Physics & Modeling of Ambipolar Snapback Behavior in Gate Grounded NMOS

This paper models first snapback ambipolar action in NMOS, when subjected to high current stress across the drain terminal. We analyze 2 − D ambipolar current in Gate Grounded NMOS (GGNMOS) devices close to pinch-off region, which is related with S shaped I-V characteristics under highly injected avalanche generated carriers. Furthermore, the first snap-back phenomenon in GGNMOS owing to surface bipolarity is investigated. Due to ambipolar current flow and barrier lowering at source-body junction a novel model of surface bipolar activity has been presented. An analytical model for the surface electrostatics is provided and further compared with 2 − D TCAD device simulation results. Moreover, the electron and hole coupling is reported through a simplified model for a complex and distributed 2 − D parasitic bipolar transistor.