Interface Passivation Strategy for Ge pMOSFET From a TID Perspective

Abstract

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 Al2O3/TiN gate-stack is experimentally investigated under different bias conditions. The N-passivation and O-passivation of Ge pMOSFETs are realized by nitrogen-plasma-passivation (NPP) and rapid-thermal-oxidation, respectively. Negative threshold voltage ( $V_{\text {th}}$ ) shift and positive $V_{\text {th}}$ 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” $V_{\text {th}}$ shifts induced by TID irradiation. The O-passivated Ge pMOSFETs show larger pure radiation-induced $V_{\text {th}}$ 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.