Model of leakage current induced by dynamic stress in thin EEPROM tunnel oxides

It has been currently observed that Fowler–Nordheim tunneling injection through thin SiO2 oxide layers (5–10 nm) induces leakage currents called stress-induced leakage currents (SILC). These could contribute to data retention loss in EEPROM non-volatile memory devices. In this work, we have stressed 7 nm thick SiO2 MOS capacitors with bipolar symmetrical pulses similar to write–erase cycles used for EEPROM cell programming. I(V), current–voltage data, have been analyzed to identify the induced conduction mechanisms after different stress levels. It has been shown that I(V) data present two zones. The first zone, for oxide electric fields greater than 7 MV cm−1, always remains governed by a classical Fowler–Nordheim effect. At smaller electric fields corresponding to the SILC domain, the current has been successfully modelled by a trap-assisted conduction mechanism. At largest injected charge levels, coulombic attractive traps generated in SiO2 overlap inducing conduction enhancement that we have described by a two-traps model.