Modeling charge variation during data retention of MLC Flash memories

Abstract

In this paper, we propose to model charge variation in Multi-Level Cells in NOR Flash memories. We first define a sensitivity-to-temperature factor to determine the number of involved mechanisms. Then, according to previous studies, we can use the Poole–Frenkel (PF) and/or the Fowler–Nordheim (FN) equations to model every charge loss, which we apply to our cells. We succeed in modeling our data retention measurements by superimposing these two phenomena, being, respectively preponderant at the beginning and at the end of the data retention measurements, as shown by the factor of sensitivity-to-temperature. We have then found a relationship between temperatures to evaluate our cells lifetime. We validate that the classical 1/ T Arrhenius law is not the most appropriate and that a T model can be better. We also model a fictive charge gain by using a negative charge front displacement in the tunnel oxide. This study can easily be extended to any floating gate non-volatile memory.