeO2/AlN stack model with AlN as buffer layer for more reliable Ge MOSFETs. Calculation suggests that AlN has the advantage of fewer border traps in the relevant energy range, high oxygen diffusion barrier and sufficiently large band offset to Ge.