Interface Passivation Strategy for Ge pMOSFET From a TID Perspective

The interface quality between the gate dielectric and germanium (Ge) channel plays a crucial role for Ge MOSFETs. The impact of different interface passivation techniques on the total ionizing dose (TID) effect of Ge pMOSFET with enclosed-layout and Al ₂ O ₃ /TiN gate-stack is experimentally investigated under different bias conditions. The N-passivation and O-passivation of Ge pMOSFETs are realized by nitrogenplasma-passivation (NPP) and rapid-thermal-oxidation, respectively. Negative threshold voltage (Vth) shift and positive Vth shift are observed for devices irradiated under on-state and TG-state, respectively, which are partially due to negative bias temperature instability (NBTI) and positive bias temperature instability (PBTI) stresses. The NBTI and PBTI effects are evaluated to obtain “pure” Vth shifts induced by TID irradiation. The O-passivated Ge pMOSFETs show larger pure radiationinduced Vth shifts than N-passivated devices, which is attributed to less irradiation-induced border trap density in the N-based interfacial layer (IL) than the O-based IL. Therefore, N-based IL is more suitable for Ge MOSFET than the O-based IL from a perspective of radiation hardness. The results may provide interface material-design guideline for radiation-hardened and high-performance Ge MOSFET fabrication.