Electric Field Induced Nitride Trapped Charge Lateral Migration in a SONOS Flash Memory

We investigated electric field-induced trapped electron lateral migration in a SONOS flash cell. The threshold voltage shift ( $\Delta \text{V}_{t}$ ) and gate-induced drain leakage (GIDL) current were measured to monitor nitride electron movement in retention. We applied different voltages to the gate and the source/drain in retention to vary the vertical and lateral electric fields. Our study shows that: 1) GIDL current can be used to monitor trapped charge lateral migration and 2) nitride charge lateral migration exhibits strong dependence on the lateral electric field. Based on measured temperature and field dependence, a nitride trapped charge emission process via thermally assisted tunneling is proposed for electron lateral migration. The emission rates of thermally assisted tunneling, direct trap-to-band tunneling and Frenkel–Poole emission were compared.