Secondary Effects of Single Ions on Floating Gate Memory Cells

A programmed Floating Gate (FG) hit by a heavy ion experiences a large charge loss, which degrades the stored information. However, as a result of irradiation, even FGs not directly hit by ions can experience a shift in the programmed threshold voltage. These latter FGs can be found only in novel technologies with very small floating gates. Further, they have particular characteristics when compared to the cells directly hit by an ion: are characterized by a tendency to cluster, feature a peculiar threshold voltage distribution after irradiation, and do not experience radiation induced leakage current. These FGs are probably generated by ions crossing the device "close enough" to the floating gate, without directly hitting it