Characterization of programmed charge lateral distribution in a two-bit storage nitride flash memory cell by using a charge-pumping technique

Abstract

In this paper, we use a modified charge pumping technique to characterize the programmed charge lateral distribution in a hot electron program/hot hole erase, two-bit storage nitride Flash memory cell. The stored charge distribution of each bit over the source/drain junctions can be profiled separately. Our result shows that the second programmed bit has a broader stored charge distribution than the first programmed bit. The reason is that a large channel field exists under the first programmed bit during the second bit programming. Such a large field accelerates channel electrons and causes earlier electron injection into the nitride. In addition, we find that programmed charges spread further into the channel as program/erase cycle number increases.