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

Abstract

We investigated electric field-induced trapped electron lateralmigration in a SONOS flash cell. The threshold voltage shift (Delta V-t) andgate-induceddrain 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 tomonitor trapped charge lateralmigration 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.