Data deletion method for security improvement of Flash memories

Abstract

For Flash memories, data remanence can cause differences in threshold voltage among the erased cells. By detecting such differences, already-erased data can be recovered. To decrease the differences, a secure deletion method of data is investigated in this paper. The effects of erase-erase (EE) operation and erase-program (EP) operation on threshold voltage are studied in theory. Based on the floating-gate device model, the optimal overwriting sequence, EPEPE, is obtained by simulation. This sequence can reduce the difference to 0.1 mV in threshold voltage among the erased Flash cells, which equals to that caused by one floating-gate electron.