Improvement of the multi-level cell performance by a soft program method in flash memory devices

•A soft program method improves the multi-level cell performance.•The initial threshold-voltage instability can be improved by removing the shallowly trapped electrons.•Different high-κ blocking oxides have been investigated.

A soft program method is proposed for charge-trap flash (CTF) memory devices. By adding a subsequent small positive gate pulse after main Fowler–Nordheim (FN) injection programming, early charge loss is greatly reduced. The multi-level cell performance as well as the initial flat-band voltage (VFB) instability can thereby be improved by removing the trapped electrons at the shallow traps in the blocking oxide layer. The proposed soft program method is a simple but very effective way to improve the fast retention property without changing the memory structure, especially for cases where the κ-value of the blocking oxide is high.