Interface trap induced thermionic and field emission current inoff-state MOSFET's

摘要

An interface trap-assisted tunneling and thermionic emission modelhas been developed to study an increased drain leakage current inoff-state MOSFET's after hot carrier stress. In the model, a completeband-trap-band leakage path is formed at the Si-SiO₂interface by hole emission from interface traps to the valence band andelectron emission from interface traps to the conduction band. Both holeand electron emissions are carried out via quantum tunneling or thermalexcitation. In experiment, a 0.5 μm n-MOSFET was subject to hotcarrier stress to generate interface traps. The drain leakage currentwas characterized to compare with the model. Our study reveals that theinterface trap-assisted two-step tunneling, hole tunneling followed byelectron tunneling, is responsible for the leakage current at a largedrain-to-gate bias (V_dg) The lateral field plays a dominantrole in the two-step tunneling process. As V_dg decreases, athermionic-field emission mechanism, hole thermionic emission andelectron tunneling, becomes a primary leakage path. At a sufficientlylow V_dg, our model reduces to the Shockley-Read-Hall theoryand thermal generation of electron hole pairs through traps is dominant